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dissertation entitled

THE STRUCTURE, COMPOSITION AND HYDROLOGY OF WET MEADOW
PLANT COMMUNITIES FRINGING SAGINAW BAY (LAKE HURON)

presented by

Kurt Edward Stanley

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Ph.D. degree in Botany and Plant Pathology

 

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THE STRUCTURE, COMPOSITION AND HYDROLOGY OF WET MEADOW
PLANT COMMUNITIES FRINGING SAGINAW BAY (LAKE HURON) \

By

Kurt Edward Stanley

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Department of Botany and Plant Pathology

2000

ABSTRACT

THE STRUCTURE, COMPOSITION AND HYDROLOGY OF WET MEADOW
PLANT COMMUNITIES FRINGING SAGINAW BAY (LAKE HURON)

By

Kurt Edward Stanley

This 1996-1997 study determined the structure, composition, and above-ground
productivity of Saginaw Bay coastal wet meadow vegetation, and the impact of
hydrology, soils, anthropogenic disturbance, and Purple Loosestrife on this vegetation
assemblage.

Groundwater, surface water, precipitation, and pan evaporation were monitored in
a reference and disturbed wet meadow. Precipitation, seiche and storm surge inundation,
and evapotranspiration controlled growing-season groundwater levels in un-flooded wet
meadows. Mid-summer ET exceeded precipitation and storm surge inputs, lowering
groundwater levels. Groundwater levels >60cm lower than Saginaw Bay were observed
20m from Saginaw Bay. Groundwater recharge occurred by vertical percolation, not
horizontal groundwater inflow.

Fifieen of 93 species encountered contributed 84.0% of total vegetation
importance value at 25 study sites. Calamagrostis canadensis, Carex aquatilis, Carex
sartwellii, and Carex stricta contributed 60.1% of total IV. Twenty-seven species
occurred in only one of 300 plots. The vegetation canopy was 1.2-1.5m tall, with half the
leaves occurring 43-84cm above ground. There were three canopy layers, and vine-like

species climbing among the three canopy layers.

Stem densities were greatest where mean mid-summer water levels ranged
between +10cm and -10cm depth. Plot biomass and species richness peaked at greatest
standing water levels due to the encroachment of marsh species. Anthropogenic
disturbance altered these patterns. The vegetation exhibited identifiable lower and upper
wet meadow sub-types. Thin peat and litter mats, short hummocks, and small-stature
species occurred more often in upper wet meadows, whereas thick peat and litter mats,
tall hummocks, and physically larger wet meadow emergent species occurred more often
in lower wet meadows.

Fluctuating surface- and groundwater levels had the greatest impact of any abiotic
factor on the vegetation. Hydroperiod directly impacted vegetation composition, and
strongly influenced the pattern of occurrence of other abiotic factors.

Mean peak wet meadow standing crop was 669g/m2. Growing-season litter
production was 152g/m2, and in-place litter decomposition was 186g/m2. Net above-
ground primary productivity was lOO7g/m2/yr.

There were few significant differences in the vegetation of either reference and
disturbed, or Loosestrife and Loosestrife-free sites. The vegetation resisted anthropogenic
disturbance impacts and Purple Loosestrife introduction, and exhibited resilience once
disturbance ended. Soil disturbances (dredging, filling, excavation, and cultivation) were
the most dismptive disturbance types. Wet meadow vegetation exhibited greater

resilience following soil disturbance when hydrology was not disturbed.

ACKNOWLEDGMENTS

Many people contributed to the successful completion of this project. I would not
have been able to complete my dissertation without their advice, assistance, and
generosity. I would like to acknowledge their help and thank them at this time.

I would like to thank my advisor, Peter G. Murphy, for his guidance and support.
His wisdom, patience, and good humor smoothed bumps in the road and made graduate
school both educational and fim. His guidance in the design and execution of my
dissertation research project, and his editorial expertise, have greatly improved the quality
of the end-product.

I would also like to thank Harold Prince, Thomas Burton, Frances Ekern, and
Frank Ewers for serving as members of my guidance committee. Their advice and
guidance was a great help. I owe Dr. Prince a special debt of gratitude, as he was
instrumental in obtaining funding to support my studies and research.

I received financial support from several sources. The Rob and Bessie Welder
Wildlife Foundation of Sinton, Texas provided a graduate fellowship which covered the
cost of graduate studies and most dissertation research expenses. This generous grant of
financial support allowed me to focus full attention on studies and research. Additional
financial support for field research was provided by Sigma Xi, the Scientific Research
Society, and by the Ecology, Evolutionary Biology and Behavior program at Michigan
State University. The College of Natural Sciences, Michigan State University, provided a
Dissertation Completion fellowship to support writing of the dissertation. Travel funds

were made available by the Paul Taylor Fund of the Department of Botany and Plant

Pathology, Michigan State University, the Society of Wetland Scientists, the National
Marine Fisheries Service, and the International Studies Program, Michigan State
University so that I could attend meetings to present the results of my research.

A number of individuals and organizations allowed me to establish study sites on
their land, including Arnold Karr of the Michigan Department of Natural Resources,
William Doerfiier, C.J. Cootes, Richard Abbott, Jim Mitchell, Phillip Gibb, William
Heaphy and the Saganing River Rod and Gun Club, Gene Viola, Walter Grobsky, Francis
Lentz, Mark Slanderer and Green Point Farms, and Horatio Davis. Many of these
individuals also provided valuable insights into the land use histories of the sites they
owned. I would like to express my sincere thanks and appreciation for the kindness and
courtesy extended to me by these people.

Several individuals assisted in my research. Anne Vaara helped me re-leam the
basics of ecological research and botanical nomenclature when I first returned to graduate
school. Joe Gathman taught me how to use a laser level. Michael Chamberland helped
identify my unknown plants, and taught me the proper use of a herbarium. My parents,
Roland and Bethe] Stanley, provided housing while I was both on campus and in the field.
The late Thomas Jahr, Jr. and his stafi‘ at the Sebewaing County Park helped make my
“field station” a pleasant place to live and work. Thanks to all of you for your help.

And finally, I’d like to thank my loving wife, Julie. She understood my desire to
return to college, and encouraged me to do so. She kept the household going while I was
away at school, and worked by my side in the field to collect the data. I could not have

completed this dissertation without her love and support.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................... ix
LIST OF FIGURES ............................................................................... xiv
CHAPTER 1

GENERAL INTRODUCTION

Wet meadows defined .............................................................................. 2
Purpose of the study ................................................................................ 5
Study Region ......................................................................................... 6
Land use history ..................................................................................... 7
Climate ................................................................................................ 9
Sofls .................................................................................................. 10
Study sites .......................................................................................... 11
Previous research ................................................................................... 12
Organization of the study ......................................................................... 14
Literature Cited .................................................................................... 15
CHAPTER 2

THE HYDROLOGY OF SAGINAW BAY COASTAL WET MEADOWS: NATURAL
SYSTEMS AND DISTURBANCE IMPACTS

Introduction ......................................................................................... 25
Objectives ........................................................................................... 28
Sites .................................................................................................. 29
Methods ............................................................................................. 32
Results ............................................................................................... 37
Discussion ........................................................................................... 43

Reference wet meadow ...................................................................... 43

Disturbed wet meadow ...................................................................... 47
Summary and Conclusions ........................................................................ 50
Literature Cited .................................................................................... 53
CHAPTER 3

THE STRUCTURE AND COMPOSITION OF SAGINAW BAY COASTAL WET
MEADOW VEGETATION

Introduction ......................................................................................... 87
Abiotic factors influencing wet meadow structure ........................................ 88
Vegetation attributes .......................................................................... 89
Goals and Objectives .......................................................................... 89

Sites .................................................................................................. 90

Methods ............................................................................................. 9]
Elevation determination ....................................................................... 91

1996 sampling ............................................................................. 91

vi

1997 sampling ............................................................................. 91

Data collection ....................................................................... , ......... 92
1996 sampling ............................................................................. 92
1997 sampling ............................................................................. 92
Vegetation sampling ...................................................................... 93
1996 .................................................................................... 93
1997 .................................................................................... 94
Soil sampling .............................................................................. 95
Statistical procedures .......................................................................... 96
1996 sampling ............................................................................. 96
1997 sampling ............ . ................................................................ 97
Results ............................................................................................... 98
Water level, vegetation, and soil at the reference and disturbed hydrologic study
sites ........................................................................................... 98
Physical attributes of Saginaw Bay coastal wet meadows .............................. 102
Vegetation attributes ........................................................................ 106
Vertical vegetation stratification ........................................................... 107
Biotic/abiotic interactions ................................................................... 109
Discussion ......................................................................................... 1 1 1
Water level, vegetation, and soil at the reference and disturbed hydrologic study
sites .......................................................................................... 111
Physical attributes ............................................................................ 116
Vegetation attributes ......................................................................... 121
Species interactions .......................................................................... 123
Vertical vegetation stratification ........................................................... 126
Summary and conclusions ....................................................................... 127
Literature Cited ................................................................................... 130
CHAPTER 4

ABOVE-GROUND BIOMASS AND PRODUCTIVITY OF THE VEGETATION IN
COASTAL WET MEADOWS BORDERING SAGINAW BAY

Introduction ....................................................................................... 172
Study area ..................................................................................... 174
Methods ............................................................................................ 175
Biomass ........................................................................................ 175
Litter ........................................................................................... 176
Results and Discussion .......................................................................... 177
Distribution of above-ground biomass .................................................... 177
Net above-ground primary productivity (N APP) ........................................ 181
Summary and Conclusions ...................................................................... 183
Literature cited ................................................................................... 184

vii

CHAPTER 5
THE IIVIPACT OF ANTHROPOGENIC DISTURBANCE AND PURPLE
LOOSESTRIFE ON SAGINAW BAY COASTAL WET MEADOW VEGETATION

Introduction ....................................................................................... 196
Goals and objectives ......................................................................... 196
Disturbance ................................................................................... 197
Purple Loosestrife ........................................................................... 199

Methods .......................................................................................... '. 200
Site selection ................................................................................. 200
Vegetation sampling ........................................................................ 203
Statistical analysis ........................................................................... 203

Results ............................................................................................. 206
Disturbance effects .......................................................................... 206
Purple Loosestrife effects ................................................................... 208

Discussion ......................................................................................... 211
Disturbance effects .......................................................................... 211
Purple Loosestrife effects ................................................................... 215
Implications for management and restoration ............................................ 221

Summary and conclusions ....................................................................... 222

Literature cited ................................................................................... 224

APPENDICES

Appendix A1. Climatological Norms .......................................................... 241

Appendix A2. Saginaw Bay Coastal Wet Meadow Sites ................................... 242

Appendix B1 - Precipitation data .................... . ........................................... 244

Appendix B2 - Well field installation ........................................................... 245

Appendix B3 - Soil moisture sampling ........................................................ 249

Appendix B4 - Detailed disturbed site groundwater hydrology ............................ 250

Appendix C1 - Soil physical and chemical data ............................................... 267

Appendix C2 - Species stem density data ...................................................... 269

Appendix C3 - Vertical distribution of vegetation parts ..................................... 272

viii

LIST OF TABLES

Table 2-1. Occurrence of water levels greater than or equal to 177.3m AMSL at
Essexville, MI: 3/1/97-10/31/97. 177.3m AMSL was the maximum elevation of the
Saginaw Bay wet meadow zone during 1997. A storm surge of this magnitude could
inundate the entire wet meadow zone. Data fiom NOS-NOAA. .......................... .65

Table 3-1. Comparison of soil variables measured at the hydrologic study sites. 4
Significantly different P-values are indicated in boldface and with an asterisk. P-values
were determined using the Mann-Whitney U test. PPM equals parts per million,
Meq/lOOml equals milli-equvalents per 100ml soil ........................................................ 146

Table 3-2. Wet meadow width, slope, peat and litter depth, and hummock height by site
for Saginaw Bay coastal wet meadows ......................................................................... 149

Table 3-3. Pearson product-moment correlation matrix of Saginaw Bay coastal wet
meadow abiotic factors. Peat depth and litter depth were square-root transformed to meet
parametric assumptions. Boldface values marked with an asterisk were significant
(Bonferroni-corrected P<0.05) ..................................................................................... 150

Table 3-4. Importance values (IV) for plant species encountered in Saginaw Bay coastal
wet meadows in 1997. Importance value is the sum of the relative above-ground biomass,
relative stem density, and relative frequency of occurrence of each species in the wet
meadow (Brower and Zar, 1977). A total of 300-0.25m2 sample plots were collected in
25 coastal wet meadows. Percent frequency of occurrence was determined from the
number of sample plots in which the species was found. N equals the number of plots in
which a species occurred .............................................................................................. 151

Table 3-5. Frequency of occurrence, contribution to total IV, life form/habit, and National
Wetlands Inventory (NWT) classification of plant species contributing 1% or more of total
Saginaw Bay coastal wet meadow (SBCWM) IV. The 15 species (5 sedges, 3 grasses, 1
cattail, and 6 forbs) contributed 840% of total SBCWM IV. A total of 300 0.25-m2
sample plots were collected in 25 SBCWM. Percent frequency of occurrence was
determined from the number of sample plots in which the species was found. N equals the
number of plots in which a species occurred. ................................................................ 155

Table 3-6. Species richness, Leaf-area index (LAI), Shannon-Wiener diversity index (I-I’),
Evenness (J), and Dominance (l-J) by site of Saginaw Bay coastal wet meadow
vegetation. ................................................................................................................... 1 56

Table 3-7. Comparison of species richness and leaf-area index (LAI) for various wet
meadow sites. .............................................................................................................. 157

Table 3-8. Pearson product-moment correlation of plant species contributing 1% or more
of total Saginaw Bay coastal wet meadow importance value. Correlation values

ix

significant at P<0.05 (rmogmg, = 10398; Snedecor and Cochran, 1980, Table All) are
indicated in boldface and with asterisks. ....................................................................... 158

Table 3-9. Median height and maximum/minimum height range of common plant species
occurring in Saginaw Bay coastal wet meadows. Canopy Emergent species were those
with median heights >90cm, Canopy Species were those with median heights between 50-
90cm, and Understory Species were those with median heights <40cm. Clingers/Climbers
were species utilizing other plants for support. N is the total number of leaf contacts
observed during sampling. Species with N<5 were excluded from the analysis ............. 159

Table 3-10. Pearson product-moment correlation among Saginaw Bay coastal wet
meadow major plant species IV and abiotic factors measured in 1997. Litter depth and
peat depth were square-root transformed to achieve normal distribution. Plots in which
litter depth was not determined were excluded fiom the analysis. Soil texture increased
fi'om fine- to coarse-textured substrates. Values indicated with boldface and an asterisk
were significant at P<0.05 (rmom 2.5, = i0.134; Snedecor and Cochran, 1980, Table A1 1)
........................................................................................................ 160

Table 3-11. Change in importance value across the elevation gradient for species found in
Saginaw Bay coastal wet meadows. Data were collected in 288 sample plots at 24 study
sites. Site #1 was isolated from Saginaw Bay by a dike, and so was excluded from the
analysis. Sites became wetter as elevation decreased. Mean annual high water mark for
Saginaw Bay (1918-1996) equaled 176.67 m AMSL .................................................... 161

Table 3-12. Change in importance value across the elevation gradient for species found at
Site #1, a wet meadow isolated fiom Saginaw Bay by a dike. Data was collected in 12
sample plots, three plots at each of four elevations, in 1997. Sites became wetter as
elevation decreased. Mean annual high water mark for Saginaw Bay (1918-1996) equaled
176.67 m AMSL. Species distribution patterns were similar for this site and 24 study sites
not isolated fiom Saginaw Bay ..................................................................................... 164

Table 3-13. Pearson product-moment correlation between Saginaw Bay coastal wet
meadow major plant species IV and hummock heights measured during 1997 vegetation
sampling. Plots in which hummocks were not present or measured were excluded from
the analysis. Values indicated with boldface and an asterisk were significant (rcvmm, 49) =
350.273; Snedecor and Cochran, 1980, Table A11(i)) .................................................... 169

Table 3-14. Physical and vegetation attributes that define the upper and lower Saginaw
Bay coastal wet meadow sub-zones. Upper wet meadow vegetation occurred above
177.0m AMSL, lower wet meadow vegetation below that elevation. Elevation was a
good integrator of the extremely dynamic Saginaw Bay hydrology. Data was collected in
300- 0.25m2 plots in 25 wet meadows. N is the number of 0.25m2 plots, except as
indicated. All means were significantly different at P<0.05. ......................................... 171

Table 4-1. Frequency of occurrence, determined from the number of sample plots in
which a species occurred, percentage biomass contribution of a species to total Saginaw

X

Bay coastal wet meadow (SBCWM) biomass, and mean above-ground biomass of plant
species encountered during SBCWM biomass sampling. A total of 228 0.25-m2 sample
plots in 19 sites were collected in July-August 1997. Samples were oven-dried at 60° C
for 48 hours before weighing. N equals the number of plots in which a species

occurred. ..................................................................................................................... 191

Table 4-2. Mean peak standing crop (PSC) biomass and range of sample values among 19
Saginaw Bay coastal wet meadows based on 12- 0.25m2 sample plots per site. Weights
determined after oven-drying at 60° C for 48 hours. .................................................... .. 193

Table 4-3. Peak standing cr0p (PSC) biomass, net biomass production, and net above-
ground primary productivity (NAPP) values for grass/sedge dominated ecosystems. Net
biomass production includes live biomass produced during the growing season. NAPP
includes net biomass production, with corrections for growing-season litter production
and decomposition losses. ............................................................................................ 194

Table 4-4. Distribution of peak above-ground biomass among biomass components for
grass/sedge dominated ecosystems. .............................................................................. 195

Table 5-1. Sites used to study the impact of anthropogenic disturbance on Saginaw Bay
coastal wet meadow vegetation .................................................................................... 229

Table 5-2. Plant species that occurred only in reference or only in disturbed Saginaw Bay
coastal wet meadow study sites. Ten species occurred only in reference sites, 32 species
occurred only in disturbed sites. The coefiicient of conservatism reflects the probability
that the species will be found in a landscape relatively unaltered from it’s pre-settlement
condition (Hennan et al., 1996). Asterisks indicate that the species was adventive.
Coefficients of conservatism are not assigned to adventive species. .............................. 231

Table 5-3. Mean coefficient of conservatism (CC ) and Floristic Quality Index (F Q1) for
reference and disturbed Saginaw Bay wet meadow sites. Number of species used to
calculate the FQI was the number of species occurring only in sampling plots, not the total
number of species observed during sampling at a site. .................................................. 232

Table 5-4. Results of statistical tests comparing the means of various plant and abiotic
wet meadow attributes for reference and disturbed Saginaw Bay coastal wet meadow
sites. Significant differences (P<0.05) are indicated in boldface and marked with an
asterisk. The effect size and power of the test provide measures of the sensitivity of
individual t-tests. ......................................................................................................... 233

Table 5-5. Comparison of mean plot importance values of major Saginaw Bay coastal wet
meadow species in reference and disturbed sites. Significant differences (P<0.05) are
highlighted in boldface and marked with an asterisk. The effect size and power of the test
provide measures of the sensitivity of individual t-tests ................................................. 234

Table 5-6. Results of statistical tests comparing mean plot importance values, above-
ground biomass, and stem densities of the six major species found to have significantly
different (P<0.05) IV in reference and disturbed Saginaw Bay coastal wet meadows.
Significant differences (P<0.05) are highlighted in boldface and marked with an asterisk.
The effect size and power of the test provide measures of the sensitivity of individual t-
tests. ............................................................................................................................ 235

Table 5-7. Results of statistical tests comparing the means of various plant and abiotic
wet meadow attributes of non-Loosestrife and Loosestrife Saginaw Bay coastal wet .
meadow plots. A total of 300 sample plots were collected at 25 sites; 37 plots contained
Loosestrife, 263 plots did not. Litter depths were determined in 215 plots. Hummocks
occurred in 51 plots. Significant differences (P<0.05) are indicated in boldface and
marked with an asterisk. The effect size and power of the test provide measures of the
sensitivity of individual t-tests. ..................................................................................... 236

Table 5-8. Comparison of mean plot importance value of major Saginaw Bay coastal wet
meadow species in non-Loosestrife and Loosestrife plots. Significant differences (P<0.05)
are highlighted in boldface and marked with an asterisk. The effect size and power of the
test provide measures of the sensitivity of individual t-tests. ......................................... 237

Table 5-9. Results of statistical tests comparing the mean importance value, above-
ground biomass, and stem density of the four major species found to have significantly
different (P<0.05) IV in non-Loosestrife and Loosestrife Saginaw Bay coastal wet
meadow plots. Significant differences (P<0.05) are highlighted in boldface and marked
with an asterisk. The effect size and power of the test provide measures of the sensitivity
of individual t-tests. ..................................................................................................... 238

Table 5-10. Comparison of plot above-ground biomass, stem density, species richness,
and Shannon-Wiener diversity (H’) of species other than Purple Loosestrife in low-
Loosestrife and high-Loosestrife plots. Stem density of the other species was significantly
greater (P<0.05) in low-Loosestrife plots. Though not significantly different, above-
ground biomass and species richness exhibited lower mean plot values in the high-
Loosestrife plots. Shannon-Wiener diversity was the same for both categories.
Probabilities determined using the Mann-Whitney U test. ............................................. 239

Table A-1. Climatological norms for Bay City and Standish, Michigan. .................. 241

Table A-2. Site number, site name (if any), site location, site ownership, and special site
access information for coastal wet meadows bordering Saginaw Bay between Port Austin
and Au Gres, MI. Sites marked with an asterisk were not included in the study. ........ 242

Table B-1. Mean monthly precipitation at the National Weather Service climatological
reporting station in Sebewaing, M]: 1961-1990. ......................................................... 244

Table C-l. Soil physical and chemical analysis for wet meadow sites located in the
Saginaw Bay coastal zone. Single sample numbers (e.g., 15, 27) indicate that one aliquot

xii

was collected and processed per site. For sarnple numbers containing a slash (e.g., 1/9,
6/1), the number left of the slash is the site number, and the number to the right of the
slash is the number of the sample collected at that site. ...................................... 267

Table C-2. Stem densities of plant species encountered in Saginaw Bay coastal wet
meadows in 1997. A total of 300-0.25m2 sample plots were collected in 25 coastal wet
meadows. Percent frequency of occurrence was determined from the number of sample
plots in which the species was found. N equals the number of plots in which a species
occurred. ................................................................................................................... 269

Table C-3. Vertical distribution of leaf, stem, and inflorescence contacts in Saginaw Bay
coastal wet meadows. Table data are expressed as percentages, with actual counts in
parentheses. ............................................................................................................... 272

xiii

LIST OF FIGURES

Figure 1-1. Western Great Lakes region, with Saginaw Bay indicated. .......................... 23

Figure 1-2. The location of coastal wet meadows in the Saginaw Bay coastal zone. Of 31
known wet meadow sites, Sites 7, 12, 16, 17, 23, and 29 were not included in the study.
There were no coastal wet meadows between Caseville and Port Austin on Saginaw Bay’s
eastern shore. Map data from US Census Bureau TIGER database and Michigan
Department of Natural Resources. ................................................................................. 24

Figure 2-1. Maximum, mean, and minimum annual water levels of Lake Huron: 1984-
1997. Data from the Detroit District, US Army Corps of Engineers. ............................. 59

Figure 2-2. Mean monthly Lake Michigan-Huron water levels: 1994-1997. The amount
and timing of winter snow melt and spring rainfall determine the shape of the annual
hydrograph: low water in winter, high water in summer. The shape of the annual
hydrograph is predictable, the year-to-year variability in lake elevation much less so. Data
fi'om the Detroit District, US Army Corps of Engineers. ................................................ 60

Figure 2-3. Map of the Saginaw Bay region. The location of the reference hydrologic
study site (Site 2; see inset) and the disturbed hydrologic study site (Site 1) are indicated.
These were two of 31 coastal wet meadows bordering Saginaw Bay in 1997. Wet
meadow vegetation was examined at the two hydrologic study sites, and 23 other wet
meadows. Sites 7,12, 16, 17, 23, and 29 were not used in the study and are not shown
(see Figure 1-2 for location of these sites). Map data fiom US Census Bureau TIGER
database and Michigan Department of Natural Resources. ........................................... 61

Figure 2-4. Map of the reference hydrologic study site, located 12km north of Sebewaing,
MI and 2km off the coast in the Wildfowl Bay State Game Area. The site sloped from
high ground on the south shore to cattail marsh on the north. The wet meadow-cattail
marsh boundary fluctuated annually depending on the level of Saginaw Bay. The boat
channel was excavated prior to 1938. The numbers identify groundwater monitoring
wells. ............................................................................................................................ 62

Figure 2-5. Map of the disturbed hydrologic study site, located 19km southwest of the
reference site on Saginaw Bay’s eastern shore. The site was either cultivated or grazed
for an 80-100 year period ending in the late 1980’s. The dike, constructed between 1941-
1949, severed the direct surface connection with saginaw Bay. The drain discharged into
Saginaw Bay (not shown). The numbers and “OW” labels identify groundwater
monitoring wells, the “SG” labels stafl‘ gauges. ................................................ 63

Figure 2-6. Change in surface water levels at the reference and disturbed hydrologic study
sites: 1996-1997. Stafi Gauge 1 was in the on-site ditch at the disturbed site. Staff
Gauge 2 was in an agricultural drain at the disturbed site that discharged to Saginaw Bay.
Staff Gauge 3 was in Saginaw Bay at the reference site. Surface water hydroperiod at the

xiv

disturbed site, altered by diking and ditching, differed from that of Saginaw Bay at the

reference site. Surface water levels for each site were referenced to site benchmark, not to
Datum, and are not directly comparable. Staff gauge readings were not collected in winter
when the gauges were encased in ice. ........................................................................... 64

Figure 2-7. Monthly precipitation at the reference and disturbed hydrologic study sites,
and the National Weather Service climatological reporting station at Sebewaing, M]:
1996-1997. The line describes the 30 year (1961-1990) mean monthly precipitation for
NWS-Sebewaing. Rainfall data were not collected in winter months. 66

Figure 2-8. Precipitation recorded at the reference and disturbed hydrologic study sites:
1996. Rainfall data were not collected in winter months. ............................................... 67

Figure 2-9. Monthly mean daily evapotranspiration (ET) for the reference and disturbed
hydrologic study sites: 1996-1997. ET estimated from pan evaporation measured at the
sites. Data were not available from the disturbed site in June 1996, and September and
October 1997. Error bars denote :1 SE of the mean. ..................................................... 68

Figure 2-10. Monthly precipitation (PPT) and estimated evapotranspiration (ET) at the
reference hydrologic study site: 1996-1997. Evapotranspiration exceeded precipitation in
June 1996, July 1996, and June 1997, driving the de-saturation of wet meadow soils and
inducing summer groundwater decline within the wet meadow. Rainfall and pan
evaporation data were not collected in winter months. .................................................. 69

Figure 2-11. Surface water and groundwater profiles for monitoring wells #201-#206 at
the reference hydrologic study site during the 1996 growing season. Wells were in line
order ranging from lowest (#201) to highest elevation (#206). Elevations indicate ground
level at each well with respect to the site benchmark. Each well was 30m from the next
well in line. Wells #201, 202, and 203 were inundated throughout the growing season.
Wells #204, 205, and 206 remained free of standing water for most of the growing season.
...................................................................................................................................... 70

Figure 2-12. Groundwater levels declined at the reference hydrologic study site in 1996.
A. In the early growing season, the wetland surface was entirely saturated, and there was
10-15cm water standing in the lower wet meadow. B. By late June, groundwater levels
in the upper wet meadow appeared to be equilibrating with surface water levels in
Saginaw Bay. C. By mid-July, groundwater levels had dropped sharply in the upper wet
meadow to levels as much as 100cm below the ground surface, or 65cm below the level of
Saginaw Bay. LS = land surface; GW = groundwater surface; SW = Saginaw Bay surface
elevation. The north site border was the wet end of the site water level gradient, and
closest to Saginaw Bay. The cast site border was the boat channel. Elevation increased,
and the site became drier, as one moved away from the north site border. Elevations were
measured at each monitoring well and determined with respect to a site benchmark.
Surface and groundwater contours between the monitoring wells were estimated using an
inverse squared distance smoothing fiinction (SPSS, Inc., 1996). View point is from the
southwest. ................................................................................................................... 71

Figure 2-13. Groundwater levels rebounded in late summer 1996 at the reference
hydrologic study site. A. Mid-summer groundwater profiles remained unchanged until
early September 1996. B. Within seven days in mid-September, groundwater levels in the
upper wet meadow rebounded to within a few centimeters of the ground surface, while the
lower wet meadow had been inundated to a depth of 15cm. LS = land surface; GW =
groundwater surface; SW = Saginaw Bay surface elevation. The north site border was the
wet end of the site water level gradient, and closest to Saginaw Bay. The cast site border
was the boat channel. Elevation increased, and the site became drier, as one moved away
from the north site border. Elevations were measured at each monitoring well and
determined with respect to a site benchmark. Surface and groundwater contours between
the monitoring wells were estimated using an inverse squared distance smoothing firnction
(SPSS, Inc., 1996). View point is from the southwest. ................................................. 73

Figure 2-14. Comparison of early growing season groundwater levels at the reference and
disturbed hydrologic study sites. Similar groundwater profiles were observed at the sites
in the early growing season. Both sites were saturated to the ground surface in mid-May
1996, and groundwater decline had commenced at both sites by early June. LS = land
surface; GW = groundwater surface; SW = Saginaw Bay surface elevation. The north site
border was the wet end of the site water level gradient, and closest to Saginaw Bay, at
each site. The cast site border was the boat channel at the reference site, and an
agricultural field at the disturbed site. Elevation increased, and the sites became drier, as
one moved away from the north site border of each site. Elevations were measured at
each monitoring well and determined with respect to a site benchmark. Surface and
groundwater contours between the monitoring wells were estimated using an inverse
squared distance smoothing function (SPSS, Inc., 1996). Elevation increases with
distance from north site border. View point is from the east. ....................................... 75

Figure 2-15. Comparison of mid-summer groundwater levels at the reference and
disturbed hydrologic study sites. By July 1, 1996, the reference and disturbed site
groundwater tables had reached nrid-summer levels. Thereafter, gradual draw down
continued in non-inundated portions of both sites through early September. LS = land
surface; GW = groundwater surface; SW = Saginaw Bay surface elevation. The north site
border was the wet end of the site water level gradient, and closest to Saginaw Bay, at
each site. The east site border was the boat channel at the reference site, and an
agricultural field at the disturbed site. Elevation increased, and the sites became drier, as
one moved away from the north site border of each site. Elevations were measured at
each monitoring well and determined with respect to a site benchmark. Surface and
groundwater contours between the monitoring wells were estimated using an inverse
squared distance smoothing function (SPSS, Inc., 1996). Elevation increases with
distance fi'om north site border. View point is from the east. ....................................... 77

Figure 2-16. Comparison of late summer groundwater levels at the reference and
disturbed hydrologic study sites. Groundwater recharge occurred within a few days in
mid-September at the reference site, but required several months at the disturbed site to be
completed. LS = land surface; GW = groundwater surface; SW = Saginaw Bay surface
elevation. The north site border was the wet end of the site water level gradient, and

xvi

closest to Saginaw Bay, at each site. The east site border was the boat channel at the
reference site, and an agricultural field at the disturbed site. Elevation increased, and the
sites became drier, as one moved away from the north site border of each site. Elevations
were measured at each monitoring well and determined with respect to a site benchmark.
Surface and groundwater contours between the monitoring wells were estimated using an
inverse squared distance smoothing function (SPSS, Inc., 1996). Elevation increases with
distance fiom north site border. View point is from the east. ....................................... 79

Figure 2-17. Percent soil moisture content of non-saturated soil in various locations at the
reference hydrologic study site: 1996. The large numbers above the graphs indicate the
elevation (in cm with respect to the site benchmark) at which the soil samples were
collected. Error bars denote i1 SE of the mean. No significant seasonal trends are
evident, but lower elevation samples exhibited higher soil moisture content than did the
higher elevation samples. ............................................................................................... 81

Figure 2-18. Percent soil moisture content of non-saturated soil in various locations at the
disturbed hydrologic study site: 1996. The large number above the graphs indicates the
elevation (in cm with respect to the site benchmark) at which the soil samples were
collected. Error bars denote 121 SE of the mean. Some locations within the site became
drier as the season progressed, some did not. Lower elevation samples generally exhibited
higher soil moisture content than did the higher elevation samples. ................................. 82

Figure 2-19. Groundwater levels rebounded in mid-June 1996 in response to heavy
rainfall and seiche activity. A. Groundwater decline had begun by 6/6/96 at the reference
hydrologic study site. B. Groundwater measurements collected on 6/13/96 indicated no
evidence of groundwater decline at the site. A total of 6.35cm precipitation, and a 20cm
seiche, occurred between 6/6/96 and 6/13/96. The rainfall and surface water rapidly
infiltrated and recharged the declining groundwater surface, bringing it back to near the
wetland ground surface. LS = land surface; GW = groundwater surface; SW = Saginaw
Bay surface elevation. The north site border was the wet end of the site water level
gradient, and closest to Saginaw Bay, at each site. The east site border was the boat
channel at the reference site, and an agricultural field at the disturbed site. Elevation
increased, and the sites became drier, as one moved away fi'om the north site border of
each site. Elevations were measured at each monitoring well and determined with respect
to a site benchmark. Surface and groundwater contours between the monitoring wells
were estimated using an inverse squared distance smoothing function (SPSS, Inc., 1996).
View point is from the southwest. ................................................................................. 83

Figure 2-20. Seasonal discharge and recharge pattern observed at the reference
hydrologic study site. In late winter and early spring, wet meadow substrates were
completely saturated. Evapotranspiration discharged groundwater more rapidly than it
was replenished by precipitation and storm surge inputs in late spring and early summer,
causing groundwater decline. Precipitation and storm surge inputs exceeded ET
discharges in late summer, recharging wet meadow groundwater. ................................ 85

xvii

Figure 3-1. Total plot biomass (g/0.25m2) and stem density (stems/0.25m2) at difi‘erent
mean mid-summer groundwater levels at the hydrologic study sites: 1996. At the
reference site, plot stem densities were greatest when water levels were just above or just
below the ground surface. Increased presence of T wha angustzfolia in inundated plots
resulted in higher plot biomass values where standing water levels were greatest. At the
disturbed site, total plot biomass and stem density varied significantly across the water
level gradient. Increased presence of Carex Iacustris and Phalaris amndinacea in shallow
groundwater plots, and Aster dumosus and Phalaris arundinacea in deep groundwater
plots, significantly increased plot biomass in those plots. Negative water level values -
indicate groundwater depth. Error bars equal :1 SEM. ................................................ 137

Figure 3-2. Change in importance value of Calamagrostis canadensis, Carex sartwellii,
Eleocharis smaIIii, and T ypha angustr'folia across the water level gradient at the reference
hydrologic study site: 1996. Each species exhibited different IV at various points along
the gradient. Positive water levels represent standing water depths, negative values
represent groundwater depths. Maximum possible IV = 300. ...................................... 138

Figure 3-3. Change in importance value of Campanula aparinoides, Carex bebbir',
Calystegia sepium, and Polygonum amphibium across the water level gradient at the
reference hydrologic study site: 1996. Each species exhibited different IV at various
points along the gradient. Positive water levels represent standing water depths, negative
values represent groundwater depths. Maximum possible IV = 300. ............................ 139

Figure 3-4. Change in importance value of Carex comosa, Cladium mariscoides, Juncus
balticus, and Lathyrus palustrr’s across the water level gradient at the reference hydrologic
study site: 1996. Each species exhibited different IV at various points along the gradient.
Positive water levels represent standing water depths, negative values represent
groundwater depths. Maximum possible IV = 300. ..................................................... 140

Figure 3-5. Change in importance value of Carex lacustris, and Leerzia oryzoides across
the water level gradient at the reference hydrologic study site: 1996. Each species
exhibited different IV at various points along the gradient. Positive water levels represent
standing water depths, negative values represent groundwater depths. Maximum possible
IV = 300 ...................................................................................................................... 141

Figure 3-6. Change in importance value of Aster dumosus, Calamagrostis canadensis,
Carex stricta, and Phalaris arundinacea across the water level gradient at the disturbed
hydrologic study site: 1996. Negative water levels represent groundwater depths. Each
species exhibited different IV at various points along the gradient. Maximum possible IV
= 300. .......................................................................................................................... 142

Figure 3-7. Change in importance value of Carex bebbii, Carex sartwellir’, Calystegia
sepium, and Spartina pectinata across the water level gradient at the disturbed hydrologic
study site: 1996. Negative water levels represent groundwater depths. Each species
exhibited different IV at various points along the gradient. Maximum possible IV = 300.143

Figure 3-8. Change in importance value of Anemone canadensis, Carex lacustrr's,
Lathyrus palustris, and Polygonum amphibium across the water level gradient at the
disturbed hydrologic study site: 1996. Negative water levels represent groundwater
depths. Each species exhibited different IV at various points along the gradient.
Maximum possible IV = 300. ....................................................................................... 144

Figure 3-9. Change in importance value of Galium obtusum, Lyc0pus americanus, and
Potentilla anserina across the water level gradient at the disturbed hydrologic study site:
1996. Negative water levels represent groundwater depths. Each species exhibited .
different IV at various points along the gradient. Maximum possible IV = 300. ........... 145

Figure 3-10. Saginaw Bay hydrographs for 1995-1997, and the average hydrograph for
1986-1996. The depth and duration of inundation for any part of the wet meadow zone
varied seasonally within years with annual variations in Saginaw Bay water level, and from
year to year with the inter-annual variations in Saginaw Bay water level. The solid
horizontal lines delimit the elevation of the Saginaw Bay coastal wet meadow zone. The
dotted horizontal lines indicate 10cm intervals within the wet meadow. Vertical lines
indicate growing season length for northern and southern Saginaw Bay. ...................... 147

Figure 3-11. Monthly mean and range of Saginaw Bay water levels recorded during the
1997 growing season. Monthly maximums averaged 36cm higher that monthly means,
and ranged as high as +67cm in October. Seiches and storm surges regularly inundated
portions of the wet meadow located above the mean elevation of Saginaw Bay. ........... 148

Figure 3- 12. Importance value of Calamagrostis canadensis, Carex aquatilis, Carex
stricta, and Carex sarrwellr‘i at different elevations within Saginaw Bay coastal wet
meadows. Each species had a different pattern of distribution with respect to elevation.
Maximum possible IV = 300. The mean Saginaw Bay high water mark (1918-1996)
equaled 176.67 m AMSL. ............................................................................................ 165

Figure 3-13. Importance value of Campanula aparinoides, Carex lacustris, Phalaris
arundinacea, and Polygonum amphibium at different elevations within Saginaw Bay
coastal wet meadows. Each species had a different pattern of distribution with respect to
elevation. Maximum possible IV = 300. The mean Saginaw Bay high water mark (1918-
1996) equaled 176.67 m AMSL. .................................................................................. 166

Figure 3-14. Importance value of C Iadium mariscoides, Lythrum salicaria, Phragmites
australis, and T ypha angustifolr’a at different elevations within Saginaw Bay coastal wet
meadows. Each species had a diflerent pattern of distribution with respect to elevation.
Maximum possible IV = 300. The mean Saginaw Bay high water mark (1918-1996)
equaled 176.67 m AMSL. ............................................................................................ 167

Figure 3-15. Mean importance value of Calystegia sepium, Galium obtusum, and Stachys
tenuifolia at different elevations within Saginaw Bay coastal wet meadows. Each species
had a difi‘erent pattern of distribution with respect to elevation. Maximum possible IV =
300. The mean Saginaw Bay high water mark (1918-1996) equaled 176.67 m AMSL. 168

xix

Figure 3-16. Principal component analysis bi-plot of major plant species importance
values and abiotic factors in Saginaw Bay coastal wet meadows. PC] was the best-fit line
describing the association among the abiotic factors. The small angular offset of the
elevation interval, soil texture, peat depth, and litter depth factors fi'om PCl indicated the
strong linkage of these factors with PCI. Species located close to the negative end of
PC] (C. stricta, G. obtusum) were most strongly linked with higher elevation wet meadow
plots containing thinner peat and litter mats and coarse-textured substrates. Those located
close to the positive end of PC] (C. aquatilis, C. lacustn‘s) were most strongly linked with
lower elevation wet meadow plots containing deeper litter mats and thicker peat. 170

Figure 4-1. Saginaw Bay region, with study sites used in the biomass study. Map data
from US Census Bureau TIGER database and Michigan Department of Natural
Resources. ................................................................................................................... 189

Figure 4-2. Percent contribution of plant types to the total oven-dry plant biomass of
Saginaw Bay coastal wet meadows (SBCWM). Biomass collected fi'om 228- 0.25m2
sample plots in 19 wet meadows. ................................................................................. 190

Figure 5-1. Map of reference and disturbed Saginaw Bay wet meadow study sites. The
reference sites, Sites 2, 8, 9, 10,11, and 13, were all located on Middle Ground Island and
Maison Island in the Wildfowl Bay State Game area (inset). The disturbed sites, Sites 1,
18, 19, 21, 26, and 31, were located on the main land. Map data from US Census Bureau
TIGER database and Michigan Department of Natural Resources. ............................... 228

Figure 52. Map of the 25 study sites used in the Purple Loosestrife portion of the study.
Sites #3, 15, 18, 19, 28, and 31 (marked by stars) were Purple Loosestrife sites. The
other 19 sites contained no Purple Loosestrife. Map data from US Census Bureau TIGER
database and Michigan Department of Natural Resources. ......................................... 230

Figure B 1. Groundwater condition on 5/9/95 at the disturbed hydrologic study site.
Groundwater levels were within 10cm of the ground surface throughout the well field in
the early growing season, with some of the lower elevation monitoring wells inundated to
depths up to 25cm. L8 = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing function (SPSS, Inc., 1996).

View point is from the northeast. ................................................................................. 252

Figure B2. Groundwater condition on 6/29/95 at the disturbed hydrologic study site.
Groundwater levels dropped between mid-May 1996 and late-June 1996 to as much as
60cm below the ground surface. This was true in wells located as little as 10m from the
on-site drainage ditch. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing function (SPSS, Inc., 1996).

View point is from the northeast. ................................................................................. 253

)0{

Figure B3. Groundwater condition on 10/20/95 at the disturbed hydrologic study site.
Groundwater levels established in late June were unchanged until late October. LS = land
surface; GW = groundwater surface. Surface and groundwater elevations were measured
at each monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing firnction (SPSS, Inc., 1996). View point is from the northeast. ................... 254

Figure B4. Groundwater condition on 12/26/95 at the disturbed hydrologic study site.
Partial groundwater level rebound has occurred across the site, with the largest increases
observed in the wells closest to the on-site drainage ditch. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing function (SPSS, Inc., 1996). View point is from the northeast. ................... 255

Figure B5. Groundwater condition on 2/14/96 at the disturbed hydrologic study site.
Groundwater levels across the site had increased by 25-30cm since December 1995.

Wells closest to the on-site ditch still showed greater groundwater increases than did wells
further from the ditch, probably due to continued infiltration of surface water from the
ditch into adjacent areas. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing function (SPSS, Inc., 1996).

View point is from the northeast. ................................................................................. 256

Figure B6. Groundwater condition on 3/21/96 at the disturbed hydrologic study site. On
this date, groundwater levels had risen to the surface across the wetland and almost all the
wet meadow was saturated to, or above, the ground surface. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing function (SPSS, Inc., 1996). View point is fi'om the northeast. ................... 257

Figure B7. Groundwater condition on 7/1/96 at the disturbed hydrologic study site.
Groundwater decline was once again observed at wells greater than 60m fiom the on-site
ditch. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an
inverse squared distance smoothing function (SPSS, Inc., 1996). View point is from the
east .............................................................................................................................. 258

Figure B8 Groundwater condition on 7/15/96 at the disturbed hydrologic study site. The
summer pattern of groundwater decline, observed previously at the disturbed site and
concurrently at the reference site, was evident here. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and

xxi

groundwater contour interpolation was performed using an inverse squared distance
smoothing function (SPSS, Inc, 1996). View point is from the east. ........................... 259

Figure B9. Groundwater condition on 9/16/96 at the disturbed hydrologic study site.
Intense rainfall event triggered fall groundwater recharge. As in 1995, the most rapid
recharge occurred closest to the on-site drainage ditch. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance .
smoothing firnction (SPSS, Inc., 1996). View point is from the east. ........................... 260

Figure B10. Groundwater condition on 12/10/96 at the disturbed hydrologic study site.
As in 1995, infiltration of surface water into the wet meadow from the on-site ditch
apparently constituted the major influence in raising groundwater levels in the wetland.

LS = land surface; GW = groundwater surface. Surface and groundwater elevations were
measured at each monitoring well and determined with respect to a site benchmark.
Surface and groundwater contour interpolation was performed using an inverse squared
distance smoothing function (SPSS, Inc., 1996). View point is from the east ............... 261

Figure B11. Groundwater condition on 1/26/97 at the disturbed hydrologic study site.
Groundwater levels mirrored the land surface throughout the site. LS = land surface; GW
= groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing function (SPSS, Inc., 1996). View point is fiom the northeast. ................... 262

Figure B12. Groundwater condition on 3/1/97 at the disturbed hydrologic study site. The
entire site was inundated to between 5-30cm depth. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing function (SPSS, Inc., 1996). View point is from the northeast. ................... 263

Figure 813. Groundwater condition on 6/11/97 at the disturbed hydrologic study site.
Groundwater decline of 30-40cm was observed at wells more than 160m from the on-site
ditch. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an
inverse squared distance smoothing function (SPSS, Inc., 1996). View point is from the
east. ............................................................................................................................. 264

Figure B14. Groundwater condition on 7/10/97 at the disturbed hydrologic study site.
Late June precipitation inundated the entire site. This condition was unchanged until early
October 1997. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an

xxii

inverse squared distance smoothing function (SPSS, Inc., 1996). View point is from the
northeast ...................................................................................................................... 265

Figure B15. Groundwater condition on 12/18/97 at the disturbed hydrologic study site.
Seasonal groundwater recharge was completed; the wetland was saturated to the land
surface throughout the site. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing function (SPSS, Inc., 1996). .
View point is fi'om the northeast. ................................................................................. 266

xxiii

Chapter 1 - General Introduction

The wetlands fringing Saginaw Bay are the largest remaining tract of freshwater
coastal wetlands in the 48 contiguous United States (US Geological Survey, 1996). Wet
meadows, the grass- or sedge-dominated herbaceous wetlands found between emergent
marsh and upland margin, are an important part of this coastal wetland complex. Little is
known about the ecology of these coastal wet meadows, because previous studies of the
region’s wetlands have focused on emergent marshes. There are two reasons for this.
Historically, there has been more interest in marshes because they produce commercially-
valuable fish, waterfowl, and fur-bearing animals. Also, agricultural conversion turned
easily drained, “unproductive” wet meadows into very fertile and profitable farm acreage.
Most Saginaw Bay coastal wet meadows were converted to agricultural uses in the late
19“ and early 20th centuries (Albert et al., 1988).

Saginaw Bay coastal wet meadows perform various ecological functions. Yet, we
lack a clear picture of their role in the overall ecological functioning of these freshwater
coastal wetlands. Detailed studies of coastal wet meadow ecology are needed to increase
our understanding of the functions performed by these wetlands.

Saginaw Bay coastal wet meadows shelter a number of threatened and endangered
plant species (Albert et al., 1988; Nature Conservancy, 1994) Preserving and protecting
threatened and endangered species requires a thorough understanding of the habitat in
which they live. Yet, no comprehensive study of the plant ecology of Great Lakes coastal

wet meadow habitat has ever been undertaken.

Previously drained Saginaw Bay coastal wet meadows present prime opportunities
for successful wetland restoration. A key factor in successfirl wetland restoration is a
clear understanding of pre-disturbance site characteristics (Prince and Burton, 1995).
However, very little base-line data has been collected for any Great Lakes coastal wet
meadow. This study was undertaken to help fill these gaps in our knowledge of this

important wetland type.

Wet meadows defined

Curtis (1959), describing Wisconsin sedge meadows, provided a concise general
definition of wet meadow vegetation. He described it as an open community growing on
wet soils, with greater than half the vegetation dominance contributed by sedges. These
communities occupy a very low position in the soil catena, with the permanent water table
lying just below the ground surface. Curtis indicated that sedge meadows graded into
cattail or reed marshes as conditions become too wet for the meadow species. Water was
always plentiful and never limiting, but excess water often resulted in stressful conditions
for the plants living there. Curtis pointed out that sedge meadows and wet prairies are
very similar wet soil community types, with wet prairies being dominated by grasses rather
than sedges (Curtis, 1959).

Keddy and Reznicek (1986) described Great Lakes coastal wet meadows as being
the grass- and sedge-dominated vegetation found in Great Lakes wetlands between the
yearly mean and yearly maximum Great Lakes high water levels. They placed wet

meadows just above the marsh on the wetland elevation continuum. Keddy and Reznicek

noted that this continuum often extended up-slope and inland to include shrub- or forest-
dominated wetlands located between the wet meadow zone and the upland boundary.
They concluded that the lower limit of successful shrub or tree invasion of coastal wet
meadows was determined by maximum annual Great Lakes high water levels, and that the
lower limit of successful wet meadow establishment was determined by mean annual Great
Lakes high water levels. They believed that the size and species composition of any
particular coastal wet meadow depended on the impact of abiotic factors such as shoreline
slope, substrate composition, wave exposure, water chemistry, and fire fi'equency (Keddy
and Reznicek, 1986).

Curtis also indicated that fire was important to wet meadow maintenance. He
observed that shrub-carr or Alder thickets commonly replaced wet meadow vegetation
within 10-20 years after fire suppression began, except in only the wettest wet meadows.
A study of Wisconsin sedge meadows described fire as a natural environmental element in
wet meadows that suppressed shrub and tree encroachment (Frolik, 1941).

Great Lakes wetlands occur in a many geomorphic settings (Minc and Albert,
1998; Chow-Fraser and Albert, 1998; Keough et al., 1999). The Michigan Natural
Features Inventory developed a hierarchical system which defined the various geomorphic
settings found along Michigan’s Great Lakes coastline ( Minc and Albert, 1998). MNFI
determined that Saginaw Bay wetlands were open coast wetlands (sensu Keough et al.,
1999) consisting of open embayments, sand-spit and protected embayments, and one
tributary embayment. Open embayments are fully exposed to wave energy, lateral
currents, and ice scour, and so often develop only a narrow fiinge of wetland. However,

the broad, shallow, gently sloping Saginaw Bay lake bottom attenuates these energies,

making the extensive, fine-textured Saginaw Bay clay lake-plains an ideal setting for
emergent marsh and wet meadow development (Ibid., 1998). Sand-spit embayments,
protected embayments, and tributary embayments are sheltered from most wave and
current energy. These lower-energy environments permit organic sediment accumulation
(Tilton et al., 1978) and extensive wetland development.

The vegetation association found in wet meadows has been variously labeled wet
meadows (Rumberg and Sawyer, 1985; Kelley et al., 1985; Keddy and Reznicek, 1986;
Kantrud et al., 1989; Keddy, 1990), sedge meadows (Curtis, 1959; Auclair et al., 1973;
Wilcox et al., 1985), fresh meadows (Shaw and Fredine, 1956), fen meadows (Jaworski
and Raphael, 1979), tussock meadow (Costello, 1936), wet prairie (Curtis, 1959; Hayes,
1964; Gunderson, 1994), wet grassland (F liervoet and Werger, 1984; Vermeer, 1986),
water meadows (Sjoberg and Danell, 1983), marsh meadow (Stout, 1914; Jeglum et al.,
1974), and graminoid fen (Jeglum et al., 1974). The different terms arose fiom regional
preferences (e. g., wet grassland is a European term) and fi'om slight variations in the biotic
and abiotic conditions found within this vegetation type. Variations among types generally
involved difi’erences in the identity of dominant species (e. g., sedges versus grasses), or
minor differences in hydroperiod, substrate composition, water chemistry, or landscape
position.

Important attributes of the wet meadow vegetation association are:

- Wet meadows are grass- or sedge-dominated herbaceous wetlands.

- They occur in low landscape positions, or as fiinging wetlands at the margin of

rivers, streams and lakes. When fringing wetlands, they occur on the landscape

between emergent shallow marshes and either shrub or forested wetlands, or the
upland boundary.

- The soils are commonly saturated to within a few centimeters of the ground
surface, but they are not normally inundated for long periods during the growing
season.

- Plants must be adapted to occasional flooding, but generally need not tolerate
long periods of inundation during the growing season.

-Fire and/or a sufficient duration of soil saturation are required to suppress woody
plant invasion.

- Wet meadows accumulate peat.

These attributes describe the coastal wetland plant community located adjacent to

Saginaw Bay between the cattail or bulrush marsh and the upland shrub or tree line. This

wet meadow vegetation association was the subject of the study.

Purpose of the study

This study had three main goals. The first goal was to determine the above-ground
vegetation structure, composition, and productivity of Saginaw Bay coastal wet meadows.
The current literature lacks such information. Once developed, this information could be
used to compare Saginaw Bay coastal wet meadows to other ecosystems, and as baseline
data for fiiture Great Lakes coastal wet meadow restoration efforts.

The second goal was to determine how hydrology influenced the above-ground

vegetation structure, composition, and productivity of Saginaw Bay coastal wet meadows.

Such information is key to understanding the plant ecology of coastal wet meadows, and
to the proper design, implementation, and completion of successful Great Lakes coastal
wet meadow restoration projects.

The third goal was to determine how above-ground vegetation structure,
composition, and productivity differed between human-impacted and relatively
undisturbed reference wet meadows. Cultivation, diking, and ditching are the most
common and most damaging human impacts in these wetlands. Such disturbances
degrade native flora and facilitate establishment of invasive exotic and native non-wetland
plants. Differences between disturbed and reference wet meadow vegetation should
provide important clues about how biotic and abiotic factors impact the plant ecology of
these wetlands. The distribution of native and exotic plants within disturbed coastal wet
meadows may provide insights into the re-vegetation trajectories to be expected in fixture

coastal wet meadow restorations.

Study Region

The study took place in the coastal zone of Saginaw Bay, the southwestern lobe of
Lake Huron, one of the five Laurentian Great Lakes of north-central North America
(Figure l-l). Formed by Pleistocene glaciation, the Saginaw Bay basin has been reshaped
many times by glacial advances and retreats (Dorr and Eschman, 1970). Since the most
recent glaciation ended approximately 12000 BP, post-glacial isostatic rebound and

changes in Great Lakes water levels have firrther altered shore line location and elevation

(Ibid., 1970). Saginaw Bay has maintained its current shoreline configuration for about
the last 2500 years (Ibid., 1970).

The Saginaw Bay watershed, contained entirely within the state of Michigan,
drains 22533km2, an amount equaling 15% of Michigan’s land area (SBNWI, 1998).
Saginaw Bay itself covers 2960km2, and has a shore line length of 622km2 (Ibid., 1998).
Saginaw Bay is a shallow embayment with a gently sloping bottom formed by the inter-
layering of glacial till, glacial outwash, and lacustrine silts and clays deposited since
glaciation ended. The average depth of the inner bay is 4.6m. The outer bay averages
14.6m deep. This favorable combination of basin morphology, substrate composition, and
hydrologic regime enhances wetland development in the Saginaw Bay coastal zone
(Jaworski et al., 1979; Geis, 1985).

Historically, wet meadow vegetation extended up to 5km inland along the eastern
Saginaw Bay shore line (Davis, 1900; Jaworski and Raphael, 1978; Albert et al., 1988).
Agricultural development has limited the present wet meadow zone to a narrow strip
along the coast. Saginaw Bay coastal wetlands may have covered more than 283 50ha
prior to European settlement (Prince and Burton, 1995). Current estimates of extant

Saginaw Bay coastal wetland range between 6075-7300ha (U SGS, 1996; SBNWI, 1998).

Land use history

Prior to Europeans settlement, the region was home to various American Indian
tribes. About 4000 BP, the “Old Copper” people inhabited sites near what is now Bay

City (W eesies, 1980). The “Hopewell” Indians occupied the region from about 500 BC to

700 AD, leaving burial mounds as evidence of their presence (Ibid., 1980). The Sauk, the
tribe from which the name for Saginaw Bay is derived, occupied the region until the 18‘”
century, when they were displaced by the Fox, Potawatomi, Ojibway, and Chippewa
Indian tribes (Clifton, 1997). These tribes were primarily hunter-gatherers who practiced
limited row crop cultivation to supplement their diet (Mettert, 1986; Clifton, 1997). -
However, by culture and custom the American Indian trod lightly on the land, so human
impacts were minimal prior to European settlement (Dodge, 1920).

European settlement began in the 18305, with early economic activity centered
around lumbering the forest-rich land. Agricultural activity increased in the 1850s on the
recently cleared landscape, but tree stumps and wet, swampy land were impediments to
farming (Linsemier, 1980). Major forest fires occurred along Saginaw Bay’s eastern shore
in 1871 and 1881, and several times between 1900 and 1920 along the western shore,
destroying the remaining forests, and clearing additional land for agricultural production
(Dodge, 1920; Mettert, 1986).

Efforts to drain coastal wetlands were well under way at the end of the 19th
century (Davis, 1908; Prince and Burton, 1995). By 1917, agricultural drains totaling
1016km had been constructed in the counties bordering southern Saginaw Bay (Miller and
Simmons, 1919). Nearly 70% of the inland wetlands of these counties have since been
converted to cropland, and less than 1% of the region’s original wet meadows still exist
today (Prince and Burton, 1995).

The 22-county Saginaw Bay watershed is home to 1.4 million people (SBNVVI,
1998). Watershed land use patterns remain mostly rural, and can be divided into

agricultural use (46%), forested land (29%), open land (11%), urban land (8%), wetlands

(4%), and open water (2%). The major agricultural crops are sugar beets, dry beans,
potatoes, corn, wheat, and barley (SBNWI, 1998). Sport fishing, pleasure boating,
swimming, and bird watching make important contributions to the local economy. The
population of the region is expected to increase, placing additional strains on the natural

resources of the Saginaw Bay watershed.

Climate

Saginaw Bay is located in the northern temperate zone, but regional climate is not
typical for its position on the North American continent. Michigan’s climate has been
described as “semi-marine” (Eichenlaub et al., 1990) due to the influence of the nearby
Great Lakes. The Great Lakes moderate climatic extremes, yielding cooler, wetter
summers and warmer, snowier winters than would normally be found in a mid-continent
climatic zone (Keen, 1993).

The regional mean annual temperature is 8°C, ranging between -32°C and +3 8°C.
Mean annual precipitation is 73 7mm, with approximately 60% of the annual total falling
between April and September (Michigan Department of Agriculture, 1989). Mean annual
snowfall is 1054mm (Ibid., 1989). Evaporation exceeds mean May-October precipitation
by 32%, highlighting the importance of fall and winter precipitation in annual soil moisture
replenishment (Ibid., 1989). The growing season ranges from 126 days at Standish to 168
days at Bay City (Appendix A1).

Michigan is located in the ecological transition zone linking North American boreal

coniferous and temperate deciduous forests. This so-called “tension zone” passes across

Michigan’s lower peninsula from Muskegon to Saginaw. It also divides Michigan’s
Thumb region on a line commencing just south of Sand Point on Saginaw Bay’s eastern
shore and proceeding south to Caro, and then southeast fiom there to Lexington on Lake
Huron’s western shore (Dodge, 1995). The existence of the tension zone has been
attributed to climatic factors (Potzger, 1948) and plant range limitations (Kapp, 1978;
McCann, 1979). However, the changes in vegetation composition associated with
Michigan’s tension zone are more strongly correlated with soil factors than with climate,
and edaphic factors probably account for the observed vegetation changes (Livingston,
1903, 1905; Elliott, 1953; Veach, 1953; Medley and Harmon, 1987). The mixture of
biomes occurring within the state contributes to the diversity of Michigan’s flora,

estimated at over 2500 vascular species (Voss, 1996).

Sofia

Regional soils were derived from shale, limestone and dolomitic bedrock located in
Michigan’s northern lower peninsula (Dorr and Eschman, 1970). The parent rock was
crushed and transported south by Pleistocene glaciation to be deposited as glacial till,
glacial outwash, or lacustrine sediments, or by wind as alluvium (Dorr and Eschman,
1970; Mettert, 1986).

Pedogenesis is well advanced in the region. Organic matter has accumulated in the
soil since the most recent glaciation event and the soils for the most part exhibit well
developed horizons (Mettert, 1986). The state of soil development provides few, if any,

limitations to plant growth.

10

The soils bordering Saginaw Bay are mostly poorly to very poorly drained sandy
and loamy soils in the south and clay and clay loam soils in the north (Linsemier, 1980;
Mettert, 1986). These loamy and clayey soils tend to be calcareous, and when properly
drained can be highly productive agricultural land (Mettert, 1986). Excessively drained
sandy soils, deposited by earlier, higher glacial lake stages, are often found on coastal
beach ridges and along the northeastern shore of Saginaw Bay. These beach ridges,
sometimes called “islands” (Davis, 1908; Dodge, 1920), are often used as sites for
residences and other purposes (Mettert, 1986).

Mucks and aquents are common in the low-lying, frequently inundated coastal
areas. Despite high organic matter content, these soils are generally unsuitable for most
human uses because proximity to Saginaw Bay make drainage difficult and expensive
(Mettert, 1986).

The USDA-NRCS has only begun describing and mapping wetland soils in the last
25 years (Tilton et al., 1978). Recent soil surveys for St. Clair and Monroe counties
(Michigan) included soil profiles for wetlands bordering Lake St. Clair and Lake Erie (see
Tilton et al., 1978). These profiles provide clues at to the probable stratigraphy of
Saginaw Bay wetland soils. However, no wetland soil profile descriptions are available

for the soils bordering Saginaw Bay.

Study sites

Using maps and aerial photographs, 31 potential coastal wet meadow study sites

were identified on the Saginaw Bay coast between Port Austin, MI and Au Gres, MI

11

(Figure 1-2). Aerial photographs were used to identify and eliminate forested or
cultivated sites, and coast line occupied by artificial structures. Visits to remaining sites
pinpointed the location of coastal wet meadows. Six sites were unsuitable for this study,
being either too small or having wet meadow vegetation that was being rapidly displaced
by cattail marsh. In the end, 25 coastal wet meadows were included in the study
(Appendix A2).

Sites 1 and 2 were used in the study of coastal wet meadow hydrology. Detailed
hydrologic and vegetation data were collected at these two sites. Vegetation surveys were
performed at the remaining 23 wet meadow sites, and soil samples were collected at all 25

wet meadow sites.

Previous research

General information concerning the botany and ecology of Great Lakes coastal wet
meadow vegetation can be found in studies of wetlands bordering Lake Michigan (Ward,
1896; Harris et al., 1981; Kelley et al., 1985; Wilcox et al., 1985), the St. Marys River
(Duffy et al., 1987), Lake St. Clair (Pieters, 1894; Reighard, 1894; Hayes, 1964;
Herdendorf et al., 1986), the Detroit River (Campbell, 1896; Manny et al., 1988), Lake
Erie (Pieters, 1901; Herdendorf, 1987; Sherman et al., 1996), and the St. Lawrence River
(Auclair et al., 1973). Keddy and others (Keddy, 1983; Wilson and Keddy, 1986a, 1986b;
Shipley et al., 1991; Weiher and Keddy, 1995; Twolan-Strutt and Keddy, 1996, as
examples) have experimentally studied the influence of environmental gradients on plant

competition, including plants of Great Lakes coastal wet meadows. Regional wetland

12

surveys (Tilton et al., 1978; Jaworski and Rapahel, 1979; Herdendorf et al., 1981) provide
data about Great Lakes coastal wetlands, and the Michigan Natural Features Inventory
compiled reports on Michigan’s coastal wetland systems (Albert et al., 1988, 1989;
Comer, et al., 1993; Minc, 1996; Minc, 1997a, 1997b). Nonetheless, the extent of
botanical research conducted in Great Lakes coastal wetlands was recently characterized
as “cursory” (Klarer and Millie, 1992).

The Saginaw Bay coastal wetland flora has been fairly well described (Davis, 1900,
1908; Michigan Geological and Biological Survey, 1911; Dodge, 1920; Herdendorf et al.,
1981; Albert et al., 1988, 1989; Prince and Burton, 1995). Early vegetation surveys
established an historical record of the coastal wetland flora of Huron County (Davis,
1900), Tuscola County (Davis, 1908), and Bay and Arenac counties, MI (Dodge, 1920).
Perhaps most remarkable was the 1908 biological survey of the eastern shore of Saginaw
Bay performed under the direction of Alexander Ruthven (Michigan Geological and
Biological Survey, 1911). Ruthven selected this region to study because “the area is
almost wholly uncultivated and in a primitive condition, and would consequently be
expected to harbor the primitive fauna and flora” (Michigan Geological and Biological
Survey, 1911, p. 13). From a base camp at Sand Point, Ruthven and a team of seven
biologists produced detailed descriptions of the identity, ecology, and distribution of the
region’s plants, mammals, birds, amphibians and reptiles, insects, and fish. CH. Coons’
descriptions of “sedge and grass swamps” and “reed swamp formation - Phragrnites
association” provide valuable insights into the structure, species composition and ecology
of the region’s pristine coastal wet meadows (Coons, 1911). C. K. Dodge documented

886 terrestrial and wetland plant species that summer, many of which can still be found in

13

the region today. Most remarkably, Ruthven photographed several coastal wetlands,
leaving a visual record of how they appeared in 1908. These sites still look very much as
they did 90 years ago.

Recent work by the Michigan Natural Features Inventory supports these earlier
observations (Comer, et al., 1995; Comer, 1996). More recent vegetation surveys
describe the current species composition (Herdendorf et al., 1981; Albert et al., 1988,
1989; Prince and Burton, 1995), location, and extent (Jaworski and Raphael, 1979;
Herdendorf et al., 1981; Albert et al., 1988, 1989; Comer, 1996) of Saginaw Bay coastal
wetland vegetation. However, ecological descriptions of the vegetation are less common,
and a detailed examination of the factors controlling the structure, productivity, and
species composition of Saginaw Bay coastal wet meadow vegetation has never been

completed.

Organization of the study

This study will be described in five chapters. Chapter 1 (this chapter) provides a
general introduction to the study. Chapter 2 will discuss the hydrologic factors acting on
Saginaw Bay coastal wet meadow vegetation. Chapter 3 will discuss the vegetation
structure, plant species composition, and plant species relationships of Saginaw Bay
coastal wet meadows. Chapter 4 will discuss the above-ground biomass and productivity
of Saginaw Bay coastal wet meadow vegetation. Chapter 5 will discuss the impact of

disturbance on the coastal wet meadow vegetation association.

r4

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Agriculture, Soil Conservation Service. Washington, DC.

Weiher, E. and RA. Keddy. 1995. The assembly of experimental wetland plant
communities. Oikos 73: 323-335. '

Wilcox, D.A., S.I. Apfelbaum, and RD. Hiebert. 1985. Cattail Invasion of Sedge
Meadows Following Hydrologic Disturbance in the Cowles Bog Wetland Complex,
Indiana Dunes National Lakeshore. Wetlands 4: 115-128.

Wilson, SD, and PA. Keddy. 1986a. Species competitive ability and position along a
natural stress/disturbance gradient. Ecology 67: 1236-1242.

21

Wilson, SD, and PA. Keddy. 1986b. Measuring diffirse competition along an
environmental gradient: results from a shoreline plant community. American Naturalist
127: 862-869.

22

 

 
   

Lake Superior

OD Lake Huron

Saginaw Bay

Lake Michigan

Lake Erie

 

 

 

 

 

Figure 1-1. Western Great Lakes region, with Saginaw Bay indicated.

23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P
13
CGSBVIIIBO 12 l
4-
10 9
,6 I_l__.l_.l
D .1 2 3
*7 KM
19 50
, Saginaw Bay - 15
ling
N
1’ 16
l 1 J l | l
.9. Cl 0 8
1 .31 KM
\ ‘7 l-F— KE.Stmlay, 1999

 

 

Figure 1-2. The location of coastal wet meadows in the Saginaw Bay coastal zone. Of 31
known wet meadow sites, Sites 7, 12, 16, 17, 23, and 29 were not included in the study.
There were no coastal wet meadows between Caseville and Port Austin on Saginaw Bay’s
eastern shore. Map data from US Census Bureau TIGER database and Michigan
Department of Natural Resources.

24

 

Chapter 2 - The hydrology of Saginaw Bay coastal wet meadows: Natural systems
and disturbance impacts

Introduction

Hydrology is the driving force behind the development and maintenance of wetland
ecosystems (Mitsch and Gosselink, 1993; National Academy of Sciences, 1995). ’
Hydroperiod, the temporal pattern of water level fluctuation in a lake, stream, or wetland,
is key to determining the structure, function, and species composition of wetland
vegetation (Mitsch and Gosselink, 1993). Any examination of wetland vegetation must be
rooted in an understanding of how hydrology influences the landscape on which the plant
community is assembled.

Early investigators noted the link between water depth and vegetation zonation in
Great Lakes coastal wetlands (Pieters, 1894; Pieters, 1901; Michigan Geological and
Biological Survey, 1911). Others have reported that fluctuating water levels enhance
wetland plant diversity in Great Lakes coastal wetlands (Stuckey, 1975; Burton, 1985,
Keddy and Reznicek, 1986; Klarer and Millie, 1992; Wilcox, 1995). Water level
fluctuations of variable fiequency and amplitude are known to produce greater plant
diversity than do regular hydroperiods (Wilcox and Meeker, 1991). Characteristics of
water level fluctuation include magnitude, duration, timing, and fi'equency of occurrence
(Wilcox, 1995) and variation in these characteristics can result in the development of
different wetland types (Keddy, 1983; Keddy and Reznicek, 1986; Keddy, 1989; Wilcox,
1995). Understanding the fluctuations of Saginaw Bay, a portion of Lake Huron, is a key

to understanding the vegetation stnrcture and distribution of its coastal wet meadows.

25

Great Lakes hydroperiods can be divided into three distinct groupings: multiple-
year, seasonal (within-year), and fluctuations that occur on the order of hours or days,
such as seiches and storm surges (Keough, 1990). The most apparent of the multiple-year
events are the 7-11 year cycles described by various investigators (Cohn and Robinson,
1976; Burton, 1985; Kelley et al., 1985, among others), though opinions difl‘er as to the
length, or even the existence, of these cycles (Keough, 1990). Between 1994 and 1997,
the Great Lakes were in the increasing phase of their most recent ll-year hydroperiod
(Figure 2-1), peaking in July 1997 at approximately 20cm below the highest Lake Huron
levels recorded since 1918 (U SACOE, 1998).

Within-year cycles are annual lake-level fluctuations driven by spring rains and
snow melt (Figure 2-2). Annual Great Lakes water-level fluctuations exhibit a certain
periodicity; they are generally at their lowest in the winter and their highest in the summer.
By contrast, the amplitude of year-to-year and within-year water-level fluctuations are
more variable, and much less predictable.

Seiches are regular, recurrent water surface oscillations, or “free standing waves”
(Mortimer and Fee, 1976), most commonly caused by winds or changes in barometric
pressure (Herdendorf, 1987; Keough, 1990; Bedford, 1992; Keough et al., 1999). Seiches
occur in all the Great Lakes, typically exhibiting a 2-14hr frequency and 20-30cm
amplitude (Sager et al., 1985; Herdendorf, 1987; Keough, 1990; Batterson et al., 1991).
Several seiche modes can operate independently and simultaneously in a lake; at least five
modes have been identified for Lake Huron (Mortimer and Fee, 1976). Difl’erent seiche
modes reinforce or cancel each other out, yielding a complex pattern of surface water

oscillation. A lake’s seiche frequency is determined by its basin geomorphology and so is

26

predictable, whereas seiche amplitude is determined by meteorological conditions, and is
therefore less predictable (Keough, 1990; Bedford, 1992).

Storm surges, the major driver of lake seiches, are unpredictable water level
fluctuations associated with the passage of storm fronts (Keen, 1993). When a storm
surge occurs, winds push water to one end of a lake, increasing lake levels on the
downwind side of the lake. When the winds decrease, the water “sloshes” back across the
lake surface, reinforcing seiche amplitude (Ibid., 1993). Storm surges of 0.5-3m occur in
the Great Lakes, and the residual effects of large storm surges can last for days
(Herdendorf, 1987; Keen, 1993).

Solar and lunar tides occur in the Great Lakes, but have negligible impact on Great
Lakes water levels (Verber, 1960; Platzrnan, 1966; Mortimer and Fee, 1976). Theoretical
studies suggest that tides up to 1.2cm occur in Lake Huron (Hamblin, 1976). In any case.
the maximum observed Great Lakes tidal fluctuations, measured in Lake Erie, were only
3.3cm (Herdendorf, 1987).

The impact of Great Lakes surface water fluctuations on coastal vegetation has
been described for Lake Michigan (Harris et al., 1981; Burton, 1985; Kelley et al., 1985;
Keough, 1990), Lake Erie (Keddy and Reznicek, 1986), and Lake Huron coastal wetlands
(Batterson et al., 1991). While focused on coastal marsh vegetation, these studies have
provided some indication of how lake hydroperiods impact coastal wet meadow
vegetation.

Less is known about how other hydrologic factors, such as groundwater,
precipitation, and evapotranspiration, influence coastal wet meadow vegetation.

Groundwater and precipitation inputs, and evapotranspiration losses, are probably of

27

minor importance in the hydrologic budget of inundated coastal marshes. However, Great
Lakes surface water levels may not always dominate coastal wet meadow hydrology.
Great Lakes coastal wet meadows occur above the lake surface elevation (Keddy and
Reznicek, 1986), so groundwater, precipitation, and evapotranspiration may play a
significant role in coastal wet meadow hydrology.

Evidence collected from similar Great Lakes coastal wetlands supports this
argument. Hydrologic studies of non-contiguous bogs, fens, and inter-dunal marshes and
swales bordering Lake Michigan in Indiana (Wilcox et al., 1986; Doss, 1993; Shedlock et
al., 1993; Souch et al., 1998), and dune ponds and wet pannes bordering Lake Michigan in
Michigan (Barko et al., 1977; Hiebert et al., 1986) have illustrated the importance of
groundwater, precipitation, and evapotranspiration in these coastal systems. However,
conclusive studies of contiguous coastal wet meadow hydrology are lacking in the

literature.

Objectives
The goal of this chapter was to describe the hydrology of Saginaw Bay coastal wet
meadows. The specific objectives were:
1. to describe the groundwater, surface water, precipitation, and
evapotranspiration hydrology of selected sites;
2. to describe how the soil moisture content of non-saturated wet meadows
varies through the growing season, and;

3. to describe how groundwater, surface water, precipitation,

28

evapotranspiration, and soil moisture content act and interact to shape the

hydrologic regime of Saginaw Bay coastal wet meadows.

Sites

Two sites were utilized in the study, one reference site, and a site which had
undergone extensive anthropogenic (human-induced) hydrologic and vegetation
disturbance. There are no truly undisturbed coastal wet meadows in the Saginaw Bay
coastal zone, so the reference site was selected not because it was pristine or even
undisturbed, but rather because it was representative of “natural or quasi-natural wetlands
that either occur presently in the region or occurred there at one time” (Brinson, 1993,
p.61).

Various methods have been used to disrupt the natural hydrology of Saginaw Bay
coastal wet meadows. Dikes or levees were often constructed to prevent flooding of low-
lying land, and then ditches, drains, tiles, or mechanical pumping were utilized to de-
saturate the newly protected land. Ditches or tiles installed on the land-ward side of dikes
collected water and conducted it away from the site, or to holding ponds near the dike.
Natural drainage features, such as swales, were sometimes modified to enhance site
drainage efiiciency. The ditches and tiles discharged into agricultural drains, which
conducted water to Saginaw Bay. Where the land surface was at or below the level of
Saginaw Bay, pumps were used to lift water fi'om ditches to drains over the dikes.
Recovered land was commonly placed into agricultural production.

The reference site was located approximately 20m west of a boat channel bisecting

Middle Ground Island, one of a small group of islands comprising the Wildfowl Bay State

29

Game Area. Wildfowl Bay SGA is located about 12km north of Sebewaing, MI and 2km
ofi‘ the coast in eastern Saginaw Bay (Figure 2-3, Site #2). Middle Ground Island is a low
barrier island consisting of highly permeable sand deposits beneath loamy sand and organic
surface soils. The reference site sloped from south to north, with its maximum elevation
occurring on the south shore of the island, where it was approximately 50cm higher than
Saginaw Bay. This low relief meant that the entire site was subject to inundation during
storms and in high water years. The island was approximately 180m wide at the site.

The reference site was not pristine. Temporary hunting and fishing camps are
occasionally established on Middle Ground Island, but none were established within 1km
of the site during the study, and no permanent residences have ever been built there (T.J.
Jahr, Jr, pers. comm). Cattle were grazed on the island during the 1930’s, but this land
use pattern was discontinued by 1940 (TI Jahr, Jr, pers. comm). No cultivation was
reported by long-time local residents.

An aerial photo chronosequence of the site indicated that the boat channel was
excavated prior to 193 8, and that it was a stable feature on the landscape. The presence
of the boat channel rendered the site a peninsula with a well-defined east-west oriented
south shoreline and north-south oriented east shorelines. These fixed and stable shorelines
provided a unique opportunity to study the hydrology of this wet meadow.

Despite these impacts, the Middle Ground Island site was suitable as a reference
site because site hydrology was minimally-disturbed compared to most Saginaw Bay
coastal wet meadows. The available evidence indicated that vegetation at the site was
representative of the current state of Saginaw Bay wet meadows (Albert et al., 1988,

1989; and see Chapter 3), and in many respects reflected the pre-settlement vegetation of

30

the region (Michigan Geological and Biological Survey, 191 1; Corner, 1996).

The disturbed site, located about 19km southwest of the reference site on Saginaw
Bay’s eastern shore (Figure 2-3, Site #1), had undergone extensive hydrologic and
vegetation alteration. It bordered Saginaw Bay in an area in which coastal wetlands
historically extended up to three miles inland (Davis, 1900; Jaworski and Raphael, 1979;
Albert et al., 1988). An agricultural drain, diked on either side, had been constructed
along the northern site boundary between 1940-1949. Immediately north of this drain and
dike system was the cattail marsh. The dike on the south side of the drain, 3m tall and 3m
wide at the base, prevented site inundation by Saginaw Bay. The drain carried excess
surface water from nearby fields to Saginaw Bay. The site, whose soils consisted of
approximately 45cm loamy sand over glacial till, had either been cultivated or used as a
pasture for 80-100 years prior to its abandonment in the late-1980’s (K. Wildner, pers.
comm). Drained and cultivated farm fields bordered the disturbed site on the east and
west. Although drainage tiles were never installed at the site (D. Schafer, pers. com), a
ditch had been constructed, and a natural swale had been modified, on the site between
1949-1955 to improve site drainage. The water level in these structures, isolated from
Saginaw Bay behind the dike, was regulated until 1989 by pumping water from the on-site
ditch over the dike into the drain (K. Streeter, pers. com.)

The growing season in southern Saginaw Bay averages 168 days, generally
running from early May to early October (Office of the Michigan State Climatologist,
unpublished data). Regional mean annual precipitation (1961-1990) was 67.9cm.

Monthly rainfall was greatest in late summer, with 16.7cm (24.6%) of the annual total

31

occurring in August and September. Mean monthly totals ranged from 2.7cm in January

to 9.0cm in September (see Appendix B1).

Methods

During 1996-1997, groundwater, surface water, precipitation, and pan evaporation
data were collected at the two hydrologic study sites. Data for these four hydrologic
variables were collected weekly from May through September. In other months,
groundwater data only were collected approximately monthly. The soil moisture content
of non-saturated wet meadow soils was determined at the two sites four times during the
1996 growing season.

Stafi‘ gauges were installed to monitor surface water levels (i0.1cm) at the sites.
One was installed in Saginaw Bay at the reference site (Staff Gauge #3, Figure 2-4), and
two staff gauges were installed at the disturbed site, one in the on-site drainage ditch
(SGI, Figure 2-5), and the other in the drain on the north side of the dike, which
discharged into Saginaw Bay (8G2). Data on the frequency and amplitude of Saginaw
Bay seiches and storm surges were obtained fi'om the National Oceanographic and
Atmospheric Administration (NCAA, 2000).

Gardeners rain gauges were employed to measure precipitation. Accumulated
rainfall was recorded and the rain gauges emptied each time groundwater data were
collected. Readings were determined to the nearest 0.01in in the field, then converted to
metric units for analysis.

Pan evaporation data were used to estimate actual wet meadow evapotranspiration

32

(“ET”). Centimeter rulers were glued into 5.7L (33cm x 17cm x 12cm) translucent plastic
containers. One of these open-top containers was placed in contact with the soil surface
at each site after all vegetation within a 1m radius of each pan had been clipped at the
substrate. Each container was filled to a pre—determined level with water, and evaporative
water loss was measured (:tO. 1cm) at each subsequent visit, after which the containers
were refilled to the pre-deterrnined level. Vegetation was clipped as necessary to maintain
the open space around the container. Evaporative losses for each time period were
determined by subtraction, after correcting for precipitation inputs.

Potential evapotranspiration (PET) was estimated from measured pan evaporation
using the formula

PET = C..,Ep (Equation 2-1)

where C6 is the pan coefficient and El) is the measured pan evaporation, usually expressed
in mm/day (Brooks et al., 1991). PET is generally lower than evaporation values obtained
by pan estimation; pan coeflicients correct for this difference.

Pan coemcients differ for Class A evaporation pans and small pans, such as those
used in this study (Pruitt, 1960; Chang, 1968; Wang and Felton, 1983). Small pans
exchange heat with the air more quickly than do Class A pans. Heat transfer between soil
and pan can accelerate or retard evaporation rates of pans resting on the soil, depending
on whether the soil is warmer or colder that the pan. Small pans can over- or
underestimate evaporation, depending on air and soil temperature and soil moisture
conditions (Chang, 1968). Chang also reported that black pans exhibited 23% greater
evaporative loss that did white pans. The impact of pan size on evaporative loss varies

with relative humidity as well (Mather, 1959). Pan size greatly influenced evaporation

33

rates when relative humidity was low, but had little impact on evaporation rates when
relative humidity was high (Ibid., 1959). However, the net influence of these factors on
small pan evaporation rates may not be as great as previously thought.

A recent Texas study found little difference in Class A and small pan evaporation
rates (Parker et al., 1999). Parker et al. compared evaporation rates from 33cm x 23 cm x
12cm translucent plastic pans, elevated 15cm above the ground on white and brown
plywood benches, to that of a Class A evaporation pan. They reported that differences in
evaporative loss from the small pans ranged between -7% and +16% of the Class A pan
rate, with the mean percentage small pan evaporation for five trials being 4% greater than
the Class A pan (Ibid., 1999). They reported no consistent difference in evaporation rates
for small pans on white versus brown backgrounds compared to the Class A pan.

Class A evaporation pan coefficients can be estimated given knowledge of the
relative humidity, winds, and fetch of unimpeded airflow at a site (Allen and Pruitt, 1991 ).
Given typical growing season mean daily relative humidity values (50%-80% near
Saginaw Bay; Michigan Department of Agriculture, Climatology office, unpublished data),
growing season wind speed (10-78km/day in southern Michigan; Michigan Department of
Agriculture, Climatology office, unpublished data), and Saginaw Bay coastal wet
meadows fetches (conservatively, IOm-IOOm; see Chapter 3), Class A pan coefficients can
be expected to range between 0.66 and 0.85 for Saginaw Bay coastal wet meadows (Allen
and Pruitt, 1991, Table 5). This estimate is consistent with Lafleur (1990a), who, using
the Bowen energy budget approach, estimated Class A pan coefficients to be 0.83 for
“wet” sedge-dominated James Bay wetland sites, and 0.61 for “dry” sedge-dominated

James Bay wetland sites.

34

Given these estimates, and given that pan coefiicients of 0.7 to 0.75 are commonly
used where they have not been experimentally determined (Eichenlaub et al., 1991;
Brooks et al., 1991), a pan coefficient of 0.7 was used in this study.

The relationship between PET and ET is complex, dependent upon the vegetation
present, vegetation rooting depths, available soil water, and the soil water capacity of the
site under study (Brooks et al., 1991). ET nearly equals PET in soils wetted to field
capacity (Ibid., 1991), and wetland soils are usually saturated to greater than field
capacity, so pan evaporation estimates of PET should provide good estimates of ET in the
wet meadow study sites.

Groundwater monitoring wells were installed at each site. Each well consisted of a
PVC well screen (1.5m long, 5.1cm diameter, with 0.0254mm mesh) placed in 10cm
diameter by 90-100cm deep bore hole. A 10-3 0cm deep sand filter pack was placed
around each screen, and then the bore holes were back-filled with native soil cuttings.
Groundwater monitoring wells were installed at each site in a rectangular grid with the
long axis perpendicular to the Saginaw Bay shoreline. Details of well field layout can be
found in Appendix B2

Groundwater depths were determined using a remote-probe sump pump overflow
alarm (Sonin Floodwatch® Model 30200). The factory-installed probe tip and
connecting-cable were removed and replaced with an incrementally-labeled cable.
Groundwater levels were measured (10. 1cm) from the well lip to the groundwater surface
inside each well. The groundwater depth beneath the ground surface was calculated later
by subtracting the height of the well lip above the ground from the groundwater

measurement determined in the field. Groundwater measurements were collected at

35

approximately the same time of day at each site to minimize variability resulting from
diurnal ET fluctuations. Diurnal variation in evapotranspiration rates are known to cause
cyclical groundwater fluctuations in cypress swamps (Heimburg, 1984; Ewel and Smith,
1992), and daily groundwater fluctuations of up to 20cm have been observed in
experimental agricultural plots near the disturbed hydrologic study site (H. Belcher, pers.
comm).

Once the well fields and staff gauges were in place, a laser level (Spectra-Physics
Model 650 Laser Level projector and Model 1175 Laser Eye detector) was used to
determine the ground elevation at each well, the elevation of each well lip, the elevation of
the top of each staff gauge, and the substrate level at each staff gauge with respect to a
benchmark installed at each site. No effort was made to tie site benchmarks to Datum.
The elevation data facilitated the study of patterns of surface water and groundwater
fluctuation at each site. These patterns helped identify the factors driving surface water
and/or groundwater flux in coastal wet meadows.

The percent soil moisture content of non-saturated soils was determined in June,
July, August, and September 1996. Soil cores (2.5cm diameter) were collected from the
top 4cm of the solum within 15m of, and at approximately the same elevation as, each
groundwater monitoring well at the two sites. Fifty-four samples were collected on each
date; three samples were collected near each disturbed-site well, and one near each
reference-site well. Sample collection was undertaken in the early morning hours near
sunrise, before the dew evaporated from the vegetation, and at least 48h after any
measurable rainfall had occurred at the sites. The soil samples were dried 72h at 80°C,

and the soil moisture content was determined gravimetrically (see Appendix B3). Soil

36

moisture content provided a measure of the range of soil moisture conditions to be

expected in wet meadows during the growing season.

Results

The study sites sloped very gradually from upland to Saginaw Bay (0.25% at the
reference site, 0.15% at the disturbed site). Local topographical variations existed within
each site, but these were minor and, in the reference wet meadow, did not significantly
alter the surface water and groundwater flow paths. The ditch and swale at the disturbed
site did alter drainage patterns somewhat. These impacts will be discussed below.

Saginaw Bay water levels at the reference site increased by 10-15cm between
June-July 1996, and then gradually declined 15cm by the end of October (Figure 2-6a).
Between April-July 1997, water levels increased 40cm from early spring levels, and then
remained within 10cm of this level throughout September. Water levels only began to
decline in October 1997.

Surface water hydroperiod differed at the disturbed site (Figure 2-6b). Water
levels in both the ditch and drain fluctuated in response to precipitation events and dry
spells, but in both years gradually decreased throughout the growing season. However, at
any given time, water levels in the on-site ditch were elevated 10-3 0cm above those in the
drain. The dike prevented excess water from draining off the site to Saginaw Bay, so it
accumulated in the on-site ditch. As a result, the surface water elevation in the on-site

ditch was higher than that of Saginaw Bay.

37

Storm surges were occasionally observed flooding non-inundated portions of the
reference site and several other Saginaw Bay coastal wet meadows. Storm surges
sometimes inundated only a small portion of a wet meadow for an hour or two, and at
other times inundated the entire wet meadow for a day or more. On 8/21/97-8/22/97,
strong northwest winds pushed 30-50cm of water onto the eastern shore of Saginaw Bay.
This storm surge completely inundated several wet meadows for 6-12h, and inundated
low-lying sections of the Sebewaing County Park for 4-6h (K. Stanley, pers. obs).

Data from Essexville, M] (NOAA, 2000) indicated that between 3/1/97-10/31/97,
Saginaw Bay water levels equaled or exceeded the maximum elevation of the Saginaw
Bay wet meadow zone (177.3m AMSL in 1997, see Chapter 3) for one or more hours on
42 different days (Table 2-1). Depending on shoreline geomorphology and orientation
with respect to the prevailing winds, various wet meadows may have been inundated
numerous times during the 1997 growing season.

The elevated south shore at the reference site protected it fi'om storm surges
generated by the prevailing southwest winds, but northwest, north, or northeast winds
could push water up onto the site. Storm surge inundation of portions of the reference
site was observed on two occasions, and the presence of water-stained vegetation,
flotsam, and drift lines on monitoring wells and the staff gauge indicated that similar
events occurred on several other occasions. The dike at the disturbed site prevented
storm surge inundation at that site.

Growing-season rainfall generally followed the long-terrn annual pattern, with the
August-September period being the wettest time of the year (Figure 2-7). However,

significant positive and negative departures from the 30-year mean monthly precipitation

38

were recorded at both sites. The most notable departure from normal occurred in June
1996, when precipitation at both sites exceeded 17cm, more than twice the normal 7cm
monthly rainfall.

There were also notable differences between sites for the same rainfall event
(Figure 2-8). More than 6cm rainfall were recorded at the reference site on 6/13/96, when
no measurable precipitation was recorded at the disturbed site. On 6/25/96, the disturbed
site recorded more than 6cm rainfall at a time when only 0.8cm rain fell at the reference
site.

Estimated ET ranged between 0.5-3mm/day at the two sites, with most mean
monthly values falling between 0.5-2mm/day (Figure 2-9). Estimated ET at the nearest
Class A evaporation pan, located in East Lansing, MI, approximately 130km southwest of
the sites and 110km from the nearest Great Lakes shoreline, ranged between 1.8-
4.4mm/day (Michigan Office of Climatology, unpublished data). Mean daily ET at the
sites fell within the range of values reported for Great Lakes coastal wetlands (Souch et
al., 1998), bogs (Campbell and Williamson, 1997) and James Bay sedge wetlands (Lafleur,
1990a; see also Lafleur, 1990b for additional wetland values). For the most part, mean
daily ET not difl'er significantly between the two sites. Mean daily ET was significantly
greater at the reference site only in July 1996 (t-test, t = 2.335, df = 23, Bonferroni-
adjusted P = 0.029) and September 1996 (t-test, t = 2.639, df = 9, Bonferroni-adjusted P
= 0.027).

ET sometimes exceeded precipitation during the growing season (Figure 2-10).
For example, precipitation at the reference site totaled 2.2cm in July 1996, and no rainfall

was recorded in August 1996. The mean daily estimated ET was 1.5mm/day in July 1996

39

and 0.3mm/day in August 1996. For the July-August period, total estimated ET equaled
5.5cm; for precipitation it was 2.2cm. ET exceeded precipitation by 3 .3cm during the
period.

Wet meadow groundwater levels followed the same annual pattern at both sites.
Groundwater was at or near the ground surface during the winter and in the early growing
season, then rapidly declined in late spring to some sub-surface summer level.
Groundwater levels remained low until late summer, then returned to near-surface
elevations in the fall.

Figure 2-11 illustrates the seasonal groundwater pattern across the elevation
gradient at the reference site. The three lowest elevation wells (#201, #202, and #203)
were inundated throughout the 1996 growing season. Water levels in these wells mirrored
Saginaw Bay water levels. The next highest well (#204) was located 30m away from, and
at an elevation 16cm above, the nearest of the low elevation wells (#203). The land
surface elevation at #204 was above the mean elevation of Saginaw Bay in 1996, and this
greatly influenced the seasonal groundwater profile observed at that well. Groundwater
levels at #204 declined to approximately 20cm below ground between late May and rnid-
June. Except for a brief rebound in late June, they remained approximately 20cm below
ground until August, when additional groundwater decline occurred, to nearly 60cm
below ground. Groundwater elevations remained at this depth until mid-September, when
they rebounded to within a few centimeters of the ground surface. Similar seasonal
groundwater profiles were observed in wells located at higher elevation within the wet
meadow (#205 and #206), though the magnitude of the groundwater decline was greater

at higher elevations.

40

Groundwater rebound was observed in the upper wet meadow wells (#204-206) in
late June. This rebound corresponded to a period in which more than 6cm precipitation
and a 20cm seiche were recorded. However, this groundwater rebound was a short-lived
event. By mid-July 1996, groundwater had once again declined to levels comparable to
those in evidence before the rainfall and seiche occurred.

Three dimensional projection of the land surface and groundwater elevation data
ofi‘ered a clearer illustration of how groundwater elevations changed across the reference
wet meadow as the 1996 growing-season progressed. In the early growing season, the
wetland surface was entirely saturated, with groundwater contours mirroring land surface
contours throughout the site (Figure 2-12a). There was 10-15cm standing water on the
lower wet meadow, and groundwater within 5cm of the ground surface in the upper wet
meadow.

By late June, upper wet meadow groundwater levels were declining, and appeared
to be equilibrating with surface water levels in Saginaw Bay, which were themselves in the
increasing phase of their annual hydroperiod (Figure 2-12b). However, groundwater
levels continued to decline to as much as 100cm below the ground surface, and 65cm
below the level of Saginaw Bay, at some points in the wetland by mid-July (Figure 2-12c).
The site groundwater profile remained essentially unchanged thereafter until early
September (Figure 2-13a), when groundwater levels rebounded site-wide to within a few
centimeters of the ground surface within seven days (Figure 2-13b). More than 6cm
precipitation, and a 35cm storm surge, occurred during that seven day period.

Similar groundwater profiles were observed at the disturbed site, but there were

some important differences between the sites. Both sites were saturated to the ground

41

surface in mid-May 1996, and groundwater decline had commenced at both sites by early
June (Figure 2-14). By July 1, the reference and disturbed site groundwater tables had
reached nrid-summer levels. Thereafter, gradual draw down continued in un-inundated
portions of both sites through early September (Figure 2-15). Groundwater recharge
occurred within a few days in mid-September at the reference site, but required several
months at the disturbed site to be completed (Figure 2-16). Also, at the disturbed site,
wells closest to the on-site ditch recharged more rapidly than did wells further from the
ditch. By contrast, recharge occurred at about the same rate at all elevations at the
reference site. A detailed description of annual SF groundwater variation can be found in
Appendix B4.

There were also differences in the soil moisture regime of the two sites. The mean
percent soil moisture established by early June in all parts of the reference site did not
change significantly for the remainder of the growing season (Figure 2-17). Also,
differences in elevation had no impact on soil moisture content at this site. By contrast,
mean percent soil moisture continued to decline as the growing season progressed at most
sampling locations within the disturbed site, and soil moisture content generally declined
as elevation increased across this site (Figure 2-18).

Mean percent soil moisture ranged from 71.7% at the disturbed site to 40.3% at
the reference site. A typical loam soil at field capacity contains approximately 25% by
volume water (F oth, 1990), so the soil moisture content at these two sites never fell below

field capacity during the growing season.

42

Wet meadow soil moisture conditions varied significantly among years. Surface
soils partially dried out at both sites for at least a portion of 1996, but all were inundated

or completely saturated throughout the 1997 growing season.

Discussion

Reference wet meadow

Saginaw Bay coastal wet meadows occur in a zone beginning at, and extending
approximately 60cm in elevation above, the mean annual Saginaw Bay high water mark
(Keddy and Reznicek, 1986; and see Chapter 3). Surface water levels determined where
coastal wet meadows occur on the landscape, so the elevation at which they occur varied
with changes in Saginaw Bay water levels. In most years, the elevation of the wet
meadow was greater than Saginaw Bay water levels, and in those years, precipitation and
storm surge inputs, and evapotranspiration discharges, controlled wet meadow
groundwater levels. In certain years, when Saginaw Bay water levels were increasing, the
bay was higher than the wet meadow zone. When this occurred, surface water flooded the
wet meadow and dominated site hydrology. When flooding persists for more than a few
weeks or months, marsh vegetation begins to displace wet meadow species (Jaworski et
al., 1979; Burton, 1985; Keddy and Reznicek, 1986), and the wet meadow zone shifts to a
higher elevation, until it is once again above the mean annual high water mark.

Storm surges occasionally deposited large volumes of water on the surface of the
reference wet meadow. While much of this water eventually returned to the lake basin,

some infiltrated the wetland surface, re-wetting the substrate. These inundation events,

43

with precipitation, helped keep soil moisture levels above field capacity in parts of the wet
meadow above the nominal elevation of Saginaw Bay.

Year-to-year Saginaw Bay water level variations greatly influenced reference site
soil moisture content. High water levels inundated site substrates for most of 1997. This
occurred just a year after soil moisture levels as low as 40% were recorded at the
reference site. These inter-annual water level differences are crucial to wet meadow
vegetation. High water drown invading shrubs and trees, whereas low water desiccate
invading marsh plants, allowing perennial sedges and grasses to dominate the wet meadow
zone (Keddy and Reznicek, 1986; and see Chapter 3).

Growing season precipitation, seiche and storm surge inundation, and
evapotranspiration interacted to determine groundwater levels in non-inundated portions
of the reference site. As vegetation grth accelerated in the late spring, increasing ET
exceeded precipitation and storm surge inputs, drawing down wet meadow groundwater
levels. Similarly, in the late summer, ET began to slow when precipitation was at its
annual high. Storm surge inundation and precipitation offset declining ET, triggering
groundwater recharge.

During the late spring and late summer periods, small changes in either inputs or
outputs resulted in noticeable changes in groundwater levels. For example, groundwater
decline had begun at the reference site by early June 1996 (Figure 2-19a), but no
groundwater decline was evident at the site seven days later (Figure 2-19b). Similarly,
groundwater was completely recharged in a nine day period in mid-September 1996 (see
Figure 2-13). Rainfall of 6.4cm, and a 20cm seiche, occurred during the June week,

whereas a 6.8cm rainfall and 35cm storm surge occurred during the mid-September

period. The water fi'om these sources rapidly infiltrated the wetland, exceeded ET
discharges, and brought groundwater levels back to the wetland surface.

A near-surface capillary fiinge may be responsible for the rapid groundwater
responses observed in the early and late growing season. Small water inputs are known to
cause large water table responses when a near-surface capillary fringe is present (Gillham,
1984; Gerla, 1992). Gillham (1984) recorded a 30cm hydraulic head increase within 15
seconds of applying the equivalent of a 3mm rainfall to a fine sand soil. A 20cm water
table increase lagged just a few seconds behind the hydraulic head response. He attributed
this rapid response to a near-surface capillary fiinge, and noted that the response would be
more pronounced in finer-textured soils.

The minor impact that precipitation and seiches had on mid-summer groundwater
levels may have been due to the absence of a near-surface capillary fiinge. Soil moisture
levels declined as groundwater levels declined in mid-summer. As the solum dried out, the
capillary fiinge withdrew from the soil surface. Once this occurred, sustained periods of
precipitation or inundation, and a decrease in ET, were required to re-saturate the solum.

Similar patterns of ET-driven summer groundwater decline and inundation-driven
fall groundwater recharge have been reported in northern Michigan shrub-carr wetlands
(Parker, 1970), prairie potholes (Meyboom, 1966; Winter, 1989; Winter and Rosenberry,
1995) and Lake Michigan dune swales (Doss, 1993). ET is also an important driver of
soil water movement in tidal marshes (Hemond and Fifield, 1982; Dacey and Howes,
1984), and is the critical pathway for pore water exchange in irregularly flooded tidal

wetlands (Odum, 1988).

45

Standing water influenced wet meadow groundwater levels, but only over short
distances. The smallest seasonal groundwater declines occurred in groundwater wells
located closest to the on-site ditch at the disturbed site. Groundwater inflow fi'om the
ditch supported groundwater levels in these wells, which were only 10m from the ditch.
However, groundwater levels in wells as little as 20m fi'om Saginaw Bay at the reference
site declined to more than 60cm below the bay surface elevation by mid-summer 1996 (see
Figure 2-12c). These groundwater declines occurred even as Saginaw Bay was in the
increasing phase of its annual hydroperiod.

Horizontal groundwater flow limitations have also been observed in tidal salt
marsh substrates. Harvey et al. (1987) noted that salt-marsh soils drained horizontally
through soil pores to nearby tidal creek-beds, but re-saturation occurred by vertical
infiltration from the marsh surface following tidal inundation. Their modeling indicated
that only 3% of sub-surface pore-water recharge occurred via groundwater inflow from
tidal creek banks, and that when it did occur, horizontal pore-water flow occurred only
over short distances (Ibid., 1987). Tide-driven horizontal pore-water fluxes were limited
to a zone extending less than 15m from the creek-bed (Nuttle, 1986; Harvey et al., 1987).
At greater distances, pore-water fluxes were mostly vertical, driven by ET and infiltration
of tidal floodwaters (Hemond and Fifield, 1982; Harvey et al., 1987).

Doss (1993) observed similar horizontal flow limitations in Lake Michigan coastal
dune swales. He noted that a 1m Lake Michigan lake level decline caused little
measurable change in the surface water elevation of dune swale wetlands with documented
sub-surface hydrologic links to the lake. The hydraulic gradient between the swales and

Lake Michigan increased, but wetland surface water and groundwater levels barely

46

changed. Doss suggested two possible explanations: that there might be relatively long
lag times between lake level changes and groundwater responses, or that the swales were
flow-through wetlands being maintained by groundwater flow fi'om points inland.
Groundwater declined in the reference Saginaw Bay coastal wet meadow for the
following reasons (Figure 2-20). Rainfall, snow melt, and storm surges saturated the wet
meadow to the ground surface in late winter and early spring, when ET was low. As ET
increased in late spring, the vegetation began removing water from wet meadow soils
more rapidly than it was replenished by rainfall, storm surges, and groundwater inflow.
The rate of infiltration and groundwater inflow decreased as soil moisture levels dropped
below the saturation point, further reducing soil moisture content. A positive feedback
loop developed; ET reduced soil moisture content, which slowed infiltration and
groundwater recharge, driving groundwater levels lower. Groundwater decline resulted.
This pattern reversed in the fall. ET began to decline in September, when annual
precipitation levels were at their highest. Soil moisture content increased as precipitation
and storm surge inputs exceeded ET. Increased soil moisture content accelerated
infiltration and groundwater inflow, firrther increasing soil moisture content. A positive
feedback loop developed, accelerating groundwater recharge. Groundwater rebound

resulted.

Disturbed wet meadow

Seasonal groundwater discharge/recharge patterns at the disturbed site were
similar to those at the reference site. However, there were difl‘erences in how the

individual hydrologic factors contributed to the overall seasonal pattern. Surface water

47

hydrology at the disturbed site was quite different than that at the reference site, because
the dike disrupted the direct surface connection between the disturbed site and Saginaw
Bay. Seiche and storm surge impacts were completely eliminated by the dike. Saginaw
Bay could only influence site hydrology indirectly, through groundwater infiltration
beneath the dike.

While the dike eliminated seiche and storm surge flooding, it also inhibited site
drainage. Surface and groundwater levels were often higher behind the dike than in the
bay-level drain, particularly in the early growing season. The dike acted as a barrier to
surface flow in either direction, either preventing site flooding or restricting site drainage,
depending on meteorological conditions and the surface elevation of Saginaw Bay at any
point in time.

Groundwater levels at the disturbed site rebounded more slowly in the fall than
they did at the reference site. Several factors probably played a role in this delayed fall
recharge. The dike eliminated seiche and storm surge inundation of the site, reducing
inputs and slowing recharge. The lower water tables in the drained agricultural fields on
either site of the disturbed site may have drawn groundwater away from the site. The
ditch and swale system enhanced site drainage within the disturbed site. Efficient drainage
1 reduced net infiltration, because standing water spent less time on the wet meadow surface
after deposition. This also slowed groundwater recharge throughout much of the site.

Differences between the study sites in seasonal soil moisture trends reflected
difl‘erences in site hydrology. The dike prevented seasonal and storm surge inundation of
the disturbed site, while the drainage swale, on-site drainage ditch, and perhaps

neighboring land uses facilitated drainage within the site. These factors allowed surface

48

soils at the disturbed site to continue drying throughout the 1996 growing season. At the
reference site, seiches and storm surges periodically inundated the wet meadow
throughout the year, negating growing-season dry-down trends, and there was no nearby
agricultural drainage to draw-down adjacent groundwater levels. Nonetheless, wet
meadow soil moisture content never fell below field capacity in either wet meadow during
the 1996 growing season.

In the absence of periodic inundation, groundwater inflow fiom sources of
standing water became a more important factor in wet meadow groundwater recharge at
the disturbed site, at least over short distances. Groundwater levels declined least at the
disturbed site in the monitoring wells closest to the on-site drainage ditch. These wells
were just 10m from the ditch, close enough that groundwater inflow could at least
partially support the nearby groundwater table. However, groundwater inflow had only a
minor influence on wet meadow groundwater levels at these wells, and no measurable
impact at greater distances fiom standing water at either the disturbed or reference sites.

Several other factors might explain why groundwater recharge differed between
the sites. As previously noted, differences in adjacent land use at the two sites may have
impacted recharge rates. The disturbed site was flanked by agricultural fields which were
tiled and mechanically-pumped to keep them dry. There was no such groundwater-
lowering activity near the reference site. Groundwater outflow from the disturbed site to
these fields may have occurred, slowing fall recharge. Glacial till subsoil was closer to the
surface at the disturbed site, and may have slowed vertical soil water movement, so that
horizontal pore-water flow became more apparent than at the reference site. Soils at the

reference site were more permeable than at the disturbed site, and this may have resulted

49

in more rapid re-saturation of reference site substrates. Groundwater recharge may sirnply
have occurred at the reference site too rapidly to be detected using the methods applied in
this study. Yet another possibility is that precipitation flowed off the disturbed wet
meadow into the ditch and swale, and only then infiltrated back into the wetland from
there.

The disturbed site generally retained more surface water in the winter and spring
months, and then dried more thoroughly in the summer months, than did the reference site.
Fall groundwater recharge required more time in the disturbed wet meadow than it did in
the reference wet meadow. In these respects, disturbed site hydrology was more similar
to inland wet meadow hydrology than it was to that of a coastal wet meadow.

Despite the difi'erences in impact of individual hydrologic factors on the hydrology
at the two sites, there were few differences in the seasonal groundwater
discharge/recharge patterns of the reference and disturbed sites. Interruptions of seiche
and storm surge flooding at the disturbed site were offset in the spring by increased
detention of winter snow melt and spring precipitation, so early growing season hydrology
was similar at the two sites. Once ET increased in late spring, groundwater levels declined
at similar rates at both sites. It was only in the fall, when the dike prevented seiche or

storm surge inundation at the disturbed site, that groundwater recharge was delayed.

Summary and Conclusions

Precipitation, seiche and storm surge inundation, and evapotranspiration controlled

groundwater hydrology in the reference and disturbed wet meadow study sites.

50

Groundwater declines of up to 100cm below the wet meadow surface occurred during the
June-August growing period at both sites, driven by evapotranspiration averaging 0.5-
2mm/day. Early and late growing-season groundwater recharge occurred when
precipitation, or at the reference site, seiche and storm surge inputs, exceeded
evapotranspiration and re-saturated wet meadow soils. ET withdrawals exceeded surface
water, groundwater, and precipitation inputs in mid-summer, driving wet meadow
groundwater levels downward.

The reference wet meadow was occasionally inundated by precipitation and
seiches or storm surges during the growing season. Such inundation maintained wet
meadow soils at a saturation level suitable for wet meadow vegetation. By contrast, the
dike at the disturbed wet meadow prevented seiche and storm surge flooding, and
inundation during high water years, while detaining excess water on the site in the early
growing-season. The ditch and swale at the disturbed site enhanced drainage as surface
water and groundwater levels declined in the summer, permitting soils at the site to
continue drying down in the late growing season. The dike, ditch, and swale altered the
annual hydroperiod at the disturbed site to resemble that of an inland wet meadow rather
than a coastal wet meadow.

Precipitation and Saginaw Bay were the principal sources of wet meadow
groundwater at these sites. Low wet meadow slopes (0.15-0.25%) and the lack of
adjacent uplands at the reference and disturbed site limited groundwater inputs fi'om
nearby uplands. Groundwater inflow from adjacent uplands may contribute water,
nutrients and pollutants to other coastal wet meadows. Studies of groundwater chemistry

or stable isotope ratios would provide useful insights into the source and fate of wet

51

meadow groundwater, and the contributions made by upland sources to the overall wet
meadow water balance.

It is not known how similar these patterns of evapotranspiration, precipitation, and
inundation may be to those found in other Saginaw Bay coastal wet meadows.
Difl‘erences among sites in shoreline aspect and geomorphology, exposure to prevailing
winds, storm surge frequency and amplitude, bay circulation and sedimentation patterns,
substrate composition, and groundwater inflow from adjacent uplands have undetermined
impacts on wet meadow hydrology. Further study would be required to determine if these
findings apply to other Saginaw Bay coastal wet meadows, or to Great Lakes coastal wet
meadows outside the Saginaw Bay basin.

Having defined the hydrologic regime of the coastal wet meadow, the question
arises at to the manner in which this hydrologic regime influences wet meadow vegetation

structure and composition. That question is addressed in Chapter Three.

52

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58

177.4 ~-
1772 -
177.0 -
176.8 l
176.6 4
176.4
176.2 +
176.0 4
175.8 1
175.6 -
175.4

I

0 Max level
—D—Mean level
A Min level

I

1

r

4;
V

4L
m

1

Elevation (meters AMSL)

1

 

1964 a»
1985 4%
1986 1»
1987 i
1988 4
1969 4—
1990 it
1991 +
1992 -
1993 «
1994 -»
1995 —~
1996 -
1997 -

Year

Figure 2-1. Maximum, mean, and minimum annual water levels of Lake Huron: 1984-
1997. Data from the Detroit District, US Army Corps of Engineers.

59

+1997

 

 

177.2
3177.0
176.8 1996
176.6
8176.4 +1994
£1752 +1995
2176.0
175.8.eiiiiieiiiiifi4
cabbxcsaat§>o
sagégewggogg
Month

Figure 2-2. Mean monthly Lake Michigan-Huron water levels: 1994-1997. Data from
the Detroit District, US Army Corps of Engineers.

60

 

 

 

 

 

 

tyPlrlgamqu

 

 

 

 

 

 

‘ 19
, Saginaw Bay

 

 

 

 

{-F— KE. Stanley, 1999

 

 

Figure 2-3. Map of the Saginaw Bay region. The location of the reference hydrologic
study site (Site 2; see inset) and the disturbed hydrologic study site (Site 1) are indicated.
These were two of 31 coastal wet meadows bordering Saginaw Bay in 1997. Wet
meadow vegetation was examined at the two hydrologic study sites, and 23 other wet
meadows. Sites 7, 12, 16, 17, 23, and 29 were not used in the study and are not shown
(see Figure 1-2 for location of these sites). Map data from US Census Bureau TIGER
database and Michigan Department of Natural Resources.

61

 

 

 

 

 

Wildfowl Bay Staff Gauge #3

Approximate Limit
of
Carter! Marsh

     
   

203 213 223
o o o

204 214 224
O O 0
Boat Channel

205 215 225
O O O

.206 .216 2.26

/ Bencnmark
Ram Gage!

Eva poratron Pan

Saginaw Bay

40 0 40 80 120 160

 

 

 

Figure 2-4. Map of the reference hydrologic study site, located 12km north of Sebewaing,
MI and 2km off the coast in the Wildfowl Bay State Game Area. The site sloped from
high ground on the south shore to cattail marsh on the north. The wet meadow-cattail
marsh boundary fluctuated annually depending on the level of Saginaw Bay. The boat

channel was excavated prior to 1938. The numbers identify groundwater monitoring
wells.

62

 

 

 

 

 

 

/
one =, gz/ -s<32
0W5911e 21a 31a 41a
On-site
Gene 9
dichg 0W49129 22$ 3289 429

  
 

Drainage
Swale

 
 
  

139 439

“East

 

OWSG 149 249 44$ Boundary
<< West
Boundary
~200m 159 259 45:1;
0W29 169 269 369 a?
Ran gage!
Evaporation pan
Kindler Rd
400m
V
V OW1B Qt\Site benchmark

50 0 50 100 150 200 250 300 350

 

Meters

 

 

 

Figure 2-5. Map of the disturbed hydrologic study site, located 19km southwest of the
reference site on Saginaw Bay’s eastern shore. The site was either cultivated or grazed
for an 80-100 year period ending in the late 1980’s. The dike, constructed between 1941-
1949, severed the direct surface connection with Saginaw Bay. The drain discharged into
Saginaw Bay (not shown). The numbers and “OW” labels identify groundwater
monitoring wells, the “SG” labels stafl‘ gauges.

63

 

-100 a
.120 4i-

-1eo -_ J R
-180 T (1% +Staff Gauge 3 -
Saginaw Say

I
§
1
T

 

Relative water level (cm)
(0 =- site benchmark)

.200-

hhhhhhh

§§§§§§SS§EES

Incarntthuaa

5 PF '06 1-
Date

A. Reference site.

 

‘20 t + Staff Gauge 1- On-

40 site drainage ditch
—a— Staff Gauge 2-Drain
.50 _ ri to Saginaw Bay

 

Relative water level (cm)
(0 a site benchmark)

so.»
-1ool
Date

B. Disturbed site.

Figure 2-6. Change in surface water levels at the reference and disturbed hydrologic study
sites: 1996-1997. Staff Gauge 1 was in the on-site ditch at the disturbed site. Staff
Gauge 2 was in an agricultural drain at the disturbed site that discharged to Saginaw Bay.
Staff Gauge 3 was in Saginaw Bay at the reference site. Surface water levels for each site
were referenced to site benchmark, not to Datum, and are not directly comparable. Staff
gauge readings were not collected in winter when the gauges were encased in ice.

64

Table 2-1. Occurrence of water levels greater than or equal to 177.3m AMSL at
Essexville, MI: 3/1/97-10/31/97. 177.3m AMSL was the maximum elevation of the
Saginaw Bay wet meadow zone during 1997. Data from NOS-NOAA.

 

Date Number of hours Peak water level Date Number of hours Peak water level

 

water level (m AMSL) water level (m AMSL)
_>.177.3m AMSL 2177.3m AMSL

5/3 11 177.47 8/2 2 177.33
5/24 2 177.39 8/3 2 177.32
5/25 8 177.49 8/4* 3 177.45
5/26 1 177.33 8/5* 7 177.44
5/27 1 177.30 8/10* 3 177.40
6/2 5 177.35 8/11* 1 177.33
6/14 2 177.31 8/17 11 177.37
6/16 1 177.33 8/20* 6 177.50
6/17 1 177.35 8/21* 15‘” 177.55
7/4 2 177.33 8/22 18 177.44
7/6 6 177.42 9/2 7 177.41
7/8* 4 177.54 9/3 8 177.41
7/9* 3 177.47 9/7 3 177.33
7/18 4 177.43 9/10 9 177.42
7/19 9 177.53 9/20 3 177.31
7/21 4 177.33 9/23 1 177.30
7/22 10 177.38 9/25 2 177.36
7/23 6 177.33 9/26 2 177.31
7/28“ 7 177.37 9/30 1 177.39
7/29* 7 177.38 10/1 5 177.47
10/26* 5 177.61
10/27* 6 177.69

 

* - Indicates that the event was continuous during the two days.
(a) - Only ten hours were continuous with the previous day (8/20).

65

s\\\\\\\‘ Disturbed site

 

 

E
.2. :1 Undisturbed site
6
3 1:1 NWS Sebewaing
a
g + 30 year (1961-1990)
a. Mean PPT
‘5 Disturbed site
0
§ 1:: Undisturbed site
.3.- EZI NWS Sebewaing
8
‘L c - - >. c - en a. > —a— 30 year (1961-1990)
3 E g 2' i 51' ‘3’ 2 «3 g 3 5 Mean PPT
1997

Figure 2-7. Monthly precipitation at the reference and disturbed hydrologic study sites,
and the National Weather Service climatological reporting station at Sebewaing, M]:
1996-1997. The line describes the 30 year (1961-1990) mean monthly precipitation for
NWS-Sebewaing. Rainfall data were not collected in winter months.

66

 

 

 

 

 

€12
2.10
58 DUndisturbed
3° IDisturbed
94
oz
Ea
SEEEEEEEEEESEEEE"?
a hhhbhnnfl oagga
Date-1996

Figure 2-8. Precipitation recorded at the reference and disturbed hydrologic study sites:
1996. Rainfall data were not collected in winter months.

67

 

6 lTTHflfil ITWTITTTH

h
l
J

 

Mean ET (mm/day)
N (A
l l
l

 

Site
e Disturbed
1:1 Undisturbed

 

 

 

 

 

wk
E11111]

0 a i
c,\9%9°g‘5°o\9fo\92~fqupx\91qfi1sg1~919916911916919\920\92\\9°
Date

 

Figure 2-9. Monthly mean daily evapotranspiration (ET) for the reference and disturbed
hydrologic study sites: 1996-1997. ET estimated from pan evaporation measured at the
sites. Data were not available fiom the disturbed site in June 1996, and September and
October 1997. Error bars denote i1 SE of the mean.

68

PPT or ET (cm/month)

 

10/96
12/96
2/97

 

4197 ‘

Date

 

 

1:1 PPT
+ET

 

12197

Figure 2-10. Monthly precipitation (PPT) and estimated evapotranspiration (ET) at the
reference hydrologic study site: 1996-1997. Rainfall and pan evaporation data were not

collected in winter months.

69

 

20.0
l

 

 

 

 

 

 

." fi’nyut75 :3: \,‘";?::!Re !'=::!:3.5¢ \fi/H
A 0-0 i . 1"” '-’ ‘ ‘ ‘ ‘ ‘ ‘ ‘ ‘?:'i‘f'{:'i:i-‘i‘
Ag 40.0.. V, "\ - . . ' Well number
5, ‘r: J - \. (Elevation from
B 51 ‘40-0 . 4 site benchmark)
5 B -60.0 - '
'2 g +201(—0.75)
g, 11 -80.0 - ! —-+—-202(-0.77)
3 §-1oo.o - ' \ ‘ +203(-o.74)
v-1 20.0 a \ +204(-O.50)
440.0 - —x— 205(-O.43)
ESEEESSSSESSS +2°6"°"’”
in in to to r~ r~ no a: «.- 2 .—
Date - 1996

Figure 2-11. Surface water and groundwater profiles for monitoring wells #201-#206 at
the reference hydrologic study site during the 1996 growing season. Wells were in line
order ranging fi'om lowest (#201) to highest elevation (#206). Elevations indicate ground
level at each well with respect to the site benchmark. Each well was 30m from the next
well in line. Wells #201, 202, and 203 were inundated throughout the growing season.
Wells #204, 205, and 206 remained free of standing water for most of the growing season.

70

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79

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100- 100» 100r

 

 

 

 

 

 

 

 

 

 

 

 

80 _ -0.87 am -o.73 80 L -0.76
Percent 60 ’ l\ I I 60 r- HM 60 P [__.|\‘
8.0" 40 _ 40 _. 40 L
morsture
20 . 20 f 20 *-
0 1 4 1 1 1 O 1 1 1 1 1 o 1 1 1 1 1
100 - 100 - 100 r-
80 P -o.55 80_ -o.4o 80 L -o.4o
percent 60 r 60 - so -
SO" 40 +- M 40 ,_ 5% 4o ,_
moisture NA
20 ~ 20 - 20 r
O 1 1 1 1 1 O 1 1 1 1 1 O 1 4 g 1 1
6196 7/96 8l96 9/96 6/96 7196 8196 9/96 6/96 7/96 8I96 9/96
Date Date Date

Figure 2-17. Percent soil moisture content of non-saturated soil in various locations at the
reference hydrologic study site: 1996. The large numbers above the graphs indicate the
elevation (in cm with respect to the site benchmark) at which the soil samples were
collected. Error bars denote :1 SE of the mean.

81

 

 

 

 

 

 

 

 

 

 

 

 

100 r -0.65 100 - -0.67 100 - -O.60
80 l 80 t 80 -
Percent 5° ’ \l/\ 6° ' W 6° r '\/I\!
soil _ 1
moisture 40 40 F 40
20 ~ 20 ~ 20 ~
0 1 1 1 J o 1 1 g 1 1 O 1 1 1 1 1
100 r -0.63 100 - -0.48 100 - -0.46
80 ~ 80 - 80 -
Percent 60 l' Nr.-l 60 ’ N 60 .. 1——\\
sell 40 _ 4o - 4O -
morsture
20 l 20 b 20 ~
0 1 1 1 1 1 o 1 1 4 1 1 o 1 1 4 J 1
6/96 7/96 8I96 9196 6/96 7/96 8/96 9I96 6/96 7/96 8/96 9I96
Date Date Date

Figure 2-18. Percent soil moisture content of non-saturated soil in various locations at the
disturbed hydrologic study site: 1996. The large number above the graphs indicates the
elevation (in cm with respect to the site benchmark) at which the soil samples were
collected. Error bars denote :1 SE of the mean.

82

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86

 

Chapter 3 - The structure and composition of Saginaw Bay coastal wet meadow
vegetation

Introduction

Saginaw Bay coastal wet meadows are the herbaceous, graminoid-dominated
vegetation zone occurring between forested beach ridges and Lake Huron cattail/bulrush
marshes and bounded by the yearly mean and yearly maximum elevation of Lake Huron
(see Chapters 1 and 2). This vegetation association shelters threatened and endangered
plants, including Asclepias hirtella (Pennell) Woodson, Rumex maritima L., Cacalia
plantaginea (Raf) Shinners, and Astragalus neglectus (T.&G.) Sheldon (Albert et al.,
1988, 1989), and supports the greatest plant diversity of any Great Lakes wetland type
(Keddy, 1990). Yet few ecological studies of these wet meadow plant communities have
been undertaken.

The pre-19OO studies of Saginaw Bay’s natural history were simple catalogues of
the region’s geology and biota (see Ruthven, 1911). Between 1900-1920, the Michigan
Geological and Biological Survey organized the first ecological studies of Saginaw Bay
coastal wetland vegetation (Davis, 1900; Davis, 1908; Michigan Geological and Biological
Survey, 1911; Dodge, 1920). Interest in the plant ecology of the Saginaw Bay coastal
zone flagged after 1920, and did not increase again until the 1970’s. Since then, numerous
Saginaw Bay and Great Lakes coastal wetland studies have been produced (Hayes, 1964;
Stuckey, 1975; Tilton et al., 1978; Jaworski and Raphael, 1979; Jaworski et al., 1979;
Herdendorf et al., 1981; Albert et al., 1988, 1989; Prince and Burton, 1995; Mine, 1997;

Minc and Albert, 1998). However, these studies have generally centered on wet meadow

87

species composition or extent, rather than on the ecological factors controlling vegetation

structure and composition.

Abiotic factors influencing wet meadow structure

Abiotic factors guide the development of Great Lakes coastal wet meadow
vegetation. The most important of these factors is hydrology (Keough et al., 1999;
Wilcox and Whillans, 1999). Periodic lake level fluctuations control vegetation zonation
in Great Lakes marshes (Burton, 1985; Kelley et al., 1985; Keddy and Reznicek, 1986;
Keough, 1990; Batterson et al., 1991, Keough et al., 1999). Other hydrologic factors,
such as precipitation, groundwater inflows, and evapotranspiration, also play an important
role in coastal wet meadow hydrology (see Chapter 2).

Geomorphic setting impacts the vegetation structure and composition of coastal
wet meadows (Mine, 1997; Mine and Albert, 1998; Keough et al., 1999; and see Chapter
1). Site geomorphology influences the depth, duration, and frequency of inundation,
intensity of wave and current action, degree of ice scour, and rate of erosion and
sedimentation at that site. These factors, in turn, impact the distribution patterns and
persistence of plant species at a site (Keough et al., 1999).

Soil type, sediment quantity or quality, and organic matter content influence the
distribution of Great Lakes coastal wetland vegetation (Tilton et al., 1978; Wilcox, 1995).
Wetland plant community composition is determined in part by substrate type, with many
plant species showing a preference for either sandy, organic, or lacustrine clay soils (Tilton
et al., 1978; Mitsch and Gosselink, 1993; Wilcox, 1995). Substrate preferences reflect,

among other things, a species’ particular nutrient requirements and its ability to compete

88

with other species for available soil resources. These abilities and requirements firnction
as filters or sieves (sensu van der Valk, 1981) to sort the plant community into

recognizable vegetation associations.

Vegetation attributes

The species composition of Saginaw Bay coastal wetland vegetation is well
documented (Davis, 1900; Davis, 1908; Michigan Geological and Biological Survey,
1911; Dodge, 1920; Herdendorf et al., 1981; Albert et al., 1988, 1989; Prince and Burton,
1995; see also Table 3-4). However, species lists reveal only one attribute of a vegetation
association. Information about community structure, and the species richness, evenness,
diversity and dominance relationships among plant community members are also needed to
fiilly understand the ecology of wet meadow vegetation.

Vertical vegetation stratification, the vertical distribution of plant species above the
ground surface, characterizes the canopy architecture of a vegetation assemblage.

Detailed study of wet meadow canopy architecture may increase our understanding of the
factors controlling species distribution within the wet meadow zone, and aid in identifying

the conditions defining wet meadow boundaries.

Goals and Objectives

The goals of this chapter were to describe above-ground wet meadow vegetation
structure and composition, and to examine the manner in which hydrology, soils, and
plants species composition act and interact to determine vegetation structure and

composition. The specific objectives were:

89

l. to describe horizontal and vertical vegetation structure;

2. to characterize plant species composition;

3. to describe wet meadow soil attributes, including texture, organic matter
content, and major mineral components; and

4. to determine how hydrology, soils, and plant species composition act and
interact to influence vegetation structure, composition, and distribution

within the wet meadow.

Sites

Vegetation sampling was performed in 1996 at the two hydrologic study sites (see
Chapter 2) to determine how hydrology impacted species distribution at those sites.
During 1997, vegetation and soil sampling were performed at these two sites and 23
additional sites distributed throughout the Saginaw Bay coastal zone to define the
vegetation structure and composition of the region’s coastal wet meadows. The 1997
sampling encompassed all of the intact coastal wet meadows in the region (see Figure l-

2). A description and list of study sites can be found in Chapter 1 and Appendix A2.

90

Methods

Elevation determination

1996 sampling

Elevation surveys were undertaken at the two hydrologic study sites after all '
hydrologic sampling devices were installed (see Chapter 2 for details). These data were
used to construct site contour maps, from which surface and groundwater elevations
throughout the two sites could be estimated. Locating sample plots on the maps allowed

estimation of sample plot surface and groundwater elevation at each sample plot.

1997 sampling

Most sites were inundated during the 1997 sampling period, so water depth in
sample plots was used to determine plot elevation. Water depth at a specific date and time
was recorded (i0.1cm) at each sample plot. Saginaw Bay water levels, measured at six
minute intervals and referenced to International Great Lakes Datum (IGLD 1985), were
obtained from the National Ocean Service of the National Oceanographic and
Atmospheric Administration (NOS-NCAA, 1999). Plot elevation in meters above mean
sea level (m AMSL) was determined by matching plot and NCAA water level data by date

and time.

91

Data collection

1996 sampling

In 1996, vegetation data were collected in 0.25m2 (50cm by 50cm) sample plots at
the two hydrologic study sites. Sampling was undertaken during July and August, the
period of peak above-ground biomass in the region (Barko et al., 1977; Kelley, 1985; and
see Chapter 4). Vegetation sampling was stratified across the elevation gradient at each
site to ensure the adequacy of sampling at all elevations within each site. Species
frequency of occurrence, stem density, and above-ground biomass was determined for

each species in each plot.

1997 sampling

Vegetation data were collected in twelve 0.25m2 (50cm by 50cm) sample plots at
each site during July-August 1997. The vertical vegetation stratification, species identity,
and the above-ground species and plot biomass, species and plot stem density, and species
frequency of occurrence were determined for each plot. Litter depth, peat depth,
hummock heights in any plot containing hummocks, and a field estimation of surface
substrate texture were also determined for each plot. The texture, organic matter content,
and major mineral components of the top mineral soil layer were determined by laboratory

analysis of soil aliquots collected at each site.

92

Vegetation sampling

1996

Species stem density, frequency, and biomass values were determined using the
harvest method. All living and dead standing plant material in each plot was clipped at the
substrate surface and sorted into living (green) and dead (brown) material. The living
material was sorted by species and counted to determine species stem densities. No
attempt was made to identify or sort dead material to species. Once stem counts were
completed, the living material from each plot was bagged by species and the dead material
was bagged en masse. Above-ground biomass by species was determined by weighing the
contents of each bag after oven-drying 72h at 60°C (see Chapter 4). Individual species
stem-density and biomass values were summed to determine plot stem-density and
biomass.

Vegetation sampling was stratified by elevation at both hydrologic study sites.
Eight strata, or zones, were established at the reference site, 13 at the disturbed site.
Zones were laid out parallel to the local Saginaw Bay shoreline, which was perpendicular
to the site elevation gradient. Each zone was 20m in length (parallel to the elevation
gradient), and sufiiciently wide to span the groundwater well field installed at the site.

The first zone began at the wet meadow-marsh boundary at the reference site, and at the
ditch and dike forming the north border of the disturbed site, and extended 20m up the
elevation gradient. Additional zones were added until sampling zones spanned the well

field at each site.

93

Sample plots were distributed randomly within each sampling zone. Vegetation
sampling continued in each zone until a species-area curve for that zone reached its

apparent asymptote.

1997

Vertical vegetation stratification was measured at four points within each plot
using a welding rod marked at centimeter intervals. The rod was positioned perpendicular
to the ground surface in the plot. Then, for all live plant contacts with the rod, the species
identity, the height above the substrate, and whether the contact was a leaf, stem, or
inflorescence were recorded. These data revealed the vegetation canopy architecture, and
provided an estimate of wet meadow leaf area index (LAI), the single surface leaf surface
area per unit ground area (mz/mz).

Stem density, frequency, and biomass values were determined using the harvest
method. The techniques and procedures were unchanged fiom 1996 (see above).

Vegetation sampling was stratified by elevation at each site, four plots each at
three difi‘erent elevations, to examine how differences in depth and duration of inundation
impacted vegetation composition. Water depth, the proxy for plot elevation, was
stratified into eight depth classes to facilitate sampling: -10-0. 1cm (-10-0. 1cm being the
only sub-surface water level class), 0.0-9.9cm, +lO-19.9cm, +20-29.9cm, +30-39.3cm,
+40-49.9cm, +50-59.9cm, and +60-69.9cm.

The three water-depth classes sampled at a site were determined by site
geomorphology and statistical requirements. Shoreline geomorphology varied among

sites. The wet meadow zone was narrow and steeply sloped at some sites, broad and very

94

gradually sloping at other sites. There were more depth classes to choose from in the
latter group of sites. Also, an attempt was made to collect enough data in each depth
class to permit valid statistical analysis of the data set. The depth classes sampled at a site
depended on which classes were available at that site, which classes were representative of
that site, and which of the available depth classes were least represented in previous
vegetation sampling.

Line-intercept transect sampling (Brower and Zar, 1977) was performed at all sites
in August-September 1997 to verify that plot sampling fairly represented site species
assemblages. Transects were established from upland to marsh across the wet meadow,
and the identity and tally of plant species intersecting the plane of the transect was
recorded every 0.5m.

Line-intercept sampling continued at a site until a species-distance curve indicated
that no new species were being encountered along the transect. A species-distance curve
difi‘ers fiom a species-area curve only in that cumulative distance rather than cumulative
area is plotted on the x-axis.

Voucher botanical specimens were deposited in the Beal-Darlington Herbarium at
Michigan State University. Botanical nomenclature follows Voss (1972, 1985, 1996) for

vascular plants, and Gleason and Cronquist (1991) for vascular cryptogams.

Soil sampling
Soil samples were collected in 1997 from each of the 25 study sites and used to

determine the mineral soil texture, pH, the Phosphorus (P), Potassium (K), Calcium (Ca),

Magnesium (Mg), and nitrate-N (NO3-N) plus Ammonium-N (NIL-N) nitrogen levels,

95

and percent organic matter content (%OM) of wet meadow substrates. Three to five
replicate soil samples were extracted from the mineral soil surface at each site, thoroughly
mixed, and an aliquot of this mixture was collected for analysis. When visually apparent
difi‘erences in mineral soil color or texture were noted within a site, a soil aliquot was
collected from each soil type. In all, 33 aliquots were collected from the 25 sites and '
delivered to the Michigan State University Soil and Plant Nutrient Laboratory for analysis.
To determine soil bulk density, a 90ml undisturbed mineral soil sample was
collected at each site using a slide-hammer soil core sampler. Samples were dried 72h at
80°C and weighed. Sample bulk density (g/ml) was calculated on a dry weight per unit

volume basis.

Statistical procedures

1996 sampling

The relative stem density, relative biomass, and relative frequency data were
summed to generate importance values for each species in each plot (Curtis and McIntosh,
1951; Brower and Zar, 1977). Several variables exhibited non-normal or heteroscedastic
distributions. Logm(X+1) transformation of species biomass data, importance values, and
species richness data resolved most problems with the distribution of these variables.
Kruskal-Wallace ANOVA was used to test hypotheses involving stem density, which
could not be transformed to meet parametric assumptions.

Mean mid-summer groundwater depths were determined by averaging
groundwater measurements at each monitoring well for the period 7/1/96 through 9/4/96.

This period reflected the length of time that groundwater levels remained at their stable

96

mid-summer levels (see Chapter 2). Mid-summer groundwater levels were the deepest
observed during the growing season. At other times of the year, groundwater levels were
either at or near the wetland surface, or rapidly fluctuating between near-surface and mid-
summer levels.

Groundwater contour maps were used to estimate mean groundwater depths of the
sample plots. Groundwater contours were linear and perpendicular to the elevation
gradient at the reference site, and varied at most by approximately 5cm within any
vegetation sampling zone, so groundwater depths were blocked by zone for analysis at the
reference site. At the disturbed site, surface and groundwater contours were complex, so

groundwater levels were blocked in 10cm intervals for analysis.

1997 sampling

The relative stem density, relative biomass, and relative fi'equency were summed to
generate importance values for each species in each plot. Shannon-Wiener diversity was
calculated for each site (Brower and Zar, 1977). Mean species richness/m2 was estimated
for each site by performing five replicate cumulative species counts of four randomly-
selected 0.25m2 plots from each site.

Several variables exhibited non-normal or heteroscedastic distributions, but
mathematical transformation remedied most data distribution problems. Log10(X+1)
transformation of species biomass data, importance values, and species richness data, and
square-root transformation of peat depth, litter depth, leaf, stem, and inflorescence height,

and mean LAI data resolved problems with the distribution of these variables.

97

Pearson product-moment correlation matrices were constructed to examine
associations among plant species and among environmental factors. Correlation and
Principal Components Analysis (PCA) were used to examine associations among plant
species and environmental factors.

Analysis of variance (AN OVA) was used to test hypotheses involving normally
distributed or transformed variables. Similarly, correlation and PCA were performed on
normally distributed or transformed variables. Kruskal-Wallace AN OVA was used to test
hypotheses involving data which could not be transformed to meet parametric

assumptions.

Results

Water level, vegetation, and soil at the reference and disturbed hydrologic

study sites

At the reference site, mean mid-summer water levels ranged between +0.34m
(34cm standing water) and -0.85m (85cm below ground) among plots. Total plot stem
densities were highest when mean water levels ranged between approximately 10cm above
and 10cm below the wetland surface (Figure 3- 1). Total plot stem density in these plots
was significantly greater than that of plots with either greater mean standing water depths
or greater groundwater depths (ANOVA, F(o,05,5,151,= 22.015, P<0.001). Total plot
biomass was significantly greater in plots with the deepest mean standing water levels
(+34cm and +24cm) compared to plots with shallower standing water or deeper

groundwater depths (ANOVA, F(o,05,5,151,= 6.492, P<0.001). The significantly greater

98

biomass of the emergent marsh species Typha angustifolia in inundated plots (ANOVA,
F(o,o5,5,151, = 19.125, P<0.001) accounted for this difi‘erence.

Plot species richness was greatest in the plots with the deepest mean water depths.
This was due to the presence of marsh species (e. g., T ypha angustifolia, Sagittaria
Iatr'folia, Sparganium ewycarpum) in addition to wet meadow species in these plots. ’
However, in plots lacking marsh species, wet meadow species richness increased as
standing water levels declined until mean mid-summer plot water levels were below
ground, after which plot species richness did not change significantly with increasing
groundwater depth (ANOVA, F(o,o5, 5, 151) = 14.682, P<0.001).

There was a significant association between mean mid-summer water levels and
the National Wetlands Inventory (NW1) classification of the species found in plots. As
surface water depths and groundwater levels declined, fewer obligate (OBL) and
facultative wetland (F ACW) species, and more facultative (F AC) and facultative upland
(FACU) species occurred in plots (Somer’s D, d = 0.163, N = 812, asymptotic SEE =
0.020; range of d = +1.0 to -1.0). FACU species only occurred in plots with mean mid-
summer water levels below the ground surface.

Fourteen species (Calamagrostis canadensis, Carex sarlwellii, T ypha
angustifolia, Eleocharr's smallii, Carex bebbii, Campanula aparinoides, Polygonum
amphibium, Calystegia sepium, C ladium mariscoides, Lathyrus palustris, Juncus
baltr'cus, Carex comosa, Leersia oozzoides, and Carex Iacustris; hereafter “major
species”) exhibited IV 21% of the total IV of all species in all plots at the reference site.
Each major species exhibited a preference for certain water levels within the reference site

(Figures 3-2 through 3-5). Four species (C. comosa, E. smallii, Leerzia oryzoides, and T.

99

angustifolia) exhibited greater IV in plots where mean mid-summer water levels were
above ground, five species (C. canadensis, C. sepium, C. aparinoides, C. bebii, and L.
paIustris) exhibited greater IV in plots where water levels were below ground, and two
species (C. lacustris, and P. amphibium) exhibited no water level preference. Three of the
fourteen major species (C. sartwellii, C. mariscoides, and J. balticus) had their greatest
IV in plots with mean water levels ranging between lOcm above and 10cm below the
wetland surface.

At the disturbed site, mean mid-summer water levels ranged between -0.04m (4cm
below ground) and -0.65m among plots. There was a significant difference in plot stem
density (ANOVA, F(o_o5, 20, .55, = 2.037, P = 0.008) and plot biomass (ANOVA, F(o,o5,20,155)
= 1.918, P = 0.014) across the site water level gradient (Figure 3-1). The increased
presence of certain large wetland species (e. g., Carex lacustris and Phalaris arundinacea)
at shallow groundwater depths (<-20cm) and certain other large species (e. g., Aster
dumosus and Phalaris arundinacea) in deeper groundwater plots (>-50cm) accounted for
the significantly higher biomass in these plots. Significantly greater stem densities
occurred in plots with intermediate mean mid-summer water levels (-3 Gem to -50cm).

The maximum stem densities of the major species Calamagrostis canadensis, Carex
stricta, Carex sartwellii, Calystegia sepium, Polentilla anserina, and Spartina pectinata
occurred in these plots.

Species richness was significantly greater (ANOVA, F(o,o5,20,155)= 2.505, P =
0.001) in intermediate depth groundwater plots (-3 0cm to -50cm) compared to the

shallowest groundwater plots (0cm to -10cm). Species richness did not significantly differ

100

between plots with intermediate groundwater levels and deeper groundwater levels, or
between plots with the shallowest and the deepest groundwater levels.

There was a significant association between mean mid-summer groundwater levels
and the NW] classification of the species observed in disturbed site plots. As at the
reference site, fewer OBL and FACW species, and more F AC and F ACU species,
occurred as mean groundwater depth increased (Somer’s D, d = 0.135, N = 1154,
asymptotic SEE = 0.022). However, unlike at the reference site, FAC and FACU species
were found in small quantities at all groundwater levels at the disturbed site.

Fifteen species (Phalaris amndinacea, Calamagrostis canadensis, Carex stricta,
Aster dumosus, Calyslegia sepium, Carex bebbii, Spartr'na pectinata, Carex sartwellii,
Polygonum amphibium, Carex Iacustris, Anemone canadensis, Lalhryus palustris,
Galium obtusum, Potentilla anserina, and Lycopus americanus) each contributed 21% of
total disturbed site vegetation IV. Most of these major species exhibited a water level
preference within the disturbed site (Figures 3-6 through 3-9). C. bebbii, C. lacustris, C.
sartwellii, L. americanus, and P. amphibium exhibited greater IV in plots with the
shallowest mean mid-summer groundwater levels, whereas A. canadensis, A. dumosus, C.
sepium, and G. obtusum exhibited greater IV where groundwater was deepest. Four
species (C. canadensis, C. stricta, P. anserr'na, and Spartina pectinata) exhibited greater
IV at intermediate (~30cm to -50cm) groundwater depths, whereas the IV of L. palustris
did not vary with groundwater levels at this site. Phalaris amndinacea had lower IV at
intermediate groundwater levels, and higher IV in plots with either shallow or deep

groundwater levels.

101

There were differences in soil structure and composition between the sites. Soil
calcium, magnesium, percent organic matter, cation exchange capacity, ammonium
nitrogen, phosphorus, and clay content were all significantly greater at the disturbed site
compared to the reference site. Soil pH, potassium, nitrate nitrogen, sand, silt, and bulk
density did not vary significantly between sites (Table 3-1).

There were two visually distinct surface soil types at the reference site. For the
most part, reference site surface soils were black loamy sand, but a tan fine sand soil
occurred where mean water levels ranged between +10cm and -10cm depth. Soil analysis
indicated that this sand soil had lower clay, silt, potassium, and calcium content, and
greater sand content and bulk density, than the adjacent loamy sands. There were no
visually distinct soil types at the disturbed site. All soil samples collected at the disturbed
site were black sandy loam soils, and these soils were uniformly underlain by glacial till at
approximately 45cm depth. Soil analysis indicated that the soil structure and composition
at the disturbed site was relatively homogenous, as might be expected of an historically

tilled soil.

Physical attributes of Saginaw Bay coastal wet meadows

Saginaw Bay coastal wet meadow vegetation occurred at elevations ranging
between 176.7-177.3m AMSL (mean iISEM = 177.0i0. 125m AMSL) during the study
period. The wet meadow vegetation zone extended from the annual mean high water
mark (176.67m AMSL) upward approximately 0.6m in elevation to a point approximately

0.1m below the maximum Saginaw Bay high water mark.

102

The depth and duration of inundation of any part of the wet meadow varied fi'om
year to year with the inter-annual variation in Saginaw Bay water levels, and seasonally
with annual water level variations (Figure 3-10). The entire wet meadow zone was above
the mean elevation of Saginaw Bay throughout the 1995 growing season, but most of the
zone was inundated for some portion of the 1997 growing season. Between 1988 and
1996, approximately 80% of the wet meadow zone was above Saginaw Bay’s mean
monthly elevation for the entire growing season. However, this did not mean that wet
meadow substrates were dry.

Portions of the wet meadow located above the bay’s nominal surface elevation
were often inundated by seiches and storm surges (Figure 3-11; and see Chapter 2). The
monthly maximum Saginaw Bay water elevation averaged 36cm higher than the monthly
mean elevation during the 1997 growing season, and ranged as high as +67cm in October
1997 (NOS-NCAA, 1999). Seiche- or storm surge-related water levels increases were
great enough to inundate the entire wet meadow zone on 42 different days during the
1996 growing season, and great enough to do so at least monthly in 1997 (see Chapter 2).

The mean(i1SEM) width of the wet meadow zone was 123.9(15.8)m (Table 3-2).
The zone ranged from 11-545m wide, with half the values falling between 65-147m. The
wet meadows sloped very gradually toward the bay (median slope = 0.27%), with half the
values ranging between 0.10-0.39%. Three sites with shallower-than-average slopes
(0.092-0.099°/o) were wider than the median site width, and six sites with steeper-than-
average slopes (0.70-2.25%) were narrower than the median site width.

Wet meadow soils generally consisted of a 1-16cm peat or muck “O” horizon

overlying a sandy mineral “A” horizon. However, several sites lacked “O” horizons,

103

instead having only black sandy loam or loamy sand “A” horizons. Mechanical soil
analysis indicated that 24 of 25 wet meadow “A” horizons were either sandy loam, loamy
sand, or sand soils. The mineral soil pH ranged from 6.1 to 8.5, with 75% of the values
>7.0 (Appendix C1).

Field texture determinations indicated that 49% of plot surface substrates were
peat or muck, 20% were fine sand, and 11% were gravelly sand. Altogether, over 90% of
plot surface substrates were organic soils or sandy mineral substrates. Marl, clay, silt or
gravel substrates were only very rarely encountered during sampling.

Sub-surface soil composition was not systematically examined in this study, but
bore holes excavated at three study sites (Sites 1, 2, and 3; see Figure 1-2) provided some
information about sub-surface soil stratigraphy to a depth of 1m. At Site 1, sandy loam
gave way to glacial till below 45cm depth, with a 10cm band of sand and gravel commonly
being encountered at approximately 90cm depth. Substrates at Sites 2 and 3 were 15-
25cm sandy loam or loamy sand layer over medium to fine sand to 1m depth. Gray clay
fines commonly lined the soil pores in the sub-surface substrates. While no clay layers
were encountered in these bore holes, lacustrine or till clays lined the bottom of canals and
Saginaw Bay adjacent to the sites, suggesting that these sands rested on clay substrates.

Channels, ditches, and shore line erosion permitted examination of sub-surface
mineral substrates in several other wet meadows. Glacial till or lacustrine clay substrates
occurred below the mineral surface layer at these sites.

The peat thickness ranged between 0-16cm among sites, with mean(i1SEM) site

values ranging between 0.4(0.1)-11.0(0.8)cm (Table 3-2). Peat depth exhibited a strong

104

negative correlation with wet meadow elevation (r = -0.644, n = 23 84; Table 3-3 a), the
thickest peat occurring at low elevation, thinner peat at higher elevation.

Litter depths, determined at 18 study sites, varied between 1-45cm, with
mean(:l:l SEM) site values ranging between 8.7(2.0)-30.5(7.0)cm. Litter depths were
negatively correlated with soil texture (r = -0. 196, n = 23 84) and elevation (r = -0.159, n =
23 84). Deeper litter was associated with finer-textured soils and lower elevation,
shallower litter depths with coarser soils and higher elevation.

Carex stricta Lam. hummocks occurred in 12 study sites. Where present,
hummocks ranged between 11-62cm height, and mean(i1SEM) site hummock heights
varied between 18(0.0)-38.0(6.4)cm. Hummock height exhibited a significant negative
correlation with wet meadow elevation (r = -0.258, n = 382; Table 3-3b). Taller
hummocks were associated with lower elevation, short hummocks with higher elevation.

Hummocks served as growth platforms for other vegetation. Several forbs
(Galium obtusum Bigelow, Campanula aparinoides Pursh, and Impatiens capensis
Meerb., among others) were observed growing on the sides and tops of hummocks, above
the level of standing water, in flooded study sites.

Ants also colonized hummocks, or constructed earthen anthills, at some sites. Wet
meadow ants apparently utilize subterranean galleries during low water periods, and live in
the upper, un-flooded portion of these structures when wet meadows are flooded

(Bruskewitz, 1981).

105

Vegetation attributes

A total of 93 plant species, representing 34 families and 63 genera, were
encountered during vegetation sampling (Table 3-4). The best-represented families were
Cyperaceae (16 species), Poaceae (10), Asteraceae (9), Lamiaceae (7), and Rosaceae (6).
The best-represented genus was Carex, with nine species. F ifieen species (three grasses,
five sedges, one cattail, and six forbs) each contributed 21% of total vegetation
importance value (Table 3-5). Thirteen of the 15 major species were native perennial
plants (Reed, 1988), and 12 of the 15 were rhizomatous species (Gleason and Cronquist,
1991). Some (e. g., Phragmites australis (Cav.) Steudel, and several sedges) rarely
produce viable seeds (Ibid., 1991). Seven of the major species were emergent wetland
species (Reed, 1988), adapted to growing in standing water (Niering, 1985). Eleven of
the major species were NWI Region 3 obligate wetland species (OBL), three were
FACW+ species, and one was a FAC species (Reed, 1988).

The 15 major species comprised 84.0% of the total species importance value.
Conversely, 27 species occurred in only one of the 300 sample plots. (See Appendix C2
for species stem density data). Four species dominated the vegetation. The grass
Calamagrostis canadensis (Michaux) Beauv. and three sedges, Carex aquatilt's Wahl.,
Carex sartwellii Dewey, and Carex stricta, contributed 60.1% of total wet meadow IV.
C. canadensis alone contributed 31.1%, and two species, C. canadensis and C. aquatilis,
by themselves contributed 45.7% of total IV.

Mean (i1SEM) wet meadow species richness equaled 15.4(0.5)spp./m2 and
ranged between 9.0-27.Zspp./m2 among study sites (Table 3-6). The mean value fell

within the range of values for similar vegetation assemblages (Table 3-7a). Similarly,

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mean wet meadow leaf-area index (LAI) was 5.0(0.1)m2/m2, ranged between 3.1-
7.7m2/m2 among sites, and fell within the range of values published for wet meadows
(Table 3-7b). Shannon-Wiener diversity averaged 1.53(0.03), ranging between 1.31-1.71,
mean Evenness was 0.77, ranging between 0.59-0.86, and mean Dominance was 0.23,

ranging between 0.14-0.41.

Pearson product-moment correlation of the major species IV revealed significant
associations among the major species (Table 3-8). Calamagrostis canadensis exhibited
significant negative association with Carex stricta, Carex sartwellii, and two physically
small species (Cladium mariscoides (Muhl) Torrey, and Galium obtusum). Campanula
aparinoides was negatively associated with Phalaris arundinacea, Polygonum amphibium
with Galium obtusum and Stachys tenuifolia, and Carex lacustris with Carex sartwellii
and Lythrum salicaria. Galium obtusum was positively associated with Carex stricta and

Stachys tenuifolia, and Carex sartwellii with Cladium mariscoides.

Vertical vegetation stratification

Wet meadow vegetation was composed of grasses, sedges, and forbs 1.2-1 .5m tall,
though in some places cattails and the taller grasses exceeded 2m in height. The median
vegetation height was 62cm (meanil SEM = 61 .49i0.001cm), attaining a maximum of
223cm. Half the stem, leaf, and inflorescence contacts occurred between 43cm-84cm
above the substrate surface. Shrubs, trees, and woody seedlings were rarely encountered,
and when they were, they occurred near the wetland-upland boundary, or at topographic
high points within the wet meadow. Where shrubs or trees did become established, the

herbaceous vegetation exhibited a reduction in height, stem density, and species richness.

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The vegetation canopy exhibited a three layer architecture, based on the median
and maximum heights of species comprising each layer. These layers were canopy
emergent species, canopy species, and understory species. A fourth group,
clingers/climbers, filled a role similar to that of lianas in a forested ecosystem (Table 3-9).

Canopy emergent species exhibited median heights >90cm and maximum heights
>2m. They extended above the general level of the wet meadow vegetation canopy. Only
two species, T ypha angustrfolia L. and Phragmites australis, were canopy emergent
species. T. angustifolia occurred in the lower, wetter portions of the wet meadow,
whereas P. australis exhibited no significant elevation preference. These species were
usually the dominant species in the plots in which they occurred. Yet, despite the apparent
ability to dominate wet meadow vegetation, they only occurred in scattered patches in the
wet meadow, except at the wet meadow-marsh boundary, where T. angustr‘folia became
the dominant species.

Canopy species exhibited median heights of 40-90cm, and maximum heights of up
to 2m. The dominant wet meadow grasses and sedges, and a number of the taller forbs,
were canopy species. The majority of plant stem and leaf contacts occurred in this height
class (Appendix C3).

Understory species were those with median heights <40cm, and, in most cases,
maximum heights <50cm. Components of this group included herb and shrub seedlings,

and low-stature grasses, sedges and forbs.

Three species (Calystegia sepium (L.) R. Br., Campanula aparinoides, and

Galium obtusum) were Clingers/climbers. The stems of Clingers/climbers were too weak

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to support their own weight. These species wrapped themselves around the stems of
other plants (C. septum), or used downward-pointing hairs or bristles (C. aparinor'des and
G. obtusum) to cling to and climb vine-like up the stems of taller plants into the canopy

layer.

Biotic/abiotic interactions

There was no significant difference in plot biomass (ANOVA, F(o,o5,7,292, = 1.510, P
= 0.163; and see Chapter 4), or plot stem density (Kruskal-Wallace ANOVA, KW =
9.231, df = 7, P = 0.236) across the wet meadow elevation gradient. However, species
richness was significantly lower in plots located below 177.0m AMSL compared to plots
located above that elevation (ANOVA, F(o,o5,7,292) = 9.472, P<0.001). There were fewer
species present in low elevation plots, but those tended to be the taller wetland emergent
species with higher per-stem biomass (see Chapter 4). Plot LAI did not differ across the
elevation gradient (ANOVA, F (0,053,292, = 1.104, P = 0.361), but the height at which leaves
occurred in the canopy did increase significantly as elevation decreased (ANOVA,
F(o,o5,7,5599, = 148.59, P<0.001).

Pearson product-moment correlation of plot elevation, peat depth, litter depth, soil
texture, and the major species IV revealed significant associations between species IV and
abiotic factors (Table 3-10). The larger, taller wetland emergent species (e. g., C.
lacustris, C. aquatilis) were associated with thicker peat and greater litter depths, and the
smaller, shorter species (e.g., C. stricta, G. obtusum, C. aparinoides) were associated with

thinner peat and litter depths.

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All 15 major species also exhibited a preference for certain elevations within the
wet meadow zone (Tables 3-11 and 3-12, and Figures 3-12 through 3-15). The smaller,
shorter plants (e.g., C. stricta, C. sepium, C. aparr'noides, S. tenutfolia) exhibited
significant positive correlation with higher wet meadow elevations (see Table 3-10),
whereas the taller, larger wetland emergent species (e. g., C. aquatilis, C. lacustris) were
positively correlated with lower elevations. Some species were positively associated with
sandy substrates (C. aparinoides, C. mariscoides, G. obtusum), and some (C. lacustris, C.
sepium, P. arundinacea, and P. amphibium) exhibited a significant positive correlation
with muck substrates.

Galium obtusum and Lythrum salicaria were significantly negatively correlated
with hummock height (Table 3-13). Hummocks occurred in only 17% (51 of 300) sample
plots. The lack of significant correlation with other species may have been an artifact of
sample size.

PCA illustrated the nature of the relationship among the species and abiotic factors
(Figure 3-16). The first principal component axis (PCI) was the best-fit line describing
the association among the abiotic factors. The relatively small angular ofi’set of the
elevation interval, soil texture, peat depth, litter depth, and hummock height factors fi'om
PCI, and the relatively long distance that these factors plotted fi'om the graph origin,
indicated the strength of the association between these factors and PC 1. Species located
near the negative end of PC] (e. g., C. stricta, G. obtusum) were associated with higher
elevation, thinner peat and litter mats, shorter hummocks, and coarse-textured substrates.

Those located near the positive end of PC] (e. g., C. aquatilis, C. Iacustris) were

110

associated with lower elevation, thicker peat and litter mats, taller hummocks, and fine-
textured substrates.

The greater the distance and angular offset of a species from PCI, the weaker the
linkage between that species and the suite of abiotic factors comprising PC1. C. sepium,
C. sartwellii, and C. mariscoides plotted away from PC] because they did not fit the ‘
pattern of association dictating the orientation of PC1. C. sartwellii and C. mariscoides
were associated with lower elevations and thicker peat, but also with coarse-textured
substrates and low hummock heights. Similarly, C. sepium was associated with higher
elevation plots and thinner peat mats, but fine-textured soils. In each case, the species
plotted at a nearly a right angle to PC1.

PCl accounted for 21% of the variance explained, whereas PC2 accounted for
12% of the variance explained in this PCA. Together, these two PCs accounted for 33%

of the variance amOng the variables explained by the analysis.

Discussion

Relationship of vegetation, water level, and soil at the reference and

disturbed hydrologic study sites

At the reference site, vegetation stem density and species richness peaked in plots
with mean mid-summer water level between +10cm and -10cm depth. Plots in this range
experienced more frequent inundation/exposure cycles than higher or lower elevation plots

at the reference site. Frequent water level variation and moderate disturbance regimes

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result in the greatest plant diversity in Great Lakes wetlands (Keough et al., 1999) and
these factors exert their greatest influence on vegetation in upper elevation Great Lakes

wetlands (Ibid., 1999), which includes the wet meadow zone.

At the reference site, plot biomass was minimal and plot stem density was maximal
in plots with mean mid-summer water level between +10cm and -100m. Large stem
densities of small, low biomass/stem plant species (e. g., Eleocharis smallii, Cladium
mariscoides, and Juncus balticus; see Chapter 4 for biomass data) occupied plots in this
water level range. By contrast, large emergent marsh species (e. g., T ypha angusttfolia,
Sparganium eurycarpum) increased plot biomass and reduced stem density in the deepest
standing water plots. A similar pattern was observed in the disturbed site, even though
there was little standing water on the site. The smaller species had their greatest stem
densities in plots with intermediate groundwater levels. The tall species Carex Iacustris
and Phalaris arundinacea dominated the plots with the shallowest groundwater, and the
similarly large species Aster dumosus and Phalaris arundinacea did the same in the
deepest groundwater plots. The mechanism controlling this species distribution was
unclear, but in addition to water level preferences, may have included light competition
(Keddy, 1989; Leps, 1999), space competition (Auclair et al., 1973), litter deposition and

smothering (Wilcox et al., 1985), and anthropogenic disturbance (see below).

Standing water reduced wet meadow species richness. In plots not being invaded
by marsh plants, species richness increased significantly as standing water levels dropped
at the reference site. However, once the mean mid-summer water level was below

ground, species richness did not change significantly. At the disturbed site, where all

112

mean water levels were below ground, species richness increased significantly only
between the shallowest groundwater plots (4cm below ground) and intermediate level
plots. There was no significant difference in species richness within either site once plot

mean mid-summer groundwater levels dropped below -10cm.

Changes in species NWI classification were significantly correlated with increasing
groundwater depths at both sites. The occurrence of OBL species decreased as
groundwater depths increased, and the occurrence of FACU species increased with
groundwater depth. However, over 20% of OBL species occurrences at both sites were
recorded in plots where mean mid-summer groundwater depths exceeded 50cm. The
major wet meadow species were tolerant of summer draw-down conditions, and appear to

be dependent on occasional draw-downs in order to maintain local vegetation dominance.

At the reference site, FACU species did not occur where mean mid-summer water
levels were above the substrate surface. However, FACU species were recorded at almost
all water levels at the disturbed site. The dike separating the disturbed site from Saginaw
Bay prevented storm surge and seiche inundation of the disturbed site, allowing it to dry
down more thoroughly than the reference site during the growing season (see Chapter 2).
The broader distribution of FACU species at the disturbed site may have been facilitated

by the elimination of site inundation by Saginaw Bay.

The elimination of occasional inundation during the growing season may also have
contributed to the increased presence of shrubs and trees at the disturbed site. Shrubs and
trees (principally C omus amomum, C ornus foemt'na, C ornus stolont'fera, F raxinus

pennsylvanica, Populus deltoides, and Salix petiolaris) occurred within 1m of 40% (75 of

113

187) sample plots at the disturbed site. Only 1.3% (2 of 157) sample plots at the reference
site were within 1m of shrubs, and those shrubs were seedlings less than 20cm tall. Davis
(1900) had observed that Saginaw Bay wet meadow soils were alternately too wet for tree
grth and too dry for tree seedling establishment during the growing season. He noted
that the lower limit of tree grth was the upper limit of annual flooding, and concluded
that flooding was the factor limiting tree invasion in Saginaw Bay wetlands. Davis also
reported considerable shrub and tree growth in formerly treeless wet meadows within five
years of the beginning of agricultural ditching in 1897 (Ibid., 1900). The elimination of
periodic inundation at the disturbed site permitted shrub-scrub and forest succession to
begin at the site, providing filrther evidence that the natural Saginaw Bay hydroperiod,
with its occasional storm surges and high water years, was important in preventing

succession from occurring in these wet meadows.

Historic land use patterns altered soil structure and composition at the disturbed
site. The higher calcium, magnesium, phosphorus, percent organic matter content, and
cation exchange capacity of disturbed site soils reflected historic use of the site as a

pasture. The uniform surface soil texture may be attributable to past cultivation.

Soil texture may have influenced species distribution at the reference site. Carex
bebbii, Carex sartwellii, C ladium mariscoides, and Juncus balticus generally favor open,
sandy shore line habitats (Voss, 1972), and many of the plots exhibiting maximum IV of
these species also had tan, sandy substrates. Soil particle size has been shown to impact
seed germination and seedling recruitment on lake shores, particularly when water levels

were at least 4cm below ground (Keddy and Constabel, 1986). They attributed this to the

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comparatively rapid drying of coarse substrates, which accelerated seed and seedling

desiccation (Ibid., 1986).

Differences in soil fertility might also have impacted species composition at the
reference site. The sand soil was lower in silt, clay, calcium, and potassium than the
adjacent loamy sand soils. Competitive asymmetry increases with soil fertility,
accelerating exclusion of competitively inferior wetland species (Keddy et al., 1997). The
relatively short Carex bebbii, Carex sartwellii, C Iadium mariscoides, and Juncus balticus
may have been excluded fiom the more fertile loamy sand plots by taller species that were
more successfill light or space competitors, and so occupied the relatively infertile sand

plots by default.

Small-scale water level fluctuations may also have been involved in sorting species
in the sand plots. Daily seiche amplitudes range between 20-40cm in southern Saginaw
Bay (Batterson et al., 1991). The sand plots occurred where mean mid-summer water
levels ranged between -10cm and +100m. Seiches could have alternately inundated and
exposed these plots on a daily basis. Disturbance caused by these inundation/exposure
cycles may have created exploitable gaps or otherwise caused the competitive advantage

to shift to the small species (Keddy, 1984).

At both sites, the major species exhibited water level preferences. Species
classified as obligate wetland species occurred at all wet meadow water levels, but most
exhibited greater plot IV where water levels were less than 10cm below the ground
surface. Emergent wetland species (e. g., T ypha angustifolia, and Carex Iacustris)

typically occurred where mean water levels were at or above ground. Most FACW

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species exhibited their greatest plot IV where mean mid-summer water levels were at or
below ground. One exception to this rule was Phalaris arundinacea, a F ACW+ species
that occurred only at the disturbed site. It exhibited a bi-modal distribution with respect to
water levels (see Figure 3-6). P. arundinacea had maximum plot IV both in plots with the
shallowest mean mid-summer groundwater and in plots with the deepest groundwater

levels.

The unusual distribution pattern displayed by Phalaris arundinacea (Reed Canary
grass) was probably the result of its deliberate introduction as a forage crop. P.
arundinacea was for many year recommended for use as a forage or hay crop on poorly
drained soils because it grows well under saturated conditions and tolerates extended
periods of inundation (Harmer, 1941; Heath and Hughes, 1951; Tesar and Shepherd,
1963). At least one of the 1997 study sites (Site #21) had been seeded in P. arundinacea
during the 1950’s on the recommendation of the county agricultural extension agent (W.
Grobsky, pers. comm; and see Chapter 5), and a long-time local resident confirmed that a
prior owner of the disturbed site had at one time experimented with P. arundinacea as a

forage crop at the site (K. Wildner, pers. comm).

Physical attributes

F luctuating wet meadow groundwater and surface water levels were the key
factors determining coastal wet meadow vegetation structure and composition.
Fluctuating water levels periodically de-saturated or re-saturated wet meadow substrates,
eliminating non-wet meadow species and spatially sorting wet meadow species (sensu van

der Valk, 1981) according to inundation and saturation tolerance. Fluctuating water levels

116

also significantly impacted peat and litter depths, soil texture, and hummock heights.
These abiotic factors influenced wet meadow species distribution as well.

While Saginaw Bay surface fluctuations display a certain periodicity (see Chapter
2), bay water levels vary literally minute-by—minute. Stochastic changes in precipitation
and evapotranspiration enhance this variability, resulting in unpredictable short-term and
long-term changes in wet meadow surface water and groundwater levels. Given the
extremely dynamic nature of Saginaw Bay hydrology, it was impractical to estimate the
amount of time that any particular point in the wet meadow was inundated. However,
plots located at similar elevations exhibited similar physical and vegetation attributes, so
plot elevation with respect to the mean high water mark was a good integrator of the net
impact of these hydrologic variations on the wet meadow.

The wet meadow zone extended 60cm in elevation above the mean annual
Saginaw Bay high water mark. Keddy and Reznicek (1986) reported that Lake Erie wet
meadows developed in this elevation range, and attributed the grass and sedge dominance
of wet meadow vegetation to a hydrologic regime that was alternately too wet for woody
plants and too dry for marsh plants (Keddy and Reznicek, 1986).

From a vegetation standpoint, the most significant elevation in the wet meadow
may have been the mean elevation of the wet meadow zone (177.0m AMSL in 1996-
1997). There was a significant decrease in species richness as elevation decreased below
this level, and the 177.0m AMSL elevation contour delineated the approximate boundary
between upper and lower wet meadow vegetation.

The 177.0m AMSL contour was approximately 33cm above the mean annual

Saginaw Bay high water level. Seiches exhibit a 24hr periodicity in southern Saginaw

117

Bay, with daily fluctuations ranging between 20-40cm (Batterson et al., 1991). Batterson
et al. linked aquatic macrophyte and periphyton distribution within Saginaw Bay bulrush
marshes to these fluctuations. Periodic precipitation and storm surge inundation maintain
wet meadow soil moisture conditions that are favorable for wet meadow vegetation (see
Chapter 2). Daily seiche inundation may have had similar impacts on wet meadow
vegetation during calm, dry weather, and may define the upper limit of the lower wet
meadow.

It is important to note that the elevation of the wet meadow zone is not fixed on
the landscape. It moves land-ward and lake-ward fiom time to time with changes in
Saginaw Bay water levels (Mine and Albert, 1998; Keough et al., 1999). 176.67m
AMSL, or 177.0m AMSL, or any other fixed elevation are not absolute values with
respect to the location of Saginaw Bay coastal wet meadows. These elevations simply
represent important reference points during 1996 and 1997.

Coastal wet meadow soils generally consisted of an organic layer up to 16cm thick
deposited over a sandy mineral substrate. Glacial till or lacustrine clay deposits were
encountered wherever lower soil layers were examined. Earlier investigators reported that
the organic layer thickness ranged fi'om a “few centimeters” (Albert et al., 1988) to as
much as 20cm in Saginaw Bay wetlands (Davis, 1908). Coons (1911) reported 5cm of
fine silt and un-decomposed organic matter at one site, and “black, amorphous peat” of
almost 60cm depth at another nearby site. The underlying mineral substrates have been
described as “gravelly or clayey” loam, clay, or sand soils and “stiff, bouldery till
clay”(Davis, 1908), firm sandy substrates (Coons, 1911), and sandy or clayey material of

lacustrine or glacial origin (Albert et al., 1988). Davis reported sharply-defined alternating

118

’3 u

strips of “clayey , gravelly”, and “organic soils” lying parallel to the Saginaw Bay shore
line as he moved inland from the coast. Albert et al. (1988) linked the predominance of
fen species in several Saginaw Bay coastal wet meadows to the calcareous soils occurring
at those sites.

Though an organic surface layer was a common feature in most wet meadows,
several sites lacked an “O” horizon. Some of these sites were former agricultural fields.
In these sites, cultivation-induced soil homogenization and oxidation of organic matter
exposed by tillage probably accounted for the lack of a distinct “O” horizon. In sites with
no agricultural disturbance history, wave action or ice scour most likely explained the
absence of “O” horizons (Tilton et al., 1978; Geis, 1985).

Peat and litter thickness varied greatly within and among sites, but were negatively
correlated with plot elevation. Ambient temperature, oxygen status, and nutrient
availability are most important in determining peat and litter decomposition rates
(Godshalk and Wetzel, 1978; Brinson et al., 1981; Kelley, 1985; Mitsch and Gosselink,
1993). Peat forms most rapidly in waterlogged sites protected from wave disturbance,
where anoxic sediments and reduced decomposition rates accelerate peat accumulation
(Tilton et al., 1978; Godshalk and Wetzel, 1978; Brinson et al., 1981; Mitsch and
Gosselink, 1993). The warm, damp, exposed conditions associated with rapid organic
matter oxidation were more likely to be found in the upper wet meadow, and probably
accounted for the thinner upper wet meadow litter and peat mats in most years. Wave
action or ice scour may have removed peat or litter fi'om the upper wet meadow in high

water years (Tilton et al., 1978; Geis, 1985).

119

Greater peat and litter depths were positively correlated with fine-textured
substrates. Decomposing organic matter increases the fine-particle fraction of underlying
mineral substrates (F oth, 1990). Thicker peat and litter mats may also have absorbed
wave energy, reducing wave-induced sorting of soil particles. Such sorting preferentially
removes fine-textured particles from the substrate (Ibid., 1990).

Tall vegetation hummocks occurred most often in the lower wet meadow. Oddly
though, the hummock-building wetland emergent species Carex stricta was negatively
(though not significantly) correlated with hummock height (r = -0.220, n = 51). There are
two possible explanations for this. First, C. stricta may not have formed all of these
hummocks; Calamagrostis canadensis reportedly forms hummocks in some Saginaw Bay
wetlands (Albert et al., 1988). Second, C. stricta was positively correlated with plot
elevation, so was more likely to be found in the upper wet meadow, where hummocks
were shorter and less common. Widely fluctuating water levels trigger hummock
production in C. stricta (Costello, 193 6), so the depth and fiequency of inundation in the
upper wet meadow was apparently insufiicient to stimulate much hummock production in
C. stricta. Where C. stricta occurred in the lower wet meadow, it may have adapted a
hununock habit in response to the greater inundation depths and frequencies found there.

Other annual and perennial plants also occupied the hummocks. These plants,
generally the shorter, physically smaller wet meadow species, utilized the hummocks as
safe sites. They became established on the hummocks at the optimal elevation (for them)
above that year’s wetland water surface. These species utilized the hummocks to
colonize, either by seed germination or rhizome extension, suitable micro-sites within the

wetland.

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Vegetation attributes

Saginaw Bay coastal wet meadows supported a diverse and stable assemblage of
native grasses, sedges and forbs. The species composition of these wet meadows was
very similar to that previously reported for Saginaw Bay and other Great Lakes coastal
wet meadows (Davis, 1900; Davis, 1908; Coons, 1911; Dodge, 1920; Hayes, 1964;
Stuckey, 1975; Tilton et al., 1978; Jaworski and Raphael, 1979; Jaworski etal., 1979;
Herdendorf et al., 1981; Albert et al., 1988, 1989; Prince and Burton, 1995). Many of the
dominant and sub-dominant species reported by Davis (1900, 1908) and Coons (1911)
were still present as dominant and sub-dominant species 90-100 years later.

Saginaw Bay coastal wet meadows were grass- and sedge-dominated vegetation
assemblages. The four most important species included a grass and three sedges, and
eight of the 15 major wet meadow species were grasses or sedges. Grass and/or sedge
dominance is an emergent property of this vegetation assemblage, one held in common
with inland wet meadows (Curtis, 1959).

These coastal wet meadows also resembled inland wet meadows in other respects.
The vegetation structure and species composition was quite similar to that described for
inland wet meadows, in some cases even with respect to the identity of the dominant
species (Stout, 1914; Curtis, 1959; van der Valk and Bliss, 1971). Hydrology was similar
as well (Curtis, 1959; and see Chapters 1 and 2). Both inland and coastal wet meadows
develop at or just above the local water table, and both experience one or more draw-
down and re-saturation cycles during the growing season.

Species richness varied significantly across the coastal wet meadow elevation

gradient. The shorter major species had much lower importance values at lower wet

121

meadow elevations, and several species were not encountered at all in the lower wet
meadow. The thicker peat and litter mats, and the greater depth and duration of
inundation occurring at lower elevations comprised a less-hospitable growing environment
for these species. The wet meadow emergent species, taller and better adapted to
prolonged inundation, persisted in the lower wet meadow. Lower species richness
resulted.

Sandy substrates and the variable Saginaw Bay hydroperiod probably played a role
in determining wet meadow species richness. Wetland plant species richness is greatest on
sand or gravel substrates (Keddy, 1989), and at or just above the water line (Keddy,
1984). Fluctuating water levels enhance species richness in lacustrine wetlands (Wilcox

and Meeker, 1991; Wilcox, 1995).

Fluctuating water levels and sandy substrates also promote wetland plant species
diversity. Sandy substrates produced higher plant species diversities and propagule
densities than organic substrates in Long Island ponds, with the highest diversities
occurring in non-flooded zones subject to periodic inundation (Schneider, 1994). In the
Great Lakes, the greatest plant diversities generally occur in gently-sloping upper
elevation wetlands subject to intermediate levels of disturbance (Keough et al., 1999).
Occasional flooding is thought to increase herbaceous wetland plant species diversity by
transporting nutrients and propagules into the wetland and eliminating woody vegetation

fi'om it (Keddy and Reznicek, 1986; Schneider, 1994).

Leaf-area index did not vary across the elevation gradient because wet meadow

vegetation physiognomy did not change with elevation. Only species composition

122

changed, and then only gradually. The dominant species, which contributed most to LAI

and vegetation physiognomy, remained the same throughout the wet meadow.

While LAI may not have changed across the elevation gradient, the height at which
leaves occurred in the canopy did increase as elevation decreased. Inundation often
triggers stem elongation in wetland plants (Ernst, 1990). Increased leaf heights in the

lower wet meadow were probably a response to increased inundation depth and duration.

Species interactions

Competitive exclusion, occurring in wet meadows via light competition (Keddy,
1989; Leps, 1999), space competition (Auclair et al., 1973), litter deposition and
smothering (Wilcox et al., 1985), and antibiosis (Leibundgut, 1952, cited in Auclair et al.,
1973) may explain the negative correlation in the importance values of the physically large
and small major wet meadow species. The intensity of above-ground wetland plant
competition is known to increase with standing crop biomass (Twolan-Strutt and Keddy,
1996). However, it does not necessarily follow that biomass determines species richness.
Environmental variables accounted for 89% of the variation in species richness in one
study of Louisiana flood plain wetlands (Gough et al., 1994). Biomass became the best
predictor of species richness only after abiotic stressors were factored out of the analysis
(Ibid., 1994). Keddy (1989) suggested that water levels, soil fertility, and disturbance
determined to what extent competition influenced vegetation structure in lacustrine
wetlands. Grace and Pugesek (1997) concluded that species richness in Louisiana’s Pearl
River flood plain was about equally impacted by abiotic influences and biomass, with

disturbance playing a secondary role.

123

Abiotic factors were important mediators of competition in Saginaw Bay coastal
wet meadows. T wha angustifolia and Phragmites australis demonstrated the ability to
dominate wet meadow vegetation in some lower wet meadow plots, yet these species
occurred only occasionally in the wet meadow. T. angustifolia and P. australt's are
wetland emergent plants, and T. angustrfolia was one of the dominant species of the '
adjacent coastal marshes. However, these species were not tolerant of the annual
substrate de-saturation that occurred in the wet meadow. So, even though they were
capable of successfully competing with wet meadow grasses and sedges for light and
space, hydrologic factors limited the ability of these two species to dominate wet meadow

vegetation.

Inundation frequency was also the principal factor determining affinities among
certain major wet meadow species. Carex stricta and Galium obtusum were positively
associated with one another, and with less frequently inundated upper wet meadow
elevations. The impact of inundation on the growth habit of C. stricta may also have
influenced the association among these species. In the drier upper wet meadow, C. stricta
grew in tufts, leaving gaps in the turf that could be occupied by this other relatively short
species. In the more fi'equently inundated lower wet meadow, C. stricta hummocks
provided safe sites for G. obtusum when water levels rose.

Both competitive factors and abiotic control were probably involved in
determining species richness, species composition, and species distribution in Saginaw Bay
coastal wet meadows. The relative impact of competition and environmental factors were

not determined in this study, but it seems likely that abiotic factors dominated the process.

124

Depth and duration of inundation impacted species distribution within the wet meadow.
Inundation depth and duration also influenced rates of peat development, litter
accumulation, and hummock development throughout the wet meadow. Adaptation to
specific combinations of these abiotic factors determined which species could compete
most successfully, exclude less competitive species, and become dominant at any
particular elevation within the wet meadow.

Using the available abiotic and species interaction data, the major wet meadow
species could be separated into three groups. The first group of species (Campanula
aparr'noides, Carex stricta, Galium obtusum, and Stachys tenuifolt’a) more commonly
occurred in higher elevation plots that had lower peat and litter depths, and a relatively
large number of species per 0.25m2 plot (Table 3-14). Higher elevation could mean either
plots above the 177.0m AMSL elevation contour in the upper wet meadow, or on the
sides and tops of hummocks in the lower wet meadow. One sedges and three forbs
comprised this group of upper wet meadow species. The plants comprising this group
were all among the smaller, shorter major plant species.

A second group of lower wet meadow species (Calamagrostis canadensis, Carex
aquatilis, Carex lacustris, Phragmites australis, and Polygonum amphibium) more
commonly occurred below the 177.0m AMSL elevation contour in plots containing deeper
peat, thicker litter mats, taller hummocks, and fewer species per plot compared to the
upper wet meadow. These species, excepting C. canadensis, were wetland emergent
species, and all were of average to above-average height, and often were the dominant or

co-dominant species in the plots in which they occurred.

125

Six species, Calystegta septum, C ladtum mariscotdes, Carex sartwelltt, Lythrum
saltcaria, Phalarts arundinacea, and T ypha angusttfolta, comprised the last group.
These species could not be easily classified as either upper or lower wet meadow species.
P. arundinacea was a native grass seeded into wet meadows as a forage crop, C. septum
and L. saltcarta were introduced exotic species (Reed, 1988), and T. angusttfolta was the
dominant species of the adjacent cattail marshes These species were either deliberately
introduced agricultural species (P. arundinacea), recent additions to the vegetation
assemblage (C. septum and L. saltcarta), or relicts from a time when different hydrologic
conditions existed at these sites (T. angustifolta). C. sartwellii and C. mariscotdes were
native wet meadow species that did not fit the pattern of association that defined the two
groups. C. sartwellti favored intermediate to lower elevation plots with thicker peat
layers, but also coarse surface substrates and low hummocks. Similarly, C. martscoides

favored intermediate to lower elevation plots, thicker peat, and coarse surface substrates.

Vertical vegetation stratification

The wet meadow canopy exhibited a three layer architecture (canopy emergent
species, canopy species, and understory species), with a fourth group (Clingers/climbers)
ranging among the other three layers. Similar canopy architecture has been observed in
Canadian wet meadows (van der Valk and Bliss, 1971). They reported that three canopy
layers existed in these wetlands, an upper layer (0.75-1.0m height) occupied by the
dominant sedges and forbs, a middle layer (0.25-0.50m) occupied by herbs and grasses,
and a ground layer occupied by vascular cryptogams. van der Valk and Bliss (1971) made

no mention of vine-like climbing species.

126

The Saginaw Bay wet meadow vegetation canopy was commonly 1.2-1.5m tall,
with 50% of the leaves occurring between 43-84cm above the substrate. This was taller
than either the Canadian wet meadows or Dutch wet grasslands, which, like their
Canadian counterparts, had a maximum height of about 1m (F liervoet and Werger, 1984).
Dutch Senecioni-Bromentum wet grasslands exhibited a vertical profile similar to that of
Saginaw Bay wet meadows, but with peak leaf densities occurring 20-50cm above the
ground. Fliervoet and Werger (1984) reported that while standing crop varied
considerably among years, the vertical distribution of phytomass and LAI differed very

little from year to year in these wetlands.

Summary and conclusions

Saginaw Bay coastal wet meadows are the grass- and sedge-dominated herbaceous
vegetation assemblage that occur in a zone extending from the mean annual Saginaw Bay
high water mark to approximately 60cm in elevation above that level. A combination of
predictable and stochastic hydrologic inputs and outputs are the primary determinants of

the landscape position and species composition of the wet meadow zone.

Mean mid-summer plot water level impacted plot biomass, stem density, and
herbaceous species distribution at both a reference and disturbed hydrologic study site.
Plot stem density at the reference site peaked when mean mid-summer water levels ranged
between +10cm and -10cm. Plot stem density and biomass also varied across the
groundwater gradient at the disturbed site, even though a dike eliminated wave action and

storm surge inundation at that site. The elimination of inundation permitted succession of

127

shrub and forest species to begin at the disturbed site. Species richness at both sites
increased significantly as water levels decreased, until mean mid-summer water levels were
below ground, after which species richness did not change. Historic land use, soil texture,
and soil fertility may also have impacted species distribution within the reference and
disturbed study sites, and the presence and distribution of Phalarts arundinacea at the

disturbed site was linked to anthropogenic factors.

Fifteen wet meadow species contributed 84% of all vegetation importance value in
Saginaw Bay coastal wet meadows. Four species (Calamagrostis canadensis, Carex
aquattlis, Carex lacustrts, and Carex stricta) contributed 60% of total IV, with the grass
Calamagrostts canadensts by itself contributing over 31% of the total. By contrast, 27 of

the 93 species encountered occurred in only one of 300 sample plots.

Coastal wet meadow vegetation was 1.2-1.5m tall, with half the leaf, stem, and
inflorescence contacts occurring between 43-84cm above the substrate surface. The
vegetation exhibited a three-layer canopy architecture (canopy emergent species, canopy
species, and canopy understory species) with certain climbing species (clingers/climbers)
comprising a fourth vertical stratification group. Canopy layers could be identified by

examining the median and maximum height of the species occupying the layers.

There were three vegetation sub-groups within the wet meadow zone: upper wet
meadow vegetation, lower wet meadow vegetation, and species that could not easily be
classified as either upper or lower wet meadow vegetation. The upper and lower wet
meadow sub-groups could be distinguished by the affinity of constituent species for certain

combinations of biotic and abiotic factors. The upper wet meadow could generally be

128

recognized by the presence of significantly thinner peat (mean = 1.1cm) and litter (mean =
8.9cm) mats, shorter hummocks (mean = 23 .4cm), higher number of species per plot
(mean = 7.3spp./0.25m2), higher elevation (mean = 177.09m AMSL), and small to average
size plants (e. g., Campanula aparinotdes, Carex stricta, Galium obtusum, and Stachys
tenutfolia). The lower wet meadow could generally be recognized by the presence of
significantly thicker peat (mean = 5.4cm) and litter (mean = 18.4cm) mats, taller
hummocks (mean = 33.2cm), lower number of species per plot (mean = 4.9spp./0.25m2),
lower elevation (mean = 176.88m AMSL), and relatively tall wetland emergent species

(e. g., Calamagrostts canadensis, Carex aquattlts, Carex lacustris, Phragmites australts,

and Polygonum amphibium).

Extrapolation of these findings beyond Saginaw Bay to other Great Lakes wet
meadows must be undertaken with caution. Lake size, shoreline geomorphology,
exposure to prevailing winds and storm surges, circulation and sedimentation patterns,
substrate composition, groundwater inflow from adjacent uplands, and species distribution
vary greatly fi'om site to site, and have uncertain impacts on the developmental trajectory
of coastal wet meadow vegetation. Further study would be required to determine if these
findings apply to other Great Lakes coastal wet meadows, or fringing wetlands in smaller

lakes.

These findings highlight the importance of a variable hydroperiod in the
development and maintenance of coastal wet meadow habitat in Saginaw Bay. The
continued existence of this ecosystem hinges on the continuation of undisturbed natural

variations in Great Lakes water levels.

129

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136

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Mean mld-eumer water level (em) Mean mld-eumer water level (cm)

Figure 3-3. Change in importance value of Campanula aparinoides, Carex bebbii,

Calystegia sepium, and Polygonum amphibium across the water level gradient at the
reference hydrologic study site: 1996. Positive water levels represent standing water
depths, negative values represent groundwater depths. Maximum possible IV = 300.

139

Carex comosa Cladlum marlscoldes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20 I I I I I I 20 I I I I I I
15 - ~ 15 —- F -<
o o
2 -— 2
0 §
§ 10 - 1 g 10 - -
g 5 l— .1 E 6 :— uni
7 1 1 m 1 1 1 0 1 m 1 1 1 1
0.34 0.24 0.1 0.13 0.00 0.05 0.34 0.24 0.1 0.13 0.00 0.05
Mean Inld-eum'ner water level (cm) Mean Inld-sumner water level (an)
Juncus baltlcus Lathyrus palustrls
2° 7 f I I I 7 20 I I I I I I
‘5 h- -I 15 I— .1
o 0 fl
2 2
1 n 9
§ 10 - H - § 10 - __ 1
E 6 l- - g 6 h- u
1 1 1 1 J 1 4 J [Tl . 1 1 1
0.34 0.24 0.1 0.13 0.00 0.05 0.34 0.24 0.1 0.13 0.00 0.05
Mean mld-eunvner water level (cm) Mean mld-eunlner water level (cm)

Figure 3-4. Change in importance value of Carex comosa, Cladium mariscoides, Juncus
balticus, and Lathyrus palustris across the water level gradient at the reference hydrologic
study site: 1996. Positive water levels represent standing water depths, negative values
represent groundwater depths. Maximum possible IV = 300.

140

Carex lacustrls

 

 

 

 

 

 

 

1‘ I I I I I I
§ 1o- 4
g -
8 —
S
a 6- .
g H

1 1 m 1 1 I—1-I

 

0.34 0.24 0.1 0.13 0.00 0.05
Mean Inld-eum‘ner water level (cm)

Figure 3-5. Change in importance value of Carex lacustris, and Leerzia oryzoides across
the water level gradient at the reference hydrologic study site: 1996. Positive water levels
represent standing water depths, negative values represent groundwater depths.

Maximum possible IV = 300.

Importance value

141

Leerzla oryzoldes

 

15

10r-

 

u-I-

 

 

 

 

l

l

L

l

 

0.34 0.24 0.1 0.13 0.09 0.15
Mean mid-aumer water level (cm)

 

Aster dumosus Calamagrostls canadensls

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1” I I I I I I I 100 I T I I I I I
so P - 00 f -
00 r- J 00 - -
g 70 - _ 1 g 10 - - -
‘g eo - 1 3 so - r '— -
8 so - — - 8 so L -
r: 6
4o - - g 40 - — -
i so - - 8 so - 1
5 2o- - 5 '20- -
10 —- l] H - 10 r- -
o m 1 . . . . o 7 . 7 1 1 1 . .
9”" 1156 a?” a?” 9" a!" 9" 09° 0"" n9” n9” 9” a?” a!"
Mean aid-smelter water level (an) Mean nid-etenmer water level (em)
Carex strlcm Phalarls arundlnacea
10° T I I I T I I 1” 41 I I I I I I
so - so - 1
so - 1 so - 1
g 70 - 1 g 70 - F J
'g so - _ ‘ - 2 so - -
g so - _ - g so - _ _ -
1 4° - 1 «r -
8. 3o - - 8 so L 1
E 20 " ‘ g 20 - -¢
10 r- - 10 - n 1
0 L 1 1 1 1 7 71 0 1 J , 1 1 1
0°" of“ .05" s9 .0” 9”" a9“ 99" 95” s96 99" 9"” 39" a!"
Mean rnld-eunrner water level (an) Mean mld-etanrner water level (cm)

Figure 3-6. Change in importance value of Aster dumosus, Calamagrostis canadensis,
Carex stricta, and Phalaris arundinacea across the water level gradient at the disturbed
hydrologic study site: 1996. Negative water levels represent groundwater depths.
Maximum possible IV = 300.

142

Carex bebbll

 

30-

20'-

I

10

Importance value

 

 

 

 

 

1

 

 

.Hm

 

 

O
.9°.9° .9°.9° 9° 9° 9°

Mean mld-eurlu'ner water level (cm)

Calystegla sepium

 

‘0 I I

301-
§
3 _
é 2o- __
E 10-

 

 

 

 

j T I I I

 

 

 

 

 

 

 

 

 

 

 

09" 95" W .0" 9” 19”" a."

Mean mId-eunl'ner water level (cm)

Importance value

Importance value

Carex sartwellll

 

301-

10-

 

 

 

l J

 

 

1 I

Hm

 

 

0
99" a?“ 19" 19” 9” a? .09"
Mean mld-eullnervlaterlevel (cm)

Spartlna pectlnata

 

 

‘0 I I I f1 I I
3o- 1
zo- — -
1o- _H
jm . [I

 

 

 

 

 

 

 

°"»‘° “fl’v‘fisfi‘ 9‘

Mean mld-eunlner water level (cm)

Figure 3-7. Change in importance value of Carex bebbii, Carex sartwellii, Calystegia
sepium, and Spartina pectinata across the water level gradient at the disturbed hydrologic
study site: 1996. Negative water levels represent groundwater depths. Maximum

possible IV = 300.

143

Anemone canadensls

 

2‘ I I I 1 I I I

2o- -

10°- -

101- -

Importmce value
I

 

 

 

1.11 . HH.

 

 

a5" a" I)” a?” 9” a!“ 99"
Mean mId-eunlner water level (cm)

Lathyrus palustrls

 

 

 

2‘ I I—Ifi I I I
zo- -
g
g 15- 1
g .
é
- 5_ _
,HD.Hmflm

 

.09" a5” a" a? a? a." a’”
Mean mld-eununer water level (cm)

Importance value

Importance value

Carex lacustrls

 

 

 

 

 

 

 

2‘ I I I I I T fi
!
zo- :-
15- 1
10. T ..
o- 1
l J E] H L l

 

o J
99‘ a?“ I)” 9’” so“ 11"” :19

Mean mld-eunlner water level (cm)

Polygonum amphlblum

 

 

 

 

 

 

3‘ I I I T I Ffi
zo- 1
15- 1
1o- _ -
"' H HH ‘
. . . -1 HH

,9” ,5” 91" ,9” ,1” ,1? ,9”
Mean mid-eunlner water level (cm)

Figure 3-8. Change in importance value of Anemone canadensis, Carex lacustris,
Lathyrus palustris, and Polygonum amphibium across the water level gradient at the
disturbed hydrologic study site: 1996. Negative water levels represent groundwater

depths. Maximum possible IV = 300.

144

Galium obtusum

a
6

 

 

 

 

 

 

 

 

 

 

 

 

Importancevalue
O .0 N 00 b an O N O O
I

I I I I I I I
I- F_' .1
’ T
F d
L- - ..
l- — F-' 4
4
j

['11 1 1 7 1

99" ,5” ,9” ,5" 91" ,3? ,9”

Mean mld-eunmer water level (cm)

Importance value

d
C

O‘NU‘OONOO

Importance value

Lycopus amerleanus

 

 

 

 

 

 

 

 

 

 

‘0 I I I j I I I

’h' d
. u-
71— -I

a

6h .1
.I— H —
4r- f— '-
3L- -
2:— -I
h H .
o l l l l

l I
e96 .95" a?” a?” 9” a? .09"
Man mld-etatlner water level (cm)

Potentllla anserlna

 

 

 

 

 

 

 

 

 

 

I I I T I I I
"' 1
l- _ .1
P- u

H
I- -<
l—H A
l- -I
_ . . . . [711:1
e 6

Mean mld-emuner water level (cm)

Figure 3-9. Change in importance value of Galium obtusum, Lycopus americanus, and
Potentilla anserina across the water level gradient at the disturbed hydrologic study site:
1996. Negative water levels represent groundwater depths. Maximum possible IV = 300.

145

Table 3-1. Comparison of soil variables measured at the hydrologic study sites.
Significantly different P-values are indicated in boldface and with an asterisk. P-values
were determined using the Mann-Whitney U test. PPM equals parts per million,

Meq/ 100ml equals milli-equvalents per 100ml soil.

 

 

Soil variable Reference site Disturbed site P-value
Mean(i1 SEM) Mean(il SEM)
Samples analyzed per site 3 4 N/A
pH 7.4(0.2) 7.0(0. 1) 0.108
P (PPM) 9.5(2.1) 25.6(3.6) 0034*
K (PPM) 29.8(10.7) S7.9(11.2) 0.154
Ca (PPM) 2182.0(714.2) 5693.5(116.4) 0.034"
Mg (PPM) 243.0(9l.0) 850.3(13.6) 0.0332"
Organic matter (%) 4.9(1.5) 35.0(4. 1) 0.032*
Cation exchange capacity (Meq/ 100ml) l3.0(3.8) 35.7(0.7) 0034*
NO3-N (PPM) 2.5(l.1) 8.9(2.4) 0.077
NH4-N (PPM) 3.3(1.2) 8.104) 0.034*
SAND (%) 74.9(11.3) 68.0(2.7) 0.480
SILT (%) 20.6(8.4) 17.1(2.2) 0.593
CLAY (%) 4.6(3.4) 14.9(0.9) 0034*
Bulk density (g/ml) 0.8(02) 0.4(0.0) 0.289

 

146

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as...U 3.... .3802. 2.9. 2... 03.0.3. 8.. £808.... 00802... 2.. as. .8238. 8.. £92083. 30 32.0% 9-... 2:0...

 

  

 

 

 

  

 

 

 

200
mmmw ONOSVPPWVWdP
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m
80. m
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..... a
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NCO? .. In . mm 520w NCO? 0N3 at...“ (m mnfihw
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«NE - 02m - mm 5.02
comaow 538 .0><

 

 

 

147

 

l l + 1......

 

 

 

-' 178.00»

% 177.50 +

a + +

$177.00 1» + i

l

- 176.50»

5

'9; 176.00»

a 175.50 1 I + T I l l I l
I. I... > C - a Q >
g 5% g i: -v 2 .3 3 2‘3

Month

Figure 3-11. Monthly mean and range of Saginaw Bay water levels recorded during the
1997 growing season. Monthly maximums averaged 36cm higher that monthly means,

and ranged as high as +67cm in October.

148

Table 3-2. Wet meadow width, slope, peat and litter depth, and hummock height by site
for Saginaw Bay coastal wet meadows.

 

Site Site width Slope Peat depth (cm) Litter depth (cm) Hummock Height (cm)

 

 

(m) (%) meangil SEM) mean(:l:l SEM) mean(:‘:lSEM)
1 265. 0.12 2.2(0.6) 14.3(1.5) N/A‘”
2 119. 0.36 4.4(09) 154(53) 38.0(6.4)
3 133. 0.28 33(04) *0) N/A
4 100. 0.32 3.0(0.6) * N/A
5 257. 0.10 5.1(13) 13.0(1.7) 28.0(6.4)
6 11. 2.00 4.0(O.8) 11.5(1.3) N/A
8 147. 0.27 4.8(1.0) 17.4(1.5) N/A
9 210. 0.11 0.4(0. 1) * 35.9(32)
10 105. 0.24 2.3(0.6) * 25.7(5.5)
11 197. 0.15 4.3(09) * N/A
13 92. 0.26 4.3(O.8) 13.1(1.4) N/A
14 110. 0.34 3.3(07) 12.6(1.8) N/A
15 252. 0.10 2.0(03) * N/A
18 25. 1.08 3.3(09) 10.1(2. 1) N/A
19 31. 0.97 4.6(O.7) 19.0(10) 30.7(29)
20 50. 0.40 3.2(0.5) * N/A
21 45. 0.82 4.4(0.7) l7.3(l.6) N/A
22 12. 2.25 3.8(1.0) 14.5(10) 18.0(0.0)
24 65. 0.15 2.3(0.6) 16.3(1.4) 37.4(3.5)
25 115. 0.13 7.40.0) 18.7(0.9) 21.0(00)
26 65. 0.71 5.5(12) 8.7(2.0) 24.5(15)
27 545. 0.09 8.8(O.9) 30.5(70) 27.7(25)
28 95. 0.12 11.0(0.8) 23.8(0.8) 19.0(00)
30 128. 0.13 3.1(0.7) 10.2(0.9) N/A
31 100. 0.30 8.4(2.0) 17£(19) _ 19.3(74)
All 123.9058) 027‘” 4.4(0.2)“" 15.4(0.5)‘5’ 3O.3(l.6)‘6’

 

(l) - Asterisk indicates that no litter measurement was collected at that site.
(2) - N/A indicates that Hummocks did not occur at that site.

(3) - Median value.

(4)-N=300.
(5)-N=215.
(6)-N=51.

149

Table 3-3. Pearson product-moment correlation matrix of Saginaw Bay coastal wet
meadow abiotic factors. Peat depth and litter depth were square-root transformed to meet
parametric assumptions. Boldface values marked with an asterisk were significant
(Bonferroni-corrected P<0.05).

(A) Hummock height data were non-normally distributed, and could not be transformed
to meet parametric assumptions, and so was excluded from the analysis. N = 23 84.

 

Variable Peat depth Litter depth Soil texture Plot elevation

 

Peat depth 1.000
Litter depth -0.042 1.000
Soil texture 0.021 -0.l96* 1.000
Plot elevation -0.644* -0.159* 0.220* 1.000

 

(B) Hummock height data were normally distributed when cases were excluded in which
hummocks were not present, or where hummock data was not collected. N = 382.

 

 

Variable Peat Litter Soil Plot
depth depth texture elevation
Hummock -0.018 0.101 -0.026 -0.258*
height

150

Table 3-4. Importance values (IV) for plant species encountered in Saginaw Bay coastal
wet meadows in 1997. Importance value is the sum of the relative above-ground biomass,
relative stem density, and relative frequency of occurrence of each species in the wet
meadow (Brower and Zar, 1977). A total of 300-0.25m2 sample plots were collected in
25 coastal wet meadows. Percent frequency of occurrence was determined from the
number of sample plots in which the species was found. N equals the number of plots in
which a species occurred.

 

 

Species Family Frequency Contribution Species IV N
of to Total IV
Occurrence (%)
(%)
Acorns calamus L. Acoraceae 0.3 <0.1 0.1 1
Agropyron repens (L) Poaceae 2.7 0.2 0.6
Beauv.
Alisma plantago-aquatica Alismataceae 0.3 <0.1 0.1 1
L.
Anemone canadensis L. Ranunculaceae 8.3 0.6 1.9 25
Apocynum canabinum L. Apocynaceae 5.3 0.3 1.0 16
Asclepias incarnata L. Asclepiadaceae 1.7 0.1 0.3 5
Aster borealis (T. & G.) Asterdaceae 7.3 0.4 1.3 22
Prov.
Aster dumosus L. Asterdaceae 10.3 0.9 2.7 31
Calamagrostis canadensis Poaceae 92.0 31.1 93.2 276
(Michaux) Beauv.
Calystegia sepium (L.) R. Convovulaceae 20.0 1.2 3.7 60
Br.
Campanula aparinoides Campanulaceae 47.0 4.5 13.4 141
Pursh
Carex aquatilis Wahl. Cyperaceae 50.0 14.6 43 .7 150
Carex bebbii (Bailey) Cyperaceae 6.3 0.9 2.7 19
Fern.
Carex buxbaumii Wahl. Cyperaceae 3 .7 0.9 2.7 11
Carex comosa Boott Cyperaceae 0.7 <0.1 0.1 2
Carex hystericina Willd. Cyperaceae 0.3 <0.1 0.1 1
Carex lacustris Willd. Cyperaceae 19.0 2.9 8.8 57
Carex sartwellii Dewey Cyperaceae 53.7 8.9 24.6 161
Carex stricta Lam. Cyperaceae 23 .3 5.5 16.5 70
Carex vulpinoidea Cyperaceae 0. 3 <0.1 0.1 1
Michaux
Cicuta bulbifera L. Apiaceae 1.3 0.1 0.2 4
Cicuta maculata L. Apiaceae 1.7 0.1 0.3 5

151

Table 3-4 (cont’d).

 

 

Species Family Frequency Contribution Species IV N
of to Total IV
Occurrence (%)
CV01
Circium arvense (L.) Asteraceae 10.0 0.6 1.8 30
Scop.
Cladium mariscoides Cyperaceae 34.3 2.5 7.6 103
(Muhl) Torrey
Camus amomum Miller Comaceae 3 .0 0.2 0.5 9
Camus stolomfera Comaceae 7.0 0.4 1 .3 21
Michaux
Eleocharis rostellata Cyperaceae 0. 7 0.1 0.2 2
Torrey
Eleocharis smallii Britton Cyperaceae 8.7 1.0 2.9 26
Epilobium hirsutum L. Onagraceae 1.0 0.1 0.2 3
Equisetum arvense L. Equisetaceae 0.3 <0.1 1.0 l
Equisetum hyemale L. Equisetaceae 0.3 <0.1 0.1 l
Eupatorium maculatum L. Asteraceae 1.7 0.1 0.4 5
Eupatorium perfoliatum Asteraceae 2.3 0.1 0.4 7
L.
Fragaria virginiana Miller Rosaceae 0.7 <0.1 0.1 2
F raxinus pennsylvanica Oleaceae <0. 1 <0. 1 <0. 1 1
Marshall
Galium obtusum Bigelow Rubiaceae 12.7 1.2 3.5 38
Geum laciniatum Murray Rosaceae 0. 3 <0.1 0.1 1
Helenium autumnale L. Asteraceae 0.7 0.1 0.2 2
Hwericum kalmianum L. Clusiaceae 1.0 0.1 0.2 3
Impatiens capensis Meerb. Balsaminaceae 8.7 0. 5 1.5 26
Iris versicolor L. Iridaceae 2.3 0.3 0.7 7
Juncus balticus Willd. Juncaceae 9.3 0.9 2.6 28
Juncus brevicaudatus Juncaceae 4.3 0. 5 1.6 13
(Englem) Fern.
Juncus efiilsus L. Juncaceae 0.3 <0. 1 0.1 1
Lathyrus palustris L. Fabaceae 17.3 1.0 3 .0 52
Leerzia oryzoides (L.) Sw. Poaceae 4.3 0.3 0.8 13
LobeIia kalmii L. Campanulaceae 0.7 <0.1 0.1 2
Lycopus americanus Lamiaceae 5.7 0.3 1.0 17
W.P.C. Barton
Lysmachia quadrrflora Primulaceae 4.7 0.4 1.3 14
Sims
Lysmachia terrestris (L.) Primulaceae 1.0 0.1 0.2 3
BSP.
Lysmachia thtysiflora L. Primulaceae 3 .7 0.2 0.7 11
Lythrum alatum Pursh Lythraceae 0. 7 <0.1 0.1 2

152

Table 3-4 (cont’d).

 

 

153

Species Family Frequency Contribution Species IV N
of to Total IV
Occurrence (%)
(%)

Lythrum salicaria L. Lythraceae 12.3 1.4 4.3 37
Mentha arvensis L. Lamiaceae 5.7 0.4 1.0 17
Onoclea sensibilus L. Polypodiaceae 0.3 <0.1 0.1 l
Panicum spp. Poaceae <0.] <0.1 <0.] 1
Panicum virgatum L. Poaceae 1.7 0.2 0.5 5
Phalaris arundinacea L. Poaceae 14.7 3 .0 9.0 44
Phragmites australis Poaceae 6.7 1.3 3 .8 20

(Cav.) Steudel
Poa palustrls L. Poaceae 1.3 0.1 0.3 4
Poa spp. Poaceae <0.] <0.] <0.] 1
Polygonum amphibium L. Polygonaceae 42.7 2.6 7.9 128
Polygonum scandens L. Polygonaceae 0.3 <0.1 0.1 1
Populus deltoides Marsh. Salicaceae 1.3 0.1 0.2 4
Potentilla anserina L. Rosaceae 5 .7 O. 5 1.4 17
Potentillafruticosa L. Rosaceae 2.0 0.2 0.6 6
Pycnanthemum Lamiaceae 1 .3 0. 1 0.4 4

virginimm (L.) BL.

Rob & Femald
Rubus spp. Rosaceae 0.3 <0.1 0.1 1
Rufieckia hirta L. Asteraceae 0.7 <0. 1 0.1 2
Sagittaria latifolia Willd. Alismataceae 1.0 0.1 0.2 3
Salix petiolaris J .E. Smith Salicaceae 4.3 0.3 0.8 13
Scirpus acutus Bigelow Cyperaceae 1.7 0.1 0.4 5
Scirpus americanus Pers. Cyperaceae 0.7 0.1 0.2 2
Scirpus atrovirens Willd. Cyperaceae 0.3 <0.] 0.1 1
Scirpus validus Vahl Cyperaceae 1.0 0.1 0.3 3
Scutellaria galericulata L. Lamiaceae 5 .3 0.3 0.9 16
Scutellaria Iateriflora L. Lamiaceae 0.3 <0.1 0.1 1
Solanum dulcwnara L. Solanaceae 0.3 <0.1 0.1 1

_ Solidago uliginosa Nutt. Asteracese 0.3 <0.1 0.1 1

Spartina pectinata Link Poaceae 4.7 0.7 2.0 14
Spiraea alba Duroi Rosaceae 1.7 0.1 0.3 5
Spiranthes Iucida (H .H. Orchidaceac 0.3 <0.] 0.1 1

Eaton) Ames
Stachys tenuifolia Willd. Lamiaceae 17.3 3 .3 52
T araxacum ofliciale Asteraceae 1.0 0.2 3

Wiggers
T eucrium canadense L. Lamiaceae 2.7 0.2 0.5 8
77re1yptrispalustris Schott Polypodiaceae 0.3 0.1 0.4 1
T ypha angustifolia L. Typhaceae 19.0 2.2 6.5 57

Table 3-4 @nt’d).

 

 

Species Family Frequency Contribution Species IV N
of to Total IV
Occurrence (%)
(%)
T wha latifolia L. Typhaceae 1.0 0.1 0.3 3
Unknown #1 unk. 0.3 <0.1 0.1 1
Unknown #2 unk. <0.1 <0.1 <01 1
Verbena hastata L. Verbenaceae 0.3 <0.1 0.1 1
Viola affinis Le Conte Violaceae 0.3 <0.1 0.1 1
Vitis riparia Michaux Vitaceae 0.3 <0.1 0.1 l

 

154

Table 3-5. Frequency of occurrence, contribution to total IV, life form/habit, and National
Wetlands Inventory (NW1) classification of plant species contributing 1% or more of total
Saginaw Bay coastal wet meadow (SBCWM) IV. The 15 species (5 sedges, 3 grasses, 1
cattail, and 6 forbs) contributed 84.0% of total SBCWM IV. A total of 300 025-1112
sample plots were collected in 25 SBCWM. Percent fiequency of occurrence was ‘
determined from the number of sample plots in which the species was found. N equals the
number of plots in which a species occurred.

 

 

Species N Frequency Contribution Life Form/ NWI
of to Habit") Region 3
Occurrence Total IV Classification
(%) (%) 0’
Calamagrostis canadensis 276 92.0 31.1 PNG OBL
Carex aquatilis 150 50.0 14.6 PNEGL OBL
Carex sartwellii 161 53.7 8.9 PNGL F ACW+
Carex stricta 70 23.3 5.5 PNEGL OBL
Campanula aparinoides 141 47.0 4.5 PNF OBL
Phalaris arundinacea 44 14.7 3.0 PNG FACW+
Carex lacustris 57 19.0 2.9 PNEGL OBL
Polygonum amphibium 128 42.7 2.6 PNEZF OBL
Cladium mariscoides 103 34.3 2.5 PNEGL OBL
Typha angustifolia 57 19.0 2.2 PNEF OBL
Lythrum salicaria 37 12.3 1.4 PIF OBL
Phragmites australis 20 6.7 1.3 PNEG FACW+
Calystegia sepium 60 20.0 1.2 PIF FAC
Galium obtusum 38 12.7 1.2 PNF OBL
Stachys tenuifolia 52 17.3 1.1 PNF OBL

 

(1) - E = Emergent, F = Forb, G = Grass, GL = Grass-like (sedges and rushes), I =
Introduced, N = Native, P = Perennial, Z = Submerged (Reed, 1988).

(2) - OBL = obligate wetland species, with >99% probability of occurrence in wetlands;
FACW+ = facultative wetland species, with 67%-99% probability of occurrence in
wetlands, ‘+’ indicates that the probability is closer to the higher rather than the lower
end of the range; F AC = facultative species, with 34%-66% probability of occurrence
in wetlands, are considered equally likely to occur in wetlands or non-wetlands (Reed,
1988)

155

Table 3-6. Species richness, Leaf-area index (LAI), Shannon-Wiener diversity index (11’),
Evenness (J), and Dominance (l-J) by site of Saginaw Bay coastal wet meadow
vegetation.

 

 

 

Site Species richness m N (2’ LAI ‘” H’ Evenness Dominance
(species/m2) imz/mz) (J ) ‘3’ (1-1)
1 20.0(0.7) 47 5.3(0.4) 1.59 0.80 0.20
2 13.8(0.8) 39 5.2(0.5) 1.50 0.75 0.25
3 14.8(1.0) 48 5.5(0.4) 1.57 0.79 0.21
4 17.5(2.8) 44 4.1(04) 1.52 0.77 0.23
5 21.8(1.9) 47 5.4(04) 1.64 0.83 0.17
6 21.6(0.9) 48 4.8(0.4) 1.63 0.82 0.18
8 9.8(1.0) 44 4.6(0.5) 1.31 0.66 0.34
9 14.4(09) 45 7.7(0.8) 1.54 0.78 0.22
10 16.4(1.8) 46 6.1(0.6) 1.66 0.84 0.16
11 13.0(0.8) 43 4.7(0.4) 1.59 0.80 0.20
13 13.8(0.6) 39 4.5(0.5) 1.53 0.77 0.23
14 17.2(1.1) 42 4.6(0.4) 1.66 0.84 0.16
15 16.8(0.4) 47 4.1(04) 1.57 0.79 0.21
18 27.2(1.7) 43 5.0(0.5) 1.71 0.86 0.14
19 11.6(0.7) 44 5.0(0.6) 1.32 0.67 0.33
20 18.6(0.4) 44 3.7(04) 1.65 0.83 0.17
21 10.2(1.6) 43 4.4(04) 1.47 0.74 0.26
22 9.0(0.8) 38 3.1(0.3) 1.17 0.59 0.41
24 10.2(1.1) 41 5.3(0.6) 1.38 0.69 0.31
25 10.8(0.8) 45 5.0(0.6) 1.40 0.71 0.29
26 17.6(0.9) 48 6.0(0.4) 1.64 0.83 0.17
27 11.4(0.5) 46 4.9(0.5) 1.43 0.72 0.28
28 11.2(0.4) 46 5.1(03) 1.70 0.86 0.14
30 22.8(1.6) 39 4.1(04) 1.62 0.82 0.18
31 13.8(1.8) 48 5.5(05) 1.39 0.70 0.30
All Sites 15.4(05) 1104 50(01) 1.53(0.03) 0.77 0.23

 

(1) - Mean(iISEM)

(2) - N = the number of samples in which leaf contact occurred. Inflorescence and stem
contacts were excluded

(3) - J = H’lH’max (H’max = 1.98)

156

Table 3-7. Comparison of species richness and leaf-area index (LAI) for various wet
meadow sites.

A. Species richness

 

 

Wetland type Location Species richness Reference

Wet meadow Michigan, USA 15.4spp./m2 This study

Wet grassland Netherlands 205pp./m2 Fliervoet and Werger, 1984“)
Wet meadow Spain 14.2spp./m2 Rey Benayas and Scheiner, 1993
Wet meadow Spain 23.9spp./m2 Rey Benayas et al., 1999

Wet meadow Kwa-Zulu Natal 20$pp./100m2 Eckhardt et al., 1996
Wet meadow Switzerland 12-36spp./4m2 Gusewell and Klotzli, 1998(2)

 

(1) - Species richness was the same for both vegetation types examined
(2) - Species richness varied depending on dominant species

B. Leaf-area index

 

 

Wetland type Location LAI Reference

Wet meadow Michigan, USA 5.0 This study

Wet grassland“) Netherlands 11.7 Fliervoet and Werger, 1984

Wet grassland”) Netherlands 8.4 Fliervoet and Werger, 1984

Ungrazed tall grass prairie Kansas, USA 3.1 Conant and Risser, 1974

Grass meadow Central Europe 2.1 Gloser, 1993

Savanna grassland Kenya 3.1 Kinyarnarino and Imbamba, 1991

Saline grassland Mexico 1.6 Garcia-Moya and Montanez

Castro, 1991

Floodplain grassland Central 4.75 Piedade et al., 1991

Amazon

 

(l) - Circr’um-Molr’nia grassland (Cirsio-Molinietum)
(2) - Agrostis-Calamagrostis—Carex grassland (Senecioni-Bromentum)

157

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2080 u 0<AM<0 528300 R080 .1. 30.0920 £030....8R0 0.3.8880 n <m<2<0 H.88880 028888.00 M 720120

 

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158

Table 3-9. Median height and maximum/minimum height range of common plant species
occurring in Saginaw Bay coastal wet meadows. Canopy Emergent species were those
with median heights >90cm, Canopy Species were those with median heights between 50-
90cm, and Understory Species were those with median heights <40cm. Clingers/Climbers
were species utilizing other plants for support. N is the total number of leaf contacts
observed during sampling. Species with N<5 were excluded fi'om the analysis.

 

 

Species N Median Height Range (cm)
Height (cm)

“Canopy Emergents”
Typha angustifolia 80 138.5 223-38
Phragmites australis 49 128 223-41

“Canopy Species”
Spartina pectinata 29 84 129-28
Carex lacustris 292 79 145-22
Carex aquatilis 1278 73 159-11
Lythrum salicaria 94 70 146-28
Juncus balticus 26 67.5 107-30
Phalaris arundinacea 236 67 188-6
Carex bebbii 73 66 104-16
Cladium mariscoides 2 1 65 88-18
Calamagrostis canadensis 2707 63 208-7
Carex buxbaumii 15 62 93 -30
Iris versicolor 7 58 75-25
Carex sartwellii 871 58 140-9
Poa palustris 8 57 99-27
Circium arvense 8 55.5 64-25
Carex stricta 354 49.5 109-7
Aster dumosus 48 44 96-16
Polygonum amphibian: 50 42 91-1 1
Eupatorium perfoliamm 7 40 62-16

“Clingers/Climbers”
Calystegia sepium 27 54 78-17
Campanula aparinoides 194 27 73-7
Galium obtusum 40 20.5 50-3

“Understory Species”
Camus stolonifera (seedlings) 10 39 54-20
Eleocharis rostellata 10 37.5 46-21
Mentha arvensis 7 37 47-1 1
Lathyrus palustris 20 32.5 51-8
Juncus brevicaudatus 12 32.5 41-23
Stachys tenuifolia 10 27.5 50-15
Anemone canadensis 15 25 52-4
Eleocharis smallii 6 25 32-13
Lysmachia quadnflora 13 23 59-10
Thelyptris palustris 10 22.5 30- 14
Potentilla anserina 8 19 23-14

 

159

Table 3-10. Pearson product-moment correlation among Saginaw Bay coastal wet
meadow major plant species IV and abiotic factors measured in 1997. Litter depth and
peat depth were square-root transformed to achieve normal distribution. Plots in which
litter depth was not determined were excluded from the analysis. Soil texture increased
from fine- to coarse-textured substrates. Values indicated with boldface and an asterisk
were significant at P<0.05 (rm/(0.05, 215, = $0.134; Snedecor and Cochran, 1980, Table Al 1).

 

Plot Elevation Peat Depth Litter Depth Soil Texture

 

Calamagrostis canadensis -0.158* 0.155* 0.221* -0.091
Campanula aparinoides 0367* -0.191* -0366* 0.275*
Carex aquatilis -0309* 0.235* 0346* -0.025
Carex lacustris -0.281* 0.189* 0394* -0.l94*
Carex stricta 0.475* -0340* -0.556* 0.119
Carex sartwellii -0.225* 0.268* 0.080 0.120
Cladium mariscoides -0.103 0.200* 0.009 0.253*
Calystegia sepium 0306* -0312* -0.089 -0.l48*
Galium obtusum 0.458* -0.183* -0.438* 0.269*
Lythmm salicaria -0.132 0.006 -0.035 -0.013
Phalaris arundinacea 0.042 -0.102 0.097 -0.l66*
Phragmites australis -0.184* 0.172* 0.165* -0.119
Polygonum amphibium -0.299* 0.267 * 0.241* -0.226*
Stachys tenuifolia 0302* -0.076 -0.289* 0.203*
Typha angustifolia -0.105 0.156* 0.100 0.156*

 

160

Table 3-11. Change in importance value across the elevation gradient for species found in
Saginaw Bay coastal wet meadows. Data were collected in 288 sample plots at 24 study

sites. Site #1 was isolated from Saginaw Bay by a dike, and so was excluded from the

analysis. Sites became wetter as elevation decreased. Mean annual high water mark for

Saginaw Bay (1918-1996) equaled 176.67 m AMSL.

 

Species

 

177.25 177.15 177.05 176.95 176.85 176.75 176.65 176.55

 

Phalaris arundinacea
Carex bebbii
Carex stricta

Calamagrostis canadensis

Lathyrus palustris
Stachys tenuifolia
Potentilla anserina
Anemone canadensis
Campanula aparinoides
Galium obtusum
Taraxacum oflicinale
Agropyron repens
Cerastium vulgatum
Spiraea alba
Calystegia sepium
Carex sartwellii

Aster dumosus
Spartina pectinata
Circium arvense
Comus stolonifera
Poa palustris
Impatiens capensis
Eupaton'um maculatum
Cornus amomum
Thelypten's palustris
Apocynum canabinum
Mentha arvensis
Lycopus americanus
Juncus brevicaudatus
Eleocharis smallii
Scutellaria galericulata
Leerzia oryzoides
Aster borealis

84.2
50.5
42.2
23.2
13.9
13.3
12.9
10.0
8.7
8.3
6.9
6.6
6.5
6.4
6.4

15.9
1.1
33.6
86.8
4.9
4.7
3.3
4.5
21.2
11.1
0.5
2.3

6.8
14.4
8.7
6.0
4.7
2.9
2.3
2.3
2.2
2.1
1.9
1.7
1.6
1.6
1.4
1.3
1.2
1.0
0.9

69.5

16.7

14.6

Elevation interval (m AMSQ
6.0 10.9 4.1 0.8
2.7 4.4 0.6
26.9 8.9 1.8 3.3
96.0 107.2 98.5 64.2
3.6 2.7 0.7
5.1 2.4 0.8 0.7
2.3
2.5 0.2 0.6
17.9 13.0 4.9 1.6
4.1 0.3
0.2
0.4 0.3 0.8
3.2 4.6 1.1
17.3 31.6 35. 55.3
2.5 1.3
3.3
3.0
2.5 0.2
0.2
1.0 2.5 0.4
0.4
1.3 0.9
1.9 0.9
1.8 0.4
4.2 1.1
7.6 1.5 2.3
1.1 1.1 0.3
1.8 0.5
3.0 1.1 0.3

161

25.2

18.0

Table 3-11 (cont’d)

 

 

 

Species Elevation interval (m AMSL)
177.25 177. 15 177.05 176.95 176.85 176.75 176.65 176.55

Lysmachia thrysiflora 0.8 0.6 1.3
Lysmachia terrestris 0.7 0.3
Iris versicolor 0.6 1.8 0.7
Populus deltoides 0.5 0.2 0.4
Eupatorium perfoliatum 0.5 1.0
Lobelia kalmii 0.5
Epilobium hirsutum 0.4 0.4
Teucrium canadense 0.4 0.8 0.8
Fragaria virginiana 0.3 0.2
Rudbeckia hirta 0.3 0.2
Vitis riparia 0.3
Geum laciniatum 0.3
Helenium autumnale 0.3 0.5
Lythmm alatum 0.2 0.2
Circium maculatum 0.2 0.6 0.4
Spiranthes lucida 0.2
Hypericum kalmianum 0.2 0.7
Fraxinus pennsylvanica“
Potentilla fruticosa 2.4
Pycnanthemum 1 .5

virginianum
Panicum spp. 1.2
Poa spp.*
Asclepias incarnata 0.9 0.2
Solidago uliginosa 0.3
Verbena hastata 0.3
Viola afiinis 0.2
Equisetum hyemale 0.2
Alisma plantago-aquatica 0.2
Unknown #1 0.2
Rubus spp. 0.2
Panicum virgatum“
Unknown #2"‘
Scirpus americanus 0.7
Onoclea sensibilus 0.2
Carex hystericina 0.2
Scutellaria lateriflora 0.2
Acorns calamus 0.2
Typha latifolia 0.8 0.4
Equisetum arvense 0.4
Polygonum scandens 0.4
Juncus effusus 0.5

162

Table 3-11 @ont’d)
Species

Elevation interval (m AMSL)

 

177.25 177.15 177.05 176.95 176.85 176.75 176.65 176.55

 

 

Solanum dulcamara 0.5

Cicuta bulbifera 0.4 0. 7

Eleocharis rostellata 0.5 1.2

Scirpus validus 0.5 2.2

Carex comosa 0.3 0.8

Carex buxbaumii 0.4 12.2 5.2

Scirpus acutus 0.4 0.2 0.3 0.6 0.8

Salix petiolaris 0.5 0.8 0.2 1.4 2.4

Phragmites australis 0.7 0.6 4.9 9.5 3.4

Juncus balticus 1.1 1.7 2.8 5.1 3.5

Lythrum salicaria 1.8 6.5 1.9 9.6 4.7

Cladium mariscoides 3.7 6.4 8.5 10.9 14.3

Typha angustifolia 2.9 3.7 5.4 10.7 20.0

Polygonum amphibium 4.2 4.7 10.2 12.2 14.6 7.4
Sagittaria latifolia O. 5 0. 7 7. 7

Scirpus atrovirens 20.9
Lysmachia quadriflora 2.5 2.9 18.1
Carex lacustris 2.0 2.7 11.8 15.6 14.7 34.3 36.6
Carex aquatilis 18.6 31.3 47.8 56.3 84.8 149.8 181.2
Totals 300 300 300 300 300 300 300

 

* - IV <0.] at all elevation intervals.

163

Table 3-12. Change in importance value across the elevation gradient for species found at
Site #1, a wet meadow isolated from Saginaw Bay by a dike. Data was collected in 12
sample plots, three plots at each of four elevations, in 1997. Sites became wetter as
elevation decreased. Mean annual high water mark for Saginaw Bay (1918-1996) equaled
176.67 m AMSL. Species distribution patterns were similar for this site and 24 study sites
not isolated from Saginaw Bay.

 

 

 

Species Elevation interval (m AMSL)
177.15 177.05 176.95 176.85
Carex stricta 72.7 56.4 38.7
Phalaris arundinacea 41.9 19.4 81.9 31.0
Spartina pectinata 36.1
Aster dumosus 33.3 14.6
Calystegia sepium 29.0 20.9 3.2
Galium obtusum 21.3
Carex sartwellii 11.6 25.4 22.7 12.7
Calamagrostis canadensis 10.3 63 .7 15.7 15.4
Mentha arvensis 8.8 4.0
Polygonum amphibium 8.1 20.8
Potentilla anserina 7.2 12.4
Anemone canadensis 6.3
Agropyron repens 3 .2
Cladium mariscoides 3.5 14.1 4.4
Lathyrus palustris 3.5 11.3 3.2
Scutellaria galericulata 3.1 3.3
Carex aquatilis 118.3 16.1
Apocynum canabinum 3.3
Salix petiolaris“
Stachys tenuifolia“
Iris versicolor 6.9
Scirpus validus 8.6
Teucrium canadense 3.5
Acorus calamus 3.8
Typha angustifolia 15.7
Cicuta bulbifera 4.0 12.4
Solanum dulcamara 16.8
Carex lacustris 22. 5 1 73 .0
Totals 300 300 300 300

 

* - IV<0.1 at all elevation intervals.

164

Calamagrostis canadensis Carex aquatilis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IIIIIIII 2MIIIIIjII
1 - 1501- H .
3 3
1 1
> — r.
i‘ _r " ‘ EMF _ 1
t
E a
5 H1] 1 5 505 ”[1 q
I] I] 0 .1711].
y"

_ l l
s4¢s436s4f¢y¢ 6‘41““?3 ‘4’6‘436‘4’9¢ ¢y¢bfis¢b¢¢y

 

 

 

 

 

 

 

 

Elevation (meters AMSL) Elevation (meters AMSL)
Carex stricta Carex sartwellii
l I I I I I I I I I I I I I I I
l . 15 -
3 3
1 1
> >
° 1 -+ 8 1 -
a a
i a
5 4 5 sol- ” q
.l—l-IHIJ—m“. I ‘ 0 rmmflmaml
‘49‘4>5~4*¢ 9&0‘90‘96“? s‘l‘fi‘fi'éx‘I‘fl“ (‘bfd'fiafi‘fis‘y
Elevation (meters AMSL) Elevation (meters AMSL)

Figure 3-12. Importance value of Calamagrostis canadensis, Carex aquatilis, Carex
stricta, and Carex sartwellii at difl‘erent elevations within Saginaw Bay coastal wet
meadows. Maximum possible IV = 300. The mean Saginaw Bay high water mark (1918-
1996) equaled 176.67 m AMSL.

165

Campanula aparinoides Carex lacustris

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

” T I I I I I I I m I I I I T I I I
so .. .4 so .. .
7o - J 70 - q
a w .— -1 0 60 :- Ill
1 '3
> so .. .1 > so - -
3 E
a '“" ‘ a “"" m '
8. 3o .. .J 8- 3o .. ..
s 2..- T s ,0. i
10 r - 10L 1'] I] n -
0‘ , 0 l ['11 m l
{\flysqfi-‘i‘fl’ W {169669 S «49“4-44 «J «JMU “6‘ «69
Elevation (meters AMSL) Elevation (meters AMSL)
Phalaris arundinacea Polygonum amphibium
” j I I I I I I I m 1 I I I I I l I
m d w I— .1
7o - 7o - -
.3 6° ‘ E. 6“ ’ ‘
U C
> 50 .. > so
3 8
40 - a 40
E E
8. 30 - a so
5 m _ s 2.,
10 1] L" - 10
—‘q‘\¢‘q‘\¢{\‘\°¢ qb¢q {‘6’} {\6-¢<\ 4‘69 ¢W #46” {‘69669
Elevation (meters AMSL) Elevation (meters AMSL)

Figure 3-13. Importance value of Campanula aparinoides, Carex lacustris, Phalaris
arundinacea, and Polygonum amphibium at difl‘erent elevations within Saginaw Bay
coastal wet meadows. Maximum possible IV = 300. The mean Saginaw Bay high water
mark (1918-1996) equaled 176.67 m AMSL.

166

Cladium mariscoides Lythrum salicaria

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

25 I I I I I I I I 25 I I I I I r I I
20 p— q 20 n- .1
E 3
g 15 - _ -‘ g 15% q
a a
a a:
E 10 - 7 ~ 5 10 - -
E E
5 - [I - 5 - [1H .1
o «I‘lflq l l J l o J [:1 n1 1
W 6-‘46' ‘66? {(4% <\’\"\° “‘46” q {(656 NW
«\Elevation (meters AMSL) Elevation (meters AMSL)
Ph ragmitea australis Typha angustifolia
25 I I I I I I I I 25 I I 1 I I I I I
20 h - m - — q
E. s
g 15 '- -' E 15 - 1
3 3
I: a
«3 10 +- - ‘3 10 - F ~
2‘ 2'
5 r- - 5 - I] 4
j m 115 [II I] L L 11?] n l l 1
44M 4“- ‘qfl- éfib¢¢ 6"” 46' {(6% «6’ «if; {V‘s-(fl *46'¢~ «6"(‘6-«6sq 6966?
Elevation (meters AMSL) Elevation (meters AMSL)

Figure 3-14. Importance value of C Indium mariscoides, Lythrum salicaria, Phragmites
australis, and Twin angustifolia at different elevations within Saginaw Bay coastal wet
meadows. Maximum possible IV = 300. The mean Saginaw Bay high water mark (1918-
1996) equaled 176.67 m AMSL.

167

Calystegia sepium Galium obtusum

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20 I I I j I I I r 20 I I j fi r I I I
15 - d 15 - -
a .2
i s _
g 10- - g 10*- w
i! E "
S. 8.
.5 s :l l l l .5 s~ -
0‘ D I] m l l l o I Hi 1 4 1
44364“ ”W 46- ¢4béx 46¢ ‘fi¢:4'\- ‘4’\-4‘\- ¢463,4 “9“", Mb?
Elevation (meters AMSL) Elevation (meters AMSL)
Stachys tenuifolia
20 I I I T 1 I r I
15 - .
3 r-
2
3 10 - ..
B
E
S.
5 5 - -
o I 39H H [Ii [11 m l J

 

 

 

 

 

y we» m? M. .9
Elevation (meters AMSL)

Figure 3-15. Mean importance value of Calystegia sepium, Galium obtusum, and Stachys
tenuifolia at different elevations within Saginaw Bay coastal wet meadows. Maximum
possible IV = 300. The mean Saginaw Bay high water mark (1918-1996) equaled 176.67
m AMSL.

168

Table 3-13. Pearson product-moment correlation between Saginaw Bay coastal wet
meadow major plant species IV and hummock heights measured during 1997 vegetation
sampling. Plots in which hummocks were not present or measured were excluded from
the analysis. Values indicated with boldface and an asterisk were significant (rmuos, 49) =
i0.273; Snedecor and Cochran, 1980, Table A1 1(i)).

 

 

Species Hummock Height
Calamagrostis canadensis -0.048
Campanula aparinoides 0.099
Carex aquatilis 0.206
Carex lacustris 0.020
Carex sartwellii -0.006
- Carex stricta -0.220
Cladium mariscoides -0.255
Calystegia sepium 0.222
Galium obtusum -0.293*
Lythrum salicaria -0.326*
Phalaris arundinacea -0.170
Phragmites australis 0.132
Polygonum amphibium 0.020
Stachys tenuifolia -0.160
Typha angustifolia -0.093

 

169

 

1.0 1

C. sepium 7%

Plot , ' I
Elevation P. arundinacea
* 7% \u \7‘: C. lacustris
C- apannordes : 7% C. aquatilis
*P. australis
_____ ,—,._..__._ __________.*__
0.0 S. tenuifolia * _: * P. amphibiuml
P02 C strict: G. obtusum I 42* T. angustifolia Litter
' | L. salicaria Depth
7% I 7p
Soil I Peat
-O.5 *- Texture : Depth ""
I
l

C. mariscoidesfi * C. sartwellii
I

_10 J l l
-1.0 -O.5 0.0 0.5 1.0

PC1

 

 

 

Figure 3-16. Principal component analysis bi-plot of major plant species importance
values and abiotic factors in Saginaw Bay coastal wet meadows. PC] was the best-fit line
describing the association among the abiotic factors. The small angular offset of the
elevation interval, soil texture, peat depth, and litter depth factors from PC] indicated the
strong linkage of these factors with PC1. Species located close to the negative end of
PCI (C. stricta, G. obtusum) were most strongly linked with higher elevation wet meadow
plots containing thinner peat and litter mats and coarse-textured substrates. Those located
close to the positive end of PC] (C. aquatilis, C. lacustris) were most strongly linked with
lower elevation wet meadow plots containing deeper litter mats and thicker peat.

170

Table 3-14. Physical and vegetation attributes that define the upper and lower Saginaw
Bay coastal wet meadow sub-zones. Upper wet meadow vegetation occurred above
177.0m AMSL, lower wet meadow vegetation below that elevation. Data was collected
in 300- 0.25m2 plots in 25 wet meadows. N is the number of 0.25m2 plots, except as

indicated. All means were significantly different at P<0.05.

 

 

Variable Upper wet meadow Lower wet meadow
N Mean(:l:lSEM) N Mean(:1:1 SEM)
Species per 0.25m2 plot 122 7.3(0. 1) 178 4.9(0. 1)
Vegetation height“) (cm) 2591 50.1(03) 4116 69.3(0.2)
Hummock height“) (cm) 15 23.4(3. 1) 36 33.2(17)
Plot elevation (m AMSL) 122 women 178 176.88(0.01)
Peat depth (cm) 122 1.1(0. 1) 178 5.4(0.1)
Litter depth“) 1cm) 78 8.9(0.2) 137 18.4(02)

 

(a) - N equals number of vegetation contacts.

(b) - Plots in which hummocks were not present were excluded. N = 51.

(c) - Plots for which litter depths were not measured were excluded. N = 215.

171

Chapter 4 - Above-ground biomass and productivity of the vegetation in coastal
wet meadows bordering Saginaw Bayl

Introduction

Wet meadows are an important component of the coastal wetland complex
flinging Lake Huron’s Saginaw Bay. Structural aspects of the macrophyte community,
such as biomass production, govern the habitat value of these wetlands, and influence their
ability to mitigate the impacts of flooding, erosion, pollution and sedimentation in the
region (BURTON, 1985; WILCOX, 1995).

Biomass production estimates are available for certain Great Lakes wet meadow
plant species (TILTON ET AL., 1978; JAWORSKI ET AL., 1979; KELLEY, 1985;
KELLEY ET AL., 1985), for inland sedge and grass wet meadows in Wisconsin (STOUT,
1914; COSTELLO, 1936; KLOPATEK & STEARN S, 1978), Minnesota (BERNARD,
1974), and North America (BERNARD & GORHAM, 1978; RICHARDSON, 1978;
BRINSON ET AL., 1981), and for wet meadow vegetation growing in prairie potholes
(VAN DER VALK & DAVIS, 1978), English and Welsh rich fens (WHEELER &
SHAW, 1991), Lake Okeechobee wetlands (HARRIS ET AL., 1995), and boreal
lacustrine sedge fens (SZUMIGALSKI & BAYLEY, 1996). However, no studies have
previously examined above-ground biomass production in Great Lakes coastal wet
meadows.

Wet meadows are the sedge and/or grass dominated vegetation of wet or saturated

soils (CURTIS, 1959; AUCLAIR ET AL, 1973; NIERING, 1985; KEDDY &

 

' The chapter has been accepted in this form for publication in the Proceeding of the XXVII Congress of
the Societas Intemationalis Limnologr‘ae.

172

REZNICEK, 1986; MNFI, 1989). While monocots dominate wet meadow vegetation,
herbaceous dicots are important secondary community constituents (CURTIS, 1959;
NIERING, 1986). Trees and shrubs are generally absent.

CURTIS (1959) provided the basic definition of wet meadows and wet prairies,
describing sedge wet meadows as open communities found on wet soils, located low on
the regional soil catena, with sedges supplying more than 50% of the vegetation
dominance. Wet prairies differed from sedge meadows principally in that grasses, rather
than sedges, were the dominant species (CURTIS, 1959). While intolerant of continuous
inundation, wet meadow plants must be adapted to growing in more or less saturated
conditions (CURTIS, 1959; AUCLAIR ET AL, 1973).

KEDDY & REZNICEK (1986) defined Great Lakes coastal wet meadows as the
grass- and sedge- dominated herbaceous vegetation assemblage found between the yearly
mean high water level and yearly maximum high water level in Great Lakes wetlands.
They included wet meadows in a lake-margin wetland continuum composed of a series of
discrete zones. These zones, from open water to uplands, were the submerged aquatic
community, emergent cattail and bulrush marshes, the beach strand, wet meadows, and
forest and shrub thickets. Keddy and Reznicek believed that the maximum high water
level determined the lower limit of successful shrub invasion, and the mean high water
level determined the lower limit of successfirl wet meadow growth.

Several factors are involved in Great Lakes coastal wet meadow development and
maintenance. The most important include intra- and inter-specific competition
(AUCLAIR ET AL, 1973; KEDDY, 1989), soil fertility (KEDDY, 1989), and water-level

fluctuations (HARRIS ET AL, 1981; KELLEY ET AL., 1985; KEDDY & REZNICEK,

173

1986; KEOUGI-I, 1990; BATTERSON ET AL, 1991; WILCOX, 1995). These factors
interact to define the composition and zonation of coastal wet meadow vegetation.

Our objectives were to determine the live biomass, standing dead biomass, and
litter production of Saginaw Bay coastal wet meadow (SBCWM) vegetation, and to use

these data to estimate SBCWM net above-ground primary productivity (NAPP).

Study area

Saginaw Bay, the southwestern lobe of Lake Huron (Figure 1-1), was formed and
reshaped by Pleistocene glaciation and post-glacial Great Lakes water-level fluctuations
(DORR & ESCHMAN, 1970). Covering 2960km2, Saginaw Bay has maintained its
current 622km shoreline for about the last 2500 years (DORR & ESCHMAN, 1970;
SBNWI, 1998).

Saginaw Bay coastal wetlands may have covered more than 28000ha prior to
European settlement (PRINCE & BURTON, 1995). Historically, wet meadow vegetation
extended up to 5km inland along the Saginaw Bay shore line (DAVIS, 1900; ALBERT
ET AL, 1988), but agricultural development has limited the present wet meadow zone to
a narrow strip along the coast. Easily drained and very fertile, coastal wet meadows were
among the first wetlands utilized after European settlement began in the 19‘” century.
Development pressure has since resulted in the destruction of more than 99% of the
region’s original wet meadows (PRINCE & BURTON, 1995). Recent estimates of extant
Saginaw Bay wetlands range between 6000-7300ha (JAWORSKI & RAPHAEL, 197 8;

USGS, 1996; SBNWI, 1998).

174

Methods

Biomass

Study sites were established throughout the Saginaw Bay coastal zone between
Caseville, MI ( 43.93° N, 8329" W) and Standish, MI ( 43.98° N, 83.96° W; Figure 4-1).
Sites were contiguous with Saginaw Bay and subject to natural bay water level
fluctuations.

Biomass samples were collected from 19 sites in July-August 1997, the period
corresponding to maximum above-ground biomass (“peak standing crop”) in Great Lakes
wetlands (BARKO ET AL, 1977 ; KELLEY, 1985). At each site, the standing biomass
contained in 12- 0.25m2 sample plots was clipped at the substrate and then sorted, live
biomass by species and dead material grouped as standing dead material. Plot placement
was stratified within each site to capture potential biomass variability resulting from
differences in inundation depth and fi'equency (see Chapter 3). Dry weights were
determined for each species and for standing dead material (i0. 1 g) after oven-drying 48h
at 60°C.

Biomass data were summed by plots, then pooled within sites to determine mean
plot biomass for each site. Biomass data were pooled across sites by species to determine
mean species biomass. Species frequency of occurrence was determined from the number
of plots in which the species was found. Contributions to total wet meadow biomass were
determined by dividing the pooled species biomass by the grand total of all biomass

collected at all sites.

175

To aid interpretation of our results, we grouped species into eight categories:
forbs, grasses, sedges, woody, dead, seedless vascular, rushes, and vines, classifying as
forbs all herbaceous plants that were not grasses, sedges, or rushes. Woody vegetation
included shrubs and trees; seedless vascular vegetation ferns and horsetails. Biomass data
for each category were pooled across sites to determine mean category biomass and the

contribution each category made to total SBCWM biomass.

Litter

Growing-season litter production was measured at two study sites in l-m2 by 0.9m
tall open-topped enclosures. Fifteen enclosures, constructed of 1.5mm mesh aluminum
screening material, were installed in groups of five, 3-5 meters from one another
approximately two weeks after visible plant growth commenced in the spring. The bottom
5cm of screening was buried to prevent introduction of litter into the enclosures under the
screening. All dead plant material was removed fiom the enclosures at the beginning of
the experiment, while disturbing living plants as little as possible. Monthly thereafter, all
vegetation located outside but within 2m of each enclosure was clipped to minimize
introduction of material from outside the enclosures.

After 94 days, the period from the start of the growing season to peak standing
crop (PSC), all standing material in the enclosures were clipped at the substrate, then all
accumulated litter was raked from the enclosures. Any plant material lying on the
substrate and not obviously fresh and green was considered litter. The standing plant

material and litter were separately bagged and transported to the laboratory, where the

176

standing plant material was sorted into living and dead material, and all samples were
weighed afier oven-drying 48h at 60°C.

Seasonal litter loss attributable to in-place decomposition was estimated at the two
sites by loss from 20cm by 20cm litter bags. Forty-five bags, constructed from 1.5mm
mesh black fiberglass screening material, received 10.0gm dry weight mixed living and
standing dead plant material cut into 15 cm lengths. The mixture of living and dead plants
simulated the decomposition of a natural mixture of fresh, unleached and old, leached
material. Three bags were placed in contact with the substrate at each biomass enclosure.
We chose 1.5mm mesh because it could contain herbaceous litter with minimal
fragmentation loss, and was the mesh size most commonly used in decomposition studies
of similar vegetation (BRINSON ET AL, 1981). Black screening matched the natural
substrate color, minimizing difi‘erences in solar heating between the bags and substrate.

All litter bags were recovered after 87 days, packed in ice, and returned to the
laboratory. The bags were gently washed to remove loose external debris, oven-dried 48h
at 60°C, then opened and the contents weighed (i0. lg). Decomposition loss was
determined by subtracting the litter mass remaining from the 10.0g initial weight of each

bag.

Results and Discussion

Distribution of above-ground biomass

Mean PSC was 669g/m2, live plants contributing 575g/m2 and standing dead

material 94g/m2 to the total. Grasses and sedges constituted 75.3%, dead material 14.3%,

177

and forbs 9.3% of total PSC. Woody and other plant types contributed <1% each to PSC
(Figure 4—2).

Of 81 plant species encountered during sampling, five species, the grass
Calamagrostis canadensis, and the sedges Carex aquatilis, C. lacustris, C. sartwellii, and
C. stricta, contributed >32% of total PSC (Table 4-1). Nine forbs (Campanula
aparinoides, C ircium arvense, C alystegia sepium, Galium obtusum, Impatiens capensis,
Lathyrus palustris, Polygonum amphibium, S tachys tenuifolia, and T ypha angustifolia)
each exhibited fiequencies of occurrence >10%, and these collectively constituted almost
27% of total PSC. The 15 species together contributed 59% of total PSC.

Twenty species, representing 24.7% of species encountered, occurred in only one
of the 228 sample plots. These species were either wetland plants uncommon to SBCWM
or upland plants opportunistically occupying suitable micro-habitats within the wet
meadow.

Mean PSC ranged between 323-933g/m2 among sites, and between 113-2501g/m2
among all sample plots (Table 4-2). The highest PSC occurred in plots containing T ypha
angustifolia, Phragmities australis, or Lythrum salicaria. The lowest PSC occurred in
plots located near the maximum elevation of Saginaw Bay and dominated by EIeocharis
spp. and short-stature wet meadow forbs.

SBCWM PSC fell within the range of values published for similar lacustrine and
palustrine wetlands (Table 4-3). TILTON ET AL. (1978) estimated that PSC of Carex-
dominated Great Lakes shoreline communities ranged between 200-1400g/m2. KELLEY
(1985) reported a PSC of 468 g/m2 for a Lake Michigan river-mouth Carex/Calamagrostis

wet meadow. HARRIS ET AL. (1981) observed increasing annual PSC (from 337g/m2 to

178

1216g/m2) for Calamagrostis canadensis in Green Bay wet meadows as Lake Michigan
water levels declined after a cyclic high (see Chapter 2). They attributed the increase to
colonization of newly exposed mudflats.

Terrestrial grasslands exhibit lower PSC than SBCWM. Precipitation and soil
moisture deficits limit grassland production (LAUENROTH, 1979), and soil moisture
extremes reduce biomass production and NAPP in Canadian grasslands (l-IARCOMBE ET
AL, 1993). However, even grasslands experiencing no significant annual drought period
exhibit lower biomass production than SBCWM (LAUENROTH, 1979). Other factors,
such as grazing intensity (WILLMS ET AL, 1996) and fire frequency (BRIGGS &
KNAPP, 1995; BLAIR 1997) also influence grassland production.

Our PSC value may underestimate SBCWM peak standing crop. During 1997,
Lake Huron water levels were among the highest recorded since 1918. Many study sites
were inundated for part of the growing season. Changes in vegetation zonation were
observed, and signs of anoxic stress, including chlorosis, increased inter-node length, and
adventitious root production, were noted in some wet meadow species (K. STANLEY,
pers. obs). Long periods of inundation negatively impact respiration and photosynthesis
in the less inundation-tolerant wetland plants, reducing photosynthesis and diverting
energy from production to survival (KOZLOWSKI, 1984; ERNST, 1990). Biomass
production lags.

The mean litter biomass generated during the litter production experiment was
152g/m2, not including decomposition losses. The mean decomposition loss measured in
the litter bag experiment was 5.46g/10.0g litter, suggesting that the 152g/m2 measured

litter production represented approximately 45% of total seasonal litter production, and

179

that an additional 186g/m2 of litter was produced and decomposed in the 94 days between
the start of the growing season and PSC.

The decomposition rate we observed (55% in 94 days) was 3-4 times higher than
other reported values (DAVIS & VAN DER VALK, 1978; BRINSON ET AL, 1981).
The comparatively low levels of refractory compounds found in herbaceous plant tissues,
and rapid leaching of labile compound in the early stages of litter decay probably
accounted for the high observed loss rate (DAVIS & VAN DER VALK, 1978;
GODSHALK & WETZEL, 1978).

The litter production (152g/m2) and litter decomposition (186g/m2) values
suggested that total growing-season litter production up to PSC was 338g/m2. This value
fell within the range of values published for similar wetlands (Table 4-4).

We measured new biomass production in September, October, and November
1998. New biomass production (plants with stem length <15cm) contributed only 5-
10g/m2/month (0.5-1.5%) to total plot biomass during that period. KELLEY (1985)
demonstrated that peak live Calamagrostis canadensis, Carex aquatilis, and Carex stricta
biomass occurred during July-August in a Lake Michigan wet meadow, after which it
rapidly declined. By November, live C. canadensis and C. aquatilis biomass was nearly
zero, and live C. stricta biomass was 30% of PSC and decreasing. Litter biomass
increased rapidly following PSC, and essentially all live biomass was converted to litter by

late fall (KELLEY, 1985).

180

Net above-ground primary productivity (NAPP)

Based on our PSC value (669g/m2), and adding growing season litter production
(152g/m2) and litter decomposition losses (186g/m2), we estimated SBCWM NAPP to be
1007g/m2/yr. Our value was similar to those published for North American
(RICHARDSON, 1978) and Taiwanese (HWANG, 1996) sedge-dominated wetlands
(Table 4-3). The lower values reported for boreal lacustrine sedge fens were probably due
to the cool, continental climate and northern latitude of the fen study site
(SZUMIGALSKI & BAYLEY, 1996).

SBCWM NAPP was higher than that reported for terrestrial grasslands. As with
PSC, precipitation and soil moisture availability are important factors in determining
grassland productivity (LAUENROTH, 1979; HARCOMBE ET AL, 1993; BRIGGS &
KNAPP, 1995), as are grazing intensity (WILLMS ET AL, 1996), and fire frequency
(BRIGGS & KNAPP, 1995; BLAIR, 1997). Grazing and fire do not appear to be major
factors in SBCWM, but hydrologic regime is (see Chapters 2 and 3), and unlike most
grasslands, water deficits rarely, if ever, occur in SBCWM. The reliable water supply in
SBCWM probably explains their greater NAPP (BERNARD, 1974).

PSC can underestimate NAPP for several reasons, including phenological
differences in the occurrence of PSC and maximum shoot weight, losses due to shoot
turnover during the growing season, herbivory losses, translocation of materials from
shoots to roots during the growing season, and the assumption of zero herbaceous grth
outside the growing season (VAN DER VALK & DAVIS, 1978; RICHARDSON, 1978;

BRINSON ET AL, 1981; WHEELER & SHAW, 1991; SZUMIGALSKI & BAYLEY,

181

1996). Accounting for these differences, where necessary, increases the accuracy of
NAPP estimates.

Differences in the timing of PSC and maximum shoot weight under-estimated
sedge NAPP by 16-22% in prairie potholes (VAN DER VALK & DAVIS, 1978).
However, peak Calmnagrostis canadensis, C arex aquatilis, and Carex stricta biomass
occurred between late-July and mid-August in a Lake Michigan wet meadow, and living
shoot biomass did not differ significantly between July, August, and September
(KELLEY, 1985). This suggested there was a minimal time differential between the
occurrence of maximum shoot weight and PSC in these species. We believe a similar
pattern also occurred in SBCWM, and that no correction for this difference was needed.

There is disagreement about the impact of herbivory on freshwater macrophytes
(CARPENTER & LODGE, 1986; LODGE, 1991; CYR & PACE, 1993; FRANCE,
I995). Herbivory estimates ranging from 1-10% for grasses, sedges, and aquatic
macrophytes (CRAWLEY, 1983; WETZEL, 1983) may accurately reflect vertebrate
consumption, but may not accurately reflect losses to invertebrate grazers (LODGE,
1991). Muskrat herbivory was apparent in some SBCWM, and extensive insect damage
to the plant Polygonum amphibium was commonly observed. However, we made no
measurements of herbivory, and so can make no quantitative statements regarding its
level. We made no correction for herbivory.

Translocation of materials from shoots to roots has been reported in alpine
(MOONEY & BILLINGS, 1960; FONDA & BLISS, 1966) and wetland plants
(GORHAM & SOMERS, 1973; BERNARD, 1974), and may involve 20-30% of summer

and fall production in some wetland sedges (BERNARD, 1974). However, it is difficult

182

to measure the volume of materials being translocated, or to determine whether
translocated materials represent existing plant reserves or new photosynthetic products
(KLOPATEK & STEARN S, 1978). Given these uncertainties, and given that we
collected no translocation data for SBCWM vegetation, we made no adjustment of
SBCWM NAPP for translocation losses.

Carex aquatilis reportedly produced winter grth of 40-50 g/m2 (GORHAM &
SOMERS, 1973). However, Lake Michigan wet meadow vegetation began growing fi'om
“near zero” in May (KELLEY, 1985), and our casual observations revealed no significant

winter grth in SBCWM, so we made no correction for extra-growing season growth.

Summary and Conclusions

The peak standing crop biomass of Saginaw Bay coastal wet meadows was
669g/m2, live plants contributing 575g/m2 and standing dead material 94g/m2 to the total.
Mean PSC ranged between 323-933g/m2 among 19 study sites. Seasonal mean litter
production was 152g/m2, with an additional 186 g/m2 of litter being produced and
decomposed between the start of the growing season and PSC. From adjusted PSC
biomass, we estimated SBCWM NAPP to be 1007g/m2/yr.

Research into the magnitude of losses attributable to herbivory, translocation of
materials from shoot to root afier PSC, and extra-growing season production in SBCWM
would help refine this estimate. Studies of below-ground plant production would permit

the estimation of total SBCWM primary productivity.

183

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LODGE, D.M., 1991: Herbivory on freshwater macrophytes. - Aquat. Bot. 41: 195-224.

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MOONEY, H.A. & W.D. BILLINGS, 1960: The annual carbohydrate cycle of alpine
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PRINCE, H.H., & TM. BURTON, 1995: Wetland restoration in the coastal zone of
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RICHARDSON, 0]., 1978: Primary productivity values in fi'eshwater wetlands. - In:
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187

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188

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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from US Census Bureau TIGER database and Michigan Department of Natural

Resources.

189

 

 

 

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Saginaw Bay coastal wet meadows (SBCWM). Biomass collected from 228- 0.25m2

sample plots in 19 wet meadows.

190

Table 4-1. Frequency of occurrence, determined from the number of sample plots in
which a species occurred, percentage biomass contribution of a species to total Saginaw
Bay coastal wet meadow (SBCWM) biomass, and mean above-ground biomass of plant
species encountered during SBCWM biomass sampling. A total of 228 0.25-m2 sample
plots in 19 sites were collected in July-August 1997. Samples were oven-dried at 60° C
for 48 hours before weighing. N equals the number of plots in which a species occurred.

 

 

Species Frequency of Contribution to Mean above-ground N
occurrence total wet meadow biomass
(%) biomass (%) (g/mz, :1 SEM)

Anemone canadensis 7.0 0.9 l3.7(4.8) 16
Apocynum intermedium 6.6 0.9 l3.0(3.7) 15
Asclepias incarnata 1.8 0. 2 l 1.0(6.2) 4
Aster borealis 5.3 0.7 390.4) 12
Aster dumosus 9.2 1.2 35.4(17.9) 21
Calamagrostis canadensis 96.5 12.4 318.5(17.7) 220
Calystegia sepium 20.2 2.6 4.3(O.7) 46
Campanula aparinoides 51.8 6.7 l 1.4(1 .5) 118
Carex aquatilis 51.3 6.6 158.9(13.8) 117
Carex bebbii 10.1 1.3 29.4(9.8) 23
Carex buxbaumii 0.9 0.1 11.2(1 1.2) 2
Carex hystericina 0.4 0.1 l.2(N/A) 1
Carex lacustris 20. 2 2.6 98.5(17.4) 46
Carex sartwellii 58.8 7.6 61.5(6.0) 134
Carex stricta 23.2 3.0 5450.3) 53
Cicuta bulbifera 0.9 0.1 <0.] 2
Cicuta maculata 1.8 0.2 0.5(0.5) 4
Circium arvense 11.8 1.5 l3.8(3.4) 27
Cladium mariscoides 31.1 4.0 8.3(] .7) 71
Camus amomum 3.9 0.5 10.9(5.2) 9
Cornus stolonifera 9.2 1.2 17.6(5.5) 21
Eleocharis rostellata 0.4 0.1 6.0(N/ A) 1
Eleocharis smallii 6.6 0.9 l.O(0.3) 15
Eleocharis spp. 2.2 0.3 3.5(2.0) 5
Epilobium hirustum 1.3 0.2 26.0( 14.8) 3
Equisetum arvense 0.4 0.1 2.0(N/A) l
Eupatorium maculatum 0.9 0.1 60.0(47.2) 2
Eupatorium perfoliatum 1.8 0.2 7.9(5. l) 4
Fragaria virginiana 0.4 0.1 1.6(N/A) l
Fraxinus pennsylvanica 0.9 0.1 <0.] 2
Galium obtusum 11.0 1.4 13.6(4.3) 25
Glyceria striata 1.8 0.2 7.8(6.3) 4
Helenium autumnale 0.9 0. l 1 l .8( 10.6) 2
Hypericum kalmianum 1.8 0.2 23.9(23.4) 4
Impatiens capensis 11.0 1.4 l.8(0.4) 25
Iris versicolor 2.2 0.3 70.2(3 1.0) 5
Juncus balticus 7.9 1.0 25.1(6.9) l8
Juncus brevicaudatus 4.4 0.6 17.8(6.4) 10
Juncus eflits‘us 0.4 0.1 19.6(N/A) l

191

Table 4-1 (cont’d)

 

Species Frequency of Contribution to Mean above-ground
occurrence total wet meadow biomass
(%) biomass (%) (g/mz, :1 SEM)

Lathyrus palustris 19.7 2. 5 5.4(0.9) 45
Leersia oryzoides 3.9 0.5 4.3(0.9) 9
Lobelia kalmii 0.4 0. 1 <01 1
Lycopus americanus 6.6 0.9 3.5(1.3) 15
Lysmachia quadriflora 4.8 0.6 l7.2(7.8) 11
Lysmachia terrestris 0.4 0.1 20.0(N/A) 1
Lysmachia thrysiflora 4.4 0.6 7.7(2.8) 10
Lythrum alatum 1.3 0.2 0.5(0.3) 3
Lythrum salicaria 7.9 1.0 128.6(31.4) 18
Mentha arvensis 5.7 0.7 6.6(2. 1) l3
Phalaris arundinacea 13.6 1.8 l29.4(46.3) 31
Phragmites australis 7.0 0.9 258.8(67.8) 16
Polygonum amphibium 40.8 5.3 9.5( 1.0) 93
Polygonum scandens 0.4 0.1 4.0(N/ A) l
Populus deltoides 1.8 0. 2 3.1(l.5) 4
Potentilla anserina 5.3 0.7 6.3(2.6) 12
Potentilla/ruticosa 2.2 0.3 53.2( 13.7) 5
Pycnantheum virginianum 1.8 0.2 54.8(26.5) 4
Rubus spp. 0.4 0.1 0.8(N/A) 1
Rudbeckia hirta 0.9 0.1 5.6(2.8) 2
Sagittaria latifolia 0.9 0. 1 14.0( 13.6) 2
Salix petiolaris 0.9 0.1 50.4(42.8) 2
Salix spp. 1.8 0.2 5.0(3.6) 4
Scirpus acutus 1.3 0.2 21.3(10.6) 3
Scirpus americanus 1.3 0.2 23.9(13.9) 3
Scirpus validus 0.9 0.1 41.4(24.6) 2
Scutellaria galericulata 5.7 0.7 2.8( l .0) 13
Scutellaria lateriflora 0.4 0.1 2.8(N/A) l
Solidago uliginosa 0.4 0.1 8.4(N/A) 1
Spartina pectinata 4.4 0.6 62.8(23 .0) 10
Spiraea alba 0.9 0.1 25.8(20.2) 2
Spiranthes lucida 0.4 0.1 0.8(N/A) l
Stachys tenuifolia 19.7 2.5 5.8(]. l) 45
Teucrium canadense 2.6 0.3 5.4(3.4) 6
Thelyptris palustris 0.4 0.1 188.0(N/A) 1
Typha angustifolia 21.5 2.8 105.5(13. l) 49
Typha latifolia 1.3 0. 2 71.3(48.4) 3
Unknown #1 0.4 0.1 l.2(N/A) 1
Viola affinis 0.4 0.1 0.4(N/A) l
Vitis riparia 0.4 0.1 8.4(N/A) l

 

192

Table 4-2. Mean peak standing crop (PSC) biomass and range of sample values among 19
Saginaw Bay coastal wet meadows based on 12- 0.25m2 sample plots per site. Weights
determined after oven-drying at 600 C for 48 hours.

 

 

Site Mean PSC biomass Range of sample plot biomass values
(g/mz, :1 SEM) (g/mz)

2 72400.7) 467 - 1214
3 74l(69.8) 366 - 1274
4 433(94.7) 146 - 1328
5 746(173.0) 166 - 2501
6 596(50.5) 338 - 860
8 814(6l.6) 368 - 1100
9 862(82.5) 553 - 1440
10 746(83.5) 391 - 1272
ll 600(64.0) 311 - 970
13 78500.9) 404 - 1300
14 37206.4) 113 - 813
15 51402.5) 172 - 921
18 933(110.l) 362 - 1558
19 69909.3) 322 - 1208
20 323(42.6) 138 - 563
21 657(59.8) 429 - 1188
22 839(87.8) 365 - 1264
24 711(9l.8) 210 - 1200
25 616(53.7) 349 - 1006
All 669(21.2L 113 - 2501

 

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Table 4-4. Distribution of peak above-ground biomass among biomass components for
grass/sedge dominated ecosystems.

 

 

Ecosystem Type Standing Live Standing Dead Litter Reference
Biomass Biomass (g/mz)
(g/mz) 421ml
Type
Wetland
Coastal wet 575 94 338‘” This study
meadow
Coastal wet 468(2) 488(2) Kelley ET AL.,
meadow 1985
Rich Fen 810 37-2115‘” Wheeler and
Shaw, 1991
Lacustrine sedge 15.3“" Szurnigalski and
fen Bayley, 1996
Terrestrial
Grassland 340-372”) 903-1113”) (5) Haroombe et al.,
1993
Grassland 398 398 1190 Willms ET AL,
1996

 

1 - Includes 152g/m2 litter produced plus lSth/m2 litter produced and decomposed prior
to measurement. Production measured over 94 day period from beginning of growing
season to collection of peak standing crop biomass. No correction made for

herbivory.

2 - Weighted mean based on areal extent of community type and percent cover of

dominant species.

3 - Range for community type.

4 - g/mz/yr.

5 - Combined standing dead and litter.

195

Chapter 5 - The impact of anthropogenic disturbance and Purple Loosestrife on
Saginaw Bay coastal wet meadow vegetation

Introduction .,

Natural disturbances, such as herbivory, fire, or fluctuating water levels, govern
the development and maintenance of wet meadow vegetation (Curtis, 1959; Keddy and
Reznicek, 1986; see Chapters 2 and 3). Saginaw Bay is in constant flux, alternately
inundating and exposing the coastal wet meadow zone (see Chapter 2). Most plants are
not adapted to this hydrologic regime (Keough et al., 1999), and are excluded from wet
meadows. However, certain grasses and sedges have successfiilly adapted to the variable
Saginaw Bay hydroperiod, allowing them to dominate wet meadow vegetation (see
Chapter 3).

European settlement introduced a new set of disturbance factors to the Saginaw
Bay region. Timber harvesting, diking, ditching, draining, plowing, filling, and paving
impacted the coastal landscape, while sediment, fertilizer, pesticide, and sewage runoff
impacted the water quality of Saginaw Bay. Exotic species introductions have increased
competitive stresses faced by native taxa. These anthropogenic, or human-induced,
disturbances represent relatively new threats to the stability of coastal wet meadow
vegetation, and little study of the problem has been undertaken to date. It is important to
understand how anthropogenic disturbance impacts coastal wet meadow vegetation if we

are to protect and maintain the integrity of this wetland plant community.

Goals and objectives

The goal of this chapter was to examine the impacts of anthropogenic disturbance,

196

and of the introduction of Lythrum salicaria L. (Purple Loosestrife), on Saginaw Bay
coastal wet meadow vegetation, and to determine in what ways, if any, that wet meadow
vegetation suffering anthropogenic disturbance or L. salicaria invasion differed from that
subject only to natural hydrologic disturbance. The specific objectives were:

1. to determine the hydrologic, edaphic, and vegetation characteristics of
anthropogenically-impacted, and L. salicaria-impacted, Saginaw Bay coastal
wet meadow vegetation; and

2. to compare and contrast the hydrologic, edaphic, and vegetation characteristics
of anthropogenically-impacted, and L. salicaria-impacted, wet meadows with

those lacking disturbance or L. salicaria.

Disturbance

Disturbance is any event that destroys biomass (Grime, 1979). Disturbance can be
natural or anthropogenic. Natural wet meadow disturbances include climatic and
hydrologic fluctuation, herbivory, and fire (Curtis, 1959; F oote et al., 1988; Thompson
and Shay, 1989; Bowles et al., 1996). Natural disturbance regimes often enhance
community spatial and temporal heterogeneity (White, 1979; Sousa, 1984; Pickett and
White, 1985). Great Lakes water-level fluctuations enhance the spatial and temporal
heterogeneity of Great Lakes coastal wetland vegetation, and are a good example of the
influence natural disturbance can have on community structure and composition (Harris et
al., 1981; Keddy and Reznicek, 1986; Keough, 1990; see Chapter 3).

Anthropogenic wet meadow disturbances include alterations of natural hydrology

such as ditching, diking, tiling, draining, and pumping to facilitate drainage, and grazing,

197

mowing, burning, cultivation, clearing of native vegetation, filling, and paving (Curtis,
1959; Moran, 1981, Mitsch and Gosselink, 1993; Bowles et al., 1996).

Anthropogenic wet meadow alteration is often, but not always, detrimental to
native vegetation. Deliberate burning was once used to improve the quality of marsh hay
harvested from Saginaw Bay coastal wet meadows (H. Davis, pers. comm). Occasional
fires increased fen species diversity, reduced exotic species diversity, and suppressed shrub
growth in Michigan and Illinois prairie fens (Kohring, 1982; Bowles et al., 1996).
Similarly, mowing increased species diversity in Czech wet meadow plots (Leps, 1999).
Mowing removed the tall plants, allowing greater light penetration to occur. Mowing also
decreased litter accumulation, increased spring soil temperatures, and promoted seed
germination in the mown plots (Ibid., 1999).

Disturbance varies in scale, sometimes impacting individual plants, sometimes
entire communities (Collins and Glenn, 1988). Disturbance frequency decreases as scale
increases from the individual to the ecosystem, creating a landscape mosaic of vegetation
patch sizes and seral stages (Ibid., 1988).

Disturbance also varies in severity. Filling generally has a greater impact on a wet
meadow than does grazing. Filling permanently alters wet meadow elevation, influencing
site hydrology, soil and seed bank composition, and fixture land use options. Grazing
impacts, which include soil compaction, changes in plant species composition via selective
grazing, and eutrophication via urine and feces deposition, can often be reversed once
grazing ceases (Jensen, 1985; Kiehl et al., 1996). On the other hand, heavy grazing

pressure can severely impact wetland soil and vegetation composition, whereas small-

198

scale, localized changes in wet meadow elevation can result in greater habitat and species

diversity.

Purple Loosestrife

Disturbance creates opportunities for aggressive species to increase their presence
on the landscape (Collins and Glenn, 1988). Many non-native plants compete extremely
effectively when first introduced into new phyto-geographic regions. When an
ecologically plastic exotic species is introduced into a disturbed landscape, the result is
ofien explosive growth and rapid dominance of the vegetation by the introduced exotic.

Lythrum salicaria, introduced from Europe in the 1800’s in ships ballast
(Thompson et al., 1987) as an escaped ornamental, and by deliberate introduction into
wetlands (Stuckey, 1980) is now widely established in eastern North America. Its
lightweight seeds are the primary dispersal mechanism. Seeds float to new sites, or are
carried on the feathers or fur of wetland vertebrates (Mullin, 1998). Wind is of minor
importance as a dispersal mode (Ibid., 1998). Purple Loosestrife is considered a
problematic wetland weed in the northeastern US and Canada because it lacks natural
enemies in North America, is thought to threaten wetland plant species diversity, and
provides relatively poor feeding and breeding habitat for native wetland fauna (Anderson,
1995)

Wetland scientists and natural resource managers are concerned about the
potential impact of L. salicaria on the biodiversity and habitat quality of Great Lakes and
other wetlands (Thompson et al., 1987; Mal, et al., 1992). Given these concerns, its

presence in Saginaw Bay coastal wet meadows, and its potential as an indicator of wet

199

meadow disturbance, the impact of L. salicaria on coastal wet meadow vegetation was

examined in the study.

Methods

Site selection

The study took place in Saginaw Bay, the southwestern lobe of Lake Huron
(Figure 1-1). Vegetation data were collected in 25 wet meadow study sites during 1997
(see Chapter 1 text, and Figure 1-2, for details of site selection). However, only 12 of the
25 sites could be reasonably classified as either disturbed or undisturbed, so only these 12
sites were included in the disturbance portion of the study.

The undisturbed sites were in fact reference sites (sensu Brinson, 1993) because,
while representative of existing Saginaw Bay coastal wet meadows, none were truly
undisturbed. All wet meadows in the Saginaw Bay coastal zone have experienced varying
degrees of human impact. Sites were accepted as reference sites if they were exposed to
the natural water level fluctuations of Saginaw Bay, and aerial photos, historical
documents, or anecdotal evidence indicated that anthropogenic disturbance had only
minimally-impacted native wet meadow vegetation and soils at the site. Sites were
accepted as disturbed if aerial photos, historical documents, or anecdotal evidence
indicated that anthropogenic activities had resulted in disturbance of the native wet

meadow hydrology, vegetation, or soils at the site.

200

The six reference sites were all located on Middle Ground Island or Maisou Island
in the Wildfowl Bay State Game area (Figure 5-1). The Wildfowl Bay SGA is a group of
low sand barrier islands located approximately 2km off the eastern shore of Saginaw Bay
near Sebewaing, MI. The island vegetation was a mix of emergent marsh, wet meadow,
shrub-scrub and forested wetlands, and upland oak-hickory forests (Albert et al., 1988).
Upland forests abutted three of the six reference sites, forested or shrub-scrub wetland the
other three. The nearest agricultural activity was 2km distant on the main land.

Anecdotal evidence and aerial photographs indicated that these sites have never been
cultivated, drained, or diked, and had not been permanently inhabited since European
settlement. One site (Site #2) was located near an artificial boat channel. Aerial
photographs indicated that the channel was excavated prior to 1938, and it was a stable
feature on the landscape. On inspection, no lingering signs of excavation-related
disturbance could be found at the site (see Chapter 2). The islands were used as cattle
pastures during the 1930’s, but all grazing activity was discontinued by 1940 (TI. Jahr, Jr,
pers. com.) The islands have been maintained as public hunting land in recent years.
Land use during that period has been limited to hunting and a few temporary camps during
the hunting season.

The disturbed sites were located throughout the Saginaw Bay coastal zone and had
suffered various anthropogenic impacts (Table 5-1). Two sites (Sites #1 and #21) were
located behind levees. Site #1 had been cultivated and cropped in the 1930’s, grazed fiom
the early 1940’s to the mid-1980’s, and mechanically drained from the 1940’s to the late-
1980’s. A levee-ditch system was installed between 1941-1949, breaking surface

hydrologic contact between the site and Saginaw Bay. Agricultural utilization was

201

discontinued and the land abandoned in the late 1980’s, but the fields immediately adjacent
to the site were under active agricultural management before and during the study. Site
#21 had had Phalaris arundinacea L. (Reed Canary grass) seeds broadcast on un-tilled
substrates in the 1950’s, and then been grazed throughout the 1960’s. The levee
protecting Site #21 was breached in the late 1970’s or early 1980’s, reestablishing the
natural hydrologic regime and terminating agricultural utilization of the site. There were
cultivated fields within 100m of the site.

Three sites (Sites #18, #19, and #31) backed up to flood-control levees. Extensive
excavation and fill deposition had occurred at these sites during levee construction,
disrupting natural vegetation assemblages, soil structures and elevation contours. They
were, however, exposed to the natural hydrologic fluctuations of Saginaw Bay. Sites #18
and #31 bordered levees constructed between 1950-1963. These sites were immediately
adjacent to cultivated fields. Site #19 bordered the outer levee of a waterfowl
management impoundment constructed between 1963-1969. This site was >lkm from
uplands or agricultural fields. It appears to have formed on sediments washed out of the
impoundment area.

The sixth site (Site #26) had no history of hydrologic or edaphic alteration, but a
greater or lesser portion of this wet meadow had been mowed approximately yearly since
the early 1960’s to suppress shrub growth. It was immediately adjacent to upland woods
and active pasture lands.

Only two of the disturbed sites had been anthropogenically disturbed in the 10-15
years before the study commenced. The levee at Site #1 continued to interrupt natural

surface hydrology until after the study was completed in 1997, and Site #26 was mowed at

202

least yearly throughout the study period. Otherwise, there had been no significant soil
disturbance, topographic or hydrologic alteration, or vegetation management of these sites
since the mid-1980’s.

Vegetation data from all 25 wet meadow study sites were utilized in the Purple
Loosestrife portion of the study. Six of the sites contained L. salicaria, 19 did not (Figure

5-2).

Vegetation sampling
Vegetation data for this study were collected at the 25 wet meadow study sites

during 1997. Details of the sampling protocol can be found in Chapter 3.

Statistical analysis

To examine disturbance impacts on wet meadow vegetation, the 12 disturbance
sites were grouped into two categories: six reference and six disturbed sites. To examine
the impact of L. salicaria on wet meadow vegetation, 300 sample plots from 25 wet
meadow sites were divided into two categories: 37 plots that contained Loosestrife
(“Loosestrife” plots) and 263 plots that did not contain Loosestrife (“non-Loosestrife”
plots).

The 37 Loosestrife plots were also examined to determine if an increase in the
relative dominance of Purple Loosestrife impacted the other species found in these plots.
To do this, the Loosestrife plots were divided into two categories: 23 plots in which the
percent IV of Purple Loosestrife was less than the mean percentage IV (7.2i1.2%) of
Purple Loosestrife for all the Loosestrife plots (“low-Loosestrife” plots), and 14 plots in

which the percent IV of Purple Loosestrife was greater than the mean percentage IV of

203

Purple Loosestrife for all Loosestrife plots (“high-Loosestrife” plots). Plot above-ground
biomass, stem density, species richness, and Shannon-Wiener diversity were compared
between low- and high-Loosestrife plots for evidence of significant differences between
the categories. As the goal of the analysis was to estimate the impact of L. salicaria on
other species in the plots, Purple Loosestrife was excluded from these analyses.

The data sets were examined to determine if the variables met parametric statistical
assumptions. Species importance values (IV), biomass, stem densities, soil texture data,
and peat and litter depths were non-normally distributed or heteroscedastic. IV and
species biomass were log10(X+l) transformed, and peat and litter depths were square-root
transformed to meet parametric assumptions for the disturbance site and non-
Loosestrife/Loosestrife plot contrasts. Stem density and soil texture data could not be
transformed to meet parametric assumptions for either site or plot contrasts, and peat and
litter depth, hummdck height, and plot elevation could not be transformed for plot
contrasts. None of the data could be transformed to meet parametric statistical
assumptions for the low-Loosestrife/high-Loosestrife plot contrasts. Data that could not
be transformed were analyzed using non-parametric statistical techniques.

For variables meeting parametric assumptions, two-sample t-tests were used to
compare differences between category means. Statistical power analysis (Cohen, 1988)
was performed post-hoe to determine the power of the test (ranging between 0.0-1 .0)
whenever a t-test failed to falsify the null hypothesis. The Mann-Whitney U test was used
to compare differences between variables failing to meet parametric assumptions. For all
tests, the critical value for rejection of the null hypothesis was established at P<0.05 before

testing. SYSTAT (v.7.0.1) was used to perform the statistical analyses.

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Differences between reference and disturbed sites were also examined using the
Michigan Floristic Quality Assessment (Herman et al., 1996). The Michigan FQA was
designed to assess the fidelity with which the plant species composition of a parcel of land
reflected the pre-settlement flora of the state. The purpose of the measure is to provide a
consistent and practical tool for identifying, comparing, and monitoring changes in the
floristic quality, and by extension the natural significance, of elements of Michigan’s
landscape (Ibid., 1996).

Briefly, to apply the F QA, a mean coefficient of conservatism and floristic quality
must be determined for the site. To do this, each native species found at the site is
assigned a coefficient of conservatism (CCi) ranging from 0-10. The CC; represents the
estimated probability that the species occurs in a landscape relatively unaltered fiom its
pre-settlement condition. The higher a species’ CCi, the greater its fidelity to a high
quality remnant natural community. Exotic species (“adventive”, sensu Herman et al.,

1996) are not a part of the pre-settlement flora, and so are not assigned a CO. The mean

 

coeflicient of conservatism (E) for the site is calculated (E7 = ; n = the number

of native species), and CC is multiplied by the square root of the total number of native

species present at the site to determine the floristic quality index (F Q1) for that site
(F Q] 2 CC x J; ). The F Ql standardizes the CC for difi’erent size sites (for a detailed

exposition of the method, see Herman et al., 1996, or Herman et al., 1997).
The EC and FQI were compared for the reference/disturbed sites using two

sample t-tests. (EC and FQI comparisons are only appropriate for site-by-site data, and

so were not applied to the non-Loosestrife/Loosestrife plot data). For both the

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disturbance and Loosestrife data sets, the relative number of native and adventive species
were compared using Fisher’s Exact test, and the relative numbers of forbs, grasses,
sedges, rushes, ferns, shrubs, and trees were compared using the Likelihood Ratio Chi-
square test.

T-tests were also used to detemrine which of 15 major species plot importance
values might difl‘er significantly between reference/disturbed and non-
Loosestrife/Loosestrife categories (see Chapter 3 for the definition of major species).
Additional statistical tests of differences in species biomass and stem density were
performed on those individual species showing an overall significant t-test result on
species IV. This procedure was used to maintain the nominal a = 0.05 significance level
throughout the analysis in a manner analogous to a protected-F procedure (Wilkinson et

al., 1996).

Results

Disturbance effects

Thirty-nine species were encountered in 36 plots at the six reference sites,
compared to 61 species encountered in 36 plots at the six disturbed sites. Ten species, or
27.1% of those encountered in the reference sites, occurred only in the reference sites,
whereas 32 species, or 52.6% of those encountered in the disturbed sites, occurred only in
the disturbed sites (Table 5-2). A total of 7.9% of species found in the reference sites
were adventive species, whereas 11.9% of species found in disturbed sites were adventive

species, a statistically non-significant difference (two-tailed Fisher’s Exact test, P = 0.73 6).

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Similarly, the relative contribution of forbs, grasses, sedges, ferns, rushes, shrubs, and
trees to wet meadow vegetation composition did not differ significantly between the
reference and disturbed sites (Likelihood Ratio Chi-square, x2 = 2.572, df = 6, P = 0.860).

The mean(i1 SEM) FQI for reference sites was 21.0(0.8), ranging between 23.5-
19.0, whereas the mean(il SEM) FQI for disturbed sites was 21 .6(2. 1), ranging between
29.5-16.6 (Table 5-3). The mean FQI values were not significantly different (t-test, t(.05.10)
= 0.092, P = 0.928, Power = 0.05).

Species with either a high or low coefficient of conservatism were found in both
reference and disturbed sites, so a species’ coefficient of conservatism could not be used
by itself to identify potential disturbance indicator species. However, several weedy
species (U SDA-ARS, 1971) uncommon in Michigan’s wetlands (Agropyron repens (L.)
Beauv., Cerastiumfontanum Baumg., Circium arvense (L.) Scop., Equisetum arvense L.,
and T araxicum ofiicinale Wiggers), were encountered only in disturbed sites. All except
E. arvense were adventive species with no assigned coefficient of conservatism, and E.
arvense had a coefficient of conservatism of zero. Lythrum salicaria and Solanum
dulcamara L., adventive wetland species, were encountered only in disturbed sites. L.
salicaria occurred in three of six disturbed sites.

There were no statistically detectable differences (statistical power: 0.55-<0.05)
between reference and disturbed sites with respect to mean plot above-ground biomass,
stem density, litter depth, hummock height, and elevation, or mean site species richness,
Shannon-Wiener diversity, coefficient of conservatism, and FQI (Table 5-4). Statistically

significant differences (P<0.05) were detected for mean plot peat depth and soil texture.

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Peat depth was greater in plots at disturbed sites, and plots in reference sites collectively
exhibited finer-textured soils than did disturbed site plots.

Six of the 15 major wet meadow species, Calamagrostis canadensis (Michaux)
Beauv., Calystegia sepium (L.) R.Br., Campanula aparinoides Pursh, Carex stricta Lam,
Phragmites australis (Cav.) Steudel, and Stachys tenuifolia Willd. exhibited statistically
significant differences in mean plot IV between reference and disturbed sites (Table 5-5).
Closer examination of these species indicated that C. stricta produced significantly greater
plot IV, above-ground biomass, and stem density in the disturbed sites, P. australis
produced significantly greater plot IV and above-ground biomass in disturbed sites, and C.
sepium produced significantly greater plot IV in disturbed sites (Table 5-6). By contrast,
S. tenuifolia exhibited significantly greater plot IV, above-ground biomass, and stem
density in reference sites, C. canadensis exhibited significantly greater plot IV and above-
ground biomass in reference sites, and C. aparinoides exhibited significantly greater plot

IV and stem density in reference sites.

Purple Loosestrife effects

Lythrum salicaria was not commonly found in Saginaw Bay coastal wet meadows,
and was not a dominant species where it was found. Purple Loosestrife occurred in only
37 (12.3%) of 300 sample quadrats. In these 37 plots, the mean(i1$EM) percentage IV
of L. salicaria was 7.2(1.2)% and the maximum percentage IV of L. salicaria in any
sample plot was 28.5%. Mean(il SEM) plot stem densities differed by a non-significant
9.4% between non-Loosestrife and Loosestrife plots (271i7.9 stems/0.25m2 in non-

Loosestrife plots versus 299i18.7 stems/0.25m2 in Loosestrife plots; v.05, 293) = -0.917, P =

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0.360, Power = 0.15). L. salicaria had the greatest individual species IV in only two
(5.4%) of 37 plots containing Loosestrife.

Three Michigan adventive species were found in non-Loosestrife plots, whereas
six were found in Loosestrife plots, a statistically non-significant difference (two tailed
Fisher’s Exact, P = 1.000). Similarly, there was no significant difference between non-
Loosestrife and Loosestrife plots in the relative contribution of forbs, grasses, sedges,
ferns, rushes, shrubs, and trees to wet meadow vegetation composition (Likelihood Ratio
Chi-square, xi = 3.717, df= 7, P = 0.812).

There were no statistically detectable differences (statistical power: 0.38-0.14)
between non-Loosestrife and Loosestrife plots with respect to mean plot above-ground
biomass, stem density, species richness, Shannon-Wiener diversity, or soil texture (Table
5-7). Statistically significant differences (P<0.05) between plots were detected for mean
plot peat depth, litter depth, hummock height, and elevation. Peat depth was significantly
greater in Loosestrife plots (mean difference = 2.8cm). Similarly, litter depth was
significantly greater in Loosestrife plots, (mean difference = 2.3cm), and plot elevation
was significantly greater in non-Loosestrife plots, (mean difference = 6cm). Hummock
heights was significantly greater in non-Loosestrife plots (mean difference = 11cm).

Four of the 15 major wet meadow species, Calystegia sepium (L.) R. Br., Carex
aquatilis Wahl., Polygonum amphibium L., and Stachys tenuifolia Willd., exhibited
statistically significant differences in mean plot IV between non-Loosestrife and
Loosestrife plots (Table 5-8). Closer examination of these four species indicated that C.
aquatilis exhibited significantly greater IV, above-ground biomass, and stem density in

non-Loosestrife plots. C. sepium, P. amphibium, and S. tenuifolia also exhibited

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significantly greater IV in non-Loosestrife plots, but no statistically significant differences
between non-Loosestrife and Loosestrife plots in above-ground biomass or stem density
were detected for these three species (Table 5-9).

The mean percentage IV of Purple Loosestrife was significantly greater (t-test,
M10535, = 8.015, P<0.001, Power > 0.98) in high-Loosestrife plots (mean iISEM =
14.6:t1.8%) compared to low-Loosestrife plots (2.7i0.35%). Plot stern densities of
species other than Purple Loosestrife were significantly greater in low-Loosestrife plots,
but there were no statistically significant differences in plot above-ground biomass of the
other species, or in species richness or Shannon-Wiener diversity between the low-
Loosestrife and high-Loosestrife plots (Table 5-10). However, while the difference was
not statistically significant, both above-ground biomass and species richness did exhibit
lower mean plot values in the high-Loosestrife plots.

Six of the 15 major species (Calamagrostis canadensis, Campanula aparinoides,
Carex aquatilis, Carex sartwellii, C ladium mariscoides, and Polygonum amphibium)
exhibited significantly lower stem densities in high-Loosestrife plots, whereas none of the
major species had significantly greater stern densities in high-Loosestrife plots. However,
the above-ground biomass of these species did not differ significantly between the
categories.

Lower stem densities did not translate into taller stems. Calamagrostis
canadensis, Carex aquatilis, and Carex sartwellii had lower maximum, median, and mean
stem height in high-Loosestrife plots, and Campanula aparinoides had greater maximum,
median, and mean stern height in high-Loosestrife plots, but these differences were not

statistically significant. There were no significant differences between low-Loosestrife and

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high-Loosestrife plots in median, mean, or maximum stem heights among any of the major

species.

Discussion

Disturbance effects

The lack of statistically significant differences between reference and disturbed
sites suggests that Saginaw Bay coastal wet meadow vegetation was resistant to
disturbance impacts and resilient once anthropogenic disturbance ended. Resistance, the
ability of a vegetation assemblage to remain relatively unchanged during a stressful period,
and resilience, the ability of a vegetation assemblage to recover after a disturbance has
occurred, are important measures of plant community stability (Barbour et al., 1987).

More species occurred in disturbed sites than in reference sites. The reference
sites were all located on islands approximately 2km from the mainland, whereas the
disturbed sites were all on the mainland itself, suggesting that proximity to upland and
agricultural propagule sources might account for the greater species richness observed at
the disturbed sites. However, three of the six reference sites were immediately adjacent to
upland forest vegetation, and all six were adjacent to at least some upland or wetland
forest or shrub-scrub vegetation. Nonetheless, there were no agricultural fields within
2km of the reference sites, whereas all the disturbed sites were in close proximity to
pastures or cultivated fields. The presence of certain agricultural weeds (e. g., Agropyron
repens = Quackgrass) only in the disturbed sites may reflect unavoidable differences in

propagule proximity between reference and disturbed sites.

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Studies have demonstrated that disturbing grassland vegetation creates
opportunities for less competitive species to infiltrate and survive within the established
grassland community, increasing the overall abundance of the less competitive community
members (Collins and Uno, 1983; Platt and Weis, 1985; Collins and Glenn, 1988).
Anthropogenic wet meadow disturbance similarly created opportunities for less
competitive native wetland species, adventive wetland species, and ruderal upland species
to gain a foothold in the wet meadow vegetation matrix. Tillage, trampling, and
construction activity disrupted the rhizomatous root matrix and exposed bare soil,
increasing colonization opportunities for other species. Topographic alteration increased
habitat diversity within the wet meadow, allowing greater plant diversity to develop.
Dikes, ditches, and drains disrupted the natural hydrologic regime, allowing scrub-shrub
and forested wetland succession to occur. The net result was a greater number of plant
species growing in disturbed wet meadow sites.

The native wet meadow species Aster borealis (T. & G.) Prov., Hypericum
kalmianum L., Juncus brevicaudatus (Englem) F ern., Lysmachia quadriflora Sims, and
Potentillafi-uticosa L. occurred only in disturbed sites. These species, all with high
coeflicients of conservatism, persisted despite anthropogenic disturbance, as did the 15
major species constituting the bulk of the vegetation. This was further evidence of the
vegetation’s resistance to anthropogenic impacts.

Wet meadow vegetation is a disclimax ecosystem, dependent upon periodic fire or
flooding to eliminate taller, more robust competitors and suppress succeeding seral stages
(Costello, 1936; Curtis, 1959; Keddy and Reznicek, 1986; and see Chapter 3). This

vegetation has successfully adapted to these disturbance regimes, and in doing so may

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have become “pre-adapted” to other types of disturbance as well. Pre-adaptation may
enhance both wet meadow vegetation stability and its resistance to anthropogenic
disturbance impacts.

The statistical power of the t-tests ranged between 0.55-<0.05. Low statistical
power can be the result of small effect or sample sizes, rather than a lack of difi‘erence
between categories (Cohen, 1988). Efl‘ect sizes are often fairly low in observational
studies because extraneous variables introduce uncontrollable noise to the system,
masking the effect under study. In such cases, improving statistical power relies on
increasing the sample size, which increases the signal-to-noise ratio, or on increasing the
critical or level used in statistical tests (Ibid., 1988).

It was not possible to increase sample sizes in this study. There were only 25 wet
meadows to study. Only 37 plots had been colonized by L. salicaria. The disturbance
status of only 12 sites could be positively determined. These facts could not be changed.
However, adjustments in experimental design, such as pairing reference and disturbed
sites, or increasing the critical 0L level used during data analysis would improved statistical
power in future studies (Ibid., 1988).

Significant differences in peat depth and soil texture were noted between reference
and disturbed sites. Soil texture was coarser and peat depth was deeper in disturbed sites
compared to reference sites. In all but one of the disturbed sites (Site #26), anthropogenic
disturbance involved cultivation or construction-related earth-moving activity. The
coarser soils found at disturbed sites may have been imported for levee construction, may

have resulted from the mixing of mucks and sandy mineral substrates during cultivation, or

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may have resulted from the loss of organic matter via oxidation afier substrates were
disturbed.

Thicker peat mats were not consistent with this soil disturbance hypothesis. Soil
disruption should have reduced peat thickness by exposing peat to the efl‘ects of oxidation
and erosion, yet this did not seem to be the case. The mean difference in peat bed
thickness between reference and disturbed sites was 1.3cm. This difference was
statistically significant, but perhaps too small to have any biological significance.

Seven major wet meadow species may act as indicators of disturbance, or lack of
disturbance, in Saginaw Bay coastal wet meadows. Calamagrostis canadensis,
Campanula aparinoides and Stachys tenuifolia exhibited significantly lower IV, biomass,
or stem density in the disturbed sites, whereas Calystegia sepium, Carex stricta, and
Phragmites australis exhibited significantly higher IV, biomass, or stem density in
disturbed sites. The presence of C. aparinoides (Marsh Bellflower) and S. tenuifolia
(Smooth Hedge Nettle) as major species appear to be good indicators of relatively
undisturbed wet meadow vegetation. On the other hand, the presence of C. sepium
(Hedge Bindweed) and P. australis (Giant Reed) may be good indicators of
anthropogenic disturbance in these wetlands. C. canadensis and C. stricta exhibited
significantly greater IV, biomass, and in the case of C. stricta, stem density in reference
and disturbed sites, respectively. However, these species, being two of the four dominant
species of these coastal wet meadow, were present in large quantities in all wet meadows
studied, and so would not make good disturbance indicator species.

The seventh potential disturbance indicator among the major species was Lythrum

salicaria. Significantly, it occurred only in disturbed sites. However, Purple Loosestrife

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was not always found in disturbed wet meadows, occurring in only three of the six
disturbed sites. Nonetheless, Purple Loosestrife is widely accepted as an indicator of
disturbance in North American wetlands, and its impacts on wet meadow vegetation will
be discussed in the following section.

Several other species, with relatively low wet meadow IVs, were also good
anthropogenic wet meadow disturbance indicators. Agropyron repens, Cerastium
fontanum, Circium arvense, Equisetum arvense, Solanum dulcamara, and T araxicum
oflicinale occurred at low fi'equency in Saginaw Bay coastal wet meadows, and then
almost exclusively in disturbed sites. All were non-native species except E. arvense
(Herman et al., 1996), and all were as much upland as wetland species. E. arvense and S.
dulcamara, facultative wetland (F AC) species, were about equally likely to occur in
wetlands and non-wetlands, and the others were facultative upland (F ACU) species, with a
1-33% frequency of occurrence in wetlands (Reed, 1988). The presence of one or more
of these species in a wet meadow was a good indication that the site had experienced

some form of anthropogenic disturbance.

Purple Loosestrife effects

Most Saginaw Bay coastal wet meadows were not heavily impacted by Lythrum
salicaria. Purple Loosestrife occurred in only six of 25 wet meadow study sites, and in
only 37 of 300 sample plots examined. L. salicaria was not a dominant species in these
wetlands, exhibiting the greatest individual species IV in just two sample plots.

There were few statistically significant differences between non-Loosestrife and

Loosestrife plots among the variable examined. The mean plot biomass, stem density,

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species richness, Shannon-Wiener diversity, soil texture, the number of native and
adventive species, and the relative contribution of forbs, grasses, sedges, ferns, rushes,
shrubs, and trees to vegetation composition did not differ significantly between non-
Lcosestrife and Loosestrife plots. Similarly, in the low-Loosestrife and high-Loosestrife
plot comparisons, Lythrum salicaria had no significant impact on plot above-ground
biomass, species richness or the Shannon-Wiener diversity of the other species in the
Loosestrife plots.

These results suggest that Purple Loosestrife was not altering the native vegetation
structure and composition of Saginaw Bay coastal wet meadows. Anderson (1995)
concluded after reviewing 71 L. salicaria-related papers that there was no evidence
supporting the idea that Purple Loosestrife was responsible for a decline in species
diversity in North American wetlands. Treberg and Husband (1999) noted no significant
difference in species richness between non-Loosestrife and Loosestrife plots in the Bar
River, Ontario, and no correlation between the percent cover of L. salicaria and species
richness. The results of the present study support these conclusions.

Treberg and Husband (1999) also reported that no species were more likely to be
found in plots lacking Loosestrife than they were to be found in plots with Loosestrife.
While this study agreed for the most part with Treberg and Husband’s findings, the two
studies differed on that point. The present study found that Carex aquatilis exhibited
greater IV, above-ground biomass, and stem density in non-Loosestrife sites than in
Loosestrife sites, and Calystegia sepium, Polygonum amphibium, and Stachys tenuifolia

had greater IV in non-Loosestrife sites. The cause of the difference in results may involve

216

difl‘erences in sampling methodology, or Treberg and Husband may have had low power
to detect statistically significant differences in their sample plots.

Previous investigators (Rawinski and Malecki, 1984; Thompson, et al., 1987;
Thompson, 1991; Mal, et al., 1992) have concluded that L. salicaria has negative impacts
on both wetland flora and fauna. However, while not denying that Purple Loosestrife may
be a problem, Anderson (1995) and Hager and McCoy (1998) reject these claims as
unsupported by the scientific evidence. Hager and McCoy state that much of the evidence
cited to support the hypothesis that Purple Loosestrife is detrimental to North American
wetlands is based on either personal observation rather that quantifiable measurements, or
faulty experimental design and execution. Both Anderson (1995) and Hager and McCoy
(1998) argue that the reliable scientific evidence on the topic is inconclusive.

The difl’erence between the findings reported in Rawinski and Malecki (1984) and
Thompson, et al. (1987) and the present study may lie in the degree to which Purple
Loosestrife dominated the vegetation being examined. Rawinski and Malecki (1984) and
Thompson, et al. (1987) studied wetlands in which Purple Loosestrife was the dominant
species. In the present study, Purple Loosestrife was not a dominant species, even in most
of the Loosestrife plots. The mean percent plot IV of Lythrum salicaria in the 37
Loosestrife plots examined in this study was 7.2%, and Purple Loosestrife IV never
exceeded 28.5% in any of the 300 sample plots examined. Purple Loosestrife was not a
significant problem in Saginaw Bay coastal wet meadows at the level at which it was
present during the study. However, this is not to say that Purple Loosestrife might not

become a problem in these wetlands in the future.

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Thompson, et al. (1987) suggested that L. salicaria could be present in wetlands
for years as a minor vegetation constituent before rapidly becoming the dominant species,
and there were signs that Purple Loosestrife was having a small, but measurable impact on
the vegetation at some study sites. Comparison of low-Loosestrife and high-Loosestrife
plots indicated that the plot stem density of species other than Purple Loosestrife was
significantly lower in high-Loosestrife plots, and even though difl‘erences in above-ground
biomass and species richness were not statistically significant, there was lower plot
biomass and species richness in the high-Loosestrife plots as well. Further, three of the
four dominant Saginaw Bay coastal wet meadow species (Calamagrostis canadensis,
Carex aquatilis, and Carex sartwellii) exhibited significantly lower stem densities in high-
Loosestrife plots, and while not statistically significant, these three dominant species also
exhibited lower maximum, median, and mean stern heights in high-Loosestrife plots.
These data suggest that while Purple Loosestrife was not yet significantly impacting these
wetlands as a whole, it might already be negatively influencing vegetation structure and
composition in portions of these sites. These data also suggest that Purple Loosestrife
may have negative impacts on wet meadow vegetation, even at low levels of relative
dominance.

There were statistically significant differences in peat depth, plot elevation and
hummock height between non-Loosestrife and Loosestrife plots. Soil texture did not
differ significantly between non-Loosestrife and Loosestrife plots. Soil disturbance (e.g.,
cultivation, levee, ditch, and drain construction, sedimentation) seemed to be a major
factor in L. salicaria establishment in the Loosestrife sites. Loosestrife IV was highest at

Sites #18, 19, and 31, where levee construction had removed native vegetation and

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disrupted native soil structures and elevation contours, and at Site #28, which occasionally
received river sediments. By contrast, Purple Loosestrife did not occur at Site #26, which
was regularly mowed, or at Site #21, which was seeded with Reed Canary grass in the
1950’s and grazed, but never cultivated. Significantly, neither of these sites had ever
experienced major disruption of the native soil profile.

Observation of other Saginaw Bay wetlands also implicated soil disturbance as a
factor in the spread of Purple Loosestrife. High L. salicaria stem densities were noted in
constructed waterfowl irnpoundments at the Nayanquing Point and Wigwam Bay State
Game areas on Saginaw Bay, near flood-control levees bordering southern Saginaw Bay,
along the dredged and sediment-laden Quanicassee River, which empties into southern
Saginaw Bay, and in farm and roadside drainage ditches throughout the region. These
sites were closely associated with past or present dredging or excavation.

There is evidence to suggest that some sort of disturbance may be a necessary
prerequisite to successful Purple Loosestrife establishment. Rachich and Reader (1999)
demonstrated that removal of above-ground vegetation and litter in a Phalaris
arundinacea stand in Ontario resulted in a significantly greater establishment rate for L.
salicaria. In fact, they reported that no Purple Loosestrife seedlings became established in
their vegetated control plots (Ibid., 1999). Rachich and Reader concluded that their
findings supported the view (Thompson et al., 1987; Wilcox, 1989) that Purple
Loosestrife cannot become established in intact wetland vegetation assemblages.

Purple Loosestrife was rarely encountered in relatively undisturbed Saginaw Bay
coastal wet meadows. However, certain natural events did create opportunities for L.

salicaria establishment. Rafts of dead cattail culms or blue-green algae occasionally

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collected in flooded wet meadows and smothered the underlying vegetation. When
floodwaters receded, L. salicaria could become established in the resulting bare patches
(K. Stanley, pers. obs). Rarely did more than a few Loosestrife plants become established
in this way at any site, and in the 3-5 years such sites were observed, Purple Loosestrife
rarely spread beyond these small patches to other parts of the wet meadow.

In some cases, the high aspect dominance of L. salicaria may result in a
rnisperception of the severity of a Purple Loosestrife outbreak. Purple Loosestrife is
highly visible when flowering, sometimes appearing to be the only plant present in a
wetland. However, if these sites were sampled, other, less apparent species might be
found to contribute substantially to vegetation composition (Hager and McCoy, 1998).
Hager and McCoy reported that much of the original data used to established the
existence of a Purple Loosestrife problem came from the study of herbarium sheets, and
personal observations in the field, rather than quantifiable data. The problem may simply
have looked worse than it actually was because Purple Loosestrife is so very visible. They
also believed that misperception due to “observer-expectancy bias” was part of the
problem; researchers saw a problem because they expected to see a problem (Hager and
McCoy, 1998).

Another factor contributing to the perception of Purple Loosestrife infestation may
be that because it benefits from anthropogenic soil disturbance, Purple Loosestrife thrives
where it can readily be observed, and so seems to be increasingly present. Large Purple
Loosestrife populations were visible near constructed waterfowl impoundments, flood-
control levees, and drainage ditches throughout the Saginaw Bay coastal zone. These

managed sites were regularly viewed by resource managers and readily accessible to the

220

general public. The more remote Saginaw Bay coastal wetlands, which did not support
large Loosestrife populations, were less often disturbed, and less often observed. This
may bias the common perception of the impact Purple Loosestrife is having on regional

wetlands.

Implications for management and restoration

Saginaw Bay coastal wet meadows are stable vegetation assemblages, resistant to
disturbance impacts, and resilient once disturbance is ended. Lythrum salicaria, though
present at some sites, has not yet significantly impacted wet meadow vegetation. Under
the influence of the natural hydrologic regime, this vegetation association resists exotic
introductions and recovers from anthropogenic disturbance without intervention.

This bodes well for future Saginaw Bay coastal wet meadow restoration.
Restoration can probably be accomplished in most cases by restoring natural hydrology at
the restoration site, because wet meadow plant propagule sources are available throughout
the region. However, wet meadow restoration should be undertaken with minimal soil
disturbance, as large-scale dredging, excavation, contouring, or other soil disturbances
encourage the establishment of L. salicaria and other wetland weeds (Mal et al., 1992).
Levees can be breached to restore natural hydrology, but they should be left to erode
naturally. Similarly, drainage ditches can be plugged at their ends, but then they should be
left to fill naturally. Slow erosion of these structures will allow natural successional
processes to occur and native vegetation assemblages to develop, while minimizing

opportunities for Loosestrife to become established as the wetland recovers.

221

Where restoration involves bare ground, such as cultivated fields, the site could be
contoured and allowed to naturally re-vegetate with upland species before restoring
hydrology to minimize the bare soil available to L. salicaria after flooding. Such actions
might facilitate a more natural wet meadow successional trajectory and minimize the

impact of adventive plants on wet meadow recovery.

Summary and Conclusions

There were few statistically significant differences in vegetation and physical
variables between reference and disturbed Saginaw Bay coastal wet meadows. Saginaw
Bay coastal wet meadows exhibited resistant to anthropogenic disturbance impacts, and
resilience once released from anthropogenic disturbance.

Lythrum salicaria was not present in most Saginaw Bay coastal wet meadows, and
had not severely impacted those wet meadows in which it was found. There were few
statistically significant differences in vegetation and physical variables between sites that
contained Purple Loosestrife and those that did not contain Purple Loosestrife. Similar
results were obtained when comparing non-Loosestrife and Loosestrife plots, and when
analyzing the impact of Purple Loosestrife on other plant species within Loosestrife plots.
Soil disturbances, such as tillage or excavation for drainage or construction, appeared to
be the anthropogenic disturbance most likely to facilitate L. salicaria success in wet
meadows.

The presence of Campanula aparinoides or Stachys tenuifolia as major species

(21% of total vegetation IV) were good indicators of relatively undisturbed Saginaw Bay

222

coastal wet meadow vegetation. The presence of Calystegia sepium, Lythrum salicaria,
or Phragmites australis as a major species, or low frequency occurrences of Agropyron
repens, Cerastium fontanum, Circium arvense, Equisetum arvense, Solanum dulcamara,
or T araxicum ofiicinale were good indicators of prior anthropogenic disturbance.
Additional studies should be undertaken to investigate the impact of L. salicaria
on Saginaw Bay wetlands, with emphasis placed on comparing Loosestrife-flee and
Loosestrife-dominated wetlands. Statistical power analysis should be used to determine
the power of the test when testing fails to falsify the null hypothesis. Low power suggests
that small sample sizes, small effect sizes, or incorrect experimental design may be
responsible for the failure to falsify the null hypothesis, and that firrther investigation is
warranted. A better understanding of the impacts of L. salicaria in these wetlands could

be obtained through the proper use of power analysis, and by carefirl experimental design.

223

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227

 

 

 

 

vi I la.

 

 

 

 

 

 

 

 

 

 

 

 

I JpPinqnminq
' l9 "
, Saginaw Bay \-
um
i l N
' f
l l l l ' l
8 o 8
— ‘ m

 

 

 

 

Figure 5-1. Map of reference and disturbed Saginaw Bay wet meadow study sites. The
reference sites, Sites 2, 8, 9, 10,11, and 13, were all located on Middle Ground Island and
Maisou Island in the Wildfowl Bay State Game area (inset). The disturbed sites, Sites 1,
18, 19, 21, 26, and 31, were located on the main land. Map data from US Census Bureau
TIGER database and Michigan Department of Natural Resources. '

228

 

Table 5-1. Sites used to study the impact of anthropogenic disturbance on Saginaw Bay
coastal wet meadow vegetation.

 

Site Location

l

10

ll

l3

l8

19

21

26

31

“Sheep Farm” - North side of Kindler Rd.,
l300m east of the intersection of Clark and
Kindler Rds, Akron Twp, Tuscola Co, MI
Middle Ground Island at Dynamite Cut,
Wildfowl Bay State Game area, F airhaven
Twp., Huron Co., MI

Middle Ground Island - on the south shore
300m east of Dynamite Cut, Wildfowl Bay
State Game area, Fairhaven Twp., Huron
Co., MI

Middle Ground Island - on the south shore
500m west of Dynamite Cut, Wildfowl Bay
State Game area, Fairhaven Twp., Huron
Co., MI

Middle Ground Island - on the south shore
lOOOm west of Dynamite Cut, Wildfowl Bay
State Game area, Fairhaven Twp., Huron
Co., MI

Maisou Island - on the east shore 500m
north of Boxcar Cut, Wildfowl Bay State
Game area Fairhaven Twp., Huron Co., MI
Maisou Island - 800m southeast of the
northern tip of island on the east shore,
Wildfowl Bay State Game area. Fairhaven
Twp, Huron Co., MI

Coryeon Point, 50m northwest of the north
end of Cotter Rd, Hampton Twp, Bay Co.,
MI

Nayanquing Point Wildlife Management
area, 800m south, and 800m east of the south
end of Tower-Beach Rd, Fraser Twp, Bay
Co., MI

East end of Bordeau Rd. at LaClair Rd,
Standish Twp, Arenac Co., MI

South end of Hale Rd at Saginaw Bay,
Arenac Twp, Arenac Co., MI

Coryeon Point, 350m south of the east end of
Nebobish Rd at Saginaw Bay, Hampton Twp,
Bay Co., MI

Disturbed Anthropogenic disturbance type

(Y/N)

229

Y

N

Behind levee, ditching, cultivation,
grazing

Natural regime only

Natural regime only

Natural regime only

Natural regime only

Natural regime only

Natural regime only

Levee construction. soil disturbance.
topographic alteration

Levee construction, soil disturbance,
topographic alteration

Behind levee, grazing

Mowing

Levee construction, soil disturbance,
topographic alteration

 

 

 

H’Br‘rs

 

 

 

 

 

 

 

 

 

 

 

 

 

P
Caseville.
V i .r‘.
091
‘ 119 ‘30
, SaginawBay 3; f“
x l" m N
L l I If I
8 o 8
— - KM
[‘— H.8tanhy,l999

 

 

Figure 5-2. Map of the 25 study sites used in the Purple Loosestrife portion of the study.
Sites #3, 15, 18, 19, 28, and 31 (indicated with stars) were Purple Loosestrife sites. The
other 19 sites contained no Purple Loosestrife. Map data from US Census Bureau TIGER
database and Michigan Department of Natural Resources.

230

 

Table 5-2. Plant species that occurred only in reference or only in disturbed Saginaw Bay
coastal wet meadow study sites. Ten species occurred only in reference sites, 32 species
occurred only in disturbed sites. The coefficient of conservatism reflects the probability
that the species will be found in a landscape relatively unaltered from it’s pre-settlement
condition (Herman et al., 1996). Asterisks indicate that the species was adventive.
Coefficients of conservatism are not assigned to adventive species.

 

 

Species occurring only in Coeflicient of Species occurring only in Coefficient of
disturbed sites conservatism reference sites conservatism
Acorus calamus 6 Epilobium hirsutum *
A gropyron repens * Leerzia oryzoides 3
Aster borealis 9 Lysmachia terrestris 6
Aster dumosus 7 Lysmachia thrysrflora 6
Cerastium fontanum * Rubus spp. N/A
C omus amomum 2 Rudbeckr'a hirta 1
Eleocharis smallii 5 Scirpus acutus 5
Equisetum arvense 0 Scirpus americanus 5
Eupatorium maculatum 4 Spiranthes lucida 7
Fraxinus pennsylvanicus 2 Thelypteris palustris 2
Fragaria virginiana 2
Geum laciniatum 2
H ypericum kalmianum 10
Iris versicolor 5
Juncus brevicaudatus 8
Juncus eflilsus 3
Lysmachia quadriflora 8
Lythrum salicaria "'
Mentha arvensis 3

Unknown Grass N/A

Panicum virgatum 4
Polygonum scandens 2
Potentilla anserina 5
Potentillafi'uticosa 10
Pycnanthemum virginianum 5
Scirpus validus 4
Solanum dulcamara *
Spartina pectinata 5
Spiraea alba 4
Taraxicum ojficinale *
Unknown #1 N/A

Viola afjinis 2

 

231

Table 5-3. Mean coefficient of conservatism (CC) and Floristic Quality Index (F QI) for
reference and disturbed Saginaw Bay wet meadow sites. Number of species used to
calculate the FQI was the number of species occurring only in sampling plots, not the total
number of species observed during sampling at a site.

 

 

Site Site disturbed? (YIN) SiteEE‘ Number of species Site FQI
1 Y 4.3 29 23.0
2 N 4.7 23 22.7
8 N 4.4 19 19.0
9 N 4.4 21 20.0

10 N 4.5 27 23.5
11 N 5.0 19 22.0
13 N 4.2 20 19.0
18 Y 4.7 39 29.5
19 Y 4.3 18 18.2
21 Y 4.2 17 17.2
26 Y 4.7 29 25.1
31 Y 3.7 20 16.6

 

232

Table 5-4. Results of statistical tests comparing the means of various plant and abiotic
wet meadow attributes for reference and disturbed Saginaw Bay coastal wet meadow
sites. Significant differences (P<0.05) are indicated in boldface and marked with an
asterisk. The effect size and power of the test provide measures of the sensitivity of

individual t-tests.

A. T-tests of variables meeting parametric assumptions.

 

 

Measure Reference N Disturbed N t-value Degrees Probability Efl‘ect Power
sites sites of Size of the
(mean, (mean, Freedom ((1) test“)
ilSEM) $151an

Plotabove-ground 624.9(25.4) 72 674.7(29.9) 72 -l.374 142 0.172 0.20 0.22
biomass (g/mz)

Site species richness 18.7(1.5) 6 22.5(2.6) 6 -l.285 10 0.228 0.74 0.19
(species /site)

Site Shannon-Wiener 1.52(0.05) 6 1.52(0.06) 6 0.038 10 0.970 <0.05 <0.05
diversity (H’)

Site Coefficient of 4.5(0.1) 6 4.3(0.1) 6 1.246 10 0.241 0.66 <0.23
Conservatism

SiteFloristic Quality 21.0(0.8) 6 21.6(2.l) 6 0.092 10 0.928 0.05 0.05
Index (FQI)

Plot peat depth (cm) 3.4(0.4) 72 4.7(O.5) 72 -2.095 142 0.038" 0.35 0.55

Plotlitterdepth (cm) 15.3(0.9) 72 14.4(0.8) 36 0.977 106 0.331 0.18 0.14

Plot elevation 176.97(0.01) 72 176.98(0.01) 72 0.448 142 0.655 0.08 <0.09
(m AMSL)

Plothummock height 32.3(3.3) 16 24.9(3.2) 8 1.419 22 0.170 0.56 0.24
(CH1)

 

(1) - Power values falling outside the table (Cohen, 1988, Table 2.3.5) are listed as less

than or greater than the nearest tabulated value for that sample size or effect size.

B. Mann-Whitney U test of variables failing to meet parametric assumptions.

 

 

Measure Reference sites N Disturbed sites N U N Probability
(mean, iISEM) (mean, i1SEM)
Plot stem density 1011.7(41.l) 72 1183.0(79.6) 72 2457.0 144 0.590
(stems/m2)
Plot soil texture Sandy loam 72 Sand 72 1789.0 144 <0.001*

 

233

Table 5-5. Comparison of mean plot importance values of major Saginaw Bay coastal wet
meadow species in reference and disturbed sites. Significant difl'erences (P<0.05) are
highlighted in boldface and marked with an asterisk. The effect size and power of the test
provide measures of the sensitivity of individual t-tests.

 

 

Species t-value Degrees Probability Effect Power
of Size of the
Freedom (d) test“)
Calamagrostis canadensis 2.625 134 0.010* 0.43 0.68
Calystegia sepium -3.541 33 0.001‘ 1.0 0.78
Campanula aparinoides 2.547 74 0.013" 0.57 0.65
Carex aquatilis -0.392 61 0.697 0.10 0.07
Carex lacustris -2.433 29 0.095 0.65 0.40
Carex sartwellii -0.351 75 0.727 0.08 <0.07
Carex stricta -2.727 35 0.010“ 0.88 0.72
Cladium mariscoides 1.058 32 0.298 0.33 0.15
Galium obtusum 2.377 12 0.096 1.29 <0.65
Lythrum salicaria (2)
Phalaris arundinacea -2. 194 32 0.082 0.68 0.41
Phragmites australis -2.036 13 0.045* 0.92 <0.40
Polygonum amphibium -0.073 67 0.942 0.33 0.27
Stachys tenuifolia 3.3 13 26 0.003" 1.0 0.69
Typha argustifolia -0.9 14 15 0.375 0.43 <0. 13

 

(1) Power values falling outside the table (Cohen, 1988, Table 2.3.5) are listed as less than
or greater than the nearest tabulated value for that sample size or effect size.

(2) Among the 12 reference and disturbed sites, L. salicaria only occurred in disturbed
sites.

234

Table 5-6. Results of statistical tests comparing mean plot importance values, above-
ground biomass, and stem densities of the six major species found to have significantly
different (P<0.05) IV in reference and disturbed Saginaw Bay coastal wet meadows.
Significant difl‘erences (P<0.05) are highlighted in boldface and marked with an asterisk.
The efl‘ect size and power of the test provide measures of the sensitivity of individual t-

tests.

A. T-test results for variables meeting parametric assumptions.

 

 

Species Measure t-value Degrees of Probability Effect Power
Freedom Size of the

(d) [681(1)

Calamagrostis canadensis IV 2.625 134 0.010" 0.43 0.68
Calamagrostis canadensis BM 3.593 134 <0.001* 0.55 0.88
Calystegia sepium IV -3 . 541 3 3 0.001 * 1.0 0.78
Calystegia sepium BM -1 .919 33 0.064 0.47 0.25
Campanula aparinoides IV 2.547 74 0.013* 0.57 0.65
Campanula aparinoides BM 2.120 74 0.059 0.55 0.51
Carex stricta IV -2.727 35 0.010" 0.88 0.72
Carex stricta BM -2.560 35 0.015" 0.74 0.57
Phragmites australis IV -2.036 13 0.045" 0.92 <0.40
Phragmites australis , BM -2.239 13 0.043* 1.09 <0.52
Stachys tenuifolia IV 3.3 13 26 0.003* 1.0 0.69
Stachys tenuifolia BM 1.850 26 0.046“ 0.62 0.33

 

(1) - Power values falling outside the table (Cohen, 1988, Table 2.3.5) are listed as less

than the smallest tabulated value for that sample size or effect size.

B. Mann-Whitney U results for stem density data, which did not meet parametric

 

 

assumptions.
Species Measure U N Probability
Calamagrostis canadensis Stem density 2285.5 136 0.936
Calystegia sepium Stem density 120.0 35 0.424
Campanula aparinoides Stern density 860.0 76 0.043“
Carex stricta Stem density 56.5 37 0.001*
Phragmites australis Stem density 12.0 15 0.071
Stachys teLur'folr'a Stem density 134.5 28 0.031“

 

235

Table 5-7. Results of statistical tests comparing the means of various plant and abiotic
wet meadow attributes of non-Loosestrife and Loosestrife Saginaw Bay coastal wet
meadow plots. A total of 300 sample plots were collected at 25 sites; 37 plots contained
Loosestrife, 263 plots did not. Litter depths were determined in 215 plots. Hummocks
occurred in 51 plots. Significant differences (P<0.05) are indicated in boldface and
marked with an asterisk. The effect size and power of the test provide measures of the
sensitivity of individual t-tests.

A. T-tests of variables meeting parametric assumptions.

 

 

Measure Non- Loosestrife t-value Degrees Probability Effect Power
Loosestrife plots of Size of the
plots (meanilSEM) Freedom (d) test
(mean,:tlSE1\®
Above-ground 563.2(16.0) 638.9(41.8) -l.665 298 0.388 0.29 0.37
biomass (g/mz)
Species richness 6.5(0.2) 7.7(0.7) -2.377 298 0.072 0.29 0.38
Shannon-Wiener 0.438(0.01) 0.472(0.04) -0.968 298 0.334 0.14 0.14
diversity (H’)

 

B. Mann-Whitney U test of variables failing to meet parametric assumptions.

 

 

Measure Non-Loosestrife N Loosestrife plots N U Probability
plots (mean,d:1SEM)
(meandflSEM)
Plot stem density (stems/m2) 1084(3 1.6) 263 1196(74.8) 37 4050.0 0.099
Plot peat depth (cm) 4.0(0.2) 263 6.8(0.8) 37 3456.0 0.004*
Plot litter depth (cm) 15.0(0.5) 180 l7.3(1.4) 35 2402.0 0.026*
Plot hummock height (cm) 31.4(1.7) 46 20.4(4.2) 5 180.0 0.039*
Plot elevation (m AMSL) 176.98(0.01) 263 176.92(0.02) 37 6305.0 0.003“
Plot soil texture Sandy loam 263 Loamy sand 37 4521.0 0.455

 

236

Table 5-8. Comparison of mean plot importance value of major Saginaw Bay coastal wet
meadow species in non-Loosestrife and Loosestrife plots. Significant differences (P<0.05)
are highlighted in boldface and marked with an asterisk. The effect size and power of the
test provide measures of the sensitivity of individual t-tests.

 

 

Species t-value Degrees Probability Effect Power
of Size of the
Freedom ((1) test“)
Calamagrostis canadensis 0.958 278 0.339 0. 15 0. l3
Calystegia sepium 1.830 58 0.044* 0.95 0.42
Campanula aparinoides 1.567 140 0. 1 19 1.04 0.91
Carex aquatilis 3.871 157 <0.001' 0.85 0.95
Carex lacustris (2)
Carex sartwellii -1.298 175 0.196 0.24 0.20
Carex stricta 1.029 77 0.307 0.48 0.15
Cladium mariscoides -0.012 102 0.991 <0.05 <0.05
Galium obtusum -0. 170 36 0.866 0.13 <0.05
Lythrum salicaria (3)
Phalaris arundinacea 1.010 48 0.3 17 0.44 0.16
Phragmites australis 0.418 18 0.681 0. 18 0.07
Polygonum amphibium 2.053 128 0.042* 0.52 0.56
Stachys tenuifolia 1.951 54 0.040* 1.00 0.46
Typha angustifolia -0.794 55 0.430 0.26 0.10

 

(1) Power values falling outside the table (Cohen, 1988, Table 2.3.5) are listed as less than
the smallest tabulated value for that sample size or effect size.

(2) C. lacustris occurred only in non-Loosestrife plots.

(3) L. salicaria, by definition, only occurred in Loosestrife plots.

237

Table 5-9. Results of statistical tests comparing the mean importance value, above—
ground biomass, and stem density of the four major species found to have significantly
different (P<0.05) IV in non-Loosestrife and Loosestrife Saginaw Bay coastal wet
meadow plots. Significant differences (P<0.05) are highlighted in boldface and marked
with an asterisk. The effect size and power of the test provide measures of the sensitivity
of individual t-tests.

A. T-test results for variables meeting parametric assumptions.

 

 

Species Measure t-value Degrees Probability Effect Power
of Size of the

Frwdom (dL test“)

Calystegia sepium IV 1.830 58 0.044" 0.95 0.42
Calystegia sepium BM 0.981 58 0.330 0.50 0.15
Carex aquatilis IV 3.871 157 <0.001* 0.85 0.95
Carex aquatilis BM 2.881 157 0.005* 0.60 0.74
Polygonum amphibium IV 2.053 128 0.042* 0.52 0.56
Polygonum amphibium BM 0.063 128 0.950 0.02 <0.07
Stachys tenuifolia IV 1.951 54 0.040* 1.00 0.46
Stachys tenuifolia BM 0.340 54 0.735 0.10 0.05

 

(l) - Power values falling outside the table (Cohen, 1988, Table 2.3.5) are listed as less
than the nearest tabulated value for that sample size or effect size.

B. Mann-Whitney U results for stem density data, which did not meet parametric

 

 

assumptions.
Species Measure U N Probability
Calystegia sepium Stem density 147.5 60 0.283
Carex aquatilis Stem density 2134.5 159 0.005*
Polygonum amphibium Stem density 975.0 130 0.412
Stachys tenuifolia Stern density 136.0 56 0.304

 

238

Table 5-10. Comparison of plot above-ground biomass, stem density, species richness,
and Shannon-Wiener diversity (H’) of species other than Purple Loosestrife in low-
Loosestrife and high-Loosestrife plots. Stem density of the other species was significantly
greater (P<0.05) in low-Loosestrife plots. Though not significantly different, above-
ground biomass and species richness exhibited lower mean plot values in the high-
Loosestrife plots. Shannon-Wiener diversity was the same for both categories.
Probabilities determined using the Mann-Whitney U test.

 

Measure Low-Loosestrife N High-Loosestrife N U N Probability
plots plots
(mean, iISEM) (mean, iISEM)
Plot above-ground 602.6(50.8) 23 448.5(57.0) 14 9496 266 0.062
biomass (g/mz)

Plot stem density 1376.3(76.7) 23 800.3(100.9) 14 3225 266 <0.001*
(stems/m2)
Site species richness 7.0(0.9) 23 6.4(1.2) 14 138 37 0.470

Site Shannon-Wiener 0.47(0.05) 23 0.48(0.07) 14 163 37 0.950
Diversity (H’)

239

APPENDICES

240

Appendix A

Supplementary Data for Chapter 1

Appendix Al. Climatological Norms

Table A-1. Climatological norms for Bay City and Standish, Michigan.

 

 

 

Average Temperature Average Growing Average Annual
°C (°F) First/Last Season Precipitation
Freeze Date cm (in)

July January
Location Max Min Max Min Spring Fall Days Rain Snow
Bay City 28(82) 16(61) -2(29) -9(15) 5/1 10/17 168 71(27.9) 98(38.7)
Standish 28(82) 13(56) -2(28) -12(11) 5/19 9/23 126 71(27.8) 115(45.3)
Adapted from Keen (1993).

241

Appendix A2. Saginaw Bay Coastal Wet Meadow Sites

Table A-2. Site number, site name (if any). site location, site ownership, and special site
access information for coastal wet meadows bordering Saginaw Bay between Port Austin
and Au Gres, MI. Sites marked with an asterisk were not included in the study.

 

Site #

Name - Location (Ownership, special site access information, if any)

 

10

11

*12

13

14

15

I"16
*17

18

19

20

Sheep Farm - 1300m east of the intersection of Clark and Kindler Rds, north side of Kindler Rd,
Akron Twp, Tuscola Co., MI. (MDNR)

Middle Ground Island, 30m northwest of the south outlet to Dynamite Cut, Wildfowl Bay State
Game area, Fairhaven Twp, Huron Co., MI. (MDNR)

Kilmanagh Road - 400m north of the intersection of Kilmanagh and Ross Rds., Fairhaven Twp,
Huron Co., Ml. (MDNR, via the Gibbs property)

On the west side of State Highway M-25, 800m south of the intersection of M-25 and F ilion Rd,
McKinley Twp, Huron Co., MI. (Doerfner property)

Finn-Feather Public Access - approximately 500m northwest of the intersection of M-25 and
Pigeon Rd (M-l42), Fairhaven Twp, Huron Co., MI. (MDNR, via the Cootes property)
Approximately 400m north of the west end of Weale Rd at Saginaw Bay, Fairhaven Twp, Huron
Co., MI. (Abbott property)

West end of Geiger Rd. at Saginaw Bay, on the north side, Fairhaven Twp, Huron Co., M].
(K1358 PYOPCH'Y)

Middle Ground Island - on the south shore 300m east of Dynamite Cut, Wildfowl Bay State Game
area. (MDNR)

Middle Ground Island - on the south shore 500m west of Dynamite Cut, Wildfowl Bay State
Game area. (MDNR)

Middle Ground Island - on the south shore 1000m west of Dynamite Cut, Wildfowl Bay State
Game area. (MDNR)

Maisou Island - on the east shore 500m north of Boxcar Cut, Wildfowl Bay State Game area.
(MDNR)

Maisou Island - on the east shore 1000m north of Boxcar Cut, Wildfowl Bay State Game area.
(MDNR)

Maisou Island - 800m southeast of the northern tip of island on the east shore, Wildfowl Bay State
Game area. (MDMR)

0.4mi east of the west end of Haist Rd. at Valley Island Rd, on the north side of Haist Rd,
Fairhaven Twp, Huron Co., Ml. (MDNR)

800m north of intersection of Kilmanagh Rd and Rose Island Rd on Rose Island Rd, Fairhaven
Twp, Huron Co., MI. (MDNR)

North end of Berger Rd at Saginaw Bay, Akron Twp, Tuscola Co., MI. (MDNR)

West bank of the Quanicassee River, between M-25 and Old State Rd, Wisner Twp, Tuscola Co.,
M]. (MDNR)

Coryeon Point, 50m northwest of the north end of Cotter Rd. Hampton Twp, Bay Co., Ml.
(MDNR)

Nayanquing Point Wildlife Management area, 800m south, and 800m east of the south end of

T ower-Beach Rd, Fraser Twp, Bay Co., M]. (MDNR)

East end of Worth Rd at the Saganing creek, Standish Twp, Arenac Co., MI (Saganing River Rod

242

Table A-2 (cont’d).

Site #

21
22
*23
24

25
26
27

28
*29
30

31

Name - Location (Ownership, special site access information, if any)

and Gun Club property)

East end of Bordeau Rd. at LaClair Rd, Standish TWp., Arenac Co., MI. (Grobsky property)
East end of Irwin Rd at Saginaw Bay, Standish Twp, Arenac Co., MI. (Viola property)

East end of Palmer Rd at Saginaw Bay, Standish Twp, Arenac Co., M]. (MDNR)

Mouth of the Pine River, near the east end of Pine River Rd. on the south side at the Public
Access boat ramp, Standish Twp. Arenac Co., MI (MDNR)

300m south of the east end of Langdon Rd, Standish Twp, Arenac Co., MI. (Waldie property)
South end of Hale Rd at Saginaw Bay, Arenac Twp, Arenac Co., MI. (Lentz property) ‘
700m south of the east end of Stover Rd, Au Gres Twp, Arenac Co., MI. (Green Point Farms
property, via the Wigwam Bay State Game area - East Unit)

South end of Big Creek Rd, Au Gres Twp, Arenac Co., Ml. (Horatio Davis property)

South end of Dreyer Rd , Au Gres Twp, Arenac Co., MI. (Luberda property)

100m south of the west end of Dutcher Rd, Fairhaven Twp, Huron Co., MI. (Hines property, via
Bayshore Dr.)

Coryeon Point, 350m south of the east end of Nebobish Rd at Saginaw Bay, Hampton Twp, Bay
Co., MI. (MDNR via USACOE levee)

243

Appendix B

Supplementary Data for Chapter 2

Appendix B1 - Precipitation data.

Table B-1. Mean monthly precipitation at the National Weather Service climatological
reporting station in Sebewaing, M]: 1961-1990.

 

 

Month Rainfall Percent of annual
(cm) total
January 2.9 4.3
February 2.7 4.0
March 4.3 6.4
April 5.9 8.7
May 6.1 8.9
June 7.1 10.4
July 6.1 9.1
August 7.7 11.4
September 9.0 13.2
October 6.0 8.8
November 5.6 8.2
December 4.4 6.5
Annual total 67.9 100.0

 

244

Appendix B2 - Well field installation

In August, 1994, five groundwater observation wells was installed at Site #1, the
disturbed hydrologic study site (see Figure 2—3). These wells, labeled OWl through 0W5,
were located 359, 259, 159, 59, and 9 meters, respectively, on a north-south line (6°
magnetic) from the on-site drainage ditch bordering the site. These pilot wells verified the
feasibility of using the groundwater monitoring equipment and techniques developed for
the study, and provided some preliminary site groundwater data.

In April, 1995, 24 additional monitoring wells were installed at the site (see Figure
2-5). These wells were oriented in a grid parallel to the pilot well transect. Wells #11
through #16 comprised well transect #1 , Wells #21 through #26 comprised well transect
#2, and so on.

First, Well #41 was installed 15m west of the east site boundary and 10m south of
the on-site ditch. Then, moving westward (276° magnetic), Wells #31, #21, and #11 were
installed at 50m intervals. Each of these monitoring wells was positioned 10m south of
the on-site drainage ditch, itself oriented east-west. Five additional observation wells were
installed southward (186° magnetic) fi'om these first wells at 50m intervals, placing
groundwater monitoring wells at distances of 10m, 60m, 110m, 160m, 210m, and 260m
south of the on-site ditch. Each transect extended 260m north to south, and 150m
separated Transect #1 fiom Transect #4. The area enclosed by the disturbed site well field
was 3.9 ha.

In May 1996, 18 groundwater monitoring wells were installed at Site #2, the

reference hydrologic study site, on Middle Ground Island at Dynamite Cut (Figure 2-4).

245

Twelve wells (#201 through #206, comprising Transect #20, and #221 through #226,
comprising Transect #22) were installed in May 1996, 30m either side of a well transect
(Wells #211 through #216, comprising Transect #21) installed in July 1995. The
groundwater wells were placed 30m apart along a north-south elevation gradient parallel
to Dynamite Cut (40 magnetic), except for wells with numbers ending in 4 and 5, which
were placed 33m apart. The 3m offset originated when Well #214 was displaced down-
gradient (to the north) by 3m to permit groundwater monitoring at an apparent change in
vegetation. The reference site well field encompassed an area 153m long by 60m wide
(0.92 ha) arrayed on a long north-south axis and spanned a vegetation gradient ranging
from cattail marsh at the north end to a Calamagrostis/Carex wet meadow at the south
end.

Water bordered the site on three sides: Saginaw Bay on the south, Wildfowl Bay
on the north, and Dynamite Cut on the east. The island, approximately 200m wide at this
point, sloped fi'om a distinct, elevated Saginaw Bay shoreline through wet meadow
vegetation to cattail marsh in Wildfowl Bay. There was no distinct Wildfowl Bay
shoreline. The site flooded from north to south according to annual variations in Saginaw
Bay levels and local seiche activity.

The site was efl‘ectively a peninsula, making it hard to determine the distances
separating various groundwater wells fi'om permanent standing water. This was important
because the distance between a well and standing water, the hydraulic head at that well,
and site soil hydraulic conductivity determine groundwater recharge rates following

groundwater draw-down.

246

Wells #201, #211, and #221, located at the north end of the well field, remained in
standing water throughout the study and fiinctioned as indicators of Saginaw Bay water
level. Wells #206, #216, and #226, located at the south end of the well field, were only
inundated during storm surges and in 1997, the peak of the most recent 11-year Saginaw
Bay hydroperiod. The three latter wells were positioned approximately 33m north of the
south shore of Middle Ground Island. However, Well #226 was also located
approximately 20m from Dynamite Cut, as were all other wells in Transect #22. Wells in
Transects #20 and #21 were positioned 80m and 50m, respectively, from Dynamite Cut.
This meant, for example, that well #204 was located 93m from Saginaw Bay, but only
80m from Dynamite Cut. Similarly, well #224 was also located 93m from the Saginaw
Bay, but only 20m from Dynamite Cut.

Distances from Wildfowl Bay to various groundwater monitoring wells varied by
hour and day with local seiche activity, and by month and year with the annual and inter-
annual Saginaw Bay hydroperiod. For example, the distance separating Well #204 and
Wildfowl Bay varied fi'om zero to more than 50m, while that separating Well #224 and
Wildfowl Bay varied from zero to 12m, depending on local seiche activity, the time of the
year, and the year in which observations were collected.

No fixed distances separated the reference site wells from surface water.
However, no well in this well field was more than 95m from surface water, or more than
39cm above the surface of Saginaw Bay during the study.

In May 1997, 6 groundwater monitoring wells were installed in two transects of
three wells each spanning the wet meadow zone at Site #3, the Kilmanagh Road site.

Wells #301 through #303 comprised Transect #30, and Wells #311 through #313

247

comprised Transect #31. The transects started 5-10m fiom the tree line marking the
upland boundary and ended 5-10m from the cattail marsh. The transects were 50m apart
and perpendicular (3 04° magnetic) to the Saginaw Bay shore line (34° magnetic at this
site). The wells in each transect were also 50m apart. The area contained within the well
field was 100m long by 50m wide (0.5ha). This site was inundated by rising Saginaw Bay
water levels approximately 30 days after the well field was installed. No usefirl

groundwater data was obtained from this site.

248

Appendix B3 - Soil moisture sampling

Each sampling period, nine soil samples were collected at the disturbed hydrologic
study site from randomly selected points in vegetation sampling zones 1, 4, 6, 9, 11, and
13, the 6 zones containing groundwater monitoring wells. (For vegetation sampling, the
reference and disturbed hydrologic study sites were divided into sampling zones: 8 zones
at the reference site and 13 zones at the disturbed site. These zones were 20m wide and
oriented perpendicular to the well transects at the sites. While not originally intended to
be part of the hydrologic and edaphic study, these zones provided a convenient method for
organizing the soil moisture sampling into easily definable areas that were similar in
elevation to the monitoring wells.) At the reference site, three samples were collected
from randomly selected points in zones 1, 2, 4/5 (wells marked the boundary between
zones 4 and 5), 7, and 8, the zones containing monitoring wells. In all, 72 soil samples, 18
from the reference site and 54 from the disturbed site, were collected each sampling
period.

Samples were collected at sunrise to minimize evapotranspiration losses. Soil
samples were not collected less than 48 hours after measurable precipitation, or in zones
exhibiting complete soil saturation. Evidence of complete saturation included inundation,
water pooling around boots when walking or standing in a sampling zone, or coring holes

filling to the surface with water after a soil sample had been collected.

249

Appendix B4 - Detailed disturbed site groundwater hydrology

In early May 1995 at the disturbed hydrologic study site, many lower elevation
monitoring wells were inundated to depths of 25cm, and groundwater was no more than
10cm below the ground surface anywhere at the site (Figure B1). As in the early growing
season at the reference site, groundwater contours mirrored ground surface contours at all
elevations.

Groundwater levels at the disturbed site gradually declined in the following six
weeks, reaching depths of as much as 60cm below the ground surface by the end of June
(Figure B2). Groundwater declines of more than 40cm were observed in wells located as
little as 10m from the on-site drainage ditch.

Groundwater levels then remained static until late October (Figure B3), when they
began to rebound towards the ground surface. By year’s end, some groundwater recharge
had occurred across the site, with the greatest changes occurring in wells closest to the
on-site drainage ditch (Figure B4). Recharge was apparently occurring in response to late
season rainfall and infiltration fi'om the on-site drainage ditch, which had partially refilled
after drying out in late October.

Groundwater recharge continued through the winter. By mid-February 1996,
groundwater levels at all monitoring wells had increased by 25-3 0cm from December 1995
levels (Figure B5). Wells closest to the on-site ditch still exhibited greater groundwater
increases than did wells fiirther fi'om the ditch. Groundwater levels had risen to the

ground surface throughout the wetland by late March; the entire wet meadow was

250

saturated to, or above, the ground surface (Figure B6). This condition persisted until the
end of June.

By 7/1/96, groundwater decline had once again occurred in wells more than 60m
fiom the on-site ditch (Figure B7), and by mid-July the summer groundwater pattern being
observed at the reference site was evident at the disturbed site as well (Figure B8). This
pattern did not change at the disturbed site until mid-September, when heavy rainfall
apparently triggered groundwater rebound (Figure B9). As in 1995, the most rapid
recharge occurred in those areas closest to the on-site drainage ditch. Groundwater
recharge continued through late fall (Figure B 10), with infiltration from the on-site ditch
appearing to contribute most to raising groundwater levels.

By late January 1997, the entire disturbed site was saturated to the ground surface
(Figure B11), and by 3/1/97, the entire site was inundated to 5-30cm depth (Figure B12).
The site remained inundated until early June, when groundwater declines of 30-40cm were
observed in wells more than 160m from the on-site ditch (Figure B13). However, this
groundwater decline was short-lived. The entire disturbed site was inundated again by
mid-July in response to late June precipitation (Figure B14) and remained so until early
October, when surface water depths began a gradual decline to site-wide surface

saturation by mid-December (Figure B15).

251

as
7
.\

.bbp.
MAO

A

 

in

AU
IIVITII

11L1111

   
 

040‘. o I 0
accounts

Elevation from site benchmark (m)
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a...

N
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1111111

AL.
35?»

 

 

.260 210160110 60 1o 15 65 115 '55
mmstebudedm) mmw*mm

Figure Bl. Groundwater condition on 5/9/95 at the disturbed hydrologic study site.
Groundwater levels were within 10cm of the ground surface throughout the well field in
the early growing season, with some of the lower elevation monitoring wells inundated to
depths up to 25cm. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing fiinction (SPSS, Inc., 1996).
Elevation increases with distance from north site border. View point is from the
northeast.

252

 

 

A 0.1» A
,5, one _,
f 0.1» a
-0.2 - d
on LS ,
'04? A z
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-0.9 _
1 01— GW _.
C - ' P.
o -1 1 ‘— , I. -7 . . ‘ *4
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El -1.4L f g

260 210160110 60 1o 15 65 115 165
Distarrcefl’unnortlrsitebude,(m) Wmeasls'bmlml

Figure B2. Groundwater condition on 6/29/95 at the disturbed hydrologic study site.
Groundwater levels dropped between mid-May 1996 and late-June 1996 to as much as
60cm below the ground surface. This was true in wells located as little as 10m from the
on-site drainage ditch. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing firnction (SPSS, Inc., 1996).
Elevation increases with distance fi'om north site border. View point is from the
northeast.

253

CO
AM
//
11
j

.1llllllllllL

 

      

LIfITIIIIIII

 

 

.._..——
.260 210160 110 so 10 15 65 1,15 ‘65
Dmmnfl'flléleba'deqm) Widow

Figure B3. Groundwater condition on 10/20/95 at the disturbed hydrologic study site.
Groundwater levels established in late June were unchanged until late October. LS = land
surface; GW = groundwater surface. Surface and groundwater elevations were measured
at each monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPSS, Inc., 1996). Elevation increases with distance fi'om north site
border. View point is from the northeast.

254

 

  
    

  
   

0.2
A 0.1 MW
g 00)- 7 .2
f 0.11— 7 _
g -0.21— : .1
'0'3F J LS «
'04)‘ .1 «A
g 41.5% .. 4
-0.6— 4
-0.8~ ~
g.,..- .
c -1.0»- ~,
0 4.17- "l
E ~12— r
o -1.3~ 7
m -1.4— «

 

   

 

“ ,
260 210160110 so 10 15 65 115 155

Figure B4. Groundwater condition on 12/26/95 at the disturbed hydrologic study site.
Partial groundwater level rebound has occurred across the site, with the largest increases
observed in the wells closest to the on-site drainage ditch. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPSS, Inc., 1996). Elevation increases with distance from north site
border. View point is fi'om the northeast.

255

l
7

 

 

1111111411111LL1

I lbé
MI I I I I I I I I I I I II

 

 

——----——I---—-

Figure B5. Groundwater condition on 2/14/96 at the disturbed hydrologic study site.
Groundwater levels across the site had increased by 25-30cm since December 1995.

Wells closest to the on-site ditch still showed greater groundwater increases than did wells
further from the ditch, probably due to continued infiltration of surface water from the
ditch into adjacent areas. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing fimction (SPSS, Inc., 1996).
Elevation increases with distance from north site border. View point is from the
northeast.

256

 
   

 

 

 

0.2
g 0.0~ i 1
x ~0.1~ “ _,
"’ 412— “‘ -
E 0.3” L5 : a
414- - J
-o.5 ,- ..
o as _
’5 -0.7— -“ a
0.8-- - s
g 09- ‘ LS ~
.1
s ‘1'?” . "
E -12- : ~
Q) -1.3~ 1 T
m w

260 210160110 so 10 15 65 115 ‘65
Distancefromnorthsiteborder(m) mefiwmm)

Figure B6. Groundwater condition on 3/21/96 at the disturbed hydrologic study site. On
this date, groundwater levels had risen to the surface across the wetland and almost all the
wet meadow was saturated to, or above, the ground surface. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPSS, Inc., 1996). Elevation increases with distance from north site
border. View point is from the northeast.

257

 

 

 

:L1Lllll

 

 

 

 

Elevation from site benchmark (m)

 

1 1 1 l l 1

260 210 160 110 60 10
Distancefromnorthsiteborder(m)

Figure B7. Groundwater condition on 7/1/96 at the disturbed hydrologic study site.
Groundwater decline was once again observed at wells greater than 60m fiom the on-site
ditch. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an
inverse squared distance smoothing firnction (SPSS, Inc., 1996). Elevation increases with
distance from north site border. View point is from the east.

258

0.2
0.1
oo-
-o.1+-
-o.2#
0.3L
-o.4
as 3;: _
-0.6 - ”
-o.7
-0.8
-o.9
4.0
-1.1
-12
-1.3
-1.4

 

I'—
(D
1111111

 

 

 

Elevation from site benchmark (m)

 

 

l 1 1 1 1 l

260 210 160 110 60 10
Distancefromnorthsiteborder(m)

Figure B8. Groundwater condition on 7/15/96 at the disturbed hydrologic study site. The
summer pattern of groundwater decline, observed previously at the disturbed site and
concurrently at the reference site, was evident here. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPSS, Inc., 1996). Elevation increases with distance from north site
border. View point is from the east.

259

 

 
   

.5
(.0
I
1111111

.1.
La
ITTV'IIIT“

  
   

 

W, ,._...,.._._..

'~fi-*- ‘- ’.>‘-d

"‘~.-o
_ .

111111

 

 

 

Elevation from site benchmark (m)
a
O)

 

1 1 1 l 1 1

260 210 160 110 60 10
Distancefromnorthsitebordeflm)

Figure B9. Groundwater condition on 9/16/96 at the disturbed hydrologic study site.
Intense rainfall event triggered fall groundwater recharge. As in 1995, the most rapid
recharge occurred closest to the on—site drainage ditch. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPSS, Inc., 1996). Elevation increases with distance fi'om north site
border. View point is from the east.

260

 

 

 

 

 

 

Elevation from site bendtmark (rn)

 

 

1.
l l 1 J 1 1 N1
260 210 160 110 60 10
Distancefromnorthsiteborder(m)

Figure B10. Groundwater condition on 12/10/96 at the disturbed hydrologic study site.
As in 1995, infiltration of surface water into the wet meadow from the on-site ditch
apparently constituted the major influence in raising groundwater levels in the wetland.
L8 = land surface; GW = groundwater surface. Surface and groundwater elevations were
measured at each monitoring well and determined with respect to a site benchmark.
Surface and groundwater contour interpolation was performed using an inverse squared
distance smoothing fimction (SPSS, Inc., 1996). Elevation increases with distance fi'om
north site border. View point is from the east.

261

 

 

 

0.2
A 01” ——1
g 0.0— a
01— J
g.,... ..
oar -
-0.4 ~
2.; ..
a, as
’3' “0.7+- a
-0.8~ -*
E 0.9% —
8 -1.0~ ‘
4.1% e
E 4.2% ..
(D -1.3- T
E 4.4+ i
___-—

260 210160 110 so 10 15 65 "5 ‘55
Distancefromnormsiteborder(m) WmWW‘m’

Figure B11. Groundwater condition on 1/26/97 at the disturbed hydrologic study site.
Groundwater levels mirrored the land surface throughout the site. LS = land surface; GW
= groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing firnction (SPSS, Inc., 1996). Elevation increases with distance fiom north site
border. View point is from the northeast.

262

 

AN

ac
III I

fromsltebenchmark(m)
bbsbsbsbbsbbo
mqmgm?c‘om
\\
'1
I

'b.
(D

elevati
I O I I
as a: iv -_. 'o

IIIfI
‘1
l
1
I
'1‘11
111:
('1
I
1
'1
1
1111L11J1111111L

IIVI

 

 

4- —"""
260 210160 110 so 10 15 as 115 ‘55
Distancefromnormsitebadedm) meflmm

Figure B12. Groundwater condition on 3/1/97 at the disturbed hydrologic study site. The
entire site was inundated to between 5-30cm depth. LS = land surface; GW =
groundwater surface. Surface and groundwater elevations were measured at each
monitoring well and determined with respect to a site benchmark. Surface and
groundwater contour interpolation was performed using an inverse squared distance
smoothing fiinction (SPS S, Inc., 1996). Elevation increases with distance fi'om north site
border. View point is from the northeast.

263

 

 

 

c--_- — .-
7 .

 
   

Elevation from site benchrrark (m)
a:
O)

 

 

 

 

 

-0.8 “7 —
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Figure B13. Groundwater condition on 6/11/97 at the disturbed hydrologic study site.
Groundwater decline of 30—40cm was observed at wells more than 160m from the on-site
ditch. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an
inverse squared distance smoothing firnction (SPSS, Inc., 1996). Elevation increases with
distance fi'om north site border. View point is from the east.

264

 

 

 

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Distancefromnorlhsiteborder(m) osmium“

Figure B 14. Groundwater condition on 7/10/97 at the disturbed hydrologic study site.
Late June precipitation inundated the entire site. This condition was unchanged until early
October 1997. LS = land surface; GW = groundwater surface. Surface and groundwater
elevations were measured at each monitoring well and determined with respect to a site
benchmark. Surface and groundwater contour interpolation was performed using an
inverse squared distance smoothing fiinction (SPSS, Inc., 1996). Elevation increases with
distance from north site border. View point is fiom the northeast.

265

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260 210160 110 so 10 15 65 115 ‘65
Distmnefrmnorflisitebu-der(m) Wmeaggmderlm)

Figure B15. Groundwater condition on 12/18/97 at the disturbed hydrologic study site.
Seasonal groundwater recharge was completed; the wetland was saturated to the land
surface throughout the site. LS = land surface; GW = groundwater surface. Surface and
groundwater elevations were measured at each monitoring well and determined with
respect to a site benchmark. Surface and groundwater contour interpolation was
performed using an inverse squared distance smoothing fimction (SPSS, Inc., 1996).
Elevation increases with distance from north site border. View point is from the
northeast.

266

 

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268

Appendix C2 - Species stem density data

Table C-2. Stem densities of plant species encountered in Saginaw Bay coastal wet

meadows in 1997. A total of BOO-0.25m2 sample plots were collected in 25 coastal wet
meadows. Percent frequency of occurrence was determined from the number of sample

plots in which the species was found. N equals the number of plots in which a species

 

 

occurred.
Species Frequency of Contribution to Mean Species Stem N
Occurrence Total Stem Density
(%) Density (%) (stems/m2, ilSEM)

Acorus calamus 0.3 0.0 20.0(N/A) 1
Agropyron repens 2.7 0.1 29.0(1 1.7) 8
Alisma plantago-aquatica 0. 3 0.0 16.0(N/A) l
Anemone canadensis 8.3 0.4 57.8( 13.6) 25
Apocynum canabin 5.3 0.0 7.8(1.S) 16
Asclepias incarnata 1.7 0.0 4.0(0.0) 5
Aster borealis 7. 7 0. 1 5.2(1.4) 23
Aster dumosus 10.7 0.4 36.8(90) 32
Calamagrostis canadensis 93.3 32.4 382.5070) 280
Calystegia sepium 20.0 0.5 25.0(5.8) 60
Campanula aparinoides 47.3 5 . 5 127.7(12.6) 142
Carex aquatilis 53 .0 21.8 454.0(3 1.2) 159
Carex bebbii 8.7 1.2 158.5(49.2) 26
Carex buxbaumii 4.0 1.3 370.3(97.6) 12
Carex comosa 0.7 0.0 24.0(8.0) 2
Carex hystericina 0.3 0.0 8.0(N/A) 1
Carex lacustris 20.3 1.4 77.5( 14.0) 61
Carex sartwellii 59.0 11.3 211.8(18.8) 177
Carex stricta 26.3 9.6 400. 5(42.6) 79
Carex vulpinoidea 0.3 0.0 20.0(N/A) 1
Cicuta bulbifera 1 .3 0.0 19.0(7. 5) 4
Cicuta maculata 1.7 0.1 41 .6(3 1.7) 5
Circium arvense 10.0 0.1 8.7(0.9) 30
Cladium mariscoides 34.7 1.8 58.1(5.3) 104
Camus amomum 3.0 0.0 12.0(4.3) 9
Camus stolonifera 7.0 0. l 9.9(1 .9) 21
Eleocharis rostellata 0. 7 0. 1 43 .0(1 5 .0) 2
Eleocharis smallii 9.3 1.4 45.1(17.4) 28

269

Table C-2 (cont’d).

 

 

Species Frequency of Contribution to Mean Species Stem N
Occurrence Total Stem Density
(%) Density (%) (stems/m2, :1 SEM)

Epilobium hirsutum 1.0 0.0 8.0(2.3) 3
Equisetum arvense 0.3 0.0 12.0(N/A) 1
Equisetum hyemale 0.3 0.0 16.0(N/A) 1
Eupatorium maculatum 1 .7 0.0 15 .2(6.2) 5
Eupatorium perfoliatum 2.3 0.0 6.9(2.3) 7
Fragaria virginiana 0.7 0.0 18.0(6.0) 2
Fraxinus pennsylvam’ca 0. 7 0.0 0.0(0.0) 2
Galium boreale 12.7 1.4 1 18.8(24. l) 38
Geum spp. 0.3 0.0 16.0(N/A) l
Helenium autumnale 0.7 0.1 94.0(82.0) 2
Hypericum kalmianum 1.7 0.0 168022) 5
Impatiens capensis 8 . 7 0.2 19.2(3 .4) 26
Iris versicolor 2.3 0.1 39.4(9.3) 7
Juncus balticus 9.7 0.7 81 .9(17.8) 29
Juncus brevicaudatus 4.3 0.8 198.8(528) 13
Juncus effusus 0.3 0.0 56.0(N/A) 1
Lathyruspalustris 18.3 0.2 12.1(1.7) 55
Leerzia oryzoides 4.3 0.2 9.4(2.0) 13
Lobelia kalmii 0.7 0.0 4.0(0.0) 2
Lycopus americanus 5.7 0.1 12.9(3 .2) 17
Lysmachia quadriflora 5.0 0.4 98.7(41.1) 15
Lysmachia terrestris 1 .0 0. 1 57.3(13.3) 3
Lysmachia thrysiflora 3 .7 0.1 24.7(8.2) 11
Lythrum alatum 1.0 0.0 6.7(3.5) 3
Lythrum salicaria 12.3 0.4 38.2(6. l) 37
Mentha arvensis 6.3 0. 1 23 .4(5.6) 19
Onoclea sensibilus 0.3 0.0 4.0(N/A) 1
Panicum spp. 0.3 0.0 0.0(N/A) 1
Panicum virgatum 0.3 0.0 0.0(N/A) l
Phalaris arundinacea 16.7 1.6 109.0(22.8) 50
Phragmites australis 6.7 0.2 3120.7) 20
Pm palustris 1 .7 0.2 123 .2(69.6) 5
P00 spp. 1.3 0.1 88.0(70.8) 4
Polygonum amphibium 43.3 0.6 14.6(1. 1) 130
Polygonum scandens 0.3 0.0 4.0(N/ A) 1
Populus deltoides 1.7 0.0 9.6(3 .2) 5
Potentilla anserina 7.0 0.4 68.2(180) 21
Potentillafruiticosa 2.0 O. 1 70.0(21.8) 6
Pycnanthemum virginimm 1.3 0.1 33 .0(1 3.6) 4
Rubus spp. 0.3 0.0 4.0(N/A) 1
Rudbeckz'a hirta 0.7 0.0 16.0(12.0) 2

270

Table C-2 (cont’cD.
Species

Frequency of Contribution to Mean Species Stem N

 

Occurrence Total Stem Density
(%) Density (%) (stems/m2, i1 SEM)
Sagittaria latifolia 1.0 0.0 28.0(8.3) 3
Salix petiolcm's 4.7 0.0 l.6(0.3) l4
Scirpus acutus 1.7 0.0 17.6(7.3) 5
Scirpus americanus l .0 0.0 42.7(23 .2) 3
Scirpus atrovirens 0. 3 0.0 4.0(N/A) 1
Scirpus validus 1.0 0.1 48.0(18.5) 3
Scutellaria galericulata 5 .3 0. 1 15.0(3. 1) 16
Scutellaria lateriflora 0.3 0.0 8.0(N/A) 1
Solomon dulcamara 0.3 0.0 28.0(N/A) 1
Solidago uliginosa 0.3 0.0 80.0(N/A) 1
Spartinapectinata 4.7 0.3 61.1(31.0) 14
Spiraea alba 1.7 0.0 5.6(] .6) 5
Spiranthes lucida 0.3 0.0 4.0(N/A) 1
Stachys tenuifolia 18.7 0. 5 29.2(5 .0) 56
Taraxacum ofliciale 1.0 0.0 16.0(8.3) 3
Teucrium canadense 2.7 0.1 32.5(16.1) 8
Thebptris palustris 0.3 0.2 656.0(N/A) 1
Twila angustifolia 19.0 0.2 10.0(1.3) S7
Twila latifolia 1.0 0.0 5.303) 3
Unknown #1 0.3 0.0 4.0(N/A) 1
Unknown #2 0.3 0.0 0.0(N/A) l
Verbena hastata 0.3 0.0 4.0(N/A) 1
Viola aflinis 0.3 0.0 32.0(N/A) 1
Vitis ”Ma 0.3 0.0 4.0(N/A) 1
Totals 100.0 2384

 

271

Appendix C3 - Vertical distribution of vegetation parts

Table C-3. Vertical distribution of leaf, stem, and inflorescence contacts in Saginaw Bay
coastal wet meadows. Table data are expressed as percentages, with actual counts in

 

 

parentheses.
Contact Type Height Class % of total
contacts
>90cm 40-90cm <40cm Total
Leaf contacts 18.5(1015) 62.2(3409) 19.3(1060) 100.0(5484) 81.8
Stem contacts 10.2(100) 53.8(530) 36.0(354) 100.0(984) 14.7
Inflorescence 73.5(175) 18.9(45) 7.6(18) 100.0(238) 3.5
contacts
All contacts 19.2(1290) 59.4(3984) 21.4(1432) 100.0(6706) 100.0

 

272