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THE EFFECTS OF LAND USE ON LACUSTRINE WETLAND CHEMISTRY AND
THE DIET OF BENTHIC CONSUMERS

By

Alyson Marie Yagiela

A THESIS
Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Zoology
2007

ABSTRACT

THE EFFECTS OF LAND USE ON LACUSTRINE WETLAND CHEMISTRY AND
THE DIET OF BENTHIC CONSUMERS

By

Alyson Marie Yagiela

One of the most widespread effects of human activities on aquatic
ecosystems is nutrient enrichment, which has been documented through
traditional nutrient analyses and more recently, through the use of stable
isotopes. However, little is known of nutrient effects on food webs in lacustrine
wetlands. The objectives of this study were to (1) determine the effects of
anthropogenic activities on nutrient concentrations in lacustrine wetlands, (2)
assess how nitrogen stable isotopes vary with increasing exposure to human
sources of nitrogen, (3) elucidate the relationships between food sources and
invertebrate feeding groups among sites, (4) assess the importance of
phytoplankton in consumer diets with increased nutrient enrichment, and (5)
investigate the variability of stable isotopes at the site-specific level and the
implications this has on food web analyses. My results indicated that
urbanization affects wetland chemistry by significantly increasing total nitrogen
and total phosphorus concentrations at impacted sites and increasing the (WM
values of wetland biota. The diet of fingernail clams, snails, amphipods, and
caenid mayflies could not be determined with stable isotopes. There were many
complications in the identification of energy sources, include the variability of

periphyton within sites, which I was able to identify in this study.

I would like to dedicate this thesis to my family for their endless encouraging
words. I would especially like to dedicate this to my loving husband, Andrew,

who has helped me throughout my master’s project.

iii

ACKNOWLEDGMENTS

I would like to thank the Michigan State University Department of Zoology
for the opportunity to enhance my education. I would also like to acknowledge
my committee members Dr. R. Jan Stevenson (Chairman), Dr. Stephen
Hamilton, and Dr. Richard Merritt for their guidance throughout this research
project. I would also like to thank Vanessa Lougheed for her field assistance and
laboratory analysis of water samples and help with plant identification, Mollie
Maclntosh for her help in the field and assistance in macroinvertebrate
identification, and Christian Parker for his help in the field. Also, many thanks to
Hasand Ghandi of the Stable Isotope Biogeochemistry Laboratory for analyzing
my samples. This research was funded by The Great Lakes Fisheries Trust to
R. Jan Stevenson et al. for “An Ecological Assessment of the Muskegon River

Watershed to Solve and Prevent Environmental Problems.”

iv

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. vi
LIST OF FIGURES ............................................................................... vii
INTRODUCTION ................................................................................... 1
METHODS ........................................................................................... 6
Site Selection ............................................................................... 6
Assessing links between land use and stable isotope signatures of
producers and consumers ............................................................... 7
Assessing variability within sites ...................................................... 9
RESULTS ........................................................................................... 10
DISCUSSION ...................................................................................... 13
APPENDIX ......................................................................................... 36
LITERATURE CITED ............................................................................ 41

LIST OF TABLES

Table 1. Site information including Michigan county, latitude, longitude, total
nitrogen (pg/L), and total phosphorus (pg/L) ............................................... 37

Table 2. 615M (960) and 613C (160) values for each site for suspended particulate
organic matter (SPOM), Epiphyton-Nuphar spp., Epiphyton-Nymphea spp.,
amphipods, caenid mayflies, bivalves, and gastropods, where present ............ 38

Table 3. Bivalve and gastropod family presence for each site. Presence is
represented by and “x” .......................................................................... 39

Table 4. 615M (%0) and 613C (960) values for epiphyton collected from the
indicated plant substrata and fine particulate organic matter (FPOM), where
present .............................................................................................. 40

vi

LIST OF FIGURES

Figure 1. Michigan map of reference sites (white circles) and impacted sites
(shaded circles) .................................................................................... 21

Figure 2. (a) Mean total nitrogen (TN) (pg/L) and (b) mean total phosphorus (T P)
(pg/L) for reference (white) and impacted (shaded) sites (error bars are +/- 1
standard error) ..................................................................................... 22

Figure 3. Plot of average EN (%0) values for each set of biota for reference
(white) and impacted (shaded) sites (error bars are +/- 1 standard error). Means
with * are significantly different (P<0.05) ..................................................... 23

Figure 4. 615N (960) vs 613C (%o) for SPOM (shaded diamonds) and bivalves (plus
sign) for reference sites .......................................................................... 24

Figure 5. 6‘5N (960) vs 6130 (960) for SPOM (shaded diamonds) and bivalves (plus
sign) for impacted sites ........................................................................... 25

Figure 6. UN (960) vs 613C (960) of epiphyton from Nuphar spp. stems (shaded
triangles), epiphyton from Nymphea spp. stems (shaded squares), and
gastropods (black circles) for reference sites ............................................. 26

Figure 7. 615M (960) vs 6130 (%o) of epiphyton from Nuphar spp. stems (shaded
triangles), epiphyton from Nymphea spp. stems (shaded squares), and
gastropods (black circles) for impacted sites ............................................... 27

Figure 8. (TN (960) vs 6130 (%o) of epiphyton from Nuphar spp. stems (shaded
triangles), epiphyton from Nymphea spp. stems (shaded squares), SPOM
(shaded diamonds), amphipods (“X”s), and mayflies (dashes) for reference

sites .................................................................................................. 28

Figure 9. (TN (96o) vs 613C (960) of epiphyton from Nuphar spp. stems (shaded
triangles), epiphyton from Nymphea spp. stems (shaded squares), SPOM
(shaded diamonds), amphipods (“X”s), and mayflies (dashes) for reference

sues .................................................................................................. 29

Figure 10. Mean difference in 613C (white) and 615N (shaded) between SPOM

and bivalves for reference sites and impacted sites (error bars are +/- 1 standard
error) ................................................................................................. 30

vii

LIST OF FIGURES (CONTINUED)

Figure 11. Mean difference in 6% (white) and WM (shaded) between (a)
epiphyton (Nuphar spp.) and gastropods and (b) epiphyton (Nymphea spp.) and
gastropods for reference sites and impacted sites (error bars are +/- 1 standard
error) ................................................................................................. 31

Figure 12. Mean difference in 613C (white) and WM (shaded) between (a)
SPOM and caenid mayflies, (b) epiphyton (Nuphar spp.) and caenid mayflies,
and (c) epiphyton (Nymphea spp.) and caenid mayflies for reference sites and
impacted sites (error bars are +/- 1 standard error) ...................................... 32

Figure 13. Mean difference in 6% (white) and WM (shaded) between (a)
SPOM and amphipods, (b) epiphyton (Nuphar spp.) and amphipods, and (c)
epiphyton (Nymphea spp.) and amphipods for reference sites and impacted sites
(error bars are +/- 1 standard error) .......................................................... 33

Figure 14. Difference in 615N between SPOM and epiphyton (averaged from
Nuphar spp. and Nymphea spp.) for reference sites (white) and impacted sites
(shaded) ............................................................................................. 34

Figure 15. 615N (960) vs 613C (960) for FPOM and periphyton collected off of

different substrates for Todd Lake (reference site) and Brooks Lake (impacted
site) ................................................................................................... 35

viii

INTRODUCTION

Anthropogenic influences have altered the global nitrogen (N) and
phosphorus (P) cycles. Some common disturbances to aquatic systems include
the addition of wastewater effluent, increased sedimentation resulting from
agricultural practices or urbanization, and the application of fertilizers that enrich
runoff and groundwater (Bennett et al. 2001). Each of these common practices
results in increased nutrient loads to aquatic ecosystems. As available nutrients
increase, there is an increase in primary production - a process known as
eutrophication. In lentic ecosystems, phytoplankton biomass can increase to a
point where light attenuation inhibits the growth of benthic aquatic macrophytes
(Wetzel 2001). This shift in primary production and biomass can accordingly
impact the diet of primary consumers. In this study, I sought to determine the
impacts of land use on wetland nutrient chemistry and, in turn, on trophic
interactions.

According to Owen et al. (1998), wetland functions fall into three main
categories: wildlife habitat, hydrologic processes, and water quality improvement.
Many wildlife species require wetlands for at least a part of their life cycles. They
also provide a variety of flora, fauna, and feeding niches for numerous
organisms. Hydrologically, wetlands are important for flood mitigation and
aquifer recharge (Mitsch and Gosselink 2000, Owen 1998). The land-water
interface links the hydrologic processes with chemical processes. Where
groundwater and surface water runoff travel through fringing wetlands before

reaching a lake, the wetlands may remove nutrients and contaminants (Mitsch

and Gosselink 2000). This results in wetlands being more susceptible to
anthropogenic contamination than the lake itself. Mitsch (1992) described
wetlands as the “buffer between uplands and lakes.” The impacts of human-
derived nutrients on wetland nutrient chemistry have been widely studied using
traditional nutrient analysis and stable isotopes (Carpenter et al. 1998;
McClelland and Valiela 1998), but less is known of the human impacts on food
webs in wetlands.

Stable isotope chemistry has become a widely used tool in recent years
for ecological studies, including determining food web structure, because it takes
into account What is actually assimilated into the tissues of the consumer. This is
unlike traditional gut content analyses that are indicative of everything that is
ingested, not just what is nutritionally available for the organism. Stable isotopes
are interpreted by comparing the ratio of the amount of a heavy isotope to its
corresponding lighter isotope in tissues of consumers relative to potential food
sources after incorporating isotopic fractionation that occurs between trophic
steps.

Food web studies often incorporate stable isotope analysis of carbon (”C
and 12C) and nitrogen (”’N and 14N). Carbon isotopic ratios of animals typically
reflect that of their diet, increasing less than 1%» per trophic level (Michener and
Schell 1994; DeNiro and Epstein 1978). The nitrogen isotopic ratios of animals
are typically enriched by an average of 3 to 5960 (Peterson and Fry 1987). Thus,

the combined use of carbon and nitrogen stable isotopes can be a powerful tool

in assessing food sources and food web structure. Therefore, I chose this
method for analyzing the diets of specific primary consumers in this study.
Consumers can be categorized by their functional feeding group. For
aquatic macroinvertebrates this is generally dependent on animal morphology
because this controls how and what an organism can consume (Merritt and
Cummins 1996). Bivalves are filter feeders and their isotopic signatures should
reflect that of a diet of phytoplankton and other seston found in the water column
(Vaughn and Hakenkamp 2001). Due to their abundance, I studied the diet of
fingernail clams (family Sphaeriidae). Gastropods are scrapers, which are
adapted for removing attached algae from substrates (Cummins 1974), so I
expected to see their diet consistent with periphyton consumption. The snails
studied included Lymnaeidae, Physidae, Planorbidae, and Viviparidae. The
isotopic ratios of these clams and snails serve as a check of my methodology.
In many macroinvertebrates, there can be a shift in diet that is dependent
on food source availability. Amphipods, from the class Crustacea, are more
omnivorous in that they can utilize multiple food sources including detritus,
filamentous algae, and animal material (Summers et al. 1997). Mayflies
(Ephemeroptera) from the family Caenidae can be collector-filterers, collector-
gatherers, or collector-gatherers/scrapers depending on genus. Therefore, they
may feed on suspended or deposited fine particulate organic matter (FPOM) or
attached material (Merritt and Cummins 1996). The study of these two

organisms may provide insight into human-induced shifts in consumer diets.

Stable isotopes are also useful in determining sources of nutrient inputs.
P has only one stable isotope and so I focused mainly on N as my tracer of
anthropogenic influences. It has been shown that anthropogenic N, either from
human or animal waste is isotopically heavier than N from natural sources
(McClelland and Valiela 1997, Macko and Ostrom 1994). Similar biota from two
separate systems, where one is more urbanized and receiving wastewater inputs
and the other is considered “pristine,” often will have different 6‘5N signatures,
with higher 615N values in the biota from the system receiving wastewater inputs.
Knowing this, I can compare the biota between sites to determine which sites are
most affected by anthropogenic nutrient inputs.

In summary, primary production in wetlands is derived from plants and
algae. Plants become more important for aquatic consumers as the
decomposition process progresses and the plants are colonized by bacteria and
fungi. Algae, on the other hand, are consumed directly by herbivores. I would
hypothesize that algal production, specifically phytoplankton, would respond
more than plant production in wetlands as nutrient enrichment increases. This
should cause a shift in food webs that can be detected by stable isotope
analysis.

The main objectives of this study were to:

(1) Determine the effects of anthropogenic activities on adjacent wetland
nutrient concentrations.

(2) Assess how nitrogen stable isotopes vary with increasing exposure to

human derived nitrogen sources.

(3) Elucidate the relationship between food sources and functional feeding
groups, despite the variability in nitrogen stable isotope values among
wetlands.

(4) Assess the importance of algae as the base of primary production for
consumer diets with increased nutrient enrichment.

(5) Investigate the variability of stable isotopes at the site-specific level and

assess the implications this has on food web analyses.

METHODS
Site Selection

In the summer of 2003, land use around lacustrine wetlands in Michigan
was evaluated to determine which sites could be used as reference or degraded
sites. Land use was used to distinguish reference and impacted sites based on
the assumption that agricultural areas and highly developed areas increase the
loading of nutrients to lacustrine wetlands. Sites were selected based on land
use characterized by visual assessments of riparian land use and land use data
from the National Land Cover Database 2001. Five sites were chosen to
represent reference wetlands (Todd Lake, Otis Lake, Tubbs Lake, Ham Lake,
and Leisure Lake) because they were located in primarily forested areas. Five
impacted sites (Brooks Lake, Hillsview Lake, Mona Lake, Round Lake, and
Wintergreen Lake) were chosen based on high levels of agricultural and urban
land use. Brooks Lake had a high density of houses and summer cottages along
its shoreline. Hillsview Lake and Round Lake were in areas with a combination
of pasture land, row crops, and urban development. The Mona Lake watershed
was highly urbanized. Wintergreen Lake was located within the Kellogg bird
sanctuary, where it is known to be receiving high nutrient inputs from visiting
waterfowl (Manny et al. 1994). All wetlands are located in the western to central
portion of Michigan’s Lower Peninsula (Figure 1).

To test the hypothesis that anthropogenic activities are affecting wetland
nutrient chemistry, surface water was collected from the littoral zone for nutrient

chemistry analysis in acid-washed bottles at each sample site. Total phosphorus

(TP) was determined using the ascorbic acid method following persulfate
digestion (APHA 1998). Total nitrogen (TN) was analyzed by second-derivative
UV spectroscopy analysis of nitrate (NOg') following a persulfate digestion
(Crumpton et al. 1992). These analyses were performed on a Skalar auto-

analyzer.

Assessing links between land use and stable isotope signatures of producers
and consumers

To determine if land use affected the isotopic signature of primary
producers and primary consumers and to elucidate the relationship between
sources and functional feeding groups, plants, epiphyton, suspended particulate
organic matter (SPOM), and aquatic macroinvertebrates were collected.

Aquatic macroinvertebrates were collected using a standard D-net. They
were then identified as far as possible in the field and sorted into separate glass
jars with filtered wetland water. Each jar was placed in a cooler for 24 hours
while the invertebrates cleared their gut contents, and then they were frozen.
Gastropods and bivalves were pulled from their shells and identified based on
their shell morphology.

The aquatic plants Nuphar spp. and Nymphea spp., which are dominant in
the littoral zones of southern Michigan lakes, were collected from each site.
Healthy petioles were collected with pruning shears and placed in plastic bags.
To collect the epiphyton from these stems and leaves, deionized water was

added to the bag and the plants rubbed vigorously until all epiphytes were

removed, and the resultant slurry was poured into 125 mL Nalgene bottles and
frozen in the field.

Six 1-liter bottles of water were collected at random throughout the
wetland for the analysis of suspended particulate organic matter (SPOM), which I
am defining as the material found in the water column, which could include
phytoplankton or seston. These were combined for one composite sample and
water was filtered through two ashed 0.45pm glass-fiber filters. All of these filters
were frozen immediately following filtration.

In preparation for carbon and nitrogen stable isotope analyses, all
samples were placed in glass beakers, oven-dried at 60°C and treated with 10 %
hydrochloric acid to avoid carbonate contamination. Lipids were removed from
gastropods, bivalves, amphipods, and caenid mayflies using the Soxhlet
extraction method with a chloroform/methanol solvent and dried again. The
sample from each SPOM filter was scraped off using a razor blade and all
samples were ground with a mortar and pestle for homogeneity. From each
sample, a 0.5 to 1 milligram subsample was weighed into a tin capsule.

Stable isotope samples were analyzed at the Stable Isotope
Biogeochemistry Laboratory in the Department of Zoology at Michigan State
University. All samples were analyzed on either a VG Prism Series II Isotope
Ratio Mass Spectrometer via dual inlet or a CV Instruments lsoprime Mass
Spectrometer interfaced with a EuroVector Elemental Analyzer. The isotope
ratios were expressed as 6130 and (WW and referenced to a known standard,

which is PeeDee Belemnite limestone for C and nitrogen gas in the atmosphere

for N. The values were expressed as 6130 and (TN as per mil (960). The 6X
values were calculated from the following equation where R is the ratio of the

heavier isotope to the lighter isotope:

6X = [(RsamplerRstandardy1] x 103 (Peterson and Fry 1987).

These data were used to test the following three hypotheses: isotopic
ratios of N will increase with increased anthropogenic activities in the watershed,
there will be a clear producer-consumer relationship identifiable via stable
isotope analysis, and phytoplankton will become a more important food web base

as nutrient enrichment increases.

Assessing variability within sites

To investigate the hypothesis that variability of periphyton from different
host species within one site is low relative to inter-lake variability and therefore
not an important source for error, I chose one impacted site (Hess Lake) and one
reference site (Todd Lake) in August 2004. From both of these sites I sampled
the periphyton on five plant species and the fine particulate organic matter
(FPOM) from the sediment surface. These samples were prepared for stable
isotope analysis in the same way as the previous samples. All tests of statistical
significance were performed using a two-sample ttest with a 0.05 significance

level.

RESULTS

In my assessment of the links between land use and lacustrine wetland
chemistry, I found that wetland nutrient concentrations were affected by
anthropogenic activities. The reference sites had significantly lower total nitrogen
(TN) and lower total phosphorus (TP) than sites predicted to be impacted (Figure
2; P=0.0057 for TN; P=0.0331 for TP). For the reference sites, TN ranged from
434.8 to 1046.8 ug/L with a mean=723.5 ug/L and TP ranged from 9.3 to 23.3
uglL with a mean=17.7 ug/L. For the impacted sites, TN ranged from 1018.6 to
1441.4 pg/L with a mean of 1195.0 ug/L and TP ranged from 34.3 to 119.2 ug/L
with a mean of 58.5 jig/L. This is consistent with other lacustrine wetland nutrient
data from the Muskegon River Watershed Ecological Assessment Project (2004)
which found TN ranging from 420 to 1620 jig/L and TP ranging from 4.7 to 35.1
pg/L.

To assess the links between land use and the stable isotope signatures of
producers and consumers, l averaged similar biota for reference sites and
impacted sites. Land use did affect the (WM value of primary producers and
consumers (Figure 3). For the reference sites, mean 6‘5N ranged from 0.54 to
3.50% versus 3.17 to 8.69%: for the impacted sites. I concluded that there was a
statistically significant increase in 6‘5N in impacted sites compared to reference
sites for epiphyton-Nuphar spp. (P=0.0027), amphipods (P=0.0016), caenids
(P=0.0156), gastropods (P=0.0039), and SPOM, which was presumably manly

phytoplankton (P=0.0480). Although the impacted sites have higher 6‘5N values

10

for epiphyton-Nymphea spp. (P=0.0904) and bivalves (P=0.2456), the
differences were not statistically significant.

Using stable isotopes, I was unable to determine the relationships
between the producers and consumers chosen for this study or determine the
importance of algae as nutrient enrichment increases. Bivalves and gastropods
have very specific feeding habitats, so I expected to see clear relationships
between these organisms and their expected diet. For all sites where bivalves
were present, there appeared to be no relationship between the (WM and 6130
values of bivalves and SPOM (Figures 4 and 5). At nine sites, the (WM and 6130
values for gastropods did not reflect that of their predicted diet of periphyton
(Figures 6 and 7). In Wintergreen Lake, however, epiphyton was a possible
primary food source for gastropods based on predicted trophic fractionation
(+1950 for 613C, +3-5%o for c‘5N).

Mayflies and amphipods span a range of functional feeding groups and
therefore were used to assess the importance of algae in the food web. There
appeared to be no significant relationships between amphipods, caenids, and the
sampled epiphyton or SPOM for any site (Figures 8 and 9). These results
indicate that there are other variables to consider when performing diet analyses
using stable isotopes. This is explored further in the discussion section.

All consumers were analyzed against their predicted diet to determine
whether their (TN and 6130 values were greater than that of the food sources.
Each relationship was analyzed by plotting the mean shift between each

consumer and its expected food sources for reference and impacted sites

11

(Figures 10, 11, 12, and 13). T-tests were performed to determine whether any

of these difference were significantly greater than 0, where I looked for P<0.05

and t>tcritjca|. The mean difference between each consumer and potential food

sources previously discussed was not significantly greater than 0, except for the

mean difference in UN between amphipods and SPOM at the impacted sites

(P=0.016, t=3.80, tcritical=2-35)- I also assessed the relationship between

epiphyton and SPOM (Figure 14) for all sites together. The mean 5‘5N signature
for epiphyton (Nuphar spp. and Nymphea spp. averaged together) (4.37) was

significantly greater than the mean 6‘5N signature for SPOM (2.63) (P=0.017,
t=2.48, tcritical=1-83)-

To assess the site level variability in stable isotopes analysis, I analyzed
the periphyton from multiple substrata for one reference site (Todd Lake) and
one impacted site (Brooks Lake) (Figure 15). For both sites, I collected fine
particulate organic matter (FPOM) from the sediment surface and periphyton
from five plants. The Todd Lake 615N values ranged from 1.3 to 6.4960 and 513C
values ranged from -11.3 to -28.8%o. For Brooks Lake the (WW values ranged
from 1.6 to 4.7% and 6130 values ranged from -24.5 to -26.7%o. This indicates a
high level of variability within sites, although the source of variation was not

determined.

12

DISCUSSION

Land use significantly affected wetland chemistry and allowed me to
successfully identify reference and impacted wetlands. The anthropogenic
contributions of nitrogen and phosphorus from urbanization and animal waste
were reflected in the water chemistry at the impacted lacustrine wetland sites by
significantly increasing TN and TP concentrations. These sources of nitrogen
carry a greater 6‘5N value that was incorporated into the tissues of the biota in
the receiving waters, resulting in higher 6‘5N values in the biota of the impacted
sites compared to the reference sites. This pattern has been observed in many
other systems, including Cape Cod estuaries (McClelland et al. 1997), streams
(Northington and Hershey 2006), and lacustrine systems (Lake et al. 2001).

To determine whether land derived nutrients influenced the diets of
primary consumers, I chose two organisms from very specific functional feeding
groups, fingernail clams and snails. F ingernail clams are filter-feeders, so I
expected their stable isotope data to reflect that of a diet consisting of SPOM.
Since snails are scrapers, l hypothesized that they would be consuming mostly
periphyton. My data did not support either of these hypotheses. There are
numerous considerations for accurate data interpretation; I explore those further
below.

Phytoplankton has been shown to be an important source of primary
production in river (Peterson et al. 1993), as well as open water and coastal food

webs (Keough et al. 1996). I collected phytoplankton from the water column and

13

concentrated the material onto filter paper. The downside of this method is that l
was actually sampling everything in the water column and not just phytoplankton,
hence referring to these samples as SPOM for this study. This could explain why
the stable isotope data did not show that bivalves are consuming and
assimilating SPOM. It is possible that bivalves are ingesting SPOM and
excreting the material that is not nutritionally valuable. In Pennak (1953), the diet
of Pelecypoda (now Bivalvia) is described as consisting of zooplankton,
phytoplankton, and organic detritus. This suspended material is removed from
the water and the inorganic silt is separated out, possibly via the labial palps.
Therefore, only a portion of the ingested material is actually getting assimilated
into their tissues. A study by Grey et al. (2001) showed that the UN and 6130
values of POM were higher than the values for phytoplankton. This may explain
why my bivalve samples had stable isotope values higher than that of the SPOM
samples.

It is also possible that SPOM could be variable within the wetland itself
and my six-sample composite was not representative of the SPOM throughout
the sample site. Wave action could be stirring up other material from within the
wetland, such as detritus or loosely attached algae. There are many variables
here and unfortunately no clear solution without knowing the composition of the
SPOM samples which were completely consumed for the stable isotope analysis.

There is also some debate about the feeding behavior of bivalves. Allen
(1914) indicated that bivalves are clearly selective feeders, rejecting harmful

material and ingesting mostly material with higher food value. The observations

14

of Gale and Lowe (1971) suggest that S. transversum (Sphaeriidae) are non-
selective and in most instances, their gut contents reflected the phytoplankton in
the water.

There are two types of feeding for bivalves, suspension and deposit.
Suspension feeding is the consumption of particles from the water column and
deposit feeding is the removal of particles from the sediment (Raikow and
Hamilton 2001). A study by Raikow and Hamilton (2001) showed that the diet of
Sphaen'um striatinum consisted of 64% episammon (detritus and algae possibly
mixed with sand collected from the surface of sand deposits), and 36%
suspended particulate organic matter. Deposit feeding or resuspension may be
a contributor to the diet of fingernail clams (Vaughn and Hakenkamp 2001). This
idea is also supported in a study by Way (1989) where he observed that
Musculium transversum could move material using ciliary tracts on the foot and
they could also direct their siphons to consume substrate with a “vacuuming
motion.” With this in mind, the fingernail clams I studied may have a mixed diet
consisting of SPOM and fine benthic organic material.

Gastropods are scrapers and I expected a diet consistent with that
functional feeding group. I did not see this relationship for the periphyton
samples that I collected. Therefore, there must be another food source not
accounted for in this study. Detritus could play a much larger role in
macroinvertebrate diet than originally predicted. Detritus was not analyzed
because of the anticipated difficulty in obtaining a clear isotopic signature.

Typically organisms that feed on detritus are actually utilizing it for the colonized

15

microorganisms, not the decaying material itself. Cummins (1974) describes this
as the “peanut butter” on the “nutritionally unsuitable cracker.” To get to the
“peanut butter,” the “cracker” must also be consumed. Similarly, the layer of
microorganisms is difficult to sample without including its substrate and therefore
was not included in this study.

Although snails are considered nonselective feeders, there is evidence
that they may not be consuming all available food. A study by McCormick and
Stevenson (1989) showed that when snails fed on periphyton, algal size and
growth form were important in the grazing of food. Algae with a more prostrate
growth form were removed less readily than other algal species. A subsequent
study by Tuchman and Stevenson (1991) showed that a snail grazer removed
the overstory filamentous cyanobacteria, leaving lower profile species that are
difficult to remove. These different layers of epiphyton may have different stable
isotope signatures. A study by Burkholder et al. (1990) demonstrated that the
adnate taxa from their periphyton community obtained more nutrients from its
substrate compared to the loosely attached algae that obtained nutrients from the
water column. I did not sample understory and overstory periphyton separately,
so I cannot evaluate this source of variability. Another variable discussed later is
the variability in periphyton stable isotope signatures at the site level (Figure 15).

As mentioned before, amphipods can consume and assimilate detritus,
filamentous algae, and animal material (Summers et al. 1997). Pennak (1953)
describes amphipods as mainly feeding on plant and animal matter and those

found within vegetation as often “browsing on the film of microscopic plants,

16

animals, and organic debris covering the leaves and stems.” Waldbauer (1968)
refers to the amphipod Gammarus spp. as a “facultative shredder,” predicting
that when certain food resources are limited, they can shift their diet (Cummins
and Klug 1979). This may result in reduced efficiency of food conversion to
growth, but Gammarus spp. can utilize coarse particulate organic matter
(CPOM), F POM or ultrafine particulate organic matter (UPOM), sediment FPOM-
UPOM, periphyton, or invertebrate prey in stream ecosystems. In this study, I
did not find that amphipods were feeding on periphyton or SPOM. Because
amphipods are primarily shredders, they are likely consuming CPOM, which was
not analyzed due to anticipated difficulty in obtaining a clear isotopic signature for
this material.

I also examined the stable isotope signatures for mayflies (family:
Caenidae), which could reflect SPOM, F POM, periphyton, or detritus (Merritt and
Cummins 1996). A study by Pupilli and Puig (2003) looked at the effects of a
major disturbance on mayflies. Before and after a flood, detritus was the major
component of their diet. Chessman (1986) conducted a study of the digestive
tract contents for caenid mayflies and found 90% ultrafine detritus and 10%
benthic algae. A diet primarily consisting of detritus was also supported by a
study of snag-dwelling mayflies where greater than 70% of mayfly production
was attributed to amorphous detritus and about 18% was based on diatom
consumption (Benke and Jacobi 1994). The results of my study are consistent

with these other studies, indicating that caenid mayflies were not consuming

17

SPOM or periphyton as their major food source, suggesting that they are likely
consuming F POM or detritus.

Nutrient loading to aquatic systems has been shown to increase primary
production (Wetzel 2001). I had hypothesized that the wetlands with higher
nutrient concentrations would have a food web more based on phytoplankton
production. Without establishing clear producer-consumer relationships, I am
unable to make any inferences about the base of the food webs that were
studied. In forested stream systems, detritus has also been shown to be the
major source of nutrition for consumers (Hall et al. 2001). When eutrophication
occurs, detrital biomass increases as well as algal production. This is because
there is greater net primary production until shading promotes the breakdown of
light—deprived macrophytes, thus contributing to the detrital pool. A study by
Keuogh et al. (1996) established phytoplankton as the base of the food webs of
both coastal wetland and adjacent offshore waters of Lake Superior, but
hypothesized that the decomposition of detritus contributed to the 613C value of

the phytoplankton. This is due to the respiration of the detritus, thus releasing

dissolved inorganic carbon that is depleted in 13C, resulting in phytoplankton

depleted in 130. This suggests that despite which source of carbon was

identified as the base of the food web, all sources of production influence the
isotopic composition of consumers, either directly or indirectly.

The final objective of this study was to assess the variability in isotopic
signatures of periphyton within a site and evaluate the importance of that source

of variability for evaluating food web structure. I collected periphyton from a

18

number of different plant substrates and found that their stable isotopic
signatures varied greatly (Figure 15). This impacts my results in that I chose
Nuphar spp. and Nymphea spp. as host plants for the periphyton component of
the diet analysis portion of this study. Due to the high variability in signatures, I

may be falsely excluding periphyton as a potential food source. A study by
Cornelisen et al. (2007) showed that irradiance affects plant 615M and 613C

values. The same plant species collected from different light regimes had
varying stable isotope signatures. Another study has shown that there is a high
degree of variability in the isotopic signatures of different plant species within the
same wetland (Boon and Bunn 1994). Pip and Robinson (1984) showed that
differences in algal periphyton compositions exist on different host macrophytes
within the same site. All of these studies show that the composition and isotopic
signatures of wetland plants and periphyton are highly variable. This is important
to consider before excluding periphyton as a potential food source for the
consumers studied. In addition to spatial variability, temporal variability is also
likely to be important. The stable isotope ratios of microalgae vary over time
while consumers integrate this variation to different degrees depending on their
growth and turnover because different instars of insect larvae have varying diets
based on their size and functional feeding group (Basaguren 2002).

Lacustrine wetlands are dynamic ecosystems that are important for a
number of lake and wetland organisms. l was able to show that land use
increases TN and TP concentrations and the 615N values of wetland biota. l was

unable to establish clear relationships between the primary producers and

19

primary consumers chosen for this study. Food web studies utilizing stable
isotope analyses are difficult to conduct due to spatial and temporal variability of
consumers and producers and the variability in consumer feeding modes. These

are all important concepts to consider when studying aquatic food webs.

20

 

1 - Ham Lake, Missaukee County
2 - Leisure Lake, Shiawassee County

3 - Otis Lake, Barry County 0 _1
4 - Todd Lake, Osceola County

5 - Tubbs Lake, Mecosta County 0 -4

6 - Brooks Lake, Newaygo County 7'0 O ‘5

7 - Hillsview Lake, Mecosta County 0 -6
8 - Mona Lake, Muskegon County 0 '3 O '9

O -2
9 - Round Lake, Clinton County 0 -3
10 - Wintergreen Lake, Kalamazoo 0-10
County

 

Figure 1. Michigan map of reference sites (white circles) and impacted sites

(shaded circles).

21

(a) Total Nitrogen

 

‘ 1600

1200 ween m

  

 

 

 

 

, 7 Reference Impacted

(b) Total Phosphorus

80 ‘

 

 

 

 

 

 

 

 

 

 

I .
u I
la 4Olii 7 c * cc
0.
‘l—
20+— 47 ,7
.L
i
, 0

Reference _ tnpacted

 

Figure 2. (a) Mean total nitrogen (TN) (pg/L) and (b) mean total phosphorus (TP)
(pg/L) for reference (white) and impacted (shaded) sites (error bars are +/- 1

standard error).

22

Impacted vs. Reference Sites

 

 

 

 

 

 

 

 

 

7. e L,
, * ‘Dlmpacted ‘.
6< at l .
.E. DReferenceq
* ,
57- .1. %
33 4 *
Z 31‘
2 3‘
no
2.
1‘ ii
0 ._ ..__ i .._.
éd. Etc .8 '08 g 8 5
08' OB. o E" o 2 O
s~ fine 9 as s s a
‘82 Sim fi 02 b 15 m
'5.“- °-z E 3
3 UJ
I-|-Iz < (D

Figure 3. Plot of average 615N (91») values for each set of biota for reference
(white) and impacted (shaded) sites (error bars are +/— 1 standard error). Means

with * are significantly different (P<0.05).

23

Reference Sites

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10 10
Ham Lake Todd Lake
e —- -—- ~ ~«~ 8 ___-___ -—-- m e e 8
,3 __-_____,_,_H_-- e .3 "nun—see» 6
I02 # Q,‘ _ f __ fi_ __ ______,, 4 I02 .‘___ _
To 9 To 7+ ”T’AHT'“ 4
+______,-___ _,___ — 2 ~~~~~~ 6 -v eeeeeeeee 2
i T . 0 ‘ ‘ I .. O
-33 -28 -23 -18 -13 -33 -28 -23 -18 -13
6‘30 (950) 613C (96°)
10 10
Otis Lake Tubbs Lake
l-——~-* -Z- ———f——- 8 ——-~—~———————-————~—~ 8
.3 ”WM"... 6 .3 cufldfim,
:22 ——— ————~+——— —e~4 522 ———————————— «4
IO IO
______A_ e2 +e*—-——eeee 2
+ $ .
l l - ' o . ‘ l O
-33 -28 -23 -18 -13 -33 -28 -23 -18 -13
0‘30 (%0) 6% (960)

Figure 4. SN (91») vs 6130 (%o) for SPOM (shaded diamonds) and bivalves (plus

sign) for reference sites.

24

Impacted Sites

 

 

 

 

 

 

 

 

 

 

10
BrooksLake
——-——— ———-~~- 8
air—*4- -—#"- 6
.02
7° ~~——fir -;— s—s— 4
+w—-<>—-'*— —e— 2
. r 0
-33 -28 -23 -18 -13
613C(%o)
10
RoundLake
i ______.._ _*i ___ 8
sere+~—»e
s=t_e-+-_+_14
l0
——-—0—— — ——~ 2
0

-33 -23 .23 -18 -13
€300»)

Figure 5. o‘5N (960) vs 5% (%o) for SPOM (shaded diamonds) and bivalves (plus

sign) for impacted sites.

25

o"1lnb)

cffiu(%n)

tf5N(am)

Reference Sites

 

Ham Lake

 

 

8
6
» 4
2
0

 

‘1’

-33 -28 -23 -18 -13
tffi:(%s)

 

Leisure Lake

 

 

 

—33 -28 .23 -18 -13
o“k:ckn

 

Otis Lake

 

 

 

-23 -18 -13

tffi3(%o)

-33 -28

DIV-503(1)

10

tVWV(%m)

cffiV(%m)

 

 

 

 

-33 ~28 —23 -18 -13
tffi:(%u)

 

Ttbbs Lake

)...__.. . . t_. 7* f

 

 

 

-33 -28 -23 -18 -13
tffis(%n)

owe-moo

Figure 6. 6‘5N (96o) vs 6130 (%o) of epiphyton from Nuphar spp. stems (shaded

triangles), epiphyton from Nymphea spp. stems (shaded squares), and

gastropods (black circles) for reference sites.

26

tffi1(%m)

o"1lna)

o“fil(xd

Impacted Sites

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10
Brooks Lake
l—e —~ —-— — - 8
__ _.-___...A__ _ _ _ .E 6
El
__7#fi-.#fi#Afl_u4
a—N * A a JP — .. 2
. - 0
-33 -28 -23 -18 -13
tffi3(%m)
10
Hillsview Lake
u_ _ “. F~-__ -L 8
—— v —— v _ # — ~ 6
A
F— .mn' —’ —* ”T 4
— — — — ~— — z- 2
- . 0
-33 -28 -23 -18 -13
tf%3(%s)
10
Mona Lake
- — —— ———— 8
.__ ._O _ 0 cc 6
E
um ._+_ .___ ...... __._. 4
~-—— ~ ~ ——n— 2
O

 

-33 -28 -23 -18 -13

tffi:(%b)

 

Round Lake

 

 

 

33 -28 -23 -18 -13
tf%:(%s)

 

Wintergr.een Lake

 

 

——<

 

ON-hODCD

 

33 -28 .23 -18 -13
effi3(%m)

Figure 7. 615N (%0) vs 613C (%o) of epiphyton from Nuphar spp. stems (shaded

triangles), epiphyton from Nymphea spp. stems (shaded squares), and

gastropods (black circles) for impacted sites.

27

Reference Sites

 

 

 

ee—e*——e~ss—~10 site-”Wis e 10
Ham Lake . Todd Lake
sve~~-~eeemf8 r+e*———w———eei8
Al . Al ‘
g) ~w~e~+~e~Te gre~e—~e~ as
azl_._z___-__,_‘,4 «FL, ‘
To l o — X To l 1313* r ~ — 4
-z__s_____.___,,cl'2 '__.__.-__,_-______.2
. ‘ I o l
L—=—~—————~*0 ,______,vz,__,_ 0
-34 -29 -24 -19 -14 -34 -29 -24 -19 -14
613C (96°) 8‘30 (960)
f ~ ———— ___,,k ~ 10 s v m ——~————-W ~~-— r 10
Leisure Lake I, Tubbs Lake ,
(l’T _ —~i 8 —r~~—- ———— * ~~ 8
l l
£E#—-E—-M+A*~6 £[LAZZZBZZL6
z
$2 -9 A2, + 44 22 l--_ _ - e 4
lo , l to .
_ . l 0 A
r“; r c- j 2 l‘x""""— rs _. 2
l._.,-__,- ——,—~~~e ”r— ~~‘- 0 Leafs—w -— as wee o
-34 -29 -24 -19 -14 -34 -29 -24 -19 -14
6‘30 (96°) 6% (960)

Figure 8. WM (960) vs 6% (%o) of epiphyton from Nuphar spp. stems (shaded

triangles), epiphyton from Nymphea spp. stems (shaded squares), SPOM

(shaded diamonds), amphipods (“X”s), and mayflies (dashes) for reference sites.

28

Impacted Sites

 

 

 

 

 

fa w e—- ~~~———~ ---————-+~ 10 m * *------*—-~--~ ~+ a _ 10
Brooks Lake ‘ , Round Lake
6 i w ____.______, —* ‘i‘ 8 -’m * -*————-- F a T 8
33 (TXA' n 22.. 6 3? LI— -D*X—~ 7* ”I 6
D i V ‘ 1
Z
IO , to .4
Fe-O—fl—ev—A ~- 2 e eeeee eeeu—eem 2
r—‘——*"""" T—F—T—T —'-'—'—“ 0 t--*——-"' ,— _ ,_. __ _____ _, ,_ 0
~34 ~29 ~24 -19 -14 -34 -29 -24 -19 -14
6‘30 (96°) 6‘30 (96o)
—— — —- — . 1O ' ——-*w——-—-— ——- ~ m 10
Hillsview Lake I l Vlfintergreen Lake ,
———-— ——-——~j8 (-——-— ———-8
gififl ‘77fi6 gt _____ wB-’3_..___,6
Z l A j Z ! x l
:90 IF~p—j3-**— 45:0.__c—______..4
| X ,
_Z,-Zfigzt l____ _ ___ _ _l.
_ o x 2 , l 2
5“"""—-i‘ '_“ T—“ '*V "‘_"T— A. 0 “‘“T-T "——_‘ "F “"TT— ”—— T“ “4’ 0
-34 -29 -24 -19 -14 -34 -29 -24 -19 -14
6% (%o) 613cm)

Figure 9. 615N (96o) vs 6130 (%o) of epiphyton from Nuphar spp. stems (shaded

triangles), epiphyton from Nymphea spp. stems (shaded squares), SPOM

(shaded diamonds), amphipods (“X”s), and mayflies (dashes) for reference sites.

29

I
I
I
I
I
I

 

.3
N

A

hmmo
I
I
I
I
I
I
I
I
l

 

 

%o
room
I
I
I

 

 

 

 

 

Sass;
I
I
I
I
I
I

 

Reference Impacted

Figure 10. Mean difference in 6130 (white) and 0‘5N (shaded) between SPOM

and bivalves for reference sites and impacted sites (error bars are +/- 1 standard

error).

30

(a) Epiphyton (Nuphar spp.) and Gastropods

I 2 I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(b) Epiphyton (Nymphea spp.) and Gastropods
r._ ____ _. .2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

; Reference Inpacted I

L __I
Figure 11. Mean difference in 6130 (white) and o‘5N (shaded) between (a)
epiphyton (Nuphar spp.) and gastropods and (b) epiphyton (Nymphea spp.) and

gastropods for reference sites and impacted sites (error bars are +/- 1 standard

error).

31

(a) SPOM and Caenid Mayflies

2

0 I
-4
38 -6

-8
-10
~12

 

 

 

 

Reference lrnpacted

(b) Epiphyton (Nuphar spp.) and Caenid Mayflies

 

 

 

 

 

Reference Impacted

(c) Epiphyton (Nymphea spp.) and Caenid Mayflies

0

4 ~" LB

-2 A

33-3 A f ‘_
.4

 

 

 

 

 

Reference Impacted
Figure 12. Mean difference in 6130 (white) and WM (shaded) between (a)
SPOM and caenid mayflies, (b) epiphyton (Nuphar spp.) and caenid mayflies,
and (c) epiphyton (Nymphea spp.) and caenid mayflies for reference sites and

impacted sites (error bars are +/- 1 standard error).

32

(a) SPOM and Amphipods

5
0 a}- l—f—I_”_l

 

 

 

 

 

33-5 r
I
-10 i

 

 

-15

 

Reference Impacted

(b) Epiphyton (Nuphar spp.) and Amphipods

 

 

 

 

 

 

 

 

O
—~'«~I

 

 

 

I-~"1

 

 

 

Reference tnpacted

(c) Epiphyton (Nymphea spp.) and Amphipods

 

 

 

 

 

 

 

 

 

 

 

Reference lrnpacted
Figure 13. Mean difference in 6130 (white) and 615N (shaded) between (a)
SPOM and amphipods, (b) epiphyton (Nuphar spp.) and amphipods, and (c)

epiphyton (Nymphea spp.) and amphipods for reference sites and impacted sites

(error bars are +/- 1 standard error).

33

 

      

 

 

 

 

4
3
A 2
z 1 r .
52 - ' .
lo . .
0 a) to a) a) of w a) To)
I—s— s a is a a if a a a
_1 x _l _I _I _l _I —I I ..J_ _l .J
3 2 2 s a 2 3 is 2 5
e a 5 ,2 g g E ,g g e
'2 i“ ‘6 I— ‘- é ' s» n: 9
I _J m -- . ‘ o
I E
-3 3r 1‘ E

 

 

 

 

Figure 14. Difference in 615N between SPOM and epiphyton (averaged from
Nuphar spp. and Nymphea spp.) for reference sites (white) and impacted sites

(shaded).

34

I Todd Lake Periphyton

 

Elodea canadensis o
oFPOM
Potamogeton

zosten‘formis

I
I
I a3 Potamogeton illinoensis::
I...2
"to
‘ x ' Nuphar spp.

A Chara spp.

 

 

 

O-KNw-hUICDN

 

Brooks Lake Periphyton

 

+ Potamogeton gramineus

:5
m2 FPOM° A Chara spp. _ _
.10 x Potamogeton zostenfonnrs ‘

Nymphea spp.). X Potamogeton pectinatus

 

O—thhCflON

 

 

613C (%0)

Figure 15. 615N (96o) vs 6130 (%o) for FPOM and periphyton collected off of

different substrates for (a) Todd Lake (reference site) and (b) Brooks Lake

(impacted site).

35

APPENDIX

36

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29 News 33 some $2 98 own 3: 08 one :53 eomoEz .98
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mm mm mm mm mm mm mm mm mw mm
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m mm. u _I w m a. m W W a. W a efl won w W W W 3:300 59:25.
a B on a S 9
m .u.. m u a m m a a m w a a cam cameo;
1 9
3
M4
3

 

 

37

20me 98:3 .muoao-awwm ocm .mo>_m>_n .moE‘flmE Eccco .muanaEm .dam 332:2-53593 :88 85:2
-cotEqu .220me 8:9: 2:890 2832th coucoagm Lo.— ozm zone .8 $29 39 020 new 39 220 .N 83....»

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.8- 8.8- 8.8- 8.8- 8.8- 8.8- 8.8- 8.8- .8.8- 88- 88288 .
88F- 88- 8.8- 5.8- 88- 8.8- 888 .
8.8- 8.8- 8.8- 8.8- 8.8- 8.8- 2.8 8.8- acids. 288 .
No.8- 88- 8.8- 8.8- 8.8- 3.8- 8.8- 88282 .
8.8- 8.8- 8 8- 8.8- 2.8- 8.8- 8.8- 8.8- 8.8- can 8858218383 .
8.8- 3 8- 8.8- 8.8- 8.8- 8.8- 8.8- 8.8- .eamccecszleogeaam .
3.8- 8.8- 8.8- 8.8. 88- 8.8- 8.8. 28- 88- 88. 20cm
39 can see 898. 288.
8.8 88 8.0 8.8 68 8a 8.8 Si :8 c: «.8883 .
8+ 8.8 8e 98 8.8 8a 8295 .
N; 8.8 84 8.8 8., 2.8 8.0 828.2288 .
NS 8.8 8.8 88 o: 8.0 888:2. .
86 8a. Re 8.8 8.... Ed 8.8 98 men 8888-8218883 .
9.8 an X? 8.0 8.8 8.8 3.... 28 c8 cceoazleoxeoam .
o:- 88 8.8 8e 8.8 8e 9: are m: 8.8 20%
is z o 88 828. 288.
M 08 H N8 1 l. 8 81 H
mm uni... m mm WW m w. m w mm m m m m. w m 88 28 cocoo=8 8.8.8..
mm m w .m u m m. m a m s w 1 m m m ..n. m 3.58 8222
a m m m w e M w m e m e p».- m x 1 am 9% 88.82,
c w a a m a a a a m a
an a
a

 

 

 

 

 

 

 

 

 

 

 

 

38

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002.335

 

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8.288.

 

 

 

 

 

 

 

 

 

 

 

002022.:

 

3.8m“: 00:009.... 00005000

 

x

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0mu__.0mcaw

 

3?ch 02.0005 0>_m>_m

 

 

oozewelex
axe-1 UGSJEJQIUIAA

 

UOIUHO
9x91 punoa

 

uofiaxsnw
axe1 euow

 

e1sooew

9X91 M9!’\SII!H

 

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9x21 S)|OO.|8

 

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exe1 sqqni

 

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39

 

Wetland Site
County
*Samples collected in August 2004

 

Todd Lake
Osceola

 

Brooks Lake
Newaygo

 

Stable isotope data of 615N (960) collected from the following substrata:

 

 

 

 

 

 

 

 

 

 

 

I FPOM 5.1 8 3.65
I Chara spp. 1.33 3.51
I Elodea canadensis 6.36
I Nuphar spp. 2.33
I Nymphea spp. 1.79
I Potamogeton gramineus 4.71
I Potamogeton illinoensis 3.86
I Potamogeton pectinatus 1.61
I Potamogeton zosten'formis 2.35 2.89

 

Stable Isotope Data 6130 (960) collected from the following substrata:

 

 

 

 

 

 

 

 

 

 

 

 

I FPOM -21.35 -26.68
I Chara spp. -28.78 -25.17
I Elodea canadensis -14.33
I Nuphar spp. -26.95
I Nymphea spp. -25.29
I Potamogeton gramineus -25.77
I Potamogeton illinoensis -1 1.28
I Potamogeton pectinatus -24.50
I Potamogeton zosten'fonnis -28.74 -26.09

 

Table 4. 615N (%o) and 613C (960) values for epiphyton collected from the

indicated plant substrata and fine particulate organic matter (F POM) from the

sediment surface, where present.

40

 

LITERATURE CITED

4]

Literature Cited

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American Public Health Association (APHA). 1998. Standard methods for the
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Basaguren, A., P. Riafio, and J. Pozo. 2002. Life history patterns and dietary
changes of several caddisfly (Trichoptera) species in a northern Spain
stream. Archiv fur Hydrobiology 155: 23-41.

Benke, Arthur C. and David I. Jacobi. 1994. Production dynamics and resource
utilization of snag-dwelling mayflies in a blackwater river. Ecology 75:
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Bennett, Elena M., Stephen R. Carpenter and Nina F. Caraco. 2001. Human
impact on erodable phophorus and eutrophication: A global perspective.
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Boon, Paul I. and Stuart E. Bunn. 1994. Variations in the stable isotope
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Burkholder, JoAnn M., Robert G. Wetzel, and Karen L. Klomparens. 1990.
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Carpenter, S.R., N.F. Caraco, D.L. Correll, R.W. Howarth, A.N. Sharpley and
V.H. Smith. 1998. Nonpoint pollution of surface waters with phosphorus
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Chessman, Bruce C. 1986. Dietary studies of aquatic insects from two Victorian
rivers. Australian Journal of Marine and Freshwater Research 37: 129-
146.

Cornelison, Christopher D., Stephen R. Wing, Kim L. Clark, M. Hamish Bowman,
Russel D. Frew, and Catriona L. Hurd. 2007. Patters in the 6130 and UN
signature of Ulva pertusa: Interaction between physical gradients and
nutrient source pools. Limnology and Oceanography 52: 820-832.

Crumpton, W. G., T. M. lsenhart, and P. D. Mitchell, 1992. Nitrate and organic N

analyses with second-derivative spectroscopy. Limnology and
Oceanography 37:907-13.

42

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45

   

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