5“... Li!
acid. 5...: .

I
h

- v.22
195's

.3
. m.

In 1’9,
uv-v -:_.
"3:3":

(2.1.3.?
T . z. x;
.

3..
l

f.

){5

v «#3.; 4h»

 

 

 

 

 

ca

#1 ....

 

 

 

 

K3? ,._.

.

3:

,.,.n..lu.

 

. hnhn.)\‘

   
  

 

Iv .t‘i

 

 

 

 

 

W“ lllllllllllllllllllll

A
\_b
“ J
\1
\/

This is to certify that the

thesis entitled

Elemental, Molecular, and Carbon Isotopic Evidence
of Reduced Algal Productivity
and Early Diagenesis in Lake Erie, 1968-1982

presented by

Joel Clemence Henry

has been accepted towards fulfillment
of the requirements for

Master's Geological Sciences

degree in

 

 

‘ - l/flwdfldv

Major professor

 

/7 ..
Y! J; -
Date October 18, 1995 421 41,11,

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

LIBRARY
Michigan State
University

 

l

 

 

PLACE fl RETURN BOX to remove We checkom from your record.

TO AVOID FINES Mum on or More dot. due.

DATE DUE DATE DUE

DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU le An Alfirmetlve Action/Equal Oppodunlly Intuition
W

”39.1

ELEMENTAL, MOLECULAR, AND CARBON ISOTOPIC EVIDENCE OF
REDUCED ALGAL PRODUCTIVITY AND EARLY DIAGENESIS IN
LAKE ERIE, 1968-1982
By

Joel Clemence Henry

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Geological Sciences

1995

ABSTRACT
ELEMENTAL, MOLECULAR, AND CARBON ISOTOPIC EVIDENCE OF
REDUCED ALGAL PRODUCTIVITY AND EARLY DIAGENESIS IN
LAKE ERIE, 1968-1982

By

Joel Clemence Henry

The 5‘3C composition of lacustrine organic sediments typically reflects the «WC
content of the primary sources of organic matter, but may be diagenetically altered.
The 6‘3C content of organic sediments from Lake Erie decreases from -24.9%o to
-25.9%o between 1968 and 1982 (”Pb dating), coincident with reduced historical
phosphorous loadings to the lake. Organic sediments deposited in the eastern basin of
Lake Erie are derived primarily from autochthonous sources, as indicated by low
organic UN, and the persistance of low molecular weight (C “-Czo) n-alkanes. The
absence of correlations between elemental, isotopic, and molecular abundances, and I
the apparent absence of change in the relative contributions from algal and terrestrial
sources, suggests that the shift in (WC is related to neither a change in source or
diagenetic alteration, but to changes in [C02]... as a function of the algal productivity

and trophic state of Lake Erie.

This thesis is dedicated in memory of my father,
Clemence James Henry
1922 - 1991

ACKNOWLEDGEMENTS

First of all, I would like to thank Drs. Nathaniel and Peggy Ostrom, who .
provided the Opportunity for me to return to school and continue my education in the
sciences. As co-advisors for this thesis, they have generously provided the materials,
the laboratory space, and much of the data and editorial assistance necessary to bring
this project to a successful conclusion.

I would also like to thank Dr. Brian Eadie, of NCAA Ann Arbor, for
providing the sediment core analyzed in this study. In addition, I wish to thank Dr.
Philip Meyers of the University of Michigan for assisting with the interpretation of
the sedimentary record, and Dr. David Long for agreeing to serve on my thesis
committee.

To members of the geochemistry lab, including Shawn Clothier, J on Kolak, '
Emily Bell, Tina Balls, Maria Sharp, and Lisa Koch, thank you for working on my
samples, teaching me how to use Freelance, and helping me in numerous other ways.
I wish you the best of success in finshing your degrees here at MSU. I also wish to
remember Kevin Pilichowski, for the help, encouragement, and friend he was to me
during late nights in the lab.

Former and current residents of the Living Rock are thanked for their patience

with me throughout the past two years, and also for their generosity in allowing me

iv

access to word processing software.

I want to thank my parents, Elimbeth Anne Henry and Clemence James
Henry, for providing me a secure environment in which to grow and learn, for giving
me encouragement in all my academic pursuits, and for sacrificing more than I will
ever know. I will do the same for my children.

I wish to thank my wife, Joy, who has seen me through the best and worst of
this thesis, and has still committed her love and her life to me. Through the help of
our Lord, Jesus Christ, I will use my degree, my talents, and earnings to provide for
you and the Henry family.

Finally, I wish to thank God the Father, the Creator of the Great Lakes and all

that is in them, and I look forward to the day when I can meet him face to face.

TABLE OF CONTENTS

LIST OF TABLES .................................................................
LIST OF FIGURES ................................................................
1. INTRODUCTION .............................................................
1.1 Purpose of Study .....................................................
1.2 Lake Erie .............................................................

1.3 Carbon isotopes ......................................................
1.3.1 Photosynthetic fractionation of organic carbon .....
1.3.2 Isotopic fractionation in phytoplankton ...............
1.3.3 Photosynthetic fractionation of inorganic carbon in lakes

1.4 Sedimentary organic matter .......................................
1.4.1 Bulk organic indicators of source and diagenesis ..
1.4.2 Geolipid indicators of source ..........................

1.5 Synopsis ...............................................................
2. METHODS .....................................................................

2.1 Sample collection and preparation ................................
2.2 cm composition and bulk 6‘3C analysis ........................

2.3 Solvent extraction of organic compounds .......................

2.4 Column chromatography ...........................................
2.4.1 Preparation of silica gel and alumina .................
2.4.2 Efficiency of compound class separation as a function
of activation temperature ...............................
2.4.3 Activation of Cu powder ...............................
2.4.4 Chromatographic techniques ...........................

ll
12

13
16
17
20
21
21
21
22
24
26

26
27

2.5 Gas chromatography / Mass spectroscopy ......................

2. 6 Quantification of unresolved complex mixture
and alkanes .......................................................

3. RESULTS OF METHOD DEVELOPMENT ..............................
3.1 Sonication vs. soxhlet extraction ..................................
3.2 Activation of silica gel and alumina ..............................
3. 3 Sample recovery .....................................................
4. EXPERIMENTAL RESULTS ..............................................
4.1 Sedimentation rate and mixed depth .............................
4.2 Removal of elemental sulfur .......................................
4. 3 Elemental abundance ................................................

4.4 Carbon isotopic composition of the bulk organic
sedimentary fraction ..............................................

4.5 Total extractable hydrocarbons ...................................
4. 6 Geolipid compound classes ........................................
4.7 Unresolved complex mixture .....................................
4. 8 Normal and branched alkane abundances ......................
3. DISCUSSION ..................................................................
5.1 Sedimentation rate and mixed depth .............................
5.2 Elemental abundances ...............................................
5 . 3 Carbon isotopic composition of bulk organic sediments .....
5.4 Total extractable hydrocarbons ............. .....................

5.5 Abundance of aliphatic, aromatic, and polar compounds . .. .

28

28
30
30
3 l
32
32
33
34

34

36
36
37
37
37

39

41
43
46

47

5.6 Relative concentration of unresolved complex mixture .......

5.7 Distribution of n-alkanes ...........................................
6. CONCLUSIONS ................................................................
APPENDIX A: TABLES AND FIGURES ....................................
APPENDIX B: ADDITIONAL DATA ........................................

BIBLIOGRAPHY ...................................................................

viii

47

47

49

52

75

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

LIST OF TABLES

Comparison of the efficiencies of sonication and soxhlet
extraction methods .................................................

Comparison of alkane and aromatic separation based on the
activation temperature of silica gel and alumina ............

Percent recovery of n-alkane standards from
silica gel/alumina column chromatography ...................

Age-depth relationship of Lake Erie sediment core as
determimd by 21°Pb dating methods ..........................

Calculation of the precision of percent organic carbon,
percent organic nitrogen, and (WC of bulk organic
sediments using Lake Superior surficial sediment ...........

Calculation of the precision of geolipid extraction by Soxhlet
extraction methods using Lake Huron surficial sediments ..

Appendix Bl . Linear regression used in the quantification of

Appendix B2. Assignments of sedimentary alkanes to linear regressions......

sedimentary n-alkanes ............................................

Appendix B3. Percent organic carbon, percent organic nitrogen, and C/N

of Lake Erie sedimentary organic matter ......................

Appendix B4. 5‘3C values of Lake Erie sedimentary organic matter, in %a

notation relative to PDB ..........................................

Appendix BS. Concentration of unbound organic matter extracted from

Lake Erie sediments in mg/ g dry sediment ..............

52

52

53

54

55

55

75

75

76

78

Appendix B6. Concentration of compound classes in Lake Erie sediment,
in mg/g of dry sediment .........................................

Appendix B7. Relative abundance of unresolved complex mixture in
Lake Erie sediments ...............................................

Appendix BB. Absolute abundances of n-alkanes extracted from Lake Erie
sediments, reported in rig/g of dry sediment .................

Appendix B9. Normalized abundance of n-alkanes extracted from
Lake Erie sediments ...............................................

Appendix B10. Odd/even preference of n-alkanes extracted from
Lake Erie sediments ..............................................

Appendix B11. Short/long index of n-alkanes extracted from
Lake Erie sediments ..............................................

Appendix BIZ. Absolute abundances of pristane and phytane extracted
from Lake Erie sediments ........................................

79

79

80

83

86

88

89

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.
Figure 7.

Figure 8.

Figure 9a.
Figure 9b.

Figure 9c.

Figure 10.

Figure 11a.

LIST OF FIGURES

Inferred bathymetry of Lake Erie .............................

Cross-section of the central and eastern basins of Lake Erie
showing mid-summer thermal stratification .............

Mixed depth and sediment dating inferred from
excess 2mPb ...................................................

Percent organic carbon in sediments from the eastern basin
of Lake Erie ..................................................

Percent organic nitrogen in sediments from the eastern basin
of Lake Erie ..................................................

Organic C/N of Lake Erie sediments .........................
Carbon isotopic composition of Lake Erie sediments ......

Concentration of organic material obtained from Lake Erie
sediment core by Soxhlet extraction using
dichloromethane ..............................................

Concentration of aliphatic material extracted from Lake Erie
sediments .............................................
Concentration of aromatic material extracted from Lake Erie
sediments ......................................................
Concentration of polar material extracted from Lake Erie

sediments ......................................................

Relative abundance of unresolved complex mixture in
Lake Erie sediments .........................................

Absolute abundance of n-alkanes extracted
from Lake Erie sediments, 1981 - 1982 .................

56

57

58

59

59

61

62
62

62

63

Figure 11b.
Figure 11c.

Figure 11d.

Figure 123.
Figure 12b.

Figure 12c.

Figure 12d.

Figure 13a.
Figure 13b.

Figure 13c.

Figure 14.

Figure 15a.

Figure 15b.

Absolute abundance of n-alkanes extracted

from Lake Erie sediments, 1979 - 1980 .................
Absolute abundance of n-alkanes extracted

from Lake Erie sediments, 1978 ..........................
Absolute abundance of n-alkanes extracted

from Lake Erie sediments, 1970 - 1977 .................

Normalized abundance of n-alkanes extracted

from Lake Erie sediments, 1981 - 1982 .................
Normalized abundance of n-alkanes extracted

from Lake Erie sediments, 1979 - 1980 .................
Normalized abundance of n—alkanes extracted

from Lake Erie sediments, 1978 ..........................
Normalized abundance of n-alkanes extracted

from Lake Erie sediments, 1970 - 1977 .................

Odd/even preference exhibited by n-alkanes extracted from
Lake Erie sediments, 1980 - 1982 ........................

Odd/even preference exhibited by n-alkanes extracted from
Lake Erie sediments, 1978 - 1979 ........................

Odd/ even preference exhibited by n-alkanes extracted from
Lake Erie sediments, 1970 - 1977 ........................

Short/long index of n-alkanec extracted from Lake Erie
sediments ......................................................

Absolute abundance of pristane extracted from Lake

Erie sediments ................................................
Absolute abundance of phytane extracted from Lake

Erie sediments ................................................

65

66

67

68
69
70

71

72

72

73

74

74

Introduction
1-1 W

The trophic status of Lake Erie has been a major environmental concern
during the latter half of this century. Excessive anthropogenic loading of phosphorus
has resulted in enhanced algal productivity and the deterioration of water quality in
the lake (Mortimer, 1987), a process known as eutrophication. The eutrophication of
Lake Erie received national attention during the 1960’s when large mats of algae
washed up on beaches to rot, fouling the shoreline of the lake (Bdrns, 1985). Less
spectacular, but more damaging to the lake, was the decomposition of the detrital
remains of the surplus algal biomass on the bottom of the lake. Increased sediment
oxygen demand led to widespread anoxia in the hypolimnion of the central basin
during the annual period of summer stratification (Burns, 1985). Low oxygen 2
concentrations eliminated species of fish and insects, precipitating the "death” of the
world’s largest freshwater fishery (Burns, 1985).

Remedial measures undertaken since the 1970’s have successfully reduced the
phosphorus load to Lake Eric at the cost of large public expenditures (Mortimer,
1987; Fraser, 1987; Rosa, 1987). In response to environmental regulations, the Lake
Erie fishery has since recovered, and the phytoplankton biomass has been significantly
reduced (Makarewicz and Bertram, 1991), yet questions remain regarding the extent
of bottom-water anoxia (Boyce et al. , 1987). Numerical models have been developed
to describe the relationships between nutrient concentrations, productivity, and anoxia,
but the associated mechanisms. are not yet fully understood (Lam and Schertzer,

1987). Definitive evidence of the beneficial effects of phosphorus reduction needs to

l

2
be demonstrated if the high cost of remediation imposed by legislation such as the

Clean Water Act is to be justified.

Organic geochemical studies of the sediments of eutrophic lakes have
previously been used to characterize changes in trophic status (reviewed and
summarized by Meyers and Ishiwatari, 1993a). The carbon isotopic composition‘ of
organic sediments may provide an indication of trophic state, owing to an inverse
relationship between the concentration of aqueous C02 and the (WC composition of
the organic constituents of phytoplankton (Degens et al., 1968; Deuser et al. , 1968;
Stuvier, 1975; Arthur et al., 1985; McCabe, 1985; Dean et al., 1986; O’Leary, 1988;
Freeman and Hayes, 1992; Rau et al., 1992). The detrital remains of phytoplankton
comprise only a small fraction of organic sediments, yet may preserve a time-
integrated geochemical record of the concentration of aqueous C02 in surface waters
(Jasper and Hayes, 1990; Rau et al., 1991, 1992; Meyers and Horie, 1993).
Fluctuations in the concentration of aqueous C02 could in turn serve as a proxy by
which changes in algal productivity may be inferred (Schelske and Hodell, 1991; Rau
et al., 1992; Shemesh et al., 1993). '

Recent evidence suggests that the 613C composition of the bulk organic

 

’ The stable isotopic composition of carbon, denoted 8‘3C, describes the ratio of
13C/ 12C in a sample relative to a given standard. Isotopic compositions of samples are
reported relative to a standard, in per mil notation, in which R = l3C/‘ZC, and

sweet.) = [W -11 x 1000

Carbon isotopic compositions in this study are reported relative to PDB, a Cretaceous
belemnite from the Peedee formation of South Carolina.

3
sedimentary fraction may also reflect the trophic status of lakes (Schelske and Hodell,

1991). Sediment cores recovered from Lake Erie and Lake Ontario exhibit maximum
6‘3C values in organic material deposited during the early 1970’s (Schelske and
Hodell, 1991; Meyers, unpublish. data). This peak is coincident with the period of
maximum historical phosphorus loading to the lakes, suggesting that changes in
trophic status are responsible for the observed isotopic shift.

In addition to the availability of aqueous C02, the 513C of organic sediments
may be affected by diagenetic alteration, and allochthonous sources of organic matter.
Extensive microbial reprocessing of organic compounds leads to the formation of
secondary and tertiary organic products, with the potential alteration of (WC values
(Spiker and Hatcher, 1984; Hayes, 1993; Meyers and Eadie, 1993; Meyers and
Ishiwatari, 1993a). Allochthonous material derived from terrestrial sources tends to
be isotopically lighter than phytoplankton, such that any change in the magnitude of
the relative contributions from aquatic or terrestrial sources would likely affect the
«WC of the organic sediments (Stuvier, 1975; Jasper and Gag'osian, 1989).

The intent of this study is: 1) to present evidence indicating that the recent
change in the (WC of the sedimentary organic matter of Lake Erie may be attributed
to changes in algal productivity, rather than a change in source or degree of
diagenetic activity, and 2) to use the relative abundance of individual hydrocarbons to
develop an understanding of the trophic state of lake Erie. Hydrocarbon distributions
and organic cm are used to characterize the sources Of organic matter contributing to
the lake sediments, and to assess the effects of early diagenesis on lake sediments.

Variations in the isotopic composition of organic sediments are interpreted in the

4
context of inferred sources, diagenetic trends, and the known trophic history of lake

Eric.

1.2 Lakejfie

lake Erie is the fourth largest of the Laurentian Great lakes by area, with a
surface area of 25,300 km2 (Figures 1, 2). The lake averages 70 km in width, and
extends 390 km on a southwest to northeast axis along the border of the United States
and Canada. Due to its relatively shallow depth, lake Eric is the smallest of the
Great lakes in volume (470 km’). Despite its location as the southernmost of the
Great lakes, most of the lake surface freezes in winter. From fall until spring, the
water column is well—mixed from top to bottom. The lake rapidly stratifies in the
spring, and the epilimnion warms rapidly to approximately 23°C (Sly, 1976; Burns, ,
1985).

The lake is typically divided into the western, central, and eastern basins, each
of which exhibit unique physical and limnological characteristics. The Detroit River
flows into the western basin, providing the bulk of the hydrologic input to the lake.
Together with the Maumee River at Toledo, these rivers deliver a large load of
suspended material to the lake. The high nutrient content of riverine inputs has
resulted in the western basin being the most eutrophic of the three. The central basin,
which extends from Pelee Island in the west to Pennsylvania Ridge in the east, is.
noted for the development of bottom-water anoxia during summer stratification (Burns
and Ross, 1972; Burns et al., 1976; Rosa and Burns, 1987). The eastern basin, the

deepest of the three, is shielded from the bottom-water anoxia of the central basin by

5
the Pennsylvania Ridge, an underwater sill at a depth of about 15 m. The deepest

portion of the eastern basin, at a maximum depth of 60 m, acts as a natural sediment
trap where rapid sedimentation has been observed (Mortimer, 1987). Sediments
deposited here preserve an integrated biogeochemical record of inputs and processes
which affect the entire lake (Mortimer, 1987).

lake Erie and its watershed have undergone dramatic change during the past
150 years. The clearance of land for farming and timber greatly increased the degree
of soil erosion. The discovery of coal and iron in the Great lakes basin, coupled
with the industrial revolution, made the Great lakes a suitable location for industry
(Burns, 1985). The cities of Detroit, Cleveland, Toledo, and Erie thrived on the
commerce and transportation that the Great lakes provided. The watershed of lake
Eric is presently home to approximately 13 million people. Detailed synopses of- the
geology, climate, and anthropogenic changes in the lake Erie basin are available in
the literature (e.g. Sly, 1976; Burns, 1985).

Anthropogenic enrichment of phosphate and nitrate prior to 1970 led to the
eutrophication of lake Erie. Eutrophication began with the clearing of forests in the
early 1800’s, which increased the amount of terrestrial runoff into the lake (Burns,
1985). Nutrient loadings increased steadily with population growth until 1945, when
the increase became exponential owing to the replacement of soap by phosphate
detergents, and the widespread use of nitrogen and phosphate fertilizers (Burns,
1985).

Geochemical and biological changes in lake Erie associated with

eutrophication have been the sirbject of extensive investigations, the results of which

6
are summarized in numerous reviews (Beeton, 1969; Kemp et al., 1972; Burns and

Ross, 1972; Dobson et al., 1974; Kemp et al., 1976; Mortimer, 1987; El-Shaarawi,
1987). Productivity of phytoplankton increased dramatically as a result of
eutrophication, and the species composition of the lake shifted to include several
nuisance and eutrophic species of phytoplankton (Auer and Canale, 1982; Burns,
1985; Makarewicz, 1987). The populations of fish and other fauna decreased 2
dramatically, due to the increased sediment oxygen demand associated with the
degradation of the excess algal biomass (Makarewicz and Bertram, 1991). Depletion
of oxygen from the bottom waters of the central basin during summer stratification
imposed anoxic conditions throughout the hypolimnion (Burns and Ross, 1972).
Anthropogenic loading of soluble, reactive forms of phosphorus has been
identified as the primary cause of the eutrophication of lake Erie (Burns et al. ,
1976). The Great lakes Water Quality Agreement (1972) between the United States
and Canada set target levels for the reduction of tributary phosphorus loadings, with
the primary goal being the reduction of bottom water anoxia within the central basin
(Boyce et al. , 1987). This resulted in significant declines in phosphorus loadings to
lake Erie through tertiary treatment of effluent phosphorus, construction of new
sewage treatment facilities, and limitations on detergent phosphorus (Boyce et al. ,
1987; Rosa, 1987; Fraser, 1987; Makarewicz and Bertram, 1991). The effectiveness
of these abatement programs is demonstrated by an 80 % decrease in phosphorus
delivered to the lake by the Detroit River (Fraser, 1987). Improvements in the lake
Erie fishery, and reduction of total chlorophyll concentrations, indicate a positive

response to phosphorus abatement (Makarewicz, 1987; Makarewicz and Bertram,

7
1991). Extensive modelling has been performed to describe the ecology of lake Erie,

linking the nutrient supply, the dynamics of water mass mixing, sediment/water
exchange processes, and consumers such as zebra mussels with the effects of
eutrophication (Burns et al., 1976; DiToro, et al., 1987; Lam et al., 1987; lam and

Schertzer, 1987; Wu and Culver, 1991; Nicholls and Hopkins, 1993).

1.3 W

Carbon has two stable isotopes, consisting of approximately 98.9% ‘2C, and
1.1% 13C. Kinetic and equilibrium isotope effects produce variations in the .
distribution of carbon isotopes among reservoirs of organic and inorganic materials.
The distribution of carbon isotopes in atmospheric C0,, photosynthetic production, '
and organic and inorganic sediments has been useful for providing insight into the
flux and cycling of carbon between these reservoirs (McKenzie, 1986; Ostrom, 1989;
Hayes, 1993).

Variation in the relative abundance of 13C to 12C is a consequence of isotopic
discrimination, or fractionation. The slight difference in the mass of the isotopes
results in different vibrational frequencies (equilibrium effects) or reaction rates
(kinetic effects) for isotopieally distinct molecules of the snare compound (McKenzie,
1986). A given molecule containing 13C has a lower vibrational frequency and lower
zero-point energy than the same molecule containing 12C. Bonds formed by the
heavier isotope are therefore stronger and less reactive. At a given kinetic energy,
isotopically heavier molecules such as ”CO; will tend to diffuse more slowly than

”C0,, and tend to be slightly less available for reaction (Fame, 1986).

8
Isotopic fractionation may occur during diffusion, dissolution, phase change,

and a variety of other kinetic and equilibrium reactions (Freeman and Hayes, 1992;
Hayes, 1993). Fractionation factors, abbreviated as a, may be calculated for
equilibrium reactions as a = RJR,” or a = K‘ZC/K‘3C for kinetic reactions, where.
R = 13C/“C, a is the initial state or substrate, b is the final state or product, and K is
the rate of reaction. Fractionation is may be expressed in %n notation as the
difference between the isotopic composition of the substrate and the product molecules
in a given reaction, where A = 5‘3C, - 6”C,,, or occasionally as

e = (a-1)*1000,wheree s A.

Isotopic compositions of samples are determined through the use of stable
isotope ratio mass spectrometers, which determine the relative abundance of isotopes
to six decimal places (atom percent). The linkage of an isotope ratio mass
spectrometer with a gas chromatograph (GC-irMS) permits the isotopic analysis of .
individual organic compounds (Matthews and Hayes, 1978; Hayes et al. , 1990; Ricci
et al., 1994; Bakel et al., 1994).

1.3.1 Phnmmmmfiacfimnnmsanimm

Kinetic and equilibrium isotopic fractionations accouru for the depletion of “C
in photosynthetically produced organic matter relative to PDB (O’Leary, 1988).
Atmospheric CD; has a 5'3C value (If approximately -8%o, due to the equilibrium
fractionation associated with the dissolution and hydration of CO, in water (Fogel,
1993). The isotopic composition of atmospheric CO2 is becoming increasingly lighter

due to the combustion of isotopically light (approximately -30%o) fossil fuels

9
(O’Leary, 1988; Keeling et al., 1989). Diffusion of CO, through air or water,

transport of C02 through cell membranes, and carboxylation of various enzymes all
demonstrate significant kinetic isotope effects, resulting in discrimination against the
heavier isotope. ‘

In complex biochemical processes such as photosynthesis, the overall degree of
isotopic fractionation is not the sum of the fractionations associated with individual
steps, but rather is primarily a function of the fractiomtion associated with the rate-'
limiting step (O’Leary, 1988). This principle is illustrated by a comparison of the
isotopic fractionation and carbon isotopic composition of C, and C, plants. These two
plant types differ in the sequence of carboxylation steps leading to the assimilation of
C02. Plants using the C, (Calvin-Benson) mechanism produce compounds depleted in
”C by -24 to -34%o relative to PDB, whereas plants using the C, (Hatch-Slack)
mechanism produce compounds depleted by only -10 to -20%o (O’Leary, 1988). The
C3 uptake mechanism concludes with the carboxylation of ribulose bisphosphate '
(RuBP), which fractionates earbon by up to -29%o (Roeske and O’Leary, 1984). The
C, mechanism similarly utilizes RuBP for the final step in its carboxylation sequence,
but a previous step involves the carboxylation of phosphoenolpyruvate (PEP). The
carboxylation of PEP, which fractionates carbon by approximately -8 to -12%o, is the
rate-limiting step of the carboxylation sequence for C, plants (O’Leary, 1988; Meyers
and Ishiwatari, 1993a). Nearly all inorganic carbon, regardless of isotopic mass, will
be incorporated into organic matter once it passes this threshold step. The isotopic
fractionation of C, plants is generally less than that of C, plants because the smaller

kinetic fractionation of PEP is expressed rather than that of RuBP.

10

The isotopic composition of primary productivity is determined not only by the
isotopic fractionation associated with carboxylation of enzymes, but also may be
affected by the (WC of the inorganic carbon assimilated, and the isotopic fractionation
associated with the diffusion of CO, through the cell membrane. The diffusion of
C02 through the cell membrane becomes the rate-limiting step to production if the
rate of enzymatic carboxylation exceeds the net rate of transport of C0, into the cell,
depleting the internal supply of C02. Again, the expressed isotopic fractionation
primarily reflects the fractionation associated with the rate-limiting step, but in cases
where two reactions in a series may be rate-limiting, the expressed fractionation
describes the extent to which the reactions jointly share the rate-limiting role.
Isotopic fractionation associated with diffusion is much smaller than that of either
enzymatic carboxylation, such that an increase in the (WC of photosynthetic
production may be interpreted as the increased importance of diffusion as the rate-
limiting step (O’Leary, 1988).

The concentration of dissolved C02 within a cell is a function of the rate of
diffusion of C02 into the cell, the rate of leakage of CO, out of the cell, and the rate
of assimilation of CO, into the biomass (Fogel and Cifuentes, 1993; Hayes, 1993).
Low levels of CO, external to .the cell result in a reduced rate of diffusion of
dissolved CO2 into the cell, which limits the rate at which CO; is assimilated and
reduces the degree of isotopic discrimination. The degree to which the availability of
CO, is rate limiting in plants has been mathematically modelled by Farquhar et al.,
(1982), and Hayes (1993) as

6'3C,,,,, = 6%,, + a + (b - a)(C ,/C,) (eq. 1)

11
where b is the fractionation attributed to carboxylation of the enzyme, and a is the

small fractionation (-4.4 %o) associated with the transport of C0, across the cell
membrane. The term C.IC,, where C, and C, are the respective internal and external
concentrations of C0,, describes the flux of C0, into and out of the cell, and
incorporates both the availability and the rate of diffusion of C0,. If C0, is
abundant, C, = C,, and the carboxylation fractionation (b) is fully expressed. lf CO,
becomes depleted, the rate of carboxylation may exceed the rate of diffusion, such
that any internal CO, is utilized regardless of isotopic mass. As C,/ C, approaches
zero, photosynthetic fractionation approaches the fractionation associated with

diffusion (Fogel and Cifuentes, 1993).

1.3.2. lsntoniciractinnaticnjnnhxtcnlanktcn
The depletion of C0, becomes particularly pronounced in aquatic systems, in.

which the concentration of aqueous C0,, and subsequently the WC of phytoplankton,
fluctuates based on biological demand and solubility of C0, (Stuvier, 1975 ; Fontugne
and Duplessy, 1978; Rau et al., 1989; Hollander and McKenzie, 1991; Ho and
Meyers, 1994). In aquatic production, full enzymatic fractionation becomes partially
reduced by the degree to which the availability of CO, limits the rate of reaction.
During periods of high productivity, aqueous C0, may become depleted, resulting in
increased, or less negative 5‘3C values. Enhanced C0, demand in eutrophic lakes
might, therefore, be recorded in the phytoplankton community of the lake, and their
sedimentary molecular remains. The degree of photosynthetic fractionation and its '

relation to aqueous C0, has been useful in the reconstruction of paleo-pCO, levels

12.
(Jasper and Hayes, 1990; Rau et al., 1991; Freeman and Hayes, 1992). The

expectation that changes in trophic status may be preserved in the isotopic
composition of organic sediments may be inferred from the results of such studies.
Recent evidence suggests that growth rates of phytoplankton may provide an
improved predictor of algal 69C values (Fry and Wainwright, 1991; laws, 1995).
The 6'3C of phytoplankton has also been related to the species composition of the
phytoplankton biomass, climate, the active transport and assimilation of dissolved CO,
and HC03', and other factors (Stuvier, 1975; Gearing et al., 1984; Descolas-Gros and
Fontugne, 1990; Takahashi et al., 1990; Falkowski, 1991; Fogel and Cifuentes, 1993;
Goericke et al. , 1994). Future research may further establish relationships between
these parameters and the availability of aqueous C0,, or describe and discriminate

between the causes of isotopic fractionation in phytoplankton.

 

Preferential assimilation of 12C into the organic constituents of phytoplankton
increasingly enriches the remaining pool of aqueous C0, in the heavier isotope. The
6‘3C of photosynthetically produced organic matter will therefore increase not only
because of reduced photosynthetic fractionation, but also because of the reduced
availability of the lighter isotope (Deuser, 1970; McKenzie, 1986; Shemesh et al. ,
1993). The isotopic composition of the inorganic pool is reflected in the isotopic
composition of carbonate precipitates. Changes in the WC of carbonate precipitates
have previously been used to provide an indication of productivity in lacustrine

environments (Schelske and Hodell, 1991; Hollander and McKenzie, 1991).

13
Calcium carbonate is formed in the epilimnion of lab as microbial tests of

microorganisms, and as a biogenically induced precipitate. As C0, is depleted from
the epilimnion through uptake by photosynthesizers, disequilibrium occurs in the
bicarbonate-carbonate buffer system. As pH rises, CaCO, is precipitated, often
nucleating on algae (Stabel, 1986). Carbonate sediments are basically in isotopic
equilibrium with the inorganic carbon from which they are formed (McKenzie, 1986),
but a -8 %o fractionation accompanies the equilibrium between C0, and HC03'. The
exact magnitude of fractionation is dependent upon temperature, and whether calcite
or aragonite is precipitated (Hayes, 1993). The isotopic composition of the inorganic
carbon source nonetheless may be approximated from the WC of the carbonate
sediments (Jasper and Hayes, 1990; Shemesh et al. , 1993), therefore changes in the
(WC of the carbonate sediments reflect the «WC of the dissolved C0, utilized by
phytoplankton.

Calcium carbonate tends to precipitate in temperate lakes in summer, rather
than during the spring bloom when the bulk of the algal matter is precipitated (Lean
et al., 1987; Schelske and Hodell, 1991). In such cases, the springtime 6‘3C of the
dissolved CO, carbon source might not necessarily be reflected in summer carbonate
precipitates, and the exact magnitude of photosynthetic fractionation may not be

accurately calculated.

1.4 W

Sedimentary organic matter consists of a complex mixture of lipids,

carbohydrates, proteins, and other biochemicals which represent the detritus of biota

14
formerly living in the lake and its watershed (Leenheer et al. , 1984; Ho and Meyers,

1993; Meyers and Ishiwatari, 1993b). The type and amount of sedimentary organic
compounds is a function of the sources of organic matter in the lacustrine
environment, and the diagenetic processes affecting its fate. Organic matter deposited
in sedimentary layers forms a geological record of these sources and processes.
Variations in the distribution of compounds contained in these sediments may be
interpreted as changes in the community structure of the lacustrine environment
(Cranwell, 1973; Meyers and Ishiwatari, 1993a).

Terrestrial higher plants and autochthonous phytoplankton comprise the
primary sources of organic matter to lakes (Meyers and Ishiwatari, 1993a). The
relative proportion of these sources at a given location varies with respect to lake
morphology, watershed topography, and the relative abundance of terrestrial and
aquatic plants (Meyers and Ishiwatari, 1993a). Secondary sources of organic matter.
include the microbial biomass, and airborne particles such as pollen (Meyers and
Ishiwatari, 1993a). Recent sediments are frequently characterized by petroleum-
related compounds, such that anthropogenic sources constitute a small but important
source of organic matter (Wakeham and Carpenter, 1976; Giger et al., 1980).

Only a fraction of the organic matter deposited or produced in lakes survives
diagenetic alteration to become preserved in the sediments (Eadie et al., 1984).
Water-soluble components of primary producers are easily remineralized by bacteria
in the epilimnion, greatly reducing the total amount of organic material present
(Vallentyne, 1962; Eadie et al., 1984; Meyers and Ishiwatari, 1993b). Hydrophobic

compounds tend to remain or become associated with sinking particles, where they

15

are subject to further alteration en route to me sediment-water interface (Parrish et
al., 1992; Meyers and Eadie, 1993; Wakeham and Lee, 1993). Once deposited,
physical processes such as bioturbation and resuspension continually reexpose the
organic matter to microbial reworking (Leenheer et al. , 1984). Below the oxic/anoxic
boundary, anaerobic bacteria continue the decomposition process (Meyers and
Ishiwatari, 1993a).

The collection of processes affecting the fate of organic compounds during
deposition, burial, and low temperature sedimentation is known as diagenesis. The
degree of diagenetic alteration in a lacustrim environment is a function of the oxicity
of the sediment, the degree of bioturbation, the microbial community, and the rate of
deposition of sinking particles (Leenheer et al. , 1984). The rate of diagenetic
alteration of organic matter is compound-specific, as easily oxidizable substituent
groups are preferentially degraded. As a result, less reactive compounds become
dominant in sediments, and more reactive compounds are preferentially reutilized and
renrineralized (Meyers and Ishiwatari, 1993a; deLeeuw and largeau, 1993). Relative
to compounds from aquatic sources, terrestrially—derived compounds are generally I
more resistant to diagenetic alteration, and subsequently the ratio of terrestrial to
aquatic compounds increases with depth in mdiments (Cranwell, 1984; Meyers and
Ishiwatari, 1993a).

Molecules which resist alteration, and are derived from known biological
origins, are referred to as biological markers, or more commonly, biomarkers (Peters
and Moldowan, 1993). These compounds assist in the identification of source

organisms, the reconstruction of paleoenvironmental conditions, and the subsequent

16
diagenetic and thermal history of sediments (Summons, 1993). Lipids as a group tend

to be more resistant to alteration relative to carbohydrates and proteins, and thus have

found particular utility in paleolimnological studies (Kemp and Johnston, 1979).

1.4.1

 

Elemental abundances have been widely used as indicators of source and
diagenesis. The relative contributions of terrestrial and aquatic sources of
sedimentary organic matter may be discermd using the ratio of organic carbon to
organic nitrogen. Phytoplankton are high in nitrogen rich proteins, while lacking
cellulose. Consequently the organic cm of phytoplankton typieally ranges between
about 4 and 10 (Muller, 1977; Ostrom, 1989; Meyers and Ishiwatari, 1993a).
Terrestrial plants have a higher cellulose and lower protein content, and therefore
C/N ranges between 14 and 30, to as high as 100 (Godell, 1972; Ostrom, 1989;
Meyers and Ishiwatari, 1993b). Fluctuaties in C/N may be indicative of changes in
the relative contributions from these sources (Ho and Meyers, 1994). An increase in
the C/N with depth is generally indicative of preferential diagenetic loss of aquatic,
nitrogen rich compounds (Muller, 1977; Macko et al., 1993)

The isotopic composition of organic carbon may also be used to provide
information regarding the various sources of organic matter. Terrestrially-derived .
organic matter tends to be isotopically lighter than aquatic production, although the
range of values for these two reservoirs varies widely (Meyers and Benson, 1988;
O’Leary, 1988). Consequently, variation in the WC of sedimentary organic matter

may indicate a change in the relative contributions from terrestrial and aquatic

17
sources, or a change in the WC of the terrestrial or aquatic organic material. An

increase in the WC of terrestrial compounds may be related to an increase of C,
relative to C3 vegetation in the watershed (Sackett et al. , 1986; Bourbonniere et al. , i
1991).

In some sedimentary environments, diagenetic alteration affects the WC of
organic matter. The 5‘30 of the organic sediments may become increasingly heavier
during reprocessing, as isotopically light CO, and CH, is preferentially respired by
microorganisms (Hayes, 1993). Preferential preservation of less reactive compound
classes could also affect 8‘3C values, as the WC of compounds which comprise
sedimentary organic matter varies widely (Spiker and Hatcher, 1984). In lacustrine
sedimentary environments with low organic carbon content, however, the 513C of
organic sediments does not seem to be significantly affected by diagenesis, as most of
the alteration occurs during deposition (Rea et al., 1980; Meyers and Eadie, 1993;

Meyers and Horie, 1993).

1.4.2. WW

Geolipids are operationally defined as the fraction of organic sediments which
may be isolated by extraction from sediments using an organic solvent (Meyers and
Ishiwatari, 1993a). The low susceptibility of lipids to diagenetic alteration has led to
their utilization in a wide range of geochemical studies (Leenheer et al. , 1984;
Meyers and Eadie, 1993; Meyers and Ishiwatari, 1993a). The lipid fraction in
sediments is comprised of a mixture of hydrocarbons including alkanes, alkenes,

aromatics, alcohols, steroids, esters, aldehydes, ketones, fatty acids, and carotenoids

18
(Cranwell, 1982). These compound classes may be partitioned using one of several

methodologies outlined in the literature (e. g. Cranwell, 1978; Leenheer et al. , 1984).
Chromatographic separation of these compound classes, and quantification of
individual members of homologous series, has led to the development of several
quantitative indexes that may be used to describe the relative magnitude of terrestrial
and aquatic sources. Carbon-chain length distribution patterns and odd-even ratios Of
n—alkanes, n-alcohols, and n-alkanoic acids assist in the assessment of terrestrial,
aquatic, microbial, and petroleum sources (Cranwell, I982; Colombo et al. , 1989).

The n—alkane homologous series has found particular utility in sediment studies
due to its persistance, abundance, and ubiquity. Distributions of n-alkanes have been .
reported in marine (Kvenvolden et al., 1987; Sandstrom, 1988), lacustrine (Brooks et
al., 1976; Ishiwatari et al., 1980; Meyers et al., 1984; Albaiges et al., 1984),
polluted (Wakeham and Carpenter, 1976; Ishiwatari et al., 1994), and pristine (Ho
and Meyers, 1994) sediments.- Distributions of n-alkanes in the biota and sediments
of eutrophic lakes have also been reported (Reed, 1977; Giger et al., 1980). Decay.
rates of n-alkanes during sedimentation have been investigated, describing patterns of
early diagenetic activity (Parrish et al. , 1992; Meyers and Eadie, 1993). Sedimentary
n-alkanes have also been a common subject of compound-specific isotopic analysis
(Kennicutt and Brooks, 1990; Bakel et al., 1994; Collister et al., 1994; Ishiwatari et
al., 1994; Lichtfouse et al., 1994; Spooner et al. 1994).

Several n-alkane indexes have been employed to quantitatively describe sources
of organic matter, and to assess diagenetic alteration (Columbo et al. , 1989). The

short/ long index (eq. 2) describes the relative contributions from terrestrial and

19
aquatic sources, and the preferential preservation of terrestrially-derived organic
matter (Ho and Meyers, 1994). In general, short-chain n-alkanes, primarily n-C,,
nC,-, + nC,, + nC3,

Short! long index = (eq. 2)
DC” + “C" + DC”

 

through n-C,o, are considered to be derived primarily from aquatic production (Clark
and Blumer, 1967; Han and Calvin, 1969; Gelpi et al., 1970). Long-chain n—alkanes
(C25'C35) are produced as terrestrial plant waxes (Eglinton and Hamilton, 1967;
Cranwell, 1973). Compound-specific isotopic analysis has recently called some of -
these generalizations into question, however (Collister et al., 1994a; Lichtfouse et al. ,
1994; Spooner et al., 1994).

The presence of petroleum contamination in sediments, and patterns of
diagenetic alteration, may be described by the odd-even preference (Eq. 3; Ho and
Meyers, 1994). A predominance of odd-carbon number chains is indicative of
naturally produced compounds (Kvenvolden et al. , 1987), whereas low or no
predominance indicates increasing petroleum contamination, or diagenetic alteration
(Colombo et al. , 1989; Ho and Meyers, 1994). The dominance of even-numbered n-
alkanes has been observed in a few sediments, and is thought to indicate microbial
activity (Nishimura and Baker, 1986; Grimalt and Albaiges, 1987; Kennicutt and
Brooks, 1990).

C,2 + 6C, + CH,

013p, =.- . (eq. 3)

 

Compound-specific stable isotopic amlysis of n-alkanes has proved useful in

20
sediment studies by providing further infmmation regarding the mechanisms by which

organic compounds are formed. The isotopic composition of terrestrial n-alkanes are
significantly different from that of n-alkams produced by phytoplankton, based on the
limited supply of CO, in aquatic environmrts (Freeman et al., 1994). Studies have
combined lipid distributions and isotopic analysis to describe terrestrial (Bailey et al. ,
1991; Spooner et al., 1994; Collister et al., 1994a), aquatic (Bakel et al., 1994;
Freeman et al., 1994), microbial (Hayes et al., 1990; Collister et al., 1994b), and

petroleum (Ishiwatari et al. , 1994) origins of sedimentary organic matter.

15 Sim-iii
The cultural eutrophication and subsequent remediation of lake Erie offers an

opportunity to gain a better insight into the interpretation of sedimentary records. A
fraction of the organic compounds produced in Lake Erie and its watershed are
deposited and preserved in its sediments. These organic sediments exhibit maximum
BBC values coincident with the maximum loading of phosphorus to Lake Erie,
suggesting that phytoplankton are the primary source of organic matter in the lake,
and that the «WC of these phytoplankton is related to changes in productivity.

The 6‘3C of the organic sediments may also be attributed to changes in the
sources of organic matter contributing to the lacustrine environment. Sources of
organic matter are assessed using the ratio of organic carbon to organic nitrogen,
geolipid abundances, and various n-alkane distribution indexes. Source changes are
distinguished from diagenetic alterations through the careful interpretation of .

geochemical data. Compound-specific isotopic analysis may be used to provide

21
further evidence linking the «WC of the sediments with productivity-induced changes

in the WC of phytoplankton. Using elemental abundances, compound-class fractions,
and n-alkane distributions, variations in the WC of the organic sediments may be

assessed with regard to recent changes in the trophic history of lake Erie.

Methods

2.1. WW
A box core with a depth of 40 cm was collected from the Eastern basin of

lake Erie in 1982, and sectioned at 1 cm intervals for the top 20 cm, and at 5 cm
intervals for the lower 20 cm for this study. Sediment samples were stored wet, but
frozen, in glass containers for 12 years prior to analysis. In preparation for analysis,
wet sediment samples were freeze-dried for 48 hrs in the original glass containers.
Each sample contained approximately 10 g dry sediment. Samples were ground to a
uniform grain size using a metal spatula. Dried sediments were stored in a freezer to
discourage the readsorption of water and to retard microbial activity.

Sediments were made available for this study courtesy of Dr. Brian Eadie,
NOAA Ann Arbor. Approximate ages were calculated using 210Pb dating techniques

by John Robbins of the Great lakes Environmental Research lab.

2.2 W
In preparation for elemental and isotopic analysis, inorganic carbon was

removed by acidification. Approximately 500 mg of freeze-dried sediment was

22
acidified using 2N HCl to remove carbonate, dried at 45°C, and ground into a fine

powder using a metal spatula. Approximately 15 mg of each acidified sample was
weighed into an 8 x 5 mm aluminum cup (Microanalysis). Organic carbon and
organic nitrogen percent compositions were determined by combustion within a Carlo
Erba 1500 elemental analyzer, where the gas abundance was quantified using a ‘
calibrated standard. The 613C composition of the bulk sediment samples was
determined using a Prism stable isotope mass spectrometer (VG lsotech) interfaced ,

with the Carlo Frba elemental analyzer, following the method of Wong et al. (1992).

2.3 W
Unbound hydrocarbons were removed from the sediment matrix by solvent

extraction methods. Soxhlet and sonieation extraction procedures were compared in
this study to assess the efficiency of extraction of organic matter from the sediment
matrix. Quartz distilled dichloromethane (Sigma, HPLC grade) was used for the
extraction of non-polar and polar compounds in both methodologies.

Sonication utilizes high—energy ultra-sonic waves to break up the sediment
matrix and expose particles to the extracting solvent. A Vibracell (Sonics and
Materials, Inc.) equipped with a microtip was used for this extraction. Approximately
3 g of sediment and 20 mL of dichloromethane (DCM) were placed in a 100 mL
round-bottom flask. The sample was sonieated in a pulsed mode for 5 minutes
(P. Meyers, pers. commumnication). After sonication, the entire contents of the flask
was transferred to a centrifuge tube and spun for 12 minutes to separate the solvent

from the sediment. An IEC Clinical Centrifuge, with a maximum speed of 4450 rpm

23
when equipped with a fixed angle rotor, was used for centrifugation. The solvent and

organic extract was pipetted off the top into a 50 mL round bottom flask.
Rotoevaporation was used to reduce the volume of solvent to approximately 2 mL.
The concentrated solvent was transferred to a small vial and dried under a stream of
filtered air.

Soxhlet extraction combines evaporation and condensation in a semi-enclosed
system to continuously rinse powdered sediments in clean, hot solvent. A volatile
solvent is heated in a round-bottom solvent flask at the base of the apparatus. Solvent
vapors are directed through a sidearm, bypassing the extraction vessel in which the
sediment sample is contained. The hot vapors are condensed above the extraction
vessel, and dripped onto the sediment. The sediment sample is held in a porous
cellulose extraction thimble (25 x 80 mm) through which solvent may flow but
sediment particles are retained. When the level of solvent in the extraction vessel
reaches the level of a sidearm siphon, the solvent and extracted organic matter are
drained to the solvent flask. Organic extracts become concentrated in the solvent
flask while the solvent continues through repeated cycles of evaporation and
condensation.

Extraction tlrimbles were precleaned with DCM in the extraction apparatus for
4 hours. In the comparison study of soxhlet and sonication extraction procedures,
approximately 4 g of lake Huron sediment was placed in the thimble (8 g of each '
sample was used for the extraction of the lake Erie sediments). A total volume of
approximately 80 mL of DCM was used in the extraction. The thimble and sediment

were moistened with DCM to reduce splashing of the sediment out of the thimble and

24
into the solvent flask. The remaining DCM was placed in the solvent flask. Clean

glass beads (Soxhlet extracted for 4 hrs in DCM) were added to the solvent flask to
reduce bumping. Sediments were extracted for 7 hours. Following extraction, DCM
was removed by rotovaporation until a residual volume of about 2 mL was obtained.
The residual 2 mL of solvent and organic extract was dried under a stream of filtered
air.

Significantly higher extraction efficiency, combined with minimal sample
handling, led to the selection of soxhlet extraction as the chosen method (see Section

3.1 for a comparison of the results).

2.4 W
Separation of organic compound classes was performed by silica gel/alumina

column chromatography using a methodology similar to that of Bakel et al. (1994). ,
This method does not result in isotopic fractionation of n-alkanes during separation
(Bakel et al., 1994). Hydrocarbons were adsorbed onto silica gel (J .T. Baker, 60-200
mesh) while polar compounds were retained by alumina (Alltech, 60-200 mesh).
Three compound classes were isolated from each of 11 samples through the elution
with solvents of increasing polarity. Aliphatic compounds, including straight chain,
branched, and cyclic alkanes and alkenes, were eluted with 15 mL n-hexane, and
aromatic compounds were eluted with 15 mL of a 2:1 hexane/DCM solution. A
column wash of 15 mL of methanol eluted the remaining polar compounds. The flow
rate for all solvents was 0.5 mL per minute. Acidic compounds such as carboxylic

acids were irreversibly retained on the column.

 

During initial tests of the extraction methodology for polar compounds, it was
discovered that columns which were not loaded with the extracted organic material
(blanks) often eluted a greater abundance of polar material than columns which had
been loaded with the organic extract. The origin of this polar material is presumably
due to the colloidal suspension of polar silica and alumina particles into the methanol.
Filtration of silica gel suspended in methanol revealed that particles smaller than I
0.45 pm became suspended in methanol and could be easily transferred to the
weighing vial and included in the quantification of the polar fraction. Consequently
both the silica gel and alumina were thoroughly cleaned with a methanol (Omnisolve,
J. T. Baker) slurry in an attempt to remove fine grained particles. Methanol
containing the dissolved particles was decanted and recycled, and replaced with clean
methanol. This procedure was repeated 15 times for each resin.

After the silica gel and alumina were dried, the resins were placed into clean
scintillation vials, plugged with ashed glass wool, and set in an aluminum foil covered
beaker inside the GC oven. Siliea gel and alumina were deactivated during the
methanol rinse, and had to be reactivated at high temperature to restore its ability to
separate molecules on the basis of polarity. Silica gel and alumina used for the
separation of lake Erie sediments were reactivated at 305°C in a GC oven. To
minimize the readsorption of water, neither the silica gel nor alumina were removed

from the GC oven until the columns were ready to be filled.

26

2.4.2 - i f cumund rec. n n -.; i l n tin . .. -' ... - I a- Li. -
Silica gel and alumina resins were acn'vated at 100°C, and at 305°C, to
determine the effects of activation temperature on chromatographic separation of
compound classes. Two chromatographic columns were constructed, from resins
activated at 100°C, and from resins activated at 305°C. A standard solution of three
alkanes and one aromatic compound was separated on these columns. The standard
solution contained between 5 to 10 pmol each of C1,, Cm pristane, and phenanthrene.
Phenanthrene is a non-polar tricyclic aromatic compound which closely approximates
the weight and retention time of the alkanes used in this experiment. Alkanes were
eluted from the columns using n-hexane. At 5 mL intervals, 1 llL of n-hexane eluent
was sampled and injected into a GC/MS to test for the presence of phenanthrene in
the eluent. The simultaneous elution of phenanthrene and alkanes from the column .
activated at 100°C indicates that the activation of silica gel and alumina at 305°C
provided more efficient separation between aliphatic and aromatic compounds than

resins activated at 100°C (see Section 3.2 of results).

2.4-3 mm
A thin layer of activated purified Cu powder (Fisher) on the silica gel/alumina

column was required for the removal of elemental sulfur. Within a few hours of use,
approximately 4 g of Cu powder was activated by rinsing with 3N HCl for a few
nrinutes. Excess HCl was decanted, and the Cu was rinsed three times with 20 mL
Omnisolve methanol. Excess methanol was decanted, and the Cu dried by warnring

the beaker in water, and continually stirring the Cu paste until dry. Careful attention

27
was necessary to avoid oxidation of the Cu powder as a consequence of drying the Cu

too slowly. If the Cu is oxidized, it cannot be reactivated by the same method.

2.4.4 WWW
Columns consisted of 25 mL glass burets fitted with teflon stopcocks. Ashed

glass wool was used to plug the bottom of the buret. The buret was filled with
n-pentane (HPLC grade, Sigma). Approximately 1.5 g (4 mL) of silica gel was
placed in the buret and allowed to settle for a few nrinutes. The silica gel was
covered with approximately 1.8 g (2 mL) of alumina. A thin layer (0.2 mL) of acid-
washed powdered Cu metal (Fisher) was placed on top of the column for the removal
of elemental sulfur. Columns remained in pentane overnight to allow additional
packing, and to reduce the likelihood of channel development.

Just prior to the introduction of the sample, the packed column was rinsed
using the overlying 25 mL of n-pentane. Twelve hours prior to chromatographic
separation, the organic extract of the sediment sample was diluted to 2.0 mL with
n-hexane. After the extract was loaded onto the column, sample vials were rinsed
3 times with 1 mL of n-hexane (HPLC grade, Sigma) and this material was also
introduced to the column. Flow rates were set at approximately 0.5 mL/min.
Collection of the eluent began immediately. An additional 10 mL of n—hexane were
added to the column to elute the aliphatic fraction with a total of 15 mL n-hexane.
Aromatics were eluted from the column by elution with 15 mL of 2:1 hexanelDCM,
and the polar compounds were removed with 15 mL of Omnisolve methanol. After

collection, solvent was removed from the individual fractions by rotoevaporation to a

28

volume of 2 mL. Concentrated extracts were quantitatively transferred to

preweighed, ashed glass vials, and dried under a stream of filtered air.

 

' ‘ - 'xi'lll'nl’r'fl)

The abundance and identity of nnjm components of the aliphatic fraction were
determined by gas chromatography - mass spectrometry (GC/MS), using an HP 5890
Series 11 gas chromatograph, fitted with a DB-S (32 um i.d. x 25 m) column, and
interfaced with an HP 5971 mass spectrometer. Helium was used as the carrier gas'
and kept at a constant head pressure of 13 Pa. Injector, detector, and transfer line
temperatures were all set at 305°C. The GC oven temperature was set at 100°C for 5
nrinutes, increased at a rate of 5°C per mimrte to a maximum of 305°C, and held at
305°C for 10 minutes. The mass spectrometm' operated in electron impact mode. An
initial mass scan of the sedimentary aliphatic fraction from M12 30 to 500 provided
an identification of each n-alkane based on the presence of the molecular ion.
Subsequent analyses for quantification of the concentration of n—alkanes were
performed using a mass scan from M12 30 to 200. Branched and cyclic alkanes and

alkenes were tentatively identified through comparison with literature spectra (Giger et

al., 1980; Kvenvolden et al., 1987; Schoell et al., 1994).

 

Samples of extracted aliphatic compounds were diluted with 250 ill. of
n-hexane spiked with 0.05 nmol/ 11L phenanthrene. Injections of 1 [1L were made into

the column. Phenanthrene was used as an internal standard, such that the concen-

29
tration of sample peaks was quantified relative to the phenanthrene peak.

The mixture of compounds that did not produce individual peaks but
contributed to a rise in baseline during GC/MS analysis is referred to as the
unresolved complex mixture, or UCM. The absolute concentration of UCM was not
calculated due to differences in the response of MS detector for phenanthrene, and the
variety of molecules comprising the UCM. The relative abundance of UCM was
calculated, however, by establishing the area under the baseline relative to the peak
area of the phenanthrene internal standard in each sample, and then by comparing the
ratio of UCM:phenanthrene in each sample, relative to the sample with the largest
ratio. The area under the baseline was limited to between 10 nrinutes and 50 minutes.
The area under the baseline, and the peak area of phenanthrene was approximated by
enlarging the chromatograms to a standard scale and display size, and cutting out and
weighing the paper beneath the curves.

A series of standards, each containing 0.05 nmol/uL phenanthrene, was used
for the purpose of quantification of n-alkanes in the sedimentary extract. Four
standards of known concentrations were used to calculate a linear regression to which
known concentrations of various n-alkane standards could be compared. Each
standard contained eight even-numbered n—alkanes (C,,, C”, C,,, C,,, C,,, C3,, C3,,
C3,). Regression equations were developed that describe the relationship between
n—alkane concentration, in terms of the ratio of n-alkane peak area to phenanthrene
peak area. The results of these regressions are summarized in Appendix Bl .
Regression equations vary in slope because the response of the MS detector varies

according to the chain length of the n-alkanes. For n-alkanes present in sediment

30
samples, but not available as standards, the regression equation of the most similar n-

alkane was used for quantification (Appendix B2).

The results of the regression equations needed to be corrected to account for
incomplete recovery of individual n-alkanes during silica gel/alumina column
chromatography. The percent recovery of n-alkanes was quantified using a
0.4 nmol/pL n—alkane standard. A 0.5 mL aliquot of the 0.4 nmol/lrL standard was
pipetted onto each of two columns, prepared with silica gel and alumina as previously
described. The compounds were eluted, concentrated, dried, redissolved, and injected
into the GC/ MS as previously described. Integrated GC/MS peaks were quantified
using calculated regression lines. The percent recovery of the individual n-alkane
standards are summarized in Section 3.3. The corrected concentration of individual
sedimentary n-alkanes was calculated by adding the amount of n-alkanes injected onto

the column, to the amount of n-alkanes lost on the silica gel/alumina column.

Results of Method Development

3.1 W

The efficiency of sonication and soxhlet extraction techniques were compared
previous to the solvent extraction of organic matter from the lake Erie sediment
samples. Triplicate analysis of a lake Huron surficial sediment demonstrated that
soxhlet extraction consistently extracted a greater mass of total organic matter, and
aliphatic hydrocarbons than did sonication (Table 1). An average of 1.51 :l: 0.10 mg

of organic material was extracted per gram of dry lake Huron surficial sediment by

31
soxhlet extraction, but only 0.92 :1: 0.05 mg/g of dry sediment was extracted by

sonication. Similarly, 0.35 :1; 0.06 mg of aliphatic compounds per gram of dry
sediment were extracted by soxhlet extraction, but only 0.28 :1: 0.01 mg/ g of dry
sediment were extracted by sonication. Previous studies have also favored soxhlet

extraction over sonication (Weaver, 1988; Brillis and Marsden, 1990).

3.25.. ['1' III'
Based on the separation of n-Cn, n-C,,, pristane, and phenanthrene, the

activation of silica gel and alumina at 305°C led to better separation of aromatic from
aliphatic hydrocarbons than activation at IWC (Table 2). The alkanes n-Cn, n-C,,,
and pristane were present, and phenanthrene was absent, in both the 0 - 5 ml and the
5 - 10 mL eluent fractions of columns activated at both 100°C and 305°C. Small
alkane peaks persisted in the 10 - 15 mL eluent fraction collected from the column
using silica gel and alumina activated at 100°C, but no alkanes were eluted from the
column constructed from silica gel and alumina activated at 305°C. A trace molecular
ion peak at M“ = 178 indicated the presence of phenanthrene in the eluent fraction
from both columns. In the 15 - 20 mL eluent fraction of the column activated at 5
100°C, a pronounced molecular ion of phenanthrene was present, and alkane peaks
persisted. The 15 - 20 mL eluent fraction from the column activated at 305°C

contained a minimal phenanthrene molecular ion, and no trace of the alkanes.

3.3 Samplcjecoxem
The percent recovery Of n-alkane standards from the silica gel/alumina column

varies with chain length (Table 3). The shortest n-alkane standard, Cm, exhibits the
lowest percent recovery at 75 % , whereas long-chain n-alkanes (C3,, C3,) are nearly
quantitative in their recovery. The loss of low molecular weight n-alkanes is
attributed in part to higher vapor pressures of these compounds relative to high
molecular weight n-alkanes, which result in their preferential vaporization during
concentration of the sample. In addition, low molecular weight n-alkanes may be
retained on the silica gel/alumina column. The absence of n-alkanes in the eluent
beyond 15 mL (see Section 3.2) suggests that if short-chain n-alkanes are retained on
the column, they are irreversibly bound, and that no memory effect is present during

column chromatography.

Experimental Results

Sedimentary organic matter recovered from Lake Erie was characterized by:
1) the elemental and isotopic composition of the bulk organic fraction, 2) the
concentration of total hydrocarbons extracted from the sediment, and the abundance of
aliphatic, aromatic, and polar compound classes contained therein, and 3) the
distribution and concentration of n-alkanes, isoprenoid alkanes, and unresolved
compounds within the aliphatic fraction. Sediment samples from various depths were
used to determine the primary sources of organic matter contributing to the lacustrine

environment, and to evaluate early diagenetic activity within the sediments. Source

33
and diagenetic information was used to provide a basis for attributing changes in the

«WC content of the sediments.

4.1 Sedimentan'gn (at: and m g] depth
The age-depth relationship of the core was calculated using 2“’Pb dating

techniques (Robbins and Edgington, 1975; Eisenreich et al., 1989). The bottom of
the core was calculated to have been deposited in 1968, fourteen years prior to
collection of the core (Figure 3, Table 4). The mixed depth was calculated to have
been 10.5 cm, equivalent to a cumulative weight of 2.84 g/cm’. The mass
sedimentation rate was determined to have been 0.88 g/cmzlyr, much higher than
previously reported estimates from the eastern basin (Mortimer, 1987; Robbins et al. ,
1989).

Maximum values of me activity in the sediment core occured at depths
between 6 and 11 cm. In the absence of sediment mixing, the highest 210Pb activity
occurs at the sediment-water interface, and decreases with depth. The pattern of me
activity is suggestive of selective feeding patterns by benthic animals such as
oligochaete worms (Matisoff and Robbins, 1987). Oligochaete worms are common in
the upper 15 cm of lake Erie sediments, and are a likely organism responsible for the
observed sediment mixing (McCall and Fisher, 1979; Fisher et al., 1980; McCall and

Tevesz, 1982; Robbins et al., 1989).

4.2 BernoxalaLelementalaulfrn

Elemental sulfur was removed as CuS from the aliphatic fraction of
sedimentary organic compounds to avoid co-elution with n—alkane peaks during
GC/MS separation. Sulfur was present in mmples taken from 11 cm and below, but
removed as CuS, as evidenced by a black coating of CuS on the activated Cu powder.
The presence of elemental sulfur approxinrates the depth of the oxic/anoxic boundary.
The co-occurence of the bottom of the mixed layer with the presence of sulfur

suggests that sediments in the mixed layer remain oxic due to bioturbation.

4.3 ElementaLAhundmrc

Carbon and nitrogen elemental abundances of the organic sedimentary fraction
are reported as percent organic carbon and percent organic nitrogen relative to total
sedimentary material, and as C/N (Figures 4, 5, 6). The range in percent organic
carbon is small (2.04% to 2.47%), with an average of 2.26 i 0.11%. The depth
profile for percent organic carbon is characterized by a series of maxima and minima,
with maxima occuring approximately every four samples. Percent nitrogen ranges
between 0.241% and 0.311%, with an average of 0.274 :1: 0.016%. The depth
profile of percent organic nitrogen is also characterized by a similar series of maxima
and minima. Comparison of the trends in percent organic carbon and percent organic
nitrogen shows that maxima and minima co-occur in most instances. The ratio of
organic carbon to organic nitrogen averages 9.60 :1: 0.38. The organic C/N profile is
not characterized by series of maxima and minima.

Procedural reproducibility for elemental analysis was established through the

35
triplicate analysis of a lake Superior surficial sediment sample (Table 5). The

precision was determined to be :1: 0.06 and :1; 0.02 for percent organic carbon and
nitrogen, respectively. Error associated with the measurement of percent organic
carbon and nitrogen is propagated in the calculation of cm. The propagated error2
associated with cm is ealculated as :l: 0.58.

Net depletion of organic matter in older sediments relative to surficial
sediments is an indicator of microbial remineralization of organic carbon and
nitrogen. There appears to be no trend in percent organic carbon as proceeding from
the bottom to the top of the core. Values of percent organic nitrogen increase slightly
from the bottom to the top of the core. Differences in both percent organic carbon
and percent organic nitrogen between maxima and subsequent nrinima are the most
striking feature of the data. The significance of these differences was considered
using procedural reproducibility. If a criteria of 20 was established to statistically
discriminate between two points, several of the differences between maxima and
subsequent nrinima in percent organic carbon and nitrogen are significant. The
largest difference in percent organic carbon between a minimum and the next
subsequent maximum is 0.30 % , five times greater than the precision. The largest
difference in percent organic nitrogen between a minimum and the following

maximum is 0.054%, exceeding the precision by a factor of three.

 

2Propagated error for a quotient is calculated by adding in quadrature the fractional
uncertainties associated with two independent measurements,

6q/q = [(tic/c)2 + (6n/n)’]"" (Taylor, 1982)
in which fix is the uncertainty associated with the measured value x.

 

The 6‘3C composition of sedimentary organic matter extracted from lake Erie
generally exhibits a trend of 12C enrichment through the 1970’s (Figure 7). The
maximum 5‘3C value of -24.9%a was recorded in sediments deposited in 1970, two
years following the maximum phosphonrs loading to lake Erie (Fraser, 1987 ; Rosa,
1987), and again in 1977. The minimum 8‘3C value of -25.9%o is recorded in
sediments deposited in 1981.

The 813C depth profile is characterized by a series of maxima and minima at
intervals of 3 - 4 cm. These variations do not co—occur with the maxima and minima
exhibited by percent organic carbon and nitrogen. The criteria of 2a was again used
to consider statistical significance of variability in the data. Procedural reproducibility
was established as 0.2 %a through 6‘3C analysis of lake Superior surficial sediment
(Table 8). The largest difference in (WC values between maxima and subsequent
minima (0.7 %o) exceed the procedural reproducibility by more than 30, indicating

that variations in the «WC content of the sediments may be significant.

4.5 W
The amount of organic material extracted from lake Erie sediments samples

varied within a small range (1.14 i 0.09 mg/g dry sediment) between 1978 and the
tap of the core (Figure 8). Sediments deposited during 1976-1977 contained as high
as 2.07 mg/g dry sediment, nearly twice the amount extracted from the most recent
sediments. Procedural reproducibility was established by triplicate analysis of a Lake

Huron surficial sediment, which yielded an average of 1.15 :t 0.07 mg/ g dry

37
sediment (Table 6).

4.6 MW

Chromatographic separation of the organic extract yielded three fractions
containing aliphatic, aromatic, and polar compounds (Figures 9a, b, c). All three
organic fractions exhibited a loss of mass in the upper five centimeters of the core
that was likely due to early diagenetic degradation. The aliphatic fractions contained
an average of 0.29 :1: 0.07 mg/g dry sediment, the aromatic fractions an average of
0.15 :l: 0.03 mg/g dry sediment, and the polar fractions an average of 0.41 :1; 0.07

mg/g dry sediment.

4.7 11W

The size of the UCM provides an indication of the abundance of branched and
cyclic aliphatic compounds present in the sediments (Giger et al. , 1980). The
concentration of these unresolved compounds is greatest at the bottom of the core, a.
consequence of the diagenetic alteration of primary molecules to branched and cyclic

compounds. Maxima in the concentration of the unresolved compounds occur during

1970 and 1979 (Figure 10).

 

Eighteen n-alkanes (C,,-C,,) and two branched alkanes (pristane and phytane)
were separated, identified, and quantified using GC/MS. Absolute abundances are

reported in ng/g of sediment. Normalized abundances are reported relative to the

38
n-alkane of highest concentration. Hydrocarbon indexes quantify the relative

distribution of short to long n-alkanes, and odd to even n-alkane chain lengths.

The absolute and normalized distributions of n-alkanes may be described as
bimodal distributions, which are generally characteristic of sediments with mixed
terrestrial and algal sources of organic matter (Giger et al. , 1980; Ho and Meyers,
1993). In terms of absolute abundance, heptadecane (Cu) is the most abundant
n-alkane in the distribution, followed by C, or C,, as the secondary mode (Figures
Ila-d). Normalized abundances of n-alkanes generally exhibit the same pattern as .
absolute abundances (Figures 12a-d). In general, the absolute abundance of short—
chain n—alkanes (C1, - C,o) tends to increase from the bottom to the top of the
sediment core, but the abundance of mid (C,,-C,,) and long- (Cu-C3,) chain n-alkanes
tends to remain constant.

Hydrocarbon indexes quantitatively describe changes in the distribution of
n-alkanes that occur with depth in the sediment core. The odd-even preference
(eq. 2, Figure 13), is a ratio of odd to even chain length n-alkanes, calculated as a
running average over a range of five consecutive hydrocarbons (Ho and Meyers,
1994). The odd—even preference (OEP) approaches unity as n-alkanes are
increasingly altered through diagenetic activity, or as petroleum becomes an
increasingly large fraction of sedimentary organic matter. Values of > 1.0 are
generally indicative of primary production, either algal or terrestrial (Ho and Meyes,
1994). Values of < 1.0 have been associated with bacterial assemblages in marine
sediments (Kennicutt and Brooks, 1990). The OEP ranges from a maximum of 10.57

for a distribution centered around C,,, to a minimum of 1.17 for a distribution

39
centered around C,o. The highest OEP values are centered around Cr, and C,,, the

dominant n—alkanes for the algal and terrestrial portions of the distributions.

The ratio of short to long chain lengths compares the absolute abundance of -
three algal n-alkanes (C1,, C1,, C,,) to three terrestrial n-alkanes (C,,, C29, C3,),
providing an approximate ratio of algal to terrestrial sources of organic matter
(Figure 14). A short/long index of < 1.0 indicates a predominance of terrestrial
n-alkanes, whereas a ratio of >1.0 indicates primarily algal compounds. The ratio
increases abruptly over time from an average of 0.92 :l: 0.11 for the seven samples at
11 cm and below, to an average of 1.48 :l: 0.15 for the four samples at 10 cm and
above. The increase of algal n-alkanes relative to terrestrial n-alkanes indicates either
a sudden change in the sources of organic matter, or a difference in the nature of
diagenetic processes operating above and below the mixed depth. The abundance of
pristane tends to increase over time, from a minimum of 0.36 jig/g of dry sediment
at the bottom of the core, to a maximum of 2.19 jig/g at the top. The concentration
of phytane remains relatively constant over time, averaging 0.26 :1: 0.09 pg/g of dry

sediment (Figures 15a, b).

Discussion
The previously observed temporal relationship between historical phosphorus
loadings and the (WC content of bulk organic sediments suggests that a record of
trophic status is preserved in the (WC content of lake sediments (Schelske and Hodell,

1991). Changes in WC, however, may be attributed to changes in source, as well as

4o

diagenetic alterations of organic matter deposited in the lake. The objective of this
discussion is to describe the sources of organic matter contributing to the depositional
environment, and to document evidence of early diagenetic alteration of the organic
sediments. Elemental, isotopic, and molecular data indicate that source changes and
diagenesis play a limited role in altering the WC content of organic sediments

deposited between 1968 and 1982.

5 .1 W

The high sedimentation rate at this site in the eastern basin of lake Erie
permits excellent resolution in the upper 20 cm of the core, such that as many as four
l-cm samples are associated with one year of sediment deposition. The mixed depth
of the core, at approximately 10.5 cm, was slightly greater than the average depth of
bioturbation in the Great lakes (Robbins and Edgington, 1975). The detection of
elemental sulfur in sediments below the mixed depth suggests that sulfate-reducing
bacteria were active below 10 cm.

Series of maxima and minima in the percent organic carbon, percent organic
nitrogen, and the organic 613C content indicate that the sediment core is not
homogenized by sediment mixing processes. Rather, it is likely that benthic feeders
such as oligochaete worms mix sediment in such a manner that features within the
sedimentary record are preserved. Tubificid oligochaetes selectively feed on organic
rich sediments, consuming bacteria associated with organic particles (Brinkhurst and
Austin, 1979; Robbins et al., 1989). Sediments are ingested by oligochaetes at depth,

and excreted at the sediment-water interface. Selective fading on organic material

41

will tend to concentrate organic compounds in the form of fecal pellets at the
sediment surface (Matisoff and Robbins, 1987). The rate of advection of buried
sediments to the sediment-water interface is exceeded, however, by the sedimentation
rate in the eastern basin of lake Erie (McCall and Fisher, 1979). The high
sedimentation rate, combined with selective feeding patterns, is most likely

responsible for the high resolution present in this sediment core.

5.2 ElementaLAhundanm

The organic carbon and nitrogen content of sediments provides an information
regarding the sources of organic matter, and the degree of diagenetic alteration of the
organic sediments. Diagenetic activity, such as the microbial remineralization of
organic matter, tends to reduce the amount of organic carbon and nitrogen preserved
in sediments. Rates of diagenetic alteration, however, are compound-specific, as
labile compounds such as carbohydrates are preferentially degraded (Meyers and
Ishiwatari, 1993a). Despite the diagenetic alteration of the organic contents of
sediments, the ratio of organic carbon to organic nitrogen has often provided a good
indicaton of the sources of organic matter contributing to lacustrine environments.

Elemental abundances of 2.26 :1: 0.11%, and 0.274 1: 0.016% (Figures 4, 5)
for organic carbon and nitrogen, respectively, are relatively high compared with ‘
marine sediments, low for lacustrine sediments, but typical for large, deep lakes such
as the Laurentian Great lakes (Meyers and Horie, 1993). The low organic content of
lake Erie is consistent with earlier studies of lake Michigan, in which the abundance

of autochthonous and allochthonous organic matter is significantly reduced, to varying

42
degrees, during deposition (Meyers and Eadie, 1993). The absence of significant

change in percent carbon, and the simultaneous increas in the nitrogen content
between the oldest and youngest sedimentary layers, suggests that labile, nitrogen-rich
compounds are more susceptible to alteration relative to carbon-rich compounds. In
general, aquatic compounds tend to be more labile, with lower carbon contents, than
terrestrial compounds (Meyers and Ishiwatari, 1993a). The preferential loss of labile
components typically leads to depositional records biased in favor of terrestrial
organic matter (Cranwell, 1984; Canuel and Martens, 1993).

The series of maxima and minima in percent organic carbon and nitrogen
appear significant, as differences between maxima and subsequent minima exceed the
precision associated with elemental analysis. The origin of the variation could be
related to changes in rates of primary productivity, deposition, degradation of organic
matter, or variation in inorganic inputs (Canuel and Martens, 1993). The vertical
flux of hydrophobic organic matter in the Great lakes is related to the types and
amounts of sedimenting particles. Seasonal variability determines the types and
amounts of the particles, derived primarily from shoreline erosion, biotic production,
and resuspension (Baker and Eisenreich, 1989). Wide variations in percent organic
carbon and percent organic nitrogen may, therefore, represent seasonal and time-
integrated changes in the nature of sedimenting particles.

The organic Cl N content of sediments is used to provide an indication of
terrestrial and aquatic productivity (Meyers and Ishiwatari, 1993a). The organic C/N
of lake Erie sediments averages 9.62 :1: 0.38, suggesting that the sediments are

dominated by autochthonously-produced organic matter (Figure 6). A mass balance

43
approach may be used to approximate the relative magnitude of aquatic and terrestrial

contributions to organic sediments. For a conservative estimate of algal contributions
to lake Erie, average C/N for phytoplankton and land plants are assumed to be 6 and
20, respectively (Meyers and Ishiwatari, 1993a). Using these estimates, it is
calculated that phytoplankton contribute approximately 74 % of the organic matter to.
the sediments. Based on these calculations, algae may be inferred to be the primary
source of organic matter in lake Erie, and terrestrial plants are inferred to constitute
a secondary source of organic material.

The slight apparent decrease in C/N values between the bottom and the top of
the core does not appear to be significant, given that the variation is less than 20.
The absence of signifieant variation in C/N between til: top and the bottom of the
sediment core indicates that there is no evidence for a change in the relative

proportion of terrestrial and algal sources of organic matter between 1968 and 1982.

53C! . . .. Elll . l'
The 5‘3C content of the organic sediments of lake Erie exhibits a trend of

increasing enrichment of 12C toward the present (Figure 7). The trend in RC
enrichment is consistent with the findings of previous Great lakes studies (Schelske
and Hodell, 1991; Bourbonniere et al., 1991). The isotopically heaviest organic
carbon is present in sediments deposited in 1970, two years following the maximum
loading of anthropogenic phosphorus to lake Erie (Fraser, 1987). Between 1970 and
1982, organic matter deposited on the bottom of the lake has become isotopically

lighter, coincident with previous records of phosphorous reductions (Fraser, 1987;

Rosa, 1987). ‘

Sediment 6‘3C values between -25.9%o and -24.9%o are consistent with a
mixture of aquatic and terrestrial sources of organic matter, although the relative
contributions of terrestrial and aquatic sources cannot be quantified. Freshwater algae
generally have 6‘3C values of -25 to -28%o, within the range of (WC values associated
with land plants of approximately -25 to -30 %o (O’Leary, 1988; Meyers and
Ishiwatari, 1993a; Fogel and Cifuentes, 1993). Isotope ratios consequently cannot be
used to quantify the relative contributions of organic matter from aquatic and
terrestrial sources in lake Erie.

Possible explanations for the enrichment of 12C in lake Erie sediments
deposited during the early 1980’s include a change in the relative size of algal and
terrestrial contributions of organic matter, and the preferential remineralization of
isotopically light carbon compounds. If the (WC content of the bulk organic
sediments is primarily a function of the sources of organic matter, then variations in
«WC values should correspond to a changes in cm. If 5'3C values are affected by
diagenetic alteration, evidence of diagenetic activity, such as trends in percent organic
carbon and nitrogen proceeding from the bottom to the top of the core, should be
apparent. Downcore decreases in percent organic carbon and nitrogen were not
observed, and therefore suggest that early diagenesis was not a dominant factor
controlling the elemental or isotopic content of the sediments.

When considered together, elemental and isotopic evidence suggests that the
change in the (WC content of bulk organic sediments is not associated with a change

in source. If the shift in WC values were related to a source change, a correlation

45
should exist between WC and C/N (Meyers and Benson, 1988). Organic cm and

(BBC values show no such correlation (r2 = 0.04). The absence of change in CM
between the bottom and the top of the core suggests that the relative contributions of
autochthonous and allochthonous material has remained constant.

The possibility remains that the (WC shift may be related to recent changes in
the proportion of C, vs. C4 plants in the watershed of Lake Erie. Terrestrial C3
plants are isotopically lighter than C4 grasses (O’Leary, 1988). An increase in the
contribution from C3 plants relative to C4 vegetation could therefore lead to the
progressive depletion of 13C in sediments (Sackett et al., 1986). Compound-specific
isotopic analysis of long—chain, terrestrial n—alkanes could be used to relate possible
changes in the (WC content of organic sediments to changes in watershed vegetation
patterns (Collister et al., 1994a; Spooner et al., 1994).

The absence of correlation (r2 = 0.14) between percent organic carbon and
(WC values supports the interpretation that the shift in «WC composition is not related
to diagenetic activity. The trend of 12C enrichment between 1970 and 1982 could be
explained in terms of the preferential remineralization of isotopically light carbon,
such that surficial sediments undergo the least alteration, retaining more ‘2C and
giving the appearance of ‘2C enrichment. No evidence of 12C remineralization,
however, is provided by the percent organic carbon profile, as the oldest sediments do
not differ significantly from the youngest in percent organic carbon content.

Previous studies have also indicated that diagenesis does not significantly alter
the WC of organic sediments containing typically low ( < 2-3 %) concentrations of

organic carbon (Jasper and Hayes, 1990; Fontugne and Calvert, 1992; Meyers and

46
Horie, 1993). Based on this generalization, the low earbon content of the Lake Erie

sediments (2.26 :1; 0.06) suggests that diagenesis has little effect on the (WC content
of the sediments.

The absence of a change in source, and the lack of evidence concerning the
remineralization of isotopically light carbon, supports the theory that the WC content
of the bulk organic sediments reflects the WC composition of the predominant source
of organic matter, namely algae. The overall shift in (WC values suggests that the
«BBC content of autochthonous production has changed between 1970 and 1982.
Significant variations in the 613C content of the core may be related to seasonal or
interannual changes in the source, type, and amount of sedimenting particles, which
affects the nature of the organic matter delivered to the sediments (Baker and
Eisenreich, 1989). Maximum values in the «WC content of the sediments may also _
reflect periodic influx of organic matter from the central basin of the lake, which is

more eutrophic than the eastern basin (Burns, 1985).

5 .4 W
The concentration of total extractable hydrocarbons in the sediments of Lake

Erie remained constant throughout the upper 16 cm of the sediment, averaging 1.14
:l; 0.09 mglg dry sediment (Figure 8). Below 16 cm, in sediments deposited during
197 6-1977, higher concentrations of organic matter were extracted, reaching a
maximum of 2.07 mglg dry sediment. The significant peak in total extractable
hydrocarbons did not coincide with an increase in aliphatic, aromatic, or polar

compounds. The increase in organic matter could represent an increase in terrestrial

47
erosion into the lake, as erosion of shoreline bluffs could have delivered a large

amount of highly refractory terrestrial organic material to the lake.

 

The concentration of aliphatic, aromatic, and polar compounds in the
sediments remains nearly constant throughout the core, with the exception of the top
5 cm of sediment (Figures 9a, b, c). Within the top 5 cm, the concentration of each
of these compound classes increases toward the surface, and indicates the diagenetic

loss of labile, predominantly aquatic compounds in surficial sediments.

 

The relative concentration of the UCM indieates that diagenesis has altered the
distribution of compounds within the aliphatic fraction (Figure 10), even if there is no
apparent decrease in the absolute concentration of aliplnrtic compounds (Figure 9a).
The relative magnitude of the UCM decreases betan the bottom and the top of the
core, consistent with the limited diagenetic alteration of the surficial sediments.
Deeper sediments tend to be characterized by larger concentrations of branched and
cyclic hydrocarbon compounds, as diagenetic alteration of organic matter decreases

the ratios of O/C and HIC with time (Peters and Moldowan, 1993).

5.7 Distributicufnsalhms
The distribution of n-alkanes in the sediments of lake Erie is a bimodal

distribution, with modes at C17, and at C29 or (1,1. Bimodal distributions of n-alkanes

48

are characteristic of sedimentary environments having multiple sources of organic
matter (Giger et al, 1980; Ho and Meyers, 1993). Heptadecane (C17) is the most
abundant n-alkane in phytoplankton (Gelpi, 1970; Giger et al., 1980) and its
dominance throughout the core is a good indieation that algae comprise the primary
source of organic matter in lake Erie (Figures lla—d). The second most abundant
n-alkane is either C29 or C3,, indicating that a large terrestrial component is also
present. The dual terrestrial and algal sources are in agreement with conclusions
drawn from organic cm.

The odd-even preference (OEP) similarly indicates that multiple sources of
n—alkanes contribute to lake Erie sediments. High OEP values are indicative of
natural sources of organic matter, whereas values of 1.0 indicate extensive diagenetic
alteration, or petroleum contamination. The highest odd predominances occur at C 17
and C31, indicating algal and terrestrial origins of n-alkanes. High OEP values also
occur around Cu, suggesting the presence of a possible third natural source of
n-alkanes not observed in the abundance distributions (Figure 13).

Although C17 remains the dominant n-alkane throughout the sediment core, the
relative proportion of algal to terrestrial n-alkanes changes with depth. The increase
of 0.5 in the short/long n-alkane index for sediments at 10 cm and above, relative to
11 cm and below, suggests that algal organic matter may be preferentially consumed
by oligochaete worms, bacteria, and other organisms in the mixed layer of the
sediments (Figure 14). The absence of change in organic C/N between 10 and 11 cm
indicates that the variation in the short to long index is not related to a change in the

relative contributions of organic matter from aquatic and terrestrial sources. The

49
preferential loss of labile compounds often leads to depositional records biased in

favor of terrestrial sources (Canuel and Martens, 1993; Meyers and Eadie, 1993;
Meyers and Ishiwatari, 1993; Bakel et al. , 1994). The loss of short-chain n-alkanes
relative to long-chain n—alkanes is consistent with the conclusions that distinct algal
and terrestrial sources of n-alkanes contribute to Lake Erie sediments, and that rates
of diagenetic alteration vary considerably between different organic fractions,
compound classes, and molecules.

The presence of pristane and phytane in sediments has previously been utilized
as indicators of oxic/anoxic deposition (Didyk, 197 8). One of the primary
biosynthetic pathways of these molecules is through the oxic or anoxic decomposition
of phytol, the alcohol side-chain of chlorophyll a, during later diagenesis (Peters and
Moldowan, 1993; Ho and Meyers, 1993). In recent sediments, however, the
presence of pristane reflects the decomposition of chlorophyll a in the digestive tract
of copepods (Blumer et al., 1963; Ho and Meyers, 1994). large fluctuations in
pristane concentration throughout the sediment core indicate the annual variability of
zooplankton grazing communities (Figure 15a). The concentration of phytane remains
relatively constant with depth, indicating a different formative process, which has

varied little during the 14 years of sediment deposition (Figure 15b).

Conclusions

The isotopic composition of the sediments of lake Erie exhibits a significant

decrease in "C content between 1968 and 1982. Elemental and isotopic data suggest

50
that the decrease in 13C is not related to a change in diagnetic activity, nor to a

change in the relative distribution of terrestrial and aquatic sources of organic matter.
Therefore, it is likely that the isotopic shift is due to a decrease in the algal
productivity, a response related to diminished phosphorus loadings to lake Erie.

The primary source of organic matter contributing to the lake Erie
sedimentary environment is algae, as indicated by organic cm and n-alkane
distributions. The distributions of n—alkanes suggests tint terrestrial sources of
organic matter contribute a secondary, but significant fraction of organic matter.
Organic C/ N indicates that the relative proportion of source inputs has changed little
between 1968 and 1982. The relative magnitude of contributions from each source is
difficult to assess, due to the preferential diagenetic alteration of aquatic, short-chain
n-alkanes, and the lack of definitive C/ N endmembers for autochthonous and
allochthonous production in the lake Erie watershed.

Series of maxima and minima in percent organic carbon, percent organic
nitrogen, and organic 6‘3C content are evident in the sediment record. In addition,
variations in 21"Pb activity indicate that sediments were not completely homogenized,
despite a mixed depth of 10.5 cm, and reflect selective feeding patterns by benthic
organisms. Selective feeding and high rates of sedimention are most likely
responsible for the high degree of resolution present in this sediment core.

The diagenetic alteration of organic matter affects individual molecules,
compound classes, and the bulk organic fraction to different degrees. Early
diagenetic alteration of the organic sediments is apparent in variations of the

concentrations of n-alkanes, compound classes, and chromatographically unresolved

51

compounds. The absence of significant change in the percent organic carbon content
of the sediments suggests, however, that diagenetic alteration alone is insufficient to
affect the (WC of the bulk organic fraction.

Future studies may utilize the distribution and isotopic composition of
additional organic fractions, such as n-alkanols and n-alkanoic acids to further
distinguish between the various sources of organic matter. Isotopic analysis may also
be useful for determining the significance and origins of the maxima and minima
observed in percent organic carbon, percent organic nitrogen, and the (WC content of

bulk organic matter.

APPENDICES

52

APPENDIX A: TABLES AND FIGURES

Table 1: Comparison of the efficiencies of sonication and soxhlet extraction methods.

 

 

Extraction mg extracted organics mg extracted aliphatics
Technique per g of dry sediment per g of dry sediment
Sonication 0.92 +/- 0.05 0.28 +/- 0.01

Soxhlet 1.51 +/- 0.10 0.35 +/- 0.06

 

Table 2: Comparison of alkane and aromatic separation based on the activation
temperature of silica gel and alumina.

 

 

Eluent fraction
(mL) 100°C 305°C

0 - 5 alkanes - trace alkanes - trace
phenanthrene - none phenanthrene - none

5-10 alkanes-largepeaks alkanes-largepeaks
phenanthrene - none phenanthrene - none

10-15 alkanes-smallpeaks alkanes-none
phenanthrene - trace phenanthrene - trace

15-20 alkanes-smallpeaks alkanes-none

phenanthrene - larger trace phenanthrene - trace

 

53

Table 3: Percent recovery of n-alkane standards from silica gel/alumina

 

 

column chromatography.
n-alkane Percent Recovery
C15 74. 8
C20 81.8
Cu 84.2
Cm 87.5
C26 90.6
C30 95.4
C34 98.6

C3,, 102.1

 

54

Table 4: Age-depth relationship of lake Erie sediment core as determined by 2mPb

 

 

dating methods.

Sediment Depth (cm) Approximate year
1 1982.75
2 1982.50
3 1982.25
4 1982.00
5 1981.67
6 1981.33
7 1981.00
8 1980.67
9 1980.33
10 1980.00
1 1 1979.67
12 1979.33
13 1979.00
14 1978.67
15 1978.33
16 1978.00
18 1977.00
20 1976.50
22 1976.00
24 1975.00
26 1974.00
28 1973.50
30 1973.00
32 1972.00
34 1971.00
36 1970.00
38 1969.00

40 1968.00

 

55

Table 5 : Calculation of the precision of percent organic carbon, percent organic
nitrogen, and «WC of bulk organic sediments using lake Superior surficial

 

 

sediment.

Sample % organic C 95 organic N 6‘3C (%o)
LS 1383 3.440 0.399 -26.80
LS 1383 3.436 0.376 -26.47
LS 1383 3.338 0.371 -26.75
Average 3.404 0.382 -26.67
St. Dev. 0.058 0.015 0.18

 

Table 6: Calculation of the precision of geolipid extraction by Soxhlet extraction
methods using Lake Huron surficial sediments.

 

 

Sample organic extract
(mg/ g dry sediment)

LH Octl 1.10

LH 0th 1.12

LH 0ct3 1.23

Average 1.15

St. Dev. 0.07

 

 

 

 

 

 

Figure 1:. Inferred bathymetry of lake Erie (after Sly and Lewis, 1972; Burns, 1985)

57

 

. A33 .838 ecu—«omega 38.85
38886:: wagon.“ new 8.3 we Emman— annao 98 33:3 2: .3 338-380 ”N onE

. and: 3:3;
8. 8 . 8 av . an
. . . _ .

 

 

 

( 20:03
0. ucaéusg
hoo— .—n .03( I 3 53¢
mam mg

 

 

MM”

 

 

Immune

Year

58

Log excess Pb-210 (DPM/G)

 

 

 

 

 

 

 

2 2.4 2.8
A A?
1932 f ‘
AA
A
1990 A
A
A
A
1979 A
A
A
1976 A
A
1974 A
A
A
1972 A
A
1970 A

 

 

 

 

 

 

1968

Figure 3: Mixed depth and sediment dating inferred from
excess 2mPb activity.

59

firm 3.3 no 589 583 05 89a
85:53» E comet? 0:8ch Eocene

 

 

- c o c
a o a o
u o o u
c o .
o o g
o o o o
o o o g
o o c .
o o o c
. o o .
............ ‘UIOIICOICOCOCCUOICOI IO'IIOII00I00l0‘ICUII--.II.A
o u o .
u o o -
c o o .
o o c o
o o c g
o o . .
u o o .
c c c u
o o a c
a o o o
............ LII.I.....'...-. .‘C--.O'II.-.’-I'|I.t.'--'.ll'l.4
- o o .
c o . .
. . . ' n .5
. . . mponv. :o_mv
. a o n
o o o o
o n n o
o o o u
o . o o
c n u .
IIIIIIIIIIII LIICOOIOOII00‘II00000 .0I'QIIIIOQIIOUOOIOOOCI000IOIa
- c o .
c o a .
a o .
- c o
o g o a
o c o o
o o o o
u a o o
u o o o
a o o .
fl 00000000000 L. IIIIIIIIIIII ‘o IIIIIIIIIIII ' IIIIIIIIIIIIIIIII
a o o
g c c
o a o a
u o o o
o . c n
o n a o
o o o o
o c o
o . a
fi sssssssssss I. llllllllllll 5 IIIIIIIIIIIIIIIIIIIII at ssssssssssss
. a .
o g u o
n a c o
. . o o
. a .
c a o
. o c .
o o .
c p .
o . o
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII .lOOIOOIOOIOOA
a 4 .
c o o a
c c o
c g o
c o o
o . c o
o c n o
o o c
c - .
u u u —
a o
............. - .0...I.-II.- .0... 000*0000I'IIII-I-II.I---I-IIIA
. u
o o
o o
.

 

 

Nady adv QNAV Quay

z 2:on .x.

"n Bnmmm

coop

Chap

Nua—

chap

chap

asap

coop

Noap

sum 93 a £3 898s 2: sea

3:053» E cop—8 cameo 883m 3. 8:9"—

 

-1--.-.--.

IIIIIIIIIIIIIIIIIIIIIIIIIII

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

 

 

 

 

coop
Chow
«haw
chap

1A
chop mm
chap
coop

«can

 

 

 

o 2:me .x.

Snug—com cameo
utm— ouj .8 acumen—Eco 333% .8980 K. Semi

 

 

 

 

 

 

meow

Oka—

«Now

who—

chap

who—

comp

«map

reek

 

 

 

 

 

vp

N-

.aaneea new 93 .6 25 2530 e 25E

moor

Chop

wha-

Vhow

chop

asap

coop

«mop

61

Extractable organic matter, ug/g sediment

0 0.5 1 1.5 2 2.5

r

 

1982

1980

1978

Year

1 974

1 972

1 970

 

 

 

 

I”

Figure 8: Concentration of organic material obtained from
lake Erie sediment core by Soxhlet extraction
using dichloromethane.

62

555.com ohm. 8.3 SE. £5868 cum. 9.3 82.. $5869. 0
. . . rm 9.3 8
3.8.56 3.22: 58 ©8235 Became nausea .8835 3.8.9: 32%...”
.0 coupe—3:00 ”om onE .3 8.255030 5a 8%.”. .«o noun—.5800 Hm .95?—

 

 

 

 

        
   

 

 

      

 
     
 

. m J. M M W 82
..... . ..... ........... mimu. .................... ...... s ......... m ......... m. ....... ......... W.-.:<.: o3.
........... .. e «3.
........... ........................... .............. ........................ ....... ........ ......... ........

. r

..... E... ........................ ........ . ......... ........ s...
........................... .............. ...... ......... ........
.. ........................... . ............. . ........................ ........ . ...... . ......... . ........ 8.:
m ........... . ........................ ....... ...... ......... ........

 

 

 

 

 

 

 

 

go no to ad and No to one to no No to o
.5868 QaE dice EoEfiow 99: 3.5602 E0868 90E 62.9.92

Year

1982

1980

1978

1976

1974

1972

1970

1968

63

Relative abundance of UCM
as as ea 1

 

................................................................

ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

 

 

Figure 10: Relative abundance of unresolved complex

mixture in lake Erie sediments.

 

 

 

 

..................................................................

....................................................................
....................................................................

.....................................................................

    

‘ ‘ ' " ....... '. . . ' .
.‘l.°.'.‘: ..............................................

........................

b. YOYOYOYOYOYOYOYOYOYO

 

 

 

    

........................................
. .... c‘ ...................... .l' ..... In.
........................................... 45......
.........................................

excavaogogogvpaxc

 

......................................................
........................................................
..........................................................................................
......................................................

 

 

   

C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 025 C26 C27 028 C29 080 031

 

1.8

..........................................
W
{OYOYC
L I I l I I 1 I
<0. V. a! .— 99 0. V. .91 o
1- 1- ° 0 O o

ruewgpe

s 6/Bn

I 1982.75 E3 1982 R 1981.33

Figure 11a: Absolute abundance of n-alkanes extracted from lake Erie sediments, 1981 - 1982.

65

 

 

1.8

1.6 -

 

 

93.392919;OLOAOLOLQLQAQAQIQAVAQLOA'

m
'O'EYOYO

 

'AVAVAVAVAVAVAVAVAVAVAVA. 'A'AVA‘

027 C28 C29 030 CS1

Dan-919.93

 

 

 

 

 

A'A’A’A'A'AVA 2'4.

 
     
 

------------------------------- -r .-.v._.-.-.- .-.-.-.

. . n
.........................

9.9.9.... 9.01.2

  

C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26

0.4 '-

l I
‘3: (‘1 V ‘0. ‘9.
1- O

rueurgpas B/Bn

0.2

I 1980 E2 1979.67 3 1979

Absolute abundance of n-alkanes extracted from lake Erie sed

ts, 1979 - 1980.

1111611

Figure 11b

66

                   

 

 

.wbm. £5569. cum 9.3 ES... .9985 «2.9.3-: ..o 8:85.... 938.? 8.. 0.5m."—

mmdhmw Nu hodhmr I
0N0 mNO 5N0 0N0 mNO VNO 0N0 N0 ..N0 0N0 9.0 2.0 5.0 0.0 mw0 v.0

        

 
       

  

       

            

                       

                              

         

              

         

     
           

      

  

      

       

               

  

  
         

  

          

          

   

       

    

      

       

. 9.. .9. C. v... . VA ... .. V a ... 0.. V.‘ ... .... C
vs. X . .9. v0. .2 o .8. co. .0. so. ..
O I . O O. O. .0 O .9.
.. a. . d .... .99. .0. .4. so.
1 vA .6 .6 O. .0 .
.0. .o. .90. .9. _ .. 1 No
. O. 9. v6 0 .
.... .... .o.. r.
. .99. .9
.o 9. .
v
....
.9. .
.0.” .. oo
3
....
.9. .
.... .. mo
'9.
.9“
v. l
as. F
1 NA
1 v.9
1 m:

 

 

m...

ruawgpas B/Bn

67

 

.E: - ca. .2858. new 93 52. 3885 8.5%.: a sadness 923.2 a: nae...

050.. I 052. B 0559. I
50 00.0. 0N0 mN0 5.N0 0N0 .m.N0 VN..0 m..N0 NNO -.....N.0 o.N0 $50 9.0 .5...0 9.0 m..0 vro

..A
v».
. .”

 

 

 

 

 

      

  

1.2
OZ.
m

I.

       

v
A

lo".
M

;-:-:- .-;«:-:;:~:-:
v
L9;

7
a

'0.

 

LO;

 

A
‘. .‘s'. . . .’.'- a - In . o'-
a _a.n.s a 0.. 3.3.-33......
a a o a - . v n
' '

.

 

. . a . . s . . n .
{RI-'4‘ a'o'.‘-
_ v n . .
' 0
A

 

 

 

m...

ruawgpes B/Bn

68

 

 

 

 

 

 

 

 

 

 

OZOZOAOAOA

 

wororoororororoz

 

 
 

 

 

 

 

 

 

 

l l l l

1- w. to. V.
O O O
eouepunqa pezuauuou

0.2 -

 

I 1982.75 E3 1982 3 1981.33

Figure 12a: Normalized abundance of n-alkanes extracted from lake Erie sediments, 1981 - 1982.

69

 

 

 

..............

 

l

r
('0
0
O
. (0
0
or
N
0
am 0
016101010 N
0
N
N
0
‘0
N
0
IO
N
0
V
N
0

. - ..............................
' ' ............................................. 5 %'

'AVAVAVAVAVAVAVAVAVAVAVAVAVAVAVAVA‘.

  

ROA'A919193

 
 
  

................. 5 . ‘-
.{vi-21':-.'!'f'Z-.-.-2'I.-.-.-..'.‘.'.' .._.-. .1.
........................

 
  

.........
.4 ...........
...........

.'.I . ....
a“..l‘ nnnnnnnnn

57' Yd

 

............... . . . .
Z’i-Z'Z‘I-I'Z-i-I-T'112+}?:.:‘r'4.-3'Z'I'I-I'l-Z'

N
191.101.101.101. (N)

   

s -

................................
.... .................... l ...........
'- n..-. ................1.. ...........
.......................................

manicure“? rota 8|

1

I 1980 E2 1979.67 a 1979

 

 

. u - ..
.....................................................
... nus-...”...V ................. ...‘ .............
..........................................
...’. .............................................

191 A 1 1 1.1919191919191910 6

 

............

:::::::::;:::::::::;;::'.:2,2:1..:;-.:-:-:-s.a~,.-_-_-...-..,..._.
-.-.-.-.-.-.'.-.-.’.-.-.‘.'.'.-.‘.-.-. -u ....................

. .................................. .. 0
01010101016101.1610:016101 6

.....
...-
.....

 

...............
...............................................
.................................................................................

 

...............................................................
.....................................................

 

 

 

l l l l l
.— 00. «D. V. N. - o
O O O O

aouapunqa pazuaulrou

ts, 1979 - 1980.

1111811

Normalized abundance of n-alkanes extracted from lake Erie sed

Figure 12b

7O

 

.wbmA £5868 arm 8:3 Set @9255 nuns—3-: me 355% BEEF—oz US «Sufi

oodsmr E 50.93? I
50 000 QNO 0N0 hNO 0N0 mNO VNO «N0 NNO ..NO 0N0 mwO mwO 2.0 9.0 9.0 vro

  
             

       
    

            

             

 

                

    

           

      

                    

          

    

       

 

        

 
                                        

     

     

       

 

  

 
 

   

     
  

   

         

  

 

         

            

 

               

          
  

      

       

   

         

       

   
  

    

   

  
    

            

 

         

   

      

                   
             

 

                  

  
        

 

   

 

          

    

       

 
     

 

   

   

      

     

   

  

          

 

 
       

           
   

 

 
  

 

 
 

 

        

                   

       

 
 

          
   

    

         

  

                      

   

 
 

          

 

         

        

 

 

   

     

   

             

   

 
            

        
      
 

  

        

 
     

         

  

         

  
   
   

    
 

      

  
        

                    
 

 

                  

     

      

 
 

 

          
   

                     

   

   

     

     

        

       

C A 9.; ... CA 9.0 9 9A ..0 C. v A ... 0.. 9A ... . 9 A ... 0-.
. .... ... .... .9. A .... .... ... ... .... .... ..A .... . ... s
0. VA .0 O. .. 9. 9A A 95. 0 9A .OA
3. 99A .9. .99. 99A .99. 99A .9 .9. v9 .99. 99A
. . 90 . .0. O 6. VA .0 ..
. . s v . A .
V . v v
0 99. 9A 90 . 9A .6A .9A
7A .. .. vA . 9A ..A
v . A .
. v A . A
v .A .
vA . v A .
96 . A .
vA .. A .
v . . A .
v . A v .
v . A
. PA . A v . .
v v
A A ND 75 ,}A v .A
v. .
9A 0. v
v A
A . v
V A
A . v
90. A
A v
v. .
A .. v
v.. A
VA 9
. 9.
. VA
VA .6
'K V.A
.9A.
.9A
0.
v
v9o.
3.
.9A.
9
3.
O.
v.
.... 1 F

  

 

 

eouepunqe pezueuuou

71

.Re - o8. .3853. Aim 93 Soc 38:3 8.53-.. do 852% Buaéoz 62 2am

one. E 059. E myth? I

      
          

       

                

     

     

 

 

 

         

     

  

00 000 mNO m 0 0

NO mNO VNO GNU NNO ..NO ONO er er NFO OrO mwO VFO
...“ “a

lJo

        
  

44-
2. .u
3. 9A.
A fl fl.

               
          

                                                  

A

   

'A
A9;

A

A. .‘v
A.

22 u
.A

A.

.A

A.

.A

c

   

A.

A-
‘L

 

'9

    

V
A

:ii;

0
.

   

v‘v

9

            

..

v
A

x” 'A
m .9
...u. A
m .9
”Au“ A
w, .4

9A

A91

                                
                               

'

           

2’.
A'.‘.
V
A:

   

 

Ave

0

  

....A'
A

A.

. 3”“; ...-A A.
'1' A' ' I I...- 'u'.‘. A
.A

'9

C

 

'v
A.

 

 

 

2'.

Q

 

O

A.
V

A.

W

AQA

   

I A i A v C A . A
A A A I A A .
. .'A A A I . ...
.I‘I.IL‘I"
‘ '.‘ ‘ ‘ '.‘.'v‘. A .
A A . A A
' A' .'. A I A A A A A
Q o -. ...

1

676?.

 

A.

V.V

)

 

 

 

 

eouepunqe pazueuuou

 

OEP

 

 

 

 

 

 

 

 

16 18 20 22 24 26 28 3°

 

 

 

 

 

197751976 1970
—.— -—o—

+

Figure 13: Ode/ever! preference exhibited by n-alkanes extracted from
Lake Ene sedrments a) 1980 - 1982; b) 1978 - 1979; c) 1970 - 1977.

Year

Short/long index

0.6 0.8 1 1 .2 1.4 1 .6 1 .8

f

 

      

197a ------.~§ ----------- ------------ ------------
1976. ............
1974 ............ ........... .

1972 ---------- ----------- g ----------- q

 

1970 » . ........... ........... .

 

 

 

1968 L 1 1 1 1

Figure 14: Short/long index of n-alkanes extracted from
Lake Erie sediments.

£5868 utm— oxfl Bob @90ng Seen—mg utm— 9—3 Bet @3255
camera no 353% 229.5. 52 oBmE 0:5th .3 85:3“ 328$. 32 Semi

 

 

mom _. . . . . mom _.

         
      

 

 

 

 

............. o3. 8.2
............. m3. wk:
............. 32 :2

.M m m m n n m u .

m m m m A m m m m
............. ospm 93.
............ 8.2 £2
............. 82 82
............. mo? . «8?

m m m m , H m u m

 

 

 

‘0.
N
(v
‘0.
o
o

m. F r no o 3 m; r
EmEfimm m3: EmEfimm 90:

N

Appendix Bl: Linear regression of n-alkane standards used in the quantification of
sedimentary n-alkanes.

APPENDIX B: ADDITIONAL DATA

 

 

n-Alkane Slope Intercept r'2
C” 30.83 0.335 0.9991
C20 31.78 0.362 0.9992
C22 31.17 0.340 0.9995
C24 28.93 0.309 0.9999
C26 26.61 0.207 0.9999
C30 20.19 -0.017 0.9959
C3. 13.46 -0.218 0.9933
C36 10.15 -0.308 0.9835

 

Appendix B2: Assignments of sedimentary alkanes to linear regressions.

 

 

Regression curves Sedimentary alkanes
(n-alkanes)

C15 Cm C151 C161 Cm Cm pristane, phytane
C20 C19: 020
C22 CH! CH
C24 C239 Cu
C26 C259 C26! C27
C30 Cm C291 C30! C31

 

76

Appendix B3: Percent organic carbon, percent organic nitrogen, and cm of Lake
Erie sedimentary organic matter.

 

 

Year % organic C % organic N C/ N
1982.75 2.22 0.286 9.09
1982.50 2.31 0.279 9.65
1982.25 2.30 0.28 9.57
1982.00 2.27 0.267 9.95
1981.67 2.24 0.274 9.51
1981.33 2.45 0.303 9.43
1981.00 2.47 0.311 9.26
1980.67 2.35 0.285 9.63
1980.33 2.24 0.265 9.86
1980.00 2.20 0.287 8.94
1979.67 2.32 0.27 10.06
1979.33 2.04 0.25 9.53
1979.00 2.08 0.258 9.41
1978.67 2.34 0.276 9.91
1978.33 2.15 0.265 9.47
1978.00 2.12 0.26 9.49
1977.50 2.22 0.284 9.13
1977.00 2.30 0.295 9.09
1976.50 2.27 0.288 9.19
1976.50 2.16 0.241 10.44
1974.00 2.25 0.267 9.81
1972.00 2.37 0.274 10.10
1970.00 2.29 0.266 10.03
1968.00 2.17 0.255 9.94

 

77

Appendix B4: 6‘3C values of Lake Erie sedimentary organic matter, in %o
notation relative to PDB.

 

 

Year 513C (700)
1982.75 -25. 80
1982.50 -25.50
1982.25 -25.32
1982.00 -25.24
1981.67 -25.49
1981.33 -25.92
1981.00 -25.88
1980.67 -25.81
1980.33 -25.47
1980.00 -25.43
1979.67 -25.70
1979.33 -25.56
1979.00 -25.00
1978.67 -25.49
1978.33 -25.43
1978.00 -25.09
1977.50 -24. 89
1977.00 -25.43
1976.50 -25.51
1976.00 -25.52
1974.00 -25.23
1972.00 -24.93
1970.00 -24.89

1968.00

-25.28

 

78

Appendix BS: Concentration of unbound organic matter extracted from
Lake Erie sediments, in mglg dry sediment.

 

 

Yar Extractable Organic Matter (mg/g sed)
1982.75 1.18
1982.50 0.97
1982.25 1.15
1982.00 1.03
1981.67 1.02
1981.33 1.16
1981.00 1.21
1980.67 1.13
1980.33 1.31
1980.00 1.14
1979.67 1.29
1979.33 1.22
1979.00 1.07
1978.67 1.15
1978.33 1.15
1978.00 1.06
1977.50 1.65
1977.00 1.87
1976.50 2.07
1976.00 1.69
1974.00 1.08
1972.00 1.50
1970.00 1.63

1968.00 1.56

 

79

Appendix B6: Concentration of compound classes in Lake Erie sediment, in
mg/ g dry sediment.

 

 

Year Aliphatic Aromatic Polar
1982.75 0.44 0.22 0.52
1982.00 0.29 0.15 0.39
1981.33 0.18 0.1 0.34
1980.00 0.26 0.14 0.39
1979.67 0.25 0.15 0.37
1979.00 0.3 0.15 0.32
1978.67 0.31 0.14 0.38
1978.33 0.27 0.13 0.33
1977.50 0.28 0.13 0.44
1976.00 0.3 0.16 0.51
1970.00 0.36 0.16 0.51

 

Appendix B7: Relative abundance of unresolved complex mixture in
Lake Erie sediments.

 

 

Year UCM
1982.75 0.85
1982.00 0.84
1981.33 0.86
1980.00 0.77
1979.67 0.94
1979.00 0.86
1978.67 0.86
1978.33 0.76
1977.50 0.86
1976.00 0.44

1970.00 1.00

 

 

bmd end 36 36 m— .o o 8.052

 

fig .0 0w .0 v0.0 2 .0 50.0 0 00.050“
”v.0 50.0 0~ A 00.0 0N0 00.0 00.2.0~
Nv.0 38.0 00.— ~00 #0 00.0 mmdham
med 5‘0 24 00.0 0N0 v0.0 b0.»b¢~
9.0 00.0 .3.— b¢.0 00.0 :.0 00.2.0“
v0.0 00.0 0v.— wvd ~¢.0 00.0 >930“
0v.0 hvd N“; 00.0 find 50.0 00.000“
00.0 05.0 054 ~00 0Y0 3.0 00.30—
00.0 00.0 0N4 00.0 ~N.0 a; .0 00.Nwou
38.0 00.0 3.4 00.0 0.0.0 3.0 0b.Nwm~

2U 20 :0 30 20 :0 a»

 

.858. E. 8 was 5 .3883. 8m 93 so... 3688 8.8%-.. .8 882:8 338...... ”mm 5289..

81

 

 

«No 0— .0 0N0 53 .0 0m.0 :0 00.053
3.0 00.0 3.0 50.0 3.0 03.0 00.053
00.0 3 .0 and g0 Nm.0 0N.0 00.553
and 3.0 3.0 $0 N00 5N0 «H.053
3.0 03 .0 3.0 5.0 3.0 0N.0 50.053
and 2.0 «m0 0~.0 0m.0 «.00 00.053
00.0 «Nd 00.0 5m.0 3.0 N30 50.053
0N.0 00.0 and and 0N.0 5N.0 00.003
nm.0 03.0 3.0 3.0 3.0 Ned 00.303
and 3.0 and m~.0 #00 and 00.33
3.0 00.0 5.0 53 .0 8.0 00.0 05.33

so an no so so so he»

 

8888 .8 528%.

82

 

 

8.8 2.8 and 2.8 88 3.8 8.82
G8 58 Rd 8.8 8.8 2.8 8.82
:8 :8 8.8 2.8 8.8 2.8 8.2.52
8.8 2.8 $8 :8 8.8 2.8 8.82
$8 28 8.8 2.8 who 2.8 8.82
who 88 8.8 2.8 and 8.8 8.2.2
8.8 :8 2.8 3.8 :3 8.8 8.22
$8 5.8 28 8.8 8.8 2.8 8.82
:8 8.8 Rd 8.8 2.8 2.8 8.32
and 88 2.8 8.8 $8 2.8 8.22
8.8 _ 8.8 $8 8.8 8.8 3 .o 8.32

:0 so go so so so 53»

 

32.88 .mm 8823...

 

83

 

0v.0 3.0 00.— 0N.0 3.0 00.0 00.053
5N.0 0~.0 00.3 3 .0 03 .0 00.0 00.053
0m.0 0‘0 00._ 00.0 0N.0 N00 00.553
3.0 3.0 00.3 3.0 30.0 00.0 3.053
00.0 3.0 00.3 3.0 0N0 00.0 50.353
3.0 5v.0 00.3 3.0 V0.0 00.0 00.053
3.0 3.0 00.3 00.0 wmd 00.0 50.053
00.0 3.0 00.3 3.0 3.0 00.0 00.033
00.0 00.0 00.3 00.0 3.0 00.0 3.33
3.0 0Y0 00. 3 0.20 53 .0 3 .0 00.33
3.0 3.0 00.3 50.0 30.0 50.0 05.33

2U 20 :0 20 :U 30 30>

 

£5863 arm 33 Bob 09896 838.: .8 8050502" 0303.32 ”mm €=000<

 

v0.0 3 .0 00.0 0N.0 00.0 0N.0 00.053

 

ad 8d ”Nd :d 2d 2d 8.2.2
8d 2d Rd 2d dad Rd SE:
8d :d and and 8d ad «.35
mmd 2d 3d 8d and Rd Sdg
Ed ad ad 8d 8d omd 8.33
ad 2d 3d Rd 8d ad $.32
Ed 8d 8d 8d Rd «3 8.82
3d 8d and 2d 8d «Nd 8.82
mad 2d 8d ad and Rd 8.3%
. 3d 8d ad ad A 3d 3d Ewe
au :0 no no so so 5»

 

325:8 .am sauna—Ac.

85

 

 

8d 2d 8d 2d 8d 2d 8.82
8d 8d 8d 2d Ed 2d 8.82
Ed 2d Rd :d Rd 2d 8.82
8d 3d 8d 2d 8d 2d 8.82
and 2d 8d 2d 2.d 3d 8.82
8d 2d 8d 2d Rd 2d 8.82
8d 2d Ed 3d Rd 2d 8.22
8d 8d 8d 8d 8d :d 8.82
8d 8d 8d 8d 8d 8d 8.52
8d 8d Ed 8d 8d :d 8.82
8d 8d 8d . 8d 3d 2d 8.82

:0 so so so no so 28»

 

8888 .2. 5825

86

 

 

054 00.3 004 0*.“ 00.3 0m.N XVN 00.053
:.N 00.3 NV; 05.3 05.N V0.0 3N6” . 00.05am
m0.— vmé “NA 30.3 mm; 0m.N 0N.N 00.550~
004 00.3 00.3 NVA N0.“ va N0.N mm.053
00.— Nmé MNA 00.3 mm.“ 3.0 5N.N 50.053
054 mm; 3 .3 0N4 N04 N04 554 00.053
00; va 0m.— NV; 00.“ 0N.N 00d 50.0503
0v; VNA 3.3 00.3 05.3 5N.N NN.N 00.003
3.— mmé 3.3 NNA V04 00.N N04 00.33
9v.— 00.— MN; 00; 004 00.3 3.3 00.N03
~54 am; am; 00.3 054 NNN .VmN 05.Nw3

«NU ~80 0ND 30 :0 3U 30 5*

 

255009. cum 8.3 80.0 09255 8:83.: .8 35.8.00:— =o>o=uvo ”05 50:89...

87

 

 

#3. ;.m an «3 98 aim «3 8.2.2
9;: 8.0 :4. a.” Ed 8d 8N . 832
8a «3. and 33 S." «.2 2 .N 32.3
W: Se 3m an RN :R n3 2&5
a3. 8;. 2.; 8a SN v2 2N $.33
8.... on... Ea SN 98 o: mom 8.3.3
$0. 8... and ”Z :5 mg mg Sane
and an m3 :3 ”3 a: a: 8.8%
R? 8.0 mm... 85 o3 ”2 an 8.32
8.» 8w «hm :3 end 22 a: 8.3%
one 3m. :3. 21“ e: 93 aim, $.32
so so so so no so an no»

 

82.9.8 65 5u=§<

88

 

 

:8 8.2.2
:8 8.82
8.8 822
8.8 8.82
8.: $.82
8: 8.2.2
8.8 $.22
:2 8.82
3: 8.52
8.: 8.22
mm: 8.82
83:88 :8»

 

35568 cum 0x3 Eat 389:5 853?: .3 5:5 $03.85 a E 28:02?

89

 

 

Rd mvd 8.052
mod who 8.053
and «56 3.532
amd cad mmdba
36 mp; $.32
omd NY: 00.22
3.0 86 50.3.3
26 m— A 8.0me
and 5nd $.33
wed mu; 8.Nma_
mad mad flamma—
98868 $5 95868 33
05%.... 0:83: 80>

 

98888 arm 83.— Bob 88on 8:53: :5 0:5th mo 883:3: 8388‘ ”NE £333.

BIBLIOGRAPHY

Albaiges, J., Algaba, 1., and Grimalt, J. (1984) Extractable and bound neutral lipids
in some lacustrine sediments. Org. Geochem. , 6, 223-236.

Arthur, M. A., Dean, W. E., and Claypool, G. E. (1985) Anomalous C-13
enrichment in modern marine organic carbon. Nature, 315, 216-218.

Auer, M. T., and Canale, R. P. (1982) Ecological studies and mathematical
modelling of Cladophora in Lake Huron: 7. Model verification and system
response. 1. Great Lakes Res., 8, 134-143.

Bakel, A. J., Ostrom, P. H. and Ostrom, N. E. (1994) Carbon isotopic analysis of
individual n-alkanes: Evaluation of accuracy and application to marine particulate
organic material. Org. Geochem, 21, 595-602.

Baker, J. E., and Eisenreich, S. J. (1989) PCBs and PAHs as tracers of particulate
dynamics in large lakes. J. Great Lakes Res., 15, 84-103.

Beeton, A. M. (1969) Changes in the environment and biota of the Great Lakes. In
Eutrophication: Causes, Consequences, Correctives - symposium, I 96 7, Proc.
Washington, D. C., National Acad. Sci. p. 150-187.

Blumer, M., Mullin, M. M., and Thomas, D. S. (1963) Pristane in zooplankton.
Science, 140, 974.

Bourbonniere, R. A., Meyers, P. A., Eadie, B. J. and Robbins, J. A. (1991)
Environmental and diagenetic effects on geolipid compositions of sediments in
Lakes Erie and Ontario. In Organic Geochemistry: Advances and Applications in
the Natural Environment. D.A.C. Manning, ed., Manchester Univ. Press,
Manchester, p. 498-501.

Brillis, G. M., and Marsden, P. J. (1990) Comparative evaluation of soxhlet and
sonication in the determination of polynuclear aromatic hydrocarbons in soil.
Ozemosphere, 21, 91-98.

90

91

Brooks, P. W., Eglinton, G., Gaskell, S. J., McHugh, D. J., Maxwell, J. R., and
Philp, R. P. (1976) Lipids of recent sediments, Part I: Straight-chain
hydrocarbons and carboxylic acids of some temperate, lacustrine and sub-tropical
lagoonal/tidal flat sediments. atern. Geol., 18, 21-38.

Boyce, F. M., Charlton, M. N., Rathke, D., Mortimer, C. H., and Bennett, J.
(1987) Lake Erie research: Recent results, remaining gaps. J. Great Lakes Res.,
13, 826-840.

Brinkhurst, R. 0., and Austin, M. J. (1979) Assimilation by aquatic oligochaeta.
Inv. Rev. Gesamten. Hydrobiol. 64, 245-250.

Burns, N. M. , and Ross, C. (1972) Oxygen-nutrient relationships within the central
basin of Lake Erie. In Nutrients in Natural Water. H. E. Allen and R. J.
Kramer, eds., Wiley-Interscience, New York, p. 193-250.

Burns, N. M., Jaquet, J.-M., Kemp, A. L. W., Lam, D. C. L., Leach, J. H.,
Munawar, M., Simons, T. J., Sly, P. G., Thomas, R. L., Watson, N. H. F., and
Williams, J. D. H. (1976) Processes within Lake Eric. J. Fish. Res. Board Can.
33, 639-643.

Burns, N. M. (1985) Erie: The Lake That Survived. Rowman and Allanheld,
Totowa, New Jersey.

Canuel, E. A., and Martens, C. S. (1993) Seasoml variations in the sources and
alteration of organic matter associated with recently-deposited sediments.
Org. Geochem, 20, 563-567.

Clark, R. C., and Blumer, M. (1967) Distributions of n-paraffins in marine
organisms and sediment. Limnol. 0ceanog., 12, 79-87.

Collister, J. W., Rieley, G., Stern, B., Eglinton, G., and Fry, B. (1994a)
Compound-specific ”C analysis of leaf lipids from plants with differing carbon
dioxide metabolisms. Org. Geochem. , 21, 619-627.

Collister, J.W., Lichtfouse, E., Hieshima, G., and Hayes, J. M. (1994b) Partial
resolution of sources of n-alkanes in the saline portion of the Parachute Creek
Member, Green River Formation (Piceance Creek Basin, Colorado) Org.
Geochem., 21, 645-659.

Colombo, J. C., Pelletier, B., Brochu, C., and Khalil, M. (1989) Determination of
hydrocarbon sources using n-alkane and polyaromatic hydrocarbon distribution
indexes. Case study: Rio de La Plata Estuary, Argentina. Environ. Sci.
Technol., 23, 888-894.

92

Cranwell, P. A. (1973) Chain-length distribution of n-alkancs from lake sediments in
relation to post-glacial environmental change. Freshwat. Biol. , 3, 259-265 .

Cranwell, P. A. (1978) Extractable and bound lipid components in a freshwater
sediment. Geochem. Cosmo. Acta, 42, 1523-1532.

Cranwell, P. A. (1982) Lipids of aquatic sediments and sedimenting particles. Prog.
Lip. Res. 21, 271-308.

Cranwell, P. A. (1984) Lipid geochemistry of sediments from Upton Broad, a small
productive lake. Org. Geochem., 7, 25-37.

Dean, W. E., Arthur, M. A., Claypool, G. E. (1986) Depletion of (WC in
Cretaceous marine organic matter: Source, diagenetic, or environmental signal?
Mar. Geol., 70, 119-157.

Degens, E. T., Cuillard, R. R. C., Sackett, W. M., and Hellebust, J. A. (1968)
Metabolic fractionation of carbon isotopes in marine plankton - 1. Temperature
and respiration experiments. Deep Sea Res. 15, 1-9.

deLeeuw, J. W. , and largeau, C. (1993) A review of macromolecular organic
compounds that comprise living organisms and their role in kerogen, coal, and
petroleum formation. In Organic Geochemistry. M. H. Engel and S. A. Macko,
eds., Plenum Press, New York, p. 23-72.

Descolas-Gros, C., and Fontugne, M. (1990) Stable carbon isotope fractionation by.
marine phytoplankton during photosynthesis. Plant, Cell, and Environment, 13,
207-218.

Deuser, W. G., Degens, E. T., and Guillard, R. R. L. (1968) Carbon isotope
relationships between plankton and sea water. Geochem. Cosmo. Acta, 32,
657-660.

Didyk, B. M., Simoneit, B. R. T., Brassell, S. C., and Eglinton, G. (1978) Organic
geochemical indicators of paleoenvironmental conditions of sedimentation.
Nature, 272, 216-222.

Di Toro, D. M., Thomas, N. A., Herdenddorf, C. E., Winfield, R. P., and
Connolly, J. P. (1987) A post audit of a Lake Erie eutrophication model.
J. Great Lakes Res., 13, 801-825.

Dobson, H. F. H., Gilbertson, M., Sly, P. G. (1974) A summary and comparison of
nutrients and related water quality in Lakes Erie, Ontario, Huron, and Superior.
J. Fish. Res. Board Can. 31, 731-738.

93

Eadie, B. J., Chambers, R. L., Gardner, W. S., and Bell, G. L. (1984) Sediment
trap studies in Lake Michigan: resuspension and chemical fluxes in the southern
basin. J. Great Lakes Res. 10, 307-321.

Eglington, G., and Hamilton, R. J. (1967) Leaf epicuticular waxes. Science, 156,
1322-1334.

Eisenreich, S. J., Capel, P. D., Robbins, J. A., and Bom'bonniere, R. (1989)
Accumulation and diagenesis of chlorinated hydrocarbons in lacustrine sediments.
Environ. Sci. Technol., 23, 1116-1126.

El-Shaarawi, A. H. (1987) Water quality changes in Lake Erie, 1968-1990. J. Great
Lakes Res., 13, 674-683. ‘

Falkowski, P. G. (1991) Species variability in the fractionation of 1“C and "C by -
marine phytoplankton. J. Plankton Res., 13 Supp., 21-38.

Farquhar, G. D., O’Lary, M. H., and Berry J. A. (1982) On the relationship
between carbon isotope discrimination and the intereellular carbon dioxide
concentration in leaves. Aust. J. Plant Physiol. 9, 121-137.

Faure, G. (1986) Principles of Isotope Geology. John Wiley and Sons, New York.

Fisher, J. B., McCall, P. L., Lick, W. J., and Robbins, J. A. (1980) Vertical
mixing of sediments by tubificid oligochaetes. J. Geophys. Res. 85, 3997-4006.

Fogel, M. L., Cifuentes, L. A., Velinsky, D. J., and Sharp, J. H. (1992)
Relationship of carbon availabilitiy in estuarine phytoplankton to isotopic
composition. Mar. Ecol. Prog. Ser., 82, 291-300.

Fogel, M. L., and Cifuentes, L. A. (1993) Isotope fractionation during primary
production. In Organic Geochemistry. M. H. Engel and S. A. Macko, eds.,
Plenum Press, New York, p. 73-97.

Fontugne, M. R., and Duplessy, J. C. (1978) Carbon isotope ratio of marine
plankton related to water masses. Earth Planetary Science Letters, 41, 365-371.

Fontugne, M. R., and Calvert, S. E. (1992) Late Pleistocene variability of the
carbon isotopic composition of organic matter in the eastern Mediterranean:
Monitor of changes in carbon sources and atmospheric CO, concentrations.
Paleooceanography, 7, 1-20. '

Fraser, A. S. (1987) Tributary and point source total phosphorus loading to Lake
Eric. J. GreatLakes Res., 13, 659-666.

94

Freeman, K. H., and Hayes, J. M. (1992) Fractionation of carbon isotopes by
phytoplankton and estimates of ancient pCO, levels. Global Biogeochem. Cycles,
6, 185-198.

Freeman, K. H., Wakeham, S. G., and Hayes, J. M. (1994) Predictive isotopic
biogeochemistry: Hydrocarbons from anoxic marine basins. Org. Geochem. , 21,
629-644.

Fry, B, and Wainwright, S. C. (1991) Diatom sources of l3C-rich carbon in marine
food webs. Mar. Ecol. Prog. Ser., 76, 149-157.

Gearing, J. N., Gearing, P. J., Rudnick, D. T., Requejo, A. G., and Hutchins, M. J.
(1984) Isotopic variability of organic carbon in a phytoplankton-based,
temperate estuary. Geochem. Cosmo. Acta, 48, 1089-1098.

Gelpi, B., Schneider, H., Mann, J. and Oro, J. (1970) Hydrocarbons of
geochemical significance in microscopic algae. Phytachemistry, 9, 603-612.

Giger, W., Schaffner, C., and Wakeham, S. G. (1980) Aliphatic and olefinic
hydrocarbons in recent sediments of Greifensee, Switzerland. Geochem. Cosmo.
Acta, 44, 119-129.

Godell, H. G. (1972) Carbon! nitrogen ratio. In Encyclopedia of geochemistry and
environmental science. R. W. Fairbridge ed. , Van Nostrand Reinhold, New
York, p. 136-142.

Goericke, R., Montoya, J. P., and Fry, B. (1994) Physiology of isotopic
fractionation in algae and cyanobacteria. In Stable Isotopes in Ecology and
Environmental Science. K. Lajtha and R. H. Michener, ed. , Blackwell Scientific
Publications, Oxford, p. 187-221.

Grimalt, J. and Albaiges, J. (1987) Sources and occurrence of Cu-Cn n-alkane
distributions with even carbon-number preference in sedimentary environments.
Geochem. Cosmo. Acta, 51, 1379-1384.

Han, J. and Calvin, M. (1969) Hydrocarbon distribution of algae and bacteria, and
microbiological activity in sediments. Proc. Natl. Acad. Sci. U.S.A. 64, 436-443.

Hayes, J. M., Freeman, K. H., Popp, B. N., and Hoham, C. H. (1990) Compound-
specific isotopic analysis: A novel tool for reconstruction of ancient
biogeochemical processes. Org. Geochem., 16, 1115-1128.

Hayes, J. M. (1993) Factors controlling l3C contents of sedimentary organic
compounds: Principles and evidence. Mar. Geol., 113, 111-125.

95

Ho, E. S., and Meyers, P. A. (1994) Variability of early diagenesis in lake
sediments: Evidence from the sedimentary geolipid record in an isolated tarn.
01cm. Geol., 112, 309-324.

Hollander, D. J. , McKenzie, J. A. (1991) CO, control on carbon-isotope fractionation
during aqueous photosynthesis: A paleo-pCO, barometer. Geology, 19,
929-932.

Ishiwatari, R. , Ogura, K., and Horie, S. (1980) Organic geochemistry of a lacustrine
sediment (Lake Haruna, Japan). arem. Geol., 29, 261-280.

Ishiwatari, R., Uzaki, M., and Yamada, K. (1994) Carbon isotope composition of
individual n-alkanes in recent sediments. Org. Geochem., 21, 801-808.

Jasper, J. P., and Gagosian, R. B. (1989) Glacial-interglacial climatically forced
6‘3C variations in sedimentary organic matter. Nature, 342, 60-62.

Keeling, C. D., Bacastow, R. B., Carter, A. F., Piper, S. C., Whorf, T. P.,
Heimann, M., Mook, W. G., and Roeloffzen, H. (1989) A three-dimensional
model of atmospheric CO, transport based on observed winds: Analysis of
observational data. In Aspects of climate variability in the Pacific and Western
Americas, Geophysical Monograph 55. D. H. Peterson, ed. American
Geophysical Union, Washington D.C., p. 165-236.

Kemp, A. L. W., Gray, C. B. J., and Mudrochova, A. (1972) Changes in C, N, P,
and S in the last 140 years in three cores from Lakes Ontario, Erie, and Huron.
In Nutrients in Natural Water, ed. H. E. Allen and R. J. Kramer. Wiley-
Interscience, New York, p. 251-279.

Kemp, A. L. W., Thomas, R. L., Dell, C. I., and Jaquet, J.-M. (1976) Cultural
impact on the geochemistry of sediments in Lake Eric. J. Fish. Res. Board Can.
33, 440-462.

Kemp, A. L. W., and Johnston, L. M. (1979) Diagenesis of organic matter in the
sediments of Lakes Ontario, Erie, and Huron. J. GreatLakes Res., 5, 1-10.

Kennicutt, M. C. and Brooks, J. M. (1990) Unusual normal alkane distributions in
offshore New Zealand sediments. Org. Geochem., 15, 193-197.

Khan, S. U. , and Schnitzer, M. (1972) The retention of hydrophobic organic
compounds by humic acid. Geochem. Cosmo. Acta, 36, 745-754.

Kvenvolden, K. A., Rapp, J. B., Golan-Bac, M., and Hostettler, F. D. (1987)
Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica. Org.
Geochem., 11, 291-302.

96

Lam, D. C. L., Schertzer, W. M., and Fraser, A. S. (1987) Oxygen depletion in
Lake Erie: Modeling the physical, chemical, and bflogical interactions, 1972 and
1979. J. GreatLakes Res., 13, 770-781.

Laws, E. A., Popp, B. N., Bidigare, R. R., Kennicutt, M. C., and Macko, S. A.
(1995) Dependence of phytoplankton isotopic composition on growth rate and
[C02],,,: Theoretical considerations and experimental results. Geochem. Cosmo.
Acta, 59, 1131-1138.

Lean, D. R. S., Fricker, H. -J., Charlton, M. N., Cuhel, R. L., and Pick, F. R.
(1987) The Lake Ontario life support system. Can. J. Fish. Aqaut. Sci., 44,
2230-2240.

Leenheer, M. J., Flessland, K. D., and Meyers, P. A. (1984) Comparison of lipid
character of sediments from the Great Lakes and tll: Northwestern Atlantic.
Org. Geochem., 7, 141-150.

Lichtfouse, E., Derenne, S., Mariotti, A., and largeau, C. (1994) Possible algal
origin of long chain odd n-alkanes in immature sediments as revealed by
distributions and carbon isotope ratios. Org. Geochem., 22, 1023-1027.

Macko, S. A., Engel, M. H., and Parker, P. L. (1993) Early diagenesis of organic
matter in sediments: Assessment of mechanisms arll preservation by the use of
isotopic molecular approaches. In Organic Geochemistry. M. H. Engel and S.
A. Macko, eds., Plenum Press, New York, p. 211-224.

Makarewicz, J. C. and Bertram, P. (1991) Evidence ft! the restoration of the Lake
Erie ecosystem. Bioscience, 41, 216-223.

Makarewicz, J. C. (1993) Phytoplankton biomass and species composition in Lake .
Erie, 1970 to 1987. J. GreatLakes Res., 19, 258-274.

Matisoff, G. and Robbins, J. A. (1987) A model for biological mixing of sediments.
J. Geological Eduction, 35, 144-149.

Matthews, D. B., and Hayes, J. M. (1978) Isotope-rat'lrmonitoring gas
chromatography-mass spectoscopy. Anal. Chem., 58, 1465-1473.

McCabe, B. (1985) The dynamics of ”C in several New Zealand lakes. PhD thesis,
Univ. Waikato.

McCall, P. L., and Fisher, J. B. (1979) Effects of tubificid oligochaetes on physical
and chemical properties of Lake Erie sediments. In: Aquatic Oligochaete Biology.
R. O. Brinkhurst and D. G. Cook, eds., Plenum Pres, New York, p. 253-318.

97

McCall, P. L., and Tevesz, M. J. S. The effects of benthos on physical properties of
freshwater sediments. In: Animal-Sediment Relations. P. L. McCall and
M. J. S. Tevesz, eds., Plenum Press, New York, p. 105-176.

McKenzie, J. A. (1986) Carbon isotopes and productivity in the lacustrine and marine
environment. In Uremical Processes in Lakes, (Werner Stumm, ed.) pp.
99 - 118.

Meyers, P. A. and Benson, L. V. (1988) Sedimentary biomarker and isotopic
indicators of the paleoclimatic history of the Walker Lake basin, western Nevada.
Org. Geochem., 13, 807-813.

Meyers, P. A., and Eadie, B. J. (1993) Sources, degradation, and recycling of
organic matter associated with sinking particles in Lake Michigan. Org.
Geochem. , 20, 47-56.

Meyers, P. A., and Ishiwatari, R. (1993a) Lacustrine organic geochemistry- an
overview of indicators of organic matter sources and diagenesis in lake
sediments. Org. Geochem., 20, 867-900.

Meyers, P. A. and Ishiwatari, R. (1993b) The early diagenesis of organic matter in
lacustrine sediments. In Organic Geochemistry. M. H. Engel and S. A. Macko,
eds., Plenum Press, New York, p. 185-209.

Meyers, P. A., and Horie, S. (1993) An organic carbon isotopic record of glacial-
postglacial change in atmospheric pCO, in the sediments of Lake Biwa, Japan.
Palegeography, Paleoclimatology, Paleoecology. 105, 171-178.

Mortimer, C. H. , (1987) Fifty years of physical investigations and related
limnological studies on Lake Erie, 1928-1977. J. Great Lakes Res., 13, 407-435.

Muller, P. J. (1977) CIN ratios in Pacific deep-sea sediments: Effects of inorganic
ammonia and organic nitrogen compounds sorbed by clays. Geochem. Cosmo.
Acta, 41, 765-776.

Nicholls, K. H., and Hopkins, G. J. (1993) Recent changes in Lake Erie (North
Shore) phytoplankton: Cumulative impacts of phosphorus loading reductions and
the zebra mussel introduction. J. Great Lakes Res., 19, 637-647.

Nishimura, M., and Baker, E. W. (1986) Possible origin of n-alkanes with a
remarkable even-to-odd predominance in recent marine sediments. Geochem.
Cosmo. Acta, 50, 299-305.

Ogner, G., and Schnizer, M. (1970) The occurence of alkanes in fulvic acid, a soil
humic fraction. Geochem. Cosmo. Acta, 34, 921-928.

98
O’Leary, M. H. (1988) Carbon isotopes in photosynthesis. BioScience, 38, 328-336.

Ostrom, N. E. (1989) Sources, cycling, and deposition of organic matter in northern
Newfoundland fjords and bays. M.Sc Thesis, Memorial Univ. of Newfoundland.

Parrish, C. C., Eadie, B. J., Gardner, W. S., and Cavaletto, J. F. (1992) Lipid class
and alkane distribution in settling particles of the upper Iaurentian Great Lakes.

Org. Geochem., 18, 33-40.

Peters, K. B., and Moldowan, J. M. (1993) The Biomarker Guide: Interpreting
Molecular Fossils in Petroleum and Ancient Sediments. Prentice Hall, Englewood

Cliffs, New Jersey.

Rau, G. H., Takahashi, T., and Des Marais, D. J. (1989) latitudinal variations in
plankton 6‘3C: Implications for CO, and productivity in past oceans. Nature,

341, 516-518.

Rau, G. H., Froelich, P. N., Takahashi, T., Des Marais, D. J. (1991) Does
sedimentary organic 6‘3C record variations in Quaternary ocean [C02 (aq)]?

Paleoceanography, 6, 335 -347 .

Rau, G. H., Takahashi, T., Des Marais, D. J., Repeta, D. J., and Martin, J. H.
(1992) The relationship between ”C of organic matter and [COz(aq)] in ocean
surface water: Data from a JGOFS site in the northmst Atlantic Ocean and a

model. Geochem. Cosmo. Acta, 56, 1413-1419.

Rea, D. K., Bourbonierre, R. A., and Meyers, P. A. (1980) Southern Lake Michigan
sediments: Changes in accumulation rate, mineralology, and organic content.

J. Great Lakes Res., 6, 321-330.
Reed, W. E. (1977) Biogeochemistry of Mono Iake, California. Geochem. Cosmo.

Acta, 41, 1231-1245.

Ricci, M. P., Merritt, D. A., Freeman, K. H., and Hayes, J. M. (1994) Acquisition
and processing of data for isotope-ratio-monitoring mass spectroscopy. Org.
Geochem., 21, 561-571.

Rieley, G., Collier, R. J., Jones, D. M., Eglinton, G., Faldn, P. A., and Fallick,
A.E. (1991) Sources of sedimentary lipids deduced from stable carbon-isotope

analysis of individual compounds. Nature, 352, 425-427.

Robbins, J. A., and Edgington, D. N. (1975) Determination of recent sedimentation
rates in lake Michigan using Pb-210 and Cs-137. Geochem. Cosmo. Acta, 39,

285-304.

99

Robbins, J. A., Keilty, T., White, D. S., and Edgington, D. N. (1989) Relationships
among Tubificid abundances, sediment composition, and accumulation rates in
Lake Erie. Can. J. Aquat. Sci., 46, 223-231.

Roeske, C. A., and O’Leary, M. H. (1984) Carbon isotope effects on the enzyme-
catalyzed carboxylation of ribulose bisphosphate. Biochemistry, 23, 6275-6284.

Rosa, F. (1987) Iake Erie central basin: Total phosphorus trend analysis from 1968
to 1982. J. GreatLakes Res., 13, 667-673.

Rosa, F., and Burns, N. M. (1987) Iake Erie central basin oxygen depletion changes
from 1929 to 1980. J. GreatLakes Res., 13, 684-696.

Sackett, W. M., Eadie, B. J., and Meyers, P. A. (1986) Stable carbon isotope
studies of organic matter in Greal Iakes sediments. Trans. Am. Geophys. Un. 76,
1058 (abs.)

Sandstrom, M. W. (1988) Aliphatic hydrocarbons in surface sediments from the
North Queensland coast and Great Barrier Reef: Effects of tropical cyclone
Winifred. Org. Geochem., 12, 445-454.

Scalan, R. S., and Smith, J. E. (1970) An improved measure of the odd-even
predominance in the normal alkanes of sediment extracts and petroleum.
Geochem. Cosmo. Acta, 34, 611-620.

Schelske, C. L., and Hodell, D. A. (1991) Recent changes in productivity and
climate of Lake Ontario detected by isotopic analysis of sediments. Limnol.
Oceanogr. 36, 961-975.

Schoell, M., Simoneit, B. R. T., and Wang, '1‘. -G. (1994) Organic geochemistry
and coal petrology of Tertiary brown coal in the Zhoujing mine, Baise Basin,
South China -4. Biomarker sources inferred from stable carbon isotope
compositions of individual compounds. Org. Geochem. , 21, 713-720.

Shemesh, A., Macko, S. A., Charles, C. D., and Rau, G. H. (1993) Isotopic
evidence for reduced productivity in the glacial southern ocean. Science, 262,
407-410.

Sly, P. G., and Lewis, C. F. M. (1972) The GreatLakes of Canada- Quaternary
Geology and Limnology. Int. Geol. Cong., Montreal, Quebec, Guidebook Trip,
A43. 92 pp.

Sly, P. G. (1976) Iake Fsie and its basin. J. Fish. Res. Board Can. 33, 355-370

100

Spiker, E. C., and Hatcher, P. G. (1984) Carbon isotope fractionation of sapropelic
organic matter during early diagenesis. Org. Geochem., 5, 283-290.

Spooner, N., Rieley, G., Collister, J. W., lander, M., Cranwell, P.A., and ,
Maxwell, J. R. (1994) Stable carbon isotopic correlation of individual biolipids in
aquatic organisms and a lake bottom sediment. Org. Geochem., 21, 823-827.

Stabel, H. H. (1986) Calcite precipitation in lake Constance: chemical equilibrium,
sedimentation and nucleation by algae. Limnol. Oceanogr., 31, 1081-1093.

Stuvier, M. (1975) Climate versus changes in 13C content of the organic component
of lake sediments during the late Quaternary. Quat. Res., 5, 251-262.

Summons, R. E. (1993) Biogeochemical cycles: A review of fundamental aspects of
organic matter formation, preservation, and composition. In Organic
Geochemistry. M. H. Engel and S. A. Macko, eds., Plenum Press, New York,
p. 3-21.

Takahashi, K., Yoshioka, T., Wada, B., and Sakamoto, M. (1990) Temporal
variations in carbon isotope ratio of phytoplankton in a eutrophic lake. J. Plan/don
Res., 12, 799-808.

Taylor, J. R. (1982) An Introduction to Error Analysis. Oxford University Press, ,
Mill Valley, California.

Vallentyne, J. R. (1962) Solubility and the decomposition of organic matter in
nature. Arch. Hydrobiol. , 58: 423-434.

Wakeham, S. G., and Carpenter, R. (1976) Aliphatic hydrocarbons in sediments of
lake Washington. Limnol. Oceanog., 21, 711-723.

Wakeham, S. G., and Lee, C. (1993) Production, transport, and alteration of
particulate organic matter in the marine water column. In Organic Geochemistry.
M. H. Engel and S. A. Macko, eds., Plenum Press, New York, p. 145-169.

Weaver, F. J. (1988) Source rock studies of natural seep oils near Parsons Pond on
the West Coast of Newaundland. M.Sc Thesis, Memorial Univ. of
Newfoundland.

Wong, W. W., Clarke, L. L.,. Johnson, G. A., Llaurador, M., and Klein, P. D.
(1992) Comparison to two elemental-analyzer gas-isotope-ratio mass spectrometer
systems in the simultaneous measurement of ”Cl 12C ratios and carbon content in.
organic samples. Anal. Chem, 64, 354-358.

101

Wu, L., and Culver, D. A. (1991) Zooplankton grazing and phytoplankton
abundance: An assessment before and after invasion of Dreissena Polymorpha.
J. Great Lakes Res., 17, 425-436.

"Inun11111111“