Elk Lake, Minnesota, is typical of the many lakes in glaciated parts of the Midwestern United States.

Characterization of Organic Matter in Lake Sediments 

from Minnesota and Yellowstone National Park

Open-File Report 2006-1053

U.S. Department of the Interior

U.S. Geological Survey
Characterization of Organic Matter in 

Lake Sediments from Minnesota and 

Yellowstone National Park

By Walter E. Dean

Open-File Report 2006-1053

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

Version 1.0

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Dean, W.E., 2006, Characterization of organic matter in lake sediments from Minnesota and Yellowstone National 

Park: U.S. Geological Survey Open-File Report 2006-1053, 40 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

The Lakes ........................................................................................................................................................2

Materials .........................................................................................................................................................5

Methods...........................................................................................................................................................5

Carbon Coulometry...............................................................................................................................5

Rock-Eval Pyrolysis ..............................................................................................................................5

Isotopic Analyses..................................................................................................................................6

Results .............................................................................................................................................................6

Organic Carbon and Calcium Carbonate ..........................................................................................6

Rock-Eval Pyrolysis ..............................................................................................................................6

Carbon and Nitrogen Isotopes ..................................................................................................................12

Discussion.....................................................................................................................................................14

Conclusions...................................................................................................................................................19

Acknowledgments.......................................................................................................................................20

Figures

1. Map of Minnesota and adjacent North and South Dakota showing the

locations of lakes.................................................................................................................3

2. Map of Yellowstone National Park showing the locations of lakes............................4

3. Cross plots of percentage of CaCO3 versus percentage of OC....................................8

4. Cross plots of Rock–Eval pyrolysis oxygen index versus hydrogen index

for samples of Minnesota lake sediments.......................................................................9

5. Cross plot of Rock–Eval pyrolysis oxygen index versus hydrogen index for

samples of sediments from lakes in Yellowstone National Park ..............................10

6. Cross plots of percentage of OC versus Rock–Eval pyrolysis S2 peak height........11

7. Ranges of values of δ13C in various plant materials and organic matter

in lake sediments ...............................................................................................................12

8. Ranges of values of δ15N in various nitrogen bearing pools and in

lake sediments ...................................................................................................................13

9. Cross plots of Rock–Eval pyrolysis hydrogen index versus values δ13C

in lake sediments. ..............................................................................................................18

10. Values of Rock-Eval pryolysis hydrogen index (HI) and 13C of organic matter

in sediments in Lake Greifen, Switzerland ....................................................................18

Appendix Tables

1. Results of carbon analyses.......................................................................................................24

2. Results of Rock-Eval pyrolysis..................................................................................................32

3. Results of carbon and nitrogen isotope analyses.................................................................37
Characterization of Organic Matter in Lake Sediments 

from Minnesota and Yellowstone National Park

By Walter E. Dean

Abstract

Samples of sediment from lakes in Minnesota and Yellowstone National Park (YNP) were analyzed for organic 

carbon (OC), hydrogen richness by Rock-Eval pyrolysis, 

and stable carbon- and nitrogen-isotope composition of bulk 

organic matter. Values of δ13C of lake plankton tend to be 

around –28 to –32 parts per thousand (‰). Organic matter 

with values of δ13C in the high negative 20s overlap with those 

of organic matter derived from C3 higher terrestrial plants 

but are at least 10‰ more depleted in 13C than organic matter 

derived from C4 terrestrial plants. If the organic matter is 

produced mainly by photosynthetic plankton and is not oxidized in the water column, there may be a negative correlation 

between H-richness (Rock-Eval pyrolysis H-index) and δ13C, 

with more H-rich, algal organic matter having lower values 

of δ13C. However, if aquatic organic matter is oxidized in the 

water column, or if the organic matter is a mixture of terrestrial and aquatic organic matter, then there may be no correlation between H-richness and carbon-isotopic composition. 

Values of δ13C lower than about –28‰ probably indicate a 

contribution of bacterial biomass produced in the hypolimnion 

by chemoautotrophy or methanotrophy. In highly eutrophic 

lakes in which large amounts of 13C-depleted organic matter 

is continually removed from the epilimnion by photosynthesis 

throughout the growing season, the entire carbon reservoir 

in the epilimnion may become severely 13C-enriched so that 13C-enriched photosynthetic organic matter may overprint 13Cdepleted chemosynthetic bacterial organic matter produced in 

the hypolimnon. 

Most processes involved with the nitrogen cycle in lakes, 

such as production of ammonia and nitrate, tend to produce 

15N-enriched values of δ15N. Most Minnesota lake sediments 

are 15N-enriched. However, some of the more OC-rich sediments have δ15N values close to zero (δ15N of air), suggesting 

that organic matter production is by nitrogen fixation, which 

further implies that nitrogen is limiting. Most lakes from YNP 

also have values of δ15N near zero.

Introduction

The sediments of moderately to highly productive (mesotrophic to eutrophic) temperate zone lakes underlain by sedimentary rocks typically contain olive-green sediments rich in 

organic matter (usually greater than 20 percent organic matter 

by loss on ignition at 550 ̊C, or greater than 10 percent organic 

carbon) called gyttja (Hansen, 1959). Because many of these 

lakes are in basins underlain by calcareous glacial drift, they 

contain calcium-magnesium-bicarbonate-rich (“hard”) waters 

and precipitate calcium carbonate (CaCO3), mostly as lowmagnesium calcite, during the late summer. This CaCO3

 may 

dilute the concentration of organic matter somewhat and produce a calcareous sediment called marl (Dean, 1981). For reasons discussed herein, most of the organic matter in gyttja and 

marl is autochthonous, produced by phytoplankton and aquatic 

macrophytes in the lake. This conclusion is contrary to a common perception that the organic matter in most temperate lakes 

is derived from terrestrial sources (for example, Mackereth, 

1966; Brunskill and others, 1971; Molot and Dillon, 1996). 

In some eutrophic lakes, particularly those with a seasonally 

anoxic hypolimnion, bacterial processes in the hypolimnion 

may contribute a significant amount of bacterial biomass to the 

total organic matter delivered to the sediments.

Plant pigment studies of Minnesota lake sediments 

(Sanger and Gorham, 1970; Gorham and Sanger, 1975) 

showed that most of the organic matter in an average Minnesota lake is autochthonous, and that only in the least productive lakes in Precambrian bedrock in the arrowhead region of 

northeastern Minnesota does allochthonous terrestrial organic 

matter make significant contributions to sedimentary organic 

matter. Autochthonous organic matter is enriched in proteinaceous, low molecular weight, H- and N-rich compounds with 

low C/N ratios (typically less than 10; Meyers and Ishiwatari, 

1993). Allocthonous terrestrial organic matter is enriched in 

humic, high molecular weight, C-rich compounds and C/N 

ratios tend to be much higher, with values typically between 

20 and 30 (Meyers and Ishiwatari, 1993). The average OC 
(organic carbon) concentration in the sediments of 46 lakes 

considered to be representative of lakes throughout Minnesota 

is 12 percent (range 3–29 percent; Dean and others, 1993). 

The average OC/N ratio in the sediments of those 46 Minnesota lakes is 9.0 (range 7.6–14), and the only sediments 

with OC/N ratios greater than 11 were from 5 of 10 lakes in 

northeastern Minnesota. 

Plant pigment analyses of sediments from lakes in the English Lake District demonstrated that most of the organic matter 

in those lakes, as in the Minnesota lakes, was autochthonous 

(Gorham and others, 1974). The average OC concentration in 

the English lakes is 7.0 percent (range 4.0–13 percent) and the 

average OC/N ratio is 12.2 (range 9.4–14.1) with little variation 

between lake productivity groups (Dean and others, 1988). 

Most of the organic matter in sediments in the depositional basins of the Great Lakes is autochthonus (plankton), 

has OC concentrations greater than 1 percent, and OC/N ratios 

of 7–9 (Kemp and others, 1977; Meyers and Ishiwatari, 1993). 

Glacial-age sediment in the Great Lakes with little organic 

matter has OC/N ratios greater than 16 (Kemp and others, 

1977). Organic contents and OC/N ratios measured in sediments in cores from three Wisconsin Lakes range from 4.4 to 

18 percent and 8.5 to 11.3, respectively, with no significant 

differences between eutrophic, mesotrophic, and oligotrophic 

productivity levels (Konrad and others, 1970). Most of the 

cited examples are from lakes in glaciated areas underlain by 

sedimentary bedrock. The importance of geology to autochthonous productivity is that glacial drift produced from sedimentary bedrock is more likely to be rich in plant nutrients, 

especially phosphorus, relative to drift produced by crystalline igneous or metamorphic bedrock. High concentrations of 

organic matter in the Experimental Lakes Area (ELA) on the 

Precambrian shield of northwestern Ontario (OC = 20±7) are 

due to lack of clastic and carbonate dilution rather than high 

productivity, but this organic matter still retains OC/N ratios 

(average = 9.7) typical of autochthonous organic matter in 

more southern lakes on glaciated sedimentary strata (Brunskill 

and others, 1971). 

These previous studies, based mainly on plant pigment 

analyses and OC/N ratios, suggest that most of the organic 

matter in all but the most oligotrophic lakes is autochthonous, 

with OC/N ratios mostly less than 10. The slightly elevated 

values in some oligotrophic northeastern Minnesota lakes and 

some oligotrophic English lakes may reflect a slightly higher 

component of allocthonous terrestrial vegetation than in most 

mesotrophic to eutrophic lakes. 

For this investigation, several other geochemical techniques were used to characterize organic matter in lakes with 

potentially variable sources of organic matter in order to 

determine if they can improve our understanding of sources of 

organic matter in lake sediments and the effects of depositional 

and diagenetic conditions on the quantity and quality of that 

organic matter. I examined the organic matter in sediments 

from cores of seven lakes along the Mississippi River valley 

in Minnesota (fig. 1) with OC concentrations ranging from 2 

percent to 35 percent. Pickerel Lake is in eastern South Dakota 

just across the border with Minnesota and has many of the 

characteristics of the lakes of the Northern Great Plains in 

northwestern Minnesota. Organic matter was also examined 

in Holocene sediments from long cores from four lakes with 

basins in the diverse bedrock of Yellowstone National Park 

(YNP) and in surface sediments from eight other lakes throughout YNP (fig. 2) with OC concentrations ranging from 4 percent to 16 percent. Techniques used include: (1) measurement 

of total and inorganic carbon (and organic carbon by difference); (2) measures of the hydrogen and oxygen richness of the 

organic matter by Rock-Eval pyrolysis of bulk sediment; and 

(3) stable carbon- and nitrogen-isotope composition of the bulk 

organic fraction. Not all techniques were applied to all samples. 

Results from Rock-Eval pyrolysis should provide information on the type of organic matter in terms of its hydrogen (hydrocarbon) richness. Carbon-isotope composition 

should provide information about sources of organic matter 

in terms of whether it is aquatic or terrestrial, and, if aquatic, 

was it produced by photoautotrophs in the epilimnion, or by 

chemoautotrophs in the hypolimnion. Carbon isotopes should 

also provide information on processes operating in the water 

column and sediments, such as sulfate reduction, methanogenesis, and methanotrophy. Nitrogen isotopes should provide 

information about whether the organic matter was produced by 

nitrogen-fixing cyanobacteria or by nitrate-utilizing phytoplankton. Nitrogen isotopes should also provide information 

about processes operating in the complicated nitrogen cycle in 

the water column, including nitrification, denitrification, and 

ammonia volatilization. 

The Lakes

Elk Lake is a deep (30 m) lake in a relatively pristine, 

forested setting in Itasca State Park, the headwaters area of the 

Mississippi River. Plant pigment analyses have been made on 

Holocene sediments from Elk Lake (Sanger and Hay, 1993) 

as have carbon-isotope analyses of the organic fraction, and 

carbon- and oxygen-isotope analyses and Rock-Eval pyrolysis of the bulk sediment (Dean and Stuiver, 1993). Williams 

and Shingobee Lakes are about 450 km southeast of Itasca 

Park in the headwaters of the Shingobee River that drains 

into the Mississippi. Williams is hydrologically closed with 

a residence time of about 3 years, whereas Shingobee is an 

open lake with a residence time of 6 months. Surface sediments of Williams Lake contain an average of 25 percent OC 

and less than 1 percent CaCO3, whereas surface sediments of 

Shingobee contain an average of 9 percent OC and 46 percent CaCO3

 (Dean and Bradbury, 1997). Carbon and nitrogen 

isotopic analyses have been made of the organic fraction, and 

carbon and oxygen isotopic analyses have been made on bulk 

sediment and ostracodes (Schwalb and others, 1995; Dean and 

Schwalb, 2002; Schwalb and Dean, 2002).

Spectacle and Green Lakes are another hydrologically 

closed/open pair of lakes on the Anoka Sand Plain of eastcentral Minnesota (fig. 1). Surface sediments of Spectacle 

 Characterization of Organic Matter in Lake Sediments
Duluth

Bemidji

St. Paul

Elk Lake

Williams 

Lake

Pickerel 

Lake

Shingobee

Lake

Lake 

Minnetonka

St. Croix River

Minnesota River

Red River

Mississippi

River

Chippewa

River Lake

Pepin

Moorhead

Minneapolis

Spectacle Lake

N

Mississippi River

Green

Lake

0 100 kilometers

90°W

97°W

49°N

44°N

South Dakota

North Dakota

50 Miles

Figure 1. Map of Minnesota and adjacent North and South Dakota showing the locations of lakes discussed 

in this report.

The Lakes 
o 111 W

45 No

0 20 kilometers

YELLOWSTONE

NATIONAL

PARK

Montana

Montana

Wyoming Wyoming

Idaho

Wyoming

Shoshone Lake

Lewis Lake

Heart

 Lake

Yellowstone

 Lake

Yellowstone

River

Yellowstone

Lamar

Firehole

River

Madison

Gardner

River Blacktail

Deer Cr.

Slough Cr.

Snake River

River

River

River

Trail

Lake

Cygnet

Lake

Cascade

Lake

Lake

of the

Woods

Grizzly

Lake

Wrangler

Lake

Goose

Lake

Sylvan

Lake

Dryad

Lake

Duck

Lake

YELLOWSTONE NATIONAL PARK

Slough

Creek

Pond

Blacktail

Pond/Fen

12 miles

Figure 2. Map of Yellowstone National Park showing the locations of lakes discussed in this report. Lakes 

with cores that collected the entire Holocene records are shown as solid squares. Lakes with only short 

cores are shown as solid circles.

 Characterization of Organic Matter in Lake Sediments
Lake contain 21 percent OC and no CaCO3

, whereas surface 

sediments of Green Lake contain 11 percent OC and 31 

percent CaCO3. Lake Minnetonka is a large, many-bayed 

hypereutrophic lake with heavily populated shores within 13 

municipalities, six of which discharge effluent from sewagetreatment plants into the lake or its tributaries (Megard, 1972). 

The OC contents of sediments from Minnetonka are highly 

variable but mostly greater than 10 percent. Lake Pepin is 

a natural pool formed by damming of the Mississippi River 

9500 years ago by an alluvial fan at the mouth of the Chippewa River, which enters the Mississippi from Wisconsin (fig. 

1; Wright and others, 1998; Brachfeld and Banerjee, 2000). 

The organic content of Lake Pepin sediments is low (1–3 

percent OC), and should contain a higher proportion of allochthonous, terrestrial organic matter than the other six Minnesota 

lakes in this study. Pickerel Lake occupies one of the many 

depressions in calcareous drift deposited by a long tongue of 

the Laurentide ice sheet that extended down the Red River 

Valley along the Minnesota–North Dakota border. Lower 

Holocene sediments in Pickerel Lake are highly variable, 

but sediments deposited during the last 6,000 years contain a 

remarkable constant 40 percent CaCO3 and 4–6 percent OC. 

Carbon and nitrogen isotopic analyses have been made of the 

organic fraction, and carbon and oxygen isotopic analyses 

have been made on bulk sediment and ostracodes (Schwalb 

and Dean, 1998; Dean and Schwalb, 2000).

Trail and Sylvan Lakes are located in lodgepole pine 

forests with basins in the andesitic Absaroka volcanic province 

of eastern and southern YNP (fig. 2). Slough Creek Pond and 

Blacktail Pond Fen are located on Precambrian metamorphic 

and Tertiary volcanic bedrock, but the glacial drift contains a 

considerable amount of limestone and dolomite clasts, mainly 

derived from Paleozoic rocks in the Beartooth Mountains of 

southern Montana. Because of this calcareous drift, many of 

the lakes of northern YNP precipitate CaCO3. In addition to 

having calcareous sediments, Slough Creek Pond and Blacktail Pond Fen differ from the other lakes studied in YNP in 

that they are situated in open Douglas-fir parkland and not 

dense forests. The remaining eight lakes studied in YNP (fig. 

2) are in dense lodgepole pine forests on the Rhyolite Plateau 

that covers central, western, and southern YNP (Whitlock and 

Millspaugh, 1996). The OC content of sediments of lakes in 

YNP is highly variable but is generally less than 10 percent. 

Materials

Most sediment samples were obtained using a squarerod modified Livingstone piston corer (Wright, 1967). Most 

cores collected the entire Holocene section. Short cores (ca 

4 m) were obtained from Green Lake, Spectacle Lake, and 

the north arm of Lake Minnetonka. Pepin core D2 is one of 

25 short cores taken primarily for phosphate studies (Engstrom and Almendinger 1997). The long core from Lake 

Pepin, collected with a Livingstone piston corer, obtained a 

8,400-year sediment record of Lake Pepin (Brachfeld, and 

Banerjee, 2000). Surface sediments from eight Yellowstone 

lakes were collected with a gravity corer to study the accumulation of ash from the 1988 Yellowstone fires (Whitlock and 

Millspaugh, 1996). Surface sediments from six Minnesota 

lakes, selected from 46 lakes reported by Dean and others 

(1993) as representative of a cross section of lake sediments 

in lakes throughout Minnesota, were collected with a Jenkins 

sampler.

Methods

Carbon Coulometry

Concentrations of total carbon (TC) and inorganic carbon 

(IC) in samples were determined by coulometric titration of 

CO2 following extraction from the sediment by combustion 

at 950 ̊C and acid volatilization, respectively (Engleman and 

others, 1985), in USGS laboratories, Denver, Colo. Weight 

percent IC was converted to weight percent CaCO3 by dividing 

by 0.12, the fraction of carbon in CaCO3. Organic carbon (OC) 

was determined by difference between TC and IC. Results of 

carbon analyses are listed in Appendix 1.

Rock-Eval Pyrolysis

Rock-Eval pyrolysis provides a rapid estimate of hydrogen and oxygen richness of organic matter in sediments and 

sedimentary rocks (Tissot and Welte, 1984; Peters, 1986). By 

this method, free and adsorbed hydrocarbons (HC) released 

by programmed heating of a sample in the Rock-Eval II 

instrument in flowing helium at a relatively low temperature 

(250°C) are measured with a flame ionization detector and 

recorded as the area under the first peak of a pyrogram (S1, in 

mg HC/g sample). The second peak on a pyrogram is composed of HC released by thermal breakdown of kerogen or 

protokerogen by programmed heating of the sample to 550°C 

(S2, in mg HC/g sample). CO2 also is generated by kerogen 

degradation and is analyzed by a thermal conductivity detector as the third peak on a pyrogram (S3, in mg CO2

/g sample). 

When normalized to the OC content, the S2 peak becomes 

the hydrogen index (HI, in mg HC/g OC), and the S3 peak 

becomes the oxygen index (OI, in mg CO2/g OC). 

The Rock-Eval pyrolysis technique has been used for 

many years as a rapid screening tool for the determination of 

the hydrocarbon source-rock potential of sedimentary rocks 

(Tissot and Welte, 1984; Peters, 1986). With careful treatment, 

pyrolysis can also be used to determine the hydrogen richness 

of “protokerogen” in modern sediments (for example Liebezeit 

and Wiesner, 1990; Calvert and others, 1991; Pedersen and others, 1992; Arthur and others, 1994; Dean and Gardner, 1998). 

Protokerogen consists largely of humic macromolecules as well 

as polysaccharides and proteins not yet completely degraded by 

heterotrophs (Whelen and Thompson-Rizer, 1993). Results of 

Rock-Eval pyrolysis are listed in Appendix 2.

Methods 
Isotopic Analyses

Stable carbon- and nitrogen-isotope ratios of bulk organic 

matter were determined by standard techniques on decalcified samples (Dean and others, 1986; Rau and others, 1987). 

A powdered sample was reacted with buffered acetic acid for 

24 hours to dissolve carbonate minerals. The residue was then 

centrifuged, decanted, washed three times, and dried. The 

residue was then combusted at 1000°C with copper oxide in a 

sealed quartz tube. The resulting CO2 and N2 were then dehydrated and purified in a high-vacuum gas-transfer system, and 

the isotope ratios were determined with an isotope-ratio mass 

spectrometer. Results are reported in the usual per mil (‰) 

δ-notation relative to the Vienna Peedee belemnite (VPDB) 

marine-carbonate standard for carbon and air for nitrogen:

δ13C ‰ (VPDB) or δ15N ‰ (N air) = [(Rsample/Rstd)-1] x 103

where R is the ratio of 13C to 12C or 15N to 14N, and std is the 

ratio in the standard (VPDB or air). Results of carbon- and 

nitrogen-isotope analyses are listed in Appendix 3.

Results

Organic Carbon and Calcium Carbonate

The concentrations of both OC and CaCO3 are highly 

variable both between and within lakes (fig. 3). Part of 

this variation is due to variation in water chemistry, which, 

in turn, could be due to differences in bedrock geology, surficial geology, and (or) climate, particularly the 

precipitation/evaporation (P/E) ratio. For example, in Minnesota there is a steep climatic gradient across the state and into 

the Dakotas, with net precipitation in the northeastern part 

of Minnesota and net evaporation in the prairies of western 

Minnesota and the Dakotas. Most lakes in eastern Minnesota 

have waters dominated by calcium and bicarbonate. As one 

goes west, evaporation increases, CaCO3 begins to precipitate, the bedrock and surfical geology change, and calcium 

and bicarbonate are replaced by magnesium, sodium, and 

sulfate ions (Gorham and others, 1983). As previously 

mentioned, the northern part of YNP is covered with calcareous glacial drift so that lakes like Blacktail Pond and Slough 

Creek Pond precipitate CaCO3. However, it is unlikely that 

the variations within the cores from Slough Creek Pond and, 

especially, Blacktail Pond (fig. 3B) are due to variations in 

the influx of CaCO3. Sediments in cores from many lakes 

show an inverse correlation between the concentrations of 

CaCO3 and OC as shown for Lake Minnetonka (fig. 3A) and 

Blacktail Pond (fig. 3B). The surface sediments from central 

Minnesota lakes that have measurable CaCO3 and up to 25 

percent OC (Group 3 lakes of Dean and Gorham, 1976) also 

show this inverse relation (fig. 3A). Some lakes also show 

an inverse correlation in surface sediments as a function 

of water depth, as shown by Shingobee Lake in figure 3A 

(higher CaCO3 samples are from shallow water and higher 

OC samples are from deeper water). I attribute this inverse 

correlation as due mostly to dissolution of CaCO3 by the 

“carbon pump.”

By carbon pump, I refer to the lacustrine carbon pump as 

described by Dean (1999) in which carbon is fixed by photosynthesis in the epilimnion, thus removing CO2

, increasing the 

pH, and increasing the dissolved O2. Respiration of this fixed 

organic carbon (OC) in the hypolimnion consumes O2, produces CO2

, and lowers the pH. This carbon pump also recycles 

phosphorus (P) and, if the carbon-fixing organisms are diatoms, silica (Si). In hardwater lakes, the increased pH in the 

epilimnion can trigger precipitation of CaCO3. However, the 

lower pH of the hypolimnion can result in the dissolution of 

much of the CaCO3 produced in the epilimnion. More CaCO3

is dissolved at the sediment/water interface before it is buried, 

and even more is dissolved in corrosive pore waters. Williams 

Lake does precipitate CaCO3 during the summer (McConnaughey and others, 1994), but the surface sediments are virtually carbonate-free (fig. 3A). Adsorbed coatings of dissolved 

organic compounds can reduce rates of CaCO3 dissolution 

(Hoch and others, 1999; Wetzel, 2001). If oxygen depletion in 

the hypolimnion is severe enough to produce seasonal anoxia, 

there is a profound effect on the cycles of redox-sensitive elements such as iron (Fe) and manganese (Mn), causing the concentration of the dissolved forms (Fe+2 and Mn+2) to increase 

in the hypolimnion (Dean and others, 2003). The carbonate 

and, especially, the redox aspects of the carbon pump have 

been summarized in detail by Wetzel (2001), although he did 

not call it that.

Increased OC content of lake sediments often accompanies 

eutrophication following land clearing and other activities by 

European settlers (about A.D. 1850 in Minnesota), and this usually is accompanied by decreased CaCO3

 content. For example, 

the average OC and CaCO3 contents of presettlement Holocene 

sediments in Shingobee Lake are 2.5 percent and 70 percent 

(fig. 3A); the average contents in surface sediments from Shingobee Lake are 8.8 percent and 46 percent, although both values 

have a considerable range (diagonal blue line in figure 3A). The 

change in Green Lake sediments is even more striking. Sediments at 150 cm (about A.D. 1850) in a core from Green Lake 

contain about 80 percent CaCO3 and 6 percent OC. However, 

sediments at 20-cm depth only contain 32 percent CaCO3 but 

almost 15 percent OC (fig. 3A). Sediments in the northern 

YNP lakes, especially Blacktail Pond, show the same inverse 

trend but with more scatter (fig. 3B). Although the lacustrine 

carbon pump probably does not operate universally in all lakes, 

it appears that burial of a large amount of OC can increase 

dissolution of CaCO3. The amount of CaCO3 that accumulates 

on the lake floor, and ultimately is buried in the sediments, is a 

function of how much is produced in the epilimnion and how 

much is destroyed in the hypolimnion and sediments. 

Rock-Eval Pyrolysis

An OI–HI cross plot, a proxy for a van Krevelen-type 

O/C–H/C diagram (Tissot and Welte, 1984), is the conventional 

 Characterization of Organic Matter in Lake Sediments
0

5

10

15

20

25

% Organic Carbon % Organic Carbon

0 10 20 30 40 50 60 70 80

%CaCO3

0 10 20 30 40 50 60 70 80

%CaCO3

Williams (surf, av.)

Elk

(AD 1970)

Elk (AD 1850)

Minnetonka

Elk

(4 ka) Shingobee

(Holocene range)

Shingobee

 (surf. av.) Green

(>150 cm)

Green 

(20 cm)

+

+

+

0

5

10

15

20

25

Slough Creek Pond

Blacktail Pond

A

B

Results 
way of displaying results of Rock-Eval pyrolysis and defining 

types of kerogen in hydrocarbon source rocks. An OI–HI plot 

for samples from Spectacle Lake, Lake Pepin, Elk Lake, and 

Lake Minntonka in Minnesota, and for samples of surface sediments from 18 Minnesota lakes is shown in figure 4. An OI–HI 

plot for samples from Trail Lake and Slough Creek Pond in 

YNP is shown in figure 5. Three types of kerogen (I, II, and III) 

and their thermal maturation pathways are shown by the curves 

on the OI–HI plots. Type I kerogen consists of extremely lipidrich, sapropelic, algal organic compounds typified by lacustrine 

oil shale of the Eocene Green River Formation (Tissot and 

Welte, 1984). Type III kerogen is the other extreme and consists of H-poor organic compounds, such as those found in terrestrial organic matter. Type II kerogen also consists of H-rich 

compounds such as those found in autochthonous lacustrine 

and marine organic matter. Marine hydrocarbon source rocks 

typically contain type II kerogen. Type III kerogen also may be 

formed by oxidation of type II kerogen, which lowers the HI 

and increases the OI (Tissot and Welte, 1984). 

The extreme range of HI values shown for the data from 

Trail Lake and Slough Creek Pond (fig. 5) could result from a 

mixture of autochthonous and terrestrial organic matter or, more 

likely, from variable oxidation of algal organic matter in the 

depositional environment. Trends in the data for the Minnesota 

lakes (fig. 4) with negative slopes, going from high HI, low OI, 

to lower HI and much higher OI are likely oxidation trends. 

The samples from Lake Pepin on the Mississippi River contain 

mostly type III terrestrial organic matter. The samples from 

Spectacle Lake contain unoxidized algal type I organic matter. 

The samples from hypereutrophic Lake Minnetonka also contain type I organic matter, but the organic matter in this urban 

lake has been variously oxidized. Most other Minnesota lakes 

fall in the range of type II organic matter but with HI values less 

than 400. The plant-pigment data of Sanger and Gorham (1970) 

and Gorham and Sanger (1975) indicate that the organic matter 

in most Minnesota Lakes is predominantly autochthonous. The 

three lakes from northeastern Minnesota, judged by plant pigments to contain significant allocthonous organic matter, plot in 

the middle for the field of Minnesota surface sediments in figure 

4. Therefore, I conclude that the low HI values in Minnesota 

surface sediments are due to oxidation of autochthonous organic 

matter that originally had higher HI values, and, for three lakes, 

are due to significant influx of allocthonous organic matter. Elk 

Lake today is seasonally anoxic below 10 m (July–October; 

Megard and others, 1993) and may have been anoxic in the 

past (Dean, 1993). Plant-pigment data (Sanger and Hay, 1993) 

indicate that the lake evolved from oligo- to mesotrophic conditions in its early history to meso- to eutrophic conditions over 

the last 3,000 years, and at no time was there large-scale influx 

of allocthonous organic matter. The entire Holocene sediment 

record in Elk Lake is laminated (varved), and, therefore, I would 

expect the autochthonous organic matter in these sediments to 

be well preserved. However, the Lake is deep (30 m) and the 

low HI values may be due to oxidation of organic matter on its 

long trip through the water column.

Because the HI is derived from S2 by normalizing to 

percentage of OC (HI = [S2/ % OC] x 100)],Langford and 

Blanc-Valleron (1990) suggested that the average value for 

HI for a particular data set could be obtained from the slope 

of a regression equation for a graph of %OC versus S2 (fig. 

6). In the examples from Lake Pepin, Lake Minnetonka, 

Spectacle Lake, and Elk Lake in Minnesota and Slough 

Creek Pond and Trail Lake in YNP, the slopes of the regression equations are 2.73, 11.6, 10.6, 2.03, 6.07, and 6.49, 

respectively (fig. 6). Multiplying these slope coefficients 

by 100 (Langford and Blanc-Valleron, 1990) yields average 

values of HI of 273, 1160, 1060, 203, 607, and 649, respectively. Langford and Blanc-Valleron (1990) further suggested 

that lines with zero intercept and slopes of 7 (HI=700) and 2 

(HI=200) separate the pyrolitic hydrocarbon yields of type 

I and type II, and type II and type III kerogen, respectively 

(dashed lines in figure 6). Figure 6 shows that the samples 

from Lake Pepin with values of S2 less than 10 are the most 

H-depleted. Likewise samples from Spectacle Lake with 

values of S2 greater than 200 are the most H-enriched. The 

samples from Lake Minnetonka and Elk Lake and from the 

two YNP lakes are of intermediate H richness, with values of 

S2 mostly between 10 and 200.

Figure 3. (previous page) Cross plot of percentage of CaCO3 versus percentage of OC in: (A) Surface 

sediments from central Minnesota lakes and in a core from Lake Minnetonka. Solid circles are surface 

sediments from central Minnesota lakes that contain both CaCO3 and OC (Group 3 sediments of Dean and 

Gorham, 1976). Red triangles are sediments from Lake Minnetonka. Horizontal and vertical lines labeled 

“Shingobee (Holocene range)” represent the ranges of concentrations of CaCO3 and OC measured in 

Holocene sediments in Shingobee Lake. The square symbol at the intersection of the horizontal and 

vertical lines represents the average concentrations of CaCO3 and OC in Holocene sediments in Shingobee 

Lake. The diagonal line is the best fit line (r=0.92; n=6) for the range of concentrations of CaCO3 and OC 

measured in surface sediments in Shingobee Lake (Dean and Bradbury, 1997), and the square symbol 

labeled “Shingobee (surf. av.)” is the average of the surface–sediment measurements. The symbol labeled 

“Green (20 cm)” is the composition of Green Lake sediments at 20 centimeter (cm) depth, and the point 

labeled “Green (greater than 150 cm)” is the average composition of Green Lake sediments deeper than 

150 cm. The points labeled “Elk (4 ka),” “Elk (AD 1850) ,” and “Elk (AD 1970)” are the compositions of 

sediments from the deepest part of Elk Lake deposited about 4,000 years ago, 155 years ago, and 35 years 

ago, respectively. (B) Cores from Blacktail Pond and Slough Creek Pond in northern Yellowstone Park.

 Characterization of Organic Matter in Lake Sediments
0

100

200

300

400

500

600

700

800

900

1000 Hydrogen Index (mg HC/g OC)

0 50 100 150 200 250 300 350 400 450

Oxygen Index (mg CO /g OC)

 Lake Pepin 

Minnesota surface

sediments

Spectacle Lake

 Minnetonka

Elk Lake (Dean and 

 Stuiver, 1993)

2

II

III

I

Figure 4. A cross plot of Rock–Eval pyrolysis oxygen index versus hydrogen index for samples of 

selected Minnesota lake sediments. Curves labeled I, II, and III describe the thermal maturation pathways 

of type I, type II, and type III kerogen.

Results 
0

100

200

300

400

500

600

700

800

900

1,000

 Hydrogen Index (mg HC/g OC)

0 50 100 150 200 250 300 350

2 Oxygen Index (mg CO /g OC)

 Slough Creek Pond

 Trail Lake

III

II

I

Figure 5. A cross plot of Rock–Eval pyrolysis oxygen index versus hydrogen index for samples of sediments 

from Trail Lake and Slough Creek Pond in Yellowstone National Park. Curves labeled I, II, and III describe the 

thermal maturation pathways of type I, type II, and type III kerogen.

10 Characterization of Organic Matter in Lake Sediments
0

100200300400500600

 S2 (mg HC/g sed)

 S2 (mg HC/g sed)

 S2 (mg HC/g sed)

0 10 20 30 

y = 10.6x - 76 r = 0.998y = 11.6x - 77.5 r = 0.956

Spectacle Lake, Minn.Lake Minnetonka, Minn.

01234567

0 0.5 1 1.5 2 2.5 3

 % Organic Carbon % Organic Carbon

 % Organic Carbon % Organic Carbo

I y = 2.73x - 2.70 r = 0.91 II

II

III

III

II

II

I

Lake Pepin, Minn.

Slough Creek Pond, Yellowstone

0

50

100150200

 S2 (mg HC/g sed)

0 5 10 15 20 25

y = 6.07x + 10.21 r = 0.94 y = 6.49x - 8.73 r = 0.96

 y = 2.0

I II

0

20406080

0 2 4 6 

Trail Lake, Yellowston

A

CD

B

Figure 6. Cross plots of percentage of OC versus Rock–Eval pyrolysis S2 peak height in milligrams of hydrocarbons (HC) per gram of OC for sample(A) Lake Pepin in Minnesota; (B) Slough Creek Pond, Yellowstone National Park; (C) Spectacle Lake and Lake Minnetonka in Minnesota; (D) Elk Lake Lake in Yellowstone National Park.
Carbon and Nitrogen Isotopes

The potential of values of δ13C and δ15N in organic matter 

in lake sediments as source signatures can be seen in figs. 6 

and 7, which show values of δ13C and δ15N in lake sediments 

from Minnesota and Yellowstone, and in different types of 

plants (δ13C) and in different forms of nitrogen in the nitrogen 

cycle (δ15N). Most higher plants follow the C3 photosynthetic 

pathway and produce organic carbon that is depleted in 13C 

(more negative values of δ13C). Usually, most C3 terrestrial 

vegetation tends to have values of δ13C around –26 to –28‰. 

Unfortunately, lake plankton also tend to fractionate isotopes 

of carbon in the same range as C3 higher plants with values 

of δ13C usually in the high negative 20s to low negative 30s 

(Oana and Deevey, 1960; Deines, 1980; fig. 7). C4 plants, 

such as warm prairie grasses, fix carbon that is significantly 

enriched in 13C (less negative values of δ13C; O’Leary, 1988; 

Cerling and Quade, 1993).

-40 -30 -20 -10 0

13 δ Corg (VPDB)

surf. seds., Minnesota lakes

algal oxidized

 (1992; core D2)

 (Holocene; core 97-P1)

 (Dean and Stuiver, 1993)

10ka 0-5ka

lake plankton

peat

Williams Lake

Elk Lake

(Dean and Anders,1991;

Collister and Hayes,1991)

Lake Minnetonka (late Holocene)

(Dean and

Schwalb

Shingobee Lake 2002)

mid-Holocene

early and late 

Holocene

early 

and late

mid

mid-late 

Holocene

early 

Holocene

C3 plants C4 plants

(Dean and Schwalb, 2000)

Green Lake (late Holocene) Spectacle Lake (late Holocene)

Pickerel Lake

surface seds., YNP

Holocene

Holocene

(Hollander and others,

1992)

(Dean and Stuiver, 1993)

Green River Oil Shale

Lake Greifen (Switzerland)

Holocene

Blacktail Pond Fen, YNP

Holocene

Holocene

Slough Creek Pond, YNP

Trail Lake, YNP

Cygnet Lake, YNP

Lake Pepin

Figure 7. Ranges of values of δ13C in various plant materials and in organic matter in lake sediments. Data for lake plankton, C3 

plants, C4 plants, and peat were compiled by Bender (1971) and Deines (1980). YNP, Yellowstone National Park.

12  Characterization of Organic Matter in Lake Sediments
These observations assume that photosynthesis is the 

primary control on the isotopic signature in an aquatic carbon 

cycle. However, in more productive aquatic systems, anoxic 

conditions in the water column or in the sediments may create conditions favorable for microbially mediated processes 

such as sulfate reduction, chemoautotrophy, methanogenesis, 

and methanotropy, which can produce distinct isotopic signatures to sedimentary carbon that may be more 13C-depleted or 

more 13C-enriched than carbon produced by photosynthetic 

processes (Hollander and Smith, 2001). Hydrologic conditions, such as increased residence time and ground-water 

interactions, also can alter carbon-isotope signatures.

For the Yellowstone lakes, the carbon isotope results 

generally support the Rock-Eval pyrolysis results: Trail 

Lake, which had the least H-rich organic matter, has values 

of δ13C ranging from –25‰ to –29‰, and Slough Creek 

Pond, which had the most H-rich (most algal) organic matter, has δ13C values in the range of –29‰ to –31‰, more 

similar to values in lake plankton and the most algal rich of 

Minnesota surface sediments (fig. 7). Samples from Blacktail Pond Fen have values of δ13C that span almost the 

entire range of values in both Slough Creek Pond and Trail 

Lake, whereas samples from Cygnet Lake are considerably 

more enriched in13C than those from the other Yellowstone 

lakes. Surface sediments from eight lakes have δ13C values 

in a narrow range of –27‰ to –30‰, suggesting that the 

organic matter is either algal or derived from C3 forest 

plants. 

15

-5 0 5 10

δ N(air)

dissolved N

Blacktail Pond Fen, YNP Holocene

N-xers

modern sediments

Slough Creek Pond, YNP Holocene

Lake Minnetonka

Lake Baldegg, Switzerland 

(Teranes and Bernasconi, 2000)

Pickerel Lake, SD

bottom 8 meters Trail Lake, YNP

late early 

early

top

Holocene Lake Pepin

Holocene

late

Williams Lake 

Shingobee Lake 

surface seds., YNP 

Green Lake

(late Holocene) 

Green River

Oil Shale Collister and Hayes, 1991 

Spectacle Lake (late Holocene) 

2

NH4

+

NO3

-

Figure 8. Ranges of values of δ15N in various nitrogen-bearing pools (from Rau and others, 1987), and in 

organic matter in lake sediments. SD, South Dakota; YNP, Yellowstone National Park.

Carbon and Nitrogen Isotopes 13
The samples from Minnesota Lakes give a somewhat 

confusing signal if simple photosynthetic isotopic fractionation is assumed. Samples of surface sediments from lakes 

thoughout Minnesota (Dean and Stuiver, 1993) have values 

of δ13C that range from –22 to –32‰. Those sediments, based 

on fossil pigments (Sanger and Gorham, 1970; Gorham and 

Sanger, 1975), that contain the most algal organic matter 

are most depleted in 13C, and sediments with the most oxidized organic matter are most enriched in 13C (fig. 7). These 

results are to be expected because samples most depleted in 

13C (values of δ13C in the high negative 20s and low negative 30s) are the most H-rich, that is, the organic matter is 

isotopically more like lake plankton and less like peat (fig. 

7). However, samples from Lake Minnetonka and Spectacle 

Lake that are H-rich (fig. 4) have higher values of δ13C than 

those from Lake Pepin that are H-poor (figs. 4 and 7), which 

is difficult to explain by photosynthetic fractionation. Values 

of δ13C in samples from Elk Lake, Williams Lake, Shingobee 

Lake, and Pickerel Lake are lowest in early Holocene sediments and highest in mid-Holocene sediments (fig. 7). In cores 

from Elk Lake and Shingobee Lake, values of δ13C return to 13C-depleted early Holocene levels in late Holocene sediments 

but remain unchanged in cores from Williams Lake and Pickerel Lake (fig. 7).

Most processes involved in the nitrogen cycle tend to 

drive values of δ15N toward more positive values relative to N2

in air, which, by definition, has a value of 0 (fig. 8). Methanogenic and nitrogen-fixing organisms can produce negative 

values of δ15N, but most processes operating in the nitrogen 

cycle tend to produce nitrogen that is more enriched in 15N. It 

is noteworthy that sediments from Lake Pepin, the wide spot 

in the Mississippi River in Minnesota with the least algal, Hrich organic matter, have the highest values of δ15N, as do the 

late Holocene sediments from Green Lake (fig. 8). Those sediments with the most H-rich organic matter (for example, Lake 

Minnetonka and Spectacle Lake in Minnesota and all of the 

Yellowstone lakes) have δ15N values around 0 (fig. 8). The low 

values in algal-rich sediments suggest that N-fixing bacteria 

(cyanobacteria) may represent a significant proportion of the 

primary producers in those lakes.

Discussion

The organic carbon and S2 data plotted in figure 6 show 

that the two variables are highly correlated, which indicates 

that most of the organic matter in these sediments is lipid-rich, 

algal organic matter. Using both the HI and the S2 peak as 

measures of H-richness (figs. 4, 5, and 6), the sediments from 

Spectacle Lake and Lake Minnetonka in Minnesota (figs. 4 

and 6C) and Slough Creek Pond in YNP (figs. 5 and 6B) are 

the most H-rich; sediments from Lake Pepin in Minnesota 

(figs. 4 and 6A) are the least H-rich, and sediments from Elk 

Lake in Minnesota and Trail Lake in YNP (fig. 6D) are intermediate in H richness. 

Based on these H-richness measurements, and the 13C-depleted isotopic signature of type I kerogen from 

lacustrine Green River oil shale (fig. 7), the sediments in 

Minnetonka and Spectacle should be much more depleted in 

13C with values of δ13C of about –30‰ to –32‰,. Spectacle 

Lake is hydrologically closed with a longer residence time 

than nearby Green Lake, which is hydrologically open and 

has a much shorter residence time. The longer residence time 

of Spectacle Lake might explain the 13C-enriched signature of 

organic matter in the sediments of that lake as 13C-depleted 

carbon is fixed by H-rich plankton causing the entire carbon 

reservoir to be enriched in 13C (McKenzie, 1985; Hollander 

and McKenzie, 1991).

Williams Lake and Shingobee Lake are another hydrologically closed/open pair of lakes in the headwaters area 

of the Shingobee River in northwestern Minnesota (fig. 1). 

Williams Lake apparently was hydrologically open in the early 

Holocene, with geochemical and isotopic characteristics of 

sediments similar to those in Shingobee Lake when the two 

lakes were connected as part of a larger lake, “Lake Willobee” formed by a debris flow across the Shingobee River 

(Dean and Schwalb, 2002; Schwalb and Dean, 2002). After 

the debris flow was breached, Williams Lake had no surface 

inflow and evolved into a closed lake by about 5 ka. This 

hydrologic closure is documented by the ca. 10‰ increase 

in δ13C (from ca –34‰ to –24‰; fig. 7). Over the same time 

period (10–5 ka), the vegetation in the drainage basins of these 

lakes evolved from coniferous forest to prairie (the so-called 

“prairie period” in Minnesota; Whitlock and others, 1993; 

Locke, 1995; Schwalb and others, 1995), synchronous with 

the eastward expansion of prairie and oak savanna that is well 

documented for the north-central United States (Webb and 

others, 1983; Whitlock and others, 1993; Baker and others, 

1998). The ca. 3‰ increase in δ13C in sediments of Shingobee 

Lake has been attributed to a change in dominant vegetation 

from forest to prairie, and 3‰ of the 10‰ increase in δ13C in 

Williams Lake (fig. 7) also has been attributed to vegetation 

change (Dean and Schwalb, 2002; Schwalb and Dean, 2002. 

After the forests returned to northwestern Minnesota, values 

of δ13C in Shingobee Lake (fig. 7; Dean and Schwalb, 2002) 

returned to early Holocene lower values of δ13C (ca. –33‰; 

fig. 7). The sediments of Williams Lake remained enriched in 

13C (δ13C –24‰ to –26‰; fig. 7) because the lake remained 

hydrologically closed.

A shift to higher values of δ13C during the mid-Holocene 

also was found in sediments from Elk Lake, northwestern 

Minnesota (Dean and Stuiver, 1993; Dean and others, 2002), 

and in sediments from Pickerel Lake in northeastern South 

Dakota (fig. 7; Dean and Schwalb, 2000). Sediments deposited in Elk Lake during the prairie period have an OC accumulation rate more than twice that for sediments deposited 

prior to the prairie period (Dean, 1993), higher plant pigment 

concentrations (Sanger and Hay, 1993), and a higher total 

flux of diatoms (Bradbury and Dieterich-Rurup, 1993). These 

different lines of evidence all suggest that productivity of Elk 

Lake was higher during the prairie period. The increase in 

14  Characterization of Organic Matter in Lake Sediments
values of δ13C of both organic and inorganic carbon during the 

prairie period was the result of increased burial of 13C-depleted 

organic matter making the entire carbon reservoir of the lake 

13C-enriched according to the model of McKenzie (1985) 

(Dean and Stuiver, 1993). Values of δ13C in late Holocene sediments of Elk Lake decreased as lake productivity decreased. 

There are distinct covariant increases in values of δ18O and 

δ13C in carbonate in the early Holocene in Pickerel Lake, 

which suggests that there was an increase in water-residence 

time (Dean and Schwalb, 2000). However, these trends are 

paralleled by an upward trend in values of δ13C in OC (from 

–30‰ to –24‰; fig. 7). This suggests that the change from 

forest to prairie conditions may have had an even greater influence than water-residence time by providing more 13C to soils 

and hence to the dissolved inorganic carbon (DIC) reservoir in 

the lake. Both factors could have produced more 13C-enriched 

carbon values in precipitated carbonate in Pickerel Lake.

So far, this discussion has only considered photoautotrophic production of organic matter. During the spring-summer 

growing season in a lake, 13C-depleted CO2 is continually 

being removed from the photic zone and fixed in 13C-depleted 

organic matter, which is sedimented. The CO2 reservoir in the 

epilimnion by the end of the growing season will be enriched 

in 13C relative to that at the beginning of the growing season 

so that any carbon fixed in organic matter at the end of the 

season will be similarly enriched in 13C (Hollander and Smith, 

2001). If the particulate organic carbon (POC) that ultimately 

accumulates in the sediments is more 13C-depleted than POC 

produced during the summer in the epilimnion, then there 

must be another source of 13C-depleted POC. Likely candidates for production of this 13C-depleted POC are chemoautotrophic or methanotrophic bacteria in the hypolimnion 

(Hollander and Smith, 2001). Lake sediments with high OC 

contents commonly are anoxic for extended periods of time 

during the year, which can result in extensive methanogenesis 

and release of 13C-depleted methane (values of δ13C typically about –50‰ to –70‰ ) to the hypolimnion (Striegl and 

Michmerhuizen, 1997). Methanotrophic bacteria can further 

fractionate the carbon-isotopic signature of the methane they 

utilize by up to 30‰ (Summons and others, 1994). By this 

combination of 13C-depleting processes (methanogenesis and 

methanotrophy), the POC produced by methanotrophy can be 

depleted by as much as –90‰ (Whiticar and others, 1986). In 

the recently deposited sediments of eutrophic Lake Mendota 

in Wisconsin, values of δ13C in organic matter in summer 

varves are 2–3‰ lower than POC produced in the epilimnion 

during the summer because of the addition of 13C-depleted 

POC produced by methanotrophic bacteria in the hypolimnion 

(Hollander and Smith, 2001). Thus, in moderately eutrophic 

lakes, such as modern Lake Mendota and pre-1930 Lake Greifen in Switzerland (Hollander and others, 1992; Hollander and 

Smith, 2001) production of 13C-enriched phytoplankton POC 

that accumulates in the sediments is insufficient to overprint 

the highly 13C-depleted POC produced by chemoautotrophic 

and methanotrophic process in the hypolimnion. In hypereutrophic lakes, such as modern Lake Greifen, epilimnetic 

production of 13C-enriched phytoplankton during the summer 

can be so intense that this POC overwhelms any 13C-depleted 

POC produced by bacteria in the hypolimnion (Hollander and 

Smith, 2001). 

Applying these principles to the lakes discussed previously, provides some insight into the extreme variability 

in values of δ13C. The lakes of southern YNP contain low 

concentrations of sulfate (SO4; National Park Service, 1994) 

and are not likely to have very much sulfate reduction occurring in their sediments or hypolimnions, but may have some 

methanogenesis. Hence the relatively high values of δ13C in 

sediments in Trail Lake and Cygnet Lake (–25‰ to –30‰; 

fig. 6) are mostly from POC produced by phytoplankton during late summer in the epilimnion. Values of δ13C in sediments 

from Trail Lake range between –24 and –28‰ and have no 

trend with values of HI (fig. A), which would be expected if 

the organic matter was a mixture of terrestrial and algal POC. 

The OC-S2 plot for Trail Lake (fig. 6D) indicates that the sediments in Trail Lake contain type II organic matter, but close 

to the I-II line. Also, values of δ13C fall within a fairly narrow 

range (fig. 9A). Therefore, the variation in HI and S2 in Trail 

Lake sediments (figs. 5, 6D, and 9A) primarily is due to variable oxidation of algal organic matter in the water column. 

The lakes in northern YNP are carbonate-rich and can 

contain up to 150 mg/L SO4 (National Park Service, 1994); 

springs in that part of YNP often have a strong odor of H2S. 

The higher dissolved ions in northern YNP lakes are derived 

from Paleozoic carbonate-rock debris in glacial drift. Consequently, some sulfate reduction should be occurring in the 

hypolimnions of Blacktail Pond Fen and Slough Creek Pond 

(fig. 2). Bacterial POC depleted in 13C resulting from sulfate 

reduction would explain the low values of δ13C (less than 

–30‰) in the sediments of these lakes. The lowest values of 

δ13C in surface sediments from eight other lakes in YNP are 

from sediments of Lake of the Woods (–31‰) and Grizzly 

Lake (–28.3‰), both in northern YNP (fig. 2). Values of δ13C 

in sediments from Slough Creek Pond are all 13C-depleted, 

ranging from –27 to –31‰, with a positive correlation with 

values of HI (fig. 9A; correlation is significant at the 95 

percent confidence level). This positive trend is the opposite of what would be expected by mixing of terrestrial and 

algal organic matter. The OC-S2 plot for Slough Creek Pond 

(fig. 6B) indicates that the sediments in Slough Creek Pond 

contain a mixture of type I and type II organic matter, but all 

samples containing type II organic matter are close to the I-II 

line. The variation in HI and S2 in sediments from Slough 

Creek Pond (figs. 5, 6B, and 9A) could be due to oxidation 

of type I organic matter, as suggested by the negative HI-OI 

trend in figure 5, but the extremely 13C-depleted values of δ13C 

(less than 29‰; fig. 9A) suggest that the POC in this lake is 

a mixture of H-rich, more 13C-enriched algal POC from the 

epilimnion, and more 13C-depleted, less H-rich bacterial POC 

from sulfate reduction in the hypolimnion. 

The 15N-depleted values of organic matter in the sediments of lakes in YNP (fig. 8) suggest that a large proportion 

of the organic matter in these lakes may be from N-fixing 

Discussion 15
phytoplankton (cyanobacteria). Prevalent N-fixation would 

also imply that the lakes of YNP are nitrogen-limited. Values 

of δ15N in sediments from Lake Minnetonka and Spectacle 

Lake in Minnesota (fig. 8) also are near zero suggesting that 

N-utilization in these lakes also was mainly by N-fixation. If 

nitrogen is not limiting, most N-utilization by plankton is from 

nitrate (NO3

–

) or ammonia (NH4

+

) (Wetzel, 2001), which most 

likely explains the positive values of δ15N in the lake sediments illustrated in figure 8. The very 15N-enriched values of 

δ15N in sediments deposited over the last 100 years in Lake 

Baldegg in Switzerland (5‰ to 13‰; fig. 8) apparently are 

due to extreme nitrate utilization caused by eutrophication 

(Teranes and Bernasconi, 2000). They found, based on sediment-trap and historical data, that values of δ15N increased 

with decreasing nitrate concentration in the water column. 

Increasing denitrification with the expansion of anoxia in the 

hypolimnion is another potential process that would increase 

the dissolved inorganic nitrogen pool in 15N, and an increase 

in δ15N of organic matter (Teranes and Bernasconi, 2000). 

(Collister and Hayes (1991) concluded that the existence of 

15N-enriched organic matter in the Green River Formation 

(fig. 8) requires a complex nitrogen cycle. They suggested that 

cyanobacterial assimilation of ammonia and nitrate, enriched 

in 15N by denitrification and nitrification (fig. 8), most likely 

accounts for 15N-enrichment in the oil shale.

In Minnesota lakes, extremely 13C-depleted (less than 

–29‰) organic matter occurs in the early and late Holocene 

sediments of Elk Lake, in all sediments of Shingobee Lake, in 

early Holocene sediments of Williams lake, and in late Holocene sediments of Green Lake (fig. 7). Today and in the early 

Holocene, Elk Lake was well stratified and at least seasonally 

anoxic; it may have been meromictic during the early Holocene (Dean and others, 2002). However, during the middle 

Holocene (prairie period), diatom evidence suggests that wind 

mixing likely kept the hypolimnion more oxic (Bradbury and 

Dieterich-Rurup, 1993; Dean and others, 2002). Values of HI 

in Elk Lake sediments are unusually low if the organic matter 

was derived from H-rich algae (figs. 3 and 9B). One possible 

explanation is that much of the organic matter produced by 

photosynthesis in the epilimnion of Elk Lake is oxidized in the 

epilimnion (low HI), and is further decomposed in the thick, 

seasonally anoxic hypolimnion of this deep (30 m) lake. The 

CO2 produced by decomposition would then be available for 

chemoautotrophic bacteria to produce 13C-depleted, H-poor 

bacterial POC. The distinctly more 13C-enriched organic matter deposited in sediments during the prairie period (fig. 9B) 

suggests that less bacterial POC was reaching the sediments. 

As discussed earlier, productivity in Elk Lake apparently was 

higher during the prairie period, perhaps producing more 

13C-enriched photosynthetic POC; during the same time, the 

lake was more turbulent (wind-mixed), limiting microbial 

activity in a more oxic hypolimnion. Whatever the mechanism 

for the relatively 13C-enriched organic matter in prairie-period 

sediments, the low values of δ13C in all Holocene sediments in 

Elk Lake suggest that bacterial POC always was an important 

component to the sedimentary organic matter, particularly 

during the early and late Holocene when the lake was more 

stratified. At those times, Elk Lake may have been much like 

Lake Uinta during deposition of the Eocene Green River Formation (fig. 7), which also has a significant microbial biomass 

contribution (Collister and Hayes, 1991). During deposition 

of the sulfide-rich Green River Formation, sulfate reduction 

likely was the most important process in the saline, anoxic 

monimolimnion of Lake Uinta (Tuttle and Goldhaber, 1991), 

producing another source of 13C-depleted microbial biomass. 

Shingobee Lake is eutrophic, and the hypolimnion 

becomes anoxic within a month after overturn in both the 

spring and fall (Dean and Schwalb, 2002). In late summer, the 

hypolimnion of Shingobee Lake contains up to 14,000 ppm 

methane with a value of δ13C of up to –73‰ (R.G. Striegl, 

U.S. Geological Survey, unpublished data). In contrast, the 

hypolimnion of Williams Lake in late summer contains a 

maximum of 3,800 ppm methane with a value of δ13C of up to 

–52‰ (R.G. Striegl, unpublished data). During late summer, 

CO2 in the hypolimnion of Shingobee Lake is up to 4‰ more 13C-depleted than CO2

 in the epilimnion. Clearly, 13C-depleted 

POC from methanotrophy is, and always has been, an important component to sedimentary organic matter in Shingobee. 

As mentioned earlier, the surface sediments from Minnesota lakes that are the most 13C-depleted (ca. –28‰ to –32‰) 

tend to contain the most algal organic matter, as indicated by 

plant pigments (fig. 7). Figures 9C and 9D show that the most 

13C-depleted samples are the most H-rich, and that the H-rich 

samples have the highest total pigment concentrations.

The samples from Lake Minnetonka (fig. 1) are from the 

hypereutrophic North Arm of the lake, one of 15 basins that 

comprise the lake (Megard, 1972). These samples are highly 

enriched in 13C (δ13C –22‰ to –26‰; fig. 7). The conditions 

in Lake Minnetonka might be like those in modern Lake Greifen where the production of 13C-enriched POC in the epilimnion in late summer overwhelms any 13C-depleted bacterial 

POC produced in the hypolimnion. In fact, the mean depth of 

the North Arm is only 4.3 m with a maximum depth of 14.0 

m (Megard, 1972) so it is unlikely that this arm of the lake has 

much of a hypolimnion. Values of 15N are near zero (fig. 8) 

suggesting that the POC in the epilimnion is mostly produced 

by N-fixing cyanobacteria. In Lower Lake Minnetonka, 

cyanobacteria are by far the dominant plankton, blooming 

mainly from July to October (Megard, 1972) when the CO2 in 

the epilimnion is likely to be the most 13C-enriched. The most 13C-depleted organic matter in Lake Minnetonka tends to be 

the most H-rich (fig. 9B), which also suggests that H-rich algal 

organic matter must be part of the POC mix in the sediments. 

In Lake Greifen in Switzerland, cultural eutrophication, 

in response to increased nutrient loading (mainly phosphate), 

produced an anoxic hypolimnion after 1930 with the deposition of laminated sediments (Hollander and others, 1992). 

Organic matter in sediments deposited before 1930 was 

mostly produced by photosynthesis in the epilimnion and 

oxidized in the oxic hypolimnion resulting in HI values of 

400–500 (fig. 10A). The slight negative correlation between 

δ13C and HI in sediments deposited before 1930 (fig. 10B) 

16  Characterization of Organic Matter in Lake Sediments
δ13C (‰; VPDB) Total Pigments (units/g organic matter) -32 -30 -28 -26

-24-22

150 200 250 300 

y = -0.022x - 21.60 r = 0.51

0

50

100150200

150 200 250 300 

Minnesota Surface Sediments

Minnesota Surface Sediments

-36-34-32-30-28-26-24-22

100 200 300 400 500 600 700 800 900

y = 0.008x - 34.69 r = 0.52

Trail Lake

Slough Creek Pond

δ13C (‰; VPDB)

 HI (mg HC/g OC) HI (mg HC/g OC

 HI (mg HC/g OC

-36-34-32-30-28-26-24-22

100 200 300 400 500 600 700 800 900

y = -0.004x - 21.57 r = 0.46

Elk Lake

Lake Minnetonka

δ13C (‰ VPDB)

 HI (mg HC/g OC)

Prairie Period

Pre- and Post-Prairie Period

A

B
-36

-35

-34

-33

-32

-31

-30

δ13Corg 

300 400 500 600 700 800 900

pre-1930

post-1930

-36 -35 -34 -33 -32 -31 -30

δ13Corg (‰; VPDB)

300 400 500 600

1930

700 800 900

HI (mg HC/g Corg)

HI (mg HC/g Corg)

0

10

20

30

40

50

60

70

Depth (cm )

A

B

----- -----

+ HI

δ13C

Figure 10. (left) Values of Rock-Eval 

pyrolysis hydrogen index and δ13C of organic 

matter in the top 60 cm of sediment from 

Lake Greifen in Switzerland are plotted in 

stratigraphic sequence (A) and as a cross 

plot (B). Data are from Hollander and others 

(1992).

Figure 9. (previous page) Cross plots of 

Rock–Eval pyrolysis hydrogen index (HI) 

versus values δ13C in organic matter in lake 

sediments from (A) Trail Lake and Slough 

Creek Pond in YNP; (B) Lake Minnetonka 

and Elk Lake in Minnesota; (C) 18 

Minnesota Lakes. A cross plot of HI versus 

concentrations of total plant pigments in 

surface sediments of the same 18 Minnesota 

lakes in shown in D. Data on pigments in 

surface sediments were provided by J.E. 

Sanger (see Sanger and Hay, 1993, for 

methods and interpretations of pigment 

results). VPDB, Vienna PeeDee Belemnite.

18  Characterization of Organic Matter in Lake Sediments
suggests that there was some mixing of terrestrial organic 

matter, but with predominantly aqueous organic matter 

(Hollander and others, 1992). The immediate post-1930 

period of intense eutrophication with methanotrophy in the 

hypolimnion is represented in figure 10 by two samples with 

values of δ13C of less than –34 ‰ and values of HI of about 

600. The lake then rapidly evolved to a condition whereby 

photoautotrophic production of 13C- and H-enriched biomass 

overwhelmed production of δ13C-depleted microbial biomass, 

producing a mix of organic matter with values of δ13C greater 

than –34 ‰ and values of HI greater than 750 (fig. 10B). The 

organic matter in sediments in hypereutrophic Lake Minnetonka are much more 13C-enriched than any in Lake Greifen 

(fig. 7), which suggests that any 13C-depleted microbial biomass that is produced in the hypolimnion is not significantly 

diluting the abundant 13C-enriched cyanobacterial biomass 

produced in the epilimnion in late summer. 

Finally, the few studies that have addressed the effect of 

diagenesis on C- and N-isotope composition have generally 

concluded that values of δ13C and δ15N in sediments do record 

primary signals and are little affected by diagenesis. Dean and 

others (1986) concluded that a 1–2‰ diagenetic 13C-depletion 

is possible in typical marine sediments, although they found 

no changes in down-core data from the Peru margin. Surdam 

and Stanley (1981) reported values of δ13C in amorphous, sapropelic kerogen from samples of the Miocene Monterey Formation. These rocks have undergone a considerable amount 

of diagenesis, and yet values of δ13C are all between –20.3‰ 

and –23.6‰. If any imprint of diagenesis on the 13C signature 

of organic matter were to occur, it should be present in the 

Monterey Formation. Galimov and others (1982) and Deines 

(1980) reviewed the effects of various diagenetic processes on 

values of δ13C in marine organic matter and found no evidence 

for diagenetic change. Cronin and Morris (1982) found no 

significant changes in δ13C with increasing diagenesis in OCrich sediments off Namibia. Meyers (1997) concluded that the 

absence of evidence of diagenetic shifts in values of δ13C in 

many lacustrine sediment records indicates that microbes and 

plankton utilize a large enough fraction of the carbon pool that 

a potentially significant diagenetic effect is minimal. Studies 

from Lake Ontario (Hodell and Schelske, 1998), Lake Baldegg 

(Teranes and Bernasconi, 2000), and Lake Lugano in Switzerland (Lehman and others, 2002), suggest that despite significant diagenetic loss of organic matter, values of δ13C and δ15N 

in sediments are little affected.

Conclusions

Sediments in cores from many lakes show an inverse 

correlation between the concentrations of CaCO3 and OC. This 

is attributed, in part, to the lacustrine carbon pump in which 

carbon is fixed by photosynthesis in the epilimnion, thus 

removing CO2 and increasing the pH and dissolved O2. Respiration of this fixed organic carbon (OC) in the hypolimnion 

consumes O2, produces CO2, and lowers the pH. The lower pH 

of the hypolimnion can result in the dissolution of much of the 

CaCO3 produced in the epilimnion. More CaCO3 is dissolved 

at the sediment/water interface and in corrosive pore waters.

The OC and Rock-Eval pyrolysis S2 data for lake sediments used in this investigation show that the two variables are 

highly correlated, which probably indicates that most of the 

organic matter in these sediments is lipid-rich, algal, organic 

matter. Using the S2 peak as a measure of H-richness, the sediments from Spectacle Lake and Lake Minnetonka in Minnesota, 

and Slough Creek Pond and Trail Lake in YNP are the most 

H-rich, and sediments from Lake Pepin in Minnesota, presently 

a wide spot in the Mississippi River, are the least H-rich.

In a moderately eutrophic lake, organic carbon fixed 

by photosynthesis in the epilimnion will become more 13Cenriched during the entire growing season as 13C-depleted 

CO2, preferentially utilized by photoautotrophic phytoplankton, is continually being removed and fixed in 13C-depleted 

organic matter. Some of this 13C-depleted organic matter may 

be decomposed in the hypolimnion producing anoxia and 13Cdepleted CO2

. Methanogenesis in anoxic sediments can release 

a considerable amount of 13C-depleted methane to the hypolimnion. Chemoautotrophic or methanotrophic bacteria in the 

anoxic hypolimnion can further fractionate the carbon-isotopic 

signature producing extremely 13C-depleted bacterial biomass. 

Bacterial biomass by sulfate reduction in Eocene Lake Uinta 

probably was a significant contributor to the extremely 13Cdepleted oil shale in the sulfide-rich Green River Formation 

(δ13C –30 to –34‰). Lake sediments with values of δ13C less 

than –28‰ likely contain a considerable amount of bacterial 

biomass produced in the hypolimnion. Sediments from several 

lakes in Minnesota included in this study (Elk, Williams, Shingobee, and Green) match this criterion, as do lakes in northern 

YNP with high concentrations of dissolved sulfate. 

In highly eutrophic lakes, rapid removal of 13C-depleted 

photosynthetic biomass early in the growing season may cause 

the carbon pool of the epilimnion to become enriched in 13C 

so that photosynthesis later in the growing season produces 

organic matter that is highly enriched in 13C, resulting in a net 13C-enriched sedimentary carbon pool. Lake Minnetonka and 

Spectacle Lake in Minnesota have the most 13C-enriched sediments (greater than –25‰) of the lakes in this study.

The 15N-depleted values of organic matter in the sediments 

of lakes in YNP suggest that a large proportion of the organic 

matter in these lakes may be from N-fixing cyanobacteria. Prevalent N-fixation would also imply that the lakes of YNP are nitrogen- limited. Values of δ15N in sediments from Lake Minnetonka 

and Spectacle Lake in Minnesota also are near zero, suggesting 

that N-utilization in these lakes also was mainly by N-fixation.

The few studies that have addressed the effect of diagenesis on C- and N-isotope composition have generally concluded 

that values of δ13C and δ15N in sediments are little affected by 

diagenesis. Apparently, the absence of evidence of diagenetic 

shifts in values of δ13C and δ15N in marine and lacustrine 

sediment records indicates that microbes and plankton utilize 

a large enough fraction of the carbon pool that a potentially 

significant diagenetic effect is minimal.

Conclusions 19
Acknowledgments

Samples of sediment from cores from Yellowstone 

National Park were provided by Cathy Whitlock, University of 

Oregon. Stephanie Brachfeld, University of Minnesota, provided samples from the long 1997 core from Lake Pepin. Dan 

Engstrom and Jim Almendinger, St. Croix Watershed Research 

Station, Minnesota, provided samples and data from one of 

the short cores (D2) from their grid of 25 cores from Lake 

Pepin. Kerry Kelts and Dawn Graber, Limnological Research 

Center, University of Minnesota, provided sediment samples 

from Spectacle Lake. Amy Myrbo, University of Minnesota, 

provided sediment samples from Lake Minnetonka and Green 

Lake. Lisa Doner provided valuable assistance in the laboratory. 

Carbon and nitrogen isotope ratios were determined by Matt 

Emmons of Mountain Mass Spectrometry, Evergreen, Colorado. 

Rock-Eval pyrolysis analyses were conducted by Ted Daws in 

the USGS Organic Geochemistry lab, Denver Colo. The studies 

of Williams, Shingobee, and Pickerel Lakes could never have 

been done without Antje Schwalb, as well as Tom Winter, Don 

Rosenberry, Renee Parkhurst, Rob Striegl, and other members 

of the USGS Shingobee Headwaters study group. A special 

thanks to Dave Hollander for his many insights into the interpretation of carbon isotopes in lake sediments. This study was 

funded by the USGS Global Change and Climate History and 

Earth Surface Dynamics Programs. Reviews of an earlier draft 

of this paper by Janet Pitman, Mike Lewan, and Phil Meyers 

were most helpful and are greatly appreciated.

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nitrate utilization and productivity limitation provided by 

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trap and core sediments from Baldeggersee, Switzerland: 

Limnology and Oceangraphy, v. 45, p. 801–813

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occurrence, 2d ed.: New York, Springer-Verlag, 538 p.

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References  23
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

Williams Lake

18 32.84 0.01 32.83

38 33.20 0.01 33.19

58 32.27 0.03 32.24

85 30.98 0.01 30.97

105 31.54 0.01 31.53

125 34.84 0.01 34.82

145 32.53 0.01 32.52

162 31.49 0.04 31.45

182 33.97 0.01 33.96

202 32.06 0.01 32.06

220 32.35 0.02 32.34

240 28.99 0.01 28.98

260 29.24 0.01 29.22

280 26.59 0.01 26.58

300 24.65 0.02 24.64

318 19.08 0.49 18.59

325 12.78 2.93 9.84

338 15.14 3.07 12.07

359 10.58 0.95 9.62

365 8.89 3.78 5.11

388 9.39 4.35 5.03

408 7.50 4.10 3.40

428 7.05 4.28 2.77

448 6.87 4.32 2.55

468 11.09 4.94 6.15

478 7.89 4.82 3.08

487 7.92 5.07 2.86

493 8.05 4.00 4.05

499 8.67 4.30 4.37

503 8.10 4.99 3.12

513 7.21 5.07 2.14

533 6.86 5.15 1.71

536 8.22 6.02 2.20

Page 1

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

546 7.39 4.93 2.47

554 4.96 4.25 0.71

562 3.28 2.99 0.29

563 7.32 5.80 1.52

578 5.50 4.41 1.10

584 4.47 3.55 0.92

588 5.37 4.13 1.24

593 6.08 4.35 1.74

598 4.90 4.19 0.70

603 3.65 2.89 0.76

608 7.88 6.20 1.68

613 7.95 6.18 1.77

623 7.85 6.57 1.27

633 8.67 7.59 1.08

643 9.36 8.36 1.00

653 8.92 8.17 0.74

660 10.30 8.71 1.59

676 11.81 10.01 1.80

686 12.70 10.26 2.43

696 11.16 9.66 1.50

706 9.58 8.39 1.19

712 10.91 10.32 0.60

Shingobee Lake

0 13.43 7.54 5.89

14 13.28 8.08 5.20

34 13.57 8.51 5.06

54 13.01 8.17 4.83

74 12.98 9.46 3.52

94 12.88 10.08 2.80

114 12.88 10.10 2.79

134 13.02 9.40 3.62

154 13.17 9.37 3.80

174 12.77 9.01 3.76

191 12.90 8.89 4.01

201 12.57 8.75 3.82

216 11.79 7.62 4.17

236 12.09 8.50 3.59

246 11.97 7.84 4.13

266 12.10 8.49 3.61

290 11.82 7.81 4.01

306 10.49 7.02 3.47

326 11.20 8.12 3.08

Page 2

24  Characterization of Organic Matter in Lake Sediments
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

346 10.64 7.68 2.96

366 11.44 8.76 2.68

396 10.54 7.69 2.85

416 9.47 7.44 2.04

436 10.02 7.92 2.11

456 11.03 8.65 2.38

476 11.24 9.01 2.23

496 11.44 9.23 2.21

506 11.35 9.25 2.11

516 10.53 9.30 1.22

536 10.69 8.58 2.11

556 10.69 8.66 2.03

566 11.06 9.20 1.86

596 10.38 8.59 1.79

606 10.01 8.27 1.74

626 10.66 8.77 1.88

636 10.68 8.84 1.84

656 10.29 8.56 1.73

676 10.29 8.52 1.77

695 10.57 8.52 2.05

715 10.71 9.17 1.55

735 10.36 9.07 1.29

755 11.40 9.89 1.51

775 8.39 6.57 1.83

794 11.55 9.68 1.88

812 11.71 9.86 1.85

832 10.90 8.92 1.98

852 10.47 8.64 1.83

870 11.48 9.18 2.31

885 11.10 9.15 1.95

897 10.97 9.02 1.96

917 10.75 7.99 2.76

925 7.79 6.57 1.22

Green Lake

20 17.61 3.48 14.13

30 18.18 3.76 14.42

40 17.69 5.34 12.35

50 17.18 5.12 12.06

60 16.61 5.09 11.52

70 14.91 5.75 9.15

80 14.94 7.10 7.84

90 15.80 8.26 7.54

Page 3

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

98 16.10 7.91 8.19

120 16.38 8.47 7.90

140 15.53 9.25 6.28

160 15.05 9.21 5.84

180 15.95 9.15 6.80

120 15.44 9.22 6.22

140 15.59 9.44 6.15

160 14.86 9.58 5.28

170 14.74 9.69 5.05

190 13.97 9.11 4.86

210 12.92 8.14 4.78

170 12.37 8.24 4.14

180 11.81 7.86 3.95

190 11.90 7.80 4.10

200 12.29 7.95 4.34

210 11.64 7.23 4.41

220 11.93 6.91 5.02

Spectacle Lake

2 23.02

12 20.78

22 21.08

32 27.30

42 30.93

52 34.15

62 34.95

72 36.29

82 34.48

92 34.80

105 34.06

113 32.09

123 30.25

133 30.41

143 25.76

153 29.49

163 30.82

173 34.12

183 32.11

193 32.27

211 33.15

334 32.76

344 32.28

359 30.94

Page 4

Appendix 1. Results of Carbon Analyses  25
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

364 29.76

374 30.95

Lake Minnetonka

21.5 13.04 2.49 10.56

31.5 14.25 1.93 12.32

41.5 15.48 1.65 13.83

51.5 14.66 0.98 13.68

61.5 14.76 1.66 13.09

71.5 12.06 1.22 10.83

81.5 9.58 0.60 8.98

91.5 11.03 0.67 10.36

101.5 18.69 0.39 18.30

111.5 20.63 0.35 20.28

121.5 22.40 0.38 22.02

131.5 22.55 0.31 22.25

141.5 18.85 0.35 18.50

151.5 18.99 0.34 18.65

161.5 18.01 0.44 17.56

171.5 17.53 0.42 17.11

181.5 16.53 0.40 16.13

201.5 17.23 0.81 16.41

211.5 17.95 0.69 17.26

221.5 19.12 0.72 18.40

231.5 18.34 0.69 17.65

241.5 19.84 0.70 19.14

251.5 19.71 0.65 19.06

261.5 19.89 0.65 19.25

271.5 20.31 0.63 19.68

281.5 19.34 0.53 18.80

291.5 20.31 0.68 19.63

301.5 23.30 0.65 22.65

311.5 18.86 0.61 18.25

321.5 19.00 0.81 18.19

331.5 18.94 0.72 18.22

341.5 14.89 1.93 12.96

351.5 15.76 1.11 14.65

361.5 15.21 1.04 14.17

371.5 16.11 0.83 15.28

381.5 13.74 1.45 12.29

391.5 13.46 1.54 11.92

401.5 13.25 2.34 10.91

411.5 13.06 1.86 11.20

Page 5

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

421.5 12.39 2.01 10.38

431.5 12.28 2.15 10.13

441.5 11.50 2.67 8.83

Lake Pepin

(long core)

11.5 4.45 1.14 3.31

31.5 4.66 1.05 3.62

51.5 4.40 0.69 3.71

71.5 4.23 0.67 3.56

91.5 3.90 0.37 3.53

111.5 3.81 0.19 3.62

131.5 3.72 0.41 3.31

151.5 3.67 0.48 3.20

171.5 3.68 0.99 2.69

191.5 3.62 1.14 2.48

211.5 3.44 0.86 2.58

231.5 3.44 1.13 2.31

251.5 3.44 1.09 2.35

271.5 3.38 1.07 2.32

286.5 3.35 1.03 2.32

421.5 3.60 0.92 2.67

441.5 3.75 0.93 2.83

461.5 3.71 0.77 2.94

481.5 3.50 0.91 2.60

501.5 3.46 0.88 2.58

521.5 3.62 0.87 2.76

541.5 3.54 0.93 2.61

558.5 3.84 0.79 3.05

581.5 3.82 0.90 2.92

601.5 3.86 0.84 3.02

621.5 3.58 0.87 2.71

641.5 3.73 0.90 2.82

661.5 3.66 0.91 2.76

681.5 3.78 1.01 2.76

701.5 3.94 0.91 3.03

721.5 3.79 0.60 3.19

754.5 3.54 1.05 2.50

771.5 3.15 0.64 2.51

791.5 3.67 1.09 2.58

811.5 3.88 0.92 2.96

831.5 3.86 0.99 2.87

851.5 3.66 0.93 2.73

Page 6

26  Characterization of Organic Matter in Lake Sediments
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

871.5 4.42 1.46 2.96

891.5 4.73 1.16 3.57

911.5 5.28 1.30 3.97

931.5 5.64 1.92 3.72

951.5 5.41 2.13 3.28

971.5 6.15 2.54 3.62

991.5 5.85 2.66 3.19

1011.5 6.36 2.65 3.71

1031.5 6.88 3.54 3.34

1051.5 4.36 1.79 2.57

1071.5 5.68 2.86 2.82

1091.5 7.38 4.51 2.87

1111.5 7.20 4.70 2.50

1131.5 5.94 3.56 2.39

1151.5 6.58 3.91 2.67

1171.5 5.92 3.29 2.63

1191.5 8.77 5.49 3.27

Pickerel Lake

1 10.01 4.12 5.89

19 9.69 4.02 5.67

39 8.39 4.04 4.35

59 10.09 4.79 5.30

79 11.08 4.93 6.15

102 11.49 5.10 6.39

102 11.40 5.06 6.34

119 10.05 4.74 5.31

139 10.00 4.47 5.53

159 9.63 4.65 4.98

179 9.43 4.96 4.47

198 9.74 4.99 4.75

219 11.20 5.45 5.75

239 10.74 5.18 5.56

239 10.76 4.84 5.92

259 8.92 4.04 4.88

279 9.23 4.66 4.57

298 10.22 5.13 5.09

319 9.10 4.37 4.73

339 9.88 4.86 5.02

359 9.16 4.59 4.57

379 8.38 4.22 4.16

397 9.56 4.64 4.92

419 10.45 5.02 5.43

Page 7

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

439 9.34 4.82 4.52

459 7.60 4.12 3.48

459 7.62 4.16 3.46

479 10.33 5.40 4.93

498 11.07 5.45 5.62

519 10.63 5.61 5.02

539 8.03 4.36 3.67

569 10.47 4.71 5.76

619 10.65 5.60 5.05

658 9.06 4.48 4.58

699 9.37 4.78 4.59

739 10.66 5.07 5.59

739 10.89 5.06 5.83

779 9.75 4.73 5.02

819 10.08 5.47 4.61

839 8.82 4.60 4.22

869 10.23 4.46 5.77

909 10.33 5.31 5.02

949 9.27 4.78 4.49

989 9.21 4.79 4.42

989 9.31

1039 10.56 4.98 5.58

1079 10.24 4.84 5.40

1120 9.31 4.17 5.14

1160 9.36 4.73 4.63

1189 7.72 3.63 4.09

1210 7.71 4.21 3.50

1230 8.82 4.19 4.63

1250 8.71 4.52 4.19

1270 8.43 4.31 4.12

1290 8.35 4.04 4.31

1310 7.15 4.04 3.11

1335 4.69 2.98 1.71

1342 5.68 3.63 2.05

1360 6.73 4.33 2.40

1390 7.53 5.02 2.51

1390 7.56 5.08 2.48

1407 6.52 4.10 2.42

1423 5.22 3.32 1.90

1430 8.09 6.19 1.90

1450 9.18 6.66 2.52

1460 9.42 7.04 2.38

Page 8

Appendix 1. Results of Carbon Analyses  27
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

1466 8.57 5.64 2.93

1477 9.75 7.12 2.63

1494 10.45 8.50 1.95

1505 11.03 8.63 2.40

1517 11.40 8.97 2.43

1534 11.42 8.59 2.83

1553 11.54 9.14 2.40

1563 11.29 8.80 2.49

1569 11.43 9.44 1.99

1576 11.32 8.58 2.74

1583 11.26 9.22 2.04

1601 9.07 4.92 4.15

1622 7.41 4.58 2.83

1637 5.01 2.95 2.06

1642 5.20 1.84 3.36

1681 4.25 2.67 1.58

1692 2.72 1.31 1.41

1695 8.68 3.94 4.74

Blacktail Pond

1 14.58 7.55 7.03

1.1 13.33 8.36 4.97

1.2 13.10 9.04 4.06

1.3 13.02 9.12 3.90

1.4 13.06 9.30 3.76

1.5 14.00 8.50 5.50

1.6 13.31 9.09 4.21

1.7 12.85 9.48 3.37

1.8 13.26 8.84 4.42

1.9 13.45 8.96 4.49

2 14.00 9.10 4.90

2.1 13.80 8.60 5.20

2.2 12.93 9.36 3.57

2.3 13.80 9.80 4.00

2.4 13.03 10.28 2.75

2.5 12.97 9.42 3.55

2.6 12.79 9.71 3.08

2.7 12.84 9.54 3.30

2.8 13.24 9.05 4.19

2.9 13.78 9.76 4.02

3 13.00 9.79 3.22

3.1 13.48 9.73 3.74

3.2 13.26 9.30 3.96

Page 9

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

3.3 14.45 9.16 5.29

3.4 12.60 8.85 3.75

3.5 13.58 9.33 4.25

3.6 13.21 8.01 5.20

3.7 13.70 8.52 5.18

3.8 13.50 8.73 4.77

3.9 13.60 7.77 5.83

4 14.14 8.57 5.57

4.1 13.59 8.54 5.04

4.2 15.91 7.20 8.71

4.3 14.83 4.75 10.08

4.4 13.93 8.09 5.84

4.5 12.12 8.63 3.49

4.6 11.91 8.71 3.20

4.7 13.43 6.40 7.04

4.8 15.37 6.18 9.19

4.9 13.58 8.31 5.27

5 14.56 6.37 8.19

5.1 15.05 6.88 8.17

5.2 14.55 7.27 7.27

5.3 13.17 7.85 5.32

5.4 23.09 3.65 19.44

5.43 13.91 8.72 5.19

5.5 13.39 8.56 4.82

5.6 14.17 8.07 6.11

5.8 13.40 8.58 4.82

6 12.43 5.18 7.24

6.08 14.79 2.85 11.94

6.18 12.89 3.94 8.96

6.28 18.00 5.65 12.35

6.38 14.83 8.32 6.51

6.48 13.67 9.60 4.07

6.58 14.81 8.90 5.90

6.68 14.23 8.49 5.74

6.78 13.57 7.99 5.58

6.9 14.04 8.12 5.92

7 9.60 6.20 3.40

7.1 2.96 1.58 1.38

7.2 1.56 0.31 1.25

7.3 1.66 0.18 1.48

7.4 1.91 0.80 1.11

7.5 0.67 0.21 0.46

Page 10

28  Characterization of Organic Matter in Lake Sediments
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

7.6 0.58 0.31 0.27

7.7 0.51 0.29 0.23

Slough Creek Pond

0.16 23.84 3.14 20.70

0.24 19.99 4.02 15.97

0.34 19.07 4.11 14.96

0.44 18.08 3.08 15.00

0.54 19.04 3.72 15.32

0.64 22.08 3.48 18.60

0.74 21.99 2.30 19.69

0.84 20.38 3.49 16.89

0.91 22.01 2.98 19.03

1.01 21.30 1.68 19.62

1.11 18.06 3.22 14.84

1.21 20.10 4.54 15.56

1.31 14.99 4.86 10.13

1.41 20.11 3.89 16.22

1.45 18.69 3.14 15.55

1.51 16.49 4.27 12.22

1.74 18.48 2.17 16.31

1.84 18.38 1.46 16.92

1.94 15.99 3.37 12.62

2.04 15.84 3.04 12.80

2.14 15.52 3.62 11.90

2.24 13.86 3.09 10.77

2.34 14.17 4.61 9.56

2.55 16.26 4.55 11.71

2.65 26.87 5.62 21.25

2.75 20.95 4.70 16.25

2.85 19.56 6.18 13.38

2.95 22.56 4.46 18.10

3.05 19.41 5.20 14.21

3.13 17.84 4.39 13.45

3.4 18.00 4.82 13.18

3.45 16.74 4.04 12.70

3.55 17.10 4.54 12.56

3.65 16.91 4.11 12.80

3.75 15.49 3.45 12.04

3.85 12.64 3.78 8.86

3.95 18.01 3.67 14.34

4.05 16.46 3.45 13.01

4.11 15.24 3.82 11.42

Page 11

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

4.25 13.67 3.62 10.05

4.35 8.86 2.18 6.68

4.45 12.91 3.70 9.21

4.55 14.17 1.72 12.45

Trail Lake

1 15.20

9 13.30

19 10.80

29 11.20

39 9.40

49 9.30

59 11.70

69 9.20

79 10.80

89 12.20

99 10.30

109 10.00

119 8.80

129 7.50

139 10.20

149 9.20

159 9.80

169 10.80

179 12.00

189 10.00

199 7.20

209 6.10

219 6.00

229 5.60

239 9.60

249 8.00

259 7.30

269 5.30

279 6.30

289 8.00

299 6.40

319 5.50

329 6.00

339 4.20

349 4.90

359 7.90

369 5.10

Page 12

Appendix 1. Results of Carbon Analyses  29
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

379 8.80

389 9.50

399 10.40

409 9.10

419 8.20

429 9.00

439 9.90

449 11.10

459 9.60

469 8.70

479 7.90

489 11.70

499 5.10

509 5.40

529 8.90

539 8.50

549 6.80

559 10.00

569 6.10

579 6.80

589 9.10

599 10.50

609 12.20

619 9.70

629 9.40

639 10.50

649 10.10

659 10.50

669 9.80

679 9.20

689 5.50

699 9.20

709 5.30

719 5.40

729 4.30

739 5.00

749 7.50

749 7.30

759 9.60

769 9.00

779 8.10

789 5.40

Page 13

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

789 5.30

799 8.60

809 8.00

819 7.50

829 7.10

839 7.10

849 7.20

859 6.40

869 8.80

869 8.60

879 9.30

889 6.50

899 5.50

909 6.50

919 4.50

929 3.40

939 2.20

949 2.80

959 0.90

969 0.60

979 0.70

989 0.70

999 0.70

Cygnet Lake

0 12.57

10 13.94

24 12.84

30 10.14

40 9.15

50 12.48

60 8.17

70 8.63

80 10.32

90 10.54

100 10.02

110 10.48

120 9.43

130 10.14

140 10.95

150 10.09

154 10.38

159 10.58

Page 14

30 Characterization of Organic Matter in Lake Sediments
Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

170 9.36

180 8.64

190 9.15

202 10.84

210 10.27

220 9.07

230 9.94

241 13.10

252 10.28

261 10.70

270 10.80

283 12.52

292 14.08

315 13.57

322 12.99

330 3.08

331 13.91

340 12.42

367 12.91

371 12.31

382 13.47

391 12.68

397 13.00

400 11.36

410 13.70

420 14.11

430 14.17

440 15.60

450 17.63

460 16.18

470 15.65

480 16.44

490 13.85

504 14.64

510 11.36

526 3.08

539 2.62

550 2.65

560 3.75

570 2.84

580 1.80

590 2.05

Page 15

Appendix 1. Results of carbon analyses.—Continued

Depth Total C Inorg. C Org. C

(centimeters) (percent)(percent)(percent)

600 4.01

610 1.29

620 0.75

630 0.74

640 0.61

649 0.49

660 0.26

670 0.62

680 0.40

690 0.45

Page 16

Appendix 1. Results of Carbon Analyses  31
Appendix 2. Results of Rock-Eval pyrolysis.—Continued

Depth Org. C S1 S2 S3 HI OI 

(centimeters) (percent)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

Spectacle Lake

2 27.9 6.6 216.3 34.0 774 121

62 59.2 10.2 549.2 50.0 928 84

153 44.2 8.0 401.9 40.8 909 92

183 49.1 5.7 440.8 43.0 898 87

334 50.6 6.5 458.6 42.3 907 83

374 46.9 6.9 430.3 40.4 917 86

Lake Minnetonka

20 - 23 8.1 0.8 42.9 25.3 532 313

30 - 33 10.3 0.9 59.2 30.6 573 296

40 - 43 11.8 0.8 64.5 33.3 548 283

50 - 53 12.2 0.9 74.3 31.9 609 261

60 - 63 12.6 0.9 76.0 31.0 601 245

70 - 73 8.1 0.5 35.6 28.1 441 349

80 - 83 2.5 0.2 10.3 15.0 414 606

90 - 93 7.0 0.6 36.2 25.2 518 361

100 - 103 19.7 1.3 125.1 38.0 634 192

110 - 113 21.7 1.3 143.2 39.0 658 179

120 - 123 25.3 1.6 176.2 40.4 695 159

130 - 133 25.7 1.4 172.9 39.0 672 151

140 - 143 25.3 1.7 175.0 37.4 691 147

150 - 153 21.4 1.2 144.4 33.6 673 156

160 - 163 20.4 1.1 136.4 31.7 668 155

170 - 173 19.5 1.1 128.1 33.1 655 169

180 - 183 14.2 0.5 73.0 37.2 515 262

200 - 203 17.6 1.0 115.9 36.2 659 205

210 - 213 18.1 0.9 112.5 36.0 620 198

220 - 223 19.8 1.2 131.7 43.4 665 219

230 - 233 17.4 1.4 106.0 40.2 608 230

240 - 243 21.9 2.0 161.3 36.9 736 168

250 - 253 22.6 2.0 163.8 34.7 723 153

260 - 263 22.9 1.5 156.9 36.1 685 157

270 - 273 22.0 2.3 152.5 38.4 691 174

280 - 283 20.6 2.9 139.0 43.1 675 209

290 - 293 18.9 0.8 122.6 43.0 649 227

300 - 303 22.7 1.8 165.6 41.0 731 180

310 - 313 21.1 1.4 152.1 37.0 721 175

320 - 323 20.5 1.2 147.3 33.2 719 162

330 - 333 20.6 1.9 144.3 35.2 701 171

340 - 343 12.7 1.0 81.1 27.8 636 218

350 - 353 15.3 1.3 104.9 32.1 687 210

360 - 363 14.4 1.4 90.4 30.1 629 209

Page 1

32  Characterization of Organic Matter in Lake Sediments
Appendix 2. Results of Rock-Eval pyrolysis.—Continued

Depth Org. C S1 S2 S3 HI OI 

(centimeters) (percent)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

370 - 373 16.0 1.1 104.1 31.1 651 194

380 - 383 11.5 0.6 70.8 26.9 617 234

390 - 393 11.0 0.7 69.8 26.9 632 243

400 - 403 9.4 0.5 56.3 25.5 599 271

410 - 413 10.2 0.6 57.6 26.1 566 256

420 - 423 8.5 0.6 46.9 25.2 552 297

430 - 433 8.4 0.5 45.1 25.4 538 303

440 - 443 6.6 0.3 28.0 24.7 423 373

Lake Pepin, core D2

0-20 3.3 0.1 6.8 5.1 250 186

40-44 9.1 0.1 5.1 5.2 171 175

60-64 9.0 0.1 5.6 4.7 186 158

76-80 9.0 0.1 4.3 5.2 150 182

92-96 9.1 0.1 4.9 5.4 169 186

116-120 8.2 0.1 2.9 4.8 119 197

140-144 6.2 0.0 2.2 3.7 120 206

164-168 5.9 0.0 1.9 2.9 118 180

196-200 6.1 0.0 1.6 3.2 101 201

228-232 6.2 0.0 1.6 3.1 98 193

256-260 6.0 0.0 1.8 2.9 107 179

Elk Lake (Dean 

and Stuiver, 1993)

50 7.0 1.2 13.1 15.9 188 228

100 6.7 0.1 18.6 18.0 277 268

220 5.7 1.6 12.4 20.4 218 358

240 6.0 0.8 12.0 18.1 201 304

400 5.7 1.0 9.8 22.0 174 384

410 5.7 1.2 10.9 18.2 193 321

490 4.6 1.1 7.9 13.3 170 287

570 4.4 0.9 9.0 16.0 205 363

600 4.3 0.9 7.7 14.2 178 331

610 4.0 1.0 9.7 12.9 242 322

700 3.7 1.6 8.7 9.4 235 253

710 3.9 0.0 5.5 13.2 139 335

1000 2.6 0.0 3.8 5.0 149 195

1010 2.1 0.6 4.6 3.6 223 176

1080 2.8 0.1 3.9 4.0 140 143

1220 2.8 1.0 7.3 4.2 257 150

1320 2.2 1.2 5.5 3.1 249 137

1330 2.4 1.2 7.2 3.2 298 134

1520 2.0 0.5 4.9 3.3 241 161

1680 2.5 1.0 6.6 3.4 268 136

Page 2

Appendix 2. Results of Rock-Eval Pyrolysis  33
Appendix 2. Results of Rock-Eval pyrolysis.—Continued

Depth Org. C S1 S2 S3 HI OI 

(centimeters) (percent)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

1700 2.4 0.5 5.3 2.8 219 116

1820 2.2 0.5 4.5 4.1 204 185

1920 2.8 0.8 4.5 6.1 162 221

2000 3.5 1.8 6.2 10.0 180 290

Trail Lake

1 10.7 5.1 67.0 18.1 628 169

19 17.0 8.9 119.1 23.4 701 137

39 8.4 2.6 48.2 19.0 573 226

59 11.2 3.8 75.1 20.9 670 186

79 10.6 3.6 62.4 18.7 588 176

99 9.9 3.0 61.2 18.4 617 185

119 7.3 2.0 38.7 15.7 531 215

139 9.0 3.0 53.2 18.0 593 201

159 8.7 2.3 52.0 18.0 595 206

179 12.1 3.1 74.7 18.4 618 152

199 6.4 1.7 31.0 13.8 487 217

219 5.4 1.8 29.2 12.6 540 232

239 8.7 2.5 51.6 16.3 589 186

259 6.4 2.1 35.1 13.3 551 208

279 5.2 2.7 27.5 11.6 533 224

299 5.1 2.4 27.6 12.3 542 242

319 4.2 1.7 19.6 9.3 470 223

339 2.9 1.4 11.7 7.4 400 255

359 7.1 2.1 36.4 12.4 511 174

379 8.2 2.8 41.7 11.5 512 141

399 9.9 2.3 47.0 14.4 475 145

419 6.9 2.4 27.7 11.6 399 166

439 9.1 2.4 43.0 13.6 472 149

459 8.8 2.1 42.2 13.5 481 153

479 6.6 2.7 25.2 10.9 384 165

499 6.2 3.0 30.2 11.0 484 175

539 7.9 2.0 35.6 13.5 451 171

559 9.6 1.1 45.8 15.2 478 159

579 5.2 0.7 14.5 10.4 280 200

599 10.4 1.3 53.2 14.0 512 134

619 9.6 1.0 50.6 13.5 526 140

639 9.5 1.0 44.8 15.1 474 160

659 10.1 1.5 47.7 15.5 473 153

679 8.9 2.3 48.8 12.5 548 141

699 8.1 2.2 39.7 13.5 492 167

719 4.5 1.5 22.4 9.7 497 216

739 3.9 1.6 17.3 7.8 442 201

759 8.4 1.7 40.3 13.1 480 156

Page 3

34  Characterization of Organic Matter in Lake Sediments
Appendix 2. Results of Rock-Eval pyrolysis.—Continued

Depth Org. C S1 S2 S3 HI OI 

(centimeters) (percent)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

779 7.8 2.1 43.2 11.3 553 144

799 7.7 0.8 35.9 12.1 464 156

819 6.4 0.9 33.3 11.5 522 180

839 6.6 0.9 33.3 11.7 505 177

859 5.8 1.0 28.8 10.5 499 182

879 9.1 1.8 54.8 14.2 601 155

899 4.9 1.6 26.5 8.9 542 181

919 3.5 1.0 13.3 6.6 380 189

939 1.7 0.5 4.3 2.3 254 134

959 0.5 0.4 1.5 0.9 282 163

979 0.4 0.2 1.1 0.8 302 210

999 0.4 0.2 0.8 0.7 186 161

Slough Creek Pond

16 20.7 2.0 138.2 37.2 654 175

24 16.0 0.5 83.2 36.2 553 240

34 15.0 0.6 82.0 33.3 602 244

44 15.0 0.9 96.2 34.0 635 224

54 15.3 1.3 116.7 33.7 724 208

64 18.6 1.0 112.3 37.0 593 195

74 19.7 1.0 117.2 36.4 571 177

84 16.9 0.7 81.4 37.0 514 234

91 19.0 1.2 130.8 38.0 646 187

101 19.6 2.0 150.5 35.6 672 159

111 14.8 1.1 95.0 30.2 637 202

121 15.6 0.9 84.3 32.9 581 226

131 10.1 0.3 49.8 27.6 541 300

141 16.2 0.7 95.6 34.7 584 211

145 15.6 1.5 105.3 32.9 674 211

151 12.2 0.7 89.1 29.8 695 232

174 16.3 0.6 94.0 34.1 609 221

184 16.9 0.9 119.2 32.6 677 185

194 12.6 0.5 68.9 29.3 624 265

204 12.8 0.8 90.2 30.3 727 244

214 11.9 0.8 88.6 28.5 758 243

224 10.8 0.6 77.2 27.8 766 275

234 9.6 0.5 59.0 26.8 738 335

255 11.7 1.3 74.2 27.0 786 286

265 21.3 1.3 74.2 27.0 786 286

275 16.3 2.3 91.7 33.7 780 286

285 13.4 1.8 78.6 26.8 787 268

295 18.1 2.4 146.6 26.3 896 160

305 14.2 2.4 103.8 19.4 898 168

313 13.5 2.6 94.8 21.5 864 195

Page 4

Appendix 2. Results of Rock-Eval Pyrolysis  35
Appendix 2. Results of Rock-Eval pyrolysis.—Continued

Depth Org. C S1 S2 S3 HI OI 

(centimeters) (percent)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

(milligram

per gram)

340 13.2 2.7 77.9 21.1 757 204

345 12.7 4.4 93.7 21.8 849 197

355 12.6 3.4 74.0 18.7 795 201

365 12.8 2.9 94.5 20.2 821 175

375 12.0 2.5 72.0 19.2 732 195

385 8.9 1.0 25.7 11.7 718 327

395 14.3 3.5 91.0 23.6 739 192

405 13.0 2.9 87.5 20.7 774 183

411 11.4 2.7 72.5 19.7 799 217

425 10.1 1.5 56.8 17.2 776 235

435 6.7 1.6 39.9 18.3 658 301

445 9.2 1.7 50.1 21.4 782 334

455 12.5 2.0 80.1 24.4 779 237

463 8.6 2.3 52.2 20.4 682 266

475 6.7 1.6 35.4 19.7 616 342

485 1.1 0.5 1.3 0.1 928 85

495 7.5 1.0 27.6 15.8 726 415

Page 5

36  Characterization of Organic Matter in Lake Sediments
Appendix 3. Results of carbon-and nitrogen-isotope analyses.—Continued

Depth G

13C G15N

(centimeter) (per mil)(per mil)

Williams Lake

910 -23.9 -2.37

957 -25.8 -2.07

997 -25.0 -2.52

1034 -24.7 -2.23

1072 -24.5 -2.58

1132 -26.3 -1.02

1211 -26.5 0.77

1260 -26.0 1.93

1300 -25.4 1.42

1339 -26.6 1.58

1436 -27.1 2.04

1460 -28.1 2.83

1505 -30.2 3.13

1538 -34.2 3.93

1564 -31.4 3.40

Shingobee Lake

14 -31.4 0.79

48 -31.4 2.74

88 -31.2 2.57

128 -30.5 2.91

168 -30.5 2.44

205 -30.0 1.51

230 -29.8 3.66

260 -30.2 3.39

304 -29.5 3.80

340 -29.5 3.15

430 -29.7 2.93

470 -29.9 2.24

510 -30.2 -0.88

530 -30.3 1.51

570 -30.9 1.80

Page 1

Appendix 3. Results of carbon-and nitrogen-isot

Depth G

13C G15N

(centimeter) (per mil)(per mil)

610 -30.3 3.25

640 -30.2 2.64

709 -29.7 1.80

749 -30.9 2.44

789 -32.5 2.76

826 -32.2 2.47

866 -32.6 1.83

899 -33.2 1.79

931 -33.7 1.08

956 -33.6 2.75

Spectacle Lake

2 -24.1 0.14

62 -22.2 -0.47

153 -22.2 1.08

183 -21.9 0.80

334 -22.5 1.05

374 -22.6 1.53

Lake Pepin, core D2

10 -27.6 2.93

42 -27.3 4.29

62 -27.0 4.15

78 -26.7 5.54

94 -27.2 6.19

118 -27.2 4.04

142 -28.2 5.06

166 -28.1 4.63

198 -28.2 3.80

230 -27.8 9.93

258 -28.2 11.97

Lake Pepin

long core

12 -28.2 6.05

52 -28.0 4.94

92 -27.8 5.34

132 -29.0 5.79

172 -29.6 5.50

212 -29.5 4.98

252 -29.4 5.01

287 -28.8 5.08

442 -28.9 4.56

482 -29.2 4.61

Appendix 3. Results of Carbon and Nitrogen Isotope Analyses  37
Appendix 3. Results of carbon-and nitrogen-isotope analyses.—Continued

Depth G

13C G15N

(centimeter) (per mil)(per mil)

522 -29.6 5.05

559 -29.7 3.90

602 -28.8 4.28

642 -28.6 4.60

682 -28.5 3.44

722 -28.7 1.43

772 -28.8 4.02

812 -29.0 4.07

852 -29.1 4.92

892 -29.0 4.56

932 -29.2 3.32

972 -29.8 3.03

1012 -29.7 3.73

1052 -30.0 2.38

1092 -29.7 2.86

1132 -30.1 2.72

1172 -29.9 2.93

Pickerel Lake

39 -24.43 4.19

119 -23.41 3.76

198 -24.32 4.22

279 -24.16 2.98

359 -24.91 3.57

439 -23.66 3.24

539 -24.57 2.67

619 -25.53 3.86

779 -24.19 3.45

909 -24.34 3.42

989 -24.34 2.89

1120 -24.93 2.99

1230 -23.66 3.21

1335 -24.61 2.26

1390 -26.02 2.89

1450 -26.48 3.33

1494 -26.67 2.25

1569 -30.95 2.05

1622 -30.43 3.45

1695 -24.73 2.02

Blacktail Pond

101 -25.5 -0.35

121 -25.3 0.45

141 -24.6 0.77

Page 3

Appendix 3. Results of carbon-and nitrogen-isotop

Depth G

13C G15N

(centimeter) (per mil)(per mil)

161 -24.5 -0.30

181 -24.1 0.02

201 -24.4 -0.41

221 -24.8 0.31

241 -25.1 0.39

281 -27.4 -0.29

301 -26.1 -0.59

321 -26.0 0.25

341 -26.4 -0.13

361 -26.6 -0.22

381 -26.9 0.39

401 -26.9 0.26

421 -28.5 0.59

441 -27.2 0.44

461 -27.2 -0.35

481 -28.6 -0.20

501 -28.7 -0.95

521 -28.2 -0.32

541 -28.0 -0.24

561 -28.3 0.12

581 -27.4 0.36

609 -25.0 -0.24

629 -29.1 0.39

648 -29.1 0.36

669 -29.6 -0.01

691 -27.4 0.43

701 -26.7 -0.11

731 -26.6 0.48

751 -30.1 0.32

771 -30.5 0.48

Slough Creek Pond

16 -30.6 -0.96

34 -30.9 -1.40

54 -32.0 -0.91

74 -30.0 -0.30

91 -30.2 -1.53

111 -31.3 -1.22

131 -30.4 -1.46

145 -29.9 -1.35

174 -28.2 -1.33

194 -29.0 -1.71

214 -28.5 -1.70

234 -28.4 -1.77

Pag

38  Characterization of Organic Matter in Lake Sediments
Appendix 3. Results of carbon-and nitrogen-isotope analyses.—Continued

Depth G

13C G15N

(centimeter) (per mil)(per mil)

265 -27.8 -1.04

285 -28.0 -1.34

305 -28.1 -1.73

340 -29.0 -1.39

355 -28.3 -0.93

375 -29.2 -0.58

395 -29.2 -0.78

411 -28.9 -1.53

435 -27.8 -1.68

455 -26.0 -1.39

475 -29.0 -0.30

495 -28.7 -1.18

Trail Lake

1 -25.5 -4.14

19 -24.7 -4.38

39 -24.3 -3.98

59 -24.5 -2.48

79 -25.9 -2.84

99 -25.7 -2.99

119 -25.9 0.62

139 -25.6 0.57

159 -26.7 0.97

179 -25.6 0.64

199 -25.7 0.56

219 -25.7 1.86

239 -26.4 2.26

259 -25.9 2.14

279 -25.8 3.21

299 -26.9 2.12

319 -27.6 1.97

339 -26.3 2.11

359 -26.5 2.55

379 -26.3 2.05

399 -27.0 3.35

419 -26.8 1.57

439 -26.6 2.16

459 -26.6 2.78

479 -26.7 1.39

499 -26.2 1.93

539 -26.1 1.15

559 -25.8 0.88

579 -25.5 1.98

599 -25.3 0.66

Page 5

Appendix 3. Results of carbon-and nitrogen-isot

Depth G

13C G15N

(centimeter) (per mil)(per mil)

619 -25.1 1.95

639 -24.7 1.88

659 -25.1 0.21

679 -25.0 0.59

699 -27.0 0.37

719 -26.1 1.43

739 -25.1 1.41

759 -25.5 1.75

779 -24.8 0.53

799 -24.7 1.58

819 -24.1 1.32

839 -24.9 1.94

859 -24.7 1.73

879 -25.0 1.84

899 -24.6 1.06

919 -24.7 1.02

939 -25.7 2.66

959 -26.7 3.97

979 -25.5 2.20

999 -25.7 2.72

Cygnet Lake

0 -28.3 2.27

20 -28.2 1.39

40 -27.8 1.77

60 -28.1 2.65

80 -26.6 1.59

100 -25.3 2.38

120 -23.9 1.44

141 -23.4 1.90

154 -22.8 2.63

159 -21.9 1.66

180 -21.8 0.37

202 -21.5 1.97

220 -21.2 1.64

252 -21.5 3.14

270 -22.9 2.11

292 -23.7 2.28

315 -22.5 2.18

330 -22.3 3.55

367 -21.6 3.53

382 -20.3 3.06

400 -21.6 2.32

420 -21.5 1.33

Appendix 3. Results of Carbon and Nitrogen Isotope Analyses  39
Appendix 3. Results of carbon-and nitrogen-isotope analyses.—Continued

Depth G

13C G15N

(centimeter) (per mil)(per mil)

440 -21.2 0.90

460 -21.1 0.47

480 -18.0 1.80

504 -17.5 1.08

526 -21.4 1.71

Page 7

40 Characterization of Organic Matter in Lake Sediments