Mercury and Methylmercury

in Reservoirs in Indiana

Professional Paper 1813 rofessional Paper 1813

U.S. Department of the Interior

U.S. Geological Survey
Cover Photos

Background. Shoreline near Hanna Creek Marina at Brookville Lake, Indiana (photograph by 

Amanda L. Fredericksen, USGS).

Insets from top to bottom.

People fishing unnamed stream (from U.S. Fish and Wildlife Service Image Library, 

http://digitalmedia.fws.gov/).

Great blue heron in Brookville Lake headwaters near Quakertown Recreation Area, Indiana 

(photograph by Martin R. Risch, USGS).

Boats moored at Fairfax Marina on Monroe Lake, Indiana (photograph by Martin R. Risch, USGS).

Common carp near Newton Stewart Marina at Patoka Lake, Indiana (photograph by Martin R. Risch, 

USGS).

Control tower at Monroe Lake dam near Harrodsburg, Indiana (photograph by Martin R. Risch, USGS).

Tailwater at Patoka Lake dam near Cuzco, Indiana (photograph by Martin R. Risch, USGS).
Mercury and Methylmercury in Reservoirs in Indiana

By Martin R. Risch and Amanda L. Fredericksen

Professional Paper 1813 

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/

pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. 

Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Risch, M.R., and Fredericksen, A.L., 2015, Mercury and methylmercury in reservoirs in Indiana: 

U.S. Geological Survey Professional Paper 1813, 57 p., http://dx.doi.org/10.3133/pp1813.

ISSN 2330-7102 (online)
iii

Preface

Scientists and health officials agree that mercury is a chemical of concern because relatively 

small amounts of a form of mercury known as methylmercury can accumulate in the food webs 

of ecosystems and pose risks to humans and wildlife. Most of the United States, including 

Indiana, has public health advisories about eating wild-caught fish because of mercury contamination. Mercury is a worldwide contaminant, meaning that freshwater and ocean fish bought at 

a grocery or restaurant may contain small but significant amounts of mercury and have a health 

advisory. It is important to understand that the highest risks from methylmercury in fish are for 

the unborn and young, but adults also can be severely affected. These health risks hold true for 

wildlife as well as for humans—and although humans can lower their risks by selecting the type 

and amount of fish they eat, wildlife cannot make such choices.

The story about mercury in the environment is complex. Most of the mercury in ecosystem food 

webs comes from the air, arriving in precipitation and dry fallout. Much of the mercury in the 

air comes from human activity, such as burning coal to make electricity, cement manufacturing, 

and steelmaking. Local and regional sources of mercury emissions to the air have been shown 

to influence mercury levels in local and regional ecosystems. Regulations to reduce mercury 

emissions to the air in the United States are based on the belief that methylmercury levels in 

ecosystem food webs will diminish in response, although the timing of this response is unknown 

and may vary among ecosystems.

Scientists have been studying mercury in the environment in Indiana since the 1990s. Mercury 

science requires highly specialized tools and techniques to properly quantify the small environmental concentrations that are important in ecosystems. By analyzing thousands of samples of 

wild fish, precipitation, stream and lake water, wastewater, air, and forest vegetation in Indiana, 

we have developed a framework for describing mercury occurrence, transport, and fate. 

A previous retrospective study of mercury in Indiana watersheds used the natural boundaries of 

water movement to group and interpret the many pieces of mercury information. A finding from 

the study led to the research about mercury and methylmercury in Indiana reservoirs described 

in this paper. Reservoirs, unlike natural lakes, are a part of river systems that are managed for 

flood control, which leads to unintended effects on mercury transport and methylmercury formation. Reservoir dams slow the velocity of water, allowing particles carrying mercury to settle in 

the reservoir pools. In the summer especially, some of the mercury in the reservoir pools can be 

transformed to methylmercury, the toxic form of mercury that accumulates in food webs. Water 

flowing out of reservoirs tends to have substantially higher ratios of methylmercury to mercury 

than does water in free-flowing streams. Methylmercury levels in the water of the reservoirs are 

related to levels of mercury in the fish. Atmospheric mercury deposition, landscape factors, and 

water chemistry appear to affect the levels of mercury and methylmercury in reservoirs.

Knowledge of reservoirs in Indiana can provide a reference about the potential for methylmercury in other reservoirs of the Great Lakes and Ohio River Valley region.

v

Contents

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

Introduction.....................................................................................................................................................2

Purpose and Scope ..............................................................................................................................2

Mercury and Methylmercury in the Environment ...........................................................................2

Reference Benchmarks for Mercury and Methylmercury ............................................................3

Previous Studies of Mercury in Reservoirs......................................................................................4

Description of the Study Area ............................................................................................................4

Methods...........................................................................................................................................................4

Data-Collection Sites ...........................................................................................................................4

Water-Quality Characteristics............................................................................................................8

Water-Sample Collection, Processing, and Analysis .....................................................................8

Quality Assurance.................................................................................................................................9

Mercury and Methylmercury in Reservoirs in Indiana .........................................................................11

Reservoir Tailwaters...........................................................................................................................11

Reservoir Pools ...................................................................................................................................14

Factors Affecting Mercury and Methylmercury in Reservoirs in Indiana ................................25

Transport of Mercury to Reservoirs........................................................................................25

Conversion of Mercury to Methylmercury in Reservoirs....................................................25

Reservoir Fish......................................................................................................................................33

Concentrations in Fish Tissue..................................................................................................33

Bioaccumulation........................................................................................................................33

Implications for Fish Consumption..........................................................................................34

Limitations of Existing Information...................................................................................................35

Summary and Conclusions.........................................................................................................................36

References....................................................................................................................................................37

Appendix 1. Supplemental Data ...............................................................................................................41

Figures

1. Flood-control reservoirs in Indiana ...........................................................................................5

2. Generalized diagram of reservoir-pool-monitoring transect, water-quality

verticals, and lake-bottom topography .....................................................................................7

3. Apparatus for collection of water samples for mercury analysis........................................9

4. Mercury and methylmercury concentrations in water samples from tailwater

sites at four reservoirs...............................................................................................................12

4. Mercury and methylmercury concentrations in water samples from tailwater

sites at four reservoirs...............................................................................................................13

5. Sampling sites and water-quality transects for Brookville Lake........................................15

6. Sampling sites and water-quality transects for Monroe Lake............................................16

7. Sampling sites and water-quality transects for Patoka Lake .............................................17

8. Whole-water mercury concentrations in water from Brookville Lake..............................20
vi

9. Whole-water mercury concentrations in water from Monroe Lake .................................21

10. Whole-water mercury concentrations in water from Patoka Lake ...................................22

11. Ratio of dissolved methylmercury to mercury in water from Monroe Lake .....................23

12. Ratio of dissolved methylmercury to mercury in water from Patoka Lake.......................24

13. Relations between mercury and sample depth in Monroe Lake and Patoka Lake.........27

14. Distributions of mercury, methylmercury, dissolved oxygen, water pH, and

dissolved sulfate in Monroe Lake ............................................................................................29

15. Distributions of mercury, methylmercury, dissolved oxygen, water pH, and

dissolved sulfate in Patoka Lake..............................................................................................30

16. Areal extent of zone of high methylation potential in summer pool of Monroe Lake .....31

17. Areal extent of zone of high methylation potential in summer pool of Patoka Lake .......32

Figures—continued

Tables

1. Selected information for flood-control reservoirs in Indiana ...............................................6

2. Reservoir-pool water-quality transect information.................................................................7

3. Methods and reporting limits for determinations of water-quality characteristics..........8

4. Methods for analysis of mercury, particulate, and supplementary constituents

in water.........................................................................................................................................10

5. Mercury data summary for tailwaters at four reservoirs in Indiana .................................11

6. Reservoir-pool and tailwater sampling-site information .....................................................18

7. Mercury data summary for pools and tailwaters at three reservoirs in Indiana.............19

8. Physiographic region, natural region, and surficial geology in the vicinity of

reservoirs in Indiana ..................................................................................................................26

9. Statistical correlations of reservoir pool mercury with sample depth and

selected constituents in Monroe Lake and Patoka Lake.....................................................28

10. Methylmercury bioaccumulation factors for five reservoirs in Indiana ...........................34

1–1. Reservoir-pool and tailwater mercury quality-control field blank sample data ..............42

1–2. Quality-control data for reservoir-pool and tailwater mercury field

duplicate samples.......................................................................................................................42

1–3. Reservoir-tailwater mercury data............................................................................................43

1–4. Hydrologic conditions at three Indiana reservoirs ...............................................................45

1–5. Reservoir-pool and tailwater data for mercury, water-quality characteristics,

and supplementary constituents..............................................................................................46

1–6. Percentages of land-cover categories in reservoir drainage areas .................................50

1–7. Mercury wet- and dry-deposition rates and loads to reservoir 

watersheds in Indiana ...............................................................................................................50

1–8. Reservoir fish-tissue sample and mercury data....................................................................51
vii

Conversion Factors and Datums 

International System of Units to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd) 

Area

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

liter (L) 1.057 quart (qt)

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as:

°C = (°F – 32) / 1.8.

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Turbidity is given in nephelometric turbidity ratio units (NTRU).

Concentrations of chemical constituents in water are given in either milligram per liter (mg/L) 

or nanogram per liter (ng/L).

Concentrations of chemical constituents in solids are given in either milligram per kilogram 

(mg/kg) or microgram per kilogram (μg/kg).

Atmospheric deposition is given in units of microgram per square meter (μg/m2

).

A milligram is 0.001 gram. A microgram is 0.001 milligram. A nanogram is 0.001 microgram.
viii

Abbreviations

BAF bioaccumulation factor

DO dissolved oxygen

DOC dissolved organic carbon

EPA U.S. Environmental Protection Agency

GIS geographic information system

GPS global positioning system

Hg mercury

IDEM Indiana Department of Environmental Management

MeHg methylmercury

NLCD National Land Cover Database

POC particulate organic carbon

RPD relative percent difference
Mercury and Methylmercury in Reservoirs in Indiana

By Martin R. Risch and Amanda L. Fredericksen

Abstract

Mercury (Hg) is an element that occurs naturally, but evidence suggests that human activities have resulted in increased 

amounts being released to the atmosphere and land surface. 

When Hg is converted to methylmercury (MeHg) in aquatic 

ecosystems, MeHg accumulates and increases in the food 

web so that some fish contain levels which pose a health risk 

to humans and wildlife that consume these fish. Reservoirs, 

unlike natural lakes, are a part of river systems that are managed for flood control. Data compiled and interpreted for six 

flood-control reservoirs in Indiana showed a relation between 

Hg transport, MeHg formation in water, and MeHg in fish that 

was influenced by physical, chemical, and biological differences among the reservoirs. Existing information precludes 

a uniform comparison of Hg and MeHg in all reservoirs in 

the State, but factors and conditions were identified that can 

indicate where and when Hg and MeHg levels in reservoirs 

could be highest.

As part of a statewide monitoring network for Hg and 

MeHg in Indiana streams, 66 water samples were collected 

from four reservoir tailwater sites (downstream near the 

dams) on a quarterly schedule for 5 years. The reservoirs were 

Brookville Lake, Cagles Mill Lake, J. Edward Roush Lake, 

and Mississinewa Lake. Particulate-bound Hg concentrations were significantly lower in tailwater samples than in 

samples from free-flowing streams in the statewide network. 

(Free-flowing streams were not affected by dams and were 

not upstream from these reservoirs.) These data indicated 

the reduced flow velocity of water upstream from dams was 

allowing particulate-bound Hg to settle out of the water in the 

reservoir pools. The concentration ratios of MeHg to Hg were 

significantly higher in the tailwater samples than in samples 

from free-flowing streams, and the MeHg to Hg ratios were 

significantly higher in summer than in other seasons.

To evaluate the conditions related to MeHg formation, 

pools of three reservoirs (Brookville Lake, Monroe Lake, 

and Patoka Lake) were investigated during summer hydrologic conditions. Water temperature and dissolved oxygen were 

measured from the water surface to the lake bottom at 

10 to 17 transects across each reservoir to identify three thermal 

strata, defined by water temperature, dissolved oxygen concentration, and depth. Depth-specific water samples were collected 

from these thermal strata throughout each reservoir, from the 

headwaters to the dam and from the tailwater. Mercury concentrations higher than 0.04 nanogram per liter (ng/L) were 

detected in all 53 samples, and MeHg concentrations higher 

than 0.04 ng/L were detected in 53 percent of the samples. 

The investigation found a zone of water below 8 or 9 meters, 

with temperatures less than 18degrees Celsiusand dissolved 

oxygen less than 3.5 milligrams per liter, extending through nearly 

half the reservoir area in Monroe Lake and Patoka Lake. This 

zone had abundant dissolved MeHg and concentration ratios 

of dissolved MeHg to Hg that ranged from 25 to 82 percent. 

This zone also had water with pH less than 7 and decreased 

dissolved sulfate, conditions indicating sulfate reduction by 

microorganisms that promoted a high potential for the conversion of Hg to MeHg. Reservoir outflow came from this zone at 

Monroe Lake and contributed to a tailwater concentration ratio 

for dissolved MeHg to Hg of 56 percent. Reservoir outflow 

at Patoka Lake was not from this zone, and dissolved MeHg 

was not detected in the tailwater. In contrast, samples from 

the summer pool at Brookville Lake had no MeHg detections 

even though Hg was detected, probably because the water pH 

higher than 7 inhibited sulfate reduction and did not promote 

the conversion of Hg to MeHg. 

Mercury and MeHg concentrations and the concentration 

ratios of MeHg to Hg in water varied among the six reservoirs 

in Indiana, and the differences were related to a combination of factors that could apply to other reservoirs. In areas 

with moderate to high rates of atmospheric Hg wet and dry 

deposition, Hg runoff and transport to streams and reservoirs 

was potentially highest for reservoirs with heavily forested 

watersheds in steep terrains of near-surface bedrock. Methylmercury concentrations and concentration ratios of MeHg to 

Hg were highest for reservoirs with the longest summer pools 

and highest inflow-to-outflow retention times, where waterchemistry conditions favoring sulfate reduction promoted 

conversion of Hg to MeHg. 

Methylmercury (reported as Hg) in fish-tissue samples 

collected for the State fish consumption advisory program was 

used to describe MeHg food-web accumulation and magnification in the reservoirs. The highest percentages of fish-tissue 

samples with Hg concentrations that exceeded the criterion 

of 0.30 milligram per kilogram for protection of human 

health were from Monroe Lake (38 percent) and Patoka Lake 

(33 percent). A review of the number and size of fish species 

caught from these two reservoirs resulted in two implications 
2 Mercury and Methylmercury in Reservoirs in Indiana

for fish consumption by humans. First, the highest numbers of 

fish harvested for potential human consumption were species more likely to have MeHg concentrations lower than 

the human-health criterion (crappie, bluegill, and catfish). 

Second, although largemouth bass were likely to have MeHg 

concentrations higher than the human-health criterion, they 

were caught and released more often than they were harvested. 

However, the average size largemouth bass (in both reservoirs) and above-average size walleye (in Monroe Lake) that 

were harvested for potential human consumption were likely 

to have MeHg concentrations higher than the human-health 

criterion.

Introduction

Mercury (Hg)1 is an environmental contaminant that can 

pose adverse health risks to humans and wildlife, especially 

in the form of methylmercury (MeHg), which accumulates 

and magnifies in aquatic food webs. This data compilation and 

interpretation of Hg and MeHg in selected reservoirs is a case 

study for Indiana that indicates the potential for similar occurrence in other reservoirs.

Purpose and Scope

The purpose of this report is to present two sets of U.S. 

Geological Survey data about Hg and MeHg in water from six 

flood-control reservoirs in Indiana and to interpret how the Hg 

and MeHg were affected by physical factors and chemical and 

biological conditions in the reservoirs. (Reservoirs consist of 

a dam with flow-control structures that include floodgates and 

bypass valves. Water discharged through the gates or bypass 

outlets enters a stream channel, where it is termed “tailwater.” 

The water impounded behind the dam is termed “pool.”) This 

report presents Hg and MeHg in analyses of water samples 

from pools and tailwaters of three reservoirs (2009) along with 

analyses of water samples from tailwaters of four reservoirs 

(2002–2006). In addition, analyses of fish-tissue samples 

from eight reservoirs (1996–2007) were compiled from State 

records and interpreted to depict food-chain accumulation and 

magnification of MeHg. 

The scope of this report is comprehensive. The introduction uses data from Indiana and the scientific literature for an 

explanation of Hg and MeHg in reservoirs, along with reference benchmarks and public health advisories for Hg in fish. 

Methods include detailed descriptions of sampling, analysis, 

measurement, and quality assurance for Hg, MeHg, and 

other constituents in water of reservoir pools and tailwaters. 

Interpretations of the data from Indiana reservoirs are used to 

1

 In this paper, Hg is the same as what is sometimes called “total Hg.” 

Total Hg includes MeHg by definition, but MeHg and Hg concentrations are 

determined separately.

identify the factors and conditions affecting Hg and MeHg in 

water that could apply to reservoirs outside the study. Land 

cover, landscape, and atmospheric Hg deposition are examined 

for their effects on the transport of Hg to reservoirs. Water 

chemistry and reservoir characteristics are used to understand 

conditions that promote formation of MeHg in the reservoirs. 

Fish-tissue Hg data for species caught and harvested from 

reservoirs are discussed with their implications for human 

consumption and wildlife.

Mercury and Methylmercury in the Environment

Aquatic ecosystems receive Hg primarily from atmospheric deposition, originating from Hg emissions to the atmosphere from human activity (National Research Council, 2000; 

Lindberg and others, 2007, Driscoll and others, 2013). Wet 

deposition transfers atmospheric Hg that is in precipitation 

(rain, snow, sleet, hail, and fog) to the land surface. Dry deposition transfers gaseous, oxidized, and particulate atmospheric 

Hg to vegetation, soil, water, snow, and urban landscapes. Dry 

deposition occurs continuously and at a slower rate than wet 

deposition, which is episodic (Zhang and others, 2009). Dry 

deposition of Hg can be greater than wet deposition of Hg in 

many ecosystems (Lindberg and others, 2007; Zhang and others, 2012).

The Hg in atmospheric deposition is primarily inorganic 

Hg, which in aquatic ecosystems can be converted to organic 

MeHg by microorganisms as a byproduct of their metabolism. 

Sulfate-reducing bacteria, which process organic matter using 

sulfate in the environment, take up inorganic Hg and convert it 

to MeHg under certain conditions in riparian wetlands that are 

hydraulically connected to streams or lakes, as well as in some 

stream or lake-bottom environments (Morel and others, 1998). 

This MeHg can be released into the water by diffusion or 

resuspension of sediment. Organic carbon can affect the levels 

and mobility of Hg and MeHg in water, thereby enhancing the 

MeHg availability to the food web (Grigal, 2002; Brigham 

and others, 2009; Chasar and others, 2009). Methylmercury is 

highly absorbable and more toxic than inorganic Hg; organisms require a longer time to eliminate MeHg than Hg, and 

the amounts of MeHg in primary producers are preserved in 

successively higher levels of consumers in individual food 

chains within the food web (Munthe and others, 2007). Bacteria with MeHg may be consumed by the next higher level in a 

food chain, or the bacteria may release the MeHg to the water, 

where it can become part of plankton and periphyton (Bell and 

Scudder, 2007) that are consumed by the next level in a food 

chain. The concentration of MeHg magnifies in organisms at 

higher levels in food chains so that the highest concentrations 

are found in large, old, top-predator and bottom-feeding fish. 

Methymercury has been linked to adverse health and 

reproductive effects in humans and wildlife. The health risks 

to humans mostly are from fish consumption (Mergler and others, 2007). People and families who catch and eat fish for subsistence have the greatest exposure to MeHg. Methylmercury 
Introduction 3

is a potent neurotoxin that can slow nervous-system and 

cognitive development in young and unborn children. Adults 

can have adverse neurological and cardiovascular effects from 

MeHg exposure. Methylmercury has been linked to congenital birth defects, increased risk of heart attack, renal damage, 

and blood pressure dysfunction in humans (National Research 

Council, 2000). Methylmercury can interfere with reproduction in vertebrates (Klaper and others, 2006). Fish-eating 

mammals and birds exposed to high, environmentally relevant MeHg levels can have reproductive and developmental 

impairments and reduced immunity (Scheuhammer and others, 

2007). Populationwide effects in terrestrial wildlife have been 

linked to MeHg (Evers, 2005). 

According to Risch and others (2010), the median concentration of MeHg in Indiana watersheds was 0.10 nanogram 

per liter (ng/L), whereas the median concentration of MeHg in 

all fish from these watersheds was 0.13 milligram per kilogram (mg/kg). This comparison demonstrates the complexity 

of the Hg cycle in that MeHg accumulates and concentrates in 

the aquatic food chain by a factor of at least 1,300,000.2

 Studies have shown a correlation between atmospheric deposition 

of Hg and MeHg in fish (Cocca, 2001) and between MeHg in 

water and in fish (Brumbaugh and others, 2001). The strength 

of these relations has led to a prediction that Hg-emissions 

reductions will decrease MeHg concentrations in fish (Harris, 

Rudd, and others, 2007).

Reference Benchmarks for Mercury and 

Methylmercury

In this paper, national criteria are used that can be 

applied throughout Indiana and other States. Methylmercury 

(as Hg) in fish-tissue samples are compared with 0.30 mg/

kg as the “reference benchmark for human health.” The U.S. 

Environmental Protection Agency (EPA) freshwater waterquality criterion for MeHg is not based on a concentration 

in water. Rather, it is based on a concentration for MeHg in 

fish tissue that is protective of human health, 0.30 mg/kg 

wet weight (hereafter, fish-tissue concentrations refer to wet 

weight unless otherwise noted) (U.S. Environmental Protection Agency, 2001a).3

 Guidance for implementing the MeHg 

criterion (U.S. Environmental Protection Agency, 2010) states 

2

 One milligram equals 1,000 micrograms and one microgram equals 1,000 

nanograms, which means the MeHg concentration increase from 0.10 ng/L in 

the water to 0.13 mg/kg in the fish is 1,000 times 1,000, which equals a MeHg 

bioaccumulation factor of 1,300,000.

3

 The 0.30 mg/kg criterion is based on a total consumption-weighted rate of 

0.175 kg of fish per day (assuming a human adult body weight default value 

of 70 kg and a reference dose of 0.001 mg/kg per day, accounting for different 

trophic levels of fish.) A reference dose is an estimate (with uncertainty) of a 

daily oral exposure to the human population (including sensitive subgroups) 

that is likely to be without an appreciable risk of deleterious effects during a 

lifetime.

the assumption that nearly all of the Hg in fish-tissue samples 

is MeHg,4 meaning that fish-tissue Hg concentrations may be 

compared with the 0.30-mg/kg MeHg criterion as if they were 

MeHg concentrations. Other reports use this same assumption (for example, U.S. Environmental Protection Agency, 

1999, 2009; Harris, Krabbenhoft, and others, 2007; Scudder 

and others, 2009; Stahl and others, 2009), as do public health 

advisories for fish consumption (U.S. Environmental Protection Agency, 2010). In this report, Hg in fish-tissue samples is 

assumed to be nearly all MeHg for comparing with the EPA 

criterion but is called Hg, consistent with the data. 

In this report, Hg in fish-tissue samples are also compared with the “reference benchmark for wildlife,” 0.10 mg/

kg. The EPA (1997) derived a 0.10-mg/kg fish-tissue MeHg 

criterion protective of fish-eating mammals, including mink 

(Mustela vison) and river otter (Lutra canadensis), and a 

0.20-mg/kg fish-tissue MeHg criterion protective of fish-eating 

birds, including bald eagle (Haliaeetus leucocephalus), osprey 

(Pandiaon haliatus), and belted kingfisher (Ceryle alcyon). 

National assessments of Hg in lakes (Yeardley and others, 

1998) and streams (Scudder and others, 2009) used the more 

conservative criterion of 0.10 mg/kg MeHg for fish-eating 

mammals and birds to compare with fish-tissue Hg concentrations. The 0.10-mg/kg reference benchmark for wildlife also 

is protective of freshwater fish. In a literature review, Sandheinrich and Wiener (2011) noted that sublethal effects of Hg 

on freshwater fish, including changes in reproductive health, 

were consistently observed in laboratory and field studies for 

Hg concentrations exceeding approximately 0.30 mg/kg in the 

whole body and 0.50 mg/kg in the fillet. 

Mercury was detected in nearly all fish-tissue samples 

from national studies of lakes (U.S. Environmental Protection Agency, 2009) and streams (Scudder and others, 2009). 

The reference benchmark for human health was exceeded 

in these studies. Results from the statistically based national 

study of chemical residues in lake fish tissue (U.S. Environmental Protection Agency, 2009) estimated that 49 percent of 

76,559 lakes in the lower 48 States had fish with Hg concentrations that exceeded 0.30 mg/kg. For comparison, a national 

compilation of fish-tissue Hg data collected by States for fish 

consumption advisory programs indicated that approximately 

40 percent of the watershed-averaged sample concentrations 

exceeded 0.30 mg/kg (U.S. Environmental Protection Agency, 

2010). 

The reference benchmark for wildlife was exceeded 

2 to 3 times more often than the reference benchmark for 

human health in national studies. Yeardley and others (1998) 

reported that Hg concentrations in fish from 26 percent of the 

lakes in the northeastern United States exceeded 0.30 mg/kg 

4

 U.S. Environmental Protection Agency (2010) references four studies in 

which the mean ratios of MeHg to Hg concentrations in fish-tissue samples 

from studies in the northeastern United States were equal to or higher than 

90 percent (Grieb and others, 1990; Bloom, 1992; Becker and Bigham, 1995; 

and Hammerschmidt and others, 1999). All of the fish species listed for these 

four studies are found in Indiana.
4 Mercury and Methylmercury in Reservoirs in Indiana

and 54 percent exceeded 0.10 mg/kg. For comparison, Scudder and others (2009) reported that Hg in fish from 27 percent 

(79 of 291) of the stream sample sites in their study exceeded 

0.30 mg/kg and that nearly 75 percent (209 of 291 sites) 

exceeded 0.10 mg/kg, the reference benchmark for wildlife. 

Previous Studies of Mercury in Reservoirs

Reservoirs, unlike natural lakes, are a part of river systems that are managed for flood control. A condition known as 

the reservoir effect highlights the importance of Hg and MeHg 

in reservoirs. Methylmercury concentrations in water from 

new reservoirs increase because decomposition of organic 

carbon from inundated forest soils and wetlands stimulate 

microorganisms that form MeHg from Hg, as documented by 

numerous investigations summarized in Bodaly and others 

(2004), Mailman and others (2006), and Stewart and others 

(2008). The result is that MeHg in the suspended particulate 

matter and water of reservoirs is higher than in natural lakes. 

Methylmercury in the water is taken up by phytoplankton and 

zooplankton, leading to elevated Hg in fish. Elevated MeHg 

may persist for many years after a reservoir is first constructed 

(Hall and others, 2005; Bodaly and others, 2007), and MeHg 

in resuspended fine particles transfers to the food chain for a 

long time in the protected shallow areas of reservoirs (Plourde 

and others, 1997). 

As summarized in Canavan and others (2000), it is 

known that during seasonal thermal stratification of lakes and 

reservoirs, conditions develop in the deepest layer of water—

a layer with relatively low dissolved oxygen—that promote 

MeHg formation. Deep reservoirs with long retention times 

and recurring stratification develop a biochemistry of MeHgenriched water near the lake bottom. Unlike lakes, reservoirs 

are designed to release water, which can be enriched with 

MeHg, depending on the season and the depth of the water 

that is released from the reservoir.

Reservoir watershed characteristics and water-management actions can increase the potential for MeHg formation 

and subsequent bioaccumulation in aquatic organisms. Mast 

and Krabbenhoft (2010) compared Hg and MeHg in water, 

sediment, zooplankton, and fish from two reservoirs in Colorado. One reservoir had a Hg fish-consumption advisory and 

the other did not because in one reservoir, annual water-level 

fluctuations stimulated MeHg formation in a more organic-rich 

sediment of a larger area during reflooding. Negry and others 

(2011) combined water chemistry, lake, and land-use variables 

to predict Hg in fish from 17 lakes and reservoirs in California. They found the strongest statistical associations of Hg 

in fish were with Hg in lake sediment, percent forested area, 

and MeHg in water. Drenner and others (2011) studied factors 

affecting Hg in largemouth bass (Micropeterus salmoides) 

from 145 reservoirs in four ecoregions of Texas. They reported 

fish with the highest Hg were from reservoirs in the ecoregion 

with the highest Hg and sulfate deposition, extensive forest 

and wetland land cover, and little agriculture. 

Description of the Study Area

Eight reservoirs (fig. 1) were constructed in Indiana 

between 1953 and 1979 to prevent downstream flood damage (U.S. Army Corps of Engineers, 2014)—Brookville 

Lake, Cagles Mill Lake, Cecil M. Harden Lake (C.M. Harden 

Lake hereafter; also called Raccoon Lake), Mississinewa 

Lake, Monroe Lake, Patoka Lake, J. Edward Roush Lake 

(J.E. Roush Lake hereafter; also called Huntington Lake), 

and Salamonie Lake. Three of these reservoirs in Indiana are 

sources for a public-water supply—Brookville Lake, Monroe 

Lake, and Patoka Lake. These riverine reservoirs differ from 

natural or other constructed lakes because the outflow, internal 

transport, and retention time are influenced by management 

for flood control, water supply, and water quality, as well as by 

inflow from precipitation runoff.

Typical operation of a flood-control reservoir involves 

impounding water from spring runoff and attaining a summer 

pool stage that is generally maintained until a drawdown in 

late summer or early fall. The winter pool stage is established 

when drawdown is completed, and the reservoir refills until 

summer pool stage is reestablished. The summer pool areas 

of the reservoirs in Indiana range from 3.7 to 43.5 square 

kilometers (km2

), and upstream drainage areas range from 

440 to 2,093 km2 (table 1). 

Methods

Data-collection sites for reservoir tailwaters and pools are 

described in this section. Ultraclean protocols and low-level 

analyses for measuring Hg and MeHg in water are explained. 

Methods for water sample collection, processing, and analysis 

are presented, along with quality assurance of Hg and MeHg 

and supplementary constituents. Methods for determination of 

water-quality characteristics are described, including vertical 

profiles along reservoir-pool transects.

Data-Collection Sites

Tailwater sites at four reservoirs—Brookville Lake, 

Cagles Mill Lake, Mississinewa Lake, and J.E. Roush Lake 

(fig. 1)—were sampled as part of a statewide network for 

Hg in Indiana streams (Ulberg and Risch, 2008). Pools at 

three reservoirs—Brookville Lake, Monroe Lake, and Patoka 

Lake (fig. 1)—were investigated because Monroe Lake and 

Patoka Lake that had not been studied previously and because 

Brookville Lake was in a different part of Indiana from the 

other two. Tailwater or pool data were not available for two 

flood-control reservoirs in Indiana—C.M. Harden Lake and 

Salamonie Lake. 

At the three reservoir pools, vertical profiles of waterquality characteristics were measured at the center of the 

5 equal-width increments along 10 to 17 shore-to-shore 

transects (table 2). The transects were established downstream 
Methods 5

Figure 1. Flood-control 

reservoirs in Indiana.

85° 87°

41°

39°

0

0 15 30 45 60 MILES

15 30 45 60 KILOMETERS

Monroe 

Lake

Patoka Lake

Brookville

Lake

Cagles 

Mill 

Lake

C.M. Harden Lake

J.E. Roush Lake

Mississinewa 

Lake

Salamonie Lake

Base from U. S. Geological Survey digital data 1:100,000 1983 

Universal Transverse Mercator projection zone 16 

North American Datum of 1983 (NAD 83)

EXPLANATION

Lake

County boundary

Stream
Table 1. Selected information for flood-control reservoirs in Indiana. [km2, square kilometer; km, kilometer; USGS, U.S. Geological Survey; --, no data] Reservoir project name Summer pool area (km2) Summer pool length (km) Winter pool area (km2) Winter pool length (km) Drainage area (km2) Average annual retention time1 (days) Difference of summer and winter pool (km2) Difference as percent of summer pool USGS gaging-station number2 Name of impounded 

Brookville Lake 21.3 26.4 18.3 24.1 984 202 3.0 14 03276000 East Fork Whitew

Cagles Mill Lake 5.9 16.1 5.7 16.1 761 44 0.3 4 03359000 Mill Creek 

C.M. Harden Lake3 8.5 17.4 4.5 10.8 562 128 4.1 48 03340900 Big Raccoon Cree

Mississinewa Lake 12.9 -- 5.2 -- 2,093 41 7.7 60 03327000 Mississinewa Riv

Monroe Lake 43.5 59.5 43.5 59.5 1,119 199 0.0 0 03372500 Salt Creek 

Patoka Lake 35.4 40.2 33.1 37.8 440 556 2.3 6 03374500 Patoka River 

J.E. Roush Lake4 3.7 11.3 2.3 8.0 1,867 10 1.4 37 03323500 Wabash River 

Salamonie Lake 9.2 27.4 3.5 17.7 1,443 51 5.7 62 03324500 Salamonie River 

1 Average annual retention time, 1984–2007 (U.S. Army Corps of Engineers, written commun., 2009); all other data from U.S. Army Corps of Engineers (2014).2 Nearest gaging station downstream from reservoir.3 Also called Raccoon Lake.4 Also called Huntington Lake.
Methods 7

from the confluence of contributing streams, downstream from 

major bays and inlets, near dams, and in places where they 

would bracket water-quality sample locations. Transects were 

identified on maps and aerial photographs, and a geographic 

information system (GIS) was used to determine the coordinates of transect endpoints and the centers of five equal-width 

increments. A global positioning system (GPS) and digital 

map interface on the watercraft were used to navigate to the 

transects and increment center points. A total of 1,440 depthspecific measurements of water-quality characteristics were 

measured at 1.52-meter (m) (5-foot [ft]) intervals from the 

water surface to the lake bottom along each transect (fig. 2), 

creating a vertical profile. 

The sampling design for the three reservoirs included 

sites in headwaters, inlets, main body, area near the dam, 

and tailwater. A depth-sounding fathometer connected to the 

GPS and digital map interface on the watercraft were used to 

record bathymetric data of the lake-bottom topography along 

each transect (fig 2). The fathometer was used to identify the 

thalweg of the original stream channel as the deepest water 

with all three thermal strata present. At sampling sites between 

transects in the main body of the lake, a vertical profile of 

water-quality characteristics was measured to selected depths 

for two or three point samples. Sites in the headwaters and 

inlets or bays typically involved water depths less than 2 m 

and included a point sample at a single depth. 

Table 2. Reservoir-pool water-quality transect information.

Reservoir Number of 

transects

Mean 

transect 

length 

(meters)

Range of 

transect 

lengths 

(meters)

Maximum 

water depth 

(meters)

Number of 

measurements1

Brookville Lake 10 235 83–408 32.3 523

Monroe Lake 14 272 131–525 13.7 333

Patoka Lake 17 166 73–413 12.8 584

1

 At each measurement, a total of five water-quality characteristics were determined. Measurements were 

made at 1.52-meter (5-foot) intervals from the water surface to lake bottom.

A B C D E

Vertical profiles of water-quality characteristics at center points of five equal-width increments along a transect

Bathymetric elevation contour of reservoir bottom along a transect

Figure 2. Generalized diagram of reservoir-pool-monitoring transect, water-quality verticals, and lake-bottom topography.
8 Mercury and Methylmercury in Reservoirs in Indiana

Water-Quality Characteristics

Five water-quality characteristics were measured at the 

tailwater and reservoir-pool sites and in the vertical profiles 

along the 10 to 17 transects in each reservoir pool. A multiparameter instrument was used to measure pH, specific conductance, dissolved oxygen, and water temperature (table 3). The 

meter was calibrated each day prior to its use, following procedures outlined in U.S. Geological Survey (variously dated). 

A portable optical turbidimeter was used to measure turbidity in three aliquots of each water sample, and the median 

was reported. The turbidimeter was checked with secondary 

standards each day prior to its use. The water sample for 

turbidity at the tailwater sites came from a composite sample 

mixed in a churn-style sample splitter. The water sample for 

turbidity at the reservoir sites was a depth-specific grab sample 

collected with a Kemmerer sampler. Water-quality characteristics were determined at the time of water-sample collection 

at the tailwater sites as described in Ulberg and Risch (2008). 

For the 2002–2006 and 2009 tailwater sites, the values of 

the water-quality characteristics were a composite integrated 

through the stream width and depth. For the 2009 reservoirpool sites, depth-specific point measurements of water-quality 

characteristics were made at the depth the water samples were 

collected. 

Water-Sample Collection, Processing, and 

Analysis

Ultraclean protocols were used for collecting water 

samples to be analyzed for Hg and MeHg, described in 

U.S. Geological Survey (variously dated). These protocols are 

designed to avoid the unintentional introduction of Hg or other 

contaminants into a sample and are comparable to trace-metals 

methods in EPA Method 1669 (U.S. Environmental Protection 

Agency, 1996) and the USGS Inorganic Protocol (Horowitz 

and others, 1994). Supplies that contacted water samples 

(sample bottles, pump tubing, and filter holders) were made of 

fluorocarbon resin (Teflon), specially cleaned in the laboratory with hot acid and Hg-free water rinses, dried, and double 

bagged. Supplies were used for one sample and returned to 

the laboratory for cleaning. Equipment that contacted water 

samples (intake weight, sampler cap and nozzle, and churn) 

also were made of fluorocarbon resin. These equipment items 

were cleaned with a series of detergent, Hg-free water, and 

acid rinses between samples. Personnel wore powder-free disposable nitrile gloves that were changed frequently to protect 

sample integrity. A minimum of two USGS personnel collected samples; one person handled sample bottles and inner 

bags of double-bagged supplies, and the other person handled 

sampling equipment and the outer bag of double-bagged 

supplies. 

Water samples at three reservoir pools were collected 

from a motorized watercraft with the motor off and the watercraft anchored fore and aft. Depth-specific point samples were 

collected with a peristaltic-pump apparatus (fig. 3) suspended 

from a handline. A Teflon weight with intake ports was lowered with a Kevlar handline to the desired sampling depths. 

The weight was connected to an optimal length of small-diameter Teflon tubing inserted in a short piece of flex tubing at the 

pump head. Water was pumped into sample bottles handled 

inside an isolation chamber on the watercraft.

Water samples were collected at tailwater sites by 

using stream-width- and streamflow-integrating techniques 

described in Ulberg and Risch (2008) and Risch and others 

(2010). Water samples were collected from a bridge, while 

wading, or from an inflatable, rubberized boat with a wooden 

floor (at Cagles Mill Lake). Samples were collected from 

a bridge by use of an isokinetic sampler suspended from a 

cable reel on a portable bridge crane. Samples were collected 

while wading or from a boat by use of an isokinetic sampler 

on a rod. Representative samples were collected according 

to USGS procedures that are intended to composite water 

collected across the full width and depth of the stream, thus 

accounting for differences in velocity and water chemistry. 

Water samples collected for Hg and MeHg analysis were 

transported or shipped overnight to the USGS Indianapolis 

office, where they were processed within 24 hours of collection. Water samples for Hg and MeHg analysis were filtered 

and preserved in a Class 100, laminar-flow, high-efficiency 

particulate-air-filter workstation. Filtered water and particulate 

samples were prepared by vacuum filtration, using equipment 

and procedures described in U.S. Geological Survey (variously dated). Water samples for Hg and MeHg analysis were 

preserved with concentrated high-purity hydrochloric acid. 

Particulate sample filters were frozen until analysis for Hg and 

MeHg. 

Table 3. Methods and reporting limits for determinations of water-quality characteristics.

[μS/cm, microsiemens per centimeter; mg/L, milligram per liter; °C, degree Celsius; NTRU, nephelometric turbidity ratio unit]

Constituent or property Method Reporting limit, precision, and unit

pH In situ measurement with multiparameter instrument 0.1 ± 0.01 standard unit

Specific conductance In situ measurement with multiparameter instrument 1 ± 1 μS/cm

Dissolved oxygen In situ measurement with multiparameter instrument 0.01 ± 0.01 mg/L

Water temperature In situ measurement with multiparameter instrument 0.01 ± 0.01 °C

Turbidity Field measurement of composite sample with portable turbidimeter 0.1 ± 0.1 NTRU
Methods 9

Peristaltic pump

Teflon weight with

sample intake ports

Kevlar handline to

raise and lower weight 

Silicone flex tubing Teflon tubing

Teflon sample bottle

Volume-measurement 

vessel

Teflon tubing

Figure 3. Apparatus for collection of water samples for mercury analysis.

Water and particulate samples collected by USGS were 

analyzed for low-level Hg5 and MeHg (table 4) at the USGS 

Mercury Research Laboratory. Mercury concentration was 

determined by oxidation, purge and trap, and cold vapor 

atomic fluorescence spectrometry (Olson and DeWild, 1997), 

equivalent to EPA Method 1631 (U.S. Environmental Protection Agency, 2002). Methylmercury samples were prepared by 

distillation and analyzed by aqueous phase ethylation and gas 

chromatography separation with cold vapor atomic fluorescence detection (DeWild and others, 2002), equivalent to EPA 

Method 1630 (U.S. Environmental Protection Agency, 2001c). 

Analytical data for the tailwater samples included determinations of Hg and MeHg in unfiltered and filtered forms, in 

which case “particulate” Hg and MeHg concentrations were 

computed as the difference of unfiltered and filtered forms. 

Analytical data for the reservoir pool and tailwater samples 

included determinations of Hg and MeHg in particulate forms 

measured on filters and dissolved forms in filtered water. In 

this case, “whole-water” Hg and MeHg concentrations were 

computed as the sum of dissolved and particulate forms.6

 If a 

dissolved or particulate concentration was less than the reporting limit for a sample, it was assumed to be zero for computing a whole-water concentration, consistent with the approach 

5

 In this report, the analytical determination of Hg means total Hg.

6

 In water samples with levels of suspended particulates consistent with 

turbidity values higher than 20 nephelometric ratio turbidity units (NTRU), 

the MeHg concentration in an unfiltered sample is generally equivalent to the 

sum of dissolved and particulate MeHg concentrations, if reporting limits are 

the same. Unfiltered water samples with less than 20 NTRU and low levels of 

suspended particulates generally will have lower MeHg concentrations than 

those determined as the sum of dissolved and particulate MeHg concentrations. This difference is attributable to the more sensitive particulate MeHg 

determination.

used by other investigators (for example, Brigham and others, 

2009). The “ratio of the MeHg to Hg concentration” in this 

report can refer to the ratios of unfiltered MeHg to unfiltered 

Hg, whole-water MeHg to whole-water Hg, or dissolved 

MeHg to dissolved Hg, depending on context. 

Reservoir-pool water samples for analysis of dissolved 

sulfate, organic carbon, particulate carbon and nitrogen, and 

chlorophyll were filtered and processed in a mobile laboratory van within a few hours of sample collection, following 

procedures in U.S Geological Survey (variously dated) and 

references in table 4.

Quality Assurance

Quality assurance included analysis of field and laboratory quality-control samples, and the USGS laboratory 

followed a written quality-assurance plan (U.S. Geological 

Survey, 2007). Field quality-control data for tailwater samples 

were explained and evaluated by Ulberg and Risch (2008). 

These quality-control data indicated that the Hg and MeHg 

data from tailwater samples were representative and unbiased. 

For the reservoir-pool water samples, field blank samples 

(source water/bottle blanks and equipment blanks) were 

prepared to evaluate cleaning of the sampling equipment. 

Field blank data were evaluated by using procedures for EPA 

Method 1631 (U.S. Environmental Protection Agency, 2001b). 

Field duplicate samples were collected by sequentially filling a 

second set of sample bottles from the same tubing. Field duplicate samples were a measure of the natural variability of Hg 

concentrations in the water and the variability associated with 

sample collection and processing, rather than a measure of 

analytical precision. Analytical precision in the determination 
10 Mercury and Methylmercury in Reservoirs in Indiana

Table 4. Methods for analysis of mercury, particulate, and supplementary constituents in water.

[ng/L, nanogram per liter; μm, micrometer (pore size of filters); HCl, hydrochloric; mg/L, milligram per liter; °C, degree Celsius]

Constituent

Reporting 

limit and 

units

Method Preparation Reference1

Dissolved total mercury 0.04 ng/L Oxidation, purge and trap, and 

cold-vapor atomic fluorescence 

spectrometry

Water passed through quartz fiber filter 

with 0.7-μm pore size, before preservation with high-purity HCl

1

Particulate total mercury 0.04 ng/L Oxidation, purge and trap, and 

cold-vapor atomic fluorescence 

spectrometry

Particle isolation on pre-baked quartz 

fiber filter

2

Dissolved methylmercury 0.04 ng/L Gas chromatographic separation 

with cold vapor atomic fluorescence detection

Water passed through quartz fiber filter 

with 0.7-μm pore size, before preservation with high-purity HCl; distillation 

and aqueous phase ethylation

3

Particulate methylmercury 0.04 ng/L Gas chromatographic separation 

with cold vapor atomic fluorescence detection

Particle isolation on pre-baked quartz 

fiber filter; distillation and aqueous 

phase ethylation

4

Total suspended particulates 15 mg/L Gravimetric from filtration and 

evaporation

Filtered in the lab 5

Total particulate carbon 0.1 mg/L Elemental analysis Particle isolation on filter 6

Particulate organic carbon 0.12 mg/L Elemental analysis Particle isolation on filter 6

Particulate inorganic carbon 0.06 mg/L Elemental analysis Particle isolation on filter 6

Total particulate nitrogen 0.034 mg/L Elemental analysis Particle isolation on filter 6

Dissolved organic carbon 0.1 mg/L Shimadzu Total Organic Carbon 

Analyzer; catalytically aided 

platinum, 680 °C combustion

Particle isolation on filter 7

Chlorophyll 0.0001 mg/L Chromatography-fluorometry Particle isolation on filter 8

Dissolved sulfate 0.18 mg/L Ion chromatography Water passed through filter with 0.45-μm 

pore size

9

1

 References:

 1. Olson and DeWild, 1997.

 2. Olson and DeWild, 1997; Olund and others, 2004.

 3. DeWild and others, 2002.

 4. DeWild and others, 2002; DeWild and others, 2004.

 5. Guy, 1969.

 6. Patton and others, 2000.

 7. Based on Bird and others, 2003.

 8. Arar and Collins, 1997.

 9. Fishman and Friedman, 1989.

of Hg concentrations was quality assured by the laboratory 

through analysis of duplicate or triplicate aliquots of water 

from the same sample bottle until a control limit for relative 

percent difference of less than 10 percent was attained. 

Field quality-control data indicated the analytical results 

for water samples from the three reservoirs were representative and comparable. Field blank samples for the pool and 

tailwater samples indicated no bias caused by Hg or MeHg 

artifacts from sampling (appendix table 1–1). Precision of Hg 

and MeHg, affected by natural variability and variability from 

sampling and processing, was measured by relative percent 

difference7

 (RPD) in pairs of field duplicate samples. Particulate Hg and dissolved Hg were reported in all duplicates, and 

the mean RPD was less than 20 percent (appendix table 1–2). 

Particulate and dissolved MeHg were reported in six duplicates, and the mean RPD was less than 25 percent.

7

 Relative percent difference is the nonnegative difference of the paired 

duplicate sample concentrations divided by the average of the concentrations, 

expressed as a percentage.
Mercury and Methylmercury in Reservoirs in Indiana 11

Mercury and Methylmercury in 

Reservoirs in Indiana

The available data for Hg and MeHg in reservoir tailwaters and reservoir pools in Indiana are presented here. Principal topics discussed are (1) factors related to the transport of 

Hg to reservoirs, (2) factors related to the conversion of Hg 

to MeHg in reservoirs, and (3) fish-tissue Hg data, which are 

presented and used to depict the food-web accumulation and 

magnification of MeHg.

Reservoir Tailwaters

Mercury and MeHg data from analysis of 66 water 

samples collected at 4 reservoir tailwater sites in Indiana—

Brookville Lake, Cagles Mill Lake, J.E. Roush Lake, and 

Mississinewa Lake—are summarized in table 5 and listed 

in appendix table 1–3. Unfiltered Hg concentrations in the 

tailwater samples ranged up to 15.0 ng/L, and the mean 

was 2.6 ng/L (figs. 4A–4D) . The ratio of particulate Hg 

to Hg was a maximum of 100 percent, and the mean was 

58.4 percent. The ratio of unfiltered MeHg to Hg was a maximum 

of 64.8 percent (fig. 4E), and the mean was 9.1 percent. By 

comparison, in samples from sites on free-flowing streams, 

the mean ratio of particulate Hg to Hg was higher (67 percent) 

and the mean ratio of unfiltered MeHg to Hg was lower 

(3.6 percent) (Risch and others, 2010). 

Statistical analysis8

 indicated significant seasonal differences in Hg and MeHg concentrations (Kruskal-Wallis, 

p = 0.035, p= 0.017) and in the ratio of unfiltered MeHg to Hg 

(p = 0.008). Unfiltered Hg concentrations in winter samples 

(median, 2.7 ng/L) were higher than those in autumn samples 

(median, 1.2 ng/L). Unfiltered MeHg concentrations in summer samples (median, 0.13 ng/L) were significantly higher 

than those in autumn samples (median, <0.04 ng/L). The ratios 

of unfiltered MeHg to Hg from summer samples (median, 

10.9 percent) were significantly higher than those in winter 

samples (median, 1.7 percent). The ratios of unfiltered MeHg 

to Hg for Cagles Mill Lake, J.E. Roush Lake, and Mississinewa Lake were nearly always highest in summer (appendix 

table 1–3, fig. 4).

8

 Nonparametric statistical methods were used to compare data from different sites and seasons and to evaluate the strength and significance of relations 

among variables. According to Helsel and Hirsch (1995), nonparametric tests 

minimize the effect of outliers and apply to sample sizes of 15 to 19. A significance level of α = 0.05 was used for the statistical tests, and a p-value less 

than 0.05 indicated a significant difference. The Kruskal-Wallis rank-sum test 

(called Kruskal-Wallis hereafter) was used to evaluate whether the distributions of data from more than two groups were different. The Tukey multiple 

comparison of medians of 95-percent confidence intervals (called Tukey 

hereafter) was used to determine which groups were significantly different, 

regardless of the group size. Strengths and significance of statistical correlations were evaluated with the Spearman rank correlation coefficient (rho), 

where near zero is weak and near 1 is strong correlation. Hereafter, rho means 

Spearman’s rho.

Table 5. Mercury data summary for tailwaters at four reservoirs in Indiana.

[Hg, unfiltered mercury; ng/L, nanogram per liter; PHg, particulate mercury; MeHg, unfiltered methylmercury]

Reservoir Summary 

description

Hg 

(ng/L)

Ratio of PHg to Hg 

(percent)1

Ratio of MeHg to 

Hg (percent)2

All four reservoirs 

(66 samples)

Maximum 15 100 64.8

Mean 2.6 58.4 9.1

Detections3 65 64 34

Brookville Lake 

(17 samples)

Maximum 1.8 100 15.4

Mean 0.6 47.3 15.4

Detections3 17 16 1

Cagles Mill Lake 

(18 samples)

Maximum 3.3 100 64.8

Mean 1.8 60.1 20.6

Detections3 18 18 8

J.E. Roush Lake 

(16 samples)

Maximum 15.0 87 15

Mean 5.0 65.5 5.2

Detections3 16 15 14

Mississinewa Lake 

(15 samples) 

Maximum 6.6 100 16

Mean 2.9 61.3 5.1

Detections3 15 15 11

1

 Ratio of particulate Hg to unfiltered Hg, multiplied by 100.

2

 Ratio of unfiltered MeHg to unfiltered Hg, multiplied by 100.

3

 Reporting limits for Hg and MeHg were 0.3 ng/L in 2002–2003 and 0.04 ng/L in 2004–2006.
2002 2003 2004 2005 2006 0 2.0 1.5 1.0 0.5 A. Brookville Lake 0 1.0 0.5

Unfiltered mercury concentration, 

in nanograms per liter

Unfiltered methylmercury concentration, 

in nanograms per liter

01234

2002 2003 2004 20B. Cagles Mill Lake

Unfiltered mercury concentration, 

in nanograms per liter

05

1015

0

123

2002 2003 2004 2005 2006

C. J.E. Roush Lake

Unfiltered mercury concentration,

 in nanograms per liter

Unfiltered methylmercury concentration,

in nanograms per liter

0

246

2002 2003 2004 2

D. Mississinewa Lake

Unfiltered mercury concentration,

in nanograms per liter

[Note differences in vertical scales]

EXPLANATION

Mercury 

concentration

Methylmercury 

concentration

Methylmercury 

reporting limit

Figure 4. Mercury and methylmercury concentrations in water samples from tailwater sites at four reservoirs.
0

204060

0

5

1015

0

5

1015

Cagles Mill L

J.E. Roush Lake Mississinewa 

Percent methymercury

Percent methymercury

Percent methymercury

2002 2003 2004 2005 

2002 2003 2004 2005 2006 2002 2003 2004 2005 

2006 0

5

1015

Percent methymercury

(No methylmercury detected before 2006)

Brookville Lake

E. Ratio of unfiltered methylmercury to unfiltered mercury in four reservoirs

[Note differences in vertical scales]

EXPLANATION

Percent methylmercury

Figure 4. Mercury and methylmercury concentrations in water samples from tailwater sites at four reservoirs.—Cont
14 Mercury and Methylmercury in Reservoirs in Indiana

Concentrations of unfiltered Hg and MeHg from 

Brookville Lake tailwater samples (appendix tables 1–3) were 

determined to be significantly lower than concentrations in 

tailwater samples from the other three reservoirs (KruskalWallis, p < 0.001; Tukey). The median whole-water Hg 

concentration from Brookville Lake tailwater samples was 

0.54 ng/L (table 5), compared with medians in the tailwater 

samples from Cagles Mill Lake (1.7 ng/L), J.E. Roush Lake 

(3.7 ng/L), and Mississinewa Lake (2.9 ng/L). Whole-water 

MeHg was detected in only 1 of 17 tailwater samples from 

Brookville Lake (0.04 ng/L).

The summer pool area of Mississinewa Lake was 

60 percent larger than the winter pool area, and the summer 

pool area of J.E. Roush Lake was 37 percent larger than the 

winter pool (table 1). For these two reservoirs, MeHg was 

reported in most of the tailwater samples—73 percent for 

Mississinewa Lake and 93 percent for J.E. Roush Lake. Other 

studies have shown that reservoirs with fluctuating water levels 

create periodic reduction and oxidation conditions, which in 

turn create and release MeHg into the water (Kelly and others, 

1997; St. Louis and others, 2004; Mast and Krabbenhoft, 2010). 

Reservoir Pools

One round of 53 water samples was collected at the 

reservoir pools—16 samples from 8 sites at Brookville Lake, 

17 samples from 9 sites at Monroe Lake, and 20 samples from 

12 sites at Patoka Lake. Maps showing locations of the sampling sites are in figures 5, 6, and 7, and information about the 

sampling sites is in table 6. Precipitation runoff was minimal 

during a 5-day time period when sampling took place at each 

reservoir, making the sets of data from each reservoir internally representative of similar hydrologic conditions (appendix 

table 1–4). 

Whole-water Hg (the sum of particulate and dissolved Hg 

fractions) was detected in all 53 water samples from the pools 

and tailwaters of the three reservoirs (appendix table 1–5). 

Median and maximum whole-water Hg concentrations in 

samples from the pools of Monroe Lake and Patoka Lake were 

considerably higher than those from Brookville Lake (table 7). 

The whole-water Hg concentration in the tailwater sample 

from Monroe Lake was higher than the median concentration 

from the Monroe Lake pool samples, unlike Brookville Lake 

and Patoka Lake, where the tailwater concentration was lower. 

At Brookville Lake, whole-water Hg concentrations were less 

than 2 ng/L in all samples (fig. 8). At Monroe Lake, wholewater Hg concentrations were higher than 2 ng/L in samples 

collected below 8-m depths in the main body of the lake and at 

headwater sites (fig. 9). At Patoka Lake, the highest wholewater Hg concentrations were in samples collected below 

9-m depths in the main body of the lake and at headwater 

sites (fig. 10). Whole-water Hg concentrations in the pool of 

Brookville Lake did not have a pattern with depth like those 

from Monroe Lake and Patoka Lake. Reservoir-pool data 

(table 7) also indicated lower median Hg in Brookville Lake 

(0.56 ng/L), compared with medians in the pool samples from 

Monroe Lake (1.36 ng/L) and Patoka Lake (1.24 ng/L). Methylmercury was detected in 1 of 16 samples from Brookville 

Lake (0.13 ng/L), compared with 14 of 17 in Monroe Lake 

and 13 of 20 in Patoka Lake (appendix table 1–5).

Particulate Hg in water from the Monroe Lake and 

Patoka Lake reservoirs pools, as a ratio to whole-water Hg 

(62 and 68 percent), was higher than in Brookville Lake 

(44 percent, table 7). Because whole-water Hg in samples 

from the Monroe Lake and Patoka Lake pools was predominantly particulate bound, the pattern with depth observed for 

whole-water Hg was repeated, and the highest ratios of particulate Hg were in samples collected below 8- and 9-m depths 

(appendix table 1–5). Brookville Lake particulate Hg did not 

have a pattern with depth. Ratios of particulate Hg to wholewater Hg in tailwaters of Monroe Lake and Patoka Lake 

(55 and 63 percent) were similar to the 58.4-percent mean for 

the tailwater samples from four reservoirs (table 5). 

Whole-water MeHg was reported in 53 percent (28 of 53) 

of the samples from the pools and tailwaters of the three 

reservoirs. At Monroe Lake and Patoka Lake, whole-water 

MeHg was detected in 14 of 17 samples and 13 of 20 samples, 

respectively, but it was in detected in only 1 of 16 samples 

at Brookville Lake. Dissolved MeHg is the fraction of the 

dissolved Hg that is most available for transfer to the aquatic 

food web. Median and maximum ratios of dissolved MeHg to 

Hg concentrations in samples from the pools of Monroe Lake 

and Patoka Lake were considerably higher than in those from 

Brookville Lake (table 7). In Monroe Lake, ratios of dissolved 

MeHg to Hg higher than 25 percent were observed for samples 

below 8-m depths in the main lake and near the dam, as well 

as in the tailwater (fig. 11). In Patoka Lake, ratios of dissolved 

MeHg to Hg higher than 25 percent were observed for all 

samples below 9-m depths in the main lake, in the Lick Fork 

inlet, and near the dam (fig. 12). 
Mercury and Methylmercury in Reservoirs in Indiana 15

#

#

#

#

#

#

#

85°03'45" 84°56'15"

39°37'30"

39°30'

#

Brookville

Whitewater Memorial

State Park

Mounds State

RecreationArea

FAIRFIELD ROAD

STATE ROAD 1

STATE ROAD 101

Liberty

STATE ROAD 44

Quakertown State

Recreation Area Hanna Creek

East Fork Whitewater River

1

2

3

4

5

6

7

8

EXPLANATION

1 Sampling site

Water-quality transect

Brookville Lake

0

2.5

5 MILES

0

2.5

5 KILOMETERS Base from U.S. Geological Survey digital data 1983 1:100,000

Universal Transverse Mercator projection zone 16, 

North American Datum of 1983 (NAD 83)

Figure 5. Sampling sites and water-quality transects for Brookville Lake.
16 Mercury and Methylmercury in Reservoirs in Indiana

# #

#

#

# #

#

#

!

!

86°30' 86°15'

39°07'30"

39°

Salt Creek

Middle Fork Salt Creek

North Fork Salt Creek

STATE ROAD 446

Bloomington

Paynetown 

State Recreation 

Area

Hardin Ridge 

Recreation Area

Fairfax 

State

Recreation 

Area

1

2

3

4

5

6

7

8

9

EXPLANATION

1 Sampling site

Water-quality transect

Monroe Lake

0 2.5

5

MILES

0 2.5

5

Base from U.S. Geological Survey digital data 1983 1:100,000 KILOMETERS

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

Figure 6. Sampling sites and water-quality transects for Monroe Lake (note variation in horizontal scale).
Mercury and Methylmercury in Reservoirs in Indiana 17

#

# #

#

# #

#

#

#

#

#

#

86°41'15" 86°33'45"

38°30'

38°22'30"

0

2.5

5 MILES

0

2.5

Base from U.S. Geological Survey digital data 1983 1:100,000 5 KILOMETERS

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

Newton Stewart 

State

Recreation Area

Lick Fork 

State

Recreation 

Area

Tillery Hill 

State 

Recreation 

Area

STATE ROAD 145

STATE ROAD 164

Fleming Creek

Little Patoka River

River

Patoka

Patoka River

Painter Creek

Jackson State

Recreation Area

1

2

3

4

5

6

7

8

9

10

11

12

EXPLANATION

1 Sampling site

Water-quality transect

Patoka Lake

Figure 7. Sampling sites and water-quality transects for Patoka Lake (note variation in horizontal scale).
Table 6. Reservoir-pool and tailwater sampling-site information. [NWIS, U.S. Geological Survey National Water Information System database; dms, degree, minute, second] Reservoir Site number Descriptive site name NWIS Site ID Latitude (dms) Longitude (dms) Lak

Brookville Lake 1 Tailwater in East Fork Whitewater River USGS 03276000 39 26 02 85 00 12 Tailwater 

2 Near dam USGS 392628084595901 39 26 28 84 59 59 Near dam 3 Near Bonwell Hill USGS 392721084585901 39 27 21 84 58 59 Main lak4 Near Mounds Recreation Area USGS 392935084583001 39 29 35 84 58 30 Inlet, wes5 South of Fairfield Road USGS 392855085004201 39 28 55 85 00 42 Inlet, eas6 Near Fairfield Marina USGS 393049084595101 39 30 49 84 59 51 Main lak7 Near Hanna Creek Marina USGS 393304084595101 39 33 04 84 59 51 Main lak8 Near Quakertown Recreation Area USGS 393700084592301 39 37 00 84 59 23 Headwat

Monroe Lake 1 Tailwater in Salt Creek USGS 03372500 39 00 16 86 30 31 Tailwater 

2 Near dam USGS 390034086304801 39 00 34 86 30 48 Near dam 3 Near Fairfax Recreation Area USGS 390026086292801 39 00 26 86 29 28 Main lak4 Near Hardin Ridge Recreation Area USGS 390229086280401 39 02 29 86 28 04 Main lak5 Near State Road 446 causeway USGS 390359086263501 39 03 59 86 26 35 Main lak6 Near Paynetown Recreation Area USGS 390552086274501 39 05 52 86 27 45 Inlet7 Near Cutright Recreation Area USGS 390412086230601 39 04 12 86 23 06 Main lak8 Near Pine Grove Recreation Area USGS 390631086232201 39 06 31 86 23 22 Headwat9 Middle Fork Waterfowl Area USGS 390337086202401 39 03 37 86 20 24 Headwat

Patoka Lake 1 Tailwater in Patoka River USGS 382618086423301 38 26 18 86 42 33 Tailwater

2 Near dam USGS 382553086420601 38 25 53 86 42 06 Near dam3 Near Lick Fork Boat Ramp USGS 382523086422701 38 25 23 86 42 27 West bran

4 Near Lick Fork Recreation Area USGS 382417086415501 38 24 17 86 15 50 West bran5 Near State Road 164 USGS 382237086411601 38 23 37 86 41 16 West bran6 Near Newton Stewart Recreation Area USGS 382538086402301 38 25 38 86 40 23 Main lak7 Near Jackson Recreation Area USGS 382631086354401 38 26 31 86 35 44 Inlet, nor8 Near Newton Stewart Marina USGS 382352086370301 38 23 52 86 37 03 Main lak9 Near State Road 145 at Fleming Creek USGS 382209086370201 38 22 09 86 37 02 Inlet, sou

10 Near Little Patoka River Boat Ramp USGS 382243086351901 38 22 43 86 37 19 Inlet, sou

11 Near Wall's Lake Boat Ramp USGS 382442086351401 38 24 42 86 35 14 Inlet, eas

12 Near King's Bridge Boat Ramp USGS 382424086332201 38 24 24 86 33 22 Headwat
Mercury and Methylmercury in Reservoirs in Indiana 19

Table 7. Mercury data summary for pools and tailwaters at three reservoirs in Indiana.

[Hg, mercury; MeHg, methylmercury; ng/L, nanogram per liter; < less than percentage listed; n.d., not determined because dissolved MeHg reported in only 

one sample]

Reservoir Number of 

samples1

Whole-water Hg2 Ratio of particulate Hg to Hg3 Ratio of dissolved MeHg to Hg4

Range 

in pool 

(ng/L)

Median 

in pool 

(ng/L)

Tailwater 

(ng/L)

Range 

in pool 

(ng/L)

Median 

in pool 

(ng/L)

Tailwater 

(ng/L)

Range 

in pool 

(ng/L)

Median 

in pool 

(ng/L)

Tailwater 

(ng/L)

Brookville Lake 16 0.33–1.91 0.56 0.31 <21–82 41 <29 18 n.d. n.d.

Monroe Lake 17 0.42–4.84 1.36 1.92 30–79 62 55 <5–64 20 56

Patoka Lake 20 0.42–5.51 1.24 0.52 25–84 68 63 <3–82 31 <16

1

 Number of samples includes one tailwater sample and multidepth pool samples.

2

 Whole-water Hg is the sum of particulate and dissolved Hg concentrations.

3

 Ratio of particulate Hg to whole-water Hg concentration, multiplied by 100.

4

 Ratio of dissolved MeHg to whole-water MeHg concentration, multiplied by 100, where whole-water MeHg is the sum of the particulate and 

dissolved fractions. Dissolved MeHg reported in a single sample from Brookville Lake pool.
20 Mercury and Methylmercury in Reservoirs in Indiana

#

#

#

#

#

#

#

85°3'45" 84°56'15"

39°37'30"

39°30'

#

Brookville

STATE ROAD 101

Liberty

STATE ROAD 44

Hanna Creek

East Fork Whitewater River

1

2

3

4

5

6

7

8

0

2.5

5 MILES

0

2.5

Base from U.S. Geological Survey digital data 1983 1:100,000 5 KILOMETERS

Universal Transverse Mercator projection zone 16 

North American Datum of 1983 (NAD 83)

EXPLANATION

1

Sampling site

Sampling-site number

Whole-water 

mercury 

concentration,

in nanograms

per liter (ng/L)

Sample

depth, in 

meters (m)

0 1 2 3 4 5

0.4

0.5

0.8

3 m 

6 m 

12 m 

6 Hg

epilimnion

metalimnion

hypolimnion

Brookville Lake

0 0.5 1.0 1.5 2.0

1 2 3 4

0.6

3 m 

12 m 

23 m 

0.5

0.5

0.5

1 1.5 2

Hg

0

3

1 2 3 4

0.8

3 m 

6 m 

12 m 

0.5

0.4

0.5

1 1.5 2

Hg

0

6

1 2 3 4

0.4

3 m 

11 m 

23 m 

0.5

0.8

0.3

1 1.5 2

Hg

0

2

1 2 3 4

1.1

5 m 

8 m 

0.5

0.5

1 1.5 2

Hg

0

7

1 2 3 4

0.6

6 m 

9 m 

0.5

0.6

1 1.5 2

Hg

0

5

1 2 3 4

 1 m 1.9

0.5 1.0 1.5 2.0

Hg

0

8

1 2 3 4

 1 m 1.3

0.5 1 1.5 2

Hg

0

4

1 2 3 4

0.3

0.5 1 1.5 2

Hg

0

1

Figure 8. Whole-water mercury concentrations in water from Brookville Lake. (Site 1 was a tailwater site; sample 

depth not applicable.)
Mercury and Methylmercury in Reservoirs in Indiana 21

# #

#

#

# #

#

#

!

!

86°30' 86°15'

39°07'30"

39°

Salt Creek

North Fork Salt Creek

0

2.5

5 MILES

0

2.5

Base from U.S. Geological Survey digital data 1983 1:100,000 5 KILOMETERS

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

Bloomington

STATE ROAD 446

Middle Fork Salt Creek

1

2

3

4

5

6

7

8

9

EXPLANATION

1 Monroe Lake Sampling site

Sampling-site number

0 1 2 3 4 5

0.5

0.6

4.8

3 m 

5 m 

8 m 

4

10 2 3 4 5

Hg

epilimnion

metalimnion

hypolimnion

Whole-water

mercury 

concentration,

in nanograms

per liter (ng/L)

Sample

depth, in 

meters (m)

1.0 3.0

0.5

1.2

2.9

2.1

0 5

0.4

1.4

4.2

0 1 2 3 4 5

0.5

0.6

4.8

0.7

3.5

0.7

0.5 1.0 1.5 2.0 2.5 3.0

2.8

1.9

1

2

3

3 m 

7 m 

8 m 

Hg

10 2 3 4 5

Hg

10 2

3 m 

7 m 

8 m 

Hg

10 2 3

3 m 

5 m 

8 m 

4

10 2 3 4 5

Hg

Hg 5

10 2 3

5 m

11 m

1 m

Hg 6

10

0.3 m

Hg 8

10 2

Hg

10 2 3

0.5 m

9

0.0 0.5 1.0 1.5 2.0 2.5

1.3

2.1 8 m 

3 m 

Hg

10 2

7

Figure 9. Whole-water mercury concentrations in water from Monroe Lake. (Site 1 was a tailwater site; sample 

depth not applicable; note variation in horizontal scale.)
22 Mercury and Methylmercury in Reservoirs in Indiana

#

# #

#

# #

#

#

#

#

#

#

86°41'15" 86°33'45"

38°30'

38°22'30"

EXPLANATION

1

Patoka Lake Sampling site

Sampling-site number

Whole-water

mercury 

concentration,

in nanograms

per liter (ng/L)

Sample

depth, in 

meters (m) 0.4

1.9

0.4

3 Hg

3 m

6 m

12 m

10 2

epilimnion

metalimnion

hypolimnion

0

2.5

5 MILES

0

2.5

Base from U.S. Geological Survey digital data 1983 1:100,000 5 KILOMETERS

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

LICK FORK WALL'S LAKE STATE ROAD 145

STATE ROAD 164

Fleming Creek

Little Patoka River

Patoka River

KINGS BRIDGE

Patoka River

Painter Creek

1

2

3

4

5

6

7

8

9

10

11

12

0.0 0.5 1.0 2.0

0.7

1.6

0.7

0.0 0.5 1.0 1.5 2.0

0.9

2.0

0.5

2.0

2.5

0.9

2.1

0.0 0.1 0.2 0.3 0.4 0.5

0.5

0.00.51.01.52.01.6

2.3

1 Hg

0 .5

2

6

8

7

11

3 m 

8 m 

12 m 

1 2

Hg

3 m

8 m

14 m

Hg

1 2

5 m 

11 m 

1 2

Hg

0.6 m

1 2

Hg

Hg

6 m 

1 2

0.5 1.5

0.4

1.9

0.4

0.4

2.1

0.6

5.5

3

4

5

9

Hg

3 m

6 m

12 m

1 2

3 m

9 m

1 2

Hg

Hg

1.5 m

0 .5

0.9 m

1 2 3 4 5

Hg

1.8

1.2

10

12

1 2

Hg

6 m 

1

Hg

5 m

0

0

0

0

0

0

0

0

0

0

Figure 10. Whole-water mercury concentrations in water from Patoka Lake. (Site 1 was a tailwater site; sample 

depth not applicable; note variation in horizontal scale.)
Mercury and Methylmercury in Reservoirs in Indiana 23

# #

#

#

# #

#

#

!

Salt Creek

86°30' 86°15'

39°07'30"

39°

0 2.5 5 MILES

Base from U.S. Geological Survey digital data 1983 1:100,000 0 2.5 5 KILOMETERS

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

Bloomington

STATE ROAD 446

North Fork Salt Creek

Middle Fork Salt Creek

1

2

3

4

5

6

7

8

9

EXPLANATION

1 Monroe Lake Sampling site

Sampling-site number

Ratio of dissolved

methylmercury to

dissolved mercury,

in percent

(n.d. means not

determined because

MeHg not detected)

Sample

depth, in 

meters (m)

8 m

MeHg

20%

7

MeHg

n.d. 

1 m

6

5 m

11 m

MeHg

n.d. 

MeHg

58%

5

2

3 m

7 m

8 m

MeHg

n.d. 

MeHg

22%

MeHg

63%

MeHg

56%

1 3

3 m

7 m

7 m

MeHg

19%

MeHg

25%

MeHg

64%

4

3 m

5 m

8 m

MeHg

n.d. 

MeHg

n.d. 

MeHg

58%

3 m

8 m

MeHg

n.d. 

MeHg

20%

7

MeHg

0.3 m n.d. 

8

MeHg

11% 0.5 m

9

Figure 11. Ratio of dissolved methylmercury to mercury in water from Monroe Lake.
24 Mercury and Methylmercury in Reservoirs in Indiana

#

# #

#

# #

#

#

#

#

#

#

86°41'15" 86°33'45"

38°30'

38°22'30"

Patoka Lake

EXPLANATION

Patoka Lake 1 Sampling site

Sampling-site number

Ratio of dissolved

methylmercury to

dissolved mercury,

in percent

(n.d. means not

determined because

MeHg not detected)

Sample

depth, in 

meters (m)

6 m

MeHg

14%

10

0

2.5

5 MILES

0

2.5

5 KILOMETERS Base from U.S. Geological Survey digital data 1983 1:100,000

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

STATE ROAD 145

STATE ROAD 164

Fleming Creek

Little Patoka River

Patoka River

Patoka River

Painter Creek

1

2

3

4

5

6

7

8

9

10

11

12

MeHg

n.d. 

MeHg

n.d. 

MeHg

57%

2

MeHg

n.d. 

MeHg

40%

MeHg

38%

6

8

MeHg

n.d. 

MeHg

60%

MeHg

n.d. 

1

7

11

12

MeHg

n.d. 

MeHg

n.d. 

MeHg

24%

MeHg

14%

10

9

3 4

5

MeHg

n.d. 

MeHg

n.d. 

MeHg

n.d. 

MeHg

n.d. 

MeHg

82%

MeHg

n.d. 

MeHg

60%

3 m

8 m

12 m

3 m

8 m

14 m

1 m

5 m

11 m

5 m

6 m

6 m

3 m

6 m

12 m

3 m

9 m

1.5 m

1 m

Figure 12. Ratio of dissolved methylmercury to mercury in water from Patoka Lake (note variation in horizontal scale).
Mercury and Methylmercury in Reservoirs in Indiana 25

Factors Affecting Mercury and Methylmercury 

in Reservoirs in Indiana

Factors affecting Hg and MeHg in reservoirs in Indiana 

are the transport of Hg and the conversion of Hg to MeHg. 

Wet and dry atmospheric deposition rates and landscape characteristics are related to the transport of Hg. Thermal strata 

and water chemistry are related to the potential for “methylation,” which is the conversion of Hg to MeHg.

Transport of Mercury to Reservoirs

Wet and dry deposition of atmospheric Hg are primary 

pathways for Hg transport to reservoir watersheds and reservoir pools. For this study, mean annual wet and dry loads of 

atmospheric Hg deposited to the reservoir watersheds were 

computed separately and summed to get a total atmospheric 

Hg load to the watershed. The mean annual total Hg-deposition rate for each reservoir watershed was computed by 

dividing the total Hg load by the drainage area. StreamStats 

(U.S. Geological Survey, 2011) was used to delineate the 

watershed and quantify the drainage area upstream from each 

reservoir dam. Explanations of wet and dry Hg deposition 

follow.

Mean annual Hg wet-deposition rates in Indiana were 

mapped as the product of Hg concentrations in precipitation 

monitored at 9 sites in Indiana and 4 nearby states and precipitation amounts monitored at 151 sites in Indiana, 2001–2006, 

by using the method described in Risch and others (2010). 

Mean annual Hg wet-deposition loads for each reservoir 

watershed were computed as a product of the Hg-deposition 

rates on the map and the drainage area upstream from the 

reservoir.

Mean annual Hg dry-deposition rates were based on the 

3-year mean annual litterfall Hg-deposition rate at four sites 

in Indiana, 2007–2009 (Risch and others, 2012). Studies have 

shown that forest canopies scavenge and retain Hg from the air 

and that forests are net sinks for dry deposition of atmospheric 

Hg (Kolka and others, 1999; Grigal, 2002; Hartman and 

others, 2009, Zhang and others, 2009). Annual litterfall Hg 

deposition in a deciduous forest is a conservative estimate of 

the Hg dry deposition to the forest canopy (Risch and others, 

2012, Zhang and others 2012). 

By use of ArcGIS software (Environmental Systems 

Research Institute, 2006), the watershed for each reservoir was 

overlain on the National Land Cover Database (NLCD; Homer 

and others, 2004) and the area in each of the NLCD land-cover 

classes was computed (appendix table 1–6). Deciduous, evergreen, and mixed NLCD forest classes were combined to get 

the area of forest land cover in the watershed. Mean annual Hg 

dry-deposition loads for each reservoir watershed were computed as a product of the mean annual litterfall Hg-deposition 

rate and the area of forest land cover in the reservoir.

For the reservoirs in Indiana, the mean annual total 

Hg-deposition rates ranged from 11.3 to 25.7 micrograms per 

square meter (mg/m2

) (appendix table 1–7) and were highest 

for Monroe Lake and Patoka Lake. Mercury wet deposition 

and litterfall Hg dry deposition tend to correlate spatially and 

statistically (Risch and others, 2012), and the same Hg emissions sources may affect Hg wet and dry deposition. Mean 

annual Hg wet-deposition rates were highest for Monroe Lake 

and Patoka Lake (12 to13 mg/m2). Forest land cover was 

highest for Monroe Lake (for 82 percent) and Patoka Lake 

(67 percent), whereas forest in the other six reservoirs was 

less than 23 percent. A full comparison of Hg deposition and 

reservoir-pool Hg could not be made for all the reservoirs in 

Indiana with the available data. 

Classifications of physiography, natural region, and 

surficial geology indicated that three reservoirs—Monroe 

Lake, Patoka Lake, and Cagles Mill Lake—are in landscapes 

with steep slopes and near-surface bedrock that promote high 

rates of precipitation runoff and low rates of infiltration. These 

landscapes have potentially higher rates of particulate and 

dissolved Hg transport to reservoirs than occurs in flat topography with glacial deposits. These three reservoirs also have 

the highest mean annual total Hg-deposition rates. Monroe 

Lake, Patoka Lake, and Cagles Mill Lake are in the Southern 

Hills and Lowlands physiographic region and the Shawnee 

Hills and Southern Bottomlands natural region; their surficial 

geology is primarily sandstone, shale, and limestone bedrock 

(table 8). The other five reservoirs are in the Central Till Plain 

physiographic and natural regions; the surficial geology is 

predominantly loamy till, outwash, and alluvium. 

Conversion of Mercury to Methylmercury in 

Reservoirs

Three layers (called thermal strata) were defined for 

discussion in this study, based on water temperature, dissolved 

oxygen, and water depth determined from vertical profiles 

along 10 to 17 transects in each reservoir pool. The three thermal strata are the following: 

1. The epilimnion, a surface layer with water temperatures 

greater than 23 degrees Celsius (°C), dissolved oxygen 

greater than 7 milligrams per liter (mg/L), and water 

depth less than 5 m.

2. The metalimnion, a transition layer with water temperatures 20 to 23 °C, dissolved oxygen 4 to 7 mg/L, and 

water depth 2 to 3 m below the epilimnion. 

3. The hypolimnion, the layer extending to the lake bottom, 

with water temperatures less than 20 °C, dissolved oxygen less than 4 mg/L, and the greatest water depths.
26 Mercury and Methylmercury in Reservoirs in Indiana

Table 8. Physiographic region, natural region, and surficial geology in the vicinity of reservoirs in Indiana.

Reservoir Physiographic region Natural region Surficial (Quaternary) geology

Brookville Lake Central Till Plain Bluegrass, Central Till Plain Loam of Wisconsinan till; Ordovician shale 

and limestone

Cagles Mill Lake Southern Hills and Lowlands Shawnee Hills, Southwestern Lowlands Loam to sandy loam of pre-Wisconsinan till 

and undifferentiated outwash

C.M. Harden Lake Central Till Plain Central Till Plain, Shawnee Hills Loam to sandy loam of pre-Wisconsinan till; 

alluvium

Mississinewa Lake Central Till Plain Central Till Plain Silty clay loam of Wisconsinan till

Monroe Lake Southern Hills and Lowlands Shawnee Hills, Highland Rim Mississippian siltstone, limestone, shale, and 

terra rossa

Patoka Lake Southern Hills and Lowlands Shawnee Hills, Southern Bottomlands Mississippian and Pennsylvanian sandstone, 

shale, and limestone

J.E. Roush Lake Central Till Plain Central Till Plain Silty clay loam of Wisconsinan till

Salamonie Lake Central Till Plain Central Till Plain Silty clay loam of Wisconsinan till

Information about the following classifications were obtained from metadata at Indiana Geological Survey (2011).

1

 Physiographic region from Indiana Geological Survey (Gray, 2000).

2

 Natural region from Indiana Department of Natural Resources, Division of Nature Preserves, Indiana Natural Heritage Data Center (Homoya and others, 

1985).

3

 Quaternary geology from Indiana Geological Survey (Gray, 1989).

Reservoir-pool MeHg concentrations and ratios of dissolved MeHg to Hg in samples from Monroe Lake and Patoka 

Lake9 demonstrated a significant correlation with sample depth 

(rho> 0.7), and a significant inverse correlation with dissolved 

oxygen (rho> −0.6) and water temperature (rho> −0.7) (fig. 13, 

table 9). These correlations indicate that deep, relatively cold, 

relatively low-dissolved-oxygen water, found primarily in the 

hypolimnion and in part of the metalimnion, coincided with 

the highest Hg and MeHg concentrations and ratios of MeHg 

to Hg. Water-sample data indicate that methylation probably 

was occurring in or near the hypolimnion because this stratum 

had the highest ratios of dissolved MeHg to Hg. The data do 

not confirm whether methylation was occurring in the water 

column, in the lake-bottom sediment, at the sediment-water 

interface, or some combination of these locations. 

Statistical differences between Hg, MeHg, and water 

quality in the hypolimnion and epilimnion were observed 

in Monroe Lake and Patoka Lake. These differences were 

evaluated by grouping samples by the three thermal strata and 

tailwater. 

In Monroe Lake, the hypolimnion had significantly 

higher concentrations of particulate Hg, dissolved Hg, particulate MeHg, and dissolved MeHg and a higher ratio of 

dissolved MeHg to Hg than the epilimnion (Kruskal-Wallis, 

p <0.05). The hypolimnion had significantly lower dissolved 

oxygen, water pH, and dissolved sulfate than the epilimnion 

(Kruskal-Wallis, p <0.05). The tailwater had dissolved Hg and 

MeHg, a ratio of dissolved MeHg to Hg, dissolved oxygen, 

water pH, and dissolved sulfate that were most similar to those 

of the hypolimnion (fig. 14). 

9

 Correlations were not computed for Brookville Lake because MeHg was 

detected once in the samples from the reservoir pool.

In Patoka Lake, the hypolimnion had significantly higher 

concentrations of particulate and dissolved MeHg and a higher 

ratio of MeHg to Hg than the epilimnion (Kruskal-Wallis, 

p <0.05). The hypolimnion had significantly lower dissolved 

oxygen, water pH, and dissolved sulfate than the epilimnion 

(Kruskal-Wallis, p <0.05). The tailwater had dissolved Hg and 

MeHg, a ratio of dissolved MeHg to Hg, dissolved oxygen, 

and water pH that were most similar to those of the epilimnion 

(fig. 15).

Through the preceding analysis, the hypolimnions of 

Monroe Lake and Patoka Lake were found to have zones of 

high methylation potential—defined by water temperature less 

than 18.5 °C, dissolved oxygen less than 3.5 mg/L, and water 

depths greater than 8 m. The estimated areal extent of these 

zones involved nearly half of the summer pools in Monroe 

Lake (fig. 16) and Patoka Lake (fig. 17). The extents of these 

zones were estimated with values of water temperature and 

dissolved oxygen measured along the vertical profiles of the 

31 water-quality transects and were processed with GIS software to interpolate the areal extent of similar values. 

Alpers and others (2008) discussed (1) how seasonal thermal stratification in reservoirs with a hypolimnion that has low 

dissolved oxygen can promote MeHg formation in deep water 

and lake-bottom sediments and (2) how the MeHg becomes 

vertically mixed into all the water during thermal destratification. Gray and Hines (2009) confirmed that methylation 

is highly influenced by a eutrophic hypolimnion with low 

concentrations of dissolved oxygen, geochemically reducing 

conditions, high organic matter in bottom sediment, and high 

concentrations of dissolved plant nutrients that increases the 

activity of Hg-methylating anaerobic organisms and increases 

the MeHg flux at the water-sediment interface.
Water-sample depth, in meters

012345

Whole-water mercury, in nanograms per liter

00.51.0

Monroe Lake

Whole-water methylmercury, in nanograms per liter

2 4 6 8 10

012345

Whole-water mercury, in nanograms per liter

Water-sample depth, in meters

2 4 6 8 10 12 14 0

0.51.0

Whole-water methylmercury, in nanograms per literPatoka Lake Patoka Lake

0

Water-sample depth, in m

2 4 6 8 1

0

100

2030405060708090

Ratio of dissolved methylmercury to 

dissolved mercury, in percent (log scale)

Water-sample depth in me

2 4 6 

Monroe Lake

100

2030405060708090

Ratio of dissolved methylmercury to 

dissolved mercury, in percent (log scale)

EXPLANATION

Whole-water mercury concentrationWhole-water methylmercury concentrationRatio of dissolved methylmercury to 

dissolved mercury (percent)

Figure 13. Relations between mercury and sample depth in Monroe Lake and Patoka Lake.
Table 9. Statistical correlations of reservoir pool mercury with sample depth and selected constituents in Monroe Lake and Patoka Lake. [Spearman rank correlation test significance (p-value < 0.05) in bold; rho, Spearman rank correlation coefficient; Hg, mercury; MeHg, methylmercury; DOC, dissolved organic ca

Reservoir Mercury determination Sample depth Dissolved oxygen Water pH Water temperature Dissolved su

p-value rho p-value rho p-value rho p-value rho p-value 

Monroe Lake Hg concentration1 0.044 0.521 0.156 −0.368 0.001 −0.822 0.008 −0.688 <0.001 −0

MeHg concentration2 0.003 0.763 0.020 −0.600 0.001 −0.854 0.001 −0.935 <0.001 −0Ratio of MeHg to Hg3 0.002 0.818 0.006 −0.708 0.002 −0.783 0.002 −0.814 0.004 −0

Ratio of dissolved MeHg to Hg4 0.002 0.787 0.003 −0.752 0.002 −0.791 0.006 −0.710 0.005 −0

Patoka Lake Hg concentration1 0.120 0.368 0.003 −0.690 0.002 −0.731 0.004 −0.684 0.009 −0

MeHg concentration2 0.001 0.757 <0.001 −0.790 <0.001 −0.827 <0.001 −0.849 0.002 −0

Ratio of MeHg to Hg3 <0.001 0.792 <0.001 −0.800 <0.001 −0.855 <0.001 −0.852 0.002 −0

Ratio of dissolved MeHg to Hg4 <0.001 0.818 0.002 −0.714 0.002 −0.726 <0.001 −0.822 0.004 −0

1Whole-water concentration determined as particulate plus dissolved concentration.2 Whole-water concentration determined as particulate plus dissolved concentration.3 Ratio of whole-water methylmercury to whole-water mercury concentration.4 Ratio of dissolved methylmercury to dissolved mercury concentration.
Mercury and Methylmercury in Reservoirs in Indiana 29

0

1

2

3

Particulate mercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

0.24

0.92

3.1

Particulate mercury

4

0

0.5

1.0

1.5

2.0

Epilimnion Metalimnion Hypolimnion

Dissolved mercury, in nanograms per liter

Dissolved mercury

0

0.2

0.4

0.6

0.8

1.0

0.46 0.55

1.1

Particulate methylmercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

0.06 0.09

0.48

Particulate methylmercury

0

0.2

0.4

0.6

0.8

1.0

Dissolved methylmercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

0.05

0.14

0.70

Dissolved methylmercury

0

20

40

60

80

Ratio of dissolved methylmercury to dissolved mercury, in percent

Epilimnion Metalimnion Hypolimnion

Ratio of dissolved methylmercury 

to dissolved mercury

22

60

15

0

5

10

15

Dissolved oxygen, in milligrams per liter

9.8

5.7

4.1

Dissolved oxygen

20

Epilimnion Metalimnion Hypolimnion

6.5

7.0

7.5

8.0

8.5

Water pH, in standard units

Epilimnion Metalimnion Hypolimnion

Water pH

7.4

6.9

6.7

10

12

14

16

18

Dissolved sulfate, in milligrams per liter

Epilimnion Metalimnion Hypolimnion

17.6 17.4

14.0

Dissolved sulfate

EXPLANATION

75th percentile (top of box)

Median (50th percentile)

25th percentile (bottom of box)

0.14 Value shown

Number of values Tailwater value Epilimnion (8)

 Metalimnion (4)

 Hypolimnion (4)

 Tailwater (1)

(Box height is variation or spread of data values,

also called the interquartile range; one step equals 

1.5 times the height of the box. Whisker includes 

adjacent values within one step above or below box)

Figure 14. Distributions of mercury, methylmercury, dissolved oxygen, water pH, and dissolved sulfate in Monroe Lake.
30 Mercury and Methylmercury in Reservoirs in Indiana

0

1

2

3

Particulate mercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

Particulate mercury

4

0.69

0.52

1.37

0

0.5

1.0

1.5

2.0

Epilimnion Metalimnion Hypolimnion

Dissolved mercury, in nanograms per liter

Dissolved mercury

0

0.2

0.4

0.6

0.8

1.0

Particulate methylmercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

Particulate mercury

<0.04

0.11

0.37

0

0.2

0.4

0.6

0.8

1.0

Dissolved methylmercury, in nanograms per liter

Epilimnion Metalimnion Hypolimnion

Dissolved methylmercury

<0.04

0.06

0.30

0

20

40

60

80

Ratio of dissolved methylmercury

to dissolved mercury, in percent

Epilimnion Metalimnion Hypolimnion

Ratio of dissolved methylmercury 

to dissolved mercury

100

24

59

Dissolved oxygen, in milligrams per liter

Dissolved oxygen

Epilimnion Metalimnion Hypolimnion

0.65 0.65

7.4

6.5

7.0

7.5

8.0

8.5

Water pH, in standard units

Epilimnion Metalimnion Hypolimnion

Water pH

7.9

7.1 7.1

Dissolved sulfate, in milligrams per liter

Epilimnion Metalimnion Hypolimnion

Dissolved sulfate 17.8 17.6

12.7

EXPLANATION

75th percentile (top of box)

Median (50th percentile)

25th percentile (bottom of box)

0.14 Value shown

Number of values Tailwater value Epilimnion (9)

 Metalimnion (5)

 Hypolimnion (4)

 Tailwater (1)

(Box height is variation or spread of data values,

also called the interquartile range; one step equals 

1.5 times the height of the box. Whisker includes 

adjacent values within one step above or below box)

0.29 0.28

0.52

0

2

4

6

8

10

5

10

15

20

 Dissolved

methylmercury

 not detected

 Dissolved

methylmercury

 not detected

Figure 15. Distributions of mercury, methylmercury, dissolved oxygen, water pH, and dissolved sulfate in Patoka Lake.
Mercury and Methylmercury in Reservoirs in Indiana 31

!

Salt Creek

Middle Fork Salt Creek

North Fork Salt Creek

86°30' 86°15'

39°07'30"

39°00'

Base from U.S. Geological Survey digital data 1983 1:100,000

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

0

2.5

5 MILES

0

2.5

5 KILOMETERS

STATE ROAD 446

Bloomington

EXPLANATION

1 Sampling site

Water-quality 

transect

Monroe Lake Zone of high 

methylation 

potential 

1

2

3

4

5

6

7

8

9

# #

#

#

# #

#

#

Figure 16. Areal extent of zone of high methylation potential in summer pool of Monroe Lake.
32 Mercury and Methylmercury in Reservoirs in Indiana

86°41'15" 86°33'45"

38°30'

38°22'30"

EXPLANATION

1 Sampling site

Water-quality 

transect

Patoka Lake Zone of high 

methylation 

potential 

0

2.5

5 MILES

0

2.5

5 KILOMETERS Base from U.S. Geological Survey digital data 1983 1:100,000

Universal Transverse Mercator projection zone 16

North American Datum of 1983 (NAD 83)

STATE ROAD 145

STATE ROAD 164

Fleming Creek

Little Patoka River

Patoka River

Patoka River

Painter Creek

#

# #

#

# #

#

#

#

#

#

#

1

2

3

4

5

6

7

8

9

10

11

12

Figure 17. Areal extent of zone of high methylation potential in summer pool of Patoka Lake.
Mercury and Methylmercury in Reservoirs in Indiana 33

The summer pools of Monroe Lake (59.5 kilometers 

[km] long) and Patoka Lake (40.2 km long) are the longest in 

Indiana (table 1). The mean annual retention times, which are 

based on reservoirs outflows and pool volume for 1984–2007, 

index the time for water to move through each reservoir 

(table 1). The highest retention times in Indiana include Patoka 

Lake (556 days) and Monroe Lake (199 days). A long summer pool and high retention time apparently combine to retain 

Hg when the extensive zone of high methylation potential 

develops in Monroe Lake and Patoka Lake. These reservoir 

characteristics may be related to the maximum ratios of 64 to 

82 percent dissolved MeHg to Hg measured in Monroe Lake 

and Patoka Lake. 

The concentrations of Hg and MeHg and the ratios of 

whole-water MeHg to Hg and dissolved MeHg to Hg in 

Monroe Lake and Patoka Lake demonstrated a significant 

inverse correlation with water pH (rho > −0.7) and concentrations of dissolved sulfate (rho > −0.6) and dissolved 

oxygen (rho > −0.6, except rho > −0.37 for Hg in Monroe 

Lake) (table 9).10 Values for water pH, dissolved sulfate, and 

dissolved oxygen were lower in the hypolimnion than the 

metalimnion and the epilimnion of both reservoirs (figs. 14 

and 15). Decreased concentrations of dissolved sulfate and 

increased hydrogen sulfide are indications of sulfate reduction. 

The odor of hydrogen sulfide was reported in all water samples from the hypolimnions of Monroe Lake and Patoka Lake, 

which coincided with the lowest concentrations of dissolved 

sulfate. Microorganisms including bacteria that reduce sulfate 

to hydrogen sulfide are thought to facilitate Hg methylation.

The role of water pH for methylation potential in the reservoir pools is shown by comparing conditions at Brookville 

Lake with Monroe Lake and Patoka Lake. At Brookville Lake, 

MeHg was not detected in samples from the reservoir pool 

even though whole-water Hg was detected in all water samples. Water pH in Brookville Lake was statistically higher in 

all water samples compared to Monroe Lake and Patoka Lake 

and also was higher in the hypolimnion samples (median 7.6) 

compared to Monroe Lake and Patoka Lake (median 6.7 and 

7.1, respectively). Dissolved sulfate in Brookville Lake was 

statistically higher in all water samples compared to Monroe 

Lake and Patoka Lake and also was higher in the hypolimnion 

samples (median 25.5 mg/L) compared to Monroe Lake and 

Patoka Lake (median 13.8 and 12.7 mg/L, respectively). These 

data indicate a potential relation of the lower sulfate reduction 

in the Brookville Lake hypolimnion with the relatively higher 

pH water. 

Particulate organic carbon (POC) and dissolved organic 

carbon (DOC) provide a substrate for particulate Hg and 

sulfate-reducing microorganisms. Both POC and DOC were 

detected in water from both reservoirs. However, DOC was 

significantly correlated only with whole-water Hg in samples 

from Monroe Lake (table 9). The DOC concentrations in 

the Monroe Lake hypolimnion samples were significantly 

10 Correlations were not computed for Brookville Lake because MeHg was 

detected once in the samples from the reservoir pool.

higher (median 4.4 mg/L) than those in Patoka Lake 

(median 3.1 mg/L). Concentrations of DOC in Brookville 

Lake water samples were not statistically different from those 

in Patoka Lake, whether all samples or hypolimnion samples 

are considered. Overall, POC and DOC were less important 

for explaining methylation potential in the reservoir pools than 

were dissolved sulfate and water pH.

Reservoir Fish

Concentrations in Fish Tissue

Methylmercury (reported as Hg) in fish-tissue samples 

was used to depict the effects of MeHg food-web accumulation and magnification in the reservoirs. Data for Hg concentrations in 203 fish-tissue samples were compiled for the eight 

reservoirs in Indiana (appendix table 1–8) and were compared 

with the reference benchmarks for human health and for 

wildlife. The wet-weight fish-tissue Hg concentrations in these 

203 samples ranged from 0.02 to 0.91 mg/kg, and the median 

was 0.16 mg/kg. Concentrations in 19 percent of the samples 

exceeded 0.30 mg/kg—a percentage approximately equal to 

1 out of every 5 fish samples, compared with 1 out of every 

8 fish samples in rivers, streams, lakes, and reservoirs statewide (Risch and others, 2010). 

Mercury concentrations that exceeded 0.30 mg/kg were 

reported in samples from all eight reservoirs and included 

species found in all eight reservoirs. The highest percentages 

of samples that exceeded 0.30 mg/kg were from Monroe Lake 

(38 percent), Patoka Lake (33 percent), and C.M. Harden 

Lake (27 percent); the lowest percentage was from Brookville 

Lake (5 percent). Mercury concentrations in fish from Monroe 

Lake (median 0.21 mg/kg) were statistically higher than those 

from J.E. Roush Lake, Brookville Lake, and Mississinewa 

Lake. Mercury concentrations in fish from C.M. Harden Lake 

(median 0.22 mg/kg) were statistically higher than those from 

Mississinewa Lake (Kruskal-Wallis, p < 0.001; Tukey). The 

Hg concentrations in 76 percent of the 203 fish-tissue samples 

exceeded the 0.10-mg/kg reference benchmark for wildlife. 

The highest percentages of samples that exceeded 0.10 mg/kg 

were from Monroe Lake (92 percent), Salamonie Lake 

(90 percent), and C.M. Harden Lake (87 percent).

Bioaccumulation

A bioaccumulation factor (BAF) is the ratio of MeHg 

in fish tissue to dissolved MeHg in the water and offers a 

comparison of the food-web effects among the six reservoirs 

in Indiana with MeHg data. The BAFs indicate that MeHg 

concentrations in water became a million times higher in fish 

because of food-chain accumulation and magnification. BAFs 

were computed with measured concentrations of fish-tissue 

MeHg (as Hg) data from all samples in the six reservoirs and 

the mean dissolved MeHg in water samples from the reservoirs. BAFs are presented as a range of values (table 10).
34 Mercury and Methylmercury in Reservoirs in Indiana

Table 10. Methylmercury bioaccumulation factors for five reservoirs in Indiana.

[Hg, mercury; wet wt., wet weight; mg/kg, milligram per kilogram; MeHg, methlylmercury; ng/L, nanogram per liter; 

BAF, bioaccumulation factor; L/kg, liter per kilogram; 106, one million]

Reservoir name

Mean 

fish tissue 

Hg wet wt. 

(mg/kg)

Maximum 

fish tissue 

Hg wet wt. 

(mg/kg)

Mean 

dissolved

MeHg in 

water (ng/L)

BAF3

 low

(L/kg)

"BAF4 high 

(L/kg)"

Misssinewa Lake1 0.126 0.322 0.07 1.80 × 106 4.60 × 106

Monroe Lake2 0.297 0.910 0.22 1.35 × 106 4.14 × 106

Patoka Lake2 0.233 0.634 0.12 1.94 × 106 5.28 × 106

J.E. Roush Lake1 0.160 0.440 0.15 1.07 × 106 2.95 × 106

Salamonie Lake1 0.170 0.395 0.15 1.15 × 106 2.63 × 106

1

Dissolved MeHg in water based on non-censored values from tailwater samples (appendix table 1–3).

2

Dissolved MeHg in water based on values from pool samples (appendix table 1–5).

3

BAF-low computed as ratio of fish mean Hg concentration to mean dissolved MeHg concentration in water. Fishtissue data from Indiana Department of Environmental Management Assessment Information Management System 

(appendix table 1–8).

4

BAF-high computed as ratio of fish maximum Hg concentration to mean dissolved MeHg concentration in water. 

Fish-tissue data from Indiana Department of Environmental Management Assessment Information Management 

System (appendix table 1–8).

The low value in the range is the ratio of the mean fish tissue MeHg (as Hg) to the mean dissolved MeHg; this value 

includes Hg found in all species in a reservoir. The high value 

in the range is the ratio of the maximum fish tissue MeHg 

(as Hg) to the mean dissolved MeHg; this value includes the 

species at the top of the food web. BAFs for Monroe Lake and 

Patoka Lake were computed with reservoir-pool MeHg data. 

BAFs for J.E. Roush Lake, Mississinewa Lake, and Salamonie 

Lake were computed with reservoir-tailwater data because 

reservoir-pool water data were not available. Methylmercury 

was not detected in Brookville Lake pool or tailwater samples, 

and a BAF was not computed. All of the BAFs were a millionfold and differed by a factor of 5 or less. The highest BAFs 

were for Patoka Lake, ranging from 1.94×106

 to 5.28×106

liters per kilogram.

Implications for Fish Consumption

Reservoir fish-tissue data indicated the highest levels 

of Hg and MeHg were observed in Monroe Lake and Patoka 

Lake, and these findings have implications for fish consumption by humans. Approximately 104,000 anglers were recorded 

to have caught fish in the pools and tailwaters of these two 

reservoirs in 2007 (Carnahan, 2008; Kittaka, 2008). Many fish 

that are caught are released, so it is important to distinguish 

which fish were “harvested” (for potential human consumption). The fish species that were reported as harvested, when 

compared with the available fish-tissue Hg concentrations data 

for each reservoir, indicate that most of the fish harvested are 

species likely to have fish-tissue Hg concentrations below the 

reference benchmark for human health. On the other hand, the 

fish species most frequently targeted and caught typically were 

not harvested but were likely to have Hg fish-tissue sample 

concentrations that exceed the reference benchmark for human 

health. These implications for fish consumption by humans are 

detailed in the following discussions.

Monroe Lake creel surveys (Kittaka, 2008) during 

the April through October 2007 fishing season, including 

30 bass tournament days, recorded 38,019 anglers who 

caught 85,248 fish and harvested 51,053 (60 percent). Of the 

fish harvested, 88 percent were crappie (Pomoxis species), 

bluegill (Lepomis macrochirus), and channel catfish (Ictalurus 

punctatus). Fish-tissue samples of these species from Monroe Lake, 1996–2007, had Hg concentrations ranging from 

0.166 to 0.320 mg/kg (n = 58). These data indicate that most, 

but not all, fish of these three species harvested from Monroe 

Lake probably had Hg concentrations lower than the reference 

benchmark for human health.

Nearly half of the anglers at Monroe Lake targeted largemouth bass (Micropterus salmoides), striped bass (Morone 

species), and walleye (Sander vitreus). These three species 

accounted for 66 percent of the fish caught and 6.9 percent of 

the fish harvested. Comparing harvest to catch, 1.4 percent of 

largemouth bass, 27 percent of striped bass, and 66 percent of 

walleye were harvested. Mercury in fish-tissue samples from 

Monroe Lake, 1996–2007, had Hg concentrations ranging 

from 0.154 to 0.556 mg/kg in 11 largemouth bass samples 

and 0.175 to 0.910 mg/kg in 6 walleye samples. No data 
Mercury and Methylmercury in Reservoirs in Indiana 35

were available for fish tissue Hg in hybrid striped bass. The 

data indicated average-length largemouth bass and aboveaverage-length walleye harvested from Monroe Lake probably contained Hg concentrations that exceeded the reference 

benchmark for human health.11,12

Patoka Lake creel surveys (Carnahan, 2008) during 

the April through October 2007 fishing season, including 

24 bass tournament days, recorded 65,860 anglers who caught 

213,680 fish and harvested 117,007 (55 percent). Of the fish 

harvested, 97 percent were crappie, bluegill, and channel 

catfish. Fish-tissue samples of these species from Patoka Lake, 

1996–2006, had Hg concentrations ranging from 0.023 to 

0.221 mg/kg. These data indicate that most fish of these species harvested from Patoka Lake probably did not contain 

Hg concentrations that exceeded the reference benchmark for 

human health.

Many anglers at Patoka Lake targeted largemouth 

bass and striped bass, and these two species accounted for 

46 percent of the fish caught and 2.2 percent of the fish harvested. Comparing harvest to catch, 2 percent of largemouth 

bass and 42 percent of striped bass were harvested. Fish-tissue 

samples from Patoka Lake, 1996–2006, had Hg concentrations 

ranging from 0.304 to 0.634 mg/kg in largemouth bass. No 

data were available for fish tissue Hg in hybrid striped bass. 

These data indicate that the average-length largemouth bass 

harvested from Patoka Lake probably contained Hg concentrations that exceeded the reference benchmark for human 

health.13,14

11 Largemouth bass harvested from Monroe Lake were 356 to 559 millimeters (mm) long, with a mean of 419 mm. The largemouth bass samples 

from Monroe Lake exceeding 0.30 mg/kg Hg were 296 to 480 mm long, 

with a mean of 361 mm. Most of the largemouth bass harvested would be in 

the size range of samples exceeding 0.30 mg/kg Hg. Walleye harvested were 

356 to 696 mm long, with a mean of 442 mm. The walleye samples exceeding 0.30 mg/kg Hg were 554 to 675 mm long, with a mean of 626 mm. The 

above-average-size walleye, more than 554 mm long, would be in the size 

range of samples exceeding 0.30 mg/kg Hg.

12 The advisory and guidelines applicable to Monroe Lake state that women 

of childbearing years, nursing mothers, and all children under age 15 may eat 

one meal per month of largemouth bass larger than 13 inches (in.) (330 mm) 

and walleye 19 to 21 in. (483 to 533 mm) but should not eat walleye larger 

than 21 in. (533 mm).

13 Largemouth bass harvested from Patoka Lake were a mean of 414 mm 

long. The largemouth bass samples from Patoka Lake exceeding 0.30 mg/kg 

Hg were 322 to 467 mm long, with a mean 371. The average-size largemouth 

bass, including those 414 mm, would be in the size range of samples exceeding 0.30 mg/kg Hg.

14 The advisory and guidelines applicable to Patoka Lake state that women 

of childbearing years, nursing mothers, and all children under age 15 may eat 

one meal per month of largemouth bass larger than 13 in. (330 mm).

Limitations of Existing Information

Existing information limits a uniform comparison of Hg 

and MeHg in the eight flood-control reservoirs in Indiana. 

Mercury and MeHg data from reservoir tailwaters and pools 

do not include the same reservoirs for the same seasons over 

the same time period. Tailwater MeHg data provide an insight 

into reservoir-pool conditions at J.E. Roush Lake, Mississinewa Lake, and Cagles Mill Lake, but reservoir-pool data, 

collected at least during summer thermal stratification, would 

provide a better comparison with the findings from the pools at 

Brookville Lake, Monroe Lake, and Patoka Lake. Multiyear, 

seasonal tailwater data are not available for Monroe Lake and 

Patoka Lake. 

Mercury and MeHg data have not been collected from 

tailwaters and pools at C.M. Harden Lake and Salamonie 

Lake. These two reservoirs have percentages of agricultural 

land cover similar to J.E. Roush Lake and Mississinewa Lake 

(more than 70 percent), and all four reservoirs are in the Central Till Plains physiographic region. Mercury was detected in 

100 percent and MeHg was detected in more than 70 percent 

of the tailwater samples from J.E. Roush Lake and Mississinewa Lake. These similarities indicate a potential for Hg and 

MeHg to be detected in tailwater samples from C.M Harden 

Lake and Salamonie Lake. 

The duration and areal extent of conditions favoring Hg 

methylation are likely related to thermal stratification, but 

current knowledge for the reservoirs in Indiana is limited to a 

single summer sampling during thermal stratification. Other 

investigators have noted the important role of thermal destratification in the cycling and transport of MeHg in a reservoir 

system (for example, Alpers and others, 2008; Gray and Hines, 

2009). In addition, autumn drawdown of water levels mixes 

and removes water from the pool, potentially changing Hg 

and MeHg transport within the reservoir and to downstream 

locations. Current knowledge does not include the distance 

downstream from a dam that MeHg from tailwaters persists, 

the annual reservoir yield of MeHg in tailwaters, and the Hg 

in fish from reaches downstream from reservoirs compared to 

fish in the reservoirs. 

Finally, collection of water from reservoir pools and 

tailwaters for Hg and MeHg analysis throughout the year for 

several years—if coordinated with periodic collection of fish 

tissue samples for Hg analysis from these same locations—

would provide a more thorough understanding of Hg delivery, 

methylation, food-web bioaccumulation, and downstream 

transport.
36 Mercury and Methylmercury in Reservoirs in Indiana

Summary and Conclusions

Mercury (Hg) is an element that occurs naturally, but evidence suggests that human activities have resulted in increased 

amounts being released to the atmosphere and land surface. 

When Hg is converted to toxic methylmercury (MeHg) in 

aquatic ecosystems, MeHg accumulates and increases in the 

food web so that some fish contain levels which pose a health 

risk to humans and wildlife that consume these fish. 

Reservoirs, unlike natural lakes, are a part of river 

systems that are managed for flood control, which has unintentional effects on mercury transport and methylmercury formation. A condition known as the reservoir effect highlights the 

importance of Hg and MeHg in reservoirs. Previous investigations in North America have shown that lakes and reservoirs 

during summer thermal stratification can develop conditions in 

the hypolimnion that promote MeHg formation. In this study, 

two sets of data from six flood-control reservoirs in Indiana 

were compiled and interpreted to evaluate how Hg transport 

and MeHg formation in the water were affected by physical factors and chemical and biological conditions. The data 

included water samples collected and processed with ultraclean protocols and analyzed for Hg and MeHg by low-level 

methods, plus field determinations for water-quality characteristics and analysis of supplementary constituents. 

One set of data was 66 seasonal samples from tailwaters 

downstream near the dams of four reservoirs—Brookville 

Lake, Cagles Mill Lake, J.E. Roush Lake, and Mississinewa 

Lake. In these samples, Hg ranged up to 15 nanograms per 

liter (ng/L), and the mean was 2.58 ng/L. Methylmercury was 

detected only once in the tailwaters of Brookville Lake. The 

concentration ratios of MeHg to Hg ranged up to 64.8 percent, 

and the mean for the four reservoirs was 9.1 percent. Statistical analysis indicated the median concentration ratio of MeHg 

to Hg in summer tailwater samples, 6.7 percent, was significantly higher than in other seasons. 

The other set of data was 53 samples from summer pools 

and tailwaters of three reservoirs: Brookville Lake, Monroe 

Lake, and Patoka Lake. Water-quality characteristics data from 

1,440 depth-specific measurements in vertical profiles along 

10 to 17 transects in each reservoir were used to select the 

depths for the water samples in the epilimnion, metalimnion, 

and hypolimnion thermal strata. Examination of changes in 

water temperature and dissolved oxygen with depth shows that 

the pool of each reservoir was thermally stratified at many of 

the transects.

Whole-water Hg (particulate plus dissolved Hg) was 

reported in all samples from the three reservoir pools and concentrations ranged up to 5.51 ng/L; the mean was 1.34 ng/L. 

Mercury concentrations were highest in the hypolimnions 

of Monroe Lake and Patoka Lake. Water samples from 

Brookville Lake had considerably lower levels of whole-water 

Hg, particulate Hg, and MeHg than the other two reservoirs. 

Methylmercury was detected in 53 percent of the samples, 

including just a single sample from the Brookville Lake 

headwaters. Dissolved MeHg is the form that is most available 

for transfer to the aquatic food web. Concentration ratios of 

dissolved MeHg to Hg in the three reservoirs ranged up to 82 

percent, and the median was 40 percent in Monroe Lake and 

48 percent in Patoka Lake.

The hypolimnions of Monroe Lake and Patoka Lake were 

found to have zones with a high potential for conversion of Hg 

to MeHg—defined by water temperature less than 18.5 degrees 

Celsius and dissolved oxygen less than 3.5 milligrams per liter 

(mg/L), and water depths greater than 8 meters. These zones 

had the highest concentrations of Hg and MeHg, the highest 

concentration ratios of dissolved MeHg to Hg, and conditions favorable for sulfate reductions (water pH< 7, decreased 

dissolved sulfate concentrations, and observed hydrogen 

sulfide in water samples) compared to other strata. These 

zones extended through nearly half of the summer pools for 

these two reservoirs. Reservoir outflow came from this zone at 

Monroe Lake and contributed to a tailwater concentration ratio 

for dissolved MeHg to Hg of 56 percent. Reservoir outflow at 

Patoka Lake was not from this zone, and dissolved MeHg was 

not detected in the tailwater. 

Factors affecting the transport of Hg to reservoirs favored 

Monroe Lake and Patoka Lake. These two reservoirs are in 

parts of Indiana with high Hg wet deposition so that the total 

wet plus dry atmospheric Hg-deposition rates at Monroe Lake 

and Patoka Lake were higher than at the other reservoirs. 

The drainage areas of these two reservoirs have the highest 

percentages of forest land cover supporting Hg dry deposition—82 percent for Monroe Lake and 67 percent for Patoka 

Lake. Furthermore, Monroe Lake and Patoka Lake are in 

landscapes with steep slopes and near-surface bedrock, which 

promote higher rates of precipitation runoff and potentially 

higher rates of Hg transport to streams and the reservoirs.

To depict food-web accumulation and magnification of 

MeHg, fish-tissue MeHg (as Hg) data for the reservoirs in 

Indiana were compiled from State records. Fish-tissue Hg 

concentrations from 203 samples ranged from 0.02 to

 0.91 milligram per kilogram (mg/kg), and the median was 

0.16 mg/kg; 19 percent exceeded the reference benchmark for 

human health, 0.30 mg/kg. Methylmercury (as Hg) concentrations in fish differed among reservoirs, and the highest 

percentages of samples that exceeded the reference benchmark were from Monroe Lake (38 percent) and Patoka Lake 

(33 percent); the lowest was from Brookville Lake (5 percent). 

Concentrations in 76 percent of the 203 fish-tissue samples 

exceeded the 0.10-mg/kg reference benchmark for wildlife. 

The highest percentage of samples that exceeded 0.10 mg/kg 

were from Monroe Lake (92 percent), Salamonie Lake 

(90 percent), and C.M. Harden Lake (87 percent).

Because fishing is a popular activity at Monroe Lake and 

Patoka Lake, the fish species harvested and Hg fish-tissue data 

were compared. The implications for human consumption were 

that the highest numbers of fish harvested were crappie, bluegill, 

and catfish, which are more likely to have MeHg levels lower 

than the 0.30-mg/kg reference benchmark for human health. 

Largemouth bass were typically caught and released at these 

reservoirs, but 66 percent of walleye caught were harvested. The 
References 37

average-size largemouth bass harvested in both reservoirs and 

the above-average-size walleye harvested from Monroe Lake 

were likely to exceed the reference benchmark for human health. 

Existing information limits a uniform comparison of Hg 

and MeHg in the eight flood-control reservoirs in Indiana. 

Mercury and MeHg data from tailwaters and pools at 

C.M. Harden Lake or Salamonie Lake have not been collected. 

Mercury and MeHg data from reservoir tailwaters and pools 

do not include the same reservoirs at the same intervals over 

the same time period. The duration and areal extent of conditions favoring Hg methylation are likely related to thermal 

stratification, but current knowledge is limited to a single time 

during thermal stratification. Currently unknown is the distance downstream that MeHg from tailwater outflow persists, 

the annual reservoir MeHg yields in tailwaters, or the associated fish Hg in downstream reaches.

In conclusion, this study has shown that MeHg is formed 

in six flood-control reservoirs in Indiana—Brookville Lake, 

Cagles Mill Lake, Mississinewa Lake, Monroe Lake, Patoka 

Lake, and J.E. Roush Lake. This MeHg accumulated and 

magnified to unsafe levels in the aquatic food web, including 

the food chains of fish caught in these lakes and consumed by 

anglers and wildlife. On the basis of information available, 

other reservoirs will have the highest rates of Hg transport and 

MeHg formation and the highest levels of MeHg in fish if they 

are located in forested landscapes with steep terrain and nearsurface bedrock, if they receive moderate to high atmospheric 

Hg wet and dry deposition, and if the water pH is less than 7 

and dissolved oxygen is less than 3.5 mg/L to promote sulfate 

reduction. These conditions will be most prevalent during 

thermal stratification in the summer, leading to the potential 

for MeHg to be released in tailwater—especially if the water 

that is released is from the hypolimnion or metalimnion. Additional multiseason studies of Hg and MeHg in water and fish 

from reservoir pools and tailwaters in Indiana and other states 

could provide the data needed to evaluate risks to humans 

and wildlife and to assess reservoir management options to 

mitigate these risks.

References

Alpers, C.N., Stewart, A.R., Saiki, M.K., Marvin-DiPasquale, 

M.C., Topping, B.R., Rider, K.M., Gallanthine, S.K., 

Kester, C.A., Rye, R.O., Antweiler, R.C., and De Wild, J.F., 

2008, Environmental factors affecting mercury in Camp 

Far West Reservoir, California, 2001–03: U.S. Geological 

Survey Scientific Investigations Report 2006–5008, 358 p.

Arar, E.J., and Collins, G.B., 1997, In vitro determination 

of chlorophyll a and phaeophytin a in marine and freshwater algae by fluorescence (rev. 1.2): Cincinnati, Ohio, 

U.S. Environmental Protection Agency, National Exposure 

Research Laboratory, Office of Research and Development, 

Method 445.0–1, 22 p., accessed June 2011 at http://www.

epa.gov/nerlcwww/m445_0.pdf.

Becker, D.S., and Bigham, G.N., 1995, Distribution of mercury in the aquatic food web of Onondaga Lake, New York: 

Water, Air, and Soil Pollution, v. 80, p. 563–571.

Bell, A.H., and Scudder, B.C., 2007, Mercury accumulation in 

periphyton of eight river ecosystems: Journal of the American Water Resources Association, v. 43, no. 4, p. 957–968.

Bird, S.M., Fram, M.S., and Crepeau, K.L., 2003, Method of 

analysis by the U.S. Geological Survey California District Sacramento Laboratory—Determination of dissolved 

organic carbon in water by high temperature catalytic 

oxidation, method validation, and quality-control practices: 

U.S. Geological Survey Open-File Report 03–366, 14 p.

Bloom, N.S., 1992, On the chemical form of mercury in edible 

fish and marine invertebrate tissue: Canadian Journal of 

Fisheries and Aquatic Science, v. 49, p. 1010–1017.

Bodaly, R.A.; Beaty, K.G.; Hendzel, L.H.; Majewski, A.R.; 

Paterson, M.J.; Rolfhus, K.R.; Penn, A.F.; St. Louis, V.L.; 

Hall, B.D.; Matthews, C.J.D.; Cherewyk, K.A.; Mailman, 

Mariah; Hurley, J.P.; Schiff, S.L.; and Venkiteswaran, 

J.J., 2004, Experimenting with hydroelectric reservoirs: 

Environmental Science & Technology, v. 38, no. 18, 

p. 346A– 352A.

Bodaly, R.A., Jansen, W.A., Majewski, A.R., Fudge, R.J.P., 

Strange, N.E., Derksen, A.J., and Green, D.J., 2007, Postimpoundment time course of increased mercury concentrations 

in fish in hydroelectric reservoirs of northern Manitoba, 

Canada: Archive of Environmental Contamination and 

Toxicology, v. 53, no. 3, p. 379–389.

Brigham, M.E., Wentz, D.A., Aiken, G.R., and Krabbenhoft, 

D.P., 2009, Mercury cycling in stream ecosystems. 1. Water 

column chemistry and transport: Environmental Science & 

Technology, v. 43, no. 8, p. 2720–2725.

Brumbaugh, W.G., Krabbenhoft, D.P., Helsel, D.R., Wiener, 

J.G., and Echols, K.R., 2001, A national pilot study of 

mercury contamination of aquatic ecosystems along multiple gradients—Bioaccumulation in fish: U.S. Geological 

Survey Biological Science Report 2001–009, 28 p.

Canavan, C.M., Caldwell, C.A., and Bloom, N.S. 2000, 

Discharge of methylmercury-enriched hypolimnetic water 

from a stratified reservoir: Science of the Total Environment, v. 260, p. 159–170.

Carnahan, D.P., 2008, Patoka Lake fish management report: 

Indiana Department of Natural Resources Division of Fish 

and Wildlife, 45 p.

Chasar, L.C., Scudder, B.C., Stewart, A.R., Bell, A.H., and 

Aiken, G.R., 2009, Mercury cycling in stream ecosystems. 

3. Tophic dynamics and methylmercury accumulation: 

Environmental Science & Technology, v. 43, no. 8, 

p. 2733–2739.
38 Mercury and Methylmercury in Reservoirs in Indiana

Cocca, Paul, 2001, Mercury maps—A quantitative spatial link 

between air deposition and fish tissue: U.S. Environmental 

Protection Agency, Office of Water, EPA–823–R–01–009, 

31 p.

DeWild, J.F., Olson, M.L., and Olund, S.D., 2002, Determination of methyl mercury by aqueous phase ethylation, followed by gas chromatographic separation with cold vapor 

atomic fluorescence detection: U.S. Geological Survey 

Open-File Report 01–445, 19 p.

DeWild, J.F., Olund, S.D., Olson, M.L., and Tate, M.T., 2004, 

Methods for the preparation and analysis of solids and suspended solids for methylmercury: U.S. Geological Survey 

Techniques and Methods, book 5, chap. A7, 13 p. 

Drenner, R.W., Chumchal, M.M., Wente, S.P., McGuire, 

M., and Drenner, S.M., 2011, Landscape-level patterns 

of mercury contamination of fish in North Texas, USA: 

Environmental Toxicology and Chemistry, v. 30, no. 9, 

p. 2041-2045

Driscoll, C.T., Mason, R.P., Chan, H.M., Jacob, D.J., and Pirrone, Nicola, 2013, Mercury as a global pollutant—Sources, 

pathways, and effects: Environmental Science & Technology, v. 47, p. 4967−4983

Environmental Systems Research Institute, 2006, ArcGIS 

version 9.2. 

Evers, D.C., 2005, Mercury connections—The extent and 

effects of mercury pollution in northeastern North America: 

Gorham, Maine, Biodiversity Research Institute, 29 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Gray, H. H., 1989, Quaternary geologic map of Indiana: 

Indiana Geological Survey Miscellaneous Map 49.

Gray, H.H., 2000, Physiographic divisions of Indiana: Indiana 

Geological Survey Special Report 61, 15 p., 1 pl.

Gray, J.E., and Hines, M.E., 2009, Biogeochemical mercury 

methylation influenced by reservoir eutrophication, Salmon 

Falls Creek Reservoir, Idaho, USA: Chemical Geology, 

v. 258, p. 157–167.

Grieb, T.M., Driscoll, C.T., Gloss, S.P., Schofield, C.L., 

Bowie, G.L., and Porcella, D.B., 1990, Factors affecting mercury accumulation in fish in the Upper Michigan 

Peninsula: Environmental Toxicology and Chemistry, v. 9, 

p. 919–930.

Grigal, D.F., 2002, Inputs and outputs of mercury from terrestrial watesheds—A review: National Research Council of 

Canada Environmental Reviews, v. 10, no. 1, p. 1–39.

Guy, H.P., 1969, Laboratory theory and methods for sediment 

analysis: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. C1, 58 p. 

Hall, B.D., St. Louis, V.L., Rolfhus, K.R., Bodaly, R.A., Beaty, 

K.G., Paterson, M.J., and Peech Cherewyk, K.A., 2005, 

Impacts of reservoir creation on the biogeochemical cycling 

of methyl mercury and total mercury in boreal upland forests: Ecosystems, v. 8, no 3, p. 248–266.

Hammerschmidt, C.R., Wiener, J.G., Frazier, B.E., and Rada, 

R.G., 1999, Methylmercury content of eggs in yellow perch 

related to maternal exposure in four Wisconsin lakes: Environmental Science & Technology, v. 33, p. 999–1003.

Hartman, J.S., Weisberg, P.J., Pillai, R., Ericksen, J.A., Kuiken, T., Lindberg, S.E., Zhang, H., Rytuba, J.J., and Gustin, 

M.S., 2009, Application of a rule-based model to estimate 

mercury exchange for three background biomes in the continental United States: Environmental Science & Technology, 

v. 43, p. 4989–4994.

Harris, R.C., Krabbenhoft, D.P., Mason, R.P., Murray, M.W., 

Reash, R., and Saltman, T., eds., 2007, Ecosystem responses 

to mercury contamination—Indicators of change: Pensacola, Fla., Society of Environmental Toxicology and Chemistry Press, 216 p. 

Harris, R.C.; Rudd, J.W.M.; Amyot, Marc; Babiarz, C.L.; 

Beaty, K.G.; Blanchfield, P.J.; Bodaly, R.A.; Branfireun, 

B.A.; Gilmour, C.C.; Graydon, J.A.; Heyes, Andrew; 

Hintelmann, Holger; Hurley, J.P.; Kelly, C.A.; Krabbenhoft, 

D.P.; Lindberg, S.E.; Mason, R.P.; Paterson, M.J.; Podemski, C.L.; Robinson, Art; Sandilands, K.A.; Southworth, 

G.R.; St. Louis, V.L.; and Tate, M.T., 2007, Whole-ecosystem study shows rapid fish-mercury response to changes in 

mercury deposition: Proceedings of the National Academy 

of Sciences, v. 104, no. 42, p. 16586–16591.

Helsel, D.R., and Hirsch, R.M., 1995, Statistical methods in 

water resources (2d printing): Amsterdam, Elsevier Science 

Publishers, 529 p.

Homer, C., Huang, C. ,Yang, L., Wylie, B., and Coan, M., 

2004, Development of a 2001 National Land Cover Database for the United States: Photogrammetric Engineering 

and Remote Sensing, v. 70, no. 7, p. 829–840.

Homoya, M.A., Abrell, D.B., Aldrich, J.R., and Post, T.W., 

1985. The natural regions of Indiana: Proceedings of the 

Indiana Academy of Science, v. 94, p. 245–268.

Horowitz, A.J., Demas, C.R., Fitzgerald, K.K., Miller, T.L., 

and Rickert, D.A., 1994, U.S. Geological Survey protocol 

for the collection and processing of surface-water samples 

for the subsequent determination of inorganic constituents: 

U.S. Geological Survey Open-File Report 94–539, 57 p.

Indiana Geological Survey, 2011, Indiana map: accessed 

August 2011 at http://maps.indiana.edu/
References 39

Kelly, C.A., Rudd, J.W.M., Bodaly, R.A., Roulet, N.P., St. 

Louis, V.L., Heyes, A., Moore, T.R., Schiff, S., Aravena, R., 

Scott, K.J., Dyck, B., Harris, R., Warner, B., and Edwards, 

G., 1997, Increases in fluxes of greenhouse gases and 

methyl mercury following flooding of an experimental 

reservoir: Environmental Science & Technology, v. 31, 

no. 5, p. 1334–1344.

Kittaka, D.S., 2008, Fishing pressure and fish harvest at 

Monroe Reservoir, 2007: Indiana Department of Natural 

Resources Division of Fish and Wildlife, 16 p.

Klaper, R., Rees, C.B., Drevnick, P., Weber, D., Sandheinrich, M., and Carvan, M.J., 2006, Gene expression changes 

related to endocrine function and decline in reproduction in 

fathead minnow (Pimephales promelas) after dietary methylmercury exposure: Environmental Health Perspectives, 

v. 114, no. 9, p. 1337–1343.

Kolka, R.K., Nater, E.A., Grigal, D.F., and Verry, E.S., 1999, 

Atmospheric inputs of mercury and organic carbon into a 

forested upland/bog watershed: Water, Air, and Soil Pollution, v. 113, p. 273–294.

Lindberg, S., Bullock, R., Ebinghaus, R., Engstrom, D., Feng, 

X., Fitzgerald, W., Pirrone, N., Prestbo, E., and Seigneur, 

C., 2007, A synthesis of progress and uncertainties in attributing the sources of mercury in deposition: Ambio, v. 36, 

no. 1, p. 19–32.

Mailman, M., Stepnuk, L., Cicek, N., and Bodaly, R.A., 2006, 

Strategies to lower methyl mercury concentrations in hydroelectric reservoirs and lakes–—A review: Science of the 

Total Environment, v. 368, p. 224–235. 

Mast, M.A., and Krabbenhoft, D.P., 2010, Comparison of 

mercury in water, bottom sediment, and zooplankton in two 

Front Range reservoirs in Colorado, 2008–09: U.S. Geological Survey Scientific Investigations Report 2010–5037, 

20 p.

Mergler, D., Anderson, H.A., Chan, L.H.M., Mahaffey, K.R., 

Murray, M., Sakamoto, M., and Stern., A.H., 2007, Methylmercury exposure and health effects in humans—A worldwide concern: Ambio, v. 36, no. 1, p. 3–11.

Morel, F.M.M., Kraepiel, A.M.L., and Amyot, Marc, 1998, 

The chemical cycle and bioaccumulation of mercury: 

Annual Review of Ecology and Systematics, v. 29, p. 

543–566.

Munthe, John; Bodaly, R.A.; Branfireun, B.A.; Driscoll, C.T.; 

Gilmour, C.C.; Harris, Reed; Horvat, Milena; Lucotte, 

Marc; and Malm, Olaf, 2007, Recovery of mercury-contaminated fisheries: Ambio, v. 36, no. 1, p. 33–44.

National Research Council, 2000, Toxicological effects of 

methylmercury: Washington, D.C., National Academy 

Press, 344 p. 

Negry, J., Melwani, A., Stephenson, M., and Davis, J., 2011, 

Mercury in California lakes and reservoirs—Factors influencing bioaccumulation, in 10th International Conference 

on Mercury as a Global Pollutant, Halifax, Nova Scotia, 

Canada, July 24–29, 2011: Proceedings, p.227.

Olson, M.L., and De Wild, J.F., 1997, Determination of total 

mercury in water by oxidation, purge and trap, and cold 

vapor atomic fluorescence spectrometry: U.S. Geological 

Survey National Mercury Laboratory Standard Operating 

Procedure SOP001, accessed June 2011 at http://wi.water.

usgs.gov/mercury-lab/forms/hg_tsop001_rev_4.pdf. 

Olund, S.D., DeWild, J.F., Olson, M.L., and Tate, M.T., 2004, 

Methods for the preparation and analysis of solids and 

suspended solids for total mercury: U.S. Geological Survey 

Techniques and Methods, book 5, chap. A8, 15 p. 

Patton, C.J.; Kammer, James; and Brenton, Ronald, 2000, 

New particulate carbon and nitrogen methods at the NWQL: 

U.S. Geological Survey, National Water Quality Laboratory, 

25 p., accessed June 2011 at http://wwwnwql.cr.usgs.gov/

htmls/pcn.ppt. 

Plourde, Yanick; Lucotte, Marc; and Pichet, Pierre, 1997, Contribution of suspended particulate matter and zooplankton 

to MeHg contamination of the food chain in midnorthern 

Quebec (Canada) reservoirs: Canadian Journal of Fisheries 

and Aquatic Sciences, v. 54, no. 4, p. 821–831.

Risch, M.R., Baker, N.T., Fowler, K.K, Egler, A.L., and 

Lampe, D.C., 2010, Mercury in Indiana watersheds—Retrospective for 2001–2006: U.S. Geological Survey Professional Paper 1780, 66 p. with appendixes.

Risch, M.R., DeWild, J.F., Krabbenhoft, D.P., Kolka, R.K., 

and Zhang, L., 2012, Litterfall mercury dry deposition 

in the eastern USA: Environmental Pollution, v. 161, p. 

284–290, http://dx.doi.org/10.1016/j.envpol.2011.06.005.

Sandheinrich, M.B., and Wiener, J.G., 2011, Methylmercury 

in freshwater fish—Recent advances in assessing toxicity 

of environmentally relevant exposures, in Beyer, W.N., and 

Meador J.P., eds., Environmental contaminants in biota—

Interpreting tissue concentrations (2d ed.): Boca Raton, Fla., 

CRC Press, p. 169–190.

Scheuhammer, A.M., Meyer, M.W., Sandheinrich, M.B., and 

Murray, M.W., 2007, Effects of environmental methylmercury on the health of wild birds, mammals, and fish: Ambio, 

v. 36, no. 1, p. 12–18.

Scudder, B.C., Chasar, L.C., Wentz, D.A., Bauch, N.J., 

Brigham, M.E., Moran, P.W., and Krabbenhoft, D.P., 2009, 

Mercury in fish, bed sediment, and water from streams 

across the United States, 1998–2005: U.S. Geological Survey Scientific Investigations Report 2009–5109, 74 p.
40 Mercury and Methylmercury in Reservoirs in Indiana

St. Louis, V.L.; Rudd, J.W.M.; Kelly, C.A.; Bodaly, R.A.; Paterson, M.J.; Beaty, K.G.; Hesslein, R.H.; Heyes, Andrew; 

and Majewski, A.R., 2004, The rise and fall of mercury 

methylation in an experimental reservoir: Environmental 

Science & Technology, v. 38, no. 5, p. 1348–1358.

Stahl, L.L., Snyder, B.D., Olsen, A.R., and Pitt, J.L., 2009, 

Contaminants in fish tissue from U.S. lakes and reservoirs—

A national probabilistic study: Environmental Monitoring 

and Assessment, v. 150, p. 3–19.

Stewart, A.R., Saiki, M.K., Kuwabara, J.S., Alpers, C.N., 

Marvin-DiPasquale, M., and Krabbenhoft, D.P., 2008, Influence of plankton mercury dynamics and trophic pathways 

on mercury concentrations of top predator fish of a miningimpacted reservoir: Canadian Journal of Fisheries and 

Aquatic Sciences, v. 65, p. 2351–2366. 

Ulberg, A.L., and Risch, M.R., 2008, Total mercury and 

methylmercury in Indiana streams: U.S. Geological Survey 

Scientific Investigations Report 2008–5176, 76 p.

U.S. Army Corps of Engineers, 2014, U.S. Army Corps 

of Engineers, Louisville District facts about the lakes: 

accessed June 2014 http://www.lrl.usace.army.mil/Missions/

CivilWorks/WaterInformation/LakeInformation/Factsaboutthelakes.aspx.

U.S. Environmental Protection Agency, 1996, Method 1669—

Sampling ambient water for trace metals at EPA water 

quality criteria levels: Office of Water, EPA 821–R–96–008, 

36 p.

U.S. Environmental Protection Agency, 1997, Mercury 

study report to Congress, Volume VII—Characterization 

of human health and wildlife risks from mercury exposure in the United States: Office of Air Quality Planning 

and Standards and Office of Research and Development, 

EPA–452/R–97–009, 152 p.

U.S. Environmental Protection Agency, 1999, The national 

survey of mercury concentrations in fish—Data base summary, 1990–1995: Office of Water, EPA–823–R–99–014 

[variously paginated]. 

U.S. Environmental Protection Agency, 2001a, Water quality criterion for the protection of human health—Methylmercury: Office of Water, EPA–823–R–01–001, accessed 

March 2010 at http://water.epa.gov/scitech/swguidance/

standards/criteria/health/upload/2009_01_15_criteria_methylmercury_mercury-criterion.pdf.

U.S. Environmental Protection Agency, 2001b, Guidance for 

implementation and use of EPA Method 1631 for the determination of low-level mercury (40 CFR pt. 136): Office of 

Water, EPA 821–R–01–023, 78 p.

U.S. Environmental Protection Agency, 2001c, Draft Method 

1630, Methyl mercury in water by distillation, aqueous ethylation, purge and trap, and CVAFS: Washington, D.C., U.S. 

Environmental Protection Agency, EPA–821–R–01–020 

[variously paginated].

U.S. Environmental Protection Agency, 2002, Method 1631, 

Revision E—Mercury in water by oxidation, purge and trap, 

and cold vapor atomic fluorescence spectrometry: Office of 

Water, EPA–821–R–99–005, 40 p. 

U.S. Environmental Protection Agency, 2009, National lakes 

assessment—A collaborative survey of the nation’s lakes: 

Washington, D.C., Office of Water and Office of Research 

and Development, EPA 841–R–09–001, 118 p.

U.S. Environmental Protection Agency, 2010, Guidance for 

implementing the January 2001 methylmercury water 

quality criterion: Office of Science and Technology, 

EPA–823–R–09–002, accessed August 2011 at http://

water.epa.gov/scitech/swguidance/standards/criteria/health/

upload/mercury2010.pdf.

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9, available online at http://pubs.water.usgs.

gov/twri9A.

U.S. Geological Survey, 2007, Quality assurance plan for U.S. 

Geological Survey Mercury Research Laboratory: Webbased manual, accessed August 2010 at http://wi.water.usgs.

gov/mercury-lab/quality-assurance-manual.html.

U.S. Geological Survey, 2011, StreamStats: Interactive map/

database, accessed June 2011 at http://water.usgs.gov/osw/

streamstats/indiana.html.

Yeardley, R.B., Jr., Lazorchak, J.M., and Paulsen, S.G., 1998, 

Elemental fish tissue contamination in northeastern U.S. 

lakes—Evaluation of an approach to regional assessment: 

Environmental Toxicology and Chemistry, v. 17, no. 9, 

p. 1875–1884.

Zhang, L., Wright, L.P., and Blanchard, P., 2009, A review 

of current knowledge concerning dry deposition of 

atmospheric mercury: Atmospheric Environment, v. 43, 

p. 5853–5864.

Zhang, L., Blanchard, P., Gay, D.A., Prestbo, E.M., 

Risch, M.R., Johnson, D., Narayan, J., Zsolway, R., 

Holsen, T.M., Miller, E.K., Castro, M.S., Graydon, J.A., 

St. Louis, V.L., and Dalziel, J., 2012, Estimation of speciated and total mercury dry deposition at monitoring locations in eastern and central North America: Atmospheric 

Chemistry and Physics, v. 12, p. 4327–4340.
Appendix 1. Supplemental Data

Table 1–1. Reservoir-pool and tailwater mercury quality-control field blank sample data .........42

Table 1–2. Quality-control data for reservoir-pool and tailwater mercury field 

 duplicate samples..................................................................................................................42

Table 1–3. Reservoir-tailwater mercury data.......................................................................................43

Table 1–4. Hydrologic conditions at three Indiana reservoirs ..........................................................45

Table 1–5. Reservoir-pool and tailwater data for mercury, water-quality 

 characteristics, and supplementary constituents ...........................................................46

Table 1–6. Percentages of land-cover categories in reservoir drainage areas............................50

Table 1–7. Mercury wet- and dry-deposition rates and loads to reservoir 

 watersheds in Indiana .........................................................................................................50

Table 1–8. Reservoir fish-tissue sample and mercury data ..............................................................51
Table 1–1. Reservoir-pool and tailwater mercury quality-control field blank sample data. [QC, quality control; Hg, mercury; ng/L, nanogram per liter; MeHg, methylmercury; n.a., not analyzed for; <, less than] Field ID Type of QC sample USGS station ID Sample date (month/day/ year) Particulate Hg (ng/L) Dissolved Hg (ng/L)1 Particulate MeHg (ng/L) Dissolved MeHg (ng/L) Un

Hg 

FB1 Field equipment/filter blank 390034086304801 7/6/2009 <0.07 0.06 <0.01 <0.04 FB2 Field equipment/filter blank 392628084595901 7/13/2009 <0.10 0.18 <0.02 <0.04 FB3 Field equipment/filter blank 382553086420601 7/20/2009 <0.10 0.06 <0.02 <0.04 

BB1 Blank source water/bottle blank 390034086304801 7/6/2009 n.a. n.a. n.a. n.a. 

BB2 Blank source water/bottle blank 392628084595901 7/13/2009 n.a. n.a. n.a. n.a. 

BB3 Blank source water/bottle blank 382553086420601 7/20/2009 n.a. n.a. n.a. n.a. 

1Average unfiltered Hg concentration in three blank source-water samples (0.27 ng/L) exceeded average dissolved Hg concentration in field equi

filter blanks (0.10 ng/L). Unfiltered Hg concentration in blank source water exceeded dissolved Hg concentration in field equipment/filter blank for date.

Table 1–2. Quality-control data for reservoir-pool and tailwater mercury field duplicate samples.[QC, quality control; Hg, mercury; ng/L, nanogram per liter; MeHg, methylmercury; n.a., not analyzed for; RPD, relative percent difference; <, less than; ND., no relative percen

for two < values]

Field ID USGS station ID

Sample 

date 

(month/

day/ year)

Particulate Hg (ng/L) Dissolved Hg (ng/L) Particulate MeHg (ng/L) 

Sample Duplicate RPD (percent)1 Sample Duplicate RPD (percent)1 Sample Duplicate RPD (percent)1 S

Monroe 5A-R 390359086263501 7/8/2009 0.23 0.23 0.9 0.52 0.33 44.7 0.06 <0.02 100.0 <Monroe 5B-R 390359086263501 7/8/2009 2.23 2.43 8.7 1.26 1.18 6.6 0.55 0.56 2.3 

Monroe 6-R 390229086280401 7/8/2009 0.25 0.23 8.3 0.47 0.33 35.0 <0.03 <0.03 ND <Brookville 3A-R 392721084585901 7/14/2009 0.16 0.15 7.8 0.36 0.26 32.3 <0.03 <0.02 ND <Brookville 3B-R 392721084585901 7/14/2009 0.12 0.12 1.7 0.40 0.32 22.2 <0.03 <0.03 ND <Brookville 3C-R 392721084585901 7/14/2009 0.23 0.21 8.1 0.35 0.32 9.0 <0.03 <0.03 ND <Patoka 2A-R 382553086420601 7/20/2009 0.18 0.18 2.8 0.53 0.28 61.7 <0.03 <0.03 ND <

Patoka 2B-R 382553086420601 7/20/2009 0.40 0.42 3.7 0.26 0.66 87.0 0.06 0.06 0 <Patoka 2C-R 382553086420601 7/20/2009 1.10 1.02 7.3 0.49 0.44 10.8 0.33 0.29 13.2 

1Relative percent difference is the nonnegative difference of the paired duplicate sample concentrations divided by the average of the concentrations, expressed as a percentag

samples with a 0.06 concentration and a <0.02 value, the <0.02 value was set to 0.019 for calculating the RPD of 100.
Appendix 1 43

Table 1–3. Reservoir-tailwater mercury data.—Continued

[Hg, unfiltered mercury; ng/L, nanogram per liter; PHg, particulate mercury; MeHg, unfiltered methylmercury; <, less than reporting limit listed; n.d., 

not determined because PHg or MeHg was not reported]

Reservoir

Sample date 

(month/day/

year)

Season Hg 

(ng/L)1

PHg 

(ng/L)1

MeHg 

(ng/L)1

Ratio of 

PHg to Hg2

(percent)

Ratio of 

MeHg to Hg 

(percent)3

Brookville Lake 3/11/2002 Winter 0.31 0.31 <0.3 100 n.d.

6/10/2002 Spring 0.61 0.33 <0.3 54 n.d.

9/9/2002 Summer 0.32 0.10 <0.3 31 n.d.

12/16/2002 Fall 0.19 0.19 <0.3 100 n.d.

4/21/2003 Spring 0.81 0.24 <0.3 30 n.d.

7/21/2003 Summer <0.3 <0.3 <0.3 n.d. n.d.

10/20/2003 Fall 0.55 0.33 <0.3 60 n.d.

1/12/2004 Winter 1.02 0.78 <0.3 76 n.d.

9/3/2004 Summer 0.54 0.14 <0.04 26 n.d.

10/22/2004 Fall 1.02 0.61 <0.04 60 n.d.

2/25/2005 Winter 1.85 0.64 <0.04 35 n.d.

6/30/2005 Spring 0.34 0.11 <0.04 32 n.d.

9/16/2005 Summer 0.32 0.10 <0.04 31 n.d.

12/19/2005 Fall 0.24 0.07 <0.04 29 n.d.

3/17/2006 Winter 1.21 0.56 <0.04 46 n.d.

5/18/2006 Spring 0.64 0.20 <0.04 31 n.d.

9/8/2006 Summer 0.26 0.04 0.04 15 15.4

Cagles Mill Lake 2/13/2002 Winter 2.23 1.41 <0.3 63 n.d.

5/21/2002 Spring 2.34 1.51 <0.3 65 n.d.

8/14/2002 Summer 0.71 0.50 0.46 70 64.8

11/19/2002 Fall 0.95 0.71 <0.3 75 n.d.

3/11/2003 Winter 3.34 2.17 <0.3 65 n.d.

6/17/2003 Spring 1.73 0.40 <0.3 23 n.d.

9/23/2003 Summer 1.83 1.31 0.32 72 17.5

12/16/2003 Fall 1.74 1.59 <0.3 91 n.d.

3/23/2004 Winter 1.31 1.31 <0.3 100 n.d.

8/31/2004 Summer 1.36 0.99 0.32 73 23.5

10/13/2004 Fall 1.17 0.85 0.12 73 10.3

3/4/2005 Winter 3.26 0.81 <0.04 25 n.d.

6/6/2005 Spring 2.18 1.22 0.14 56 6.4

9/2/2005 Summer 2.32 0.15 0.57 6 24.6

12/2/2005 Fall 1.39 0.65 <0.04 47 n.d.

3/3/2006 Winter 1.67 0.77 <0.04 46 n.d.

5/8/2006 Spring 1.94 1.00 0.06 52 3.1

8/21/2006 Summer 1.56 1.25 0.23 80 14.7

1

 Concentrations in italics were higher than the method detection limit and lower than the reporting limit.

2

 Ratio of particulate Hg to unfiltered Hg, multiplied by 100.

3

 Ratio of unfiltered MeHg to unfiltered Hg, multiplied by 100.
44 Mercury and Methylmercury in Reservoirs in Indiana

Table 1–3. Reservoir-tailwater mercury data.—Continued

[Hg, unfiltered mercury; ng/L, nanogram per liter; PHg, particulate mercury; MeHg, unfiltered methylmercury; <, less than reporting limit listed; n.d., 

not determined because PHg or MeHg was not reported]

Reservoir

Sample date 

(month/day/

year)

Season Hg 

(ng/L)1

PHg 

(ng/L)1

MeHg 

(ng/L)1

Ratio of 

PHg to Hg2

(percent)

Ratio of 

MeHg to Hg 

(percent)3

J.E. Roush Lake 4/22/2002 Spring 5.35 4.22 0.14 79 2.6

7/8/2002 Summer 2.06 1.31 0.24 64 11.7

10/21/2002 Fall 1.58 1.40 <0.3 89 n.d.

1/13/2003 Winter 5.82 3.61 0.26 62 4.5

5/19/2003 Spring 3.11 <0.3 <0.3 n.d. n.d.

8/18/2003 Summer 5.50 3.92 0.66 71 12.0

2/23/2004 Winter 12.62 9.22 0.14 73 1.1

8/26/2004 Summer 1.48 1.08 0.13 73 8.8

10/25/2004 Fall 1.24 0.89 0.08 72 6.5

3/7/2005 Winter 7.66 4.04 0.13 53 1.7

6/20/2005 Spring 2.59 0.91 0.40 35 15.4

8/29/2005 Summer 2.67 2.21 0.04 83 1.5

12/5/2005 Fall 7.14 3.35 0.05 47 0.7

3/13/2006 Winter 15.00 9.15 0.14 61 0.9

5/22/2006 Spring 4.37 1.91 0.12 44 2.7

8/28/2006 Summer 2.10 1.63 0.05 78 2.4

Mississinewa Lake 4/22/2002 Spring 4.96 3.32 <0.3 67 n.d.

7/8/2002 Summer 2.89 2.42 <0.3 84 n.d.

10/21/2002 Fall 1.14 1.14 <0.3 100 n.d.

5/19/2003 Spring 5.13 2.97 <0.3 58 n.d.

8/18/2003 Summer 3.42 2.73 0.16 80 4.7

2/23/2004 Winter 6.65 4.56 0.11 69 1.7

8/26/2004 Summer 2.38 1.39 0.16 58 6.7

10/25/2004 Fall 2.31 1.99 0.05 86 2.2

3/7/2005 Winter 1.74 0.73 0.05 42 2.9

6/20/2005 Spring 1.12 0.44 0.18 39 16.1

8/29/2005 Summer 1.19 0.81 0.12 68 10.1

12/5/2005 Fall 3.25 1.09 0.05 34 1.5

3/13/2006 Winter 3.39 1.63 0.06 48 1.8

5/22/2006 Spring 3.33 1.24 0.06 37 1.8

8/28/2006 Summer 1.38 0.69 0.09 50 6.5

1

 Concentrations in italics were higher than the method detection limit and lower than the reporting limit.

2

 Ratio of particulate Hg to unfiltered Hg, multiplied by 100.

3

 Ratio of unfiltered MeHg to unfiltered Hg, multiplied by 100.
Appendix 1 45

Table 1–4. Hydrologic conditions at three Indiana reservoirs.

[ft, elevation in feet (National Geodetic Vertical Datum 1929) at 0600 or 0700; °C, degree Celsius; ft3/s, cubic feet per 

second; in., inch in previous 24 hours]

Reservoir Date 

(month/day/year)

Daily pool 

elevation 

(ft)

Tailwater 

temperature 

(°C)

Tailwater 

discharge 

(ft3

/s)

Precipitation 

(in.)

Brookville Lake 7/13/2009 748.17 17.1 181 0

7/14/2009 748.13 17.1 104 0

7/15/2009 748.12 16.9 72 0

7/16/2009 748.12 17.0 72 0

7/17/2009 748.09 17.1 72 0

Monroe Lake 7/6/2009 538.33 21.7 50 0

7/7/2009 538.35 21.3 200 0

7/8/2009 538.36 20.1 200 0.43

7/9/2009 538.36 20.5 200 0.18

7/10/2009 538.33 20.5 200 0.13

Patoka Lake 7/20/2009 537.48 26.7 200 0

7/21/2009 537.43 27.2 200 0

7/22/2009 537.45 26.7 200 1.27

7/23/2009 537.58 26.2 50 1.76

7/24/2009 537.59 26.4 50 0
Table 1–5. Reservoir-pool and tailwater data for mercury, water-quality characteristics, and supplementary constituents. [m, meter; Hg, mercury; ng/L, nanogram per liter; whole water, sum of particulate and dissolved (nondetection assumed to be zero); MeHg, methylmercury; μS/cm; microsiemens per centimeter; mg/L, milligram per lCelsius; NRTU, nephelometric turbidity ratio unit; n.a. not applicable (depth-integrated sample); <, less than reporting limit or percentage listed; n.d., not determined because particulate and dissolved MeHg were not d

Brookville Lake Sample ID Sample date Sample depth (m) Particulate Hg (ng/L) Dissolved Hg (ng/L) Whole-water Hg (ng/L) Ratio of particulate Hg to Hg1 Particulate MeHg (ng/L) Dissolved MeHg (ng/L) Whole-water MeHg (ng/L) Ratio of dissolved MeHg to Hg2 

1 7/17/2009 n.a. <0.10 0.31 0.31 <29 <0.03 <0.04 <0.04 n.d. 

2A 7/13/2009 3.05 0.16 0.60 0.76 21 <0.03 <0.04 <0.04 n.d. 2B 7/13/2009 10.67 <0.10 0.43 0.33 <27 <0.02 <0.04 <0.04 n.d. 2C 7/13/2009 22.86 <0.10 0.33 0.43 <21 <0.03 <0.04 <0.04 n.d. 3A 7/14/2009 3.05 0.16 0.36 0.52 30 <0.03 <0.04 <0.04 n.d. 3B 7/14/2009 12.19 0.12 0.40 0.52 24 <0.03 <0.04 <0.04 n.d. 3C 7/14/2009 22.86 0.23 0.35 0.58 39 <0.03 <0.04 <0.04 n.d. 

4 7/15/2009 0.91 1.00 0.29 1.29 77 <0.03 <0.04 <0.04 n.d. 

5A 7/15/2009 6.1 0.26 0.37 0.63 42 <0.03 <0.04 <0.04 n.d. 

5B 7/15/2009 9.14 0.19 0.37 0.56 33 <0.03 <0.04 <0.04 n.d. 

6A 7/15/2009 3.05 0.19 0.23 0.42 46 <0.03 <0.04 <0.04 n.d. 

6B 7/15/2009 6.1 0.17 0.29 0.46 37 <0.03 <0.04 <0.04 n.d. 

6C 7/15/2009 12.19 0.45 0.34 0.79 57 <0.03 <0.04 <0.04 n.d. 

7A 7/16/2009 4.57 0.21 0.31 0.52 41 <0.03 <0.04 <0.04 n.d. 

7B 7/16/2009 7.62 0.82 0.29 1.11 74 <0.02 <0.04 <0.04 n.d. 

8 7/16/2009 1.22 1.57 0.34 1.91 82 0.07 0.06 0.13 18 

Sample 

ID

pH 

(standard 

unit)

Specific 

conductance 

(μS/cm)

Dissolved 

oxygen 

(mg/L)

Water 

temperature 

(°C)

Turbidity 

(NRTU)

Suspended 

sediment 

(mg/L)

Dissolved 

sulfate 

(mg/L)

Particulate 

carbon 

(mg/L)

Particulate 

organic 

carbon (mg/L)

Dissolved 

organic 

carbon (mg/L)

To

1 7.9 479 9.3 16.9 1.5 <15 25.5 0.2 0.2 3.2 

2A 8.4 423 9.5 25.2 2 <15 26.1 1.3 1.24 3.3 

2B 7.7 479 0.4 18.6 2 <15 26.1 0.2 0.22 3.8 

2C 7.7 478 1.3 12.0 1 <15 25.3 0.2 0.18 3.8 

3A 8.4 419 10.0 25.1 3 <15 25.6 1.4 1.42 3.4 

3B 7.5 482 0.5 17.0 2 <15 25.7 3.6 3.58 3.1 

3C 7.6 483 0.6 12.3 4 <15 25.6 0.4 0.40 3.2 

4 8.3 416 9.1 25.3 19 18 25.5 2.5 2.47 3.4 

5A 7.9 431 5.4 24.2 7 <15 25.6 0.6 0.60 3.4 

5B 7.4 480 0.4 19.8 4 <15 24.8 0.6 0.56 3.1 

6A 8.2 426 9.0 25.0 3 <15 25.6 1.6 1.60 3.5 

6B 7.5 445 1.6 23.7 3 <15 25.7 1 0.98 3.3 

6C 7.4 496 0.4 17.0 8 <15 24.0 0.8 0.80 3.5 

7A 8.2 423 9.6 25.0 5 <15 25.8 1.4 1.41 3.3 

7B 7.4 491 0.6 26.8 15 <15 26.2 1.4 1.41 3.3 

8 8.1 699 7.7 21.8 16 19 36.8 1 1.03 2.4 

1 Ratio of particulate Hg to whole-water Hg concentration, multiplied by 100. For particulate Hg concentrations <0.10 ng/L, the ratio was computed with particulate Hg set to 0.09 ng/L and the ratio of particulate Hg to Hg was d2 Ratio of dissolved MeHg to dissolved Hg concentration, multiplied by 100. For dissolved MeHg concentrations <0.04 ng/L, the ratio was computed with dissolved MeHg set to 0.03 ng/L and the ratio of dissolved MeHg to Hg 3 Ratio of whole-water MeHg to whole-water Hg concentration, multiplied by 100.
Table 1–5. Reservoir-pool and tailwater data for mercury, water-quality characteristics, and supplementary constituents.—Continued[m, meter; Hg, mercury; ng/L, nanogram per liter; whole water, sum of particulate and dissolved (nondetection assumed to be zero); MeHg, methylmercury; μS/cm; microsiemens per centimeter; mg/L, milligram per lCelsius; NRTU, nephelometric turbidity ratio unit; n.a. not applicable (depth-integrated sample); <, less than reporting limit or percentage listed; n.d., not determined because particulate and dissolved MeHg were not d

Monroe Lake

Sample 

ID

Sample 

date

Sample 

depth 

(m)

Particulate 

Hg (ng/L)

Dissolved Hg 

(ng/L)

Whole-water 

Hg (ng/L)

Ratio of 

particulate Hg 

to Hg1

Particulate 

MeHg (ng/L)

Dissolved 

MeHg (ng/L)

Whole-water 

MeHg (ng/L)

Ratio of 

dissolved 

MeHg to Hg2

1 7/10/2009 n.a. 1.06 0.86 1.92 55 0.08 0.48 0.56 56 

2A 7/6/2009 3.05 0.17 0.32 0.49 35 <0.02 <0.04 <0.04 n.d. 2B 7/6/2009 7.01 0.69 0.55 1.24 56 0.08 0.12 0.20 22 

2C 7/6/2009 8.23 1.79 1.12 2.91 61 0.25 0.70 0.95 63 

3A 7/7/2009 3.05 0.15 0.27 0.42 36 <0.03 0.05 0.05 19 

3B 7/7/2009 7.01 0.92 0.49 1.41 65 0.11 0.12 0.23 24 

3C 7/7/2009 7.92 3.12 1.10 4.22 74 0.49 0.70 1.19 64 

4A 7/7/2009 3.05 0.18 0.30 0.48 37 <0.03 <0.04 <0.04 n.d. 

4B 7/7/2009 5.49 0.30 0.28 0.58 51 0.03 <0.04 0.03 <11 4C 7/7/2009 7.92 3.47 1.37 4.84 72 0.57 0.80 1.37 58 

5A 7/8/2009 4.57 0.23 0.52 0.75 30 0.06 <0.04 0.06 <6 

5B 7/8/2009 10.67 2.23 1.26 3.49 64 0.55 0.73 1.28 58 

6 7/8/2009 1.22 0.25 0.47 0.72 35 <0.03 <0.04 <0.04 n.d. 

7A 7/9/2009 3.05 0.85 0.46 1.31 65 0.19 <0.04 0.19 <7 

7B 7/9/2009 7.62 1.31 0.81 2.13 62 <0.03 0.16 0.16 20 

8 7/9/2009 0.30 1.41 0.66 2.07 68 0.06 <0.04 0.06 <5 

9 7/9/2009 0.46 2.18 0.57 2.75 79 <0.03 0.06 0.06 11 

Sample 

ID

pH 

(standard 

unit)

Specific 

conductance 

(μS/cm)

Dissolved 

oxygen 

(mg/L)

Water 

temperature 

(°C)

Turbidity 

(NRTU)

Suspended 

sediment 

(mg/L)

Dissolved 

sulfate 

(mg/L)

Particulate 

carbon 

(mg/L)

Particulate 

organic 

carbon (mg/L)

Dissolved 

organic 

carbon (mg/L)

To

1 6.8 129 5.9 21.3 13 <15 14.8 1.1 1.10 3.8 

2A 7.5 116 7.6 25.0 2 <15 18.2 0.6 0.60 3.3 

2B 7.0 117 7.0 24.3 5 <15 17.5 0.9 0.89 3.7 

2C 6.8 122 4.1 19.5 14 <15 14.8 1.0 0.98 3.9 

3A 7.5 116 7.5 25.1 3 <15 18.1 0.9 0.89 3.6 

3B 7.0 124 5.5 22.0 6 <19 17.4 0.8 0.78 3.5 

3C 6.6 138 3.7 19.3 27 38 14.0 1.6 1.54 4.4 

4A 7.6 116 7.4 25.0 4 <15 17.8 0.9 0.92 3.8 

4B 6.9 135 5.7 22.5 5 <15 17.6 0.6 0.58 4.1 

4C 6.7 146 4.2 20.0 40 40 13.3 1.9 1.85 4.6 

5A 7.4 118 9.0 24.8 6 <15 17.5 0.7 0.72 3.2 

5B 6.7 147 3.9 18.1 31 36 13.5 1.5 1.44 4.4 

6 8.1 120 10.7 26.6 6 <15 17.6 1.2 1.14 3.5 

7A 7.2 129 11.0 23.9 25 21 16.5 1.0 1.00 3.9 

7B 6.8 169 8.5 21.5 27 21 14.7 1.1 1.10 4.0 

8 7.2 170 12.1 24.8 50 44 17.7 3.0 2.95 3.9 

9 7.2 130 15.0 27.2 30 34 17.4 2.0 1.99 4.9 

1 Ratio of particulate Hg to whole-water Hg concentration, multiplied by 100. For particulate Hg concentrations <0.10 ng/L, the ratio was computed with particulate Hg set to 0.09 ng/L and the ratio of particulate Hg to Hg was d2 Ratio of dissolved MeHg to dissolved Hg concentration, multiplied by 100. For dissolved MeHg concentrations <0.04 ng/L, the ratio was computed with dissolved MeHg set to 0.03 ng/L and the ratio of dissolved MeHg to Hg 3 Ratio of whole-water MeHg to whole-water Hg concentration, multiplied by 100.
Table 1–5. Reservoir-pool and tailwater data for mercury, water-quality characteristics, and supplementary constituents.—Continued [m, meter; Hg, mercury; ng/L, nanogram per liter; whole water, sum of particulate and dissolved (nondetection assumed to be zero); MeHg, methylmercury; μS/cm; microsiemens per centimeter; mg/L, milligram per lCelsius; NRTU, nephelometric turbidity ratio unit; n.a. not applicable (depth-integrated sample); <, less than reporting limit or percentage listed; n.d., not determined because particulate and dissolved MeHg were not d

Patoka Lake Sample ID Sample date Sample depth (m) Particulate Hg (ng/L) Dissolved Hg (ng/L) Whole-water Hg (ng/L) Ratio of particulate Hg to Hg1 Particulate MeHg (ng/L) Dissolved MeHg (ng/L) Whole-water MeHg (ng/L) Ratio of dissolved MeHg to Hg2 

1 7/24/2009 n.a. 0.33 0.19 0.52 63 0.03 <0.04 0.03 <16 

2A 7/20/2009 3.05 0.18 0.53 0.71 25 <0.03 <0.04 <0.03 n.d. 2B 7/20/2009 7.62 0.40 0.26 0.66 61 0.06 <0.04 0.06 <12 

2C 7/20/2009 12.19 1.10 0.49 1.59 69 0.33 0.28 0.61 57 

3A 7/21/2009 3.05 0.21 0.21 0.42 49 <0.02 <0.04 <0.02 n.d. 3B 7/21/2009 6.10 0.22 0.21 0.43 51 <0.02 <0.04 <0.02 n.d. 3C 7/21/2009 12.19 1.45 0.45 1.90 76 0.37 0.37 0.74 82 

4A 7/21/2009 3.05 0.23 0.22 0.45 52 <0.03 <0.04 <0.03 n.d. 

4B 7/21/2009 9.14 1.02 1.07 2.09 49 0.59 0.64 1.23 60 

5 7/21/2009 1.52 0.28 0.29 0.57 49 <0.03 <0.04 <0.03 n.d. 

6A 7/22/2009 3.05 0.34 0.18 0.52 65 <0.02 <0.04 <0.02 n.d. 

6B 7/22/2009 7.62 0.64 0.30 0.94 68 0.16 0.12 0.28 40 

6C 7/22/2009 13.72 1.30 0.71 2.01 65 0.38 0.28 0.66 39 

7 7/22/2009 0.61 1.33 0.25 1.58 84 0.06 <0.04 0.06 <12 

8A 7/22/2009 4.57 0.69 0.17 0.86 80 0.08 <0.04 0.08 <18 

8B 7/22/2009 10.67 1.50 0.55 2.05 73 0.75 0.33 1.08 60 

9 7/23/2009 0.91 4.47 1.04 5.51 81 <0.03 <0.04 0.07 <3 

10 7/23/2009 6.10 1.54 0.29 1.83 84 <0.03 0.04 0.16 14 

11 7/23/2009 6.10 1.59 0.68 2.27 70 <0.03 0.16 0.55 24 

12 7/24/2009 4.57 0.95 0.29 1.24 77 <0.03 <0.04 <0.04 n.d. 

Sample 

ID

pH 

(standard 

unit)

Specific 

conductance 

(μS/cm)

Dissolved 

oxygen 

(mg/L)

Water 

temperature 

(°C)

Turbidity 

(NRTU)

Suspended 

sediment 

(mg/L)

Dissolved 

sulfate 

(mg/L)

Particulate 

carbon 

(mg/L)

Particulate 

organic 

carbon (mg/L)

Dissolved 

organic 

carbon (mg/L)

To

1 7.8 170 8.0 23.7 4 <15 17.5 0.8 0.75 3.1 

2A 7.9 166 7.7 24.5 3 <15 17.8 0.7 0.65 2.3 

2B 7.1 175 0.6 18.0 4 <15 17.5 1.0 1.00 2.6 

2C 7.0 189 0.6 13.8 9 21 14.2 0.8 0.74 2.9 

3A 8.2 167 8.6 25.7 3 <15 18.0 0.7 0.68 3.1 

3B 7.9 166 5.8 24.1 8 <15 17.9 0.3 0.32 3.1 

3C 7.2 192 0.7 13.9 7 20 13.5 1.3 1.33 3.0 

4A 8.3 163 8.3 25.3 1 <15 18.1 0.8 0.80 3.2 

4B 6.8 185 0.6 16.0 8 <15 12.6 0.8 0.77 3.4 

5 8.9 161 9.7 25.8 5 <15 19.1 1.5 1.48 3.1 

1 Ratio of particulate Hg to whole-water Hg concentration, multiplied by 100. For particulate Hg concentrations <0.10 ng/L, the ratio was computed with particulate Hg set to 0.09 ng/L and the ratio of particulate Hg to Hg was de2 Ratio of dissolved MeHg to dissolved Hg concentration, multiplied by 100. For dissolved MeHg concentrations <0.04 ng/L, the ratio was computed with dissolved MeHg set to 0.03 ng/L and the ratio of dissolved MeHg to Hg 3 Ratio of whole-water MeHg to whole-water Hg concentration, multiplied by 100.
Table 1–5. Reservoir-pool and tailwater data for mercury, water-quality characteristics, and supplementary constituents.—Continued[m, meter; Hg, mercury; ng/L, nanogram per liter; whole water, sum of particulate and dissolved (nondetection assumed to be zero); MeHg, methylmercury; μS/cm; microsiemens per centimeter; mg/L, milligram per lCelsius; NRTU, nephelometric turbidity ratio unit; n.a. not applicable (depth-integrated sample); <, less than reporting limit or percentage listed; n.d., not determined because particulate and dissolved MeHg were not d

Patoka Lake—continued

Sample 

ID

pH 

(standard 

unit)

Specific 

conductance 

(μS/cm)

Dissolved 

oxygen 

(mg/L)

Water 

temperature 

(°C)

Turbidity 

(NRTU)

Suspended 

sediment 

(mg/L)

Dissolved 

sulfate 

(mg/L)

Particulate 

carbon 

(mg/L)

Particulate 

organic 

carbon (mg/L)

Dissolved 

organic 

carbon (mg/L)

To

6A 7.9 170 7.7 24.5 4 <15 18.1 0.7 0.68 3.0 

6B 7.2 178 0.7 17.9 4 <15 17.7 0.6 0.59 2.5 

6C 7.1 199 0.7 13.7 12 <30 11.9 0.9 0.92 3.1 

7 7.3 165 6.4 25.1 17 21 16.4 1.2 1.24 3.5 

8A 8.0 174 7.4 24.5 8 <15 15.0 1.4 1.42 2.4 

8B 7.1 201 0.6 15.9 10 17 11.2 0.8 0.75 3.1 

9 7.2 217 5.4 21.9 88 94 22.2 2.8 2.82 3.9 

10 7.3 209 0.6 22.7 31 22 16.9 1.9 1.82 3.3 

11 7.2 237 0.6 21.2 21 25 6.3 2.5 2.49 4.0 

12 7.4 191 4.3 23.7 11 <15 12.9 1.2 1.20 3.8 

1 Ratio of particulate Hg to whole-water Hg concentration, multiplied by 100. For particulate Hg concentrations <0.10 ng/L, the ratio was computed with particulate Hg set to 0.09 ng/L and the ratio of particulate Hg to Hg was 2 Ratio of dissolved MeHg to dissolved Hg concentration, multiplied by 100. For dissolved MeHg concentrations <0.04 ng/L, the ratio was computed with dissolved MeHg set to 0.03 ng/L and the ratio of dissolved MeHg to Hg 3 Ratio of whole-water MeHg to whole-water Hg concentration, multiplied by 100.
50 Mercury and Methylmercury in Reservoirs in Indiana

Table 1–6. Percentages of land-cover categories in reservoir drainage areas.

[<, less than; km2, square kilometer]

Land-cover category1

Percentage of drainage area

Brookville 

Lake

Cagles Mill 

Lake

C.M. Harden 

Lake

Mississinewa 

Lake

Monroe 

Lake

Patoka 

Lake

J.E. Roush 

Lake

Salamonie 

Lake

Forest, shrubland2 22.5 22.8 12.9 9.1 82.4 67.2 6.1 9.4

Cultivated crops 53.1 61.4 73.0 76.3 3.6 3.8 78.6 79.6

Pasture hay 9.0 7.8 5.5 2.5 4.3 12.0 3.9 1.7

Developed3 11.9 5.5 5.8 9.6 2.2 3.9 8.0 6.9

Grassland, barren4 0.8 1.3 1.1 1.0 3.1 4.9 1.0 0.8

Open water 2.5 1.1 1.6 0.9 4.3 8.1 1.8 1.1

Wetland5 0.2 0.1 0.1 0.5 <0.1 <0.1 0.5 0.6

Drainage area (km2

) 984 761 562 2,093 1,119 440 1,867 1,443

1

 Land-cover categories derived from combining area of some land-cover classes in National Land Cover Database (Homer and others, 2004).

2

 Deciduous, evergreen, and mixed forest land-cover and shrubland classes combined.

3

 High, medium, and low intensity and open space combined.

4

 Grassland and barren land-cover classes combined.

5

 Woody and herbaceous wetland combined.

Table 1–7. Mercury wet- and dry-deposition rates and loads to reservoir watersheds in Indiana.

[km2, square kilometer; Hg, mercury; mg/m2, microgram per square meter; g, gram].

Reservoir 

watershed

Drainage 

area

(km2

)

Hg wet 

deposition 

rate1

(μg/m2

)

Hg wet 

deposition 

load2

 (g)

Percent 

forest 

cover

Forest 

cover area3

(km2

)

Hg dry 

deposition 

rate4

(μg/m2

)

Hg dry 

deposition 

load2

 (g)

Total Hg 

load5

 (g)

Total Hg 

deposition 

rate6

(μg/m2

)

Brookville Lake 984 11.5 11,318 22.5 221 16.0 3,543 14,861 15.1 

Cagles Mill Lake 761 11.5 8,757 22.8 173 17.4 3,014 11,771 15.5 

C.M. Harden Lake 562 11.5 6,463 12.9 73 17.4 1,265 7,728 13.8 

Mississinewa Lake 2,093 10.5 21,973 9.1 190 13.9 2,647 24,621 11.8 

Monroe Lake 1,119 12.5 13,986 82.4 922 16.0 14,751 28,737 25.7 

Patoka Lake 440 12.5 5,504 67.2 296 16.0 4,734 10,238 23.3 

J.E. Roush Lake 1,867 10.5 19,607 6.1 114 13.9 1,583 21,191 11.3 

Salamonie Lake 1,443 11.5 16,590 9.4 136 13.9 1,885 18,475 12.8 

1

 Value is the middle of the range, based on mean annual rate for 2001–2006.

2

 Watershed mean annual atmospheric mercury load for 2001–2006 computed as drainage area multiplied by deposition rate.

3

 Forest drainage area computed as drainage area multiplied by percent forest cover from table 1–6 (as decimal).

4

 Dry deposition rate based on 3-year mean litterfall Hg dry deposition rates for 3 sites in Indiana (Risch and others, 2012). Brookville, Monroe, and Patoka 

are based on IN21 Clifty Falls; Cagles Mill and Harden are based on IN26 Fort Harrison; and Mississinewa, J.E. Roush, and Salamonie are based on IN20 

Roush Lake.

5

 Sum of Hg wet and dry deposition loads.

6

 Total Hg deposition rate for watershed is total Hg load divided by drainage area.
Table 1–8. Reservoir fish-tissue sample and mercury data.[g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg]

Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Brookville Lake Dam end 2002 3 Lepomis macrochirus bluegill 2 113 

Dam end 2002 5 Cyprinus carpio carp 2 1,661 

Dam end 2002 4 Ictalurus punctatus channel catfish 1 721 

Dam end 2002 5 Micropterus salmoides largemouth bass 2 663 

Dam end 2002 5 Pomoxis annularis white crappie 2 207 

Dam end 2007 4 Cyprinus carpio carp 2 1,382 

Dam end 2007 1 Ictalurus punctatus channel catfish 1 1,928 

Dam end 2007 5 Micropterus salmoides largemouth bass 2 795 

Dam end 2007 3 Micropterus dolomieu smallmouth bass 2 404 

Dam end 2007 3 Sander vitreus walleye 2 631 

Quakerstown SRA 2002 5 Lepomis macrochirus bluegill 2 91 

Quakerstown SRA 2002 5 Cyprinus carpio carp 2 1,350 

Quakerstown SRA 2002 5 Micropterus salmoides largemouth bass 2 700 

Quakerstown SRA 2002 2 Micropterus salmoides largemouth bass 2 2,141 

Quakerstown SRA 2002 5 Morone chrysops white bass 2 707 

Quakerstown SRA 2007 4 Pomoxis nigromaculatus black crappie 2 271 

Quakerstown SRA 2007 2 Cyprinus carpio carp 2 1,928 

Quakerstown SRA 2007 4 Ictalurus punctatus channel catfish 1 1,023 

Quakerstown SRA 2007 3 Micropterus salmoides largemouth bass 2 602 

Quakerstown SRA 2007 4 Morone chrysops white bass 2 551 

Cagles Mill Lake Near dam 1996 4 Cyprinus carpio carp 2 957 

Near dam 1996 1 Micropterus salmoides largemouth bass 2 912 

Near dam 1996 1 Micropterus salmoides largemouth bass 2 564 

Near dam 2001 10 Lepomis macrochirus bluegill 2 123 

Near dam 2001 3 Cyprinus carpio carp 2 1,351 

Near dam 2001 1 Ictalurus punctatus channel catfish 1 1,106 

Near dam 2001 4 Micropterus salmoides largemouth bass 2 579 

Near dam 2001 1 Morone saxatilis striped bass 2 255 

Near dam 2001 2 Pomoxis annularis white crappie 2 226 

Near dam 2006 4 Lepomis macrochirus bluegill 2 83 

Near dam 2006 3 Cyprinus carpio carp 2 1,068 

Near dam 2006 1 Aplodinotus grunniens freshwater drum 2 252 

Near dam 2006 3 Micropterus salmoides largemouth bass 2 851 

Near dam 2006 2 Micropterus salmoides largemouth bass 2 323 

Near dam 2006 6 Pomoxis annularis white crappie 2 113 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued [g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg] Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Cecil M. Harden Lake Main lake 1999 3 Lepomis macrochirus bluegill 2 60 

Main lake 1999 3 Micropterus salmoides largemouth bass 2 737 

Main lake 1999 4 Micropterus salmoides largemouth bass 2 312 

Main lake 1999 1 Carpiodes cyprinus quillback 2 946 

Main lake 2004 4 Pomoxis nigromaculatus black crappie 2 159 

Main lake 2004 9 Lepomis macrochirus bluegill 2 78 

Main lake 2004 5 Cyprinus carpio carp 2 1,049 

Main lake 2004 2 Ictalurus punctatus channel catfish 1 755 

Main lake 2004 1 Ictalurus punctatus channel catfish 1 2,892 

Main lake 2004 3 Micropterus salmoides largemouth bass 2 1,314 

Main lake 2004 1 Morone saxatilis striped bass 2 2,693 

Main lake 2004 2 Morone saxatilis striped bass 2 7,201 

Main lake 2004 3 Morone chrysops white bass 2 460 

Main lake 2004 4 Pomoxis nigromaculatus black crappie 2 159 

Main lake 2004 9 Lepomis macrochirus bluegill 2 78 

Main lake 2004 5 Cyprinus carpio carp 2 1,049 

Main lake 2004 2 Ictalurus punctatus channel catfish 1 755 

Main lake 2004 1 Ictalurus punctatus channel catfish 1 2,892 

Main lake 2004 3 Micropterus salmoides largemouth bass 2 1,314 

Main lake 2004 1 Morone saxatilis striped bass 2 2,693 

Main lake 2004 2 Morone saxatilis striped bass 2 7,201 

Main lake 2004 3 Morone chrysops white bass 2 460 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued[g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg]

Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

J. Edward Roush Lake Main lake 1998 4 Cyprinus carpio carp 2 593 

Main lake 1998 5 Cyprinus carpio carp 2 1,656 

Main lake 1998 1 Cyprinus carpio carp 2 2,551 

Main lake 1998 4 Micropterus salmoides largemouth bass 2 196 

Main lake 1998 3 Pomoxis annularis white crappie 2 144 

Main lake 2004 3 Ictiobus cyprinellus bigmouth buffalo 2 1,200 

Main lake 2004 3 Cyprinus carpio carp 2 2,079 

Main lake 2004 2 Ictalurus punctatus channel catfish 1 2,850 

Main lake 2004 2 Micropterus salmoides largemouth bass 2 957 

Main lake 2004 8 Micropterus salmoides largemouth bass 2 184 

Main lake 2004 1 Sander vitreus walleye 2 600 

Main lake 2004 4 Pomoxis annularis white crappie 2 396 

Main lake 2004 9 Pomoxis annularis white crappie 2 180 

Main lake 2004 3 Ictiobus cyprinellus bigmouth buffalo 2 1,200 

Main lake 2004 3 Cyprinus carpio carp 2 2,079 

Main lake 2004 2 Ictalurus punctatus channel catfish 1 2,850 

Main lake 2004 2 Micropterus salmoides largemouth bass 2 957 

Main lake 2004 8 Micropterus salmoides largemouth bass 2 184 

Main lake 2004 1 Sander vitreus walleye 2 600 

Main lake 2004 4 Pomoxis annularis white crappie 2 396 

Main lake 2004 9 Pomoxis annularis white crappie 2 180 

Main lake 2008 3 Cyprinus carpio carp 2 2,410 

Main lake 2008 3 Cyprinus carpio carp 2 1,030 

Main lake 2008 2 Aplodinotus grunniens freshwater drum 2 403 

Main lake 2008 1 Aplodinotus grunniens freshwater drum 2 1,021 

Main lake 2008 3 Micropterus salmoides largemouth bass 2 759 

Main lake 2008 3 Micropterus salmoides largemouth bass 2 394 

Main lake 2008 5 Pomoxis annularis white crappie 2 399 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued [g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg] Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Mississinewa Lake Dam end 1998 3 Ictalurus punctatus channel catfish 1 0 

Dam end 1998 1 Micropterus dolomieu smallmouth bass 2 516 

Dam end 1998 2 Sander vitreus walleye 2 289 

Dam end 1998 3 Pomoxis annularis white crappie 2 0 

Dam end 2008 6 Lepomis macrochirus bluegill 2 92 

Dam end 2008 3 Cyprinus carpio carp 2 1,701 

Dam end 2008 3 Ictalurus punctatus channel catfish 1 1,833 

Dam end 2008 5 Micropterus salmoides largemouth bass 2 1,134 

Dam end 2008 5 Micropterus salmoides largemouth bass 2 611 

Upper end 1998 3 Micropterus salmoides largemouth bass 2 419 

Upper end 1998 3 Micropterus salmoides largemouth bass 2 901 

Red Ridge SRA 2004 5 Cyprinus carpio carp 2 1,576 

Red Ridge SRA 2004 2 Aplodinotus grunniens freshwater drum 2 996 

Red Ridge SRA 2004 5 Micropterus salmoides largemouth bass 2 639 

Red Ridge SRA 2004 5 Micropterus salmoides largemouth bass 2 834 

Red Ridge SRA 2004 6 Morone chrysops white bass 2 254 

Red Ridge SRA 2004 5 Cyprinus carpio carp 2 1,576 

Red Ridge SRA 2004 2 Aplodinotus grunniens freshwater drum 2 996 

Red Ridge SRA 2004 5 Micropterus salmoides largemouth bass 2 639 

Red Ridge SRA 2004 5 Micropterus salmoides largemouth bass 2 834 

Red Ridge SRA 2004 6 Morone chrysops white bass 2 254 

Pearson Mill Public Access 2008 2 Ictiobus cyprinellus bigmouth buffalo 2 1,588 

Pearson Mill Public Access 2008 5 Lepomis macrochirus bluegill 2 111 

Pearson Mill Public Access 2008 4 Cyprinus carpio carp 2 1,758 

Pearson Mill Public Access 2008 5 Micropterus salmoides largemouth bass 2 504 

Pearson Mill Public Access 2008 4 Micropterus salmoides largemouth bass 2 204 

Pearson Mill Public Access 2008 5 Carpiodes carpio river carpsucker 2 640 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued[g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg]

Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Monroe Lake Salt Creek Boat Ramp 1996 2 Ameiurus melas black bullhead 1 400 

Salt Creek Boat Ramp 1996 2 Cyprinus carpio carp 2 3,363 

Salt Creek Boat Ramp 1996 3 Cyprinus carpio carp 2 2,204 

Salt Creek Boat Ramp 1996 2 Micropterus salmoides largemouth bass 2 332 

Salt Creek Boat Ramp 2002 8 Lepomis macrochirus bluegill 2 97 

Salt Creek Boat Ramp 2002 3 Cyprinus carpio carp 2 2,457 

Salt Creek Boat Ramp 2002 2 Ictalurus punctatus channel catfish 1 720 

Salt Creek Boat Ramp 2002 4 Micropterus salmoides largemouth bass 2 338 

Salt Creek Boat Ramp 2002 2 Sander vitreus walleye 2 1,120 

Salt Creek Boat Ramp 2002 1 Morone chrysops white bass 2 380 

Salt Creek Boat Ramp 2002 1 Pomoxis annularis white crappie 2 784 

Dam end 1996 5 Lepomis macrochirus bluegill 2 92 

Dam end 1996 1 Micropterus salmoides largemouth bass 2 780 

Dam end 1996 3 Micropterus salmoides largemouth bass 2 339 

Dam end 1996 3 Micropterus salmoides largemouth bass 2 563 

Dam end 2002 5 Lepomis macrochirus bluegill 2 102 

Dam end 2002 3 Cyprinus carpio carp 2 1,587 

Dam end 2002 2 Micropterus salmoides largemouth bass 2 1,077 

Dam end 2002 9 Micropterus salmoides largemouth bass 2 418 

Dam end 2002 4 Lepomis megalotis longear sunfish 2 65 

Dam end 2002 2 Lepomis microlophus redear sunfish 2 121 

Dam end 2002 1 Sander vitreus walleye 2 3,175 

Pinegrove SRA 2007 9 Lepomis macrochirus bluegill 2 70 

Pinegrove SRA 2007 3 Cyprinus carpio carp 2 2,183 

Pinegrove SRA 2007 1 Ictalurus punctatus channel catfish 1 1,474 

Pinegrove SRA 2007 3 Micropterus salmoides largemouth bass 2 964 

Pinegrove SRA 2007 5 Micropterus salmoides largemouth bass 2 414 

Pinegrove SRA 2007 2 Sander vitreus walleye 2 1,418 

Pinegrove SRA 2007 2 Pomoxis annularis white crappie 2 432 

Pinegrove SRA 2007 1 Morone chrysopsxsaxatilis wiper 2 2,155 

Allens Creek SRA 2007 10 Lepomis macrochirus bluegill 2 87 

Allens Creek SRA 2007 3 Cyprinus carpio carp 2 2,901 

Allens Creek SRA 2007 3 Micropterus salmoides largemouth bass 2 2,003 

Allens Creek SRA 2007 5 Micropterus salmoides largemouth bass 2 526 

Allens Creek SRA 2007 2 Sander vitreus walleye 2 2,835 

Allens Creek SRA 2007 3 Sander vitreus walleye 2 1,729 

Allens Creek SRA 2007 3 Sander vitreus walleye 2 983 

Allens Creek SRA 2007 4 Pomoxis annularis white crappie 2 163 

Allens Creek SRA 2007 3 Morone mississippiensis yellow bass 2 155 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued [g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg] Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Patoka Lake Lick Fork Branch 1996 1 Cyprinus carpio carp 2 3,490 

Lick Fork Branch 1996 1 Cyprinus carpio carp 2 829 

Lick Fork Branch 1996 5 Micropterus salmoides largemouth bass 2 382 

Lick Fork Branch 2001 8 Lepomis macrochirus bluegill 2 53 

Lick Fork Branch 2001 3 Cyprinus carpio carp 2 2,136 

Lick Fork Branch 2001 3 Micropterus salmoides largemouth bass 2 1,247 

Lick Fork Branch 2006 2 Cyprinus carpio carp 2 2,197 

Lick Fork Branch 2006 2 Aplodinotus grunniens freshwater drum 2 556 

Lick Fork Branch 2006 5 Micropterus salmoides largemouth bass 2 869 

Lick Fork Branch 2006 1 Micropterus dolomieu smallmouth bass 2 808 

Lick Fork Branch 2006 2 Minytrema melanops spotted sucker 2 782 

Patoka River, upper end 1996 2 Micropterus salmoides largemouth bass 2 412 

Patoka River, upper end 2001 8 Lepomis macrochirus bluegill 2 47 

Patoka River, upper end 2001 3 Cyprinus carpio carp 2 2,315 

Patoka River, upper end 2001 3 Micropterus salmoides largemouth bass 2 1,493 

Patoka River, upper end 2006 5 Lepomis macrochirus bluegill 2 58 

Patoka River, upper end 2006 3 Cyprinus carpio carp 2 2,637 

Patoka River, upper end 2006 2 Ictalurus punctatus channel catfish 1 3,147 

Patoka River, upper end 2006 1 Aplodinotus grunniens freshwater drum 2 848 

Patoka River, upper end 2006 2 Micropterus salmoides largemouth bass 2 933 

Patoka River, upper end 2006 2 Micropterus salmoides largemouth bass 2 609 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.
Table 1–8. Reservoir fish-tissue sample and mercury data.—Continued[g, gram; mm, millimeter; Hg conc., mercury concentration; mg/kg, milligram per kilogram; wt., weight; bold indicates wet weight concentration >0.30 mg/kg]

Reservoir Sample location Sample date Number of fish Genus Species Common name Sample type1 Mean fish weight (g) 

Salamonie Lake Lost Bridge SRA 2004 1 Cyprinus carpio carp 2 1,814 

Lost Bridge SRA 2004 4 Ictalurus punctatus channel catfish 1 980 

Lost Bridge SRA 2004 1 Aplodinotus grunniens freshwater drum 2 487 

Lost Bridge SRA 2004 5 Micropterus salmoides largemouth bass 2 364 

Lost Bridge SRA 2004 3 Micropterus salmoides largemouth bass 2 1,125 

Lost Bridge SRA 2004 1 Pomoxis annularis white crappie 2 346 

Lost Bridge SRA 2004 6 Pomoxis annularis white crappie 2 121 

Lost Bridge SRA 2004 1 Cyprinus carpio carp 2 1,814 

Lost Bridge SRA 2004 4 Ictalurus punctatus channel catfish 1 980 

Lost Bridge SRA 2004 1 Aplodinotus grunniens freshwater drum 2 487 

Lost Bridge SRA 2004 5 Micropterus salmoides largemouth bass 2 364 

Lost Bridge SRA 2004 3 Micropterus salmoides largemouth bass 2 1,125 

Lost Bridge SRA 2004 1 Pomoxis annularis white crappie 2 346 

Lost Bridge SRA 2004 6 Pomoxis annularis white crappie 2 121 

Dam end 1998 2 Lepomis macrochirus bluegill 2 140 

Dam end 1998 4 Cyprinus carpio carp 2 2,297 

Dam end 1998 4 Cyprinus carpio carp 2 1,595 

Dam end 1998 3 Micropterus salmoides largemouth bass 2 807 

Dam end 1998 2 Micropterus salmoides largemouth bass 2 1,021 

Dam end 1998 2 Micropterus salmoides largemouth bass 2 1,215 

Dam end 1998 1 Sander vitreus walleye 2 992 

Dam end 1998 1 Morone chrysops white bass 2 554 

Dam end 1998 2 Pomoxis annularis white crappie 2 210 

Dam end 1998 12 Pomoxis annularis white crappie 2 74 

Lost Bridge SRA 2008 1 Ictiobus cyprinellus bigmouth buffalo 2 5,982 

Lost Bridge SRA 2008 3 Cyprinus carpio carp 2 3,119 

Lost Bridge SRA 2008 1 Aplodinotus grunniens freshwater drum 2 1,758 

Lost Bridge SRA 2008 3 Aplodinotus grunniens freshwater drum 2 243 

Lost Bridge SRA 2008 6 Micropterus salmoides largemouth bass 2 511 

Lost Bridge SRA 2008 4 Micropterus salmoides largemouth bass 2 300 

Lost Bridge SRA 2008 10 Pomoxis annularis white crappie 2 174 

1Sample type code: 1=skin-off fillet; 2=skin-on, scaleless fillet.


Risch and Fredericksen—Mercury and Methylmercury in Reservoirs in Indiana—Professional Paper 1813

ISSN 2330-7102 (online)

http://dx.doi.org/10.3133/pp1813