U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1780

Prepared in cooperation with the Indiana Department of Environmental Management

Mercury in Indiana Watersheds: 

Retrospective for 2001–2006
Front cover

Upper Left  Mill Creek at tailwater pool near Manhattan, Ind., USGS site 392911086550701

(photograph by Martin R. Risch, USGS)

Upper Right  Fisherman in Big Walnut Creek near Reelsville, Ind.

(photograph by Amanda L. Egler, USGS)

Middle Left  Ultra-clean sampling with depth-integrating sampler and bridge crane,

Maumee River at New Haven, Ind., USGS Site 04183000 (photograph by Martin R. Risch, USGS)

Middle Center  Boy holding big fish (from U.S. Fish and Wildlife Service, Midwest Image

Library, http://images.fws.gov)

Middle right  Low-head dam and stormwater outfall, Patoka River at Winslow, Ind.,

USGS site 03376300 (photograph by Amanda L. Egler, USGS)

Lower Left  Measuring sampling cross section in Busseron Creek near Carlisle, Ind.,

USGS site 03342500 (photograph by Amanda L. Egler, USGS)

Lower center  Bald eagle (from U.S. Fish and Wildlife Service Image Library,

http://images.fws.gov)

Lower Right  Recording field determinations of water-quality characteristics with electronic

multimeter, Sugar Creek near New Palestine, Ind., USGS site 03361650

(photograph by Amanda L. Egler, USGS)
Mercury in Indiana Watersheds: 

Retrospective for 2001–2006

By Martin R. Risch, Nancy T. Baker, Kathleen K. Fowler, Amanda L. Egler, and David C. Lampe

Prepared in cooperation with the Indiana Department of Environmental Management

U.S. Geological Survey Professional Paper 1780

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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

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

U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

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. plus appendixes.

Library of Congress Cataloging-in-Publication Data

Mercury in Indiana watersheds : retrospective for 2001-2006 / by Martin R. Risch ... [et al.].

 p. cm. -- (U.S. Geological Survey professional paper ; 1780)

At head of title: In cooperation with the Indiana Department of Environmental Management

Includes bibliographical references.

ISBN 978-1-4113-2952-2

1. Mercury--Environmental aspects--Indiana. 2. Mercury--Bioaccumulation--Indiana. 3. River sediments--Mercury 

content--Indiana. 4. Watersheds--Indiana--Environmental conditions. I. Risch, Martin R. II. Geological Survey (U.S.) 

III. Indiana. Dept. of Environmental Management. IV. Title: In cooperation with the Indiana Department of Environmental Management. V. Series: U.S. Geological Survey professional paper ; 1780. 

TD427.M4M459 2010

363.738’4--dc22

 2010034112
iii

Preface

If you are reading this report, you probably have a reason to learn more about mercury in Indiana 

watersheds. Your reason may be linked to your involvement with fishing, outdoor recreation, 

science, and resource management or to concerns about one or more of Indiana’s watersheds. 

This preface addresses those reasons to make the report relevant to you. 

If you are like many Indiana adults, you enjoy catching and perhaps eating fish from Indiana 

streams and lakes. You may have some questions about the fish you catch and that you and your 

family eat. One question may be about mercury—a colorless, flavorless metal that is known 

to be present in a very small amount in many fish. If you consult one of the annual Indiana Fish 

Consumption Advisory booklets or check online, you will learn that mercury cannot be removed 

from the fish by cutting it out or cooking it out. Health officials in Indiana have advised that some 

sizes and species of fish or fish from certain streams or lakes should be eaten infrequently or not 

at all because of the potential health risks associated with mercury in the fish. They state that 

these health risks are greatest for young children, the unborn, and new or expectant mothers, 

who may be advised to avoid some fish from Indiana streams altogether because of mercury.

Most Indiana adults participate in outdoor recreation (92 percent, according to a recent survey). 

If you enjoy boating, hiking, bird watching, nature study, hunting, or other outdoor pursuits, your 

experiences are enriched by the wildlife. You may not know that mercury can negatively affect 

the reproduction and early development of wild birds and mammals, but this problem has been 

documented by scientists. Mercury accumulates in the food chain in aquatic ecosystems so that 

creatures at the top of the food chain acquire the highest amount. Mercury also accumulates in 

forest canopies, but the mercury exposure in food chains of forest ecosystems has received less 

study than those of aquatic systems.

If you are interested in the quality of the environment, you may know some of the issues 

involving mercury. If you work in natural-resources management, environmental protection, or 

earth science, you may deal with mercury issues. Knowledge gathered by studies of mercury 

in natural systems worldwide during the past 20 years has provided a scientific basis for 

concern about effects on humans, fish, and wildlife. Findings have indicated that human activity 

has a dominant role in releasing mercury into the environment—into the air and the water. 

Experimental evidence indicates that it is the mercury most recently introduced to water, often 

from the air, which primarily enters the food chain. 

Groups of scientists have proposed a national plan to monitor the indicators of change in 

ecosystem responses to mercury contamination. The plan emphasizes the value of integrated, 

long-term monitoring for documenting progress in reducing mercury in the environment on a 

large scale, such as a state, a region, or a nation.
iv

For a statewide scale, monitoring data have been collected over a time span long enough to 

present a retrospective view about mercury in Indiana watersheds. Watersheds are the land 

areas that drain surface water. Watersheds make meaningful boundaries for grouping and 

interpreting mercury monitoring data and information about landscape characteristics, human 

activities, and natural communities. The purpose of this report is to summarize and interpret 

the occurrence of mercury in Indiana watersheds for the decade preceding 2006, primarily for 

2001–2006. Changes in the levels and distribution of mercury that result from regulatory actions 

and pollution-prevention initiatives after 2006 can be compared to this baseline. Public officials 

and interested citizens can evaluate policies and programs directed toward mercury with the 

perspective of the data and interpretations in this study.

 —M.R.R.
v

Contents

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

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

Mercury Cycling in Aquatic Ecosystems..........................................................................................2

Health Effects, Criteria, and Advisories for Mercury......................................................................4

Description of the Study Area ............................................................................................................5

Purpose and Scope ..............................................................................................................................5

Methods of Study...........................................................................................................................................6

Sources of Data.....................................................................................................................................6

Organization of Data...........................................................................................................................14

Mercury Load Calculations...............................................................................................................14

Mercury in Indiana Watersheds ...............................................................................................................19

Mercury in Streams ...........................................................................................................................19

Mercury in Fish....................................................................................................................................36

Sources of Mercury ...........................................................................................................................41

Atmospheric Mercury Deposition...........................................................................................41

Mercury Emissions to the Atmosphere..................................................................................47

Mercury in Wastewater............................................................................................................50

Land Cover..................................................................................................................................53

Summary and Conclusions.........................................................................................................................60

References ...................................................................................................................................................62

Appendix 1. Supplemental Data ................................................................................................................67

Figures

1. Diagram showing the mercury cycle in aquatic ecosystems ...............................................3

2–4. Maps showing:

2. Indiana monitoring stations for mercury in streams, with upstream

watershed boundaries, monitoring stations for mercury in precipitation,

and sampling locations for mercury in fish tissue .........................................................7

3. National Atmospheric Deposition Program Mercury Deposition Network

stations used to compute average annual total mercury concentrations

in precipitation in Indiana, and National Weather Service Cooperative

Observer Network sites used to compute average annual precipitation

in Indiana, 2001–2006 ..........................................................................................................9

4. Treatment works in Indiana with total mercury analyses of wastewatereffluent samples, 2002–2005; upstream watershed boundaries are shown

for monitoring stations on streams.................................................................................10

5. Graph showing annual emissions of mercury to the atmosphere from all

categories of sources in Indiana in 2002 and 2005 ...............................................................11
vi

6–7. Maps showing:

6. Stationary sources of mercury emissions to the atmosphere in Indiana in

2002 and 2005; upstream watershed boundaries are shown for monitoring

stations on streams ...........................................................................................................12

7. Permitted wastewater outfalls in Indiana in 2005; upstream watershed

boundaries are shown for monitoring stations on streams........................................13

8. Box plots showing distributions of unfiltered total mercury concentrations in

water samples at monitoring stations on Indiana streams, 2002–2006 .............................21

9. Graph showing average percentages of filtered and particulate total mercury

in water samples at monitoring stations on Indiana streams, 2002–2006.........................24

10. Graph and box plots showing relations of particulate total mercury concentrations in water samples to turbidity values and ranges of turbidity in water at the

time of sample collection at monitoring stations on Indiana streams, 2002–2006...........26

11. Box plots showing distributions of unfiltered and filtered total mercury concentrations in water samples at monitoring stations on Indiana streams, grouped by

daily mean streamflow category for instantaneous streamflow at time of sample

collection, 2002–2006 .................................................................................................................30

12. Map showing average annual stream yields of total mercury in watersheds

upstream from monitoring stations on Indiana streams, 2002–2006..................................32

13. Box plots showing distributions of wet-weight and dry-weight mercury concentrations in fish-tissue samples from watersheds in Indiana, 1993–2004 ...........................37

14. Isopleth map of average annual mercury wet-deposition rates, 2001–2006,

showing upstream watershed boundaries for monitoring stations on

Indiana streams ..........................................................................................................................42

15–17. Maps showing:

15. Ratios of average annual stream mercury yield to atmospheric mercury

wet -deposition loading in watersheds upstream from monitoring stations

on Indiana streams, 2001–2006........................................................................................46

16. Treatment works upstream from monitoring stations on Indiana streams,

with average total mercury concentrations in samples of wastewater

effluent, 2002–2005 ............................................................................................................51

17. Land-cover types in watersheds upstream from monitoring stations on

Indiana streams .................................................................................................................59

Tables

1. Monitoring stations on Indiana streams, 2002–2006, and upstream

drainage areas ............................................................................................................................16

2. Summary statistics for mercury concentrations in water samples from

monitoring stations on Indiana streams, 2002–2006 .............................................................20

3. Total mercury concentrations in water samples from monitoring stations on

Indiana streams, 2002–2006, with comparisons to Indiana water-quality criteria ..........22

4. Filtered total mercury and estimated particulate mercury concentrations in

water samples from monitoring stations on Indiana streams, 2002–2006 ........................25

5. Unfiltered methylmercury concentrations in water samples at

monitoring stations on Indiana streams, 2002–2006 .............................................................28
vii

6. Seasonal Kendall test for trends in unfiltered total mercury concentrations in

water samples from monitoring stations on Indiana streams, 2002–2006 ........................29

7. Average annual stream loads and yields of unfiltered total mercury and

unfiltered methylmercury in watersheds upstream from monitoring stations

on Indiana streams, 2002–2006.................................................................................................34

8. Mercury concentrations in fish-tissue samples from watersheds upstream

from monitoring stations on Indiana streams, 1993–2004....................................................38

9. Mercury concentrations in fish-tissue samples near monitoring stations on

Indiana streams, 1993–2004 ......................................................................................................40

10. Average annual atmospheric mercury wet-deposition loads and loading rates,

2001–2006, and average annual stream yields of total mercury, 2002–2006,

in watersheds upstream from monitoring stations on Indiana streams............................44

11. Atmospheric mercury species concentrations, vertical deposition velocities,

and annual dry-deposition rates in Indiana, 2004 .................................................................45

12. Annual atmospheric mercury dry-deposition and wet-deposition loading rates

and annual stream yields of total mercury in watersheds upstream from

monitoring stations on Indiana streams .................................................................................48

13. Average total mercury concentrations in grab samples of wastewater

effluent at treatment works upstream from monitoring stations on

Indiana streams, 2002–2005 ......................................................................................................52

14. Number of permitted outfalls in 2005 for watersheds upstream from monitoring

stations on Indiana streams......................................................................................................54

15. Land-cover types, by percentage of watershed drainage area and land area in

watersheds upstream from monitoring stations on Indiana streams................................56

16. Watersheds upstream from monitoring stations on Indiana streams, grouped

by upstream drainage-area size ..............................................................................................58

Appendix 1 Tables

1– 1. Correlations of mercury concentrations with instantaneous streamflow at

monitoring stations on Indiana streams, 2002–2006 .............................................................68

1– 2. Statistical values separating categories of daily average streamflow at

monitoring stations on Indiana streams, 2002–2006 .............................................................69

1–3. Annual stream loads and yields of unfiltered total mercury and unfiltered

methylmercury in watersheds upstream from monitoring stations on Indiana

streams, 2002–2006.....................................................................................................................70

1–4. Model characteristics of annual stream loads of mercury in watersheds upstream from monitoring stations on Indiana streams, 2002–2006 ......................................75

1–5. Number of stationary sources of mercury emissions to the atmosphere and

annual mercury emissions in 2002 and 2005 for watersheds upstream from

monitoring stations on Indiana streams .................................................................................76

1–6. Percentages of land-cover classes in watersheds upstream from monitoring

stations on Indiana streams......................................................................................................77
viii

Conversion Factors

Multiply By To obtain

micrometer (μm) 0.00004 inch (in.)

centimeter (cm) .3937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) .6214 mile (mi)

mile (mi) 1.609 kilometer (km)

square meter (m2) 10.76 square foot (ft2)

square kilometer (km2) .3861 square mile (mi2)

square mile (mi2) 2.590 square kilometer (km2) 

cubic meter (m3) 35.31 cubic foot (ft3)

gram (g) .03527 ounce, avoirdupois (oz)

kg (kilogram) 2.205 pound, avoirdupois (lb)

million gallons per day (Mgal/d) .04381 cubic meter per second (m3/s)

cubic feet per second (ft3/s) .02832 cubic meter per second (m3/s)

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

°F=(1.8×°C)+32

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

Concentrations of chemical constituents in water are given in nanograms per liter (ng/L).

Concentrations of chemical constituents in solids are given in milligrams per kilogram (mg/kg)

and micrograms per kilogram (μg/kg); 1 mg/kg is equivalent to 1,000 μg/kg.

Concentrations of mercury in air are given in picograms per cubic meter (pg/m3).

A kilogram is 1,000 grams.

A milligram is 0.001 gram, and 1,000 milligrams equal 1 gram.

A microgram is 0.001 milligram, and 1,000 micrograms equal 1 milligram.

A nanogram is 0.001 microgram, and 1,000 nanograms equal 1 microgram.

A picogram is 0.001 nanogram, and 1,000 picograms equal 1 nanogram.

Atmospheric mercury deposition rates, atmospheric mercury loading rates, and stream mercury

yields are given in micrograms per square meter per year (μg/m2/yr).

Stream mercury loads from watersheds and atmospheric mercury loads to watersheds are

given in grams per year (g/yr).

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

Abbreviations 

GEM Gaseous Elemental Mercury

GIS Geographic Information System

IDEM Indiana Department of Environmental Management

MDN Mercury Deposition Network

NACWA National Association of Clean Water Agencies

NADP National Atmospheric Deposition Program

NLCD National Land Cover Database

NWS National Weather Service

PHg Particulate-Bound Mercury

POTW Publicly Owned Treatment Works

RAPIDS Regional Air Pollutant Inventory Development System

RGM Reactive Gaseous Mercury

USGS U.S. Geological Survey
x

Acknowledgments

The authors are most grateful for the exceptional contribution of James Stahl, biologist with 

the Indiana Department of Environmental Management Office of Water Quality Surveys Section. 

James is the individual most responsible for the database of mercury concentrations in fish 

tissue used in this study. He provided the information in a highly organized format and supplied 

ideas for its interpretation
Mercury in Indiana Watersheds: Retrospective for 

2001–2006

By Martin R. Risch, Nancy T. Baker, Kathleen K. Fowler, Amanda L. Egler, and David C. Lampe

Abstract 

Information about total mercury and methylmercury 

concentrations in water samples and mercury concentrations 

in fish-tissue samples was summarized for 26 watersheds in 

Indiana that drain most of the land area of the State. Mercury 

levels were interpreted with information on streamflow, atmospheric mercury deposition, mercury emissions to the atmosphere, mercury in wastewater, and landscape characteristics. 

Unfiltered total mercury concentrations in 411 water 

samples from streams in the 26 watersheds had a median of 

2.32 nanograms per liter (ng/L) and a maximum of 28.2 ng/L. 

When these concentrations were compared to Indiana waterquality criteria for mercury, 5.4 percent exceeded the 12-ng/L 

chronic-aquatic criterion, 59 percent exceeded the 1.8-

ng/L Great Lakes human-health criterion, and 72.5 percent 

exceeded the 1.3-ng/L Great Lakes wildlife criterion. Mercury concentrations in water were related to streamflow, and 

the highest mercury concentrations were associated with the 

highest streamflows. On average, 67 percent of total mercury 

in streams was in a particulate form, and particulate mercury 

concentrations were significantly lower downstream from 

dams than at monitoring stations not affected by dams.

Methylmercury is the organic fraction of total mercury 

and is the form of mercury that accumulates and magnifies 

in food chains. It is made from inorganic mercury by natural 

processes under specific conditions. Unfiltered methylmercury concentrations in 411 water samples had a median of 

0.10 ng/L and a maximum of 0.66 ng/L. Methylmercury 

was a median 3.7 percent and maximum 64.8 percent of the 

total mercury in 252 samples for which methylmercury was 

reported. The percentages of methylmercury in water samples 

were significantly higher downstream from dams than at other 

monitoring stations. Nearly all of the total mercury detected in 

fish tissue was assumed to be methylmercury. 

Fish-tissue samples from the 26 watersheds had wetweight mercury concentrations that exceeded the 0.3 milligram per kilogram (mg/kg) U.S. Environmental Protection 

Agency (USEPA) methylmercury criterion in 12.4 percent of 

the 1,731 samples. The median wet-weight concentration in 

the fish-tissue samples was 0.13 mg/kg, and the maximum was 

1.07 mg/kg. A coarse-scale analysis of all fish-tissue data in 

each watershed and a fine-scale analysis of data within 5 kilometers (km) of the downstream end of each watershed showed 

similar results overall. Mercury concentrations in fish-tissue 

samples were highest in the White River watershed in southern Indiana and the Fall Creek watershed in central Indiana. 

In fish-tissue samples within 5 km of the downstream end of a 

watershed, the USEPA methylmercury criterion was exceeded 

by 45 percent of mercury concentrations from the White River 

watershed and 40 percent of the mercury concentration from 

the Fall Creek watershed. A clear relation between mercury 

concentrations in fish-tissue samples and methylmercury 

concentrations in water was not observed in the data from 

watersheds in Indiana.

Average annual atmospheric mercury wet-deposition 

rates were mapped with data at 156 locations in Indiana and 

four surrounding states for 2001–2006. These maps revealed 

an area in southeastern Indiana with high mercury wet-deposition rates—from 15 to 19 micrograms per square meter per 

year (μg/m2/yr). Annual atmospheric mercury dry-deposition 

rates were estimated with an inferential method by using 

concentrations of mercury species in air samples at three 

locations in Indiana. Mercury dry deposition-rates were 5.6 

to 13.6 μg/m2/yr and were 0.49 to 1.4 times mercury wetdeposition rates.

Total mercury concentrations were detected in 96 percent 

of 402 samples of wastewater effluent from 50 publicly owned 

treatment works in the watersheds; the median concentration 

was 3.0 ng/L, and the maximum was 88 ng/L. When these 

concentrations were compared to Indiana water-quality criteria 

for mercury, 12 percent exceeded the 12-ng/L chronic-aquatic 

criterion, 68 percent exceeded the 1.8-ng/L Great Lakes 

human-health criterion, and 81 percent exceeded the 1.3-ng/L 

Great Lakes wildlife criterion.

Annual stream mercury yields were calculated with a 

model by using the mercury concentrations in water samples 

and daily average streamflows for 2002–2006, normalized 

to the watershed drainage areas. The average annual total 

mercury stream yields ranged from 0.73 to 45.2 μg/m2/yr and 

were highest in two White River watersheds in central Indiana. 

Median methylmercury stream yield was 1.9 percent of the 

median total mercury stream yield. 
2 Mercury in Indiana Watersheds: Retrospective for 2001–2006

In most watersheds, average annual stream yields of 

total mercury were a fraction of the combined average annual 

atmospheric mercury wet-deposition and estimated annual 

dry-deposition loading rates, indicating that much of the 

stream mercury was attributable to atmospheric deposition. In 

two watersheds, average annual stream yields of total mercury 

were approximately twice the atmospheric mercury loading, 

indicating that some of the stream mercury apparently was 

not attributable to atmospheric deposition. Rather, some of the 

stream mercury yield potentially was contributed by mercury 

in wastewater discharges.

Land-cover type corresponded with the mercury levels 

in three watersheds: (1) A watershed of the White River in 

central Indiana with a high percentage of urban land cover had 

some of the highest total mercury concentrations and stream 

mercury yields. The urban land cover and numerous permitted 

wastewater outfalls with mercury in treated effluent potentially contributed mercury to this watershed. (2) A monitoring 

station on the Maumee River in northeastern Indiana, downstream from a large area of urban land cover, recorded the 

highest stream mercury concentrations. The urban land cover 

and mercury detected in treated effluent potentially contributed to the high mercury concentrations at this station. (3) A 

watershed of the Patoka River in southern Indiana with a high 

percentage of forest land cover had the highest atmospheric 

mercury dry-deposition rate. The high dry-deposition rate 

from the forest land cover potentially contributed to the high 

mercury concentrations in this watershed.

From a retrospective view, mercury concentrations in 

Indiana watersheds routinely exceeded criteria protective of 

humans and commonly exceeded criteria protective of wildlife. Atmospheric mercury wet deposition was a predominant 

factor, but not the single factor, affecting mercury in Indiana 

watersheds. Mercury in wastewater discharges and atmospheric mercury dry deposition apparently contributed a substantial part of the mercury yield from some watersheds. Dams 

and impoundments increased the percentage of methylmercury 

in downstream waters. Long-term monitoring of mercury in 

wet and dry atmospheric deposition, and in streams and reservoirs, coordinated with monitoring of mercury in fish, will be 

needed to detect whether mercury levels in Indiana watersheds 

change in the future.

Introduction

Mercury is a public-health concern and a threat to wildlife because it accumulates and magnifies in food chains. The 

State of Indiana has designated mercury as a “bioaccumulative 

chemical of concern” (Indiana Administrative Code, 2007a). 

Indiana watersheds constitute a valuable resource for water 

supply, recreation, and wildlife habitat. This report presents 

information about the geographic distribution of mercury 

in water and fish of Indiana watersheds for 2001–2006 and 

interprets factors that influence mercury concentrations and 

loads in water. During the analysis that resulted in this report, 

more than 384,000 data values were assembled and computed 

from mercury-monitoring records, mercury-source inventories, 

ancillary data, and maps of land-cover classes. This information was organized and examined for 26 watersheds that drain 

most of the land area in Indiana. 

Mercury Cycling in Aquatic Ecosystems

Mercury is a metallic element that is found worldwide, 

arising from natural sources and dispersed through human 

activity. Mercury can be released by volcanic eruptions, forest 

fires, volatilization from oceans and continents, fossil-fuel 

combustion, waste incineration, and industrial processes 

(U.S. Environmental Protection Agency, 1997). Aquatic 

and terrestrial ecosystems receive mercury from wet and 

dry atmospheric deposition (U.S. Environmental Protection 

Agency, 1997; National Research Council, 2000), and this 

deposition occurs even in remote areas (Fitzgerald and others, 

1998). In some places, discharges from stormwater-collection 

systems and from wastewater-treatment plants add mercury 

to aquatic ecosystems (National Association of Clean Water 

Agencies, 2000).

 Inorganic mercury in ecosystems can be converted to 

organic methylmercury by micro-organisms as a byproduct of 

their metabolism. Methylmercury is highly absorbable, and 

the amounts in primary producers are preserved in successively higher levels of consumers in the food chain (Munthe 

and others, 2007). After atmospheric deposition or wastewater discharge contributes inorganic mercury to surface water 

(fig. 1), mercury enters a complex cycle in which one form 

can be converted to another, as explained by Krabbenhoft 

and Rickert (1995). Inorganic mercury in the water can enter 

sediments by particle settling and later can be released into the 

water by diffusion or resuspension. Mercury in the water can 

be released back to the atmosphere by volatilization and later 

can redeposit to water. Organic carbon relates to the levels and 

mobility of mercury in water, enhancing the availability to the 

food chain (Grigal, 2002; Brigham and others, 2009; Chasar 

and others, 2009). The way mercury enters the food chain is 

not fully understood and probably varies among ecosystems. 

Sulfate-reducing bacteria, which process organic matter using 

sulfate in the environment, take up inorganic mercury and convert it to methylmercury (Morel and others, 1998). The conversion of inorganic mercury to methylmercury is important 

because methylmercury is more toxic than inorganic mercury 

and organisms require a longer time to eliminate methylmercury. Methylmercury-containing bacteria may be consumed 

by the next higher level in the food chain, or the bacteria may 

release the methylmercury to the water, where it can adsorb 

to plankton and periphyton (Bell and Scudder, 2007). Plankton are consumed by the next level in the food chain (fig. 1). 

The concentration of methylmercury magnifies in organisms 
VOLATILIZATION and

REDEPOSITION

INORGANIC MERCURY

SEDIMENTATION

METHYLATION

METHYLMERCURY FOOD-CHAIN MAGNIFICATION

ATMOSPHERIC DEPOSITION

OVERLAND RUNOFF

METHYLMERCURY

SEDIMENTATION

DEMETHYLATION

OUTFLOW WASTEWATER

DISCHARGE

STORMWATER

DISCHARGE

DRY DEPOSITION WET DEPOSITION

INORGANIC MERCURY METHYLMERCURY

METHYLATION

DEMETHYLATION

DIFFUSION and

RESUSPENSION

Introduction 3

at higher levels in the food chain. Some methylmercury can 

convert back to inorganic mercury or enter sediments by way 

of particle settling. Details of the aquatic-mercury cycle are 

still areas of active research.

Total mercury and methylmercury in water have been 

monitored in many ecosystems and are expected to be an indicator of response to changes in atmospheric mercury deposition, according to Mason and others (2005), who state that 

interpreting the response of mercury concentrations in water 

to changes in atmospheric mercury input may be difficult. 

Water concentrations can be influenced by factors unrelated 

to mercury inputs, such as variation in organic carbon and 

particulate matter. Studies have shown a correlation between 

atmospheric deposition of mercury and mercury in fish 

(Cocca, 2001) and between methylmercury in water and in 

fish that reflects changes at the base of the food chain, including a prediction that mercury-emissions reduction will rapidly 

decrease methylmercury concentrations in fish (Harris, Rudd, 

and others, 2007).

Figure 1.  The mercury cycle in aquatic ecosystems (modified from Krabbenhoft and Rickert, 1995).
4 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Health Effects, Criteria, and 

Advisories for Mercury

Very low concentrations (more than 12 ng/L) of total 

mercury in water can lead to concentrations of methylmercury 

in fish tissue that constitute a health risk. An important route 

of exposure to methylmercury for some humans and wildlife is 

eating fish from streams and lakes. Methylmercury is a potent 

neurotoxin and potential endocrine disruptor that can affect 

humans and wildlife. Infants and young children are believed 

to have a high susceptibility to the detrimental effects of methylmercury because their nervous systems are still in development (National Research Council, 2000). Adults also may risk 

adverse neurological and cardiovascular effects from methylmercury exposure (Mergler and others, 2007). Fish-eating 

mammals and birds exposed to high, environmentally relevant 

methylmercury levels can suffer reproductive and developmental impairments and reduced immunity (Scheuhammer 

and others, 2007). Populationwide effects in terrestrial wildlife 

also have been linked to mercury (Evers, 2005).

The U.S. Environmental Protection Agency (2001) 

freshwater criterion for methylmercury is based on the safe 

level for protecting human health from methylmercury in fish 

for consumption, which is a concentration of 0.3 mg/kg in fish 

tissue. The Indiana Water-Quality Standards list three criteria 

for total recoverable mercury (which is called unfiltered total 

mercury in this report and includes methylmercury). Statewide, the chronic aquatic criterion1

 for mercury is 12 ng/L to 

protect humans, animals, and aquatic life from chronic toxic 

effects (Indiana Administrative Code, 2007a). For water in 

the Great Lakes System, Indiana’s human-health criterion2 for 

mercury is 1.8 ng/L to protect humans from possible noncancer effects resulting from consumption of aquatic organisms such as fish and shellfish (Indiana Administrative Code, 

2007b). Also for water in the Great Lakes System, Indiana’s 

wildlife criterion2 for mercury is 1.3 ng/L to protect wild bird 

and mammal populations from adverse effects that may result 

from consumption of aquatic organisms (Indiana Administrative Code, 2007b).

Permitted wastewater discharges in Indiana are required 

to meet the applicable surface-water standards for mercury 

or obtain a permit variance, as of 2005.3 The mercury permit 

variance focuses on pollution prevention and source control to 

achieve mercury-discharge reductions because of a recognized 

lack of economically viable end-of-pipe treatment options 

for mercury (Indiana Department of Environmental Management, Office of Water Quality, written commun., 2006). The 

availability of a permit variance acknowledges that mercury 

has been reported at appreciable concentrations in treated 

1Criterion is a 4-day average concentration.

2Criterion is 30-day average concentration. The Great Lakes System in 

Indiana includes surface water in Lake Michigan and streams connected to 

Lake Michigan or Lake Erie.

3 Indiana Administrative Code 327 IAC 5–3.5.

wastewater, as described in this report. Also, mercury in Indiana streams includes nonpoint-source contributions, primarily 

runoff and direct input from atmospheric deposition. For reference, concentrations of mercury in precipitation in Indiana 

were greater than the 12-ng/L criterion in 47 percent of 517 

samples in 2001–2003 and in 41 percent of 441 samples in 

2004–2005; nearly all samples exceeded the 1.3-ng/L criterion 

(Risch, 2007; Risch and Fowler, 2008).

Mercury has been detected in nearly all fish-tissue 

samples collected in Indiana since 1983 (Stahl, 1997), 

and the detected mercury is assumed to be methylmercury 

(U.S. Environmental Protection Agency, 1999 and 2009; Harris, Krabbenhoft, and others, 2007). Concentrations of mercury in some fish-tissue samples have prompted State health 

officials to issue advisories that limit consumption of sport fish 

caught in Indiana streams and lakes (Indiana State Department 

of Health, 2006, 2007). The annual Indiana Fish Consumption Advisory is based on the U.S. Environmental Protection 

Agency Reference Dose4 and measured concentrations of 

mercury in fish-tissue samples collected throughout the State. 

This advisory recognizes a greater risk to some members of 

the population. The advisory can be summarized generally 

with the following statements. If advisory status is unknown, 

women (pregnant, breast feeding, or planning pregnancy) and 

children less than 15 years of age may assume that one meal 

of Indiana sport fish per month is safe. Women and children 

in this group should not eat any large carp, flathead catfish, 

walleye, sauger, or striped bass. Adult men and women not 

in the previous group may assume that one meal of Indiana 

sport fish per week is safe; however, some Indiana rivers and 

streams have “do not eat” advisories for all fish (Indiana State 

Department of Health, 2007).

According to the Indiana Department of Environmental 

Management (IDEM) (2006), mercury advisories affected 

5,010 km (3,113 mi) of streams, 164 km2 (63.5 mi2) of lakes, 

and 95 km (59 mi) of Great Lakes shoreline in Indiana as 

of 2006. Also according to the IDEM, 524 Indiana stream 

segments were classified as having impaired beneficial use 

because of fish consumption advisories for mercury. Each 

year, some 833,000 resident anglers 16 years and older 

spend 15.5 million person-days and $469 million fishing. An 

estimated 286,000 more resident anglers were 6 to 15 years 

old (U.S. Fish and Wildlife Service and U.S. Census Bureau, 

2003). On the basis of these numbers, fish consumption advisories could affect approximately one of six Indiana residents.5

A different survey (Indiana Department of Natural Resources, 

4The U.S. Environmental Protection Agency Reference Dose is 0.1 μg 

mercury per kilogram of body weight per day of exposure for women of childbearing years, nursing mothers, and all children under age 15. The Reference 

Dose is 0.3 μg mercury per kilogram of body weight per day of exposure for 

women beyond their childbearing years and adult men (Indiana State Department of Health, 2006).

5The sum of 833,000 Indiana resident anglers over 16 years in age and 

an estimated 286,000 resident anglers 6 to 15 years in age is approximately 

1.2 million Indiana anglers out of 6.3 million Indiana residents in 2006 (Indiana Business Research Center, 2009).
Introduction 5

2007) reported that 92 percent of Indiana adult respondents 

were involved in outdoor recreation in the previous year and 

52.3 percent of them participated in fishing, indicating they 

could be affected by fish consumption advisories.6

Description of the Study Area

Indiana is 92,947 km2 (35,887 mi2) in size, 38th in geographic area in the Nation. The estimated population of Indiana in 2006 was 6.3 million, 15th in the Nation, and children 

represent one-fourth of the Indiana population (Indiana Business Research Center, 2009).7

 Indiana has an extensive and 

abundant water resource that includes 57,410 km (35,673 mi) 

of rivers, 575 publicly owned lakes and reservoirs that total 

430 km2 (166 mi2), 3,290 km2 (1,270 mi2) of wetlands, and 

95 km (59 mi) of Lake Michigan shoreline (Indiana Department of Environmental Management, 2006).

The climate of Indiana is continental, influenced mainly 

by eastward-moving cold polar air masses and warm gulf air 

masses. The low-pressure centers formed by the interaction 

of these air masses are the major sources of precipitation in 

Indiana. Spring and early summer are normally the wettest 

periods of the year, as storm systems tap moisture from the 

Gulf of Mexico and travel across Indiana. Early fall is generally the driest period. Seasonal precipitation patterns vary 

statewide, particularly in the summer (when isolated thunderstorms are common) and winter (when lake-effect snows fall 

in northern Indiana). Mean annual temperature in Indiana is 

approximately 11°C (52°F) and ranges from 9.8°C (49.6°F) in 

the north to more than 12.7°C (54.8°F) in the south (Purdue 

Applied Meteorology Group, 2005). 

The statewide average annual precipitation is 107 cm 

(42 in.) and ranges from 94 cm (37 in.) in northern Indiana 

to nearly 119 cm (47 in.) for southern Indiana. Snowfall (as 

liquid) accounts for 5 to 18 cm (2 to 7 in.) of the average 

annual precipitation, with the greatest amounts of snowfall in 

northern Indiana (Morlock and others, 2004; Purdue Applied 

6

The Indiana Statewide Outdoor Recreation Plan 2006–2010 (Indiana 

Department of Natural Resources, 2007) includes results from the Indiana 

Outdoor Recreation Participation Survey in 2003–2004, which found that 

92 percent of Indiana adults responding to the survey said they were involved 

in outdoor recreation in the previous year; of that group, 52.3 percent 

participated in fishing. This survey, if representative of the state population, 

indicates approximately 4.34 million Indiana adults may participate in outdoor 

recreation (92 percent of 4.72 million adults) and approximately 2.27 million 

of these Indiana adults may participate in fishing (52.3 percent of 4.34 million)—which is approximately 48 percent of Indiana adults in 2006.

7According to the Indiana Business Research Center (2009), children 

less than 4 years in age (0.43 million) plus children 5 to 17 years in age 

(1.15 million) total 1.6 million of the 6.3 million total Indiana population 

(25.4 percent).

Meteorology Group, 2005). According to Clark (1980), 

approximately 68 percent of the mean annual precipitation in 

Indiana returns to the atmosphere through evapotranspiration, 

24 percent enters streams and lakes through surface runoff, 

and 8 percent recharges groundwater. Generally, runoff is 

greatest in areas with steep slopes and relatively impermeable 

soils, which are characteristic of much of the southern third 

of Indiana.

In this report, watersheds are used to organize data for 

interpretation. A watershed, from a water-resources standpoint, 

is the area that gathers water from precipitation and delivers 

it to a stream. All streams have watersheds from which their 

flow is derived, including the flow during dry weather that 

comes from groundwater. There are two main watersheds in 

Indiana; one drains to the Great Lakes and the other drains to 

the Mississippi River (Clark, 1980). Approximately 10 percent 

of the land area in Indiana is part of the Great Lakes watershed—Lake Michigan and Lake Erie. The Mississippi River 

watershed in Indiana consists of two parts. The Kankakee and 

Iroquois River watersheds are approximately 8 percent of the 

State land area; these rivers flow to the Illinois River and then 

to the Mississippi River. The larger part of the Mississippi 

River watershed is approximately 82 percent of the State land 

area, consisting of the Wabash River watershed, the Whitewater River watershed, and minor tributaries of the Ohio River 

watershed; these rivers all flow to the Ohio River and then to 

the Mississippi River.

Purpose and Scope

This report summarizes and interprets mercury-monitoring data and the relation to mercury-source inventories 

and land-cover classes in 26 Indiana watersheds. Although it 

includes fish-monitoring data from the decade preceding 2006, 

the focus is primarily on the period 2001–2006. This report 

presents an inquiry into factors that influence mercury levels 

in Indiana watersheds. Atmospheric mercury—monitored in 

wet deposition in Indiana—is evaluated as an input to streams. 

Mercury sources—emissions to the atmosphere and wastewater discharges—are evaluated by their location, number, 

and mercury contribution. Land-cover classes grouped as 

land-cover types are investigated for their relation to mercury 

in watersheds. The report examines whether and where the 

mercury in fish of these watersheds was related to the mercury 

in the streams.

Environmental regulators, public-health officials, and 

natural-resource managers use data about mercury in the 

environment to design policies for voluntary and regulatory 

compliance with environmental-protection objectives and to 

assess the effectiveness of these policies. This report aims to 

serve their needs while also providing information for environmental scientists and interested citizens.
6 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Methods of Study

A conceptual model was used to approach the data compilation and interpretation for this report: 

• Mercury in stream water is related to streamflow and to 

what happens in the upstream watershed—atmospheric 

deposition, mercury emissions to the atmosphere, 

discharges of mercury in wastewater, and mercury 

retention and runoff in the watershed land cover.

• Mercury in the fish is related to mercury in the stream 

water. 

In this report, a retrospective of mercury in Indiana watersheds 

is presented in the following progression: 

• Total mercury and methylmercury concentrations in 

water from streams are summarized, compared with 

water-quality criteria, and examined for geographic 

differences and temporal patterns and trends. The 

relation to streamflow is explained. Stream loads and 

yields of total mercury and methylmercury are determined. 

• The mercury concentrations in fish-tissue samples are 

summarized, compared with a water-quality criterion, 

and examined for geographic differences.

• The ways that sources of mercury potentially influence 

mercury concentrations in streams and fish from watersheds are surveyed with regard to atmospheric mercury 

deposition, mercury emissions to the atmosphere, 

discharges of mercury in wastewater, and land cover.

Sources of Data

The data used in this report can be classified as mercurymonitoring data, ancillary data, mercury-source inventories, 

and landscape characteristics. Monitoring data were compiled 

from national and state databases of water, precipitation, 

wastewater, and fish-tissue samples that had been analyzed 

for mercury. Collecting and interpreting information about 

mercury in the environment requires specialized techniques, 

tools, and knowledge. Care was taken to restrict the monitoring data to those documented to have ultraclean protocols for 

collecting, processing, and analyzing samples. These protocols 

include precautions to minimize the unintended introduction 

of mercury into the samples. The low-level mercury analysis 

techniques that were used achieved detections of mercury and 

methylmercury in water at concentrations less than 1.0 ng/L 

and concentrations in fish tissue less than 10 μg/kg. Ancillary 

data compiled for this report include streamflow and precipitation at selected locations that were used to estimate atmospheric and stream loads of mercury. Information from Federal 

and State inventories of mercury sources were obtained, and 

maps of land-cover classes were consulted to help explain 

differences in mercury levels of Indiana’s watersheds. In 

overview, the mercury-monitoring data, ancillary data, and 

mercury-source inventories include

• mercury concentrations in streams at 26 locations statewide, 2002–2006;

• instantaneous streamflow at the time of mercury 

sampling and daily average streamflow at or near these 

26 locations, 2002–2006 (ancillary data);

• mercury concentrations in weekly precipitation 

samples at nine locations in Indiana, Illinois, Kentucky, 

Wisconsin, and Ohio, 2001–2006;

• daily precipitation amounts at 151 locations in 

Indiana, Illinois, Michigan, and Ohio, 2001–2006 

(ancillary data);

• mercury concentrations in grab samples of wastewater 

from 64 publicly owned treatment works statewide, 

2002–2005; 

• mercury concentrations in fish-tissue samples from 

502 locations statewide, 1993–2004;

• annual mercury emissions to the atmosphere and locations of stationary sources statewide, 2002 and 2005; 

• locations of outfalls for permitted discharges of wastewater to streams statewide, 2005; and

• land-cover classes, 2001.

Mercury in streams.—Mercury concentrations were 

compiled for water samples collected from streams at 26 locations in a statewide network, 2002–2006 (fig. 2). The locations 

of 24 monitoring stations in the network were selected by 

the IDEM in 2002 to represent major watersheds, reservoirs, 

sources of water supply, urban wastewater discharges, special 

habitats, and areas with active and abandoned coal minelands. 

Two monitoring stations were added by the U.S. Geological 

Survey (USGS) in 2004. Twenty monitoring stations were 

located at bridges at USGS streamflow-gaging stations. The 

remaining six monitoring stations (stations 5, 6, 12, 17, 18, 

and 25) were within 2.7 km upstream or downstream from 

USGS streamflow-gaging stations. 

During 2002–2004, the IDEM statewide reconnaissance 

of trace-metal and mercury concentrations in Indiana streams 

utilized 24 monitoring stations in the network. At these 

24 stations, 3 to 4 times per year, IDEM collected grab samples of water that were analyzed for total mercury and methylmercury (Indiana Department of Environmental Management, 

Assessment Information System database, unpublished data, 

2005). During 2004–2006, the USGS mercury monitoring 
Monitoring station for mercury 

in precipitation, 2001-2006,

with station identifier

Monitoring station for mercury 

in streams, 2002-2006,

with station number

Sampling location for mercury 

in fish tissue, 1993-2004

2

24

23

22

21

20

19

17 18

8

1

9

10

12 11

14 13

15

25

5

16

6 7

4

3

MICHIGAN

ILLINOIS OHIO

KENTUCKY

INDIANA

26

IN34

IN20

IN26

IN21

IN28

IN21

22

EXPLANATION

Watershed upstream from

monitoring station

39°00'

40°00'

41°00'

87°00' 86°00' 85°00'

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

Universal Transverse Mercator projection zone 16, NAD 1983 0 25 50 MILES

0 25 50 KILOMETERS

 1. Fall Creek near Fortville

 2. Eel River near Logansport

 3.Tippecanoe River at Winamac

 4. Wildcat Creek near Lafayette

 5. Wabash River at Terre Haute

 6. Mill Creek near Manhattan

 7. White River near Centerton

 8. White River near Nora

 9. Sugar Creek at New Palestine

10. East Fork Whitewater River 

 at Brookville

11. Vernon Fork Muscatatuck River

 at Vernon

12. East Fork White River near Seymour

13. Blue River at Fredericksburg

14. Patoka River at Winslow

15. White River at Petersburg

16. Busseron Creek near Carlisle

17. Mississinewa River near Peoria

18. Wabash River near Huntington

19. Maumee River at New Haven

20. Fish Creek near Artic

21. St. Joseph River at Elkhart

22. Trail Creek at Michigan City

23. Deep River at Hobart

24. Kankakee River at Shelby

25. Wabash River at Vincennes

26. Wabash River at Mt. Carmel, Ill.

STATION NUMBERS AND NAMES

STATION NUMBERS AND NAMES

IN20 Roush Lake, Huntington

IN21 Clifty Falls, Madison

IN26 Fort Harrison, Indianapolis

IN28 Monroe Airport, Bloomington

IN34 Indiana Dunes, Porter

Methods of Study 7

Figure 2.  Indiana monitoring stations for mercury in streams, with upstream watershed boundaries, monitoring stations for mercury in

precipitation, and sampling locations for mercury in fish tissue. (Some station names are slightly shortened in the list above and in most

of the tables in this report. Full names are given in table 1.)
8 Mercury in Indiana Watersheds: Retrospective for 2001–2006

program utilized 23 of the 24 stations in the network, excluding station 26, and added new stations 15 and 25 for a total of 

25. At these 25 stations, the USGS collected water samples 

once each season, using stream-width and streamflow-integrating techniques described in Ulberg and Risch (2008). Water 

samples were analyzed for total mercury and methylmercury 

at the USGS Mercury Research Laboratory (Middleton, 

Wis.), and the data for 2004–2006 are described in Ulberg 

and Risch (2008). 

Mercury in fish.—The IDEM collected fish-tissue 

samples targeted to support the annual Fish Consumption 

Advisory that is prepared by the Indiana State Department 

of Health in collaboration with the IDEM and the Indiana 

Department of Natural Resources. The locations, species, 

sample characteristics, and total mercury concentrations for 

2,225 fish-tissue samples collected at 502 locations statewide 

(fig. 2), 1993 through 2004, were obtained from the IDEM 

(Indiana Department of Environmental Management Assessment Information System database, unpublished data, 2005). 

Mercury in precipitation.—Mercury concentrations and 

precipitation amounts in weekly samples were compiled for 

five stations in Indiana and one station each in Wisconsin, 

Illinois, Ohio, and Kentucky, 2001–2006 (fig. 3). These nine 

monitoring stations are part of the National Atmospheric 

Deposition Program (NADP) Mercury Deposition Network 

(MDN), which operated nearly 100 monitoring stations in 

North America by late 2006. At these nine stations, weekly 

composite precipitation samples were collected with automated samplers. The total mercury concentrations in the 

samples were analyzed by the MDN laboratory. Precipitation 

was measured with a recording rain gage. Mercury wet deposition (mass per unit area per time) was computed by multiplying the mercury concentration reported in each sample by the 

associated weekly precipitation. Annual mercury wet deposition was computed as the sum of the weekly mercury deposition. The study methods for Indiana also were used at the 

other four MDN stations outside Indiana. The study methods 

and data for Indiana are in Risch (2007) for 2001–2003 and 

in Risch and Fowler (2008) for 2004–2005. The data for 2006 

in Indiana and for the stations in the other four states are from 

the MDN online archive (National Atmospheric Deposition 

Program, 2007a).

Mercury in wastewater.—Data on mercury concentrations 

in treated wastewater were compiled for 64 publicly owned 

treatment works (POTWs) in Indiana, 2002–2005 (fig. 4). The 

POTW operators collected 534 grab samples of wastewater 

that were analyzed for total mercury at private laboratories 

using low-level techniques. The samples were collected as part 

of an IDEM program directed at mercury in wastewater. The 

data for mercury concentrations in wastewater were archived 

in the U.S. Environmental Protection Agency Permit Compliance System database and retrieved for this report (U.S. Environmental Protection Agency, Region 5, written commun., 

2006). Outfalls for permitted wastewater discharges, including 

all POTWs in Indiana, are part of a mercury-source inventory 

described in a subsequent section of this report.

Mercury emissions.—Information regarding stationary sources, nonpoint sources, and estimated annual mercury 

emissions to the atmosphere was summarized from the 2002 

and 2005 Regional Air Pollutant Inventory Development 

System (RAPIDS) data for Indiana (Indiana Department of 

Environmental Management, Office of Air Quality, written 

commun., 2005, 2008). The 2002 and 2005 RAPIDS data 

include emissions reported by the owner or operator of the stationary source. Emissions from electric powerplants reported 

in RAPIDS had been calculated with an emission factor (for 

the type of coal and type of electric powerplant) multiplied by 

the amount of coal used as fuel. For this report, data have been 

summarized for stationary sources reporting annual emissions 

greater than or equal to 0.045 kg (0.1 lb). 

In 2002, an estimated 4,604 kg (10,150 lb) of mercury 

was released to the atmosphere from 179 stationary sources; 

in 2005, an estimated 3,365 kg (7,418 lb) was released from 

145 stationary sources. Among all types of stationary sources, 

the highest proportions of the estimated mercury emissions in 

Indiana were from coal-fueled electric powerplants, cement 

plants, and steel mills (fig. 5). The statewide distribution of 

stationary sources and their annual mercury emissions were 

not uniform (fig. 6).

Estimated mercury emissions from nonstationary/nonpoint sources such as gasoline and diesel fuel combustion in 

motor vehicles; natural gas, fuel oil, and wood combustion 

in heating units; human cremation; and miscellaneous human 

activities were 4 percent of all mercury emissions—191 kg in 

2002 and 139 kg in 2005 (fig. 5). The mercury emissions from 

all sources in Indiana totaled 4,795 kg in 2002 and 3,504 kg 

in 2005.

Outfalls for permitted discharges.—Wastewater outfalls can discharge mercury to Indiana streams by channeling treated municipal and industrial wastewater, by diverting 

untreated stormwater runoff, and by mine dewatering. As of 

2005, according to the Permit Compliance System database 

(Indiana Department of Environmental Management, Office 

of Water Quality, written commun., 2006), Indiana had issued 

permits under the National Pollutant Discharge Elimination 

System for 5,551 active and inactive wastewater outfalls, 

including 4,231 listed as active (fig. 7). Outfalls of a major 

facility have the capacity to discharge more than 1 million 

gallons per day. As these data are used in this report, a facility 

such as a POTW, industry, or mine can have multiple outfalls. 

All of the active and inactive outfalls were included because 

the time period of the inactive status was unavailable. 

Land cover.—Landscape characteristics in Indiana were 

determined from 20 land-cover classes in the National Land 

Cover Database (NLCD) (Multi-Resolution Land Characteristics Consortium, 2001), which is based on satellite thematicmapper imagery and supplemental data compiled with a 30-m 

resolution in 2001. Information on coal mine lands, which 

include active, reclaimed, and abandoned surface coal mines 

in Indiana compiled in 2000, was used to supplement the 

NLCD (Eaton, 2002; Indiana Geological Survey, 2002). 
IN21

IN34

IL11

WI99

KY10

OH02

OHIO

INDIANA

KENTUCKY

MICHIGAN

ILLINOIS

WISCONSIN

Lake

Michigan

Lake

Erie

EXPLANATION

National AtmosphericDeposition ProgramMercury DepositionNetwork monitoringstation and identifier

M

ILLINOIS

INDIANA

IN26

IN20

IN28

IN26

87° 86° 

41°

40°

39°

88°W 86°W 84°W

42°N40°N38°N

0 50 100 Miles0 50 100 Kilometers

Figure 3.  National Atmospheric Deposition Program Mercury Deposition Network stations used to compute average annual total mercury concentraIndiana, and National Weather Service Cooperative Observer Network sites used to compute average annual precipitation in Indiana, 2001–2006.
2

24

23

22

21

20

19

18

17

8

1

9

10

11

12

13

14

15

25

5

16

6 7

4

3

26

87°00' 86°00' 85°00'

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

Universal Transverse Mercator projection zone 16, NAD 1983 0 25 50 MILES

0 25 50 KILOMETERS

39°00'

40°00'

41°00'

MICHIGAN

ILLINOIS

OHIO

KENTUCKY

INDIANA

Monitoring station for

mercury in streams,

with station number

22

EXPLANATION

Watershed upstream from

monitoring station

Treatment works with

mercury analysis

of wastewater effluent

10 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Figure 4.  Treatment works in Indiana with total mercury analyses of wastewater-effluent samples, 2002–2005 (from

U.S. Environmental Protection Agency Permit Compliance System); upstream watershed boundaries are shown for

monitoring stations on streams.
2002

2005

Mercury emissions from all sources,

in kilograms per year and percent of total

Mercury emissions from all sources,

in kilograms per year and percent of total

COAL-FUELED

ELECTRIC POWERPLANTS

(2,229) (46%)

COAL-FUELED

ELECTRIC POWERPLANTS

(2,030) (58%)

CEMENT PLANTS

(865) (18%)

STEEL MILLS

(856) (18%)

CEMENT PLANTS

(338) (10%) STEEL MILLS

(542) (15%) FOUNDRIES

(167)

(5%)

FOUNDRIES

(228) (5%)

INDUSTRY

(279) (6%)

INDUSTRY

(205) (6%)

COKE AND REFINERY

(146) (3%)

COKE (81) (2%)

NONPOINT SOURCES

(191) (4%)

NONPOINT SOURCES

(139) (4%)

Methods of Study 11

Figure 5.  Annual emissions of mercury to the atmosphere from all categories of sources in Indiana in 2002

and 2005 (from Regional Air Pollutant Inventory Development System).
2

24

23

22

21

17

8

1

9

12

13

14

15

25

5

16

6 7

4

3

26

40°

39°

87° 86° 

41°

2005

2

24

23

22

21

20

19

18

17

8

1

9

10

11

12

13

14

15

25

5

16

6 7

4

3

26

40°

39°

87° 86° 85°

41°

2002

EXPLANATION

Monitoring station formercury in streams,with station number

12

Watershed upstream frommonitoring stations 1 - 26

Stationary source ofmercury emissions

0 

0 

Base from U.S. Geological Survey digital data 1983 1:100,000Universal Transverse Mercator projection zone 16, NAD 1983

Figure 6.  Stationary sources of mercury emissions to the atmosphere in Indiana in 2002 and 2005 (from Regional Air Pollutant Development System)boundaries are shown for monitoring stations on streams.
EXPLANATION

Monitoring station for

mercury in streams,

with station number

12

Watershed upstream from

monitoring stations

Permitted wastewater

outfall

40°00'

39°00'

87°00' 86°00' 85°00'

41°00'

Wastewater outfall of a

major facility

MICHIGAN

ILLINOIS OHIO

KENTUCKY

INDIANA

0 25 50 MILES

0 25 50 KILOMETERS Base from U.S. Geological Survey digital data 1983 1:100,000

Universal Transverse Mercator projection zone 16, NAD 1983

2

24

23

22 21

20

19

17 18

8

1

9

10

12 11

13 14

15

25

5

16

6

7

4

3

26

Methods of Study 13

Figure 7.  Permitted wastewater outfalls in Indiana in 2005 (from U.S. Environmental Protection Agency Permit Compliance

System); upstream watershed boundaries are shown for monitoring stations on streams.
14 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Organization of Data

Geographic information system (GIS) software ArcGIS (Environmental Systems Research Institute, Inc., 2006) 

was used to organize the mercury data for this report. These 

data included point features and polygon features with their 

attributes. Examples of point features and their attributes are 

stream-sampling, precipitation-sampling, and fish-sampling 

sites with their mercury concentrations; and mercury-emission-source locations with their annual mercury emissions. 

Land cover is an example of a polygon feature with the attributes land-cover class and size. 

A natural, hydrologic boundary was defined to group the 

point and polygon features. The boundary was delineated with 

the GIS as the drainage area upstream from each monitoring 

station. The 26 monitoring stations (fig. 2) had upstream drainage areas that ranged from 152 km2

 at station 22 to 74,293 km2

at station 26 (table 1). The 73,919-km2 combined area of these 

26 watersheds inside the Indiana border represents approximately 79.5 percent of the land area in Indiana. Hereinafter, 

each of these upstream drainage areas is called a “watershed.” 

The locations of the monitoring stations are identified by a 

station number (1 through 26), and this station number is also 

used in places to refer to the watershed. Two characteristics of 

these watersheds were taken into account during interpretation 

of data for this study: nested watersheds and watersheds that 

extend beyond the Indiana border.

In the case of “nested” watersheds, the watershed boundaries (fig. 2) for 12 of the monitoring stations lie within the 

watershed boundaries of 5 other stations (table 1). In some 

cases, a watershed is nested within other watersheds proceeding upstream. For example, the station 26 watershed includes 

the watersheds for stations 14, 15, and 25. The watershed for 

station 25 (which is part of the station 26 watershed) includes 

the watersheds for stations 5 and 16. Further upstream, the 

watershed for station 5 (which is part of the station 25 watershed) includes the watersheds for stations 2, 3, 4, 17, and 18. 

Some of the computations for this study, such as counting 

the number of sample locations or mercury sources, have to 

account for watersheds that are nested inside other watersheds 

upstream. “Unique” watershed areas that exclude the other 

watersheds nested upstream are used for these computations 

so that sample locations or mercury sources are counted 

only once. For example, the fish-sampling sites in the unique 

watershed area of station 5 excludes the fish-sampling sites in 

the nested watersheds for stations 2, 3, 4, 17, and 18 (fig. 2). 

Continuing the example, the calculation of mean annual 

stream mercury concentration at station 5 was not affected by 

the nested watersheds because the stream mercury concentration data for station 5 (and stations 2, 3, 4, 17, and 18) were 

site specific.

The 94,624-km2 total area of the 26 watersheds in this 

study includes 20,705 km2 (approximately 22 percent of total) 

outside of Indiana. The fraction of each watershed in another 

state is in table 1. In the case of watersheds that extend beyond 

the Indiana border, data from Illinois, Ohio, or Michigan were 

obtained if they were needed and available. For example, daily 

precipitation data for computing atmospheric mercury wet 

deposition were obtained for these three other states. Some 

interpretations, however, were made without data from other 

states, but the data were qualified as such. For example, data 

for mercury concentrations in fish-tissue samples and data on 

mercury-emissions sources and wastewater outfalls were not 

obtained for other states.

Statewide map layers of the mercury-monitoring data, 

mercury-source inventories, and land-cover classes were 

aggregated by watershed boundary for summary and interpretation. The GIS was used for a spatial analysis of attributes 

of polygon features in a watershed, such as the total area of 

each land-cover class. Specific attributes for point features 

were selected with the GIS, using logical expressions, and 

made into new datasets. The GIS allowed the original and new 

datasets, grouped by watershed, to be displayed in maps for 

interpretation and illustration. The GIS also was used to create 

atmospheric mercury wet-deposition isopleth maps and to 

estimate atmospheric mercury loads to the watersheds.

Mercury Load Calculations

Mercury load, rather than mercury concentration, is the 

measure used for comparing the amount of mercury delivered from a watershed with the amount of mercury entering a 

watershed. In this report, “stream mercury load” means a mass 

of mercury, per time unit, that was delivered from a watershed 

at the downstream end. Stream mercury load is based on the 

mercury concentration in the stream and streamflow. In this 

report, “atmospheric mercury load” means a mass of mercury, 

per time unit, that entered the watershed.8 Atmospheric mercury load includes “mercury wet deposition,” which is based 

on the mercury concentration in precipitation and precipitation 

amount. Stream mercury loads can account for the case, for 

example, where large streams with higher streamflow transport higher masses of mercury than small streams with lower 

flow, although the mercury concentrations in water samples 

from the streams are similar. Atmospheric mercury loads can 

account for the case, for example, where higher masses of 

atmospheric mercury are deposited in watersheds with the 

largest areas, although the mercury concentrations in precipitation and precipitation amounts are similar in the watersheds. 

The following method was used to calculate stream mercury loads for Indiana watersheds, 2002–2006. A regression 

model for instantaneous stream mercury load was calculated 

with the program S-LOADEST (David Lorenz, U.S. Geological Survey, written commun., 2009), an adaptation of 

8Atmospheric mercury input to a watershed by precipitation is wet deposition. Atmospheric mercury also can be input to a watershed by dry deposition 

of gaseous and particulate fractions or “species.” Extensive monitoring data 

were available for mercury in precipitation, which is the reason this section 

describes the method to estimate atmospheric mercury wet-deposition loading 

rates. Mercury dry deposition data are limited for Indiana, but mercury drydeposition are discussed in the section “Atmospheric Mercury Deposition.” 
Methods of Study 15

LOADEST by Runkel and others (2004) written for S-Plus 

statistical software (Insightful Corporation, 2005). The 

regression model related the concentrations of unfiltered total 

mercury or unfiltered methylmercury from 15 to 18 quarterly 

water samples at each monitoring station during the 5-year 

period with the instantaneous streamflows at the time of 

sample collection. An option in the S-LOADEST program 

was used to rank predefined regression models applied to the 

data for each watershed, based on a set of criteria. The highest 

rank model with streamflow as the explanatory variable was 

used. The S-LOADEST program computed the intercept and 

coefficients for the equation of the regression model by means 

of the Adjusted Maximum Likelihood Estimate method. The 

daily average streamflow from the USGS streamflow-gaging 

station at or near each monitoring station (U.S Geological 

Survey, 2008) for calendar years 2002–2006 was input to the 

model. The program used the regression equation and these 

1,825 daily average streamflow values to calculate a daily flux 

of mercury. The annual stream mercury load was computed as 

the sum of the daily fluxes for 365 days. The average annual 

stream mercury load for 2002–2006 was computed as the 

average of the five annual loads. Stream mercury loads were 

not calculated for some watersheds because of insufficient 

concentration data for total mercury (stations 15, 25, and 26) 

or for methylmercury (stations 1, 4, 8, 12, 15, 20, 21, 25, 

and 26); in some other watersheds, loads were not calculated 

because streamflow records included stream-stage control 

from dam structures (stations 6, 10, 17, and 18) or flow stagnation and flow reversals (station 22). 

The stream mercury load from each watershed in grams 

per year (g/yr) was converted to “stream mercury yield” by 

dividing the load by the watershed area to give units of micrograms per square meter per year (μg/m2

/yr). Stream mercury 

yields enable watersheds of different sizes to be compared. 

The stream mercury yields for a watershed are reported in the 

same units (μg/m2/yr) as the watershed atmospheric mercury 

wet-deposition loading rate (defined later in this section). See 

the “Mercury in Streams” section of this report for a discussion of the Indiana watersheds.

The following method was used to calculate atmospheric 

mercury wet-deposition loads and loading rates to Indiana 

watersheds, 2001–2006. This method is a modification of the 

traditional method used by the NADP each year since 2003. 

In the traditional method, data were used from MDN stations 

in North America where more than 75 percent of the weekly 

samples in a year were valid. The annual mercury wet-deposition rates at these MDN stations were computed as a product 

of the annual precipitation-weighted mercury concentration 

and annual precipitation (National Atmospheric Deposition 

Program, 2007b). The NADP used GIS software to illustrate 

one interpretation of the spatial distribution of annual mercury 

wet-deposition rates in North America, based on the rates at 

the MDN stations. The GIS software applied an inverse-distance-weighing algorithm to interpolate a deposition rate for 

each cell in a map grid of North America. At least two MDN 

stations within 500 m of a grid cell were required for a rate to 

be interpolated. An isopleth map was made from the interpolated map grid. Isopleth bands generated by the GIS software 

spatially connected grid cells that had the same rates and 

represented 2-μg/m2 ranges of annual mercury wet-deposition 

rates with different colors. These NADP isopleth maps are 

widely used and served as a starting point for load calculations 

in this report.

Maps of mercury wet-deposition rates for watersheds in 

Indiana, if derived from the NADP maps, would not have the 

desired level of detail required for interpretations at a watershed scale. The number and spatial distribution of monitoring 

stations is limited, and the deposition range in each isopleth 

is broad. For this report, a more detailed map of mercury 

wet-deposition rates was made with an alternate method. This 

alternate was based on the traditional method and incorporated data from 9 MDN stations and precipitation data from 

151 National Weather Service (NWS) Cooperative Observer 

Program sites in and near Indiana (fig. 3). As in the traditional method, data from an MDN station or NWS site was 

included if more than 75 percent of the daily records per year 

were valid. 

Making the map of mercury wet-deposition rates for the 

Indiana watershed study area required four steps. First, the 

average annual precipitation-weighted total mercury concentrations for 2001–2006 were computed for nine MDN stations 

(five in Indiana and four in surrounding states, fig. 3), by use 

of weekly monitoring data from each station. GIS software 

(ArcGIS, Environmental Systems Research Institute, Inc., 

2006) was used to interpret the spatial distribution of mercury 

concentrations in the Indiana study area, based on the concentrations at the nine MDN stations. The GIS applied an inversedistance-weighing algorithm to interpolate a mercury concentration for each cell in a 2-km2

 map grid of the study area. 

Second, the average annual precipitation, 2001–2006, was 

computed with daily precipitation values from 5 MDN stations 

in Indiana and from 151 NWS sites: 126 in Indiana, 19 in 

Illinois, 4 in Ohio, and 2 in Michigan (Midwestern Regional 

Climate Center, 2007). The 25 NWS sites outside Indiana 

were in the parts of 6 watersheds that extend beyond the State 

boundary. Third, a map of the 5 MDN stations and 151 NWS 

sites was overlaid with the interpolated mercury-concentration 

map grid, and a mercury concentration was assigned to every 

NWS site. For each of the 5 MDN stations and 151 NWS sites, 

the average annual mercury concentration was multiplied by 

the average annual precipitation to obtain the average annual 

mercury wet-deposition rate. Fourth, the inverse-distanceweighing algorithm was used to interpolate the spatial distribution of average annual mercury wet-deposition rates in the 

study area, 2001–2006, on the basis of deposition rates at the 5 

MDN stations and 151 NWS sites. An isopleth map of deposition rates was made with the interpolated map grid. Isopleth 

bands generated by the GIS software spatially connected grid 

cells that had the same rates and represented 1-μg/m2 ranges of 

annual mercury wet-deposition rates with different colors.
Table 1.  Monitoring stations on Indiana streams, 2002–2006, and upstream drainage areas.—Continued [km2, square kilometer; NA, not applicable] Station number Station name Latitude1 (degrees, minutes, seconds) Longitude1 (degrees, minutes, seconds) National Water Information System station identifier USGS streamflow- gaging station identifier Total upstream drainage area (km2) Unique2 upstream drainage area (km2) 

 1 Fall Creek near Fortville, Ind. 39 57 17 85 52 03 03351500 03351500 447 447  2 Eel River near Logansport, Ind. 40 46 55 86 15 50 03328500 03328500 2,043 2,043  3 Tippecanoe River 

at Winamac, Ind.

41 02 59 86 35 57 03331753 03331753 2,438 2,438 

 4 Wildcat Creek 

near Lafayette, Ind.

40 26 26 86 49 45 03335000 03335000 2,056 2,056 

 5 Wabash River at U.S. Highway 40 

at Terre Haute, Ind.

39 28 01 87 25 13 392801087251301 03341500 31,936 21,321 

 6 Mill Creek at tailwater 

pool near Manhattan, Ind.

39 29 11 86 55 08 392911086550701 03359000 759 759 

 7 White River near Centerton, Ind. 39 29 51 86 24 02 03354000 03354000 6,324 2,728  8 White River near Nora, Ind. 39 54 38 86 06 20 03351000 03351000 3,149 3,149  9 Sugar Creek 

at New Palestine, Ind.

39 42 51 85 53 08 03361650 03361650 243 243 

10 East Fork Whitewater 

River at Brookville, Ind.

39 26 02 85 00 12 03276000 03276000 986 986 

11 Vernon Fork Muscatatuck 

River at Vernon, Ind.

38 58 35 85 37 11 03369500 03369500 512 512 
Table 1.  Monitoring stations on Indiana streams, 2002–2006, and upstream drainage areas.—Continued[km2, square kilometer; NA, not applicable]

Station 

number Station name

Latitude1

(degrees,

minutes,

seconds)

Longitude1

(degrees,

minutes,

seconds)

National Water 

Information 

System station 

identifier

USGS 

streamflowgaging 

station 

identifier

Total

upstream 

drainage 

area

(km2)

Unique2

upstream 

drainage 

area 

(km2)

12 White River at State Road 258 

near Seymour, Ind.

38 58 23 85 55 46 385823085554501 03365500 6,056 6,056 

13 Blue River 

at Fredericksburg, Ind.

38 26 02 86 11 30 03302800 03302800 732 606 

14 Patoka River 

at Winslow, Ind.

38 22 49 87 13 00 03376300 03376300 1,559 1,559 

15 White River 

at Petersburg, Ind.

38 30 39 87 17 22 03374000 03374000 28,794 14,854 

16 Busseron Creek 

near Carlisle, Ind.

38 58 27 87 25 33 03342500 03342500 591 591 

17 Mississinewa River 

at County Road 275 Eastnear Peoria, Ind.

40 43 30 85 59 09 404330085590901 03327000 2,093 2,093 

18 Wabash River 

at County Road 200 West near Huntington, Ind.

40 51 12 85 29 23 405112085292301 03323500 1,985 1,985 

19 Maumee River 

at New Haven, Ind.

41 05 06 85 01 20 04183000 04183000 5,077 5,077 

20 Fish Creek 

near Artic, Ind.

41 27 54 84 48 51 04177810 04177810 248 248 

21 St. Joseph River 

at Elkhart, Ind.

41 41 30 85 58 30 04101000 04101000 8,756 8,447 

22 Trail Creek at

 Michigan City Harbor, Ind.

41 43 22 86 54 15 04095380 04095380 152 152 
Table 1.  Monitoring stations on Indiana streams, 2002–2006, and upstream drainage areas.—Continued [km2, square kilometer; NA, not applicable] Station number Station name Latitude1 (degrees, minutes, seconds) Longitude1 (degrees, minutes, seconds) National Water Information System station identifier USGS streamflow- gaging station identifier Total upstream drainage area (km2) Unique2 upstream drainage area (km2) 

23 Deep River at Lake George outlet at Hobart, Ind. 41 32 10 87 15 25 04093000 04093000 321 321 24 Kankakee River at Shelby, Ind. 41 10 58 87 20 25 05518000 05518000 4,597 4,542 25 Wabash River at Vigo Street at Vincennes, Ind. 38 40 53 87 32 07 384156087310701 03343000 35,628 3,100 26 Wabash River at Mt. Carmel, Ill. 38 24 07 87 45 10 03377500 03377500 74,293 8,312 

1Horizontal coordinate information is referenced to the North Amercian Datum of 1983 (NAD 83).2Unique watershed areas exclude watersheds nested upstream.
Mercury in Indiana Watersheds 19

To calculate atmospheric mercury loads to the 26 watersheds, the watershed boundaries were overlaid on the isopleth 

map of average annual mercury wet-deposition rates. The 

mass of mercury in all of the grid cells within the boundary of 

each watershed was summed to yield the atmospheric mercury 

load for that watershed (in grams per year). The atmospheric 

mercury load was divided by the watershed area to provide 

an average annual atmospheric mercury wet-deposition 

loading rate for each watershed, 2001–2006 (in micrograms 

per square meter per year). See the “Atmospheric Mercury 

Deposition” section of this report for a discussion of the 

Indiana watersheds.

Mercury in Indiana Watersheds

Indiana watersheds exhibited geographic differences 

when mercury concentrations in water samples from streams, 

stream mercury yields, and mercury concentrations of fishtissue samples were compared. Watersheds also differed in the 

percentage of atmospheric mercury loading that contributed 

to stream mercury yield. Some of the geographic differences 

appear to be related to mercury emissions, wastewater discharges, and land-cover types. 

Mercury in Streams 

This section describes and compares mercury concentrations in water samples from monitoring stations in the 

statewide network, 2002–2006. Stream mercury yields from 

watersheds upstream from the monitoring stations are presented. The section concludes with a discussion of studies of 

mercury in streams by other investigators and a comparison 

with the findings for Indiana watersheds, 2002–2006.

Two groups of water samples were combined for this 

study—186 samples collected and analyzed by IDEM, 

2002–2004, and 225 samples collected and analyzed by 

USGS, 2004–2006 (table 2). The IDEM and USGS laboratories analyzed unfiltered and filtered water samples for total 

mercury and methylmercury. Comparisons of mercury concentrations in streams at the 26 monitoring locations for the 

entire time period were represented best in the determinations 

of unfiltered total mercury as compared with determinations 

of filtered total mercury, unfiltered methylmercury, or filtered 

methylmercury. There was no significant difference9 between 

the unfiltered total mercury concentrations in the IDEM and 

9A significance level (α) of 0.05 or less was used to accept a statistically 

significant difference for the statistical tests in this report, including the 

generalized Wilcoxon test, Wilcoxon rank-sum test, Kruskal-Wallis test, and 

Tukey’s test. The p-value is the significance attained by the data—the smaller 

the p-value, the lower the probability of incorrectly rejecting the hypothesis 

of no significant difference and the lower the probability that a significant 

difference arose by chance. The smaller the p-value, the more believeable the 

statistical difference.

the USGS samples (p = 0.356, generalized Wilcoxon test10). 

In contrast, concentrations of filtered total mercury, unfiltered 

methylmercury, and filtered methylmercury in the IDEM 

samples were significantly different from the USGS samples 

(p < 0.001, generalized Wilcoxon test). The difference in these 

three mercury determinations was at least in part due to the 

higher number of censored values (less than the laboratory 

reporting limits) for the samples collected by IDEM during 

2002–2004 (table 2). 

Unfiltered total mercury concentrations reported in the 

411 water samples combined from the two groups had a 

median of 2.32 ng/L, and the maximum concentration was 

28.2 ng/L (table 2). Boxplots showing the distributions of the 

unfiltered total mercury concentrations (fig. 8) indicate differences among the 26 monitoring stations that were significant (p < 0.001; Kruskal-Wallis test11). The concentrations in 

samples from station 19 (median 7.05 ng/L) were significantly 

higher than those in samples from 10 other stations (1, 2, 3, 4, 

6, 9, 10, 13, 21, and 23; Tukey’s test12). The concentrations in 

samples from station 7 (median 6.0 ng/L) were significantly 

higher than those from 9 of these 10 stations, the exception 

being station 23. The concentrations from station 14 (median 

4.58 ng/L) were significantly higher than those in samples 

from 7 of these 10 stations, the exceptions being stations 6, 13, 

and 23.

The highest unfiltered total mercury concentrations 

reported in the 411 samples are defined here as the top 10 

percent—41 samples with concentrations greater than the 90th 

percentile, 8.62 ng/L. At least one sample from 18 of the 26 

monitoring stations had an unfiltered total mercury concentration that was among the top 10 percent. Stations 7, 14, and 19 

each had five or more samples with mercury concentrations 

that were among the top 10 percent (table 3).

For reference, the 411 unfiltered total mercury concentrations were compared to the three Indiana water-quality criteria 

for total mercury. The 12-ng/L chronic-aquatic criterion was 

equaled or exceeded in 5.4 percent of samples (22 of 411), 

including at least 1 sample from 13 of the 26 monitoring stations. The 1.8-ng/L Great Lakes human-health criterion was 

equaled or exceeded in 59 percent of samples (242 of 411), 

including at least 1 sample from all of the 26 monitoring stations. The median concentration at 16 stations exceeded this 

criterion (table 3, fig. 8). The 1.3-ng/L Great Lakes wildlife 

10The generalized Wilcoxon test (Helsel, 2005) is a nonparametric procedure used to evaluate whether the distribution of data from the two groups was 

statistically different. It is a score test that assigns an estimated rank, or score, 

to each censored value. A censored value is one that is less than the laboratory reporting limit, which means either the constituent was not detected or a 

concentration was not quantified. 

11The Kruskal-Wallis rank-sum test (Helsel and Hirsch, 1995) is a nonparametric procedure used to evaluate whether the distributions of the data from 

more than two stations were different. 

12Tukey’s test (Helsel and Hirsch, 1995) is a parametric multiple-comparison test of the means of the data for each station to determine whether there is 

a significant difference in the groups of data. Tukey’s method is applicable to 

multiple comparisons of groups that are equal or unequal in size.
20 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 2.  Summary statistics for mercury concentrations in water samples from monitoring stations on Indiana

streams, 2002–2006.

[ng/L, nanogram per liter; <, less than; IDEM, Indiana Department of Environmental Management; USGS, U.S. Geological Survey; 

NA., not applicable]

Description

Unfiltered

total 

mercury

Filtered 

total

mercury

Estimated 

particulate

total 

mercury1

Unfiltered

methylmercury

Filtered

methylmercury

Percentage

of methylmercury2

Concentration

Median3 (ng/L) 2.32 0.56 1.74 0.10 0.07 3.7

Maximum (ng/L) 28.2 6.14 26.8 .66 .68 64.8

Uncensored values 410 387 387 252 129 252

Censored values4

IDEM 1 23 23 121 172 NA

USGS 0 0 0 38 109 NA

Total 1 23 23 159 281 NA

Number of samples

IDEM 186 185 185 186 185 106

USGS 225 225 225 225 225 146

Total 411 410 410 411 410 252

1Particulate mercury concentration was estimated by subtracting filtered concentration from unfiltered concentration for samples 

with both concentrations greater than the reporting limit.

2Percentage of methylmercury is the ratio of unfiltered methylmercury to unfiltered total mercury for samples with both concentrations greater than the reporting limit, expressed as a percentage.

3Medians for unfiltered and filtered total mercury and methylmercury include censored values and were computed with the Adjusted 

Maximum Likelihood Estimate procedure (Helsel, 2005) by use of statistical software (S-Plus, Tibco Software, 2008). Medians for 

estimated particulate mercury and percentage of methylmercury were computed with uncensored values.

4A censored value is one that is less than the laboratory reporting limit, which means either the constituent was not detected or a 

concentration was not quantified. A censored value is not a missing value. One IDEM sample was missing a value for filtered total 

mercury and methylmercury, which is reflected as 185 IDEM samples for those constituents, compared to 186 IDEM samples for 

unfiltered total mercury and methylmercury.

criterion was equaled or exceeded in 72.5 percent of samples 

(298 of 411), including at least 1 sample from all 26 stations 

and all of the samples from 6 stations. The median concentration at 20 stations exceeded this criterion (table 3, fig. 8). 

Three monitoring stations had high unfiltered total mercury 

concentrations:

Station 7—White River near Centerton

Station 14—Patoka River at Winslow

Station 19—Maumee River at New Haven

These three stations (fig. 2) had the most samples with concentrations higher than the 12-ng/L, 1.8-ng/L, and 1.3-ng/L 

Indiana water-quality criteria, the highest maximum concentrations, and the most samples with concentrations higher than 

the 90th percentile (table 3). 

On average, more of the total mercury in the water samples was in a particulate form than a dissolved form (fig. 9). 

The dissolved total mercury is the filtered total mercury concentration measured in water passed through a 0.7-micrometer (μm) nominal pore-size filter. Particulate total mercury 

concentrations were determined with uncensored values by 

subtracting filtered concentrations from unfiltered concentrations (n = 387). The percentage of particulate total mercury is 

the ratio of the particulate total mercury concentration to the 

corresponding unfiltered total mercury concentration. 

For all stations combined, the average particulate total 

mercury values were 2.93 ng/L and 67 percent. The highest 

average particulate total mercury concentration was 7.35 ng/L 

in samples from station 7 (table 4); these samples had 
x

x

o

xx

oo

xx

xx

xx

o

x

o

x

oo

x

oo

x

x

o

x

oo

xx

x

x

x

x

o

x o

o

o

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

25201510

50

UNFILTERED TOTAL MERCURY CONCENTRATION,

IN NANOGRAMS PER LITER

EXPLA

x

o

Whisker includvalues within o75th percentile Median (50th 25th percentile Whisker includvalues within oUpper detachethan two steps Upper outside one to two ste

(Box height is variatiovalues, also called the one step equals 1.5 ti

Indiana watwildlife crite

Indiana watcriterion (12 

18 Number of sa

18 18 18 18 18 18 18 18 17 17 17 17 17 17 9 17 15 16 16 15 16 15 16 15 9 6

S

T

R

E

A

M-M

O

NIT

O

RIN

G-S

T

A

TIO

N

N

U

M

B

E

R

Indiana wathuman heal

Figure 8.  Distributions of unfiltered total mercury concentrations in water samples at monitoring stations on Indiana streams, 2002–2006. Locations stations are shown on figure 2.
22 Mercury in Indiana Watersheds: Retrospective for 2001–2006

88 percent average particulate total mercury. The percentage 

of particulate total mercury was highest in samples from station 26 (90 percent). The lowest average particulate total mercury concentration was 0.28 ng/L in samples from station 10, 

which is downstream from a dam. For all stations combined, 

the average filtered total mercury values were 0.91 ng/L and 

33 percent. The highest average filtered total mercury concentration was 2.28 ng/L in samples from station 18, downstream 

from a dam; these samples had 39 percent average filtered 

mercury (table 4). The percentage of average filtered total 

mercury was highest in samples from station 10 (63 percent). 

Other investigators have reported a positive correlation 

between mercury concentrations in water and suspended sediment (Brigham and others, 2009; Scudder and others, 2009). 

Suspended-sediment concentrations were not analyzed in the 

water samples analyzed for mercury during 2002–2006, so 

turbidity is used in this report as a qualitative indication of the 

level of suspended sediment. Turbidity measures the intensity of light scattering caused by suspended solids in a water 

sample (Wilde and Gibs, 1988). Suspended solids that affect 

turbidity include sediment particles, fine organic and inorganic 

matter, soluble colored organic compounds, plankton, and 

Table 3.  Total mercury concentrations in water samples from monitoring stations on Indiana streams, 2002–2006, with comparisons to

Indiana water-quality criteria.—Continued

[>, greater than; ng/L, nanogram per liter]

Station 

number Station name

Number 

of 

samples

Median 

concentration2

(ng/L)

Maximum 

concentration 

(ng/L)

Samples with 

concentration3

> 8.62 ng/L

Comparisons with water-quality criteria1

Samples with 

concentration 

> 12 ng/L

Samples with 

concentration

> 1.8 ng/L

Samples with 

concentration 

> 1.3 ng/L

1 Fall Creek near Fortville 19 1.22 21.2 1 1 5 8

2 Eel River near Logansport 19 1.12 14.7 2 1 6 9

3 Tippecanoe River 

at Winimac

19 1.23 7.42 0 0 6 8

4 Wildcat Creek 

near Lafayette

19 1.03 12.7 2 1 6 8

5 Wabash River at Terre Haute 18 3.65 13.8 3 2 16 17

6 Mills Creek 

at Cagles Mill Dam

19 1.73 3.34 0 0 8 15

7 White River near Centerton 18 6.00 28.2 5 3 17 18

8 White River at Nora 19 2.36 11.3 2 0 11 12

9 Sugar Creek 

near New Palestine

17 1.21 7.74 0 0 4 8

10 East Fork Whitewater River 

near Brookville

17 .54 1.85 0 0 2 1

11 Vernon Fork Muscatatuck 

River at Vernon

17 2.80 16.2 2 1 12 14

12 East Fork White River 

at Seymour

17 2.59 20.1 2 2 11 14

13 Blue River at Fredericksburg 17 1.74 3.79 0 0 8 12

14 Patoka River at Winslow 17 4.58 27.9 6 3 16 17
Mercury in Indiana Watersheds 23

Table 3.  Total mercury concentrations in water samples from monitoring stations on Indiana streams, 2002–2006, with comparisons to

Indiana water-quality criteria.—Continued

[>, greater than; ng/L, nanogram per liter]

Station 

number Station name

Number 

of 

samples

Median 

concentration2

(ng/L)

Maximum 

concentration 

(ng/L)

Samples with 

concentration3

> 8.62 ng/L

Comparisons with water-quality criteria1

Samples with 

concentration 

> 12 ng/L

Samples with 

concentration

> 1.8 ng/L

Samples with 

concentration 

> 1.3 ng/L

15 White River at Petersburg 9 5.63 12.0 1 1 9 9

16 Busseron Creek 

near Carlisle

17 2.49 6.89 0 0 11 16

17 Mississinewa River 

near Peoria

15 2.89 6.65 0 0 10 12

18 Wabash River 

near Huntington

16 3.74 15.0 2 2 13 15

19 Maumee River 

at New Haven

16 7.05 26.9 5 3 15 16

20 Fish Creek near Artic 15 2.20 8.66 2 0 8 10

21 St. Joseph River at Elkhart 16 1.75 9.05 1 0 7 10

22 Trail Creek at Michigan City 15 1.67 11.7 1 0 7 10

23 Deep River at Lake George 

at Hobart

16 1.83 6.89 0 0 9 13

24 Kankakee River at Shelby 15 3.16 12.2 1 1 11 11

25 Wabash River at Vincennes 9 4.11 9.73 1 0 9 9

26 Wabash River 

at Mt. Carmel, Ill.

6 5.36 14.5 2 1 6 6

1 Indiana chronic aquatic criterion (12 ng/L); Indiana Great Lakes human health criterion (1.8 ng/L); Indiana Great Lakes wildlife criterion (1.3 ng/L).

2Medians for unfiltered total mercury include censored values and were computed with the Adjusted Maximum Likelihood Estimate procedure (Helsel, 2005) 

by use of statistical software (S-Plus, Tibco Software, 2008).

3The 90th percentile of unfiltered total mercury concentrations in 411 samples, 2002–2006, was 8.62 ng/L.

microbes (American Public Health Association and others, 

1992). Turbidity values do not correspond directly to concentrations of suspended solids or sediment, but these measures 

are typically strongly correlated. In this report, particulate 

total mercury is assumed to be adsorbed to or entrained in 

particles larger than 0.7 μm, based on the definition of dissolved total mercury presented earlier. These particles include 

sand, silt, and clay particles, excluding fine clay less than 0.7 

μm (Horowitz, 1991). Turbidity values for 2002–2004 were 

from IDEM (Indiana Department of Environmental Management Assessment Information System database, unpublished 

data, 2005), and those for 2004–2006 were from Ulberg and 

Risch (2008). 

Particulate total mercury showed a strong positive correlation13 with turbidity (r = 0.73, fig. 10). Turbidity of the water 

samples from the 26 monitoring stations, when classified by 

range, show that the distribution of particulate total mercury 

concentrations generally increases as turbidity increases 

(fig. 10). Nearly all particulate total mercury concentrations 

13For this report, a strong positive correlation was indicated by a Pearson 

correlation coefficient greater than 0.70.
0

20

40

60

80

100

PER

CENTA

GE OF UNFILTERED TOTAL MER

CURY

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

STREAM-MONITORING-STATION NUMBER

EXPLANATION

Average filtered total mercury concentration as a percentage of unfiltered total mercury concentration

Average particulate total mercury concentration as a percentage of unfiltered total mercury concentration

24 Mercury in Indiana Watersheds: Retrospective for 2001–2006

exceeding the 12-ng/L Indiana chronic aquatic criterion were 

in water samples with turbidity higher than 60 nephelometric 

turbidity ratio units (NTRU).

Particulate total mercury concentrations at six stations 

were likely affected by impeded streamflow velocity, which 

can allow suspended particles to settle. Dams were within 

4.3 km upstream from monitoring stations 6, 10, 17, 18, and 

23; station 22 was subject to flow stagnation and flow reversal 

because of Lake Michigan influence. Particulate total mercury concentrations in samples from these 6 stations (n = 90) 

were significantly lower than those from the other 20 stations 

(n = 287; p < 0.001, Wilcoxon rank-sum test). The difference was significant when only the five stations with dams 

upstream were tested. The difference in median particulate 

total mercury in the two groups was twofold—1.01 ng/L in 

samples from the 5 stations with dams upstream compared 

with 2.02 ng/L at the other 20 stations. Ulberg and Risch 

(2008) reported a similar effect of significantly lower particuFigure 9.  Average percentages of filtered and particulate total mercury in water samples at monitoring stations on Indiana streams,

2002–2006. (Locations of stream-monitoring stations are shown on figure 2.)

late total mercury concentrations from these six stations with 

impeded streamflow velocity in 2004–2006. 

Unfiltered methylmercury as a percentage of unfiltered 

total mercury, called the percentage of methylmercury in this 

report, was computed for 252 samples from 26 stations where 

uncensored methylmercury and total mercury concentrations 

were reported. The percentage of methylmercury ranged from 

0.4 to 64.8 percent, with a median of 3.7 percent. Station 6, 

Mill Creek at Cagles Mill Dam, had the most samples with 

concentrations above the 90th percentile, the highest median 

methylmercury concentration, and the highest median and 

maximum percentages of methylmercury (table 5).

Percentages of methylmercury in samples at the 6 stations with impeded streamflow that were identified previously 

(stations 6, 10, 17, 18, 22, and 23) were significantly higher 

than in samples at the other 20 stations (p = 0.031, Wilcoxon 

rank-sum test). The difference also was shown when only the 

five stations with dams upstream were tested. The median 
Mercury in Indiana Watersheds 25

Table 4.  Filtered total mercury and estimated particulate mercury concentrations in water samples from monitoring stations on

Indiana streams, 2002–2006.

[ng/L, nanograms per liter]

Station 

number Station name

Number 

of 

samples

Filtered total mercury Particulate total mercury 

Average 

concentration1

(ng/L)

Average 

percentage 

filtered 

mercury2

Average 

concentration1

(ng/L)

Average 

percentage 

particulate 

mercury3

1 Fall Creek near Fortville 18 0.64 43 2.15 57

2 Eel River near Logansport 18 1.02 44 1.96 56

3 Tippecanoe River at Winimac 18 .56 34 1.58 66

4 Wildcat Creek near Lafayette 18 .64 37 2.67 63

5 Wabash River at Terre Haute 18 .75 16 4.34 84

6 Mills Creek at Cagles Mill Dam4 18 .83 42 1.02 58

7 White River near Centerton 18 .77 12 7.35 88

8 White River at Nora 18 .67 23 2.82 77

9 Sugar Creek near New Palestine 17 .53 37 1.29 63

10 East Fork Whitewater River near Brookville4 17 .38 63 .28 37

11 Vernon Fork Muscatatuck River at Vernon 17 1.80 52 2.48 48

12 East Fork White River at Seymour 17 .78 21 3.91 79

13 Blue River at Fredericksburg 17 .70 37 1.17 63

14 Patoka River at Winslow 17 1.60 21 6.20 79

15 White River at Petersburg 9 1.02 17 4.82 83

16 Busseron Creek near Carlisle 17 .78 26 2.34 74

17 Mississinewa River near Peoria4 15 1.18 41 1.86 59

18 Wabash River near Huntington4 16 2.28 39 3.05 61

19 Maumee River at New Haven 16 1.76 20 7.10 80

20 Fish Creek near Artic 15 1.15 46 1.55 54

21 St. Joseph River at Elkhart 16 .54 34 1.75 66

22 Trail Creek at Michigan City4 15 .66 29 2.65 71

23 Deep River at Lake George at Hobart4 16 .93 40 1.36 60

24 Kankakee River at Shelby 15 .64 21 3.19 79

25 Wabash River at Vincennes 9 .84 18 3.70 82

26 Wabash River at Mt. Carmel, Ill. 6 .60 10 6.09 90

1

Averages for filtered total mercury at each station include censored values and were computed with the Adjusted Maximum Likelihood Estimate procedure 

(Helsel, 2005) by use of statistical software (S-Plus, Tibco Software, 2008).

2The percentage of filtered mercury is the ratio of filtered to unfiltered concentration, expressed as a percentage. 

3The percentage of particulate mercury is the ratio of filtered to unfiltered concentration, expressed as a percentage. Particulate total mercury was estimated 

with uncensored total mercury concentrations.

4Flow was impeded at station because of a dam or because of flow stagnation and reversal.
x

x

x

xx

o

o

o

o

o

o x

x

x

o

o

o

o

o

o

o

xx

x

x

x x

o

x

x

118 114 43 41 23 18 10 9 EXPLANATION

x

o

Whisker includes adjacent

values within one step above box

75th percentile (top of box)

Median (50th percentile)

25th percentile (bottom of box)

Whisker includes adjacent

values within one step below box

Upper detached values more

than two steps above box

Upper outside values within

one to two steps above box

(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)

118 Number of samples

Indiana chronic aquatic criterion

(12 nanograms per liter)

8 12 10 4

0

5

10

15

20

25

0 - 10

11 - 2021 - 3031 - 4041 - 50

51 -60

61 - 7071 - 80

81 - 100

100 - 140141 - 180181 - 500

RANGES OF TURBIDITY IN WATER SAMPLES AT TIME OF COLLECTION,

IN NEPHELOMETRIC TURBIDITY RATIO UNITS

PARTICULATE TOTAL MERCURY CONCENTRATION,

IN NANOGRAMS PER LITER

1 10 100

1

10

PARTICULATE TOTAL MERCURY CONCENTRATION,

IN NANOGRAMS PER LITER

TURBIDITY IN WATER SAMPLES AT TIME OF COLLECTION,

IN NEPHELOMETRIC TURBIDITY RATIO UNITS

r = 0.73

26 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Figure 10.  Relations of particulate total mercury concentrations in water samples to turbidity values and ranges of turbidity in water at

the time of sample collection at monitoring stations on Indiana streams, 2002–2006.
Mercury in Indiana Watersheds 27

percentage of methylmercury for the group of 5 monitoring 

stations downstream from dams was 4.7 percent, compared to 

3.6 percent for the other 21 stations. Ulberg and Risch (2008) 

reported a similar effect of statistically higher percentage of 

methylmercury at the six stations with impeded streamflow 

velocity in 2004–2006. 

The degree to which mercury concentrations and turbidity in water samples were related to instantaneous streamflow 

at the time of sample collection varied considerably among the 

monitoring stations. A strong positive correlation of unfiltered 

and filtered total mercury concentrations with instantaneous 

streamflow was indicated for stations 1, 2, 8, 9, 11, 19, 20, 

23, and 26 (appendix table 1–1). Particulate total mercury and 

unfiltered methylmercury concentrations generally did not correlate well with instantaneous streamflow. 

Instantaneous streamflow at the time of sample collection was classified by assigning it to one of four categories14 of 

daily mean streamflow for 2002–2006 (fig. 11; appendix table 

1–2). Unfiltered total and filtered total mercury concentrations 

and turbidity were significantly higher when streamflow at the 

time of sample collection was in either the high or the event 

category rather than the low or the medium category (p<0.001, 

Kruskal Wallis test; Tukey’s test). 

For all unfiltered total mercury concentrations that 

exceeded the 12-ng/L Indiana chronic aquatic criterion, 

instantaneous streamflow was in the high or the event category. Median unfiltered total mercury was 3.2 ng/L at high 

streamflow and 6.8 ng/L at event streamflow; median filtered 

total mercury was 0.78 ng/L at high streamflow and 1.4 ng/L 

at event streamflow (fig. 11). Median turbidity was 21 NTRU 

at high streamflow and 36 NTRU at event streamflow. Ulberg 

and Risch (2008), using these streamflow categories, reported 

similar findings for total mercury concentrations and streamflow, 2004–2006.

The 411 water samples described in this report were collected on a seasonal schedule, and the unfiltered and filtered 

total mercury and unfiltered methylmercury concentrations 

and instantaneous streamflow at the time of sample collection 

were significantly different among the four seasons15—winter, 

14 Instantaneous streamflow values for 2002–2004 were from IDEM 

(Indiana Department of Environmental Management Assessment Information System database, unpublished data, 2005), and instantaneous streamflow 

values for 2004–2006 were from Ulberg and Risch (2008). Daily mean 

streamflow category, for this report, was based on the daily mean streamflow 

record from the USGS streamflow-gaging station near each monitoring station 

for January 2002 through December 2006 (U.S. Geological Survey, 2008). 

For stations 15, 25 and 26, which had a shorter period of sample collection, 

the streamflow record for August 2004 through December 2006 was used. 

Daily mean streamflow categories were based on the rank-ordered daily 

mean streamflow data and are defined as “low” (less than or equal to the 

10th percentile), “medium” (greater than the 10th percentile and less than or 

equal to the median), “high” (greater than the median and less than or equal to 

the 90th percentile), and “event” (greater than the 90th percentile).

15 In this report, astronomical seasons in the northern hemisphere temperate 

zone are used, bounded by the winter solstice on December 22, vernal equinox 

on March 21, summer solstice on June 21, and autumnal equinox on September 22 (American Meteorological Society, 2000).

spring, summer, and fall (p <0.001, Kruskal-Wallis test). Most 

of the seasonal pattern in unfiltered and filtered total mercury 

concentrations corresponds to seasonal patterns in instantaneous streamflow, whether flow-adjusted concentrations are 

used or not and whether data from six stations with impeded 

flow (6, 10, 17, 18, 22, and 23) are included or not. Total 

mercury concentrations and streamflow in winter and spring 

were higher than in summer and fall (p <0.001, Tukey’s test). 

The median unfiltered total mercury concentrations in samples 

grouped by season were winter, 2.71 ng/L; spring, 3.28 ng/L; 

summer, 2.08 ng/L; and fall, 1.25 ng/L. Unfiltered methylmercury concentrations in spring and summer (medians 0.14 and 

0.12 ng/L) were higher than in fall (median 0.08 ng/L).

Any 5-year statistical trend in total mercury concentrations would not confound interpretations of geographic differences. Five-year trends in unfiltered total mercury concentrations were examined by using the Seasonal Kendall test for 

trend (Hirsch and others, 1982).16 The use of nonparametric 

procedures adjusted for serial correlation optimizes the sensitivity of the test for correctly detecting a significant trend. The 

median concentrations for the four seasons (winter, spring, 

summer, and fall) were used in the test because seasonal differences had been demonstrated. The test was made with data 

from each of the 26 monitoring stations and “statewide,” combining 5 years of data from all stations (table 6). A significant 

trend of increasing unfiltered total mercury concentration was 

indicated for station 19 (p = 0.003) and station 8 (p = 0.035), 

but these trends in concentration corresponded closely with 

increases in streamflow. A significant trend in unfiltered 

mercury concentrations from all stations combined was not 

shown, whether data from the six stations with impeded 

streamflow (stations 6, 10, 17, 18, 22, and 23) were included 

(p = 0.482, n = 411) or excluded (p= 0.673, n = 314).

Annual stream loads of unfiltered total mercury and 

unfiltered methylmercury were calculated with data for 

2002–2006 (appendix table 1–3). The method for determining stream mercury loads is described in the “Mercury Load 

Calculations” section of this report, and the characteristics of 

the load models are in appendix table 1–4. The standard error 

of prediction for the 89 annual stream loads of total mercury 

indicated that 4 out of 5 of the calculated loads were within 

25 percent of actual loads; 64 of these 89 loads were within 

10 percent of actual loads (appendix table 1–3). The highest 

uncertainty was associated with a standard error of prediction 

16The Seasonal Kendall test was developed by the USGS to analyze trends 

in water quality and has become the most used test for trend in the environmental sciences (Helsel and others, 2006). This test is a generalization of the 

Mann-Kendall test (Mann, 1945; Kendall, 1970) and reduces the effect that 

seasonal variations may have on trend detection by making comparisons of 

data from similar seasons (Schertz and others, 1991). The Seasonal Kendall 

test counts the number of increases and decreases in a parameter during a 

period of record, conducts the test within each season, and then combines 

the results from each season into an overall test for trend (Frans and Helsel, 

2005). The direction of the trend is indicated by the Kendall’s tau correlation 

coefficient. A negative tau indicates a decrease, and a positive tau indicates 

an increase. In this analysis, a significant trend is indicated by a p-value less 

than 0.05.
28 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 5.  Unfiltered methylmercury concentrations in water samples at monitoring stations on Indiana streams, 2002–2006.—Continued

[>, greater than; ng/L, nanogram per liter; ND, not determined]

Station 

number Station name

Number of 

uncensored 

concentrations

Samples

with

concentrations1

> 0.29 ng/L

Median 

concentration 

of methylmercury2

(ng/L)

Maximum 

concentration 

of methylmercury 

(ng/L)

Median 

percentage 

of methylmercury 3

Maximum 

percentage 

of methylmercury3

1 Fall Creek near Fortville 8 1 0.07 0.29 4.4 11.6

2 Eel River near Logansport 10 0 .08 .27 4.2 17.9

3 Tippecanoe River 

at Winimac

8 0 .07 .19 4.6 9.9

4 Wildcat Creek 

near Lafayette

8 1 .08 .33 2.9 14.7

5 Wabash River at Terre Haute 14 4 .16 .66 3.8 30.5

6 Mills Creek 

at Cagles Mill Dam

8 4 .09 .57 16.1 64.8

7 White River near Centerton 15 2 .15 .29 2.2 4.4

8 White River at Nora 9 0 .10 .26 4.3 10.2

9 Sugar Creek 

near New Palestine

8 0 .06 .20 7.4 42.6

10 East Fork Whitewater River 

near Brookville

1 0 ND .04 ND 15.4

11 Vernon Fork Muscatatuck 

River at Vernon

14 0 .11 .32 3.3 11.0

12 East Fork White River 

at Seymour

13 0 .11 .44 3.1 9.8

13 Blue River at Fredericksburg 8 0 .08 .20 4.4 10.8

14 Patoka River at Winslow 13 3 .12 .42 1.9 5.1

15 White River at Petersburg 9 2 .20 .41 2.7 9.9

16 Busseron Creek 

near Carlisle

11 0 .17 .22 4.9 6.5

17 Mississinewa River 

near Peoria

11 0 .09 .18 2.9 16.1

18 Wabash River 

near Huntington

14 2 .13 .66 2.7 15.4

19 Maumee River at New 

Haven

13 3 .21 .43 3.6 18.1

20 Fish Creek near Artic 11 0 .12 .26 7.9 15.4

21 St. Joseph River at Elkhart 8 0 .07 .12 4.5 12.5

22 Trail Creek at Michigan City 8 1 .07 .39 5.0 6.3
Mercury in Indiana Watersheds 29

Table 5.  Unfiltered methylmercury concentrations in water samples at monitoring stations on Indiana streams, 2002–2006.—Continued

[>, greater than; ng/L, nanogram per liter; ND, not determined]

Station 

number Station name

Number of 

uncensored 

concentrations

Samples

with

concentrations1

> 0.29 ng/L

Median 

concentration 

of methylmercury2

(ng/L)

Maximum 

concentration 

of methylmercury 

(ng/L)

Median 

percentage 

of methylmercury 3

Maximum 

percentage 

of methylmercury3

23 Deep River 

at Lake George at Hobart

9 0 .06 .15 3.6 24.5

24 Kankakee River at Shelby 8 0 .07 .13 1.9 4.2

25 Wabash River at Vincennes 9 1 .16 .42 2.3 16.5

26 Wabash River 

at Mt. Carmel, Ill.

4 1 .22 .33 2.7 14.9

1The 90th percentile of unfiltered methylmercury concentrations is 0.29 ng/L (n = 252).

2Medians for unfiltered methylmercury at each station include censored values and were computed with the Adjusted Maximum Likelihood Estimate procedure 

(Helsel, 2005) by use of statistical software (S-Plus, Tibco Software, 2008).

3Ratio of unfiltered methylmercury concentration to unfiltered total mercury concentration, expressed as a percentage.

Table 6.  Seasonal Kendall test for trends in unfiltered total mercury concentrations in water samples from

monitoring stations on Indiana streams, 2002–2006.

[ng/L, nanogram per liter]

Station 

number

Number

of

samples

p-value

of test1

Kendall’s

tau2

Station

number

Number

of

samples

p-value

of test1

Kendall’s

tau2

1 18 0.068 0.438 14 17 0.878 −0.071

2 18 .325 − .250 15 9 1.000 .000

3 18 .482 .188 16 17 .878 − .071

4 18 .673 − .125 17 15 .382 − .273

5 18 1.000 .000 18 16 .744 .120

6 18 .888 .062 19 16 .003 .760

7 18 1.000 .000 20 15 .221 .364

8 18 .035 .500 21 16 .192 .360

9 17 .284 − .286 22 15 .600 − .182

10 17 .535 .179 23 16 .328 .280

11 17 .878 .071 24 15 .382 .273

12 17 .646 − .143 25 9 .245 .667

13 17 .284 .286 26 6 1.000 .000

1

A statistically significant p-value is less than 0.05.

2The Kendall’s tau correlation coefficient indicates the strength and direction of change for the trend. A negative sign indicates 

a decrease. 
LOW

MEDIUM

HIGH

EVENT

1015202530

xx

o x

xxxx

o

xxxxx

ooo

xxx

64 148 159 39

5

0

UNFILTERED TOTAL MERCURY CONCENTRATION,

IN NANOGRAMS PER LITER

EXPLANATION

x

o

Whisker includes advalues within one st75th percentile (top Median (50th perce25th percentile (botWhisker includes advalues within one stUpper detached vathan two steps abovUpper outside valueone to two steps ab

(Box height is variation ovalues, also called the intone step equals 1.5 times 

64 Number of samples

DAILY

MEAN STREA

for instantaneous streamflow compared to rank-ordered daUSGS streamflow-gaging stafor mercury in Indiana stream

x

xxxxx

o x

xxxxxxx

oo

54 143 152 38

LOW

MEDIUM

HIGH

EVENT

DAILY

MEAN STREA

MFLO

W CATEG

ORY, 2002-2006

FILTERED TOTAL MERCURY CONCENTRATION,

IN NANOGRAMS PER LITER

0123456 Indiana chronic 

(12 nanograms 

EVENT - gre

HIGH - gre

less 

MEDIUM - gre

less 

LO

W - les

the 

90th10th50th

DAILY MEAN STREAMFLOW

PERCENTILES

Figure 11.  Distributions of unfiltered and filtered total mercury concentrations in water samples at monitoring stations on Inddaily mean streamflow category for instantaneous streamflow at time of sample collection, 2002–2006.
Mercury in Indiana Watersheds 31

overview, Ulberg and Risch (2008) summarized previous 

studies of mercury in U.S. streams that were done at multiple 

scales and compared the findings of those studies to mercury 

concentrations in Indiana streams, 2004–2006.

Total mercury and particulate mercury concentrations in 

Midwestern streams have been shown to be related predominantly to levels of particulates and suspended sediment. The 

mercury concentrations increase when streamflow increases 

because of storm runoff and snowmelt (Balogh and others, 

1997; Babiarz and others, 1998; Hurley and others, 1998; 

Risch, 2005; Ulberg and Risch, 2008). In addition, mercury 

transport is often episodic and tied to streamflow and season 

(Schuster and others, 2007; Shanley and others, 2008). In a 

multiyear study of U.S. streams in different settings, Brigham 

and others (2009) concluded that particulate total mercury and 

methylmercury concentrations were positively correlated with 

streamflow. They also reported that (whole-water) total mercury and methylmercury concentrations17 correlated strongly 

with dissolved organic carbon and suspended-sediment 

concentrations (data that were unavailable for interpretation of 

the 2002–2006 Indiana mercury data). Walling (1983) reported 

that a limitation of comparing constituent yields among watersheds of widely different upstream drainage areas is that many 

constituent yields, such as those for suspended sediment, 

tend to decrease substantially as the upstream drainage area 

increases. Understanding particulate mercury transport may be 

confounded by this limitation.

In a study of mercury cycling in different environments, 

Shanley and others (2008) determined that methylmercury 

tracked total mercury at a fairly constant ratio. They proposed 

that methylmercury production occurs in wetlands, riparian 

areas, and instream sediments where total mercury is sequestered in conditions that promote methylation. These areas 

for methylmercury production are hydraulically connected 

to streams and allow the methylmercury to be transported 

when storms cause increased streamflow. Brigham and others 

(2009) and Marvin-DiPasquale and others (2009) concluded 

that methylmercury production in stream-channel sediments 

was not important to the methylmercury load in the watershed. 

Rather, methylmercury in streams is predominantly produced 

in hydrologically connected wetlands and delivered in runoff 

to the streams. Similarly, Scudder and others (2009), in a 

national study of streams sampled during low flow, reported a 

positive correlation of methylmercury concentrations in water 

with total mercury concentrations in water, dissolved organic 

carbon, and percentage of wetlands relative to total land cover 

within the watershed.

Other investigators have reported that dams and 

impoundments increase methylmercury concentrations and 

percentages of methylmercury in water samples from reservoirs. Methylmercury concentrations in water from new 

reservoirs increases because organic carbon from inundated 

17Brigham and others (2009) reported whole-water concentration as the sum 

of filtered and particulate concentrations, which are similar to the unfiltered 

concentrations in this report.

greater than 100 percent for six annual loads calculated for 

years that had one to three multi-day episodes of extremely 

high streamflow which were outside the fit of the load model. 

The standard error of prediction for the 54 annual stream loads 

of methylmercury indicated 49 of the calculated loads were 

within 7 percent of actual loads; 51 of these 54 loads were 

within 21 percent of actual loads. 

The average standard error of prediction for the 18 average annual stream loads of total mercury indicated that 4 out 

of 5 of the calculated average loads were within 35 percent of 

actual loads (appendix table 1–4). The highest uncertainty was 

associated with an average standard error of prediction greater 

than 100 percent for two watersheds. The standard error of 

prediction for 10 of the 11 average annual stream loads of 

methylmercury indicated the calculated average loads were 

within 10 percent of actual loads. 

Annual stream mercury loads were normalized to stream 

mercury yields by dividing the stream load by the watershed’s 

upstream drainage area. Hereinafter, the term “stream mercury 

yield” will mean the normalized load, and a watershed will be 

designated by the monitoring-station number.

The 89 annual stream yields of total mercury from 

18 watersheds ranged from 0.47 μg/m2/yr (watershed 21 in 

2002) to 78.9 μg/m2/yr (watershed 12 in 2005); the median 

was 3.47 μg/m2/yr. The 10 highest annual stream yields of 

total mercury ranged from 31.9 to 78.9 μg/m2/yr; 5 of the 10 

were from watershed 7 and watersheds 1 and 8 nested inside 

watershed 7 (fig. 12) and 4 of the 10 were from watershed 12 

(appendix table 1–3). 

The average annual stream yield of total mercury from 

18 watersheds (table 7, fig. 12) ranged from 0.73 μg/m2/yr 

(watershed 21) to 45.2 μg/m2/yr (watershed 12); the median 

was 4.22 μg/m2/yr. The highest average annual stream yields 

of total mercury were in:

Watershed 7–White River near Centerton (39.6 μg/m2/yr)

Watershed 12–East Fork White River at Seymour 

(45.2 μg/m2/yr)

The annual stream total mercury loads and yields from the 

18 watersheds were significantly different (p <0.001, KruskalWallis test). The average annual stream yields of total mercury 

indicate these differences are substantial. For example, the 

yield from watershed 12 (45.2 μg/m2/yr) is approximately 

63 times the yield from watershed 21 (0.73 μg/m2/yr).

In 11 watersheds combined, the median annual stream 

yield of methylmercury was 1.9 percent of the median annual 

stream yield of total mercury. The 54 annual stream yields of 

methylmercury from 11 watersheds ranged from 0.03 μg/m2/yr 

(watersheds 3, 1, and 23) to 0.18 μg/m2/yr (watershed 16 in 

2006); the median was 0.07 μg/m2/yr (appendix table 1–3). 

The average annual stream yield of methylmercury from 

11 watersheds (table 7) ranged from 0.03 μg/m2/yr (watershed 23) to 0.12 μg/m2

/yr (watershed 16); the median was 

0.07 μg/m2/yr. 

The following discussion highlights conclusions from 

other investigations of mercury in streams and ties them to 

observations from Indiana presented in this report. In an 
1-1-1

39°00'

40°00'

41°00'

87°00' 86°00' 85°00'

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

Universal Transverse Mercator projection zone 16, NAD 1983

0 25 50 MILES

0 25 50 KILOMETERS

KENTUCKY

Average annual stream yield of total

mercury in watershed, in micrograms

per square meter per year

Monitoring station for mercury in

streams, with station number

2

24

23

22

21

20

19

18

17

8

1

9

10

12 11

13 14

15

25

5

16

6 7

4

3

MICHIGAN

ILLINOIS OHIO

INDIANA

26

22

EXPLANATION

Watershed upstream from

monitoring station

20.1 - 45.7

15.1 - 20

10.1 - 15

5.1 - 10

< 5

No Data

32 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Figure 12.  Average annual stream yields of total mercury in watersheds upstream from monitoring stations on Indiana streams,

2002–2006.
Mercury in Indiana Watersheds 33

forest soils and wetlands stimulate microorganisms that methylate inorganic mercury that is present (Bodaly and others, 

2004). Decomposition of the organic carbon promotes anoxic 

conditions that favor microorganisms involved with methylation. Elevated methylmercury may persist for many years 

after a reservoir is first flooded (Hall and others, 2005; Bodaly 

and others, 2007). Methylmercury in the water is taken up by 

phytoplankton and zooplankton, in early years as dissolved 

methylmercury released from soils and in later years from 

methylmercury in resuspended fine particles (Plourde and 

others, 1997). Reservoirs with fluctuating water levels create 

periodic reduction and oxidation conditions that create and 

release methylmercury into the water (Kelly and others, 1997; 

St. Louis and others, 2004). Seasonal thermal stratification 

in reservoirs with a hypolimnion that is anoxic is thought to 

encourage methylmercury formation in the deep, anoxic water 

and shallow sediments; this methylmercury becomes vertically 

mixed into all the water during thermal destratification (Alpers 

and others, 2008).

With the knowledge from these other investigators, the 

following observations are made about the mercury-in-streams 

data for Indiana.

• Unfiltered total mercury concentrations in streams 

without impeded streamflow were predominantly 

particulate mercury. When streamflow was highest, 

unfiltered and filtered total mercury concentrations 

were highest. Turbidity of water, a surrogate for suspended particulates and sediment in water, increased 

as streamflow increased. Total mercury concentrations 

were highest in winter and spring, as was streamflow. 

Total mercury concentrations did not show a temporal 

trend during 2002–2006. Continuation of the seasonal 

monitoring of mercury in streams has the potential 

to detect long-term trends with underlying seasonal 

patterns and to identify geographic differences among 

watersheds and regions of the State.

• Mercury concentrations in streams had a 3.7 median 

percentage of methylmercury. Median annual stream 

yields of unfiltered methylmercury were 1.9 percent 

of median annual stream yields of unfiltered total 

mercury. Methylmercury concentrations were highest 

in summer and fall but were not related to available 

water-quality or streamflow information for Indiana 

streams. Methylmercury data for this report included a 

substantial number of censored values, which limited interpretations of percentage methylmercury and 

stream yields of methylmercury. A consistent laboratory reporting limit of 0.05 ng/L for all mercury analyses would have resulted in a better dataset.

• As shown by other investigators, mercury data for 

streambed sediments associated with the mercury 

data for stream water is unlikely to explain the source 

of methylmercury in the streams. However, data for 

dissolved organic carbon and suspended-sediment 

concentrations associated with water samples analyzed 

for mercury in Indiana could be useful for interpreting 

differences in total mercury and methylmercury among 

watersheds.

• Dams and impoundments increased the percentage of 

methylmercury in waters downstream and lowered 

the percentage of particulate total mercury during 

2002–2006. As reported in other studies, reservoirs of 

various ages are likely to have conditions that increase 

the production of methylmercury. The methylmercury 

concentrations and percentages of methylmercury can 

be highest in the hypolimnion during summer thermal 

stratification, or they can be mixed in the water at other 

times. The effect of methylmercury on food chains and 

sport fish in reservoirs and downstream from reservoirs 

can be important. Investigations of mercury in Indiana 

reservoirs could help to explain the high percentages 

of methylmercury downstream from some of them and 

may provide information useful for natural-resources 

management.

• Stream mercury loads and yields were not meaningful 

for locations with impeded streamflow and potentially 

were confounded by large upstream drainage areas. A 

revised network of stream-monitoring locations without impeded streamflow and more uniform upstream 

drainage areas could improve capabilities for estimating stream mercury loads and yields.
34 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 7.  Average annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream

from monitoring stations on Indiana streams, 2002–2006.—Continued

[km2, square kilometer; g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station 

number Station name

Upstream

drainage area

(km2)

Average annual 

stream load of 

total mercury

(g/yr)

Average annual 

stream yield1 of 

total mercury

(μg/m2/yr)

Average annual 

stream load of 

methylmercury

(g/yr)

Average annual 

stream yield1 of 

methylmercury

(μg/m2/yr)

1 Fall Creek near Fortville 447 7,918 17.7 ND ND

2 Eel River near Logansport 2,043 7,636 3.74 148 0.07

3 Tippecanoe River 

at Winimac

 2,438 1,832 .75 90 .04

4 Wildcat Creek 

near Lafayette2

 2,056 37,187 18.1 ND ND

5 Wabash River at Terre Haute 31,936 65,325 2.05 2,138 .07

6 Mills Creek 

at Cagles Mill Dam3

 759 ND ND ND ND

7 White River near Centerton2 6,324 250,132 39.6 569 .09

8 White River at Nora 3,149 64,560 20.5 ND ND

9 Sugar Creek 

near New Palestine

 243 491 2.02 12 .05

10 East Fork Whitewater River 

near Brookville3

 986 ND ND ND ND

11 Vernon Fork Muscatatuck 

River at Vernon

 512 6,694 13.1 36 .07

12 East Fork White River 

at Seymour

 6,056 273,693 45.2 ND ND

13 Blue River at Fredericksburg 732 764 1.04 27 .04

14 Patoka River at Winslow4 1,559 9,429 6.05 123 .08

15 White River at Petersburg5 28,794 ND ND ND ND
Mercury in Indiana Watersheds 35

Table 7.  Average annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream

from monitoring stations on Indiana streams, 2002–2006.—Continued

[km2, square kilometer; g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station 

number Station name

Upstream

drainage area

(km2)

Average annual 

stream load of 

total mercury

(g/yr)

Average annual 

stream yield1 of 

total mercury

(μg/m2/yr)

Average annual 

stream load of 

methylmercury

(g/yr)

Average annual 

stream yield1 of 

methylmercury

(μg/m2/yr)

16 Busseron Creek 

near Carlisle

 591 2,780 4.70 73 .12

17 Mississinewa River 

near Peoria3

 2,093 ND ND ND ND

18 Wabash River 

near Huntington3

 1,985 ND ND ND ND

19 Maumee River 

at New Haven

 5,077 27,510 5.42 419 .08

20 Fish Creek near Artic 248 372 1.50 ND ND

21 St. Joseph River at Elkhart 8,756 6,354 .73 ND ND

22 Trail Creek 

at Michigan City6

 152 ND ND ND ND

23 Deep River at Lake George 

at Hobart

 321 503 1.57 10 .03

24 Kankakee River at Shelby 4,597 6,017 1.31 ND ND

25 Wabash River at Vincennes5 35,628 ND ND ND ND

26 Wabash River 

at Mt. Carmel, Ill.7

74,293 ND ND ND ND

1Stream load values were normalized by dividing the stream load, in grams, by the upstream drainage area, in square kilometers.

2High uncertainty in unfiltered total mercury or unfiltered methylmercury load; see appendix table 1–4.

3Station located downstream from dam; loads were not calculated because of stream-stage control.

4Loads in 2006 were not included because of insufficient streamflow data.

5Data collected 2004–2006; loads were not calculated because of insufficient concentration data.

6Loads were not calculated because of streamflow stagnation and reversal.

7Data collected 2002–2004; loads were not calculated because of insufficient concentration data.
36 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Mercury in Fish

Mercury concentrations reported in fish-tissue 

samples were assumed to be nearly all methylmercury 

(U.S. Environmental Protection Agency, 1999, 2009; Harris, 

Krabbenhoft, and others, 2007), and hereinafter are called 

“mercury concentrations” when referring to fish tissue. 

Comparisons of mercury concentrations in different types of 

fish-tissue samples with different fractions of moisture and 

solids were improved by converting the wet-weight concentrations to dry-weight concentrations. Fish-tissue samples were 

analyzed for percent total solids, and wet-weight mercury 

concentrations were multiplied by the reciprocal of the total 

solids fraction to get dry-weight mercury concentrations.18

(These dry-weight mercury concentrations are not appropriate 

for comparison with the mercury water-quality criterion.) 

Data for mercury concentrations in 2,225 fish-tissue 

samples from 502 locations statewide, 1993–2004, were compiled for this report. These fish-tissue samples were from 68 

species and were collected at 439 sites on rivers and streams19

and 63 sites on lakes and reservoirs. Wet-weight mercury concentrations from the 2,225 fish-tissue samples had a median 

of 123 μg/kg and a maximum of 1,070 μg/kg. When compared with the U.S. Environmental Protection Agency (2001) 

water-quality criterion of 0.3 mg/kg methylmercury in fish 

tissue (equivalent to 300 micrograms per kilogram, μg/kg, the 

units used in the following discussion), 11.6 percent of these 

concentrations exceeded this criterion. Dry-weight mercury 

concentrations in the 2,225 fish-tissue samples had a median 

of 549 μg/kg and a maximum of 4,854 μg/kg.

Data for mercury concentrations in the 26 watersheds 

included 1,731 fish-tissue samples from 417 locations. These 

samples were from 83 percent of the 502 locations statewide—358 rivers and streams and 59 lakes and reservoirs. The 

concentrations were evaluated for the unique drainage areas 

so that the effect of nested watersheds is not present. Watersheds upstream from nine stations include some areas outside 

the Indiana border (table 1); the areas outside Indiana range 

from 2 percent of the watershed (station 18) to 57 percent of 

the watershed (station 21). Data for mercury concentrations 

in fish-tissue samples for areas of these watersheds outside 

Indiana were not available for this study. It is likely that any 

missing data for areas in other states that could change the 

interpretations from this study would be in two watersheds 

with the highest fraction of their total area outside Indiana—

station 19 with 47 percent in Ohio and Michigan and station 

21 with 57 percent in Michigan (table 1). 

Wet-weight mercury concentrations in the 1,731 fishtissue samples had a median of 130 μg/kg and a maximum 

18Dry-weight mercury concentration was computed as the wet-weight mercury concentration multiplied by a conversion factor. The conversion factor is 

1 divided by the percent total solids in the sample, multiplied by 100.

19The IDEM database distinguishes natural and manmade lakes from floodcontrol reservoirs; “streams” are first-order headwaters, and “rivers” are all 

other flowing waters.

of 1,070 μg/kg (from a river in watershed 15); 12.4 percent 

exceeded the U.S. Environmental Protection Agency (2001) 

methylmercury criterion. Dry-weight mercury concentrations 

in the 1,731 fish-tissue samples had a median of 571 μg/kg and 

a maximum of 4,854 μg/kg (from a lake in watershed 15).

Mercury concentrations in all fish-tissue samples from 

the 26 watersheds (table 8, fig. 2) were highest in 

 Watershed 1 – Fall Creek near Fortville,

Watershed 15 –White River at Petersburg,

Watershed 25 – Wabash River at Vincennes, and

Watershed 26 – Wabash River at Mount Carmel, Ill.

The percentage of wet-weight mercury concentrations exceeding the water-quality criterion were highest in watershed 1 

(30 percent), watershed 25 (30 percent), and watershed 15 

(24 percent). The median wet-weight mercury concentrations were highest in watershed 26 (250 μg/kg), watershed 1 

(190 μg/kg), and watershed 25 (170 μg/kg). The percentage 

of samples with dry-weight mercury concentrations exceeding 1,495 μg/kg (the 90th percentile of concentrations in the 

26 watersheds) were highest in watershed 1 (30 percent) and 

watershed 15 (19 percent). The median dry-weight mercury 

concentrations were highest in watershed 26 (1,164 μg/kg), 

watershed 1 (825 μg/kg), and watershed 15 (768 μg/kg).

Graphical and statistical examination of mercury concentrations in fish-tissue samples indicated that watersheds 1, 15, 

25, and 26 did not differ significantly and that concentrations 

in watersheds 15 and 26 were the highest. Boxplots of the 

distributions of the wet-weight and dry-weight mercury concentrations in fish-tissue samples from 21 of the 26 watersheds 

with more than 4 samples (fig. 13) showed differences among 

the watersheds that were significant (p < 0.001; Kruskal-Wallis test). Wet-weight mercury concentrations in watersheds 15 

and 26 and dry-weight mercury concentrations in watershed 

15 were significantly higher than those in watersheds 3, 4, 8, 

10, and 24 (Tukey’s test). 

A coarse-scale review of all fish-tissue mercury samples 

in the 26 watersheds included samples from streams and lakes 

of different sizes and different distances from the monitoring 

station at the downstream end of the watershed. A fine-scale 

review was done with only the fish-tissue samples collected 

within 5 km upstream from the monitoring stations at the 

downstream end of the watersheds. Groups of 5 or more fishtissue samples were identified for 11 stations: 7 were collected 

from streams and 4 were collected from reservoirs (table 9). 

Mercury concentrations in fish-tissue samples collected 

within 5 km of the downstream end of 11 watersheds were 

highest near the following monitoring stations (table 9, fig. 2):

Station 1 – Fall Creek near Fortville

Station 7 – White River near Centerton

Station 15 – White River at Petersburg

The percentage of wet-weight mercury concentrations exceeding the water-quality criterion were highest near station 15 

(45 percent), station 1 (40 percent), and station 7 (32 percent). The median wet-weight mercury concentrations were 

highest near station 15 (240 μg/kg), station 7 (198 μg/kg), 

and station 1 (190 μg/kg). The median dry-weight mercury 
x

x

o

x

x

x

x

xxx

x

xx

x

xx

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o

o

o

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x

o

x

o

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x

x

x

x

x

x

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xxx

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x

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x

x

x

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x

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x

x x

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oo

x

EXPLANATION

x

o

Whisker includes adjacent

values within one step above box

75th percentile (top of box)

Median (50th percentile)

25th percentile (bottom of box)

Whisker includes adjacent

values within one step below box

Upper detached values more

than two steps above box

Upper outside values within

one to two steps above box

(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)

Median mercury concentration

in fish tissue from 21 watersheds,

1993-2004 (130 micrograms per

kilogram wet-weight; 571 micrograms per kilogram dry weight)

U.S. Environmental Protection

Agency fresh water-quality

criterion (300 micrograms mercury

per kilogram wet-weight fish tissue)

10 25 93 107 327 11 102 88 41 90 21 293 8 65 40 78 154 23 83 44 36

36 Number of samples

WET-WEIGHT MERCURY 1,000

800

600

400

200

0

WET-WEIGHT MER

CUR

Y

C

ONCENTR

ATION IN FISH TISSUE,

IN MIC

R

O

G

R

A

MS PER KILO

G

R

A

M

1 2 3 4 5 6 7 8 10 12 14 15 16 17 18 19 21 22 24 25 26

MONITORING-STATION NUMBER FOR UPSTREAM WATERSHED

1 2 3 4 5 6 7 8 10 12 14 15 16 17 18 19 21 22 24 25 26

MONITORING-STATION NUMBER FOR UPSTREAM WATERSHED

DRY-WEIGHT MERCURY

10 25 93 107 327 11 102 88 41 90 21 293 8 65 40 78 154 23 83 44 36

5,000

4,000

3,000

2,000

1,000

0

DR

Y-WEIGHT MER

CUR

Y

C

ONCENTR

ATION IN FISH TISSUE,

IN MIC

R

O

G

R

A

MS PER KILO

G

R

A

M

90th percentile dry-weight

mercury concentration in fish

tissue from 21 watersheds,

1993-2004 (1,495 micrograms

per kilogram )

(Box plots shown for 21 of 26 watersheds in

Indiana that had more than 4 fish-tissue

samples analyzed for mercury, 1993-2004)

1,200

Mercury in Indiana Watersheds 37

Figure 13.  Distributions of wet-weight and dry-weight mercury concentrations in fish-tissue samples from watersheds in Indiana,

1993–2004 (from Indiana Department of Environmental Management Assessment Information Management System).
Table 8.  Mercury concentrations in fish-tissue samples from watersheds upstream from monitoring stations on Indiana streams, 1993–2004.—Contin[≥, greater than or equal to; >, greater than; μg/kg, microgram per kilogram; — no data] Station number Station name for upstream watershed Total number of fish tissue samples Total number of fish- sampling locations Number of river and stream sampling locations Number of lake and reservoir sampling locations Number of wet-weight mercury- concen- trations ≥criterion1 Percentage of wet- weight mercury concen- trations ≥ criterion1 Median wet-weight mercury concen- tration (μg/kg) Number of dry-weight mercury concen- trations >90th percentile2 

1 Fall Creek near Fortville 10 3 3 0 3 30 190 3 2 Eel River near Logansport 25 10 9 1 1 4 124 0 3 Tippecanoe River at Winimac 93 23 14 9 6 6 105 4 4 Wildcat Creek near Lafayette 107 18 17 1 3 3 105 2 5 Wabash River at Terre Haute 327 72 67 5 34 10 129 31 6 Mills Creek 

at Cagles Mill Dam

11 3 2 1 0 0 120 0 

7 White River near Centerton 102 24 22 2 13 13 140 10 8 White River at Nora 88 22 21 1 3 3 110 3 9 Sugar Creek 

near New Palestine

0 0 0 0 0 0 — 0 

10 East Fork Whitewater River 

near Brookville

41 17 14 3 1 2 102 0 

11 Vernon Fork Muscatatuck 

River at Vernon

4 3 3 0 0 0 — 0 

12 East Fork White River 

at Seymour

90 31 30 1 11 12 110 11 

13 Blue River at Fredericksburg 4 3 3 0 0 0 — 0 14 Patoka River at Winslow 21 10 8 2 4 19 154 4 15 White River at Petersburg 280 78 66 12 67 24 160 53 16 Busseron Creek 

near Carlisle

8 2 1 1 1 13 140 1 
Table 8.  Mercury concentrations in fish-tissue samples from watersheds upstream from monitoring stations on Indiana streams, 1993–2004.—Contin[≥, greater than or equal to; >, greater than; μg/kg, microgram per kilogram; — no data]

Station

number

Station name 

for upstream watershed

Total 

number of 

fish tissue 

samples

Total 

number 

of fishsampling 

locations

Number of 

river and 

stream 

sampling 

locations

Number of 

lake and 

reservoir 

sampling 

locations

Number of 

wet-weight 

mercuryconcentrations

≥criterion1

Percentage 

of wetweight 

mercury 

concentrations

≥ criterion1

Median 

wet-weight 

mercury 

concentration

(μg/kg)

Number of 

dry-weight 

mercury 

concentrations

>90th 

percentile2

17 Mississinewa River 

near Peoria

65 20 20 0 5 8 100 4 

18 Wabash River 

near Huntington

40 10 7 3 5 13 144 5 

19 Maumee River 

at New Haven

78 16 16 0 8 10 129 6 

20 Fish Creek near Artic 1 1 1 1 0 0 — 0 21 St. Joseph River at Elkhart 154 8 8 0 19 12 142 17 22 Trail Creek at Michigan City 23 3 3 0 5 22 150 4 23 Deep River 

at Lake George at Hobart

1 1 1 0 0 0 — 0 

24 Kankakee River at Shelby 83 28 17 11 6 7 90 4 25 Wabash River at Vincennes 44 6 5 1 13 30 170 7 26 Wabash River 

at Mt. Carmel, Ill.

36 4 0 4 6 17 250 6 

1Criterion is U.S. Environmental Protection Agency (2001) water-quality criterion of 300 μg/kg methylmercury in fish tissue. Percentage greater than criterion was computed 

centrations in a watershed that were greater than or equal to 300 μg/kg by the number of samples in the watershed. 

2The 90th percentile of dry-weight total mercury concentrations is 1,495 μg/kg, in 1,731 samples in Indiana, 1993–2004. Percentage greater than the 90th percentile was comp

concentrations in a watershed that were greater than 1,495 μg/kg by the number of samples in the watershed.
Table 9.  Mercury concentrations in fish-tissue samples near monitoring stations on Indiana streams, 1993–2004. [km, kilometer; >greater than; μg/kg, microgram per kilogram; ng/L, nanogram per liter; —, no data] Station number Station name Number of fish-tissue samples within 5 km upstream Number of wet-weight mercury concen- trations > criterion1 Percentage of wet- weight mercury concen- trations > criterion1 Median wet-weight mercury concen- tration (μg/kg) Number of dry-weight mercury concen- trations >90th percentile2 Percentage of dry- weight mercury concen- trations >90th percentile2 Median dry-weight mercury concen- tration (μg/kg) Number of uncensored methyl- mercury concen- trations 

Stream locations 1 Fall Creek near Fortville 5 2 40 190 2 40 841 8 

5 Wabash River at Terre Haute 21 6 29 190 4 19 769 14 7 White River near Centerton 22 7 32 198 5 23 930 15 

15 White River at Petersburg 11 5 45 240 2 18 1,020 9 19 Maumee River at New Haven 23 5 22 170 4 17 734 13 22 Trail Creek at Michigan City 23 5 22 150 4 17 644 8 25 Wabash River at Vincennes 6 0 0 135 0 0 550 9 

Reservoir locations

6 Mills Creek

 at Cagles Mill Dam

9 0 0 149 0 0 663 8 

10 East Fork Whitewater River 

near Brookville

10 1 10 140 0 0 683 1 

17 Mississinewa River 

near Peoria

6 0 0 93 0 0 477 11 

18 Wabash River 

near Huntington

5 0 0 65 0 0 301 14 

1Criterion is U.S. Environmental Protection Agency (2001) water-quality criterion of 300 μg/kg methylmercury in fish tissue. Percentage greater than criterion was computed 

centrations that were greater than 300 μg/kg by the number of samples within 5 km of the monitoring station. 

2The 90th percentile of dry-weight total mercury concentrations is 1,495 μg/kg, in 1,731 samples in Indiana, 1993–2004. Percentage greater than the 90th percentile was comp

concentrations that were greater than 1,495 μg/kg by the number of samples within 5 km of the monitoring station.
Mercury in Indiana Watersheds 41

concentrations were highest near station 15 (1,020 μg/kg), station 7 (930 μg/kg), and station 1 (841 μg/kg). Consistent with 

this fine-scale analysis, mercury also was highest in fish from 

watersheds 1 and 15, based on the coarse-scale analysis. 

Mercury concentrations in fish-tissue samples and 

unfiltered methylmercury concentrations in water samples 

from nearby monitoring stations did not indicate a consistent 

relation (table 9). Statistical examination of mercury concentrations in fish-tissue samples collected within 5 km of the 

downstream end of 11 watersheds indicated that stations 1, 7, 

and 15 did not differ significantly, although differences among 

the 11 stations were significant (p < 0.001; Kruskal-Wallis 

test). Wet-weight mercury concentrations near stations 7 and 

15 were significantly higher than those near stations 10 and 17 

(Tukey’s test). Statistical examination of methylmercury concentrations in water samples at these 11 monitoring stations 

indicated that stations 1, 7, and 15 did not differ significantly, 

although differences among the 11 stations were significant 

(p < 0.001; Kruskal-Wallis test). Unfiltered methylmercury 

concentrations in water from stations 7 and 15 were significantly higher than those from station 10 (Tukey’s test).

Chasar and others (2009) reported that mercury levels in 

fish were related to methylmercury concentrations in water, 

regardless of the trophic level of the fish. The fish-tissue data 

available for this study were not designed to correspond with 

the stream mercury- and methylmercury-concentration data. 

In large watersheds, some of the fish-sampling sites are distant 

from the stream-monitoring station—as much as 150 km in 

watershed 15 and 225 km in watershed 25 (fig. 2). The number 

of fish-tissue samples and the dates of collection vary considerably among the watersheds. Coordination of the fish-tissue 

sampling sites and schedules with the stream-monitoring 

network has the potential to reduce these limitations.

Sources of Mercury 

The mercury concentrations in stream samples, stream 

mercury loads, and mercury concentrations in fish-tissue 

samples from Indiana watersheds, 2002–2006, were influenced 

by sources of mercury in several ways. 

• Atmospheric mercury deposition is a nonpoint source 

that contributes mercury to a watershed. 

• Local stationary sources of mercury emissions in 

a watershed and their combined annual emissions 

potentially contribute atmospheric mercury deposition 

to that watershed. (Regional, continental, and global 

sources of atmospheric mercury also contribute deposition to a watershed.)

• Mercury in wastewater discharges from permitted 

outfalls are point sources that potentially contribute 

mercury to a watershed. (Monitoring data show that 

mercury was reported in most of the samples of wastewater effluent collected in Indiana.)

• Land cover can affect the rate at which mercury is 

retained, transformed, and transported to streams in a 

watershed. 

Atmospheric Mercury Deposition

This section of the report summarizes monitoring data 

for atmospheric mercury wet-deposition rates in Indiana, 

discusses atmospheric mercury wet- and dry-deposition loading to watersheds, and compares stream mercury yields to the 

atmospheric-deposition loading rates. In addition, estimates 

of atmospheric mercury dry-deposition rates are presented, 

including loads to watersheds and comparisons with atmospheric wet deposition.

As described in the “Mercury Load Calculations” section 

of this report, average annual atmospheric mercury wetdeposition rates for 2001–2006 were computed with average 

annual mercury concentrations in precipitation from 9 MDN 

stations and average annual precipitation from 151 NWS sites 

in Indiana and 4 surrounding states. The spatial distribution of 

average annual mercury wet- deposition rates in the study area 

were interpreted in an isopleth map (fig. 14). The boundaries of the 26 watersheds in this report, including the parts of 

6 watersheds outside Indiana, were superimposed on this map. 

Average annual mercury wet-deposition rates in the study 

area ranged from a low of 9 to 10 μg/m2/yr in northern Indiana, which includes isolated areas with less than 9 μg/m2

/yr, to 

a high of 15 to 16 μg/m2/yr in at least six counties in southeastern Indiana (fig. 14), which includes two counties with 15 

to 19 μg/m2/yr. The area in southeastern Indiana with the high 

mercury deposition rate well exceeds the 12-μg/m2/yr average 

annual mercury wet-deposition rate for five MDN stations in 

Indiana, 2001–2006 (Risch, 2009). 

Some uncertainty exists as to whether the area in southeastern Indiana with the high mercury deposition rate extends 

further to southwestern Indiana, for two reasons. First, the 

MDN does not include a station in southwestern Indiana, 

southeastern Illinois, or northwestern Kentucky that would 

be sufficiently close to resolve the average annual mercury 

concentrations in precipitation in southwestern Indiana to a 

degree that is comparable to other parts of Indiana (fig. 3). In 

contrast, the number of NWS stations in southwestern Indiana 

does resolve the average annual precipitation to a degree 

that is comparable to other parts of Indiana (fig. 3). Second, 

a substantial number of stationary sources with high annual 

mercury emissions are in southwestern Indiana (Indiana 

Department of Environmental Management RAPIDS data for 

2002 and 2005), which could contribute to higher mercury 

concentrations in precipitation. Uncertainty about the boundaries of the area in southern Indiana with a high mercury wetdeposition rate also was reported in an analysis of 2004–2005 

data by Risch and Fowler (2008).

Average annual atmospheric mercury wet-deposition 

loads, in grams per year, were computed for each watershed 

with data from the isopleth map (fig. 14) by using the method 
National Weather Service Cooperative Observer Network site

0 25 50 MILES

0 25 50 KILOMETERS

< 9.00

9.01 - 10.00

10.01 - 11.00

11.01 - 12.00

12.01 - 13.00

13.01 - 14.00

14.01 - 15.00

15.01 - 19.00

Ranges of average annual mercury wet-deposition rates,

2001-2006, micrograms per square meter per year

Watershed upstream from

monitoring station

MICHIGAN

ILLINOIS

OHIO

INDIANA

2

24

23

22 21

20

19

18

17

8

1

10

12 11

13 14

15

25

5

16

6

7

4

3

26

9

Monitoring station for mercury in streams, with station number

Indiana county boundary

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

Universal Transverse Mercator projection zone 16, NAD 1983

12

87°00' 86°00' 85°00'

41°00'

40°00'

39°00'

EXPLANATION

42 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Figure 14.  Isopleth map of average annual mercury wet-deposition rates, 2001–2006, showing upstream watershed boundaries

for monitoring stations on Indiana streams.
Mercury in Indiana Watersheds 43

described in the “Mercury Load Calculations” section of the 

report. The average annual atmospheric mercury loadings 

entering the watersheds (also called loading rates), in micrograms per square meter per year, were computed by dividing 

the loads by the watershed upstream drainage areas. 

Atmospheric mercury loading rates for Indiana watersheds, 2001–2006, ranged from 9.60 to 14.8 μg/m2

/yr, with a 

median of 11.3 μg/m2/yr (table 10). Watershed 11, which had 

the highest atmospheric mercury loading rate, 14.8 μg/m2/yr, 

is in the area in southeastern Indiana with the high mercury 

wet-deposition rate (fig. 14). Watersheds 12, 13, 14, and 15 in 

southern Indiana (fig. 14) had atmospheric mercury loading 

rates higher than the 12 μg/m2 average for five MDN stations 

in Indiana, 2001–2006 (Risch, 2009).

The average annual stream yields of total mercury were 

positively correlated with the average annual atmospheric 

mercury wet-deposition loading rates in 18 watersheds for 

which yield and loading rates were available (Kendall’s tau20

= 0.47; p = 0.007). Stream mercury yields were not related 

uniformly to atmospheric mercury loadings. The percentage of 

stream mercury yield from atmospheric mercury wet-deposition loading ranged from 7 percent at station 3 to 360 percent 

at station 12 (table 10, fig. 15). Stream mercury yields from 

13 of the 18 watersheds were less than 100 percent of the 

atmospheric loading, indicating that some of the atmospheric 

mercury entering the watersheds was not delivered by the 

stream. Rather, this mercury was retained in the watershed or 

re-emitted to the air. 

Other investigators reported that much of atmospheric 

mercury wet deposition apparently is retained in the watershed 

before reaching the stream, a finding that is consistent with 

this observation in Indiana. Shanley and others (2008) used 

MDN data and stream-monitoring data for five watersheds to 

observe that 60 to 97 percent of the mercury wet deposition 

was retained. Brigham and others (2009) used MDN data and 

stream-monitoring data for eight watersheds and observed that 

stream mercury loads were less than 50 percent of atmospheric 

mercury loads. Hintelmann and others (2002) used an experimental approach to monitor the fate of atmospheric mercury 

in wet deposition. They found that much of the mercury was 

retained in vegetation and soils in a boreal forest study site, 

and the mercury levels in runoff responded slowly to changes 

in mercury deposition rates. 

A ratio of mercury yield to mercury loading less than 100 

percent also may involve inputs other than atmospheric deposition. Mason and Sullivan (1998) studied mercury transport 

in an urbanized watershed and observed stream mercury yields 

that were 60 to 80 percent of atmospheric wet-deposition 

20The Kendall’s tau correlation coefficient (Helsel and Hirsch, 1995) is a 

nonparametric, rank-based procedure to evaluate the relation between two 

variables. A strong positive correlation is indicated by a Kendall’s tau of 0.70 

or higher. In this report, a moderate positive correlation is indicated by a Kendall’s tau higher than 0.35 and less than 0.70. A significance level (α) of 0.05 

or less was used to accept a statistically significant difference. The p-value is 

the significance attained by the data. The smaller the p-value, the more believable the statistical difference. 

loads, concluding that sources other than regional atmospheric 

deposition were contributing some of the mercury load to the 

stream.

Atmospheric mercury dry deposition was not measured 

directly in Indiana during 2001–2006. Other investigators 

have reported that atmospheric mercury dry deposition can be 

a substantial portion of the total atmospheric mercury deposition. Depending on location, modeled predictions and inferential estimates of atmospheric mercury dry-deposition rates 

can be equal to, or several times, the atmospheric mercury 

wet-deposition rates (Cohen and others, 2004; Poissant and 

others, 2004; Seigneur and others, 2004; Miller and others, 

2005; Lyman and others, 2007). 

Atmospheric mercury dry-deposition rates in Indiana 

were estimated for this report. These estimates are not based 

on a dataset as extensive as that for wet deposition in Indiana. In 2004, air samples were collected every six days at 

three MDN stations in Indiana (IN20, IN21, and IN26; fig. 2) 

by means of manual methods described in Risch and others (2007). Concentrations of three atmospheric mercury 

fractions or “species”— reactive gaseous mercury (RGM), 

particulate-bound mercury (PHg), and gaseous elemental 

mercury (GEM)—were determined in these air samples with 

low-level methods. Dry-deposition rates for the three mercury 

species were estimated with the inferential method described 

by Seigneur and others (2004), Miller and others (2005), and 

Lyman and others (2007). Annual dry-deposition rates for each 

species (table 11), in micrograms per square meter per year, 

were computed in a series of steps. Seasonal median daily 

concentrations of RGM, PHg, and GEM in samples from the 

Indiana stations, reported in Risch and others (2007), were 

multiplied by a representative vertical deposition velocity 

for each species reported in the scientific literature (summarized in Seigneur and others, 2004). The resulting daily 

dry-deposition rates were multiplied by the number of days 

for each season—winter/fall (180 days), spring (90 days), and 

summer (90 days) to get seasonal dry-deposition rates. Annual 

dry-deposition rates for each species were the sum of the three 

seasonal rates. 

The annual dry-deposition rates for each mercury species (table 11) were multiplied by the upstream drainage area 

of each watershed to determine the atmospheric mercury 

dry-deposition loading rate for each watershed. The vertical 

deposition velocity for GEM in forest land cover is higher than 

that in nonforest land cover, and the GEM dry-deposition rate 

in forest land cover is 6 times higher (table 11). The reason for 

the higher dry-deposition rate is that forest canopies are sinks 

for GEM (Grigal, 2002). Therefore, the GEM dry-deposition 

rate in forest land cover was applied to the upstream drainage 

area in forest cover in each watershed, and the GEM dry-deposition rate in nonforest land cover was applied to the remaining upstream drainage area in the watershed (table 12). Data 

for forest land cover was from the NLCD (Multi-Resolution 

Land Characteristics Consortium, 2001), as described in the 

“Sources of Data” section of this report. Further discussion is 

in the “Land Cover” section later in this report.
44 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 10.  Average annual atmospheric mercury wet-deposition loads and loading rates, 2001–2006, and average annual stream yields

of total mercury, 2002–2006, in watersheds upstream from monitoring stations on Indiana streams.—Continued

[g, gram; km2, square kilometer; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station

number Station name

Average annual 

atmospheric 

mercury 

wet-deposition 

load 

(g)

Upstream

drainage area

(km2)

Average annual

atmospheric 

mercury wetdeposition

loading rate

(μg/m2/yr)

Average annual 

stream mercury 

yield 

(μg/m2/yr)

Ratio of stream 

mercury yield to 

wet atmospheric 

mercury loading

(percent)

1 Fall Creek near Fortville 5,278 447 11.8 17.7 150 

2 Eel River near Logansport 21,831 2,043 10.7 3.74 35 

3 Tippecanoe River 

at Winimac

26,044 2,438 10.7 .75 7 

4 Wildcat Creek 

near Lafayette

23,409 2,056 11.4 18.1 159

5 Wabash River at Terre Haute 348,329 31,936 10.9 2.05 19 

6 Mills Creek

 at Cagles Mill Dam

8,856 759 11.7 ND ND

7 White River near Centerton 72,051 6,324 11.4 39.6 347 

8 White River at Nora 35,634 3,149 11.3 20.5 181 

9 Sugar Creek 

near New Palestine

2,724 243 11.2 2.02 18 

10 East Fork Whitewater River 

near Brookville

11,820 986 12.0 ND ND

11 Vernon Fork Muscatatuck 

River at Vernon

7,571 512 14.8 13.1 88 

12 East Fork White River 

at Seymour

76,042 6,056 12.6 45.2 360 

13 Blue River at Fredericksburg 9,422 732 12.9 1.04 8 

14 Patoka River at Winslow 19,168 1,559 12.3 6.05 49 

15 White River at Petersburg 352,794 28,794 12.23 ND ND

16 Busseron Creek 

near Carlisle

6,505 591 11.0 4.70 43 

17 Mississinewa River 

near Peoria

23,774 2,093 11.4 ND ND

18 Wabash River 

near Huntington

21,517 1,985 10.8 ND ND 

19 Maumee River 

at New Haven

52,580 5,077 10.4 5.42 52 

20 Fish Creek near Artic 2,516 248 10.1 1.50 15 

21 St. Joseph River at Elkhart 89,035 8,756 10.2 .73 7 

22 Trail Creek at Michigan City 1,457 152 9.60 ND ND
Mercury in Indiana Watersheds 45

Table 10.  Average annual atmospheric mercury wet-deposition loads and loading rates, 2001–2006, and average annual stream yields

of total mercury, 2002–2006, in watersheds upstream from monitoring stations on Indiana streams.—Continued

[g, gram; km2, square kilometer; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station

number Station name

Average annual 

atmospheric 

mercury 

wet-deposition 

load 

(g)

Upstream

drainage area

(km2)

Average annual

atmospheric 

mercury wetdeposition

loading rate

(μg/m2/yr)

Average annual 

stream mercury 

yield 

(μg/m2/yr)

Ratio of stream 

mercury yield to 

wet atmospheric 

mercury loading

(percent)

23 Deep River 

at Lake George at Hobart

3,494 321 10.9 1.57 14 

24 Kankakee River at Shelby 48,416 4,597 10.5 1.31 12 

25 Wabash River at Vincennes 388,993 35,628 10.9 ND ND

26 Wabash River 

at Mt. Carmel, Ill.

852,659 74,293 11.5 ND ND

Table 11.  Atmospheric mercury species concentrations, vertical deposition velocities, and annual dry-deposition rates in

Indiana, 2004.

[cm/s, centimeter per second; pg/m3, picogram per cubic meter; μg/m2/yr, microgram per square meter per year]

Atmospheric 

mercury species

Vertical 

deposition 

velocity1

(cm/s)

Winter/Fall Spring Summer

Annual

dry

deposition 

rate5

(μg/m2/yr)

Median

daily

concentration2

(pg/m3)

Seasonal 

dry

deposition 

rate3

(μg/m2)

Median

daily

cocentration

(pg/m3)

Seasonal

dry

deposition 

rate4

(μg/m2)

Median

daily 

concentration

(pg/m3)

Seasonal

dry

deposition 

rate4

(μg/m2)

Reactive gaseous 0.50 2.90 0.225 1.50 0.058 0.80 0.033 0.317

Particulate bound .10 3.70 .057 5.95 .046 4.10 .034 .137

Gaseous 

elemental 

(land)

.01 1,480 2.30 1,320 1.03 1,340 1.10 4.43

Gaseous 

elemental 

(forest)

.06 1,480 13.8 1,320 6.16 1,340 6.60 26.6

1From Seigneur and others (2004).

2From Risch and others (2007).

3Seasonal dry deposition rate computed as the product of the vertical deposition velocity and median daily concentration. Units were converted to μg/m2

/day 

and multiplied by 180 days.

4Seasonal dry deposition rate computed as the product of the vertical deposition velocity and median daily concentration. Units were converted to μg/m2

/day 

and multiplied by 90 days.

5

Annual dry deposition rate computed as the sum of the three seasonal dry deposition rates.
1-1-1

39°00'

40°00'

41°00'

87°00' 86°00' 85°00'

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

Universal Transverse Mercator projection zone 16, NAD 1983

0 25 50 MILES

0 25 50 KILOMETERS

Ratio of average annual stream

mercury yield to atmospheric mercury

wet-deposition loading (percent)

Monitoring station for mercury

in streams, with station number

2

24

23

22

21

20

19

18

17

8

1

9

10

12 11

13 14

25 15

5

16

6 7

4

3

MICHIGAN

ILLINOIS OHIO

KENTUCKY

INDIANA

26

22

EXPLANATION

Watershed upstream from

monitoring station 1 - 26

< 25

26 -50

51 - 75

76 - 100

> 101

No Data

46 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Figure 15.  Ratios of average annual stream mercury yield to atmospheric mercury wet -deposition loading in watersheds

upstream from monitoring stations on Indiana streams, 2001–2006.
Mercury in Indiana Watersheds 47

Annual atmospheric mercury dry-deposition loading 

rates to the watersheds ranged from 5.6 μg/m2/yr (watershed 

4) to 13.6 μg/m2/yr (watershed 14). The median rate was 

7.2 μg/m2/yr. The atmospheric mercury dry-deposition loading 

rates to the watersheds were 0.49 to 1.4 times the atmospheric 

mercury wet-deposition loading rates. 

Watersheds 7 and 12 had stream mercury yields that 

were 224 and 233 percent, respectively, of the combined 

atmospheric mercury wet and dry loadings (table 12). Other 

mercury inputs besides atmospheric deposition apparently 

contributed approximately half of the stream mercury yields 

in watersheds 7 and 12. The stream mercury yields were 3.9 to 

120 percent of the combined atmospheric mercury wet and dry 

loading in 16 of 18 watersheds (table 12). 

Ratios of stream mercury yields to the combined atmospheric mercury wet- and dry-deposition loading rates, 

combined with knowledge from other investigators, indicate 

that three conditions may be present in Indiana: (1) Uncommonly, watersheds have stream mercury yields higher than 

the combined atmospheric mercury wet and dry loading rates 

and receive mercury input from sources other than atmospheric deposition. One of these other sources is mercury in 

wastewater discharges, discussed in a following section of this 

report. Another source is mercury from atmospheric deposition that was retained on soil in the watershed until that soil 

was eroded and washed into streams. Typically, watersheds 

have stream mercury yields less than the combined atmospheric mercury wet and dry loading rates and either receive 

(2) mercury input entirely from atmospheric deposition, with 

the excess loading retained in the watershed or re-emitted to 

the air, or (3) mercury input from atmospheric deposition and 

other sources, with excess loading retained in the watershed or 

re-emitted to the air.

Mercury Emissions to the Atmosphere

Mercury emissions to the atmosphere were examined for 

their potential influence on total mercury concentrations and 

stream yields of total mercury in the watersheds. Locations 

of stationary sources of mercury emissions to the atmosphere 

(fig. 6) and their annual mercury emissions in 2002 and 2005 

were obtained from the RAPIDS data for Indiana (Indiana 

Department of Environmental Management, Office of Air 

Quality, written commun., 2005, 2008). The number of mercury-emission sources and the annual emissions in 2002 and 

2005 were totaled for each watershed (appendix table 1–5). 

In 2002, 128 stationary sources in the 26 watersheds 

emitted 2,830 kg (6,289 lb) of mercury. The highest emissions and highest number of stationary sources were 1,097 

kg (2,438 lb) of mercury from 25 sources in watershed 5 and 

617 kg (1,371 lb) of mercury from 20 sources in watershed 15. 

In watersheds 2, 7, 19, and 24, annual emissions in 2002 were 

greater than 150 kg. 

In 2005, 99 stationary sources in the 26 watersheds 

emitted 1,906 kg (4,236 lb of mercury). Similar to 2002, the 

highest emissions in 2005 were 376 kg (836 lb) of mercury 

from 22 sources in watershed 5 and 586 kg (1,302 lb) of mercury from 18 sources in watershed 15. Annual emissions were 

greater than 150 kg in watersheds 7, 19, and 24. 

For the 26 watersheds in Indiana, there were positive 

correlations between the average total mercury concentrations 

in water and four variables: the number of emission sources 

in the watersheds in 2002 and 2005 and the annual mercury 

emissions in 2002 and 2005.21 Even so, a consistent relation 

was not observed, and atmospheric mercury transport and 

source-area modeling for the watersheds was beyond the scope 

of this report. 

A number of factors determine how much, if any, of the 

mercury emitted within a watershed will contribute to the 

mercury concentrations and stream mercury yield at the downstream end of that watershed. These factors include the location of an emission source in the watershed, prevailing wind 

direction, precipitation conditions, height above ground for 

the emissions from the stationary source, and type of mercury 

species in the emissions. 

The influence of local and regional sources on atmospheric mercury deposition has been reported by other investigators. Using a model to trace atmospheric mercury wet and 

dry deposition to emissions sources, the U.S. Environmental 

Protection Agency (2008) found that areas of high deposition 

frequently were dominated by one or more nearby sources 

and by collective sources within a state. For a location of high 

deposition in Indiana, their model calculated that 54 percent 

of the deposition came from local sources in the state. Seigneur and others (2006) used different models to predict 

atmospheric mercury wet and dry deposition in the vicinity of 

powerplants. The models calculated that 9 to 53 percent of the 

mercury emitted by typical powerplants fell within 9.3 km; 

1 to 8 percent fell within 50 km. Keeler and others (2006) 

applied two multivariate statistical models and meteorological 

analysis to monitoring data collected in 2003–2004 at a site 

in the Ohio River valley of eastern Ohio. They found that the 

majority of the mercury wet deposition was contributed by 

coal combustion from local and regional sources. Cohen and 

others (2004) used a sophisticated source-receptor model to 

estimate mercury wet and dry deposition to the Great Lakes. 

For Lake Michigan, as an example, they found that approximately half the deposition came from local sources within 

100 km of the lake and that the largest contribution was from 

coal combustion. 

Continued monitoring of atmospheric mercury wet deposition in Indiana provides a dataset for modeling the contribution of local and regional sources to stream mercury yields 

from watersheds. However, long-term monitoring data for 

21The moderate positive correlation of average unfiltered total mercury concentration to the following factors is based on the Kendall’s tau statistics and 

p-values listed (α = 0.05): 2002 mercury emissions (tau = 0.35, p = 0.013); 

2002 emissions sources (tau = 0.40, p = 0.004); 2005 mercury emissions 

(tau = 0.35, p = 0.010); and 2005 mercury sources (tau = 0.35, p = 0.010).
Table 12.  Annual atmospheric mercury dry-deposition and wet-deposition loading rates and annual stream yields of total mercury in watersheds upstations on Indiana streams.—Continued [km2, square kilometer; μg/m2/yr, microgram per square meter per year; ND, not determined] Station number Station name Upstream drainage area with forest land cover (km2) Upstream drainage area with non-forest land cover (km2) Annual atmospheric mercury dry-deposition loading rate (μg/m2/yr) Average annual atmospheric mercury wet-deposition loading rate (μg/m2/yr) Combined atmospheric mercury wet and dry loading (μg/m2/yr) Avera

annu

stream m

yiel

(μg/m2

1 Fall Creek near Fortville 24 423 6.1 11.8 17.9 17.7 2 Eel River near Logansport 169 1,874 6.7 10.7 17.4 3.73 Tippecanoe River at Winimac 217 2,221 6.9 10.7 17.5 0.74 Wildcat Creek near Lafayette 64 1,992 5.6 11.4 17.0 18.1 5 Wabash River at Terre Haute 2,757 29,179 6.8 10.9 17.7 2.06 Mills Creek 

at Cagles Mill Dam

116 643 8.3 11.7 19.9 ND 

7 White River near Centerton 396 5,928 6.3 11.4 17.7 39.6 8 White River at Nora 128 3,021 5.8 11.3 17.1 20.5 9 Sugar Creek near New 

Palestine

12 231 6.0 11.2 17.2 2.0

10 East Fork Whitewater River 

near Brookville

171 815 8.7 12.0 20.7 ND 

11 Vernon Fork Muscatatuck 

River at Vernon

176 336 12.5 14.8 27.3 13.1 

12 East Fork White River 

at Seymour

530 5,526 6.8 12.6 19.4 45.2 

13 Blue River at Fredericksburg 202 530 11.0 12.9 23.9 1.014 Patoka River at Winslow 613 946 13.6 12.3 25.9 6.0
Table 12.  Annual atmospheric mercury dry-deposition and wet-deposition loading rates and annual stream yields of total mercury in watersheds upstations on Indiana streams.—Continued[km2, square kilometer; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station

number Station name

Upstream 

drainage area 

with forest 

land cover

(km2)

Upstream

drainage area 

with non-forest 

land cover

(km2)

Annual 

atmospheric 

mercury 

dry-deposition 

loading rate 

(μg/m2/yr)

Average annual 

atmospheric 

mercury 

wet-deposition 

loading rate

(μg/m2/yr)

Combined 

atmospheric 

mercury 

wet and dry 

loading 

(μg/m2/yr)

Avera

annu

stream m

yiel

(μg/m2

15 White River at Petersburg 6,884 21,910 10.2 12.2 22.4 ND 16 Busseron Creek 

near Carlisle

150 441 10.5 11.0 21.5 4.7

17 Mississinewa River 

near Peoria

154 1,939 6.5 11.4 17.9 ND 

18 Wabash River 

near Huntington

111 1,874 6.1 10.8 17.0 ND 

19 Maumee River 

at New Haven

506 4,571 7.1 10.4 17.5 5.4

20 Fish Creek near Artic 45 203 8.9 10.1 19.1 1.521 St. Joseph River at Elkhart 1,313 7,443 8.2 10.2 18.4 0.722 Trail Creek at Michigan City 58 94 13.3 9.60 22.9 ND 23 Deep River 

at Lake George at Hobart

58 263 8.9 10.9 19.8 1.5

24 Kankakee River at Shelby 515 4,082 7.4 10.5 17.9 1.325 Wabash River at Vincennes 3,454 32,174 7.0 10.9 17.4 ND 26 Wabash River 

at Mt. Carmel, Ill.

11,973 62,320 8.5 11.5 17.5 ND 
50 Mercury in Indiana Watersheds: Retrospective for 2001–2006

estimating dry deposition of atmospheric mercury are unavailable for locations in Indiana. The addition of datasets for 

atmospheric mercury dry deposition in Indiana would improve 

modeling certainty regarding the sources of stream mercury 

yields from watersheds; these data should include air-quality 

mercury, throughfall mercury, and litterfall mercury (Harris, 

Krabbenhoft, and others, 2007). 

Mercury in Wastewater

The potential influence of mercury in wastewater on 

total mercury concentrations and stream mercury yields in the 

watersheds was examined by using monitoring data for mercury in wastewater-effluent samples and the number of permitted outfalls in the watersheds. Total mercury was routinely 

detected in treated wastewater effluent in Indiana, often at 

concentrations exceeding a water-quality criterion. Although 

there are thousands of wastewater outfalls and only a small 

percentage of these outfalls have been analyzed for mercury, 

the potential was demonstrated for mercury in wastewater to 

be discharged to Indiana watersheds. In some watersheds, discharges of mercury in wastewater may be contributing to total 

mercury concentrations in water and stream mercury yields.

Statewide, total mercury concentrations were determined 

in 534 grab samples of treated wastewater effluent collected 

by operators of 64 POTWs throughout Indiana. Total mercury 

concentrations ranged from <0.05 to 88 ng/L, with a median 

of 2.3 ng/L. Total mercury concentrations were higher than 

the reporting limit in 96 percent of the effluent samples that 

were analyzed. Compared to Indiana water-quality criteria for 

mercury, the 12-ng/L Indiana chronic-aquatic criterion was 

equaled or exceeded in 10 percent of the samples; the 1.8-ng/L 

Great Lakes human-health criterion was equaled or exceeded 

in 60 percent, and the 1.3-ng/L Great Lakes wildlife criterion 

was equaled or exceeded in 72 percent.

Among the 26 watersheds, total mercury concentrations 

were reported in 402 grab samples of wastewater effluent from 

50 POTWs in 15 watersheds. Concentrations ranged from 

<0.05 to 88 ng/L, with a median of 2.9 ng/L. Concentrations 

were higher than the reporting limit in 96 percent of the effluent samples that were analyzed. Compared to Indiana waterquality criteria for mercury, the 12-ng/L Indiana chronicaquatic criterion was equaled or exceeded in 12 percent of 

the samples; the 1.8-ng/L Great Lakes human-health criterion 

was equaled or exceeded in 68 percent, and the 1.3-ng/L Great 

lakes wildlife criterion was equaled or exceeded in 81 percent. The average mercury concentration in effluent samples 

was computed for the 50 POTWs (table 13, fig. 16) and for 

those with 3 or more samples, the values ranged from 0.83 

to 22.2 ng/L. The average mercury concentrations in effluent 

samples equaled or exceeded the 1.3-ng/L Great Lakes wildlife criterion at 45 of the 50 POTWs. 

Information from the literature indicates that wastewater 

may be a source of total mercury in watersheds. The National 

Association of Clean Water Agencies (NACWA, 2000) 

reported a 138-ng/L average concentration of mercury in 

domestic wastewater in different parts of the country with no 

industrial or commercial inputs. Several common household 

and toiletry items were found to contain levels of mercury that 

could account for part of this average, but most of the mercury was attributed to human waste. A laboratory evaluation 

of mercury removal by amalgam separators used in dentists’ 

offices (Fan and others, 2002) showed 95-percent effectiveness, indicating some mercury in wastewater could be contributed by dentists’ offices, even when amalgam separators are in 

use. The NACWA 2000 report observed that POTWs remove 

97 percent of the mercury in their influent, consistent with a 

removal rate for a POTW studied by Balogh and Liang (1995). 

A study of the Scioto River near Columbus, Ohio, in 2004 

by Lyons and others (2006) reported that the highest mercury 

concentrations were downstream from two POTWs.

This information demonstrates the potential for mercury 

in wastewater to be contributing to stream mercury yields 

in some Indiana watersheds, including three in particular. 

Watersheds 7 and 19 had high total mercury concentrations in 

water (table 3). Watersheds 7 and 12 had high stream mercury 

yields (table 12), and the high ratios of stream mercury yield 

to atmospheric mercury wet- and dry-deposition load indicated 

that inputs other than atmospheric mercury deposition were 

likely. Mercury was reported in samples of treated wastewater 

effluent in watersheds 7, 12, and 19 (table 13). At a POTW 

upstream from station 7, the average mercury concentration 

was 10.9 ng/L in 20 samples. At a POTW upstream from station 12, the average mercury concentration was 11.5 ng/L in 

22 samples. One of the highest average effluent concentrations 

was 22.2 ng/L in 39 samples at a POTW upstream from station 

19. These average mercury concentrations in effluent samples 

were higher than the median total mercury concentrations in 

water samples at stations 7, 12, and 19 (table 13). 

According to the Permit Compliance System database 

for National Pollutant Discharge Elimination System permits 

in Indiana in 2005, there were 5,551 permitted outfalls of 

treated and untreated wastewater. In the watersheds upstream 

from the 26 monitoring stations on Indiana streams, there 

were 4,144 permitted outfalls (fig. 7, table 14). Of these, 1,044 

(25 percent) were classified as outfalls at a major facility with 

the capacity to discharge up to 1 Mgal/d. The outfalls are characterized in the permit database as discharging sanitary wastewater, process wastewater, cooling water, storm runoff, and 

mixtures of these types, along with some mine-pit dewatering.

Total mercury in some watersheds could be attributed 

to mercury in wastewater because the average total mercury 

concentrations in water showed a moderate correlation with 

the number of outfalls (Kendall’s tau = 0.47, p = 0.001). 

Three watersheds with high mercury concentrations in water 

and high stream mercury yields had a substantial number of 

outfalls: 401 in watershed 7, 225 in watershed 12, and 182 in 

watershed 19. 
1.15

2.84

0.31

22.2

4.15

3.02

1.80 3.10

3.46

3.47

2.63

1.19

4.42

2

24

23

22

21

20

19

18

17

8 1

9

10

12 11

13

14

15

25

5

16

6 7

4

3

EXPLANATION

Wastewater sample site

and average total

mercury concentration,

2002-2005, in nanograms

per liter

Monitoring station for

mercury in streams,

with station number

12

1.67

Watershed upstream from

monitoring station

26

40°00'

39°00'

87°00' 86°00' 85°00'

41°00'

6.86

2.50

9.85

40.2

2.43

2.69

3.63

4.47

2.50

9.67

2.60

3.60 4.30

2.14

PA

2.95

1.49

2.62

3.14

1.66 0.83

11.5

2.50

1.26

3.30

0.74 2.56

10.9

5.26

4.05

2.16 2.30

1.86

3.00 7.83

1.84

5.56

5.12

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

Universal Transverse Mercator projection zone 16, NAD 1983

0 25 50 MILES

0 25 50 KILOMETERS

Mercury in Indiana Watersheds 51

Figure 16.  Treatment works upstream from monitoring stations on Indiana streams, with average total mercury concentrations in

samples of wastewater effluent, 2002–2005 (from U.S. Environmental Agency Permit Compliance System).
52 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Although the number of outfalls indicates a potential for 

discharge of mercury in wastewater, the volume of the wastewater discharge may be important because the average total 

mercury concentrations in water samples showed a moderate correlation with the number of outfalls at major facilities 

(Kendall’s tau = 0.37, p = 0.008). Three watersheds with high 

mercury concentrations in water and high stream mercury 

yields had outfalls at major facilities: 45 percent in watershed 

7, 24 percent in watershed 12, and 37 percent in watershed 19 

(table 14).

Monitoring of flow volumes and mercury concentrations 

in wastewater, over a range of flow conditions at permitted 

outfalls in selected watersheds, would be needed to characterize the relative importance of discharges of mercury in 

wastewater as compared to atmospheric deposition. The two 

watersheds with approximately half of the stream mercury 

yield from sources other than atmospheric deposition (watersheds 7 and 12) might be appropriate locations to start this 

type of monitoring.

Table 13.  Average total mercury concentrations in grab samples of wastewater effluent at treatment

works upstream from monitoring stations on Indiana streams, 2002–2005.—Continued

[ng/L; nanograms per liter; sample data not available for stations 1, 4, 6, 9, 10, 14, 16, 18, 20, 25, and 26]

Station

number

Station name 

for upstream watershed

Average

total mercury

concentration

in samples1

(ng/L)

Number of 

wastewatereffluent

samples

Number of

censored 

values

2 Eel River near Logansport 5.12 8 4

3 Tippecanoe River at Winimac 1.84

5.56

2

19

0

0

5 Wabash River at Terre Haute 2.60

2.14

9.67

4.30

3.60

 3.10

3

12

 10

 11

 1

 2

0

1

0

1

0

0

7 White River near Centerton 3.30

 5.26

 .74

 2.56

 10.9

 4.05

 1.26

13

 10

 1

 9

 20

 8

 6

0

 0

 0

 0

 0

 0

 2

8 White River at Nora 3.00

 3.63

 2.50

 4.47

 1.86

 7.83

 2.30

14

 6

 7

 13

 9

 8

 2

0

 0

 0

 0

 2

 1

0

11 Vernon Fork Muscatatuck River at Vernon 3.14 7 0

12 East Fork White River at Seymour 2.43

 2.69

 11.5

 .83

18

 8

 22

 4

0

0

0

0
Mercury in Indiana Watersheds 53

Table 13.  Average total mercury concentrations in grab samples of wastewater effluent at treatment

works upstream from monitoring stations on Indiana streams, 2002–2005.—Continued

[ng/L; nanograms per liter; sample data not available for stations 1, 4, 6, 9, 10, 14, 16, 18, 20, 25, and 26]

Station

number

Station name 

for upstream watershed

Average

total mercury

concentration

in samples1

(ng/L)

Number of 

wastewatereffluent

samples

Number of

censored 

values

13 Blue River at Fredericksburg 2.50 1 0

15 White River at Petersburg 3.47

 1.19

 1.66

 40.2

 2.63

 4.42

 3.46

13

 2

 5

 2

 3

 5

 7

0

 0

 1

 0

 1

 0

 1

17 Mississinewa River near Peoria 3.02

 1.80

 4.15

 2.16

8

 2

 4

 6

0

 0

 0

 1

19 Maumee River at New Haven 22.2 39 0

21 St. Joseph River at Elkhart .31

 2.62

 2.84

2

 3

 8

0

0

0

22 Trail Creek at Michigan City 1.15 7 0

23 Deep River at Lake George at Hobart 1.49

 2.95

1

 14

0

0

24 Kankakee River at Shelby 9.85

6.86

2.50

10

 5

 2

0

0

0

1

Average total mercury concentrations that include censored values were computed with the Adjusted Maximum Likelihood Estimate procedure (Helsel, 2005) by using statistical software (S-Plus, Tibco Software, 2008).

Land Cover

Land cover affects the rate at which mercury is retained, 

transformed, and transported to streams in a watershed. For 

this report, land cover was examined graphically, statistically, and with lines of evidence for relations to mercury 

concentrations in stream samples, stream mercury yields, and 

mercury in fish-tissue samples. Land-cover classes from the 

2001 NLCD (Multi-Resolution Land Characteristics Consortium, 2001) were summarized as described in the “Sources of 

Data” section. For each of the 26 watersheds upstream from 

the monitoring stations on Indiana streams, the percentage 

of the drainage area in each land-cover class was determined 

(appendix table 1–6). Some land-cover classes were sparsely 

represented in the watersheds; some classes that were represented were similar. The 20 land-cover classes were combined 

into 7 land-cover types for discussion in this report:

• Urban: Low-intensity residential, high-intensity residential, and commercial/industrial/transportation.

• Forest: Deciduous forest, evergreen forest, mixed forest, and shrubland.
54 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 14.  Number of permitted outfalls in 2005 for watersheds upstream from monitoring stations on

Indiana streams.

[km2, square kilometer]

Station

number

Station name 

for upstream watershed

Upstream

drainage

area

(km2)

Number of 

permitted 

outfalls

Number 

of outfalls

for major

facilities1

1 Fall Creek near Fortville 447 20 2

2 Eel River near Logansport 2,043 81 28

3 Tippecanoe River at Winimac 2,438 61 9

4 Wildcat Creek near Lafayette 2,056 96 33

5 Wabash River at Terre Haute 31,936 587 191

6 Mills Creek at Cagles Mill Dam 759 17 0

7 White River near Centerton 6,324 401 182

8 White River at Nora 3,149 235 105

9 Sugar Creek near New Palestine 243 9 1

10 East Fork Whitewater River near Brookville 986 31 9

11 Vernon Fork Muscatatuck River at Vernon 512 13 5

12 East Fork White River at Seymour 6,056 225 53

13 Blue River at Fredericksburg 732 18 2

14 Patoka River at Winslow 1,559 162 8

15 White River at Petersburg 28,794 1,009 140

16 Busseron Creek near Carlisle 591 155 9

17 Mississinewa River near Peoria 2,093 135 38

18 Wabash River near Huntington 1,985 49 14

19 Maumee River at New Haven 5,077 182 67

20 Fish Creek near Artic 248 2 0

21 St. Joseph River at Elkhart 8,756 170 51

22 Trail Creek at Michigan City 152 10 6

23 Deep River at Lake George at Hobart 321 21 7

24 Kankakee River at Shelby 4,597 94 45

25 Wabash River at Vincennes 35,628 100 34

26 Wabash River at Mt. Carmel, Ill. 74,293 261 5

1

A major facility has the capacity to discharge more than 1 million gallons per day.
Mercury in Indiana Watersheds 55

• Minelands: Bare sand/rock/clay, quarries/strip mines/

gravel pits, coal minelands, and transitional.

• Wetlands: Woody wetlands and emergent herbaceous 

wetlands. 

• Open water.

• Grassland/herbaceous.

• Agricultural: Orchards/vineyards/other, pasture/hay, 

rowcrop, small grains, fallow.

For each of the 26 watersheds, the land area and the percentage of the drainage area in each land-cover type were determined (table 15). More than half of the drainage area in 24 of 

these 26 watersheds is in the agricultural land-cover type; the 

exceptions are watersheds 16 and 22.

Four of the land-cover types are of interest for their 

potential relation to mercury in watersheds: urban, forest, 

minelands, and wetlands. Urban land cover includes residential and commercial/industrial/transportation classes. All of 

the watersheds had area with urban land cover, although three 

watersheds had less than 1 percent. Forest land cover includes 

deciduous, evergreen, and mixed forest classes. The deciduous 

forest class was the most common; the shrubland land-cover 

class was uncommon. All of the watersheds had area with 

forest land cover. Minelands includes quarries, gravel pits, and 

active and abandoned (reclaimed and unreclaimed) surface 

coal mines. There are no gold or mercury mines in Indiana. 

Seven of the watersheds had more than 0.25 percent mineland, 

mostly coal mines, and one watershed had by far the most 

(19.6 percent). Wetlands land cover includes woody and emergent herbaceous wetlands. More than half the watersheds had 

greater than 1 percent of the area in wetlands, but the percentages generally were small—0.07 to 7.73 percent (table 15).

The percentages and areas of the 7 land-cover types were 

not correlated with average concentrations of total or methylmercury, percent methylmercury, average annual atmospheric 

mercury loading rates, stream mercury yields, or median 

dry-weight mercury concentrations in fish tissue samples in 

the 26 watersheds (Kendall’s tau test). The differences among 

watersheds in these measures of mercury levels were demonstrated with graphical and statistical evaluations in earlier 

sections of this report. Therefore, in the absence of a statistical 

correlation, a weight-of-evidence approach was used to determine whether land-cover type corresponds with the apparent 

mercury levels in the watersheds.

The percentage of a watershed drainage area in a landcover type does not take into account the square kilometers of 

area involved or the distribution and continuity of that landcover type in a watershed, so two types of information were 

used to interpret and compare the percentages of land-cover 

types: drainage-area category and map image. The 26 watersheds were grouped into small, medium, and large categories 

on the basis of the size of the upstream drainage area: less 

than 1,000 km2; from 1,000 to 10,000 km2; and more than 

10,000 km2 (table 16). The boundaries of the watersheds were 

mapped with color-coded land-cover types (fig. 17).

A high percentage of urban land corresponds with the 

high levels of mercury in watershed 7, the White River 

watershed in central Indiana. Watershed 7 is 12.6 percent 

urban (table 15), the highest percentage among medium-size 

watersheds (table 16, fig. 17). Watershed 8 is nested in watershed 7 and is 6.43 percent urban, the second-highest percentage among medium-size watersheds. Watershed 7 had total 

mercury concentrations that were among the highest (table 3). 

It also had a stream mercury yield that was higher than the 

atmospheric mercury wet- and dry-deposition loading (table 

12). Consistent with the urban population and urban land use 

in watersheds 7 and 8, mercury was reported in nearly all of 

the 131 wastewater-effluent samples from 14 POTWs in these 

watersheds (table 13). Watershed 7 had 401 wastewater outfalls with 182 of them at major facilities (table 14). 

A mapped density of urban land cover upstream from 

station 19 in the Maumee River watershed in northeastern 

Indiana (fig. 17) corresponds with the high mercury concentrations in water there (table 3) that were significantly higher 

than at other stations. Consistent with the urban population 

and urban land use upstream from station 19, a high average 

mercury concentration was reported for the 39 wastewatereffluent samples collected upstream (table 13). Watershed 19 

had 182 wastewater outfalls and 67 of them were at major 

facilities (table 14).

Other studies support the potential influence of urban 

land cover on mercury in a watershed. High total mercury 

concentrations in Indiana streams, 2004–2006, were reported 

at stations with upstream watersheds that included urban and 

industrial wastewater discharges (Ulberg and Risch, 2008). 

Lyons and others (2006) reported that particulate mercury 

loads in the Scioto River in Ohio were higher in areas with 

urban activity compared to rural areas. Brightbill and others 

(2004) examined the correlations between total mercury and 

methylmercury in fish and water in the Delaware River Basin 

in New Jersey, New York, and Pennsylvania. They reported a 

positive correlation of total mercury concentrations in water 

and fish with urban land cover, population density, and percent 

impervious surfaces. Engstrom and others (2007) used agedated sediment cores from 55 lakes in Minnesota to observe 

that modern mercury loading from atmospheric deposition was 

higher in urban areas than in rural areas.

A high percentage of forest land cover corresponds with 

the high mercury concentrations in water of the Patoka River 

watershed in southern Indiana (table 3); these concentrations were significantly higher than other stations. Watershed 

14 is 39.3 percent forest (the highest percentage among all 

26 watersheds; table 15). The estimated atmospheric mercury 

dry-deposition loading rate of 13.6 μg/m2 was the highest 

(table 12), and the average annual mercury wet-deposition 

loading rate of 12.3 μg/m2 was one of the highest (table 10). 

Watershed 14 does not have high annual mercury emissions 

or a high number of wastewater outfalls compared to other 
Table 15.   Land-cover types, by percentage of watershed drainage area and land area in watersheds upstream from monitoring stations on Indiana Land Cover Database).—Continued [pct, percentage of upstream drainage area; km2, square kilometer] Station number Urban Forest Mineland Wetland Water Grassland 

 (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2

1 5.23 23 5.45 24 0.11 <1 0.87 4 0.17 1 0 0 2 .92 19 8.28 169 0 0 1.63 33 .59 12 0 0 3 1.54 38 8.92 217 0 0 3.85 94 2.09 51 .01 0 4 3.29 68 3.10 64 .01 <1 1.19 24 .34 7 0 0 5 1.85 590 8.63 2,757 .32 102 1.70 543 .81 259 .39 124 6 .81 6 15.3 116 .23 2 .13 1 1.06 8 0 0 7 12.6 795 6.26 396 .11 7 .80 51 .94 60 0 0 8 6.43 203 4.07 128 .07 2 1.15 36 .72 23 0 0 9 1.95 5 4.97 12 0 0 .72 2 .23 1 0 0 

10 3.55 35 17.4 171 0 0 .64 6 2.18 22 0 0 

11 1.09 6 34.3 176 .34 2 .43 2 .44 2 0 0 

12 2.90 176 8.74 530 .06 4 .76 46 .39 24 0 0 13 1.06 8 27.6 202 .06 <1 .07 1 .20 1 0 0 14 1.01 16 39.3 613 5.38 84 .75 12 2.70 42 0 0 15 4.22 1,215 23.9 6,884 1.27 366 .72 208 .95 273 0 0 16 2.11 12 25.4 150 19.6 116 6.35 37 2.20 13 4.63 27 17 2.91 61 7.36 154 .04 1 1.08 23 .84 18 0 0 18 1.31 26 5.60 111 .08 2 .75 15 2.92 58 0 0 19 4.17 212 9.97 506 .03 2 1.96 99 .74 38 .04 2 20 .62 2 18.1 45 .11 <1 3.66 9 2.04 5 .44 1 21 2.11 184 15.0 1,313 .03 3 6.01 527 2.82 247 .01 1 22 13.3 20 38.4 58 .08 <10 7.73 12 .89 1 6.21 9 
Mercury in Indiana Watersheds 57

Table 15.   Land-cover types, by percentage of watershed drainage area and land area in watersheds upstream from monitoring stations on Indiana streams (from 2001 NationalLand Cover Database).—Continued[pct, percentage of upstream drainage area; km2, square kilometer]

Station

number

Urban Forest Mineland Wetland Water Grassland Agricultural

 (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2) (pct) (km2)

23 18.7 60 18.1 58 0 0 3.76 12 1.34 4 4.16 13 54.0 17324 1.93 89 11.2 515 .08 3 3.06 140 1.04 48 2.08 96 80.6 3,70525 1.87 666 9.69 3,454 .79 281 1.97 701 .94 335 .48 173 84.2 29,73626 2.70 2,005 16.1 11,973 1.24 921 1.57 1,168 .96 714 .28 211 77.1 56,380

watersheds (appendix table 1–5; table 14). Therefore, mer-

cury in regional or continental air masses likely contributed 

to the high mercury wet- and dry-deposition loading to forest 

land cover in this watershed. Litterfall and throughfall are the 

potential pathways transporting mercury from the forest to 

the water. 

Other studies support the potential influence of forest 

land cover on mercury in a watershed. Forests have been 

described as a sink for atmospheric mercury deposition and 

mercury accumulation (Lindberg, 1996; St. Louis and others, 

2001; Grigal, 2002; Rea and others, 2002; Miller and others, 

2005). Mercury deposition to forest land cover has been dem-

onstrated to be higher than deposition to nonforest land cover, 

because the dry-deposition rate is higher in forests.

Other studies reported the potential influence of wetland 

abundance on total and methylmercury concentrations in water 

(St. Louis and others, 1994; Hurley and others, 1995; Brigham 

and others, 2009; Scudder and others, 2009). A significant 

correlation was not observed for Indiana watersheds, however, 

when the percentages of wetlands were compared with the 

average total and methylmercury concentrations and percent-

ages of methylmercury. The absence of significant correlation 

may be due to the low percentage of wetland land cover in the 

Indiana watersheds (less than 7.7 percent; table 15), although 

it is unclear whether a significant correlation corresponds to a 

threshold of wetland abundance. The study areas in Brigham 

and others (2009) correlated mercury concentrations in water 

to wetland abundance of 13.2 to 35.6 percent. Brightbill and 

others (2004) and Krabbenhoft and others (1999) identified 

weak or nonsignificant correlations of mercury concentrations 

in water and wetland abundance.
58 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 16.  Watersheds upstream from monitoring stations on Indiana streams, grouped

by upstream drainage-area size.

[km2, square kilometer; <, less than; >, greater than]

Drainage-area

size category

Station

number Station name

Upstream 

drainage area

(km2)

Small

(< 1,000 km2)

22 Trail Creek at Michigan City 152 

9 Sugar Creek near New Palestine 243 

20 Fish Creek near Artic 248 

23 Deep River at Lake George-Hobart 321 

1 Fall Creek near Fortville 447 

11 Vernon Fk Muscatatuck R at Vernon 512 

16 Busseron Creek near Carlisle 591 

13 Blue River at Fredericksburg 732 

6 Mills Creek at Cagles Mill Dam 759 

10 East Fork Whitewater R near Brookville 986 

Medium

(1,000 km2 to

 10,000 km2)

14 Patoka River at Winslow 1,559 

18 Wabash River near Huntington 1,985 

2 Eel River near Adamsboro 2,043 

4 Wildcat Creek near Lafayette 2,056 

17 Mississinewa River near Peoria 2,093 

3 Tippecanoe River at Winimac 2,438 

8 White River at Nora 3,149 

24 Kankakee River at Shelby 4,597 

19 Maumee River at New Haven 5,077 

12 East Fork White River at Seymour 6,056 

7 White River at Centerton 6,324 

21 St. Joseph River at Elkhart 8,756 

Large

(> 10,000 km2)

15 White River at Petersburg 28,794 

5 Wabash River at Terre Haute 31,936 

25 Wabash River at Vincennes 35,628 

26 Wabash River at Mt. Carmel, Ill. 74,293 
1-1-1

39°00'

40°00'

41°00'

87°00' 86°00' 85°00'

Land-cover type

Agricultural

Urban

Forest

Mineland

Wetland

Grassland

Open water

Monitoring station on Indiana

stream, with station number

2

24

23

22

21

20

19

18

17

8

1

9

10

12 11

13 14

15

25

5

16

6 7

4

3

MICHIGAN

ILLINOIS OHIO

KENTUCKY

INDIANA

26 22

EXPLANATION

Watershed upstream from

monitoring station

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

Universal Transverse Mercator projection zone 16, NAD 1983

0 25 50 MILES

0 25 50 KILOMETERS

Mercury in Indiana Watersheds 59

Figure 17.  Land-cover types in watersheds upstream from monitoring stations on Indiana streams (from 2001 National Land

Cover Database).
60 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Summary and Conclusions

This report presents a retrospective view of mercury in 

Indiana watersheds for 2001–2006 and interprets the ways 

sources of mercury influence mercury concentrations in water, 

stream mercury yields, and mercury concentrations in fish. 

More than 384,000 data values were assembled and computed 

from mercury-monitoring records, mercury-source inventories, 

ancillary data (instantaneous streamflow, daily average streamflow, and daily precipitation), and maps of land-cover classes. 

A natural hydrologic boundary was used to group the data 

that were analyzed, defined by the drainage area (watershed) 

upstream from each of 26 monitoring stations for mercury in 

streams. These watersheds range from 152 km2 to 74,293 km2

in area and drain approximately 79.5 percent of the land area 

of Indiana. 

Unfiltered total mercury concentrations reported in 

411 water samples, 2002–2006, had a median of 2.32 ng/L 

and a maximum of 28.2 ng/L. The percentage of total mercury 

concentrations that equaled or exceeded Indiana water-quality 

criteria were 5.4 percent for the 12-ng/L chronic-aquatic 

criterion, 59 percent for the 1.8-ng/L Great Lakes humanhealth criterion, and 72.5 percent for the 1.3-ng/L Great Lakes 

wildlife criterion. 

Three monitoring stations had the most samples with 

total mercury concentrations higher than water-quality criteria, 

the highest maximum concentrations, and the most concentrations higher than the 90th percentile: station 7, White River 

near Centerton in central Indiana; station 14, Patoka River at 

Winslow in southern Indiana; and station 19, Maumee River at 

New Haven in northeast Indiana. Total mercury concentrations 

at these stations were significantly higher than those at other 

stations. Interpretations of the geographic differences in mercury concentrations were not confounded by any seasonal patterns or long-term trends. Overall, unfiltered and filtered total 

mercury concentrations tended to be highest when instantaneous streamflow at the time of sample collection was highest.

On average, 67 percent of the total mercury in all samples 

was particulate (determined by subtracting filtered from unfiltered concentrations). Particulate total mercury concentrations 

showed a strong positive correlation with turbidity in water 

samples, and nearly all that exceeded the 12-ng/L chronicaquatic criterion were associated with turbidity higher than 

60 NTRU. Turbidity tended to be highest when instantaneous 

streamflow was highest. Particulate total mercury was significantly lower in samples collected downstream from dams.

Unfiltered methylmercury as a percentage of unfiltered 

total mercury ranged from 0.4 to 64.8 percent, with a median 

of 3.7 percent. Percentages of methylmercury in samples at 

five monitoring stations downstream from dams were significantly higher than at 20 other stations.

Annual stream mercury yields, 2002–2006, were computed with a model by using the mercury concentrations in the 

streams and the daily average streamflows, normalized to the 

watershed area. Estimates of 89 annual stream yields of total 

mercury at 18 stations ranged from 0.47 to 78.9 μg/m2/yr, with 

a median of 3.47 μg/m2/yr. The 5-year average annual stream 

yield of total mercury ranged from 0.73 to 45.2 μg/m2/yr, with 

a median of 4.22 μg/m2/yr. The median annual stream yield of 

methylmercury was 1.9 percent of the median annual stream 

yield of total mercury. The highest average annual stream 

yields of total mercury were 39.6 μg/m2/yr from watershed 7, 

White River near Centerton; and 45.2 μg/m2/yr from watershed 12, East Fork White River near Seymour. 

Mercury concentrations in fish tissue were evaluated 

for 1,731 samples from 59 lakes and reservoirs and 358 rivers and streams in the 26 watersheds (83 percent of the sites 

statewide for 1993–2004). Wet-weight concentrations had a 

median of 130 μg/kg, and 12.4 percent of samples exceeded 

the 300-μg/kg USEPA methylmercury criterion. A coarse-scale 

review of all fish-tissue samples and a fine-scale review of 

samples within 5 km of the downstream end of watersheds 

indicated that fish mercury concentrations were highest in 

watershed 15, White River at Petersburg and watershed 

1, Fall Creek near Fortville. Near the downstream end of 

watershed 15, 45 percent of wet-weight mercury concentrations were greater than the USEPA methylmercury criterion; 

the next highest proportion greater than the criterion was 

40 percent in watershed 1.

A GIS grid map of atmospheric mercury wet-deposition 

rates for 2001–2006 was made with average annual precipitation data from 151 National Weather Service Cooperative Observer Program sites and average annual mercury 

concentration data from 9 National Atmospheric Deposition 

Program Mercury Deposition Network (MDN) stations in 

and around Indiana. The average annual atmospheric mercury 

wet-deposition loading rates were computed for each watershed and ranged from 9.60 to 14.8 μg/m2

/yr, with a median 

of 11.3 μg/m2/yr. Four watersheds in southern Indiana had 

wet-deposition loading rates higher than the statewide average 

of 12 μg/m2/yr.

Atmospheric mercury dry-deposition rates were estimated 

with an inferential method by using concentrations of three 

mercury species measured in air samples at three MDN sites in 

Indiana in 2004. Seasonal mercury dry-deposition rates were 

summed for forest and nonforest land cover in each watershed to obtain annual loadings. Estimated annual atmospheric 

mercury dry-deposition loading rates to the watersheds ranged 

from 5.6 μg/m2/yr (watershed 4) to 13.6 μg/m2/yr (watershed 

14). The median was 7.2 μg/m2/yr. Dry-deposition loading 

rates were 0.49 to 1.4 times the wet-deposition loading rates.

The average annual stream mercury yields were less 

than 100 percent of combined atmospheric mercury wet and 

dry-deposition loadings in 14 watersheds. The stream yield to 

atmospheric loading ratio was 224 percent for watershed 7, 

White River near Centerton, and 233 percent for watershed 12, 

East Fork White River near Seymour, indicating that sources 

other than atmospheric deposition contributed to the stream 

mercury yield. Some of the mercury in these two watersheds 

potentially was contributed by wastewater discharges. 
Summary and Conclusions 61

Total mercury was detected in 96 percent of 402 wastewater-effluent samples from publicly owned treatment works 

in the 26 watersheds, 2002–2005, and ranged from <0.05 to 88 

ng/L, with a median of 2.9 ng/L. The 12-ng/L Indiana chronicaquatic criterion was equaled or exceeded by 12 percent of the 

concentrations; 68 percent equaled or exceeded the 1.8-ng/L 

Great Lakes human-health criterion, and 81 percent equaled or 

exceeded the 1.3-ng/L Great Lakes wildlife criterion. Mercury 

was reported in nearly all of the samples of wastewater effluent from watersheds 7, 12, and 19.

There were 4,144 permitted outfalls of treated and 

untreated wastewater effluent in the 26 watersheds in 2005, 

including 1,044 classified as outfalls of a major facility with 

the capacity to discharge up to 1 million gallons per day. 

Watershed 7 had 401 outfalls (45 percent at a major facility), watershed 12 had 225 outfalls (24 percent at major 

facility), and watershed 19 had 182 outfalls (37 percent at a 

major facility). 

Land-cover type corresponded with measures of the 

apparent mercury levels in three watersheds. (1) Watershed 7, 

White River in central Indiana, had a high percentage of urban 

land cover and some of the highest total mercury concentrations and stream mercury yields. The urban land cover and 

numerous permitted wastewater outfalls (most with mercury 

detected in treated effluent) potentially contributed mercury to 

this watershed. (2) A monitoring station on the Maumee River 

in northeast Indiana, downstream from a large area of urban 

land cover, recorded the highest stream mercury concentrations. The urban land cover and mercury detected in treated 

effluent potentially contributed mercury to this watershed. 

(3) A watershed of the Patoka River in southern Indiana with 

a high percentage of forest land cover had the highest atmospheric mercury dry-deposition rate. The forest land cover 

contributed to the high dry-deposition rate that potentially 

contributed mercury to this watershed.

In conclusion, this study showed that total mercury in 

Indiana watersheds can be attributed mostly to wet and dry 

deposition of atmospheric mercury. Total mercury in some 

watersheds also can be attributed to discharges of mercury in 

wastewater. Total mercury concentrations in streams are moderately correlated to the number of mercury-emission sources 

in the watershed and their annual emissions of mercury, as 

well as to the number of wastewater outfalls in the watershed.

Regulatory programs for air quality and water quality 

in Indiana will need long-term monitoring data for detecting 

changes in mercury concentrations and stream yields resulting 

from reductions in mercury emissions and mercury discharges. 

Future monitoring that includes mercury in precipitation, air 

samples, litterfall, and throughfall; mercury in streams and 

reservoirs; and mercury in fish tissue would yield data for 

comparison with the 2001–2006 data presented in this report. 

Future inventories of mercury-emission sources, annual emissions, wastewater outfalls, and mercury concentrations in 

wastewater could be compared with the 2001–2006 baseline in 

this report. 

Interpretations presented in this report provide a perspective for identifying modifications in future monitoring that 

likely would reduce limitations and uncertainties in future 

interpretations, including the following.

• Investigation of mercury in water from reservoirs in 

Indiana would help to explain the locations, conditions, 

and timing that affect percentages of methylmercury in 

water downstream. 

• Coordination of mercury monitoring in fish tissue with 

mercury monitoring in water would improve the capability for correlating mercury concentrations in fish 

with mercury concentrations in water and with stream 

mercury loads in Indiana watersheds. 

• Adjustment of the stream-monitoring stations in the 

statewide network to locations where streamflow is not 

impeded by dams or by flow stagnation/flow reversals 

would allow stream mercury loads to be computed for 

all stations in the network. 

• Adjustment of the locations of stream-monitoring 

stations in the statewide network to sites with a more 

uniform range of upstream drainage areas may result 

in refined assessments of correlations between mercury 

sources and mercury concentrations in water and fish. 

• Direct analysis of particulate total and methylmercury 

would reduce the uncertainty in concentrations (which 

were determined for this report by subtracting filtered 

from unfiltered concentrations).

• Analysis of methylmercury with a consistent reporting limit of 0.05 ng/L would reduce the uncertainty 

associated with censored values that have inconsistent 

reporting limits.

• Analysis of supplementary constituents in water analyzed for mercury—specifically, suspended sediment, 

dissolved organic carbon, and sulfate—would improve 

the capability for interpreting the sources and transport 

of mercury and methylmercury in watersheds.

• Investigation of the flow volumes and mercury concentrations in wastewater effluent, during conditions 

ranging from base flow to stormflow, would help to 

characterize the relative importance of mercury in 

wastewater discharges compared to atmospheric mercury deposition loading.

• Establishment of a monitoring station for mercury in 

precipitation in southwestern Indiana would increase 

the resolution for mapping atmospheric wet-deposition 

rates. This information could clarify the effect of atmo-
62 Mercury in Indiana Watersheds: Retrospective for 2001–2006

spheric mercury loading on stream mercury loads and 

mercury in fish in this part of the State. 

• Establishment of long-term monitoring for dry deposition of atmospheric mercury—including analysis of 

mercury concentrations in air, litterfall, throughfall and 

surrogate surfaces—would improve the calculation and 

modeling of atmospheric mercury dry-deposition loading to watersheds.

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Appendix 1: Supplemental Data 67

Appendix 1: Supplemental Data

Some station names in this appendix are slightly abbreviated. See table 1 in main part of report 

for full names.
68 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 1– 1.  Correlations of mercury concentrations with instantaneous streamflow at monitoring stations

on Indiana streams, 2002–2006.

Station 

number Station name

Correlation coefficient for mercury1 and

instantaneous streamflow at time of sample collection

Unfiltered 

total mercury

Estimated 

particulate 

total mercury

Filtered 

total mercury

Unfiltered 

methylmercury

1 Fall Creek near Fortville 0.95 −0.03 0.84 0.72

2 Eel River near Logansport .89 − .08 .82 .70

3 Tippecanoe River at Winimac .25 .33 .41 .49

4 Wildcat Creek near Lafayette .78 − .03 .65 .36

5 Wabash River at Terre Haute .26 − .01 .44 − .04

6 Mills Creek at Cagles Mill Dam .16 − .08 .04 − .29

7 White River near Centerton .78 − .19 .45 .16

8 White River at Nora .85 .40 .87 .52

9 Sugar Creek near New Palestine .83 − .05 .72 .31

10 East Fork Whitewater River near Brookville .26 .16 .19 − .21

11 Vernon Fork Muscatatuck River at Vernon .89 − .04 .82 .46

12 East Fork White River at Seymour .84 − .10 .67 .68

13 Blue River at Fredericksburg .20 .09 .04 .01

14 Patoka River at Winslow .38 − .01 .46 .12

15 White River at Petersburg .10 .52 .04 − .75

16 Busseron Creek near Carlisle .75 − .14 .34 − .28

17 Mississinewa River near Peoria .50 .16 .65 − .22

18 Wabash River near Huntington .80 .01 .71 − .11

19 Maumee River at New Haven .72 − .17 .76 .03

20 Fish Creek near Artic .76 − .22 .93 .02

21 St. Joseph River at Elkhart .53 .39 .64 .34

22 Trail Creek at Michigan City .64 .18 − .06 − .02

23 Deep River at Lake George at Hobart .83 .26 .77 .36

24 Kankakee River at Shelby .56 .06 .70 .66

25 Wabash River at Vincennes .34 − .29 .85 − .48

26 Wabash River at Mt. Carmel, Ill. .99 − .46 .89 − .01

1Pearson correlation coefficient computed with statistical software (S-Plus, Tibco Software, 2008); censored mercury concentrations were 

set equal to half the reporting limit for computing correlations.
Appendix 1: Supplemental Data 69

Table 1– 2.  Statistical values separating categories of daily average streamflow at monitoring stations

on Indiana streams, 2002–2006.

[ft3/s, cubic feet per second; streamflow categories are low (less than or equal to the 10th percentile), medium (greater than 

the 10th percentile and less than or equal to the median); high (greater than the median and less than or equal to the 90th 

percentile); and event (greater than the 90th percentile)]

Station 

number Station name

Daily average streamflow (ft3/s)1

10th

percentile Median 90thpercentile

1 Fall Creek near Fortville 51 150 486 

2 Eel River near Logansport 169 438 1,770 

3 Tippecanoe River at Winimac 270 628 1,910 

4 Wildcat Creek near Lafayette 152 469 1,920 

5 Wabash River at Terre Haute 3,030 8,705 30,900 

6 Mills Creek at Cagles Mill Dam 28 216 1,300 

7 White River near Centerton 730 2,020 7,165 

8 White River at Nora 309 905 3,624 

9 Sugar Creek near New Palestine 10 60 319 

10 East Fork Whitewater River near Brookville 53 265 1,305 

11 Vernon Fork Muscatatuck River at Vernon 10 107 531 

12 East Fork White River at Seymour 636 2,070 7,334 

13 Blue River at Fredericksburg 15 197 858 

14 Patoka River at Winslow 74 473 1,990 

15 White River at Petersburg 3,260 10,900 29,860 

16 Busseron Creek near Carlisle 11 103 667 

17 Mississinewa River near Peoria 103 353 2,590 

18 Wabash River near Huntington 51 280 2,370 

19 Maumee River at New Haven 200 988 5,915 

20 Fish Creek near Artic 10 42 228 

21 St. Joseph River at Elkhart 1,230 2,485 4,990 

22 Trail Creek at Michigan City 39 70 145 

23 Deep River at Lake George at Hobart 16 50 316 

24 Kankakee River at Shelby 629 1,290 3,160 

25 Wabash River at Vincennes 3,700 9,960 31,940 

26 Wabash River at Mt. Carmel, Ill. 8,662 26,800 74,300 

1Daily average streamflow for calendar years 2002–2006 from the USGS streamflow gaging station at or near the monitoring station (U.S. Geological Survey, 2008).
Table 1–3.  Annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream from monitoring stations 2002–2006.—Continued [g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined] Station1 number Station name Year Annual stream load of total mercury (g/yr) Standard error of prediction2 for annual stream load of total mercury (percent) Annual stream yield of total mercury (μg/m2/yr) Annual stream load of methylmercury (g/yr) Standar

of pred

for an

stream 

methylm

(perc

1 Fall Creek near Fortville 2002 5,184 35.5 11.6 ND N

2003 15,222 151 34.1 ND N2004 5,274 32.1 11.8 ND N2005 11,190 77.1 25.0 ND N2006 2,723 9.7 6.1 ND N

2 Eel River near Logansport 2002 6,384 13.7 3.1 129 

2003 5,276 2.0 2.6 135 2004 7,604 2.8 3.7 175 2005 13,399 73.4 6.6 165 22006 5,519 3.3 2.7 136 

3 Tippecanoe River at Winimac 2002 2,016 2.0 .83 101 

2003 1,385 1.4 .57 63 2004 1,834 1.5 .75 85 2005 2,049 1.6 .84 98 2006 1,877 2.3 .77 101 

4 Wildcat Creek near Lafayette 2002 14,260 11.5 6.9 ND N

2003 65,549 1,710 31.9 ND N2004 35,973 409 17.5 ND N2005 52,220 1,040 25.4 ND N2006 17,934 11.4 8.7 ND N
Table 1–3.  Annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream from monitoring stations 2002–2006.—Continued[g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station1

number Station name Year

Annual 

stream load of 

total mercury

(g/yr)

Standard error 

of prediction2

for annual

stream load of 

total mercury

(percent)

Annual 

stream yield of

total mercury 

(μg/m2/yr)

Annual

stream load

of methylmercury 

(g/yr)

Standar

of pred

for an

stream 

methylm

(perc

5 Wabash River at Terre Haute 2002 65,418 1.4 2.0 2,100 

2003 71,823 1.3 2.2 2,335 2004 66,939 1.2 2.1 2,172 2005 51,177 1.9 1.6 1,899 2006 71,267 1.0 2.2 2,186 

7 White River near Centerton 2002 189,458 28.7 30.0 565 14

2003 451,023 92.5 71.3 638 2,962004 83,911 9.6 13.3 448 12005 438,960 85.3 69.4 520 3,362006 87,307 5.0 13.8 674 

8 White River at Nora 2002 44,518 24.7 14.1 ND N

2003 119,475 32.3 37.9 ND N2004 19,468 8.8 6.2 ND N2005 121,137 40.2 38.5 ND N2006 18,200 5.1 5.8 ND N

9 Sugar Creek near New Palestine 2002 434 2.7 1.8 9.6 

2003 350 2.1 1.4 14 2004 436 3.1 1.8 9.4 2005 702 3.8 2.9 14 2006 533 2.3 2.2 15 
Table 1–3.  Annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream from monitoring stations 2002–2006.—Continued [g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined] Station1 number Station name Year Annual stream load of total mercury (g/yr) Standard error of prediction2 for annual stream load of total mercury (percent) Annual stream yield of total mercury (μg/m2/yr) Annual stream load of methylmercury (g/yr) Standar

of predi

for an

stream l

methylm

(perc

11 Vernon Fork Muscatatuck River at Vernon 2002 7,897 6.2 15.4 52 1

2003 6,459 9.7 12.6 36 12004 4,708 5.6 9.2 32 12005 5,757 7.8 11.2 23 12006 8,649 8.3 16.9 77 6

12 East Fork White River at Seymour 2002 325,707 77.6 53.8 ND ND 

2003 70,649 9.0 11.7 ND ND 2004 203,790 234 33.6 ND ND 2005 477,625 322 78.9 ND ND 2006 290,694 65.2 48.0 ND ND 

13 Blue River at Fredericksburg 2002 759 2.0 1.0 27 3

2003 639 1.7 .87 24 32004 923 2.4 1.3 31 42005 566 2.2 .77 20 32006 930 2.0 1.3 32 3

14 Patoka River at Winslow 2002 13,558 2.0 8.7 158 4

2003 7,588 1.5 4.9 113 22004 8,513 1.6 5.5 124 22005 8,056 2.0 5.2 97 32006 ND ND ND ND ND 
Table 1–3.  Annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream from monitoring stations o2002–2006.—Continued[g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined]

Station1

number Station name Year

Annual 

stream load of 

total mercury

(g/yr)

Standard error 

of prediction2

for annual

stream load of 

total mercury

(percent)

Annual 

stream yield of

total mercury 

(μg/m2/yr)

Annual

stream load

of methylmercury 

(g/yr)

Standard 

of predi

for an

stream l

methylm

(perc

16 Busseron Creek near Carlisle 2002 3,408 14.6 5.8 76 

2003 2,049 5.4 3.5 68 2004 1,329 24.9 2.2 45 2005 3,354 78.1 5.7 72 12006 3,759 12.4 6.4 105 

19 Maumee River at New Haven 2002 20,841 1.4 4.1 330 2

2003 38,085 1.5 7.5 554 32004 23,855 1.3 4.7 376 22005 27,399 1.5 5.4 398 32006 27,367 1.2 5.4 437 1

20 Fish Creek near Artic 2002 402 1.9 1.6 ND ND 

2003 324 1.6 1.3 ND ND 2004 290 1.6 1.2 ND ND 2005 396 1.9 1.6 ND ND 2006 446 1.6 1.8 ND ND 

21 St. Joseph River at Elkhart 2002 7,314 1.8 .84 ND ND 

2003 4,141 1.3 .47 ND ND 2004 6,848 1.6 .78 ND ND 2005 6,693 1.9 .76 ND ND 2006 6,774 1.5 .77 ND ND 
Table 1–3.  Annual stream loads and yields of unfiltered total mercury and unfiltered methylmercury in watersheds upstream from monitoring stations 2002–2006.—Continued [g/yr, gram per year; μg/m2/yr, microgram per square meter per year; ND, not determined] Station1 number Station name Year Annual stream load of total mercury (g/yr) Standard error of prediction2 for annual stream load of total mercury (percent) Annual stream yield of total mercury (μg/m2/yr) Annual stream load of methylmercury (g/yr) Standar

of pred

for an

stream 

methylm

(perc

23 Deep River at Lake George at Hobart 2002 451 1.4 1.4 9.0 2

2003 408 1.2 1.3 8.7 2004 462 1.1 1.4 10 2005 460 1.3 1.4 9.2 22006 736 1.2 2.3 15 2

24 Kankakee River at Shelby 2002 7,190 1.7 1.6 ND ND 

2003 4,439 1.3 1.0 ND ND 2004 5,684 1.3 1.2 ND ND 2005 6,960 1.7 1.5 ND ND 2006 5,813 1.3 1.3 ND ND 

1Stream loads and stream yields for total mercury and methylmercury were not calculated for stations 6, 10, 15, 17, 18, 22, 25, and 26 because of insufficient data.2The Standard Error of Prediction (SEP) begins with an estimate of parameter uncertainty (the Standard Error) and adds the unexplained variability about the model (random err

parameter uncertainty and random error, it is larger than the Standard Error and provides a better description of how closely estimated loads correspond to actual loads. The SEP is ing uncertainty in loads (Runkel and others, 2004). Here, the SEP is presented as a percentage of the annual load.
Table 1–4. Model characteristics of annual stream loads of mercury in watersheds upstream from monitoring stations on Indiana streams, 2002–200[UTHG, unfiltered total mercury; UMHG, unfiltered methylmercury;—, insufficient data; lnQ = ln(streamflow) - center of ln(streamflow)]

Station 

number1 Station name

Number of 

samples with

UTHG for

regression model

Average

standard error

of prediction

for stream load2

of UTHG

(percent)

Number of

samples with

UMHG for 

regression model

Average 

standard error 

of prediction 

for stream load2

of UMHG

(percent)

1 Fall Creek near Fortville 18 89.3 — — a2 Eel River near Logansport 18 29.4 10 8.40 a3 Tippecanoe River at Winimac 18 1.80 8 1.91 a4 Wildcat Creek near Lafayette 17 974 — — a5 Wabash River at Terre Haute 18 1.36 14 2.46 a7 White River near Centerton 18 68.7 15 1,310 a8 White River at Nora 18 31.3 — — a9 Sugar Creek near New Palestine 17 2.91 8 4.45 a

11 Vernon Fork Muscatatuck River at Vernon 17 7.60 14 1.69 a

12 East Fork White River at Seymour 17 180 — — a13 Blue River at Fredericksburg 17 2.07 8 3.72 a14 Patoka River at Winslow 17 1.79 13 3.36 a16 Busseron Creek near Carlisle 17 29.0 11 .85 a19 Maumee River at New Haven 16 7.54 13 2.60 a20 Fish Creek near Artic 15 2.60 — — a21 St. Joseph River at Elkhart 16 1.19 — — a23 Deep River at Lake George at Hobart 16 1.26 9 1.99 a24 Kankakee River at Shelby 15 1.49 — — a

1Stream loads and stream yields for total mercury and methylmercury were not calculated for stations 6, 10, 15, 17, 18, 22, 25, and 26 because of insufficient data.2Average standard error of prediction for stream load of mercury is the average of the annual standard error of prediction values divided by the average annual stream load of 

centage.

3Models from Runkel and others (2004).
76 Mercury in Indiana Watersheds: Retrospective for 2001–2006

Table 1–5.  Number of stationary sources of mercury emissions to the atmosphere and annual mercury emissions in 2002

and 2005 for watersheds upstream from monitoring stations on Indiana streams.

[kg, kilogram]

Station

number

Station name 

for upstream watershed

2002 2005

Number of 

stationary 

sources of 

mercury

emissions

Annual

mercury

emissions

(kg)

Number of 

stationary 

sources of 

mercury 

emissions

Annual

mercury

emissions

(kg)

1 Fall Creek near Fortville 1 0.04 0 0

2 Eel River near Logansport 2 208 2 81.9

3 Tippecanoe River at Winimac 5 28.3 4 31.5

4 Wildcat Creek near Lafayette 6 10.3 6 1.49

5 Wabash River at Terre Haute 25 1,097 22 376

6 Mills Creek at Cagles Mill Dam 0 0 0 0

7 White River near Centerton 20 152 13 189

8 White River at Nora 4 5.7 4 7.74

9 Sugar Creek near New Palestine 0 0 0 0

10 East Fork Whitewater River near Brookville 1 17.4 2 11.3

11 Vernon Fork Muscatatuck River at Vernon 0 0 0 0

12 East Fork White River at Seymour 8 25.8 5 32.2

13 Blue River at Fredericksburg 0 0 0 0

14 Patoka River at Winslow 4 7.63 2 .73

15 White River at Petersburg 20 617 18 586

16 Busseron Creek near Carlisle 0 0 0 0

17 Mississinewa River near Peoria 3 2.44 0 0

18 Wabash River near Huntington 1 1.47 0 0

19 Maumee River at New Haven 7 339 5 250

20 Fish Creek near Artic 0 0 0 0

21 St. Joseph River at Elkhart 5 15.3 2 6.41

22 Trail Creek at Michigan City 2 59.8 2 61.3

23 Deep River at Lake George at Hobart 0 0 0 0

24 Kankakee River at Shelby 8 187 7 197

25 Wabash River at Vincennes 5 55.9 4 73.6

26 Wabash River at Mt. Carmel, Ill. 1 .05 1 .06
Table 1–6.  Percentages of land-cover classes in watersheds upstream from monitoring stations on Indiana streams.[Percentages computed as land are in watershed in each land-cover class divided by the total watershed upstream drainage area, multiplied by 100; —, no area in land-cover clas

Land cover class1

Monitoring station number for upstream watershed

 1 2 3 4 5 6 7 8 9 10 1

Low intensity residential 4.15 0.61 0.92 2.21 1.02 0.54 8.31 4.50 1.55 1.84 0High intensity residential .22 .06 .14 .21 .27 .03 1.07 .49 .05 .48 Commercial/

industrial/transportation

.87 .25 .48 .87 .56 .23 3.19 1.45 .35 1.23 

Bare rock/sand/clay — — — — .01 — — — — — — Quarries/strip mines/

gravel pits

.11 —

< .01 < .01

.05 .07 .06 .07 — — 

Coal mine lands2 — — — — .32 — — — — — — Transitional — < .01 — < .01 .01 .16 .05 Deciduous forest 5.45 8.25 8.79 3.09 8.17 15.20 6.23 4.05 4.96 17.03 33Evergreen forest < .01 .03 .12 .01 .29 .11 .03 .02 .01 .28 1Mixed forest < .01 < .01 .01 < .01 .17 < .01 .01 < .01 < .01 .05 Shrubland — — — — .01 — — — — — — Grassland/herbaceous — < .01 .01 .39 — — — — — — Orchards/vineyards/

other

— — — — .02 .02 .02 — — .03 — 

Pasture/hay 19.54 15.73 1.66 1.66 1.53 18.28 16.67 13.27 16.44 16.37 38Rowcrop 66.43 72.81 72.80 8.24 75.29 64.00 6.16 72.26 75.45 59.57 24Small grains — — — — .01 — — — — — — Fallow 2.20 .03 .14 1.18 .45 .15 2.47 2.01 .23 .30 Woody wetlands .75 1.37 3.02 1.12 1.48 .11 .75 1.09 .69 .61 Emergent herbaceous

wetlands

.12 .26 .83 .07 .22 .01 .05 .06 .03 .03 

Open water .17 .59 2.09 .34 .81 1.06 .94 .72 .23 2.18 
Table 1–6.  Percentages of land-cover classes in watersheds upstream from monitoring stations on Indiana streams. —Continued [Percentages computed as land are in watershed in each land-cover class divided by the total watershed upstream drainage area, multiplied by 100; —, no area in land-cover clas

Land cover class1 Monitoring station number for upstream watershed 14 15 16 17 18 19 20 21 22 23 2

Low intensity residential .66 2.80 1.35 2.04 .76 2.54 .38 1.31 6.24 8.70 1High intensity residential .09 .33 .16 .24 .14 .47 .06 .15 3.40 6.40 Commercial/ industrial/transportation .26 1.09 .60 .63 .41 1.16 .19 .64 3.69 3.57 Bare rock/sand/clay — < .01 < .01 — — — — — .08 < .01 Quarries/strip mines/ gravel pits .24 .12 1.70 .04 .06 .02 — .01 — < .01 

Coal mine lands2 5.38 1.27 19.61 — — — — — — — — Transitional .31 .25 .21 .02 .02 .11 .03 — — Deciduous forest 37.15 23.21 2.36 7.32 5.55 9.84 17.82 14.64 27.07 14.29 9Evergreen forest 2.09 .66 1.18 .04 .05 .10 .15 .32 9.00 3.31 1Mixed forest .06 .04 3.42 .01 .01 .03 .11 .03 2.35 — Shrubland — — .49 — — — — — — .51 — Grassland/herbaceous — .00 4.63 — — .04 .44 .01 6.21 4.16 2Orchards/vineyards/

other

— .01 .03 — — — — .04 — — 

Pasture/hay 24.08 21.01 11.22 11.64 9.35 16.23 29.61 16.19 14.63 14.48 11Rowcrop 26.72 47.16 31.81 75.47 79.88 66.54 45.41 57.45 16.94 33.79 68Small grains < .01 .08 — — — — — .12 .08 Fallow .06 .75 1.08 .66 .10 .32 — .34 1.66 5.61 Woody wetlands .64 .68 5.94 .99 .62 1.71 2.97 4.91 6.36 2.60 2Emergent herbaceous

wetlands

.11 .04 .40 .09 .12 .25 .70 1.11 1.37 1.16 

Open water 2.70 .95 2.20 .84 2.92 .74 2.04 2.82 .89 1.34 1

1Land-cover class description from National Land-Cover Dataset (Multi-Resolution Land Characteristics Consortium, 1992).2Coal mine lands supplemental data for active and abandoned (reclaimed/unreclaimed) aboveground coal mines (Eaton, 2002 and Indiana Geological Survey, 2002)

Risch and others—Mercury in Indiana Watersheds: Retrospective for 2001–2006—Professional Paper 1780

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