Atmospheric Deposition and Biogeochemistry of 

Mercury and other Trace Contaminants in Aquatic 

Ecosystems 

Final Project Report 

Part II: 

Mercury Studies

2002-2004

Prepared for: 

Nate Gulden 

FCPC Tribal EPA 

Forest County Potawatomi Community 

Crandon, WI 54520 

Prepared by 

K. A. Morrison and C. J. Watras

Wisconsin Department of Natural Resources 

UW Trout Lake Station 

Boulder Junction, WI 54512 

June 2006 
Table of Contents 

1. Executive Summary........................................................................................................ 1 

2. List of Tables.................................................................................................................. 6 

3. Methods........................................................................................................................... 7 

3.a. Site Description........................................................................................................ 7 

3.b. Sampling and Analysis ............................................................................................ 8 

3.b.1. Stream Sampling............................................................................................... 8 

3.b.2. Lake Sampling .................................................................................................. 9 

3.b.3. Precipitation Sampling.................................................................................... 10 

3.b.4. Air Sampling................................................................................................... 12 

3.b.5. Aqueous Mercury Analysis............................................................................. 12 

3.b.6. Ancillary Solutes............................................................................................. 13 

3.b.7. QAQC Criteria for Mercury Analyses............................................................ 14 

3.b.8. Other analyses................................................................................................. 15 

3.c. Mass Balance Calculations .................................................................................... 16 

4. References..................................................................................................................... 20 

5. Published works............................................................................................................ 22

5a. Eckley C., Watras C.J., Hintelmann H., Morrison K., Kent A., Regnell O. 2005. 

Mercury methylation in the hypolimnetic waters of lakes with and without 

connection to wetlands in northern Wisconsin. Can. J. Fish. Aquat. Sci. 62: 400-

411. 

5b. Watras C.J., Morrison K.A., Kent A., Price N., Regnell O., Eckley C., Hintelmann 

H., Hubacher T. 2005. Sources of methylmercury to a wetland-dominated lake in 

northern Wisconsin. Environ. Sci. Tech. 39(13): 4747-4758. 

5c. Watras C.J., Morrison K.A., Regnell O., Kratz T.K. 2006. The methylmercury 

cycle in Little Rock Lake during experimental acidification and recovery. Limnol. 

Oceanogr. 51(1): 257-270. 

5d.i. Kent, A.D., C. J. Watras, C. Eckley, O. Regnell, K. D. McMahon and H. 

Hintelmann. 2005. Microbial community composition and mercury methylation in 

the anoxic hypolimnia of stratified Wisconsin lakes. ASLO Annual Summer 

Meeting, June 19-24, 2005, Santiago de Compostela, Spain 

5d.ii. Kent, A.D., C. J. Watras, C. Eckley, O. Regnell, K. D. McMahon and H. 

Hintelmann. 2005 Mercury Methylation Varies with Pelagic Microbial 

Community Composition in Lakes Within the Great Lakes Basin. International 

Association for Great Lakes Research: 48th Annual Meeting, Ann Arbor MI, May 

23-27, 2005. 

5d.iii. Kent, A.D. C.J. Watras, O. Regnell, C. Eckley and H. Hintelmann. 2005. 

Analysis of microbial community structure associated with mercury methylation 

in northern Wisconsin lakes. Am. Soc. Limnol Oceanogr. Aquatic Sciences 

Meeting, Salt Lake City, February, 2005 

6. Appendices 

A1. DL Stream Data 

A2. DL Lake Data 

A3. Precipitation Data 

A4. Total Gaseous Mercury Data 
1. Executive Summary. 

In 2001, the Forest County Potawatomi Community (FCPC) and the Wisconsin 

Department of Natural Resources (WDNR) initiated a cooperative research project 

entitled “Atmospheric Deposition and Biogeochemistry of Mercury and other Trace 

Contaminants in Aquatic Ecosystems.” This project involved intensive studies of the 

mercury cycle in Devils Lake and other nearby lakes in northern Wisconsin. The broad 

research objective was to document similarities and differences between hydrologically 

different lakes in the region, focusing primarily on the sources and fates of total mercury 

(HgT) and methylmercury (meHg - the chemical form of mercury that accumulates in fish 

and poses a health risk to humans and piscivorous wildlife). 

When the planning stage of this project began in 1995, research on mercury 

contamination in lakes of Wisconsin, Canada and Sweden suggested that the mercury 

cycles in seepage lakes and drainage lakes might be significantly different (Rudd, 1995). 

Within the scientific community, it was thought that this difference could help to explain 

why fish in some lakes were more contaminated than fish in others. At that time, research 

by the WDNR had focused on the seepage lakes, as exemplified by the well-studied Little 

Rock Lake (LRL) in Vilas County. Studies of mercury in LRL began in 1984 as part of 

an EPA-sponsored acid rain project and they continue today (Frost et al., 1999; Watras et 

al., 2006). Results of the LRL work indicate that the major source of Hg is direct 

atmospheric deposition to the lake surface, and the major source of meHg is in-lake 

production in anoxic regions of the water column and sediments. In contrast, studies of 

drainage systems in Canada and Sweden suggested that the major sources of Hg and 

meHg in drainage lakes might be the terrestrial watershed – especially areas of the 

watershed containing wetlands. 

In June, 1995 the Director of Natural Resources for the FCPC, Ms Christine Hansen, 

requested technical assistance on a research project involving mercury studies for Devils 

Lake on the reservation. Since Devils Lake is a drainage lake, closely coupled to a large 

wetland, it was jointly felt that this project could potentially enhance our understanding 

1 
of the mercury cycle in many lakes and, thereby, benefit all parties involved. A 

cooperative agreement was formally implemented in February, 2001 and preliminary 

research on the lake by WDNR began that summer. For each of the next three years, 

comprehensive studies on the hydrology and biogeochemistry of the Devils Lake 

watershed were conducted jointly by WDNR and FCPC staff, along with associated 

scientists and engineers. 

Preparation of the Final Project Report began in 2005, under a contract extension 

agreement signed by the Tribe on 14 September. Pursuant to that agreement, the WDNR 

submitted Part I of the Final Report in December 2005, summarizing the hydrologic 

studies conducted in the DL watershed. This present report constitutes Part II of the Final 

Project Report to the Tribe. Part II summarizes the mercury studies, and it has two main 

objectives. The first objective is to summarize the findings of biogeochemical 

investigations conducted in the Devils Lake watershed during 2002, 2003 and 2004 and 

to compare them to findings for other lakes. The second objective is to compile and 

tabulate the large amount of mercury data that were collected so that they will be useful 

to the Tribe in future studies. 

Devils Lake is a small (11.7 ha), dystrophic drainage lake in Forest County, Wisconsin 

(45o

 33’ N, 88o 50’ W) that supports a warm water fishery of perch and bass. The lake is 

situated in a relatively pristine, forested watershed and it is fed by a small tributary 

stream that flows seasonally from spring to fall. The tributary stream emanates from a 

headwater wetland, which accounts for the dystrophic status of the lake (dark, tea-stained 

water). The lake is drained by a single distributary stream and by seepage to groundwater. 

Intensive hydrological investigations of the Devils Lake catchment were conducted in 

conjunction with the mercury study. These investigations involved measuring or 

estimating the sources of water to the lake (precipitation, tributary stream flow, nonchannelized runoff and groundwater discharge), losses of water from the lake 

(distributary stream flow, groundwater recharge and evaporation) and the change in the 

volume of water in the lake (change in water storage) over time. The hydrologic data 

2 
were used to construct water budgets for the lake during each year of study. In this 

second part of the Final Report, the hydrologic data are coupled with chemical data to 

construct budgets for mercury in the lake. Based on these budgets, the importance of 

various sources and sinks in the watershed can be assessed. 

Annual budgets for total Hg (HgT) and seasonal budgets for meHg are shown on Table 1 

and Table 2 for each of the three studies years. Annual budgets were computed for 

calendar years, January 1 – December 31. The seasonal budgets were computed for the 

time period when meHg accumulates in the water column of the lake, generally from the 

beginning of spring melt to late summer stratification (e.g. April to late August). The 

annual budgets are useful in assessing the major sources and sinks for waterborne HgT, 

while the seasonal budgets are needed to identify the major sources of meHg – the 

chemical form that accumulates in fish. MeHg is produced in anoxic regions of the lake 

and in anoxic wetland porewaters. A major goal of this research project was to quantify 

the relative importance of these two sources. 

Table 1. Annual Budgets for waterborne total mercury (HgT) in Devils Lake, 2002 – 04 

-------------Inputs-------------- ----------------------Outputs---------------- 

Change 

in 

Storage 

(ΔS) 

Year 

Precip 

(P) 

Surface 

Runoff 

(RO) 

Stream 

Flow 

(Qin) 

Sedimentation 

& Evasion 

(S+E) 

Stream 

Flow 

(Qout) 

Lake 

Seepage 

(GO) 

2002 1.50 0.19 3.27 3.62 0.91 0.11 0.33 

2003 1.01 0.05 0.91 1.85 0.62 0.04 -0.52 

2004 0.99 0.07 1.18 1.47 0.53 0.06 0.18 

mean 1.17 0.11 1.79 2.31 0.69 0.07 0.00 

SD 0.29 0.08 1.29 1.15 0.20 0.04 0.46 

3 
Table 2. Seasonal Budgets for waterborne methylmercury (meHg) in Devils Lake, 2002-

04 

Year 

Precip 

(P) 

Surface 

Runoff 

(RO) 

Stream 

Flow 

(Qin) 

Net 

methyl. 

(M) 

Sedimentation 

(S) 

Stream 

Flow 

(Qout) 

Lake 

Seepage 

(GO) 

Change 

in 

Storage 

(ΔS) 

2002 0.012 0.002 0.056 0.408 0.026 0.066 0.004 0.382 

2003 0.007 0.001 0.027 0.132 0.009 0.078 0.002 0.078 

2004 0.007 0.001 0.023 0.081 0.012 0.048 0.002 0.049 

mean 0.009 0.001 0.035 0.207 0.016 0.064 0.003 0.170 

SD 0.003 0.000 0.018 0.176 0.009 0.015 0.001 0.184 

The mass balances for HgT indicate that the tributary stream was an important external 

source to the lake, contributing 50% to 70% of the HgT that entered the lake each year. 

HgT in the tributary stream-water is ultimately attributable to atmospheric Hg deposition 

onto the watershed as a whole. Given the size of the tributary catchment and the rate of 

atmospheric Hg deposition, it is clear the terrestrial watershed is a net sink for HgT. In 

other words, most of the atmospherically-deposited HgT is either sequestered in soils or 

evades back into the atmosphere, and only a small fraction bleeds out into stream-water 

and enters the lake. 

The mass balances for meHg indicate that the tributary stream contributes more meHg to 

the lake than does direct precipitation. As such, the tributary stream constitutes the largest 

external source of meHg to the lake. However, in contrast to HgT, internal sources of 

meHg are larger than external sources in each year. In other words, more meHg is 

produced within the lake itself than is derived from the watershed and the airshed 

combined. Parallel investigations indicate 1) that meHg production rates in Devils Lake 

are greater than those in Wisconsin lakes that are not connected to wetland; and 2) that 

the meHg is produced by bacteria that inhabit the anoxic hypolimnion of the lake during 

summer. 

In a comparative study of mercury methylation in the dark-water, wetland-dominated 

Devils Lake and the clear-water, precipitation-dominated Pallette Lake in neighboring 

Vilas County, Eckley et al. (2005) showed that methylation rates in Devils lake were up 

4 
to two-fold greater than those in Pallette Lake – potentially accounting for the higher 

concentrations of waterborne meHg in Devils Lake. In both lakes, in-lake methylation 

was sufficient to account for all the meHg that accumulated during summer. 

In a companion study, Kent et al (2005a, b, c) showed that similar microbial communities 

were associated with meHg production in three regional lakes (Devils Lake, Pallette Lake 

and Little Rock Lake). This finding suggests that environmental factors which affect the 

activity of the resident microbial communities may partly explain the differences in 

meHg production observed among these lakes. In Devils Lake, the influx of runoff from 

the headwater wetland may supply nutrient supplements and additional Hg substrate – 

both of which could result in higher rates of meHg production in this lake. 

In conclusion, investigations of the aquatic mercury cycle in Devils Lake indicate that 

wetland runoff may have both direct and indirect effects that increase the potential for 

mercury methylation relative to lakes without hydrological connection to wetland. These 

effects may interact synergistically – producing a larger effect together than either would 

have separately (sensu Watras et al., 2006). Since meHg is the chemical form of mercury 

that accumulates in fish and poses the major risk to humans and piscivorous wildlife, 

these findings are directly relevant to the potential for fish contamination in Devils Lake. 

5 
2. List of Tables 

Table 1. Annual Budgets for waterborne total mercury (HgT) in 

Devils Lake, 2002 – 04...................................................................3 

Table 2. Seasonal Budgets for waterborne methylmercury (meHg) 

in Devils Lake, 2002-04..................................................................4 

Table 3. Comparison of atmospheric mercury data collected at DL study 

site with other sites in region over 117 weeks of parallel 

collection...................................................................................11 

Table 4. Annual and seasonal VWA HgT concentrations (ng/L) in 

precipitation from three NADP/ MDN sites (WI36, WI32 

and WI10) in the Devils Lake region...................................................12 

Table 5. Annual Hydrologic Budgets for Devils Lake, 2002-2004..........................18 

Table 6. Seasonal Hydrologic Budgets for Devils Lake, 2002-2004.........................18 

Table 7. HgT concentrations (ng/L) used to construct annual 

budgets for waterborne HgT in Devils Lake, 2002 – 2004.........................19 

Table 8. MeHg concentrations (ng/L) used to construct seasonal 

budgets for waterborne meHg in Devils Lake, 2002 – 2004......................19 

6 
3. Methods 

3.a. Site Description 

Devil’s Lake (N 45o 32.954’, W 88o 50.040’) is a dark-water drainage lake in Forest 

County, Wisconsin, with a surface area of 11.7 h, a volume of 3.5 × 105 m3, a maximum 

depth of 7.6 m, a mean depth of 3.0 m and a water residence time of roughly 1 year. The 

terrestrial watershed comprises a headwater wetland approximately twice the size of the 

lake encircled by gently sloping, forested uplands that surround the headwater wetland 

and the lake itself. A small stream emanates from the headwater wetland and it flows 

directly to the northeast end of the lake through a narrow valley. Water leaves the lake 

via a small out-flowing stream to the southwest. A small wetland fringes the downgradient end of the lake at the mouth of the outlet. A narrow, unimproved, gravel road 

circumscribes the remaining lake shore, roughly defining a near-shore watershed of 12.3 

ha. Further details on the hydrologic setting can be found in Horsley and Witten (2003). 

The lake and its forested watershed are situated in thick, unconsolidated glacial till 

(Simpkins, McCartney and Mickelson, 1987). Groundwater flow directions within the 

unconfined glacial deposits of the region often follow the land-surface topography, 

moving from upland to lowland areas and discharging in some lakes, streams, and land 

depressions. Saturated thickness of the aquifer ranges from 18 m to 49 m in general 

(Lidwin and Krohelski, 1993). The moderate to low permeability of the glacial tillderived soils that comprise the Devil’s Lake surface watershed contributes to a “perched” 

hydrologic system where surface water elevations sit well above the local groundwater 

table. The perched nature of the entire Devil’s Lake hydrologic system has been 

demonstrated by surface water levels significantly higher than groundwater levels 

throughout the system and by a consistent loss of flow volume from upstream to 

downstream locations in the inlet stream (Horsley & Witten, 2003). This hydrologic 

setting simplifies construction of water budgets and mercury mass balances since 

groundwater inputs may be considered negligible. 

7 
3.b. Sampling and Analysis 

3.b.1. Stream Sampling 

Surface water monitoring was conducted from 1996 through 2001 to roughly characterize 

the spatial and temporal variability of solutes within the watershed. Stream monitoring 

was performed routinely at three locations: the Upstream and Inlet sites on the tributary 

stream and the Outlet (Roadside) site on the distributary stream. 

Intensive monitoring of the chemistry and discharge volumes of the tributary and 

distributary streams was initiated in 2002 and continued through 2004. Stream water 

samples for chemical analysis were collected weekly beginning at the onset of melt each 

year. Sampling and analytical protocols were similar to those used during the background 

monitoring years. Grab samples were obtained at the inlet and outlet sampling sites on 

the same day that manual hydrologic flow measurements were made (DL Hydrology 

Report). The stream water samples were shipped on ice in dark coolers. Mercury samples 

were hermetically sealed in double plastic bags. 

At regular intervals (generally each week), stage was determined visually by reading the 

level of the water surface at each monitoring site on a staff gauge. Concurrently, 

discharge was estimated using mini (pygmy) Price “AA” flow meters with top-set wading 

rods. Flow measurement began at the onset of spring melt and continued until the stream 

stopped flowing in fall. This information was used to compute the stage-discharge rating 

curves for each site (DL Hydrology Report). 

Stream stage was also recorded continuously at 15-minute intervals using barocompensated, data-logging pressure transducers during the unfrozen portion of the year 

(early April through November). The logger data were converted to discharge units by 

applying the rating curves described above. The resultant 15-minute estimates of water 

discharge were integrated over appropriate time intervals to calculate daily, weekly and 

annual flow volumes (DL Hydrology Report). 

8 
3.b.2. Lake Sampling 

Lake sampling was conducted at a single mid-lake station, in part because background 

monitoring had indicated no significant differences between sites L1 and L2 during the 

period 1996-2001. To obtain vertical concentration profiles, sampling depths were 

selected after establishing the physical structure of the water column using a SeaBird-19 

plus CTD. Prior to profiling, the non-metallic sampling boat was tethered fore and aft to 

buoys that were permanently anchored to mark the northerly and southerly bounds of the 

7 m depth contour. The tethering line thus spanned the lake surface overlying the 

hypolimnion. The CTD was lowered through the water column at a descent rate of 1 to 2 

cm s

-1 at a station located about 3 to 5 m from the southernmost buoy. Data from the 

sensors were logged at a rate of 4 Hz and graphically displayed in real-time with an onboard laptop computer. In addition to conductivity, temperature and depth, the Seabird 

unit also measured in situ chlorophyll fluorescence, transmissometer beam attenuation, 

pH and dissolved oxygen so that thermal structure, redox conditions and particle layers 

could all be used to target the collection of water samples during the second deployment. 

After obtaining a first Seabird profile, the boat was moved along the tether line toward 

the northernmost buoy to a second station and an acrylic outrigger was attached to the 

SeaBird profiler. A submersible, non-metallic pump was fixed to the end of the outrigger 

so that water could be pumped to the surface through acid-washed C-Flex tubing and 

collected on deck as described by Watras et al. (1998). The collection of water samples 

began when the unit reached the first target depth. Generally 5 to 7 depths were sampled 

in the 7 m water column. On every sampling date, the two SeaBird profiles were 

compared to ensure that the physical, chemical and biological structure of the water 

column was horizontally uniform across the deep pelagic region of the lake. The single 

sampling profile was then considered representative of the entire water column. The lake 

water samples were hermetically sealed in double plastic bags and transported on ice in 

dark coolers to the UW Trout Lake Clean Laboratory. 

9 
3.b.3. Precipitation Sampling 

Bulk precipitation was sampled continuously and collected weekly from 2002 through 

2004 using modified IVL-type collectors (as described by Morrison et al. 1995) at two 

sites. One site was the US NADP/MDN site WI36 located at Trout Lake in neighboring 

Vilas County (roughly 80 km from Devils Lake) where the deposition of mercury has 

been monitored continuously since 1995, along with total precipitation amount and 

ancillary precipitation chemistry (http://nadp.sws.uiuc.edu/mdn). A second site was 

established on the Potawatomi Reservation less than 2 km from Devils Lake. The IVL 

sampler at this site was maintained by FCPC personnel and operated continuously from 

May 28, 2002 to August 25, 2004. Duplicate IVL-collectors were operated from May 28, 

2002 to September 4, 2002. All IVL samples were stored in the dark and transported to 

the Trout Lake Clean Laboratory for HgT analysis. The mercury data for the IVL samples 

collected at the FCPC and Trout Lake air monitoring sites (2002-2004) are presented in 

Appendix A3. 

A continuous record of precipitation was not available for the FCPC site for the entire 

study period. For the purposes of this study, we assumed that mercury concentrations in 

precipitation were regionally coherent whereas precipitation amount could demonstrate 

significant local variability. Therefore, we estimated precipitation amount using data 

from the site with a complete record located nearest to the study site and we estimated 

HgT concentrations in precipitation from regional means. 

The nearest site to the Devils Lake study site with a complete record of precipitation 

amount for the entire study period was the Laona 6 SW weather station (ID# 474582; 

Wisconsin State Climatology Office, http://www.aos.wisc.edu/~sco/) approximately 13 

km due west of DL. Data from this site was used to estimate precipitation amounts for the 

annual hydrologic budgets reported in the DL Hydrology Report. The use of Laona 6 SW 

data was validated by comparison with the data collected weekly from the FCPC site for 

the period May 2002 through August 2004. The similarity of the two records indicated 

10 
that the Laona site is a reasonable surrogate for FCPC precipitation (DL Hydrology 

Report). 

Table 3. Comparison of atmospheric mercury data collected at DL 

study site with other sites in region over 117 weeks of 

parallel collection 

FCPC 

IVL 

TRL 

IVL 

WI36 

MDN 

WI09 

MDN 

WI32 

MDN 

HgT deposition (μg/m2) 19.9 17.5 19.5 16.6 19.5 

VWA HgT (ng/L) 10.7 9.7 10.9 10.5 12.2 

# weeks missing precip data 0 0 0 0 7 

# weeks w/o Hg data 0 7 15 23 11 

Precip (cm) w/o Hg data 0 0.03 4.2 5.1 5.0 

Annual and seasonal HgT concentrations at the DL study site were estimated as the mean 

of the volume-weighted average (VWA) HgT concentrations from three US NADP/MDN 

sites. These sites were i) the Trout Lake site (WI36) described above, ii) the Popple River 

site in Fence, Florence County, WI 50 km northeast of DL (WI32) and the Middle 

Village site in Shawano County, WI 75 km south of DL (WI09) 

(http://nadp.sws.uiuc.edu). Comparison between the IVL collector at Devils Lake and the 

mean of the three MDN sites showed that the VWA concentration of HgT differed by 

roughly 5% during the 117 weeks of parallel sampling in 2002-2004 (10.7 ng/L vs. 11.2 

ng/L, respectively), indicating locally coherent Hg depositional regimes (Table 3). The 

annual and seasonal mean VWA concentrations used to construct the mercury mass 

balances are shown in Table 4. The mean concentrations were multiplied by the 

precipitation amounts from Laona 6 SW to estimate HgT deposition at the study site. The 

atmospheric deposition of meHg to the surface of Devils Lake was estimated to be 1.2% 

of the atmospheric HgT deposition, based on NADP/MDN data for the Trout Lake site 

(WI36). During 2002, 2003, and 2004 meHg constituted 0.5%, 1.9% and 1.5%, 

respectively, of the annual HgT deposition at this site (http://nadp.sws.uiuc.edu/mdn). 

These data agree well with earlier estimates of 1.5% based on measurements at nearby 

Little Rock Lake (Watras et al. 1994, Fitzgerald et al. 1991). 

11 
Table 4. Annual and seasonal VWA HgT concentrations 

(ng/L) in precipitation from three NADP/ MDN sites 

(WI36, WI32 and WI10). Values are mean ± SD. 

Year Annual Seasonal 

2002 12.1 ± 0.9 14.0 ±0.7 

2003 11.2 ± 1.9 12.2 ± 1.8 

2004 9.1 ± 0.4 12.4 ± 0.8 

3.b.4. Air Sampling 

A Tekran Model 2537A Mercury Vapor Analyzer was operated at NADP/MDN site 

WI36 (Trout Lake) from October 3, 2002 until January20, 2004 taking continuous 5-

minute integrated samples. The sampling inlet was connected to a Teflon manifold which 

also served ozone and sulfur dioxide analyzers maintained by the WDNR Bureau of Air 

Management. The manifold was connected by 1⁄2-inch plastic tubing to an inverted funnel 

atop a tower which extended above treetops. Airflow was maintained by a vacuum pump 

and monitored with a flow meter. The Tekran 2537A was equipped with an internal 

mercury vapor permeation source which was used to perform automatic calibrations at 

regular intervals. Manual injections of saturated mercury vapor were also occasionally 

performed. 

Daily means of the 5-minute continuous TGM concentrations are complied in Appendix 

A4.1. Hourly means of TGM and all of the original TEK files are in Appendices A4.2

and A4.3 (CD only). 

3.b.5. Aqueous Mercury Analysis 

Samples for mercury analysis collected for background monitoring from 1995 to 2001 

were analyzed using purge-trap/CVAFS for HgT (Bloom & Fitzgerald 1988) and 

ethylation/GC/CVAFS for meHg (Bloom 1989, Liang et al. 1994) at Frontier 

12 
Geosciences, Inc. (Seattle, WA). Stream samples for mercury analysis collected in 2002 

were also analyzed by Frontier Geosciences. Lake samples for mercury analysis collected 

for intensive monitoring from 2002 through 2004 were analyzed at UW Trout Lake Clean 

Laboratory where they were analyzed following protocols similar to those used at 

Frontier Geosciences, i.e. EPA Methods 1630 & 1631 (US EPA 2001, 2002). Intercalibration between these two analytical facilities has shown good agreement for both 

HgT and meHg analysis in freshwater samples (Bloom et al. 1995). Stream samples 

collected in 2003 were also sent to UW Trout Lake. All UW Trout Lake samples were 

analyzed in duplicate for HgT and meHg. In 2004, stream samples were analyzed at State 

Laboratory of Hygiene (Madison, WI). 

Mercury data for the tributary and distributary streams are in Appendix A1. Data for 

Devils Lake are found in Appendix A2. 

3.b.6. Ancillary Solutes 

Conductivity and pH were monitored in the field using hand-held meters throughout the 

study period. Samples for ancillary solutes analyses collected for background monitoring 

from 1995 to 2001 and stream samples collected in 2002 were sent to ERA Labs, Inc., 

Duluth, MN. These samples were analyzed for alkalinity, dissolved organic carbon 

(DOC), total Kjeldahl nitrogen (TKN), total phosphorus (TP) and chlorophyll-a (Chl-a). 

Results of these analyses are reported in Appendices A1.1 (stream data) and A2.1 (lake 

data). 

Lake water samples collected during intensive monitoring 2002 – 2004 and stream 

samples collected in 2003 were analyzed for pH, DOC, SO4

2-, total sulfide, methane, 

suspended particulate matter (SPM), major cations, anions and metals. SPM, chl a, pH, 

methane and sulfide determinations were performed at Trout Lake lab by WDNR 

personnel. DOC determinations were performed by UW-Madison personnel at the Center 

for Limnology. Cations, anions and metals were sent to the State Laboratory of Hygiene 

13 
(SLH), Madison, WI. Methods are described by Watras et al. (2006) (see Section 5c). 

Results are reported in Appendices A1.2 (stream data) and A2.2 (lake data). 

All ancillary solute analyses on stream samples collected in 2004 were performed by 

SLH. Results are in Appendix A1.3. 

3.b.7. QAQC Criteria for Mercury Analyses 

Quality control and quality assurance criteria for UW-Trout Lake clean laboratory 

mercury analyses, 1997 – 2005 with DL site specific values where applicable are as 

follows: 

HgT analysis following EPA Method 1631 

General Criteria 

1. On-going precision (mean ± SD) 99.7% ± 6.2%, n=735 

2. Quality control samples (mean ± SD) 97.6% ± 5.9%, n=158 

3. Bubbler blanks (mean ± SD) 3.7 pg ± 3.5 pg, n=1628 

Aqueous HgT

1. Reagent blank (mean ± SD) 15.3 pg ± 6.5 pg, n =228 

2. Daily detection limit (3·sd reagent blanks) (mean, range) 

0.05 ng/L, 0.01 – 0.18 ng/L 

3. Method detection limit (pooled variance of reagent blanks): 0.05 ng/L 

4. Method blanks (mean ± SD) 16.8 pg ± 4.6 pg, n =28 

5. Method detection limit (pooled variance of method blanks): 0.04 ng/L 

6. Lab duplicate RPD (mean ± SD) 

Lake and stream samples 4.8% ± 4.4%, n=171 

DL Lake and stream samples 5.0% ± 4.6%, n=99 

Rain samples 10.3% ± 9.7%, n=107 

7. Field duplicate RPD (mean ± SD) 

Lake and stream samples 4.8% ± 9.1%, n=36 

DL Lake and stream samples 7.0% ± 7.2%, n=32 

DL “A” and “B” rain samples 15% ± 15%, n=12 

8. Matrix spike recovery (mean ± SD) 

Lake and stream samples 94.8% ± 6.7%, n=111 

DL Lake and stream samples 92.7% ± 7.2%, n=37 

Rain samples 103.8% ± 18.4%, n=98 

9. Matrix spike duplicate RPD (mean ± SD) 

Lake and stream samples 4.3% ± 5.0%, n=52 

DL Lake and stream samples 6.6% ± 5.9%, n=22 

Rain samples 7.2% ± 10.3%, n=128 

14 
Particulate HgT

1. Method blanks (mean ± SD) 22.3 pg ± 9.2 pg, n =44 

2. Reagent blanks (mean ± SD) 18.2 pg ± 4.1 pg, n =24 

3. Filter blanks (mean ± SD) 42 pg ± 32 pg, n =38 

4. Yield CRM (DOLT-2) (mean ± SD) 100.6% ± 7.0%, n =18 

5. Duplicate RPD (mean ± SD) 27% ± 30%, n =128 

MeHg analysis following EPA Method 1630 

General Criteria 

1. On-going precision (mean ± SD) 100.4% ± 10.5%, n=609 

2. Quality control samples (mean ± SD) 105.7% ± 11.5%, n=78 

Aqueous meHg 

1. Reagent blank (mean ± SD) 0.4 pg ± 1.1 pg, n =268 

2. Method detection limit (pooled variance of reagent blanks): 0.05 ng/L 

3. Distillation blanks (mean ± SD) 0.3 pg ± 0.8 pg, n =123 

4. Method detection limit (pooled variance of distillation blanks): 0.03 ng/L 

5. Lab duplicate RPD (mean ± SD) 

Lake and stream samples 10.9% ± 9.0%, n=195 

DL Lake and stream samples 8.4% ± 7.1%, n=88 

6. Field duplicate RPD (mean ± SD) 

Lake and stream samples 7.8% ± 7.7%, n=36 

DL Lake and stream samples 7.9% ± 7.7%, n=29 

7. Matrix spike recovery (mean ± SD) 

Lake and stream samples 96% ± 11%, n=118 

DL Lake and stream samples 93% ± 9%, n=41 

8. Matrix spike duplicate RPD (mean ± SD) 

Lake and stream samples 5.4% ± 5.7%, n=39 

DL Lake and stream samples 5.3% ± 4.9%, n=19 

Particulate meHg 

9. Reagent blanks (mean ± SD) 1.1 pg ± 2.4 pg, n =49 

10. Filter blanks (mean ± SD) 1.6 pg ± 2.7 pg, n =69 

11. Matrix spike recovery (mean ± SD) 104.3% ± 0.1% pg, n =5 

12. Yield CRM (DOLT-2) (mean ± SD) 101.1% ± 0.2%, n =14 

13. Duplicate RPD (mean ± SD) 28.2% ± 0.5%, n =92 

3.b.8. Other analyses 

In addition to sampling Devils Lake for mercury species and ancillary chemical 

analytes, water samples were also collected to characterize the microbial community and 

15 
to estimate methylation and demethylation rate constants at specific depths during peak 

stratification in 2002. Microbial community composition was characterized with 

molecular genetic techniques (ARISA and clone libraries). Details of methods and results 

can be found in Kent et al. (2005a, b, c) in Section 5.d). Rates of mercury methylation 

and demethylation were measured using stable isotopes of mercury. Methods described in 

detail and results presented in Eckley et al. (2005) in Section 5.a.

3.c. Mass Balance Calculations 

Annual budgets for waterborne HgT in Devils Lake were constructed for years 

2002 – 2004. Annual budgets were computed for calendar years, January 1 to December 

31. A seasonal mass balance for waterborne meHg for the time period when mercury 

accumulates in the water column also was compiled for each year. This seasonal period 

began with the onset of stream flow in spring and continued until peak summer 

stratification (mid-August). The governing expression was: 

ΔSHg = (PHg + Qin-Hg + ROHg) – (Qout-Hg + Gout-Hg + EHg + SHg) + Mnet 

where ΔSHg is the change in waterborne mercury mass (storage); PHg is the mass 

deposited atmospherically directly on the lake; Qin-Hg is the mass delivered from the 

upstream wetland via the tributary stream; ROHg is the mass of mercury in nonchannelized runoff in the nearshore zone; Qout-Hg is the mass lost to the distributary 

stream; Gout-Hg is the mass lost to groundwater; EHg is the mass lost by evasion across the 

air/water interface; SHg is the mass lost to sediments; and Mnet is the mass of meHg in the 

water column attributable to net in-lake methylation. For the HgT budget, Mnet is zero. 

Change in storage (ΔSHg) was estimated as the difference in waterborne mass at 

the beginning and end of the season or water year. The total mass of mercury in the water 

column was determined as the sum of masses over all depths sampled, according to 

Σci·vi, for i = 1 to n, where ci and vi represent the concentration and volume for a given 

depth stratum (i). Midpoints between successive sampling depths were used to bound (i); 

16 
and the lake volume was adjusted for changes in stage. Atmospheric deposition (PHg) was 

the product of the volume-weighted average mercury concentration times the amount of 

precipitation falling directly on the lake (Sec 3.b.3 and Table 4). Stream in-flow (Qin-Hg) 

was estimated as Σct·vt, for t = 1 to n, where ct and vt represent the mercury concentration 

and water discharge volume for a given time interval. Stream sampling dates were used 

as mid-points between successive time intervals. Non-channelized runoff (ROHg ) was 

calculated as the product of the runoff coefficient from the hydrologic budget (0.1), 

precipitation volume and the volume-weighted concentration of mercury in tributary 

stream water (i.e. assuming the same mercury concentration in channelized and nonchannelized overland flow). Stream out-flow (Qout-Hg) was estimated as the product of 

distributary stream discharge volume and the mean epilimnetic concentration of lake over 

the appropriate time period. Groundwater output (Gout-Hg) was the product of groundwater 

outflow volume times the mean concentration of mercury in the epilimnion (assuming no 

profundal recharge). Groundwater recharge was seasonally pro-rated from the annual 

hydrologic budget for the meHg budgets. Evasion and sedimentation were estimated as a 

pooled residual loss term: (E + S)Hg = (PHg + Qin-Hg + ROHg) – (Qout-Hg + Gout-Hg + ΔSHg). 

For meHg, this term was approximated as 1% of (E + S)HgT since meHg constitutes 

roughly 1% of the HgT in sediments but it does not evade across the air-water interface to 

a significant degree (Watras et al. 1996, Ullrich et al. 2001, Watras et al. 1998, Hudson et 

al. 1994). Note that (E + S)MeHg is probably a lower limit since demethylation in the 

sediment is not considered. Net methylation (Mnet) was calculated according to: Mnet = 

ΔSMeHg + (Qout-MeHg + Gout-MeHg + (E + S)MeHg) – (PMeHg + ROMeHg + Qin-MeHg). Mnet is a 

conservative estimate for the mass in the water column attributable to in-lake production 

(regardless whether the site of production is in sediments or the water column) if (E + 

S)MeHg underestimates the gross flux to sediments. By definition, Mnet includes 

demethylation in the water column. 

The annual mass balances for waterborne HgT in Devils Lake, 2002 – 2004, are shown in 

Table 1; the seasonal mass balances for waterborne, meHg are presented in Table 2. The 

annual and seasonal hydrologic budgets upon which the mercury budgets are based are 

17 
given in Tables 5 & 6. The annual HgT concentrations assigned to hydrologic fluxes are 

in Table 7; seasonal VWA meHg concentrations are in Table 8. 

Table 5. Annual Hydrologic Budgets for Devils Lake, 2002-2004 (from DL Hydrology 

Report) 

-------------Inputs--------- ------------Outputs------------ 

Year Precip 

(P) 

(m3

) 

Surface 

Runoff 

(RO) 

(m3

)

Tributary 

Flow 

(Qin) 

(m3

)

Evap 

(E) 

(m3

)

Distributary 

Flow 

(Qout) 

(m3

)

Lake 

Seepage 

(GO) 

(m3)

Change 

in Lake 

Storage 

(ΔS) 

(m3

)

2002 124,007 16,917 287,331 65,988 318,986 38,474 4,808 

2003 90,442 7,589 128,889 65,988 175,704 10,520 -25,293 

2004 108,208 7,595 128,990 65,988 163,389 17,167 -1,751 

mean 107,552 10,700 181,737 65,988 219,360 22,053 -7,4121 

SD 16,792 5,384 91,448 6,243a 86,498 14,604 15,829 

Table 6. Seasonal Hydrologic Budgets for Devils Lake, 2002-2004 

-------------Inputs--------- ------------Outputs------------ 

Year Precip 

(P) 

(m3

) 

Surface 

Runoff 

(RO) 

(m3

)

Stream 

Flow 

(Qin) 

(m3

)

Evap 

(E) 

(m3

)

Stream 

Flow 

(Qout) 

(m3

)

Lake 

Seepage 

(GO) 

(m3)

Calc. 

Change 

in Lake 

Storage 

(ΔS) 

(m3)

Obs. 

Change 

in Lake 

Storage 

(ΔS) 

(m3

)

Residu

al 

(m3) 

2002 71394 7482 231360 39593 231182 13914 25547 25547 42373 

2003 48858 5121 128888 39593 175704 4208 -36638 -34811 -1827 

2004 47427 4971 128990 39593 163389 6679 -28273 -36633 8360 

mean 55893 5858 163079 39593 190092 8267 -13121 -29423 16302 

SD 13443 1409 59132 - 36114 5044 33748 10947 23146 

P calculated from seasonal Laona 6SWprecipitation amount and lake area 

RO estimated from seasonal precipitation, run-off coefficient = 0.10, and near-shore 

area = 12.3 ha 

Qin estimated as seasonal Inlet discharge (DL Hydrology Report) 

E 60% annual evaporation 

Qout estimated as seasonal Outlet discharge (DL Hydrology Report) 

GO prorated from GO in annual hydrologic budgets 

Calc.. ΔS calculated by difference 

Obs. ΔS calculated from staff gauge readings and hypsometric curve 

Residual Calc ΔS – Obs ΔS 

18 
Table 7. HgT concentrations (ng/L) used to construct 

annual budgets for waterborne HgT in Devils Lake, 2002 - 

2004 

Year Precip 

(P) 

Tributary 

Stream 

(Qin) and 

Surface 

Runoff 

(RO) 

Distributary 

Stream 

(Qout) and 

Lake 

Seepage 

(GO) 

2002 12.1 11.4 2.9 

2003 11.2 7.1 3.5 

2004 9.1 9.1 3.2 

mean 10.8 9.2 3.2 

SD 1.5 2.2 0.3 

Table 8. MeHg concentrations (ng/L) used to construct 

seasonal budgets for waterborne meHg in Devils Lake, 

2002 - 2004 

Year Precip 

(P) 

Tributary 

Stream 

(Qin) and 

Surface 

Runoff 

(RO) 

Distributary 

Stream 

(Qout) and 

Lake 

Seepage 

(GO) 

2002 0.17 0.24 0.28 

2003 0.15 0.21 0.44 

2004 0.15 0.18 0.30 

mean 0.15 0.21 0.34 

SD 0.01 0.03 0.09 

19 
4. References 

Citations of DL Hydrology Report refer to: 

Atmospheric Deposition and Biogeochemistry of Mercury and other Trace Contaminants 

in Aquatic Ecosystems, Final Project Report Part 1: Devils Lake Watershed Hydrology 

2002 – 2004, prepared by Morrison KA and Watras CJ, December 2005. 

The following references are completely cited in Section 5. Complete copies of the 

published papers and abstracts of the oral presentations are included. 

Eckley et al. 2005 

Watras et al. 2005 

Watras et al. 2006 

Kent et al. 2005a, b, c 

Other works cited: 

Frost 1995 

Frost T.M., Montz P.K., Kratz T.K., Badillo T., Brezonik P.L., Gonzalez M.J., Rada 

R.G., Watras C.J., Webster K.E., Wiener J.G., Williamson C.E., Morris D.P. 1999. 

Multiple stresses from a single agent: diverse responses to the experimental 

acidification of Little Rock Lake, Wisconsin. Limnol. Oceanogr. 44(3, part 2): 784-

794. 

Bloom N.S., Watras C.J. 1989. Observations of methylmercury in precipitation. Sci. Tot. 

Environ. 87/88: 199-207. 

Bloom N.S., Fitzgerald W.F. 1988. Determination of volatile mercury species at the 

picogram level by low temperature gas chromatography with cold vapor atomic 

fluorescence detection. Anal. Chim. Acta 208: 151-161. 

Bloom N.S., Horvat M., Watras C.J. 1995. Results of the international aqueous mercury 

speciation intercomparison exercise. Water Air Soil Pollut. 80: 1257-1268. 

Fitzgerald W.F., Mason R.P., Vandal G.M. 1991. Atmospheric cycling and air-water 

exchange of mercury over mid-continental lacustrine regions. Water Air Soil Pollut.

56: 745-768. 

Horsley & Witten Inc. 2003. Devil's Lake Summary Report: Water Years 1996 to 2002. 

Horsley & Witten Inc., 90 Route 6A, Sandwich, MA 02563, 57 p. 

Hudson R.J.M., Gherini S.A., Watras C.J., Porcella D.B. 1994 Modeling the 

biogeochemical cycling of mercury in lakes: the Mercury Cycling Model (MCM) and 

its application to the MTL study lakes. In: Watras C.J. and Huckabee J.W., eds. 

Mercury Pollution: Integration and Synthesis, Lewis Publishers. p. 473-526. 

20 
Liang L., Horvat M., Bloom N.S. 1994. An improved speciation method for mercury by 

GC/CVAFS after aqueous phase ethylation and room temperature precollection. 

Talanta 41(3): 371-379. 

Lidwin R.A., Krohelski J.T. 1993. Hydrology and Water Quality of the Forest County 

Potawatomi Indian Reservation, Wisconsin. USGS, 91-4136. 

Morrison K.A., Kuhn E.S., Watras C.J. 1995. Comparison of three methods of estimating 

atmospheric mercury deposition. Environ. Sci. Tech. 29(3): 571-576. 

Rudd J.W.M. 1995. Sources of methylmercury to aquatic ecosystems: a review. Water 

Air Soil Pollut. 80: 697-713. 

Simpkins W.W., McCartney M.C., Mickelson D.M. 1987. Pleistocene Geology of Forest 

County, Wisconsin. Wisconsin Geological and Natural History Survey, Circular 61. 

Ullrich S.M., Tanton T.W., Abdrashitova S.A. 2001. Mercury in the aquatic environment: 

A review of factors affecting methylation. Critical Reviews in Environmental Science 

and Technology 31(3): 241-293. 

US EPA. 2001. Method 1630: Methyl mercury in water by distillation, aqueous 

ethylation, purge and trap, and CVAFS (EPA-821-R01-020). Office of Water, 

Engineering and Analysis Division, Office of Science and Technology, EPA-821-

R01-020. Washington, DC 

US EPA. 2002. Method 1631, Revision E: Mercury in Water by Oxidation, Purge and 

Trap, and Cold Vapor Atomic Fluorescence Spectrometry (EPA 821-R-02-019). 

Office of Water, Engineering and Analysis Division, Office of Science and 

Technology, EPA 821-R-02-019. Washington DC. 

Watras C.J., Bloom N.S., Hudson R.J.M., Gherini S., Munson R., Claas S.A., Morrison 

K.A., Hurley J., Wiener J.G., Fitzgerald W.F., Mason R., Vandal G., Powell D., Rada 

R., Rislov L., Winfrey M., Elder J., Krabbenhoft D., Andren A.W., Babiarz C., 

Porcella D.B., Huckabee J.W. 1994 Sources and fates of mercury and methylmercury 

in Wisconsin lakes. In: Watras C.J. and Huckabee J.W., eds. Mercury Pollution: 

Integration and Synthesis, Lewis Publishers. p. 153-177. 

Watras C.J., Morrison K.A., Back R.C. 1996 Mass balance studies of mercury and 

methylmercury in small, temperate/boreal lakes of the northern hemisphere. In:

Baeyens W., Ebinghaus R. and Vasiliev O., eds. Global and Regional Mercury 

Cycles: Sources, Fluxes and Mass Balances., NATO Advanced Science Institute 

Series 2: Environment, Kluwer Academic Publishers. p. 329-358. 

Watras C.J., Back R.C., Halvorsen S., Hudson R.J.M., Morrison K.A., Wente S.P. 1998. 

Bioaccumulation of mercury in pelagic freshwater food webs. Sci. Tot. Environ. 219: 

183-208. 

21 
5. Published works 

To date, results of the cooperative FCPC/WDNR project have been published in three 

peer-reviewed technical papers and three oral papers that were presented at international 

scientific meetings in the US and Europe. The peer-reviewed technical papers were 

published in three highly-regarded international journals: 1) The Canadian Journal of 

Fisheries and Aquatic Sciences, 2) Environmental Science and Technology and 3) 

Limnology and Oceanography. Those citations, in order of publication are: 

Eckley C., Watras C.J., Hintelmann H., Morrison K., Kent A., Regnell O. 2005. Mercury 

methylation in the hypolimnetic waters of lakes with and without connection to 

wetlands in northern Wisconsin. Can. J. Fish. Aquat. Sci. 62: 400-411. 

Watras C.J., Morrison K.A., Kent A., Price N., Regnell O., Eckley C., Hintelmann H., 

Hubacher T. 2005. Sources of methylmercury to a wetland-dominated lake in 

northern Wisconsin. Environ. Sci. Tech. 39(13): 4747-4758. 

Watras C.J., Morrison K.A., Regnell O., Kratz T.K. 2006. The methylmercury cycle in 

Little Rock Lake during experimental acidification and recovery. Limnol. 

Oceanogr. 51(1): 257-270. 

Citations for the oral papers are: 

Kent, A.D., C. J. Watras, C. Eckley, O. Regnell, K. D. McMahon and H. Hintelmann. 

2005. Microbial community composition and mercury methylation in the anoxic 

hypolimnia of stratified Wisconsin lakes. ASLO Annual Summer Meeting, June 

19-24, 2005, Santiago de Compostela, Spain 

Kent, A.D., C. J. Watras, C. Eckley, O. Regnell, K. D. McMahon and H. Hintelmann. 

2005 Mercury Methylation Varies with Pelagic Microbial Community 

22 
Composition in Lakes Within the Great Lakes Basin. International Association for 

Great Lakes Research: 48th Annual Meeting, Ann Arbor MI, May 23-27, 2005. 

Kent, A.D. C.J. Watras, O. Regnell, C. Eckley and H. Hintelmann. 2005. Analysis of 

microbial community structure associated with mercury methylation in northern 

Wisconsin lakes. Am. Soc. Limnol Oceanogr. Aquatic Sciences Meeting, Salt 

Lake City, February, 2005 

Complete copies of the technical papers and published abstracts of the oral papers follow. 

23 
6. Appendices 

Appendix A1. DL Stream Data 

A1.1. H&W data: 1995 - 2002 

A1.1.1. Tributary Stream (Upstream site) 

A1.1.2. Tributary Stream (Inlet site) 

A1.1.3. Distributary Stream (Outlet site) 

A1.2. TRL data: 2003 

A1.2.1. Tributary Stream (Inlet site) Summary 

A1.2.2. Tributary Stream (Inlet site) Total mercury data 

A1.2.3. Tributary Stream (Inlet site) Methylmercury data 

A1.2.4. Tributary Stream (Inlet site) pH, SPM and Chl a data 

A1.2.5. Distributary Stream (Outlet site) Summary 

A1.2.6. Distributary Stream (Outlet site) Total mercury data 

A1.2.7. Distributary Stream (Outlet site) Methylmercury data 

A1.2.8. Distributary Stream (Outlet site) pH, SPM and Chl a data 

A1.3. FCPC data: 2004 

A1.3.1. Tributary Stream (Upstream site) 

A1.3.2. Tributary Stream (Inlet site) 

A1.3.3. Distributary Stream (Outlet site) 

Appendix A2. DL Lake Data 

A2.1. H&W data: 1995-2002 

A2.1.1. Lake1 site 

A2.1.2. Lake2 site 

A2.2. TRL data: 2002-4 

A2.2.1. Data summary 

A2.2.2. Total mercury data 

A2.2.3. Methylmercury data 

 A2.2.4. pH, SPM and Chl a data 

A2.3. FCPC data: 2004 

Appendix A3. Precipitation Data: 2002-2004 

A3.1. FCPC site 

A3.1.1. FCPC summary 

A3.1.2. FCPC duplicate IVL data 

A3.2. Trout Lake site 

Appendix A4. Total Gaseous Mercury Data 

A4.1. Mean Daily TGM at Trout Lake site 

A4.2. Mean Hourly TGM at Trout Lake (CD only)

A4.3. TEK files (CD only)