Minnesota National Lakes Assessment Project - Minnesota Pollution

Minnesota National Lakes Assessment Project - Minnesota Pollution

Minnesota National Lakes Assessment Project: Water Mercury Concentrations in Minnesota Lakes This report is part of a series based on Minnesota’s part...

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Minnesota National Lakes Assessment Project: Water Mercury Concentrations in Minnesota Lakes This report is part of a series based on Minnesota’s participation in U.S. EPA’s 2007 National Lake Assessment October 2008

wq-nlap-02

Minnesota Pollution Control Agency 520 Lafayette Road North Saint Paul, MN 55155-4194 http://www.pca.state.mn.us 651-296-6300 or 800-657-3864 toll free TTY 651-282-5332 or 800-657-3864 toll free Available in alternative formats

Authors and Contributors Bruce Monson Steve Heiskary Report review Ed Swain Environmental Analysis and Outcomes Division October 2008

The MPCA is reducing printing and mailing costs by using the Internet to distribute reports and information to wider audience. For additional information, see the Web site: http://www.pca.state.mn.us/water/nlap.html

Mercury Concentrations in MN Lakes 10/2008

Minnesota Pollution Control Agency 1

Table of Contents

Page

INTRODUCTION............................................................................................................. 3 National Lakes Assessment Project (NLAP) Overview............................................................. 3 Minnesota’s NLAP Overview ...................................................................................................... 3 REPORT FOCUS: WATER MERCURY (HG) CONCENTRATIONS IN MINNESOTA LAKES ............................................................................................................................ 5 Background on Mercury in Minnesota....................................................................................... 5 Methods.......................................................................................................................................... 6 Results and Discussion.................................................................................................................. 7 Summary Statistics ................................................................................................................................... 7 Relationships Among Variables ............................................................................................................... 8 Spatial Distributions ............................................................................................................................... 10

Summary and Conclusions......................................................................................................... 10 References.................................................................................................................................... 12

List of Tables Table 1 Statistical summary of unfiltered total mercury (THg), unfiltered methylmercury (MeHg), methyl mercury fraction (MeHg/THg x 100), and dissolved organic carbon (DOC) for the NLAP lakes in 2007 .................................................................................................... 7 Table 2 Pearson correlation matrix of log-transformed THg, MeHg, DOC, and Area ................. 9

List of Figures Figure 1 Location of Minnesota's NLAP lakes as surveyed in 2007............................................. 4 Figure 2 Density plots of THg, MeHg, DOC, and Lake Area ....................................................... 8 Figure 3 Density plots of Log-transformed THg, MeHg, DOC, and Area.................................... 8 Figure 4 Scatterplot matrix of log-transformed THg, MeHg, DOC, and Area, with LOWESS smoother and histogram of data distributions ......................................................................... 9 Figure 5 Spatial distributions of THg and MHg concentrations, and MeHg fraction, overlying ecoregions ............................................................................................................................. 11 Appendix A. THg, MeHg, DOC, UV Absorbance at 254 nm, and SUVA for All Sites

Mercury Concentrations in MN Lakes 10/2008

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Introduction National Lakes Assessment Project (NLAP) Overview The U.S. Environmental Protection Agency (EPA) has a responsibility to assess the health of the nation’s water resources. One of the methods for assessment is a statistically based survey. The Survey of the Nation’s Lakes, conducted in 2007, is one of a series of water surveys being conducted by states, tribes, EPA, and other partners. In addition to lakes, partners will also study coastal waters, wadable streams, rivers, and wetlands in a revolving sequence. The purpose of these surveys is to generate statistically valid and environmentally relevant reports on the condition of the nation’s streams, lakes, wetlands, and estuaries at nation-wide and regional scales. The goal of the Lakes Survey is to address two key questions about the quality of the Nation’s lakes, ponds, and reservoirs: • •

What percent of the Nation’s lakes are in good, fair, and poor condition for key indicators of trophic state, ecological health, and recreation? What is the relative importance of key stressors such as nutrients and pathogens?

The sampling design for this survey is a probability-based network that provides statistically valid estimates of the condition of all lakes, with a known degree of confidence. Sample sites are selected at random to represent the condition of all lakes across the nation and each region. A total of 909 lakes in the conterminous U.S. are included in the Lakes Survey. The sample set is comprised of natural and built freshwater lakes, ponds, and reservoirs greater than 10 acres and at least one meter in depth located in the conterminous United States. The typical sampling effort at each site includes a variety of samples and measurements collected at a mid-lake index site, which is often at the deepest point in the lake. Samples include a two meter integrated sample for water chemistry, chlorophyll-a, microcystin and algal identification; oxygen and temperature profiles; zooplankton tow; and sediment core sample for diatom reconstruction of total phosphorus (based on top and bottom slices from the core) and surface sediment sample for mercury. In addition, 10 random near-shore sites are qualitatively assessed for various littoral and riparian habitat-related measures and a sample for a bacterial indicator was collected. Further details on the survey including methods, parameters measured, and statistical design may be found on the EPA NLAP web page at: http://www.epa.gov/owow/lakes/lakessurvey/.

Minnesota’s NLAP Overview Minnesota’s 2007 NLAP effort was led by the Minnesota Pollution Control Agency (MPCA) and Minnesota Department of Natural Resources (MDNR). Various other collaborators were engaged in this study as well including the U.S. Forest Service (USFS), Minnesota Department of Agriculture (MDA), and U.S. Geological Survey (USGS). MPCA and MDNR cooperated on initial planning of the survey and conducted a vast majority of the sampling, which took place in July and August for most lakes. USFS staff sampled remote lakes in the Boundary Waters Canoe Area Wilderness (BWCAW). Minnesota received 41 lakes as a part of the original draw of lakes for the national survey–the most of any of the lower 48 states. Minnesota chose to add nine lakes to the survey to yield the 50 lakes needed for statistically-based statewide estimates of condition (Figure 1). In addition to the 50 lakes, several Mercury Concentrations in MN Lakes 10/2008

Minnesota Pollution Control Agency 3

reference lakes were later selected and sampled by USEPA as a part of the overall NLAP effort. Data from the reference lakes provide an additional basis for assessing lake condition as a part of NLAP. In addition to adding lakes, Minnesota chose to add several value-added measurements to the survey of lakes. The additional data collection included: pesticide samples (in conjunction with the MDA); water mercury (in conjunction with USGS); sediment samples for analysis of metals, trace organics and other parameters; identification of macrophytes and maximum rooting depth of macrophytes at the random near-shore sites; and samples for microcystin at the index and a random near-shore site. Each of these add-ons and several of the standard assessments is the subject of a series of reports that draw from the NLAP work.

Figure 1 Location of Minnesota's NLAP lakes as surveyed in 2007

Mercury Concentrations in MN Lakes 10/2008

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Report Focus: Water Mercury (Hg) Concentrations in Minnesota Lakes Background on Mercury in Minnesota Humans and wildlife are primarily exposed to mercury from the consumption of fish. Minnesota has a four-decade record of mercury in fish from lakes and rivers throughout the state and has the most extensive fish consumption advisory in the United States. Fish are excellent indicators of mercury levels in a waterway because they integrate the mercury over the life of the fish; however, mercury levels in water are important in showing natural variability and responsiveness to changes in mercury loading to watersheds. Mercury in water is considerably less well known, mostly because the concentrations are extremely low in water, requiring special sampling and analytical techniques. Mercury concentrations in fish are 1 million to 10 million times higher than in water and therefore fish analysis for mercury requires less sensitive techniques than water analysis. Despite the greater difficulty of obtaining mercury concentrations in water, it is important to gather the data because it is useful to build an understanding of how the mercury content of fish is related to the water in which the fish grow. Minnesota currently has a water quality standard for mercury in water of 6.9 ng/L (with a lower standard of 1.3 ng/L in the Lake Superior Basin, as adopted for waters within the Great Lakes basin by each bordering state). In 2008 the state promulgated a water quality standard for methylmercury in fish tissue (0.2 mg/kg). To translate the new fish tissue-based water quality standard to a water concentration, a bioaccumulation factor (BAF) would be necessary, which is the ratio of mercury concentrations in fish and water. Mercury concentrations in lake water have been collected as part of temporary projects rather than routine monitoring. Gary Glass, USEPA, and John Sorensen, University of Minnesota – Duluth, collected mercury samples from water, zooplankton, and fish from 80 lakes in northeast Minnesota (Sorensen et al. 1990). From 1992 to 1994, the Acid Precipitation program at the MPCA seasonally monitored 12 low alkalinity lakes in northern Minnesota, which included sample collection for total and methylmercury in water and zooplankton (Monson and Brezonik 1998). An intensive five year study of water, soil, invertebrates, and fish in 17 interior lakes of Voyageurs National Park in northern Minnesota (Wiener et al. 2006). Other data have been collected as part of environmental review and as part of the routine lake monitoring program. Generally the additional data collection projects included 10-15 lakes sampled at least three times (spring, summer, and fall) per year for one to two years. None of these previous data collection efforts were probability based site selection. Nevertheless, they provide a basis for comparison with the NLAP Hg results. The purpose of the mercury data collection and analysis was to provide unbiased estimates of water mercury concentrations (total and methyl) for Minnesota and other Midwestern states. Hypotheses being pursued based on the NLAP and related datasets are as follows: • How does NLAP distribution of values compare to previous estimates? • What are the spatial patterns in water mercury? • What is the relationship among water mercury concentrations and other physicochemical factors (e.g. dissolved organic carbon)

Mercury Concentrations in MN Lakes 10/2008

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Methods All lakes were sampled once, except Pebble (Lake ID: 56082900) and South (Lake ID: 43001400). The second sampling from these two lakes was excluded for statistical analysis so that all lakes were represented by a single sample event collected in July or August of 2007. The US Geological Survey Mercury Research Laboratory in Middleton, Wisconsin, provided the sample bottles and analyzed the water samples for NLAP lakes in Illinois, Minnesota, and Wisconsin. The lab also analyzed water samples for dissolved organic carbon (DOC). The laboratory is a state-of-the-art analytical facility for low level speciation of mercury, directed by Dr. D. Krabbenhoft. Sample acquisition followed ultra-clean protocols, referred to as “Clean Hands – Dirty Hands” and is prescribed in US EPA Method 1669. Methods for sample collection, storage, and analysis of total mercury and methylmercury are described in two US Geological Survey documents (Dewild et al. 2002; Olson and Dewild 1999). Descriptive and inferential statistics were performed with SYSTAT 12 (SYSTAT Software, Inc., 2007).

Mercury Concentrations in MN Lakes 10/2008

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Results and Discussion Summary Statistics NLAP lakes have a broad distribution of surface areas and dissolved organic carbon (DOC) concentrations (Table 1). Lake areas range from 11 acres to 15,958 acres. DOC concentrations range from 4.2 ppm-C to 25.7 ppm-C. Median total mercury (THg) concentration is 0.53 ng/L, with a range of 0.16 – 5.24 ng/L. A previously sampled set of 102 Minnesota lakes, located throughout the state but nonrandomly selected, had a median THg of 1.11 ng/L and a range of 0.27-12.43 ng/L (unpublished MPCA data). Thus, the NLAP lakes as a set have lower THg than the nonrandom set of lakes; however, the comparison is problematic because the values from the nonrandom set are lakes are averages for usually multiple samples per lake (1 – 17 per lake), samples were collected before 2007, and the THg analysis was done by a different lab. Median methylmercury (MeHg) concentrations in the NLAP lakes is 0.053 ng/L, with a range of 0.006 – 0.522 ng/L. A previously sampled nonrandom set of 37 lakes had a median MeHg concentration of 0.054 ng/L, with a range of 0.013 – 0.260 ng/L. The MeHg medians are, therefore, very similar, while the NLAP lakes have a broader range of MeHg concentrations. Table 1 Statistical summary of unfiltered total mercury (THg), unfiltered methylmercury (MeHg), methyl mercury fraction (MeHg/THg x 100), and dissolved organic carbon (DOC) for the NLAP lakes in 2007 Statistic N of Cases Arithmetic Mean Standard Deviation Minimum 25th percentile 50th percentile (median) 75th percentile Maximum

Lake Area (ac)

DOC (ppm C)

THg (ng/L)

MeHg (ng/L)

MeHg Fraction (%)

54 822 2,423 11 87 174 417 15,958

51 11.8 5.2 4.2 8.1 10.4 14.8 27.7

53 0.875 0.926 0.162 0.313 0.526 1.123 5.242

51 0.093 0.105 0.006 0.022 0.053 0.121 0.522

50 11.8 10.9 1.4 5.1 9.2 15.9 63.0

THg and MeHg concentrations are combined to give the MeHg fraction (MeHg/THg), which is referred to as “methylation efficiency” because it indicates the efficiency of conversion of THg to MeHg in a particular system. The MeHg fraction is typically 5-10% in lakes and that agrees with the median of 9.2% in the NLAP set of lakes. The 63% MeHg fraction in Victoria Lake (Lake ID 21005400) is an outlier, despite the reasonable concentrations of THg (0.216 ng/L) and MeHg (0.136 ng/L) (see Appendix A). Unnamed Lake (Lake ID 60030700) also has a very high MeHg fraction of 41%, with THg of 0.892 ng/L and MeHg of 0.368 ng/L. There are another six lakes with MeHg fraction between 20% and 25%. These lakes need additional examination to see if the lakes or their watersheds are wetland-dominated or have physical characteristics that promote anoxic conditions necessary for methylation of mercury. In a normal distribution, means and medians are equal. A comparison of arithmetic means and medians indicates the distributions of THg, MeHg, and lake area are skewed to the left (medians < arithmetic means). As density plots demonstrate (Figure 2), the distribution of DOC concentrations is nearly symmetrical, whereas THg, MeHg, and lake area are strongly skewed to the left. Logarithmic transformation of THg, MeHg, and lake area improved the symmetry of the distributions (Figure 3); therefore, the log-transformed variables were used for inferential statistical analysis (e.g., bivariate plots and regression).

Mercury Concentrations in MN Lakes 10/2008

Minnesota Pollution Control Agency 7

0

1

2

3

4

5

6

0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6

TH G

0

10

MEHG

20

30

0

5000 10000 15000 20000

D OC _PPM C

AREA_AC

Figure 2 Density plots of THg, MeHg, DOC, and Lake Area

-2

-1

0

1

2 -6

-5

LO G _THG

1

2

3

-4

-3

-2

-1

0

LOG_M EHG

2

4

3

4

5

6

7

8

9 10

LOG_AREA

LOG_D OC

Figure 3 Density plots of Log-transformed THg, MeHg, DOC, and Area

Relationships Among Variables The four key variables are compared in a scatterplot matrix (Figure 4), which compares all variables in bivariate plots, along with a LOWESS (locally weight least squares) smoother through the data and a histogram of the data distributions. Positive relationships are evident for THg–MeHg, THg–DOC, and MeHg–DOC. There appears to be a negative relationship between lake area and DOC, implying that the water of smaller lakes is more affected by sources of DOC such as wetlands. Pearson correlation coefficients support these graphical observations (Table 2). An ordinary least squares regression of logtransformed) THg and DOC has an r2 = 0.42 and is highly significant (p < 0.001). The regression for MeHg and DOC has an r2 = 0.33 and is highly significant (p < 0.001), too.

Mercury Concentrations in MN Lakes 10/2008

Minnesota Pollution Control Agency 8

LO G _TH G LO G _M EH G LO G _AREA LO G _D O C LO G _T H G

LO G _M E H G

LO G _A R E A

LO G _DO C

Figure 4 Scatterplot matrix of log-transformed THg, MeHg, DOC, and Area, with LOWESS smoother and histogram of data distributions

Table 2 Pearson correlation matrix of log-transformed THg, MeHg, DOC, and Area LOG_THG

LOG_MEHG

LOG_AREA

LOG_THG

1.000

LOG_MEHG

0.657

1.000

LOG_AREA

-0.330

-0.320

1.000

LOG_DOC

0.649

0.573

-0.387

Mercury Concentrations in MN Lakes 10/2008

LOG_DOC

1.000

Minnesota Pollution Control Agency 9

The positive relationship between MeHg and THg is somewhat surprising because they are often not correlated in lakes, rivers, and wetlands. The strong positive relationship between THg and MeHg with DOC has been observed in other lakes (Driscoll et al. 1995; Watras et al. 1995b). DOC is associated with wetland drainage (Gergel et al. 1999) and much of the Hg is methylated in wetlands by sulfate reducing bacteria (Gilmour and Henry 1992); MeHg and Hg are transported to lakes sorbed to DOC (Ravichandran 2004). In addition to the MeHg from wetlands, MeHg can also be formed within the anaerobic hypolimnion of lakes and lake sediments (Watras et al. 1995a; Watras et al. 2005). Victoria Lake, on the eastern edge of Alexandria, Minnesota, has steep shoreline slopes and a maximum depth of 60 feet, suggesting that the high MeHg fraction could be caused by internally produced MeHg rather than wetland contributions from the watershed. Spatial Distributions Spatial distributions of THg, MeHg, and MeHg fraction (MeHg/THg) categorized into three concentration levels—low, medium, and high—indicate that high concentrations of THg and MeHg are distributed throughout the state (Figure 5). Northeastern region of the NLF ecoregion has higher THg and MeHg concentrations compared to the southwestern region of the NLF; although the MeHg fraction may actually be somewhat higher in the southwestern NLF. Otherwise, high THg and MeHg concentrations are distributed throughout the range of NLAP lakes. THg and MeHg concentrations can vary by an order of magnitude among adjacent lake watersheds, as shown in the Voyageurs National Park (Wiener et al. 2006). As already indicated, the dominance of wetlands in a watershed hydrologically-connected to a lake has a substantial influence on the THg and MeHg concentrations.

Summary and Conclusions THg and MeHg concentrations in the NLAP lakes are positively correlated to DOC and negatively correlated to lake surface area. The lakes in the northeastern corner of the state have consistently high THg concentrations and many have high MeHg concentrations. Elsewhere in the state, the spatial distribution does not show apparent patterns. Follow-up data analysis should compare the land cover characteristics, especially connected wetlands, within in each lake watershed to the THg and MeHg concentrations. An acceptable comparison of mercury concentrations in water and fish is not possible, because only 16 of the lakes currently have mercury concentrations in standard length northern pike or walleye (the indicator species for mercury trends in Minnesota), and only 7 of the lakes have fish-Hg data collected after 1995. Therefore, additional fish collection and tissue analysis in the NLAP lakes would be beneficial for comparison to THg and MeHg concentrations.

Mercury Concentrations in MN Lakes 10/2008

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Figure 5 Spatial distributions of THg and MeHg concentrations, and MeHg fraction, overlying ecoregions

Mercury Concentrations in MN Lakes 10/2008

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References Dewild, J. F., M. L. Olson, and S. D. Olund. 2002. Determination of Methyl Mercury by Aqueous Phase Ethylation, Followed by Gas Chromatographic Separation wtih Cold Vapor Atomic Fluorescence Detection. U.S Geological Survey. Driscoll, C. T., V. Blette, C. Yan, C. L. Schofield, R. Munson, and J. Holsapple. 1995. The Role of Dissolved Organic-Carbon in the Chemistry and Bioavailability of Mercury in Remote Adirondack Lakes. Water Air and Soil Pollution 80: 499-508. Gergel, S. E., M. G. Turner, and T. K. Kratz. 1999. Dissolved organic carbon as an indicator of the scale of watershed influence on lakes and rivers. Ecological Applications 9: 1377-1390. Gilmour, C. C., and E. A. Henry. 1992. Mercury Methylation by Sulfate-Reducing Bacteria Biogeochemical and Pure Culture Studies. Abstr. Pap. Am. Chem. Soc. 203: 140-GEOC. Monson, B. A., and P. L. Brezonik. 1998. Seasonal patterns of mercury species in water and plankton from softwater lakes in Northeastern Minnesota. Biogeochemistry 40: 147-162. Olson, M. L., and J. F. Dewild. 1999. Techniques for the Collection and Species Specific Analysis of Low Levels of Mercury in Water, Sediment, and Biota. U.S. Geological Survey. Ravichandran, M. 2004. Interactions between mercury and dissolved organic matter - a review. Chemosphere 55: 319-331. Sorensen, J. A., G. E. Glass, K. W. Schmidt, J. K. Huber, and J. Rapp, G.R. 1990. Airborne mercury deposition and watershed characteristics in relation to mercury concentrations in water, sediments, plankton, fish of eighty northern Minnesota lakes. Environmental Science & Technology 24: 1716-1727. Watras, C. J., N. S. Bloom, S. A. Claas, K. A. Morrison, C. C. Gilmour, and S. R. Craig. 1995a. Methylmercury Production in the Anoxic Hypolimnion of a Dimictic Seepage Lake. Water Air and Soil Pollution 80: 735-745. Watras, C. J., K. A. Morrison, J. S. Host, and N. S. Bloom. 1995b. Concentration of Mercury Species in Relationship to Other Site-Specific Factors in the Surface Waters of Northern Wisconsin Lakes. Limnology and Oceanography 40: 556-565. Watras, C. J. and others 2005. Sources of methylmercury to a wetland-dominated lake in northern Wisconsin. Environmental Science & Technology 39: 4747-4758. Wiener, J. G. and others 2006. Mercury in soils, lakes, and fish in Voyageurs National Park (Minnesota): Importance of atmospheric deposition and ecosystem factors. Environmental Science & Technology 40: 6261-6268.

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Appendix A THg, MeHg, DOC, UV Absorbance at 254 nm, and SUVA for All Sites

Lake Name Allen Alruss Arthur Aspen August Becoosin Cass Cokato Crow Wing Darling Eagle (North) Elk (Geraldine) Fairy Fanny Fish Flat Hungry Man Island Jennie Lamb Long Long Long (Main Bay) Lookout Lost (Horseshoe) Maine (Round) Mayo Musquash Nest Nokomis North Ash North Drywood North Mayfield Norway Okamanpeedan Pebble Pebble

Lake ID 44015700 69000500 69015400 16020400 38069100 38047200 4003000 86026300 18015500 21008000 7006001 15001000 56035600 21033600 70006900 3024200 3002900 11010200 47001500 69034100 86006900 11048000 31026601 18012300 69061100 56047600 18040800 16010400 34015400 27001900 41005500 76016900 14002900 34025100 46005100 56082900 56082900

EPA_SITEID NLA06608-0211 NLA06608-1102 NLA06608-1342 NLA06608-0890 NLA06608-1038 NLA06608-0526 NLA06608-0403 NLA06608-0551 NLA06608-0990 NLA06608-1390 NLA06608-0279 MN:15-0010 NLA06608-1326 NLA06608-0686 NLA06608-0935 NLA06608-1134 MN:03-0029 MN:11-0102 NLA06608-1175 NLA06608-1150 NLA06608-0743 NLA06608-0942 NLA06608-0958 NLA06608-0771 NLA06608-0318 NLA06608-1198 NLA06608-1262 NLA06608-1274 NLA06608-0215 NLA06608-0679 NLA06608-1111 NLA06608-0871 NLA06608-0558 NLA06608-1383 NLA06608-0759 NLA06608-0174 NLA06608-0174

Mercury Concentrations in MN Lakes 10/2008

Ecoregion NCHF NLF NLF NLF NLF NLF NLF NCHF NLF NCHF WCBP NLF NCHF NCHF NCHF NLF NLF NLF NCHF NLF NCHF NLF NLF NLF NLF NCHF NLF NLF NCHF NCHF NGP NGP NCHF NCHF WCBP NCHF NCHF

Area (ac) 143 29 76 141 229 59 15958 545 355 1156 246 271 134 38 173 1838 91 277 1064 110 361 284 87 226 81 86 175 133 1008 201 84 117 35 2319 2268 170 170

County Mahnomen St. Louis St. Louis Cook Lake Lake Beltrami Wright Crow Wing Douglas Blue Earth Clearwater Otter Tail Douglas Scott Becker Becker Cass Meeker St. Louis Wright Cass Itasca Crow Wing St. Louis Otter Tail Crow Wing Cook Kandiyohi Hennepin Lincoln Swift Clay Kandiyohi Martin Otter Tail Otter Tail

Sample Date 8/7/07 7/16/07 7/17/07 7/30/07 8/3/07 7/18/07 8/6/07 8/20/07 7/30/07 7/19/07 8/8/07 8/9/07 8/6/07 7/11/07 8/6/07 8/7/07 8/8/07 8/11/07 8/21/07 7/17/07 6/26/07 7/10/07 8/15/07 8/13/07 7/20/07 7/25/07 7/9/07 8/1/07 8/22/07 6/27/07 7/10/07 7/12/07 8/9/07 8/22/07 8/7/07 7/25/07 8/28/07

THg (ng/L) 0.696 0.615 1.989 1.193 1.916 1.528 0.211 0.427 0.166 0.257 2.019 0.253 0.293 0.651 0.302 0.526 0.466 0.162 0.693 0.801 0.217 0.378 0.355 0.388 0.366 0.335 0.709 0.560 0.638 0.324 1.812 3.197 0.395 1.138 2.454 0.455 0.465

Minnesota Pollution Control Agency 13

MeHg (ng/L) 0.166 0.044 0.108 0.095 0.124 0.133 0.012

% MeHg/ THg 24% 7% 5% 8% 6% 9% 6%

0.023 0.041 0.053 0.022 0.006 0.034 0.009 0.012 0.091 0.018 0.019 0.033 0.008 0.067

14% 16% 3% 9% 2% 5% 3% 2% 20% 11% 3% 4% 4% 18%

0.035 0.034 0.083 0.106 0.012 0.009 0.017 0.025 0.225 0.037 0.112 0.201 0.082 0.015

9% 9% 25% 15% 2% 1% 5% 1% 7% 9% 10% 8% 18% 3%

DOC (mg/L) 27.40 11.60 9.90 11.30 14.70 9.70 6.30 7.80 8.60 8.50 15.10 8.00 9.90 20.30 12.40 12.10 9.30 9.90 12.70

UV-Abs (254nm) 0.405 0.076 0.190 0.311 0.456 0.172 0.096 0.160 0.139 0.111

SUVA 1.1 0.7 1.9 2.8 3.1 1.8 1.5 2.1 1.6 1.3

0.126 0.126 0.540 0.146 0.172 0.133 0.188 0.196

1.6 1.3 2.7 1.2 1.4 1.4 1.9 1.5

7.40 5.40 9.20 10.50

0.139 0.061 0.201 0.181

1.9 1.1 2.2 1.7

7.50 14.90 6.20 9.10 7.10 13.50 21.30 13.50 15.40 12.00 10.40 10.10

0.094 0.415 0.098 0.162 0.099 0.255 0.402 0.211 0.215 0.220 0.116 0.114

1.3 2.8 1.6 1.8 1.4 1.9 1.9 1.6 1.4 1.8 1.1 1.1

Lake Name Pelican Pickerel Pine Mountain Red Rock Richey Snail South South Spring Spring Spring Straight Unnamed Upper Hatch Upper Sakatah Vesper Victoria West Leaf Woodcock

Lake ID 18030800 3028700 11041100 21029100 16064300 62007300 43001400 43001400 33002700 69012900 11002200 3001000 60030700 31077000 40000200 16041400 21005400 56011400 34014100

EPA_SITEID NLA06608-0238 NLA06608-0110 NLA06608-0494 NLA06608-1454 NLA06608-1018 NLA06608-1447 NLA06608-0167 NLA06608-0167 NLA06608-1283 NLA06608-1347 ELS:2D3-008 NLA06608-0366 NLA06608-0915 NLA06608-0190 NLA06608-1303 NLA06608-0782 NLA06608-0622 NLA06608-0878 NLA06608-1239

Ecoregion NLF NLF NLF NCHF NLF NCHF NCHF NCHF NCHF NLF NLF NLF NCHF NLF NCHF NLF NCHF NCHF NCHF

Area (ac) 8367 353 1558 300 104 64 173 173 18 99 89 470 11 16 892 15 417 693 180

County Crow Wing Becker Cass Douglas Cook Ramsey McLeod McLeod Kanabec St. Louis Cass Becker Polk Itasca Le Sueur Cook Douglas Otter Tail Kandiyohi

Sample Date 7/11/07 7/31/07 7/11/07 7/25/07 8/2/07 7/18/07 7/23/07 8/29/07 6/27/07 6/28/07 8/10/07 7/31/07 8/8/07 8/14/07 8/8/07 7/31/07 7/24/07 8/1/07 7/24/07

THg (ng/L) 0.210 0.278 0.317 0.489 2.103 0.322 5.242 1.672 1.119 0.762 0.251 0.892 0.635 2.020 0.216 0.290 0.662

MeHg (ng/L) 0.047 0.009 0.032 0.113 0.389 0.069 0.522 0.183 0.247 0.153 0.099 0.006 0.368 0.202 0.129 0.136 0.053 0.079

% MeHg/ THg 22% 3% 10% 23% 19% 21% 10% 15% 14% 13% 3% 41%

6% 63% 18% 12%

DOC (mg/L) 4.20 7.00 6.00 17.80 16.90 9.40 27.70 25.30 15.50

UV-Abs (254nm) 0.035 0.082 0.106 0.274 0.263 0.156 0.510 0.496 0.597

SUVA 0.9 1.2 1.8 1.5 1.6 1.7 1.8 2.0 3.9

15.40 4.50 18.10 11.40 14.50 10.30 8.00 8.80 19.30

0.418 0.063 0.444 0.233 0.311 0.274 0.136 0.131 0.238

2.7 1.4 2.5 2.0 2.2 2.7 1.7 1.5 1.2

Ecoregions: North Central Hardwood Forest (NCHF); Northern Glaciated Plains (NGP); Northern Lakes and Forests (NLF); Western Corn Belt Plain (WCBP) SUVA = UV254nm x 100 / DOC

H:\NLAP\wq-nlap Hg report draft2.doc

Mercury Concentrations in MN Lakes 10/2008

Minnesota Pollution Control Agency 14