Spatial Variation in Fish-Tissue Mercury Concentrations in the St. Croix River Basin, Minnesota and Wisconsin, 2004
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Prepared in cooperation with the National Park Service Spatial Variation in Fish-Tissue Mercury Concentrations in the St. Croix River Basin, Minnesota and Wisconsin, 2004 Scientific Investigations Report 2006–5063 U.S. Department of the Interior U.S. Geological Survey Spatial Variation in Fish-Tissue Mercury Concentrations in the St. Croix River Basin, Minnesota and Wisconsin, 2004 By Victoria G. Christensen, Stephen P. Wente, Mark B. Sandheinrich, and Mark E . Brigham Prepared in cooperation with the National Park Service Scientific Investigations Report 2006–5063 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior P. Lynn Scarlett, Acting Secretary U.S. Geological Survey P. Patrick Leahy, Acting Director U.S. Geological Survey, Reston, Virginia: 2006 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS 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: Christensen, V.G., Wente, S.P., Sandheinrich, M.B., and Brigham, M.E., 2006, Spatial variation in fish-tissue mercury concentrations in the St. Croix River Basin, Minnesota and Wisconsin, 2004: U.S. Geological Survey Scientific Investi- gations Report 2006–5063, 26 p. Prepared by the U.S. Geological Survey, Mounds View, Minnesota (http://mn.water.usgs.gov) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Description of Study Area ...................................................................................................................2 Purpose and Scope ..............................................................................................................................4 Acknowledgments ................................................................................................................................4 Methods...........................................................................................................................................................4 Sample-Collection Methods ...............................................................................................................4 Laboratory Analysis ..............................................................................................................................6 Quality Assurance.................................................................................................................................6 Model Description and Assumptions ................................................................................................6 Model Performance Assessment ......................................................................................................8 Spatial Variation in Fish-Tissue Mercury Concentrations in the St. Croix River Basin ......................8 Observed Fish-Tissue Mercury Concentrations ..............................................................................9 Comparison of Observed and Predicted Fish-Tissue Mercury Concentrations .........................9 Standardized Fish-Tissue Mercury Concentrations .....................................................................15 Relation of Standardized Fish-Tissue Mercury Concentrations to Land Use in the St. Croix River Basin ........................................................................................17 Relation of Standardized Fish-Tissue Mercury Concentrations to Water and Sediment Mercury Concentrations ...........................................................................18 Implications...................................................................................................................................................18 Summary........................................................................................................................................................20 References ....................................................................................................................................................20 Supplemental Information ..........................................................................................................................23 Figures 1. Map showing location of the St. Croix River Basin, Minnesota and Wisconsin, and sites where fish-tissue samples were collected during 2004. ......................................3 2. Boxplots showing distribution of observed fish-tissue mercury concentrations for fish collected from the St. Croix River and tributary streams, 2004 .............................10 3. Graphs showing comparison of observed to predicted fish-tissue mercury concentrations for the species and cuts of fish across the range of each species’ fish length measured for the site ...............................................................11 4. Boxplots showing distribution of standardized fish-tissue mercury concentrations for fish collected from the St. Croix River and tributary streams, 2004 ............................16 5. Graph and map showing comparison of standardized fish-tissue mercury concentrations from four sites sampled in the St. Croix River Basin, 2004 ......................17 iv Tables 1. Sampling sites, drainage area, land-use type, and sampling date, St. Croix River Basin, Minnesota and Wisconsin, 2004 ....................................................................................5 2. Summary results of quality-assurance analyses by River Studies Center, University of Wisconsin, LaCrosse, during determination of total mercury in composite samples of fish from the St. Croix River Basin, Minnesota and Wisconsin, 2004 ..............7 3. Results for total mercury reference materials from the U.S. National Institute of Standards and Technology and the National Research Council of Canada analyzed by the River Studies Center, University of Wisconsin, LaCrosse ..........................................7 4. Comparison of model fit and prediction error across a wide range of observed fish-tissue mercury concentrations at each of the 14 sites sampled in the St. Croix River Basin, Minnesota and Wisconsin, 2004 ........................................................................13 5. Fish-tissue mercury concentrations exceeding U.S. Environmental Protection Agency’s human-health criterion in the St. Croix River Basin, Minnesota and Wisconsin, 2004 ..........................................................................................................................14 6. Comparison of standardized fish-tissue mercury, total mercury and methylmercury in water, and total mercury in sediment at selected sites in the St. Croix River Basin, Minnesota and Wisconsin, 2000–01 and 2004 .......................................................................19 7. Sites where species occurred and number of fish-tissue mercury samples in the National Fish-Tissue Mercury Data Set for all species captured at the 14 St. Croix River Basin sites studied, Minnesota and Wisconsin, 2004 ................................................24 v Conversion Factors, Abbreviations, and Datum Multiply By To obtain Length centimeter (cm) 0.3937 inch (in.) inch (in.) 2.54 centimeter (cm) kilometer (km) 0.6214 mile (mi) millimeter (mm) 0.03937 inch (in.) Area square kilometer (km2) 247.1 acre square kilometer (km2) 0.3861 square mile (mi2) Mass gram (g) 0.03527 ounce, avoirdupois (oz) kilogram (kg) 2.205 pound avoirdupois (lb) Hydraulic gradient meter per kilometer (m/km) 5.28 foot per mile (ft/mi) Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32 Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C=(°F-32)/1.8 Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Concentrations of chemical constituents in fish tissue are given in micrograms per kilogram (μg/kg). Concentrations of chemical constituents in water are given in nanograms per liter (ng/L). Concentrations of chemical constituents in sediment are given in micrograms per gram (μg/g). NOTE TO USERS: Use of hectare (ha) as an alternative name for square hectometer (hm2) is restricted to the measurement of small land or water areas. vi Introduction Spatial Variation in Fish-Tissue Mercury Concentrations in the St. Croix River Basin, Minnesota and Wisconsin, 2004 By Victoria G. Christensen1, Stephen P. Wente2, Mark B. Sandheinrich3, and Mark E. Brigham1 Abstract123 predicted concentrations exceeding USEPA’s criterion at all of the seven sites where exceedances were observed and four Parts of the St. Croix River in Minnesota and Wisconsin of the seven sites where exceedances were not observed. The are under fish-consumption advisories because of elevated implication is that fish-consumption advisories that are based mercury concentrations that have