The St Louis River (SLR) is the second largest tributary to Lake Superior and a designated area of concern (AOC) due to past industrial contamination of organic chemicals and heavy metals, including mercury (Hg). Sediments, prey items (odonates, mixed benthic invertebrates, and spiders), and game fish were targeted within this study to determine if industrial sources of Hg were bioaccumulating into the food web. Samples from SLR were directly compared to a reference site in the Bad River, WI to assess if legacy contamination resulted in elevated Hg concentrations in comparisons to background regions with no known point sources. Carbon and nitrogen isotopes were also employed as food web tracers to determine if dietary shifts within the estuary or migration influenced Hg source signatures. These data are a part of a larger study and associated journal article documented in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2021.146284).

The St Louis River (SLR) is the second largest tributary to Lake Superior and a designated area of concern (AOC) due to past industrial contamination of organic chemicals and heavy metals, including mercury (Hg). Sediments, prey items (odonates, mixed benthic invertebrates, and spiders), and game fish were targeted within this study to determine if industrial sources of Hg were bioaccumulating into the food web. Samples from SLR were directly compared to a reference site in the Bad River, WI to assess if legacy contamination resulted in elevated Hg concentrations in comparisons to background regions with no known point sources. Carbon and nitrogen isotopes were also employed as food web tracers to determine if dietary shifts within the estuary or migration influenced Hg source signatures. These data are a part of a larger study and associated journal article documented in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2021.146284).

Mercury concentration, mercury stable isotope ratio, and carbon and nitrogen stable isotope ratio data as applicable for sediment, water, invertebrates, and fish collected from the St. Louis River Area of Concern (MN-WI) and the associated reference site, the lower Bad River (WI). This dataset is associated with the following publication: Janssen, S., J. Hoffman, R. Lepak, D. Krabbenhoft, D. Walters, C. Eagles-Smith, G. Peterson, J. Ogorek, J. DeWild, A. Cotter, M. Pearson, M. Tate, R. Yeardley, and M. Mills. Examining historical mercury sources in the St. Louis River estuary: How legacy contamination influences biological mercury levels in Great Lakes coastal regions. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 779: 146284, (2021).

Mercury concentration, mercury stable isotope ratio, and carbon and nitrogen stable isotope ratio data as applicable for sediment, water, invertebrates, and fish collected from the St. Louis River Area of Concern (MN-WI) and the associated reference site, the lower Bad River (WI). This dataset is associated with the following publication: Janssen, S., J. Hoffman, R. Lepak, D. Krabbenhoft, D. Walters, C. Eagles-Smith, G. Peterson, J. Ogorek, J. DeWild, A. Cotter, M. Pearson, M. Tate, R. Yeardley, and M. Mills. Examining historical mercury sources in the St. Louis River estuary: How legacy contamination influences biological mercury levels in Great Lakes coastal regions. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 779: 146284, (2021).

In 2021, the U.S. Geological Survey (USGS) Mercury Research Laboratory (MRL) conducted a large-scale assessment of mercury (Hg) concentrations and Hg stable isotope values in tributaries of Lake Superior in order to define the sources and amounts of Hg entering the lake. Water samples were collected monthly from 18 tributaries in the United States from April through October in 2021 and during 2022 spring melt (May 2022). As a complement, 10 tributaries on the Lake Superior Northshore were sampled three times a year (spring, summer, and fall) by Lakehead University and Lakehead Region Conservation Authority. Nine tributaries were also sampled twice per year (spring and summer) in Pukaskwa National Park by Parks Canada. Filtered total Hg (THg) concentrations from United States and Canadian Northshore ranged from 0.2 to 8.8 nanograms per liter (ng L-1), with a median value of 1.2 ng L-1. Unfiltered THg in Pukaskwa National Park ranged from 0.6 to 5.0 ng L-1 with a median of 3.2 ng L-1, but encompassed both the filtered and particulate bound Hg. Median methylmercury (MeHg) values were approximately 0.1 ng L-1 for both filtered and unfiltered waters, but could reach levels greater than 1 ng L-1 during higher flow events. THg and MeHg concentrations were positively correlated to dissolved organic carbon (DOC) concentrations for most tributaries. Hg loads to Lake Superior were calculated for U.S. tributaries using the R package loadflex ( http://dx.doi.org/10.1890/ES14-00517.1 ), median loads for THg were 18 grams per day, but could increase to 590 grams per day under high flow and snow melt conditions.

In 2021, the U.S. Geological Survey (USGS) Mercury Research Laboratory (MRL) conducted a large-scale assessment of mercury (Hg) concentrations and Hg stable isotope values in tributaries of Lake Superior in order to define the sources and amounts of Hg entering the lake. Water samples were collected monthly from 18 tributaries in the United States from April through October in 2021 and during 2022 spring melt (May 2022). As a complement, 10 tributaries on the Lake Superior Northshore were sampled three times a year (spring, summer, and fall) by Lakehead University and Lakehead Region Conservation Authority. Nine tributaries were also sampled twice per year (spring and summer) in Pukaskwa National Park by Parks Canada. Filtered total Hg (THg) concentrations from United States and Canadian Northshore ranged from 0.2 to 8.8 nanograms per liter (ng L-1), with a median value of 1.2 ng L-1. Unfiltered THg in Pukaskwa National Park ranged from 0.6 to 5.0 ng L-1 with a median of 3.2 ng L-1, but encompassed both the filtered and particulate bound Hg. Median methylmercury (MeHg) values were approximately 0.1 ng L-1 for both filtered and unfiltered waters, but could reach levels greater than 1 ng L-1 during higher flow events. THg and MeHg concentrations were positively correlated to dissolved organic carbon (DOC) concentrations for most tributaries. Hg loads to Lake Superior were calculated for U.S. tributaries using the R package loadflex ( http://dx.doi.org/10.1890/ES14-00517.1 ), median loads for THg were 18 grams per day, but could increase to 590 grams per day under high flow and snow melt conditions.

Under the Great Lakes Restoration Initiative, the U.S. Geological Survey Mercury Research Lab (USGS MRL) conducted a multiyear assessment of mercury across the Laurentian Great Lakes. Biannual sampling was conducted across all five lakes onboard the U.S. Environmental Protection Agency (US EPA) research vessel Lake Guardian (in years 2010–2014, 2018) at pelagic sampling locations established by the long-term US EPA Great Lakes monitoring program. In addition to the regularly scheduled biannual sampling, in September 2013 and 2014 Lake Michigan and Lake Erie (respectively) were sampled with increased focus on shallow nearshore locations. Throughout these sampling efforts, sediments, mussels, surface water, and plankton were collected from open-water locations within all five of the Great Lakes. Additionally, surface water from Great Lake tributaries were sampled by the USGS MRL and preceded (2005 or 2006) or overlapped (2010-2015) with the open lake sampling efforts. All surface water samples were analyzed for methylmercury, total mercury, and dissolved organic carbon. Plankton and mussel tissue were analyzed for methylmercury, total mercury, and carbon/nitrogen stable isotopes and concentrations (plankton only). Sediments were analyzed for methylmercury, total mercury, and carbon content.

Under the Great Lakes Restoration Initiative, the U.S. Geological Survey Mercury Research Lab (USGS MRL) conducted a multiyear assessment of mercury across the Laurentian Great Lakes. Biannual sampling was conducted across all five lakes onboard the U.S. Environmental Protection Agency (US EPA) research vessel Lake Guardian (in years 2010–2014, 2018) at pelagic sampling locations established by the long-term US EPA Great Lakes monitoring program. In addition to the regularly scheduled biannual sampling, in September 2013 and 2014 Lake Michigan and Lake Erie (respectively) were sampled with increased focus on shallow nearshore locations. Throughout these sampling efforts, sediments, mussels, surface water, and plankton were collected from open-water locations within all five of the Great Lakes. Additionally, surface water from Great Lake tributaries were sampled by the USGS MRL and preceded (2005 or 2006) or overlapped (2010-2015) with the open lake sampling efforts. All surface water samples were analyzed for methylmercury, total mercury, and dissolved organic carbon. Plankton and mussel tissue were analyzed for methylmercury, total mercury, and carbon/nitrogen stable isotopes and concentrations (plankton only). Sediments were analyzed for methylmercury, total mercury, and carbon content.

This data release includes mercury concentrations and mercury stable isotope measurements measured in sediments and biological tissues collected from the Saint Louis River located in Minnesota. Sediments and biota were collected by the U.S. Geological Survey, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and federal contractors (Battelle) from 2017-2021. Collection regions included nearshore zones within the main estuary, remedial sites within the lower river, and upstream reservoir sites. Sediments were analyzed for total mercury, methylmercury, and mercury stable isotopes by the U.S. Geological Survey Mercury Research Laboratory (MRL, Madison, Wisconsin). Biological samples were analyzed for total and methylmercury by the MRL or the Contaminant Ecology Research Laboratory (CERL, Corvallis, Oregon); mercury stable isotopes were analyzed by the MRL.

This data release includes mercury concentrations and mercury stable isotope measurements measured in sediments and biological tissues collected from the Saint Louis River located in Minnesota. Sediments and biota were collected by the U.S. Geological Survey, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers, and federal contractors (Battelle) from 2017-2021. Collection regions included nearshore zones within the main estuary, remedial sites within the lower river, and upstream reservoir sites. Sediments were analyzed for total mercury, methylmercury, and mercury stable isotopes by the U.S. Geological Survey Mercury Research Laboratory (MRL, Madison, Wisconsin). Biological samples were analyzed for total and methylmercury by the MRL or the Contaminant Ecology Research Laboratory (CERL, Corvallis, Oregon); mercury stable isotopes were analyzed by the MRL.