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).

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.

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.

Samples were collected from Clear Lake, California from 2019-2022 by the U.S. Geological Survey (USGS) California Water Science Center, the USGS Forest and Rangeland Ecosystem Science Center (FRESC), the US Environmental Protection Agency, and EA Engineering Science and Technology Inc. to assess the extent and cycling of legacy mercury (Hg) contamination from Sulphur Bank Mine. Samples of waste rock, sediments, groundwater, and biological tissue (zooplankton, bluegill, smallmouth bass, Mississippi silversides, and largemouth bass) were analyzed for Hg stable isotopes by the U.S. Geological Survey Mercury Research Laboratory. Mercury concentrations for sediments, waste rocks, and groundwaters are included within this data release and information for biological Hg concentrations can be found in the companion data release (https://doi.org/10.5066/P96912PN).

Samples were collected from Clear Lake, California from 2019-2022 by the U.S. Geological Survey (USGS) California Water Science Center, the USGS Forest and Rangeland Ecosystem Science Center (FRESC), the US Environmental Protection Agency, and EA Engineering Science and Technology Inc. to assess the extent and cycling of legacy mercury (Hg) contamination from Sulphur Bank Mine. Samples of waste rock, sediments, groundwater, and biological tissue (zooplankton, bluegill, smallmouth bass, Mississippi silversides, and largemouth bass) were analyzed for Hg stable isotopes by the U.S. Geological Survey Mercury Research Laboratory. Mercury concentrations for sediments, waste rocks, and groundwaters are included within this data release and information for biological Hg concentrations can be found in the companion data release (https://doi.org/10.5066/P96912PN).

As part of the larger Great Lakes Cooperative Science and Monitoring Initiative (CSMI) , the U.S. Geological Survey Mercury Research Laboratory (MRL) completed a binational assessment partnering with the U.S. Environmental Protection Agency (US EPA), Environmental Climate Change Canada (ECCC), Michigan-DNR (MI-DNR), University of Minnesota-Duluth Natural Resources Research Institute (UM-NRRI), and the National Oceanographic and Atmospheric Association (NOAA), to assess contaminant concentrations within seston, mussels, preyfish, waters, and surface sediments within Lake Huron. All matrices were assessed for mercury and methylmercury concentrations to examine spatial trends of mercury within the lakes. Sediments were also analyzed for total mercury stable isotope composition to approximate sources of mercury contamination to the lake.

As part of the larger Great Lakes Sediment Surveillance Program (GLSSP), the U.S. Geological Survey Mercury Research Laboratory (MRL) partnered with the U.S. Environmental Protection Agency and the University of Minnesota-Duluth to assess contaminant concentrations within surface sediments and sediment cores from the Laurentian Great Lakes. Sediments were assessed for mercury concentrations and mercury stable isotopes to examine spatial trends and sources of mercury within the lakes. In 2021, 30 sites were surveyed in Lake Superior. Mercury concentrations within Lake Superior surface sediment ranged from 1.1 to 161.2 ng/g. Mercury isotopes displayed a range in δ202Hg from -0.12 to -1.74 ‰ with measurable Δ199Hg and Δ200Hg across all Lake Superior sites. In 2022, 32 surface sediment sites were surveyed in Lake Huron. Mercury concentrations within Lake Huron sediment ranged from 0.7-to- 113.7 ng/g across all samples. Mercury isotopes displayed a range in δ202Hg from -0.12 to -1.74 ‰. In 2023, surface sediments were collected at 30 sites across Lake Ontario. Total mercury concentrations in surface sediments ranged from 19 ng/g to 2001.1 ng/g. Three deep sediment cores were collected in each lake. The sediment cores ranged in length from 15 cm to 50 cm. All cores showed a similar pattern for HgT except for cores at H038 and H054. From the top of the core, HgT concentrations increase to a maximum concentration (127.4 - 3035.3 ng/g) that occurs between 5 and 15 cm below the surface and then decreases to concentrations that range from 18.7 ng/g to 40 ng/g. The cores from H038 and H054 show decreasing or no change in HgT concentration in the upper portion of the core and then follow similar trends to the third core (H012) collected in Lake Huron.