Mercury isotope measurements were made across nine sediments cores from remote North American lakes to examine changes in the Hg isotope profiles. The lakes spanned regions of Alaska, Minnesota, and Newfoundland as well as a range of temperate to arctic climates. This data describes the natural record of mass dependent (MDF) and mass independent (MIF) Hg isotope fractionation related to depositional changes over time. Mercury isotope measurements were also compared to factors such as latitude, precipitation, watershed size, and approximate age of sediment intervals. The companion article referencing this data set was published in Environmental Science and Technology and can be found at https://doi.org/10.1021/acs.est.0c00579.

These data were collected as part of the Southwest Alaska Inventory and Monitoring Network (SWAN) freshwater contaminants protocol. The protocol outlines a framework for monitoring mercury (Hg) concentrations in resident lake fish within SWAN parks. The primary goal of this monitoring is to understand the spatial differences, temporal trends, and health ramifications of Hg contamination in resident lake fish. Monitoring relies on total Hg in fish axial muscle as an indicator of methyl Hg exposure. It targets four high-priority lakes which vary in size, depth, wetland cover, glacial influence, and Hg concentration. These lakes are located in two parks: Lake Clark National Park and Preserve (LACL) and Katmai National Park and Preserve (KATM). The focal species is lake trout (Salvelinus namaycush), a widespread, long lived, top predator in SWAN lakes. However, if other species are sampled as bycatch, they may be retained and analyzed if they represent species-specific data gaps in Hg concentration. Two broad types of data are generated from this protocol. The first type includes observations and measurements that are recorded while sampling and processing fish (e.g., length, weight, gender). The second type includes results of analyses performed by contract laboratories (e.g., age, total Hg). This particular dataset includes those two broad types of data for 49 fish sampled in 2019 and 2020 from 2 lakes in LACL: Lake Clark and Kijik Lake. Of those 49 fish, 40 were lake trout, 6 were burbot (Lota lota), 2 were Arctic grayling (Thymallus arcticus), and 1 was Arctic char (Salvelinus alpinus).

These data were collected as part of the Southwest Alaska Inventory and Monitoring Network (SWAN) freshwater contaminants protocol. The protocol outlines a framework for monitoring mercury (Hg) concentrations in resident lake fish within SWAN parks. The primary goal of this monitoring is to understand the spatial differences, temporal trends, and health ramifications of Hg contamination in resident lake fish. Monitoring relies on total Hg in fish axial muscle as an indicator of methyl Hg exposure. It targets four high-priority lakes which vary in size, depth, wetland cover, glacial influence, and Hg concentration. These lakes are located in two parks: Lake Clark National Park and Preserve (LACL) and Katmai National Park and Preserve (KATM). The focal species is lake trout (Salvelinus namaycush), a widespread, long lived, top predator in SWAN lakes. However, if other species are sampled as bycatch, they may be retained and analyzed if they represent species-specific data gaps in Hg concentration. Two broad types of data are generated from this protocol. The first type includes observations and measurements that are recorded while sampling and processing fish (e.g., length, weight, gender). The second type includes results of analyses performed by contract laboratories (e.g., age, total Hg). This particular dataset includes those two broad types of data for 49 fish sampled in 2019 and 2020 from 2 lakes in LACL: Lake Clark and Kijik Lake. Of those 49 fish, 40 were lake trout, 6 were burbot (Lota lota), 2 were Arctic grayling (Thymallus arcticus), and 1 was Arctic char (Salvelinus alpinus).

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.

Atmospheric mercury (Hg) deposition, which has been declining in North America since 1985, is the preeminent delivery pathway to the Great Lakes, making them sentinels for tracking shifts in atmospheric deposition. Lake productivity is changing as a result of reductions in phosphorus inputs and habitat shifts in productivity due to invasive mussels. This has altered Hg cycling and energetic coupling within the Lakes. Seven fish species were analyzed for bulk carbon, nitrogen, and Hg isotope ratios and amino acid-specific nitrogen isotopes ratios in fish from the U.S. Environmental Protection Agency Great Lake Fish Monitoring and Surveillance Program archives (1975 – 2021) and the 1994 Lake Michigan Mass Balance to reconstruct the energetic- and Hg-source spatial and temporal trends within each lake. Data for the following fish species are included in this dataset: alewife, bloater, chub, coho salmon, lake trout, rainbow smelt, walleye.

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.

These data were collected as part of the Southwest Alaska Inventory and Monitoring Network (SWAN) freshwater contaminants protocol. The protocol outlines a framework for monitoring mercury (Hg) concentrations in resident lake fish within SWAN parks. The primary goal of this monitoring is to understand the spatial differences, temporal trends, and health ramifications of Hg contamination in resident lake fish. Monitoring relies on total Hg in fish axial muscle as an indicator of methyl Hg exposure. It targets four high-priority lakes which vary in size, depth, wetland cover, glacial influence, and Hg concentration. These lakes are in Katmai National Park and Preserve (KATM). The focal species is lake trout (Salvelinus namaycush), a widespread, long lived, top predator in SWAN lakes. However, if other species are sampled as bycatch, they may be retained and analyzed if they represent species-specific data gaps in Hg concentration. Two broad types of data are generated from this protocol. The first type includes observations and measurements that are recorded while sampling and processing fish (e.g., length, weight, sex). The second type includes results of analyses performed by contract laboratories (e.g., age, total Hg). This particular dataset includes those two broad types of data for 40 fish sampled in 2021. Of those fish, all 40 were lake trout.

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).