Spatial and temporal patterns of mercury accumulation in lacustrine sediments across the Laurentian Great Lakes region

Data from 104 sediment cores from the Great Lakes and “inland lakes” in the region were compiled to assess historical and recent changes in mercury (Hg) deposition. The lower Great Lakes showed sharp increases in Hg loading c. 1850–1950 from point-source water dischargers, with marked decreases during the past half century associated with effluent controls and decreases in the industrial use of Hg. In contrast, Lake Superior and inland lakes exhibited a pattern of Hg loading consistent with an atmospheric source – gradual increases followed by recent (post-1980) decreases. Variation in sedimentary Hg flux among inland lakes was primarily attributed to the ratio of watershed area:lake area, and secondarily to a lake’s proximity to emission sources. A consistent region-wide decrease (∼20%) of sediment-Hg flux suggests that controls on local and regional atmospheric Hg emissions have been effective in decreasing the supply of Hg to Lake Superior and inland lakes.

► Mercury data were compiled from 210Pb-dated sediment cores from the Great Lakes and “inland lakes” in the region.
► Sedimentary mercury flux is declining in both the Great Lakes and inland lakes, region-wide.
► Management of mercury discharges to water and air is making significant progress in decreasing mercury loads to lakes.