Mercury in remote Rocky Mountain lakes of Glacier National Park, Montana, in comparison with other temperate North American regions

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Abstract
We determined concentrations of mercury (Hg) and methylmercury (MeHg) in 12 pristine lakes of Glacier National Park (GNP) and compared our observations with data from published studies of remote lakes in north-central Wisconsin and the Adirondack region of New York. Despite marked differences in water chemistry, biology, and hydrogeology, concentrations of Hg and MeHg in all regions were strongly correlated with dissolved organic carbon (DOC). Variables related to the acid–base status of lake waters had secondary effects on the concentration of waterborne mercury species. Although Hg and MeHg were strongly correlated with DOC in all three regions, MeHg concentrations were lower and increased less per unit organic carbon in GNP lakes than in either Wisconsin or New York. In GNP lakes, MeHg averaged only 4 ± 2% (mean ± SD) of the Hg, while in Wisconsin and New York lakes MeHg averaged 10–14% of the Hg. Based on simple regression modelling, we estimate that the maximum MeHg fraction (MeHg/Hg) in dystrophic GNP lakes would be three- to six-fold lower than in Wisconsin or New York waters of similarly high DOC. Our results suggest that this regional difference involves factors regulating the net production of MeHg in lakes or watersheds.