Rocky Mountain High — Mercury in Cold Environments of the Western United States

Atmospheric deposition of mercury in remote areas in the Western United States is sufficient to pose a risk to human and ecosystem health at sites favorable for methylation, a process in which mercury in the environment is converted into a highly toxic form that accumulates in organisms and is amplified up the food chain. USGS researchers and partners measured mercury in snowpack samples during 2003-2005 as part of the National Park Service Western Airborne Contaminants Assessment Project. Eight high-altitude, high-latitude sites were selected for study in or near national parks in Colorado, Montana, California, Oregon, and Alaska. Mercury levels were lowest in the North Cascades, highest in the Rocky Mountains, and were related to the amount of particulate carbon in the snow, with both found at higher levels in forested sites than in open meadows. Seasonal variations were lowest in Denali National Park and highest in Olympic National Park. Mercury concentrations were higher during the warm season than the snow season. Total annual fluxes of mercury were as high as 10 mg m-2 at some sites in the Rocky Mountains, which receive mercury deposition equal to that in the Upper Midwest or Northeast. Global and regional sources of mercury emissions contribute to its deposition, with regional sources likely contributing more in the Rocky Mountains, where there are more upwind sources of emissions. For more information, contact Don Campbell at Donald.Campbell@usgs.gov or 303-236-4882, ext. 298.