The dry deposition of mercury into the Great Salt Lake

The Great Salt Lake (GSL) in the western United States has been identified as the most mercury laden body of water in the United States with a median water mercury concentration of 42 nanograms per liter. When Hg enters an aquatic ecosystem, it can be converted to the toxic organic mercury compound, methylmercury. Methylmercury bioaccumulates up the food chain and has been the cause of consumption advisories for game fish in many lakes and rivers in the historically pristine Intermountain West. In 2005, the Utah Department of Health and the Fish and Wildlife Service placed a similar consumption advisory on waterfowl on the GSL. The primary goal of this study is to identify the pathway of greatest influx of Hg pollution to the GSL to give insight toward the source and an eventual solution to the Hg pollution problem. Speciated atmospheric mercury measurements were collected at a field site on the eastern shore of the GSL for a 1-year period beginning on July 1, 2009. These atmospheric mercury concentrations, along with turbulence measurements, were used as input to a resistance-in-series dry deposition model (based on Wesley and Hicks 1977). The dry deposition flux of mercury was determined from the modeled dry deposition velocity and the measured concentrations. This dry deposition flux was compared to the wet deposition flux measured by the National Deposition Network and the riverine influx measured by the USGS. It was found that in the 1 year from July 1, 2009 through June 30, 2010, 10.7 nanograms per square meter of Hg was deposited into the GSL by dry deposition from the atmosphere. Dry deposition makes up 60% of the total Hg influx from all measured pathways. The flux from the dry deposition of the global background pool of Hg (1.5 ± 0.2 nanograms per square meter) dominated the dry deposition flux, making up 82.5±8.5% of the dry deposition flux and 50% of the total Hg influx to the GSL. Lake sediment cores from the GSL suggest a much larger annual flux of between 55 nanograms per square meter and 150 nanograms per square meter. This discrepancy may suggest that measurements of coarse particulate mercury and gaseous elemental mercury oxidation within the surface boundary layer above the lake may be necessary and should be a topic for future research.