Collaborative Research: Mercury Biogeochemistry in a Semi-Arid Aquatic Ecosystem: Processes Controlling Methylation and Demethylation

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9523894 Hines The biogeochemistry of mercury is important because of the toxicity of methylmercury, its accumulation in biota, and its biomagnification in food chains. A knowledge of the concentration, transport, and dynamics of methylmercury is needed to predict its potential impact on human and aquatic life. The proposed program combines biogeochemical, microbiological, and molecular investigations of the formation and degradation of methylmercury with certain abiotic factors, and a robust modeling effort, to depict factors controlling methylmercury dynamics in the Carson River/Lahontan Reservoir System in Nevada. The Carson System received 7000 tons of elemental mercury during the 19th century for gold amalgamation, and now provides a strong gradient in mercury concentrations. Specific goals are to: 1) locate sources and sinks of methylmercury; 2) examine bacterial processes including genetic controls and the role of terminal decomposition; 3) investigate the relationship between the sulfur and mercury cycles, and 4) develop simulation models. The project will consist of two major overlapping activities. First, surveys of : 1) rates of mercury transformation; 2) expression of bacterial genes incurring mercury resistance; 3) rates of model will be developed and validated, and used to fine tune future sampling programs. Second, the program will address hypotheses encompassing: 1) interactions among mercury concentration and speciation; 2) the role of bacteria as producers and consumers of methylmercury; 3) changes in genetics and methylmercury concentrations; 4) the role of suspended particles, and; 5) fluxes of methylmercury from sediments. The simulation model will be refined using biogeochemical data and used for predictive purposes. The project will provide data essential for determining controls on the accumulation of methylmercury in fish and other higher forms of life in semi-arid ecosystems, and will be useful for comparison to wet and northern environments. In general, the research will distinguish aspects of aquatic systems that most influence the production, degradation, and transport of methylmercury, one of the Earth's most insidious pollutants.