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Return to Project List Project Title: Enhanced Rates of Mercury Methylation from Sulfate Deposition: A Whole Wetland Experiment Synopsis: This study explored the impact of increased atmospheric sulfate deposition on methylmercury (MeHg) production and transport from forested wetlands in northern Minnesota. Recent studies suggest that mercury (Hg) concentrations in fish in sensitive ecosystems have been exacerbated relative to atmospheric Hg deposition by enhanced Hg methylation in upstream wetlands. Laboratory and microcosm studies point toward anthropogenic sulfate as the most likely cause of enhanced methylation. The primary objective of this study was to conduct a whole wetland sulfate-addition experiment to elucidate methylation enhancing processes. The study built on a recently concluded investigation funded by the EPA STAR program. The STAR project established a whole-wetland irrigation system for amending sulfate deposition through simulated rainfall. Two years of experimental additions provided evidence that sulfate additions at near-ambient strength can substantially increase MeHg production at the watershed scale. This preoject has extended the experimental sulfate additions for three additional years. A longer experimental period is critical to a robust evaluation of atmospheric sulfate in contributing to MeHg production and ultimately mercury contamination of aquatic food chains. Chemicals Studied: Total and methyl mercury was monitored in the experimental wetland. In addition, a suite of general water chemistry parameters was monitored, including cations, anions, dissolved organics, nitrogen and sulfate. Geographic Areas: The experiment took place at the Marcell Experimental Forest in Northern Minnesota. The results are applicable to similar ecosystems, which are common across the Great Lakes basin. Project Duration: Monitoring took place April through October of 2004, 2005, and 2006. Data analysis and a final report will be completed during 2007, with result availabile in early 2008. Methods Used: The approximately two hectare wetland was artificially amended with additional sulfate though a sprinkler system designed to simulate rain events. The sulfate added was approximately four times the ambient contribution. Water chemistry and mercury levels were monitored in the wetland following sulfate amendment events and during control periods. The data was be analyzed to determine the impact of the increased sulfate deposition on the methylmercury production within the wetland. Potential Results and Implications: If atmospheric sulfate deposition has enhanced wetland Hg methylation as hypothesized, the implications for management of Hg contamination of fish and wildlife are large. Specifically, a dual control strategy of reducing both atmospheric sulfate and mercury could have a synergistic effect on lowering Hg contamination in the Great Lakes (and elsewhere). And because emission controls for sulfate are more effective on the regional scale than those for Hg (much of the Hg deposition in the Great Lakes is from global sources), the potential for lowering Hg contamination with regional/domestic strategies for emission controls on sulfate as well as mercury are high. The results will also have important implications for the accuracy of mercury transport and distribution models. Reports and Presentations: Project Contact: |
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