Heyes, A. Academy of Natural Sciences, Estuarine Research Center, heyes@acnatsci.org
Gilmour, C. Academy of Natural Sciences, Estuarine Research Center, gilmour@acnatsci.org

The atmospheric deposition of mercury (Hg) across North America is not uniform and higher levels of deposition can contribute to elevated levels of methylmercury (MeHg) in fish. However, because Hg must be methylated prior to bioaccumulation, the biogeochemical controls on Hg methylation are also important in assessing the impact of anthropogenic Hg deposition. Methylmercury concentrations and production rates appear to vary more than does Hg deposition across North America. We have examined Hg methylation in a number of freshwater and estuarine ecosystems, including lakes, rivers and wetlands. In addition to the rate of Hg supply, sulfate and sulfide influence MeHg production both within and across ecosystems. Because sulfate-reducing bacteria mediate Hg methylation, sulfate is required and can stimulate methylation in oligotrophic freshwater systems. However, sulfide production in sediments often limits MeHg production when surface water sulfate concentrations exceed about 100uM. Methylmercury production in oligotrophic freshwater ecosytems is therefore sensitive to changes in anthropogenic sulfate and mercury deposition, while MeHg production in estuarine ecosystems and eutrophic freshwater systems is less so. Ecosystems that support high rates of both microbial sulfate reduction and sulfide removal, e.g. wetlands, are particularly sensitive to sulfate and Hg deposition.
Day: Wednesday, Feb. 3
Time: 12:15 - 12:30pm
Location: Sweeney Center
Code: SS50WE1215S