Microbial mercury cycling in sediments of the San Francisco Bay-Delta |
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Authors: | Email author" target="_blank">Mark?Marvin-DiPasqualeEmail author Jennifer?L?Agee |
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Institution: | (1) Department of Environmental Health Sciences, University of South Carolina, Arnold School of Public Health, Columbia, South Carolina 29208, USA;(2) United States Army Corps of Engineers, Savannah, Georgia 31402-0889, USA;(3) Westinghouse Savannah River Company, Aiken, South Carolina 29808, USA;(4) University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29808, USA |
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Abstract: | Microbial mercury (Hg) methylation and methylmercury (MeHg) degradation processes were examined using radiolabled model Hg
compounds in San Francisco Bay-Delta surface sediments during three seasonal periods: late winter, spring, and fall. Strong
seasonal and spatial differences were evident for both processes. MeHg production rates were positively correlated with microbial
sulfate reduction rates during late winter only. MeHg production potential was also greatest during this period and decreased
during spring and fall. This temporal trend was related both to an increase in gross MeHg degradation, driven by increasing
temperature, and to a build-up in pore water sulfide and solid phase reduced sulfur driven by increased sulfate reduction
during the warmer seasons. MeHg production decreased sharply with depth at two of three sites, both of which exhibited a corresponding
increase in reduced sulfur compounds with depth. One site that was comparatively oxidized and alkaline exhibited little propensity
for net MeHg production. These results support the hypothesis that net MeHg production is greatest when and where gross MeHg
degradation rates are low and dissolved and solid phase reduced sulfur concentrations are low. |
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