School of Marine Sciences and Dept. of Wildlife, Fisheries and Conservation Biology
October 21, 2016
11:00 a.m. ~ Senator George Mitchell Center
Dr. Brian Bergamaschi
USGS – Sacramento Field Office
The Estuarine Axis of Evil: How Tidal Wetlands Toxify Mercury From the Air and Spit It Out Into Coastal Waters
Elevated mercury levels have been widely reported in wading birds, raptors, alligators, sport fish and other animal species in the South Florida’s coastal and inland waters, and in sport fish and birds in San Francisco Bay. In the case of South Florida, the source of the mercury entering the food web is unknown because there are no nearby geological sources. In the case of San Francisco Bay, although there is a great deal of mercury in aquatic environments due to legacy of gold mining, the process by which mercury is altered into methyl mercury (MeHg) — the organic form that can bio -accumulate — is not understood. Tidal wetlands in estuaries contain the “biogeochemical axis of evil”: a witch’s brew of sulfate, mercury, and easily-degradable organic material that leads to formation of MeHg right where tidal exchange can transport it into the estuary. We developed methods to characterize the flux of MeHg from tidal wetlands and found that both tidal wetlands produce and export the highest amount of MeHg ever reported from wetlands, indicating that tidal wetlands can be significant sources to estuarine foodwebs. Further, our results show that the source of mercury being methylated can be atmospheric, suggesting that remediation efforts focused on source control may not achieve desired results in these settings. In collaboration with JA Fleck, kR Fujii, B Downiing, DP Krabbenhoft, GR Aiken, and many others.
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