SGER:Collaborative Research: Assessing the Impact of Hurricanes on Mercury Biogeochemistry and Methylation in the Gulf of Mexico

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ABSTRACTOCE-0601098 / OCE-0600624With funding from this Small Grant for Exploratory Research (SGER), investigators at the University of Connecticut and the Harvard School of Public Health will investigate the impacts of Hurricanes Katrina and Rita on mercury (Hg) biogeochemistry and the formation of methylmercury (MeHg) in the Gulf of Mexico (GOM). Mercury in the form of MeHg is a neurotoxin that biomagnifies in aquatic food chains and has human health impacts. Seafood consumption is an important route of exposure. Little is known, however, about the locations and factors influencing the production of MeHg (methylation), which is carried out primarily in sediments by sulfate reducing bacteria (SRB). Coastal zones are one important location for methylation. Hg methylation rates depend on both the activity of SRB and availability of Hg(II) for uptake by SRB. Any environmental perturbation, such as storm disturbance, that alters SRB activity or the availability of Hg(II) has the potential to impact Hg methylation rates. The following hypotheses will be explored: (1)?Hurricanes Katrina and Rita have disrupted sediments by mixing and redepositing the upper layer of sediments, which will have resulted in important changes in redox conditions, and in the speciation and lability of Hg already present in these sediments; (2)?hurricane-derived runoff has resulted in a substantial pulse of Hg(II) via the Mississippi R. and Atchafalaya R. into the GOM, which, when deposited, is likely more available for methylation than the current Hg in Gulf sediment; (3) the Mississippi and Atchafalaya Rivers have also transported fresh terrestrial organic carbon into the GOM, along with a pulse of nutrients that will lead to enhanced production of marine organic carbon. A large fraction of this organic carbon will end up in the sediments and enhance SRB activity, and, as a result, lead to enhanced mercury methylation. ?4) increased inputs of organic carbon and the enhanced productivity will promote water column hypoxia, which in turn will enhance methylation and/or methylmercury levels.These hypotheses will be tested by collecting sediment cores and water samples during Fall 2005 and Spring 2006 from multiple locations along the Louisiana coast in areas that have been impacted by Hurricane Katrina or Rita. Hg methylation and demethylation rates will be determined in sediment cores, along with total Hg and MeHg. Short-lived (234Th, 7Be) and longer-lived (210Pb) radioisotopes will be measured to characterize sediment deposition history. Indicators of sediment redox conditions will also be measured.In terms of broader impacts, this research will help determine the degree to which hurricanes (and other major storm events) impact Hg biogeochemistry and assess the need for incorporating hurricane/storm impacts into annual MeHg production budgets. It will also provide research opportunities for graduate students and post-docs, and will provide information of interest to scientists, managers and the general public.