GC53I-08
Recent Advances in Understanding the Sources of Methylmercury to Coastal Waters
Friday, 18 December 2015: 15:25
3003 (Moscone West)
Robert P Mason1, Prentiss H Balcom1, Celia Chen2, Kathleen Joehr Gosnell3, Sofi Jonsson3, Nashaat Mazrui1, Veronica Ortiz4, Emily Seelen3, Amina Traore Schartup5 and Elsie M Sunderland5, (1)University of Connecticut, Groton, CT, United States, (2)Dartmouth College, Hanover, NH, United States, (3)University of CT at Avery Point, Groton, CT, United States, (4)CT Department of Public Health Laboratory, Rock Hill, CT, United States, (5)Harvard University, Cambridge, MA, United States
Abstract:
Understanding the sources of methylmercury (MeHg) to the food chain in coastal waters is important given the related health concerns from consumption of seafood containing elevated MeHg. While water column dissolved or particulate MeHg is the best predictor of bioaccumulation into pelagic organisms in coastal waters, there is debate concerning the dominant sources of MeHg to the water column, and how the relative importance of these sources vary with ecosystem characteristics. Potential sources include both external inputs from the watershed and offshore waters and internal sources (net methylation in sediments and the associated flux of MeHg to the water column and/or net MeHg production in the water column). We will report the results from our various studies in estuarine and coastal waters which have examined the distribution and partitioning of sediment and water column MeHg, and its formation and degradation, across a geographic range from Labrador, Canada to the Chesapeake Bay, USA. The ecosystems studied vary from shallow estuarine bays to deeper systems, and from salt wedge to tidally-dynamic systems. Additionally, both pristine and contaminated environments were examined. The studies examined the factors controlling the net production of MeHg in sediments, and in our more recent work, the potential formation of MeHg in the oxic water column of coastal waters. Sediment measurements (core and grab samples) included both solid phase and porewater MeHg and total mercury (HgT) and important ancillary parameters. Water column parameters included dissolved and particulate MeHg and HgT, TSS, nutrients, and DOC. Stable Hg isotope tracer incubations were used to assess the degree of methylation and demethylation in sediments and surface waters. Average suspended particle MeHg ranged from <5 to 120 pmol/g, and was 1-8% of HgT across sites. Mass balance estimates provide insights into the importance of external MeHg sources to coastal waters. We will use the information to evaluate the following questions: 1) what conditions favor external sources of MeHg over internal production? 2) what conditions enhance net in situ water column formation of MeHg? and 3) what conditions enhance the exchange of MeHg at the sediment/water interface in coastal waters?
