THURSDAY, MAY 4, 2006

Topic: Mercury (Hg) Cycling in Sulfide-rich Sediments: Contaminant Storage in the Penobscot River Estuary, Maine

Research concerning the fate and biogeochemical cycling of both inorganic and methyl-mercury in coastal ecosystems frequently suggests that organic matter (OM) controls the thermodynamic partitioning of Hg between the sediment dissolved (i.e., porewater) and particulate phases. Equilibrium speciation calculations suggest, however, that this proposed OM control is only significant in non-sulfidic environments. As all marine and/or estuarine environments demonstrate sulfide generation (via microbial sulfate reduction) at some depth within the sediment, OM control on porewater Hg speciation may range from significant (in well-oxygenated, coarse-grained continental shelf sediments) to inconsequential (in poorly-oxygenated, fine-grained estuarine muds). As Hg speciation within sediment porewater likely dictates its methylation potential, it is critical to understand the means by which such environment-specific variations in porewater chemistry ultimately control Hg bioavailability. Furthermore, as estuaries have often historically functioned as sites of industrial activity, it is important to assess the extent to which porewater sulfide-domination affects the environment’s source-versus-sink potential for Hg retention.

Speaker: Karen Merritt, Dept. of Civil & Environmental Engineering, UMaine

Karen Merritt is currently working on a Ph.D. in Environmental Engineering at the University of Maine. Karen holds a B.A. in Geology from Carleton College and a M.S. in Environmental Chemistry from the University of Maine. Before beginning graduate school, Karen worked for 7 years in the fields of Marine Science and Engineering.