Biogeochemistry of Methylmercury in Lacustrine and Coastal Marine SedimentsEPA Grant Number: U915918
Title: Biogeochemistry of Methylmercury in Lacustrine and Coastal Marine Sediments
Investigators: Hammerschmidt, Chad R.
Institution: University of Connecticut
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $87,240
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Oceanography , Academic Fellowships , Aquatic Ecosystems
The objective of this research project is to examine how microbial and geochemical factors interrelate to influence the rates of mercury (Hg) methylation and monomethylmercury (MMHg) demethylation, dissolved and particulate concentrations, and sediment-water fluxes of MMHg. Microbial methylation of inorganic Hg in sediments is a major source of MMHg—the highly toxic and bioaccumulative form of Hg—in both lacustrine and coastal marine systems. Levels of MMHg are influenced by environmental factors that affect either the activity of methylating organisms or the availability of inorganic Hg for methylation. Profiles of MMHg in sediment show its variability both with depth and between dissolved and particulate phases. Such vertical distributions appear to be related with geochemical and microbial parameters that follow changes in the reduction-oxidation potentials of sediment pore water. The objective of this research project is to examine how microbial and geochemical factors interrelate to influence the rates of Hg methylation and MMHg demethylation, dissolved and particulate concentrations, and sediment-water fluxes of MMHg.
I will focus on how microbial and geochemical factors interrelate to control the biogeochemical cycling of MMHg in aquatic sediments. Sediment cores will be collected from Long Island Sound and Connecticut lakes to examine vertical stratigraphy of pore water and solid-phase concentrations of inorganic Hg and MMHg; rates of Hg methylation and MMHg demethylation; activities of microbial functional groups (e.g., sulfate reduction, sulfide oxidation, methanogenesis); and geochemistry of sediments (e.g., organic matter, sulfide, oxygen, iron). These field observations will be followed by a suite of laboratory experiments that will include: (1) examining oxidative and reductive MMHg demethylation in oxic and anoxic pore waters; (2) identifying functional groups of bacteria methylating inorganic Hg and demethylating MMHg with selective substrates and inhibitors; (3) identifying mechanisms of MMHg demethylation using metabolic inhibitors; (4) examining quantitatively the complexation and precipitation of dissolved MMHg by metal oxyhydroxides; (5) assessing the effects of metal oxyhydroxide sorption on MMHg demethylation by bacteria; (6) examining desorption of MMHg complexed with metal oxyhydroxides when subjected to reducing conditions; and (7) quantifying fluxes of MMHg from sediments to overlying water with variations in the location of the redox transition zone induced by additions of organic carbon. It is expected that levels of MMHg are greatest near redox transition zones, where rates of Hg methylation and MMHg demethylation also are highest because of substrate availability. Also, surficial oxic sediments are hypothesized to play a critical role in influencing sediment-water fluxes of MMHg.