W4 AM Environmental Fate of Mercury
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(BER-1117-656429) The impact of sediment resuspension and clam density on the cycling and bioaccumulation of methylmercury.

Bergeron, C¹, Mason, R¹, Porter, E¹, ¹ University of Maryland Center for Environmental Science Chesapeake Biological Laboratory, Solomons, MD, USA

ABSTRACT- Sediment is an important repository for mercury (Hg) and the dominant site for Hg methylation in estuarine environments. Benthic organisms in contact with contaminated sediment have the opportunity to accumulate high levels of Hg, especially methylmercury (MeHg) from porewater, overlying water and food. Resuspension provides a potential mechanism for transferring Hg and MeHg from the sediment to the pelagic food chain and filter feeding organisms and has been found to enhance Hg methylation. The objective of this study was to determine the effect of sediment resuspension and clam density (M. mercenaria) on Hg cycling and bioaccumulation of Hg and MeHg into benthic organisms and zooplankton. Clam density potentially impacts methylation since clams initially destablize the sediments and enhance resupension. Clam feeding can also impact the density and growth of phytoplankton and potentially their Hg concentration. Tidal resuspension was simulated in mesocosm tanks that had realistic bottom shear stress and water column turbulence. In a further effort to examine the complex trophic dynamics in the systems, a Hg stable isotope was added as a tracer to examine of the rate of Hg transfer from the water to sediments, its subsequent in situ methylation, and the resultant cycling and bioaccumulation of the isotope through the system. The added isotope rapidly partitioned to particles so that little Hg remained dissolved after 24 hours. Furthermore, there was sufficient evidence to suggest that this Hg was methylated and bioaccumulated over the four-week experiment. Overall, the results suggest that Hg cycling is affected more by resuspension than clam density, and that Hg added to the system is initially more bioavailable for methylation and becomes increasing less bioavailable with time.

Key words: methylmercury, resuspension, bioaccumulation, mesocosms