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PT17 Assessment and Remediation of Mercury Contaminated Sites
(PT270) The effect of sediment resuspension on the bioaccumulation of methylmercury into benthic and pelagic organisms.
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. The objective of this study was to determine the effect of sediment resuspension on Hg cycling and bioaccumulation of sedimentary Hg and MeHg to benthic organisms and zooplankton. Tidal resuspension was simulated in mesocosm tanks that had realistic bottom shear stress and water column turbulence. Previous month-long experiments comparing resuspension to no resuspension found that resuspension enhances Hg methylation and that clams (M. mercenaria) added to tanks did not accumulate a significant amount of Hg compared to their background levels. However, MeHg concentrations in zooplankton (>210 mm) were higher in resuspension tanks. The current experiments investigated the effect of differences in clam density on Hg methylation and bioaccumulation up the food chain. Clam density impacts methylation since clams initially destablize the sediments and enhance resupension. In a further effort to examine the complex trophic dynamics in these systems, Hg stable isotope was also added to allow examination of the rate of Hg transfer from the water to sediments, its subsequent in situ methylation to MeHg, and resultant cycling and bioaccumulation of the isotope through the system. Sediment, water, zooplankton, and clam samples were analyzed for total Hg and MeHg, and ancillary parameters. The results of this study will be discussed in detail in terms of the working hypothesis that increasing clam density leads to higher MeHg concentrations in herbivores (clams and zooplankton) as a result of the interaction between MeHg biogeochemical cycling and system productivity.
Key words: resuspension, methylmercury, bioaccumulation, mesocosms
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