Mercury Sources and Species in Waquoit Bay and Other Cape Cod Massachusetts Water Bodies

Previous work in Waquoit Bay, Massachusetts (USA), has found high concentrations of dissolved mercury (Hg) in bay water and implicated groundwater as a potentially important source of this toxic metal to that coastal ecosystem (Bone et al., 2007). On-going research is testing this hypothesis by examining the spatial distribution and temporal variability of Hg within the subterranean estuary, the open water of Waquoit Bay, and in selected water bodies elsewhere on Cape Cod. Survey sampling indicated that Waquoit Bay was unusually elevated in total dissolved Hg concentration when compared to Vineyard Sound, fresh ponds within its watershed and nearby tidal salt ponds. This suggests that groundwater and diffusion from sediments are key sources of Hg to Bay waters. Watershed Hg transfer efficiencies, calculated by comparing rain fluxes measured at the Cape Cod National Seashore Coastal Lab (MA01) with groundwater fluxes at the head of Waquoit Bay, are typical of other temperate systems but lower than those estimated previously for this site. Furthermore, while the total Hg concentrations of local sands and soils from around Cape Cod are often very small and strongly a function of organic carbon (as determined by LOI), the partition coefficients (Kd) were not unusually low. This potentially contradicts our hypothesis that the cause of high Hg concentrations in the Bay are the result of little retention of Hg within the watershed compared to other temperate systems. In addition to total Hg studies, monomethyl Hg (MMHg) fluxes into the Bay with advecting groundwater are being determined. The flux with groundwater will be compared to the flux of mmHg generated in surficial sediments of the central bay, less affected by groundwater, and released via diffusion and/or tidal pumping.