Haskins, J: Trace Metal Cycling in South San Francisco Bay

The non-point source sediment fluxes of Cd, Cu, and Ni from the sediment-water interface in South San Francisco Bay are described and compared to known point sources of both anthropogenic and watershed origins. Fluxes of these metals were determined by benthic flux chambers and by the mathematical modeling of gradients in metal concentrations in pore water taken from sediment cores. Experiments were also performed to assess benthic macrofaunal contributions of sediment fluxes using the invasive Asian clam Potamocorbula amurensis. Because of major clean-up efforts conducted since the 1970 s fluxes of contaminants from point sources have decreased significantly yet metal contamination remain high. Fluxes from non-point sources must comprise a significant source to the South Bay waters. The addition of clams reversed the direction and increased the magnitude of the fluxes of these metals. These data suggest 1) non-point sources such as sedimentary flux is important and 2) that invasive species such as P. amurensis, can have profound affects on benthic bioirrigation in the sediments due to burrowing and feeding generating exchange of pore waters with the overlying water column.