Contaminant flux measurements across the sediment-water interface in San Diego Bay

Marine sediments often serve as important sinks for anthropogenic contaminants from the overlying water column. In certain cases the sediments may also serve as contaminant sources, releasing contaminants later when water column and/or pore water conditions change. Variations in sediment chemical and physical properties make it impossible to rely on bulk sediment contaminant concentrations alone to predict contaminant flux, bioavailability, and therefore toxicity. In situ measurements of contaminant fluxes across the sediment-water interface provide important information for addressing these concerns. The Navy has recently developed the Benthic Flux Sampling Device (BFSD) to assess contaminant fluxes across the sediment-water interface. The BFSD has recently undergone several modifications to allow improved operation. The oxygen regulation system has been modified to allow better control of chamber oxygen levels. Some deployments have utilized real-time sensors that allow monitoring of BFSD operations and offer the potential to serve as field-screening tools to evaluate contaminant mobility. These real-time sensor techniques include potentiometric stripping analysis (PSA) for metals and laser-induced fluorescence (LIF) for hydrocarbon contaminants. As part of the Navy´s ongoing program to monitor environmental conditions in San Diego Bay, this study used multiple deployments of the BFSD to assess contaminant fluxes across the sediment-water interface. In coastal areas, directly measured BFSD fluxes are often preferable to model-dependent fluxes obtained from pore water profiles. Target contaminants in this study included the trace metals Cd, Cu, Ni, Pb, and Zn. Initial results indicate fluxes occur both into and out of the sediments depending on contaminant type and site location. The metals that showed the most consistent flux out of the sediments included Zn and Mn