Biogeochemical Control on the Flux of Trace Elements from Estuarine Sediments: Water Column Oxygen Concentrations and Benthic Infauna

Trace element (arsenic, copper and manganese) fluxes between sediment and water were examined for approximately 2 months in replicated sediment/water microcosms. Treatments consisted of three oxygen levels in the water column (saturated, 10% saturation and anaerobic) and three different organism treatments (control,Macoma balthicaandNereis succinea). Both arsenic and manganese were released from the sediment in the anoxic treatment, while copper was lost from the water. With the water column either saturated or at 10% oxygen saturation, both arsenic and manganese fluxes were negligible. In contrast, copper fluxes out of the sediment increased with increasing oxygen concentrations. The effect of organisms on the trace element fluxes were greatest immediately after their introduction to the microcosms, and declined substantially thereafter.Nereiscaused a substantial initial increase in manganese fluxes, but caused a negative flux (out of the water column) for arsenic.Macomahad a much smaller effect on flux thanNereis. Neither organism had a substantial effect on copper fluxes. Porewater profiles gave good predictions of arsenic and manganese fluxes in the anoxic treatment, but not in the 10% or saturated-oxygen treatments. Porewater profiles underestimated copper fluxes in the oxygenated treatments somewhat, and predicted copper flux in the opposite direction in the anoxic treatment. These results suggest that the annual cycle of anoxia in systems like Chesapeake Bay, and the resulting annual cycle of organism death and recruitment, can significantly alter the cycling of trace elements between the sediment and water column.