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 far approximately 2 months in replicated sedim ent/water microcosms. Treatments consisted of three oxygen levels in t he water column (saturated, 10% saturation and anaerobic) and three di fferent organism treatments (control, Macoma balthica and Nereis succi nea). Both arsenic and manganese were released from the sediment in th e anoxic treatment, while copper was lost from the water. With the wat er column either saturated or at 10% oxygen saturation, both arsenic a nd manganese fluxes were negligible. In contrast, copper fluxes out of the sediment increased with increasing oxygen concentrations. The eff ect of organisms on the trace element fluxes were greatest immediately after their introduction to the microcosms, and declined substantiall y thereafter. Nereis caused a substantial initial increase in manganes e fluxes, but caused a negative flux (out of the water column) for ars enic. Macoma had a much smaller effect on flux than Nereis. Neither or ganism had a substantial effect on copper fluxes. Porewater profiles g ave good predictions of arsenic and manganese fluxes in the anoxic tre atment, but not in the 10% or saturated-oxygen treatments. Porewater p rofiles underestimated copper fluxes in the oxygenated treatments some what, and predicted copper flux in the opposite direction in the anoxi c treatment. These results suggest that the annual cycle of anoxia in systems like Chesapeake Bay, and the resulting annual cycle of organis m death and recruitment, can significantly alter the cycling of trace elements between the sediment and water column. (C) 1997 Academic Pres s Limited.