Biogeochemical control on the flux of trace elements from estuarine sediments: effects of seasonal and short-term hypoxia

A long-term (162-day) study of fluxes of trace elements (Mn, As, Cu, Cd) was conducted with intact sediment cores collected from Baltimore Harbor, MD. Under hypoxic conditions large amounts of Mn initially fluxed out of the sediment; however, the rate of Mn flux diminished substantially over time. No Mn flux was seen under oxic conditions. After an initial ‘pulse’, As flux held steady through the hypoxic period. Under oxic conditions, As flux was very low initially and increased near the end of the experiment, with greater fluxes from formerly hypoxic sediments. Initially, fluxes of Cu and Cd were stimulated by hypoxic conditions; however, after a few days, flux of either was completely inhibited. Fluxes of both Cu and Cd occurred under oxic conditions and after the conclusions of hypoxic periods. At the average flux rates measured under oxic conditions, benthic fluxes of Cu and Cd were comparable to point sources, and storm-water runoff inputs to Baltimore Harbor, and significantly greater than atmospheric inputs. Benthic fluxes of As were estimated to be less than storm-water runoff, but considerably higher than point sources or other inputs. ©