An examination of the factors influencing the flux of mercury, methylmercury and other constituents from estuarine sediment

The flux of mercury (Hg), methylmercury (MeHg), other metals (zinc (Zn), cadmium (Cd) and lead (Pb)), arsenic (As), nutrients, dissolved organic carbon (DOC) and sulfide from sediments collected in Baltimore Harbor, Maryland, USA were measured over the period of approximately 5 days. Fluxes of the various constituents changed over time and the magnitude and direction of the fluxes of the major metals (Fe and Mn) correlated with the extent of oxygen depletion and the presence or absence of sulfide in the water column. It appeared that the heavy metals, Zn, Cd, Pb, and Hg, were taken up into the sediment under hypoxic/anoxic conditions but were released under more oxic conditions. The fluxes of As and phosphate followed that of Fe. Overall, the fluxes of these constituents confirmed expectation based on thermodynamic considerations. For Hg and MeHg, there appeared to be little relationship between their flux and that of the major metals, or sulfide, or DOC. For MeHg, there is a suggestion that processes occurring at the sediment/water interface, including methylation, may play a major role in determining the extent of the MeHg flux to the water column.