Mechanisms and temporal variability of dissolved gaseous mercury production in coastal seawater

Coastal waters are regions of rapid and significant biogeochemical transformations of mercury, but they have received little attention with regards to the mechanisms and seasonality of processes driving measured air–sea fluxes. We examined controls on the net rate of Hgo production from additions of Hg(II) to dark and light-incubated coastal seawater samples from Long Island Sound, CT. Multiple controls were evident, with approximately 70% of bulk reduction driven photochemically, 20% by microbial mediation, and 10% by uncharacterized dark reduction in the dissolved phase. Positive relations were observed between (1) dark bottle reduction rates and total bacterial abundance and (2) light bottle rates and total solar irradiance. Evasional fluxes were estimated for LIS using a simple model framework, with an estimated 363 pmol Hgo m−2 day−1 delivered to the atmosphere ( 35% of annual inputs to LIS). This value agrees well with an independent estimate, and underscores the geochemical significance and complexity of Hgo cycling within LIS and other coastal zones.