Evidence for microbially mediated production of elemental mercury (Hg0) in subarctic lake sediments

The production and fate of Hg-0 in lake sediments remains poorly characterized, although it can potentially influence Hg toxicity and mobility. Using slurry incubations, we assessed the effect of nutrients, pH, ionic strength, and tested the role of microbes, on Hg-0 production from pristine lake sediments of the Hudson Bay Lowlands in Ontario, Canada. We showed that Hg-0 production from oxygenated sediments was low (<1% of the Hg flux to sediments), biogenic, and did not appear to be dependent on the predicted Hg-II speciation in the slurry. The addition of biologically labile carbon sources and ionic strength, particularly [Na+], had the greatest impact on Hg-0 production, increasing it by over 10-fold. These results suggest that under changing conditions, such as increasing temperature or alteration of water chemistry as observed in numerous locations throughout Arctic and subarctic environments, a fraction of sedimentary Hg may be remobilized and available for microbial reduction. (C) 2013 Elsevier Ltd. All rights reserved.