The production of methylmercury (MeHg), a bioaccumulative neurotoxin, in freshwater systems is primarily driven by naturally occurring sulfate reducing bacteria in anoxic sediment and waters. This research used laboratory microcosms to examine the influence of sulfate on MeHg production and partitioning in sulfate-impacted freshwater estuary sediment. A laboratory sulfate addition experiment exposed 20cm diameter intact sediment cores with varying organic carbon content to sulfate concentrations in the overlying water ranging from 5 to 50mgL-1. Results from the 6month incubation suggest that net MeHg production in sediment from open-water areas of the St. Louis River Estuary was not directly related to overlying water sulfate. Mercury mobility, as indicated by porewater concentrations, appeared to be related to the quantity of organic carbon and sulfur in sediment. Laboratory flux estimates were consistent with porewater concentrations and provided a means to compare diffusion-driven MeHg loading from sediment to MeHg loading from upstream sources.
Bibliographical noteFunding Information:
This study was jointly funded by the Minnesota Department of Natural Resources through the Environmental Cooperative Research Fund, Minnesota’s Environmental and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR), and the Grant/Cooperative Agreement Number G11AP20087 from the United States Geological Survey administered by the University of Minnesota Water Resources Center. The contents of this paper are solely the responsibility of the authors and do not necessarily represent the official views of the Minnesota DNR, LCCMR, or the USGS. The authors are particularly indebted to Dr. Michael Berndt (Minnesota Department of Natural Resources) for providing funding, project oversight, and support as well as feedback during manuscript preparation. Additionally, three anonymous reviewers provided significant constructive feedback.
© 2014 Elsevier Ltd.