Ecosystem-Scale Modeling and Field Observations of Sulfate and Methylmercury Distributions in the Florida Everglades: Responses to Reductions in Sulfate Loading

Abstract

The Florida Everglades has one of the most severe methylmercury (MeHg) contamination issues in the USA, resulting from factors including high rates of atmospheric mercury (Hg) deposition and sulfate inputs from agricultural lands. Sulfate loading stimulates microbial sulfate reduction and production of toxic and bioaccumulative MeHg. Controls on regional Hg emissions have been successful in reducing Hg deposition and MeHg production in wetlands in other areas, but this has not been the case for the Everglades as the Hg deposited here appears to come from unknown global sources of emissions. We posit that reductions in sulfate loading to the Florida Everglades can be an effective alternative approach used to reduce MeHg production. This study tested this hypothesis (1) by evaluating temporal trends in MeHg concentrations in response to a reduction in sulfate loading at a site in central Water Conservation Area (WCA) 3 and (2) using ecosystem-scale models to predict the effects of reductions in sulfate loading on sulfate concentrations in surface water and MeHg Risk. At the WCA site, we report a decline in sulfate concentrations (from about 9 mg/L in the late 1990s to levels of 33% in sulfate loading will significantly benefit the Everglades by reducing MeHg Risk.