Mercury Methylation Assay Along a Salinity Gradient in Coastal Peat Soils in the Florida Everglades

This data was collected as part of a laboratory study examining the effects of sea level rise on mercury (Hg) methylation and demethylation rates in peat cores collected from the Florida Everglades. Peat cores were collected from a freshwater region of the Everglades, Water Conservation Area 3, in 2022 and taken to the University of California-Davis for methylation and demethylation studies. Prior to the incubations peat cores were inundated with water of different salinities (0.16 parts-per-thousand (ppt), 0.25 ppt, 0.50 ppt, 1.0 ppt, 6.0 ppt) to simulate saltwater intrusion in coastal regions of Everglades National Park. Incubations were run for 20 days. An enriched isotope tracer of inorganic Hg (201Hg) was added to the cores to track the methylation process. In tandem isotopically enriched methylmercury (204MeHg) was tracked to examine demethylation. Porewater and peat material were collected from the incubations and analyzed for Hg and MeHg. Additional parameters such as dissolved organic carbon concentration and quality, reduction-oxidation potential, major cation and anions, and other metals were monitored during the incubations to examine the controlling variables dictating Hg methylation. Across all salinity treatments, porewaters became increasingly anoxic, sulfate concentrations decreased, and MeHg concentrations increased over the course of 20 days. The findings highlight the potential for enhanced production and mobilization of MeHg in coastal wetlands of the Florida Everglades due to the onset of saltwater intrusion.