Effects of salinization on mercury bioavailability in coastal wetlands at Albemarle-Pamlico Peninsula, North Carolina

Abstract

The primary purpose of this study was to assess salinization impact (spatial and temporal) on mercury (Hg) cycling in coastal plain wetlands of North Carolina. We hypothesized that salinization of coastal freshwater wetlands increases methylmercury (MeHg) levels, as the sulfate-reducing bacteria (SRB), dominant groups that promote methylation of an inorganic form of mercury Hg (II) is stimulated by elevated levels of sulfate (SO₄²-) derived from saltwater. To achieve our goal, we collected water, sediment, and biota (note that biota was not included in the proposal) samples every month, between April and September 2019. We measured total Hg, MeHg, sulfate (SO₄²-), and dissolved organic carbon (DOC) levels along with the necessary field measurements (e.g., salinity, temperature, and dissolved oxygen). Total mercury (THg) levels for surface water samples ranged widely among the sites, and the highest levels were observed in Freshwater Wetland (at Point Peter site), where the DOC levels were the highest as well. Also, we observed increasing aqueous filtered MeHg concentrations (3.13 and 3.72 ng/L) in May and July in Freshwater Wetland, when the sulfate levels were at the peak (i.e., 4.85 and 4.79 mg/L, respectively). So far, our results for water samples suggest that the salinization of freshwater wetlands elevates MeHg levels in surface water. However, our analyses for sediment and biota samples are still ongoing (will be finalized in summer 2020) and will give us a better understanding of salinization impact on mercury cycling in coastal plain wetlands.