Mercury dynamics in Tivoli South Bay, a freshwater tidal mudflat wetland in the Hudson River

Abstract

The accumulation of total mercury (HgT) andmethylmercury (MeHg) was evaluated in sediments ofTivoli South Bay, a freshwater tidal mudflat wetlandin the Hudson River National Estuarine ResearchReserve system. HgT concentrations in sedimentcores were measured to evaluate the spatialvariability of HgT deposition, and to establisha chronology of HgT accumulation. Cores takenfrom the northern, middle, and southern sections ofthe bay had similar distribution patterns andconcentrations of HgT, suggesting a common sourceof HgT throughout the bay. Sedimentconcentrations ranged from 190 to 1040 ng Hg g−1,2 to 10 times greater than concentrations expected insediments from non-anthropogenic sources. HgTdeposition rates were similar in different regions ofthe bay, and increased from 200 ng Hg cm−2yr−1in the 1930s to a maximum of 300 ngHg cm−2 yr−1 in the 1960s. Deposition rateshave steadily declined since the 1970s and arecurrently at 80 ng Hg cm−2 yr−1. Transportof HgT by tidal waters from the Hudson River islikely the main source of HgT in the bay.Distribution patterns and absolute concentrations ofMeHg in sediment cores were similar throughout thebay, with concentrations ranging from 0.43 to 2.95ng g−1. Maxima in MeHg concentration profilesoccurred just below the sediment-water interface andat a depth of 30 cm. The maximum at 30 cm wascoincident with maximum HgT concentrations. MeHgconcentrations in suspended particulate matter (SPM)from the Hudson River suggest that MeHg in the baycould be derived from riverine SPM rather than formedin situ.