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

The accumulation of total mercury (Hg-T) and methylmercury (MeHg) was evalu ated in sediments of Tivoli South Bay, a freshwater tidal mudflat wetland i n the Hudson River National Estuarine Research Reserve system. Hg-T concent rations in sediment cores were measured to evaluate the spatial variability of Hg-T deposition, and to establish a chronology of Hg-T accumulation. Co res taken from the northern, middle, and southern sections of the bay had s imilar distribution patterns and concentrations of Hg-T, suggesting a commo n source of Hg-T throughout the bay. Sediment concentrations ranged from 19 0 to 1040 ng Hg g(-1), 2 to 10 times greater than concentrations expected i n sediments from non-anthropogenic sources. Hg-T deposition rates were simi lar in different regions of the bay, and increased from 200 ng Hg cm(-2) yr (-1) in the 1930s to a maximum of 300 ng Hg cm(-2) yr(-1) in the 1960s. Dep osition rates have steadily declined since the 1970s and are currently at 8 0 ng Hg cm(-2) yr(-1). Transport of Hg-T by tidal waters from the Hudson Ri ver is likely the main source of Hg-T in the bay. Distribution patterns and absolute concentrations of MeHg in sediment cores were similar throughout the bay, with concentrations ranging from 0.43 to 2.95 ng g(-1). Maxima in MeHg concentration profiles occurred just below the sediment-water interfac e and at a depth of 30 cm. The maximum at 30 cm was coincident with maximum Hg-T concentrations. MeHg concentrations in suspended particulate matter ( SPM) from the Hudson River suggest that MeHg in the bay could be derived fr om riverine SPM rather than formed in situ.