16-27 Establishing Pre-Dredging Mercury Baselines in Fish Across Legacy-Contaminated and Reference Aquatic Systems

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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This study establishes baseline mercury (Hg) concentrations in fish from a pond scheduled for dredging, prior to potential sediment disturbance and contaminant remobilization. Sediment cores from the pond indicate severe legacy Hg contamination, with concentrations reaching over 4500 ppb at 1.6 m depth. In contrast, sediments at the sediment–water interface contain ~200 ppb Hg, consistent with modern (post-1990) atmospheric deposition. Dredging may reintroduce Hg from deeper sediments into the water column, increasing bioavailability to aquatic organisms.

Fish Hg concentrations from this pond were compared with two nearby systems: a protected reservoir with sediment Hg concentrations suggesting no legacy Hg source other than atmospheric (≤190 ppb), and an off-Connecticut River waterbody, where sediment Hg peaks at ~530 ppb at 75 cm depth with values decreasing to ~250 ppb at the sediment-water interface. Fish from all sites were collected by fishing, and muscle and liver tissues were sampled,  freeze-dried, and analyzed for Hg.

Initial results from a variety of species (n = 5) along the Connecticut exhibited a positive relationship (r² ranging from 0.9 to 0.5) between body size and Hg concentration, consistent with bioaccumulation. In contrast, two stocked trout from the contaminated pond showed relatively low and size-independent Hg concentrations (97 ppb at 37 cm length; 122 ppb at 31 cm), likely reflecting differences in residence time since stocking, dietary differences, or growth dilution. Across sites, liver Hg concentrations were approximately 30% lower than muscle concentrations, consistent with preferential methylmercury binding to cysteine-rich muscle proteins. These results provide a critical pre-dredging benchmark for evaluating future Hg mobilization and ecological risk.

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