Studies of mercury in water, sediment, and fish in Mississippi: Concentrations, speciation, cycling, and isotopic composition

The goal of this project is to better understand the biogeochemical cycle of mercury (Hg) in Mississippi to aid those managing the resources and developing related policy. To that end, Hg levels were determined in a total of 202 fish from Enid, Sardis and Grenada Lakes; Enid and Grenada have fish consumption advisories due to Hg. In addition, total-Hg and methylmercury (MeHg) levels were determined in the inflow and outflows from Enid and Sardis Lakes and in bottom sediment and suspended solids in Enid Lake. Potential sources of Hg to Enid Lake were investigated, including precipitation and runoff from urban, agricultural, and wetland/forest areas, which flow into the Yocona River. A range of water quality parameters were measured to determine the primary factors controlling the distribution and transport of Hg species in the watershed. Concentrations in the fish generally increased with fish size (age) and trophic position. The suggested consumption limit for bass and crappie, commonly targeted by fishers, are \u3c5 meals per month for adults and \u3c12 meals per year for children. Wetland areas were determined to be hotspots for MeHg in the watershed with relatively high concentrations in water and fish, but runoff from agricultural areas likely provides the largest input of Hg to Enid Lake by transport of particle-bound-Hg. Wet deposition accounts for an estimated 33 kg and 15 kg of Hg deposited annually via rainfall to the Little Tallahatchie (Sardis) and Yocona River (Enid) watersheds, respectively. Mercury fluxes for Enid Lake based on concentrations in the inflow and outflow, and water-flow measurements are reported by season and during a storm event. The feasibility of using remote sensing (satellite imagery) to model the distribution of total suspended solids and Hg following a rainstorm event will be shown. Finally, results from the first study of total-Hg, MeHg, and Hg isotopic composition in sediment from a cold seep from the northern Gulf of Mexico is discussed. Hg levels in the sediment from the cold seep were similar to background sites, and cold seeps are likely not significant sources of MeHg to Gulf waters