Effects of trophic status and wetland morphology, hydroperiod, and water chemistry on mercury concentrations in fish

We sampled fish and selected water chemistry variables (dissolved organic carbon, sulfate, and pH) in nine southeastern depression wetlands to determine relationships among wetland morphology (surface area and maximum depth), hydrology, water chemistry, and bioaccumulation of mercury (Hg) in fishes. We concentrated on three fish species representing the range of trophic levels occupied by fish in southeastern depression wetlands. Whole-body Hg concentrations were lowest in lake chubsucker (Erimyzon sucetta), a benthic detritivore, and highest in redfin pickerel (Esox americanus americanus), a top carnivore. However, variation in Hg concentrations among wetlands was greater than variation among species. Regression analyses indicated that maximum depth and hydroperiod accounted for significant portions of variation among wetlands in standardized lake chubsucker and redfin pickerel Hg concentrations. Maximum depth and dissolved organic carbon had a negative effect on standardized Hg concentrations in mud sunfish (Acantharchus pomotis). Path analysis confirmed the results of regression analyses, with maximum depth and hydroperiod having relatively large direct negative effects on Hg concentrations. Our results suggest that leaching of Hg from sediments during the drying and reflooding cycle and binding of Hg species by dissolved organic carbon in the water column are primary factors controlling the bioavailability of Hg in southeastern depression wetlands.