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Thursday, June 7, 2007 - 10:15 AM
369
Mercury bioaccumulation in streams: the role of food web length, carbon sources, and proximity to emission sources
Timothy D. Jardine1, Karen A. Kidd1, and Richard A. Cunjak2. (1) Biology Department, University of New Brunswick, PO Box 5050, Tucker Park Road, Saint John, NB E2L 4L5, Canada, (2) Department of Biology, University of New Brunswick, Loring Bailey Hall, Fredericton, NB E3B 5A3, Canada
Mercury contamination of freshwater ecosystems remains a major health concern in industrialized nations. In order to assess mechanisms leading to different degrees of Hg bioaccumulation in aquatic food webs, we sampled biota from streams and rivers at 30 sites in New Brunswick, Canada in 2005 and 2006. Samples included biofilm and terrestrial leaves (alder), primary consumers (freshwater mussels and mayflies), predatory invertebrates (dragonflies, stoneflies and water striders), and insectivorous (dace and sculpin) and piscivorous (brook trout) fish. Stable isotope analysis was used to measure trophic level (with d15N) and food source pathway (with d13C) of biota and interpret their total Hg concentrations. As expected, strong relationships were observed between trophic level and total Hg, with some fishes having concentrations above the Health Canada guideline for consumption (0.5 ppm wet weight). Organisms connected to the aquatic food source pathway had higher Hg concentrations than those using terrestrial energy. Striders collected at increasing distances from a coal-fired power plant (annual Hg emissions of 100 kg) did not show any spatial trends, suggesting that this point source did not affect Hg bioaccumulation in nearby streams. Taken together, these findings suggest that in-stream processes are important determinants of Hg bioaccumulation in riverine food webs.