The Impacts of forest management practices on mercury contamination in small stream biota
Effect of mercury on
Thunder Bay region
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Mercury is a contaminant of global concern as it is present in all biota and ecosystems around the world. Small streams are influenced by the terrestrial systems that feed them. I examined the presence of mercury in small stream biota, the bioaccumulation of the mercury in higher trophic levels and the stream characteristics, including catchment disturbance that are associated with differences in mercury contamination among trophic levels. Sampling of periphyton, benthic invertebrates and fish occurred in 31 sites across 6 watersheds having different forest management histories. Mercury was present in all three biota types sampled with a wide range of mercury concentrations between and among sites and biota. Biota mercury concentrations were highest in the smaller size streams (small and medium) compared to the large streams with no differences between the different forest management histories. Biota mercury concentrations tended to have the highest association with local conditions including pH, conductivity, stream gradient and temperature. Brook trout Salvelinus fontinalis (Mitchill)] had the lowest average concentrations of the two fish species collected with average mercury concentrations 50% less than dace species collected within the same stream. While biota mercury concentrations have been associated with disturbance in other studies, local stream conditions and stream size tended to have the highest association in my study.