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A multiple stable isotope approach to determine how fish life-history effects mercury bioaccumulation
Hoffman, J., S. Janssen, R. Lepak, M. Pearson, A. Cotter, AND D. Krabbenhoft. A multiple stable isotope approach to determine how fish life-history effects mercury bioaccumulation. SETAC North America, Fort Worth, TX, November 15 - 19, 2020.
Mercury (Hg) contamination within the St. Louis River estuary (SLRE) is of long-term concern because fish Hg concentrations are elevated above human health guidelines, contributing to an existing Beneficial Use Impairment under the Area of Concern program. Our goal was to understand the potential impact of remediation and restoration on mercury bioaccumulation by using a combination of carbon, nitrogen, and mercury stable isotopes in aquatic invertebrates and small prey fishes to reconstruct diet, trophic level, and mercury source. Our results demonstrate the utility of a multi-isotope approach to document and quantify the effect of habitat restoration on source-specific mercury bioaccumulation.
In the St. Louis River Area of Concern, an important natural resource management goal is to reduce or eliminate fish consumption advisories by remediating contaminated sediments and restoring aquatic habitat. One of the two contaminants of concern is mercury, derived from historical industrial and sewage effluents, which is distributed heterogeneously in sediments throughout the St. Louis River estuary (SLRE). However, routine monitoring in fish tissue to assess the problem has proven difficult because mercury concentrations vary widely. We hypothesize because mercury is distributed heterogeneously in sediments that differences in habitat use and life history, and potentially mercury source, will have a direct effect on mercury bioaccumulation. Therefore, to understand the potential impact of remediation and restoration on mercury bioaccumulation, we used a combination of carbon, nitrogen, and mercury stable isotopes in aquatic invertebrates and small prey fish (Yellow Perch, shiners) to reconstruct diet, trophic level, and mercury source. Both invertebrates and prey fish had carbon and nitrogen isotopic compositions that were distinct among habitats, indicating location- and species-specific differences in energy pathways. Associated mercury stable isotope analysis revealed how small-scale differences in mercury sources (industrial versus watershed) are conserved in the food web across different habitat zones of the SLRE. Further, nitrogen stable isotope analysis demonstrated, as expected, mercury bioaccumulation was dependent on trophic level, after correcting for differences in habitat use. The small-scale variation highlights the importance of habitat-scale processes for mercury bioaccumulation and reveals an opportunity to use a multi-isotope approach to document and quantify the effect of habitat restoration on source-specific mercury bioaccumulation.