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Characterizing sources, biogeochemistry, and accumulation of Hg in food webs of the St. Louis River Area of Concern.
Citation:
Hoffman, J., M. Mills, G. Peterson, M. Pearson, T. Angradi, D. Walters, M. Elliot, S. Janssen, J. DeWild, D. Krabbenhoft, AND E. Pilgrim. Characterizing sources, biogeochemistry, and accumulation of Hg in food webs of the St. Louis River Area of Concern. 2019 SETAC North America Annual Meeting, Toronto, CANADA, November 03 - 07, 2019.
Impact/Purpose:
Presentation covers work we are doing on the St Louis AOC
Description:
The St. Louis River Area of Concern (AOC) was designated in 1987 due to Beneficial Use Impairments (BUIs), including “Restrictions on Fish and Wildlife Consumption” (BUI 1) from historical pollutants. Minnesota and Wisconsin posted fish consumption advisories for the St. Louis River, in part, because fish have elevated mercury concentrations. Mercury bioaccumulation in the food web can be from legacy sources in sediment and from present-day ambient sources (from both local, regional, and global sources). In 2017 a study was conducted which had four goals to support the understanding of Hg sources in the AOC : 1) Compare mercury methylation and bioaccumulation by characterizing the macroinvertebrate assemblages, geochemistry, ecosystem type, and food web structure between the AOC and a reference location (Bad River); 2) Compare age- and size-specific mercury residues in select fish species between the AOC and Bad River; 3) Trace food web pathways and identify mercury sources in select fish species using stable isotopes of carbon and nitrogen. 4) Develop a mercury-specific BUI restoration target for the AOC derived from the long-term, post-remediation projected change in fish mercury residues based on the inferred differences in mercury-source bioaccumulation between the AOC and Bad River. For each location, up to five samples each were collected for mayfly (Hexagenia) larvae, dragonfly larvae, riparian spiders, and a composite benthic invertebrate assemblage sample using multi-plate artificial substrate samplers. We deployed artificial substrates to collect macroinvertebrates in order to assess Hg accumulation and biotic condition across the St. Louis AOC and Bad River. When artificial substrates were retrieved, 12 of 14 were disassembled, scraped, sieved and then picked for biomass. The remaining two samplers were set aside for identification and metabarcoding to assess similarity in benthic communities. Macroinvertebrate assemblage (traditional identification and metabarcoding), stable isotope analyses, water, sediment and biota mercury, plus other water quality analyses will be presented and discussed.