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A multi-stable isotope approach to determine mercury sources in migratory and resident coastal fishes
Citation:
Janssen, S., J. Hoffman, R. Lepak, B. Monson, G. Peterson, A. Cotter, G. Hanson, AND D. Krabbenhoft. A multi-stable isotope approach to determine mercury sources in migratory and resident coastal fishes. Coastal and Estuarine Research Federation, Mobile, AL, November 03 - 07, 2019.
Impact/Purpose:
An important final ecosystem service provided by coastal habitats is fish that are caught either for consumption or recreation. This service is diminished where fish are contaminated, resulting in fish consumption advisories. Remediation for specific contaminants is challenging if the contaminant originates from multiple sources. Here, we demonstrate the application of a suite of a tracers to identify how differences sources of mercury, including legacy mercury in aquatic sediments associated with past industrial activities, contribute to bioaccumulation in a coastal ecosystem. We conclude the technique has strong potential to evaluate remedy effectiveness in mercury clean-up sites.
Description:
In coastal ecosystems such as urban estuaries and coastal wetlands, it is difficult to infer the sources of mercury (Hg) to fish owing to multiple potential Hg inputs (e.g. precipitation, legacy, or upstream runoff). The aim of this study was to utilize Hg stable isotopes along with carbon and nitrogen stable isotopes to elucidate Hg sources to the St Louis River food web, including benthic invertebrates, prey fish, and game fish. Invertebrates and resident prey fishes from the St Louis River exhibited Hg isotopic fingerprints similar to Hg-contaminated sediments (ä202Hg = -0.6 to -0.4), indicating bioaccumulation of legacy Hg. In contrast, migratory game fishes displayed greater variability in Hg stable isotope ratios, with some individuals exhibiting highly enriched signatures (ä202Hg = 0.8 to 1.2) compared to prey species, likely due to precipitation. Relationships between ä202Hg and ä13C values of migratory fish revealed that substantial variability was related to foraging between coastal tributary and open coastal habitats. Further, relationships between Hg concentration and ä15N values among resident fishes reveal expected bioaccumulation patterns based on trophic level, but were influenced by the amount of foraging between coastal tributary and open coastal habitats based on ä13C values. This indicates that legacy Hg is the prevalent source to smaller fish species in the St Louis River, but larger, migratory species can be exposed to different Hg sources and bioaccumulate Hg at different rates based on foraging habitats. We conclude the approach paves the way for source- and habitat-specific consideration of Hg management activities.