Gulf of Alaska | Ecosystem Perspectives
Tracking the fate of mercury in downstream freshwater habitats affected by rapid deglaciation in Alaska using stable isotopes
Presenter: Drew Porter , dporter13@alaska.edu, University of Alaska Fairbanks Matthew Wooller , mjwooller@alaska.edu, University of Alaska Fairbanks Michelle Trifari , mtrifari@alaska.edu, University of Alaska Fairbanks Katrin Iken , kbiken@alaska.edu, University of Alaska - Fairbanks Anne Beaudreau , annebeau@uw.edu, University of Washington Benjamin Barst , bdbarst@alaska.edu, University of Alaska Fairbanks
Climate warming is resulting in rapid deglaciation at some locations in Alaska, which is in turn reshaping both streamflow and watershed coverage. The export of non-essential elements, like mercury, into Alaska watersheds and nearshore environments is potentially increasing due to this enhanced level of deglaciation. In this study, we conducted a suite of analyses on mussels ( Mytilus trossulus ) and juvenile coho salmon ( Oncorhynchus kisutch ) collected from 10 coastal Alaska watersheds (5 in Kachemak Bay and 5 along Lynn Canal) that span a gradient of non-glacial to glacial influence. We analyzed tissue samples for total mercury concentrations and compound-specific stable nitrogen isotope values in amino acids. The novel pairing of these techniques enabled determination of total mercury concentrations, trophic positions, and nitrogen isotopic baseline values of individuals in each watershed, therefore revealing linkages between trophic pathways and the concentrations of mercury in these ecosystems. Total mercury concentrations varied by species and location. In general, coho salmon had higher mercury concentrations than mussels did, and individuals of both species from Kachemak Bay watersheds had higher concentrations than conspecifics from Lynn Canal watersheds. Notably, total mercury concentrations were higher in mussels from watersheds with more glacial coverage relative to individuals from less glaciated areas, a trend that suggests mercury contamination of these sedentary filter feeders is being driven by watershed export. Further, total mercury concentrations of coho salmon were not correlated with trophic position, suggesting that differences in mercury concentrations were driven by feeding location rather than trophic level differences. Nitrogen isotope values of phenylalanine from both salmon and mussels were different among watersheds, indicating baseline variation in sources of nitrogen supporting each ecosystem. Our study will also use compound-specific stable isotope analysis of carbon in amino acids to resolve the primary production sources supporting these species and the degree of terrestrial input in each study watershed. The results of this project will reveal how deglaciation is influencing mercury export to nearshore environments in Alaska.
Alaska Marine Science Symposium 2023 163
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