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Abstract Title: Understanding Mercury Accumulation through Food Webs in Subarctic Lakes
Presenter Name: Heidi Swanson
Company/Institution: University of Waterloo
Session: Communities, Hg and Climate Change
Co-Authors: Heidi Swanson,Mehdi Moslemi-Aqdam

Abstract Information :

Lakes in the subarctic Dehcho region of the NT, Canada, support fish populations that are critical for food security in Indigenous communities. While it has been known for some time that mercury (Hg) concentrations in subsistence food fishes vary considerably among lakes in the region, it was not known why mercury concentrations vary so widely. Addressing this knowledge gap is a key priority for communities who wish to also better understand how climate change may affect fish mercury concentrations. From 2013-present, we have undertaken a joint community-research project that aims to elucidate causes of among-lake variation in fish mercury concentrations, how changes on the landscape (e.g., permafrost thaw) may affect fish mercury concentrations. Together, Indigenous Guardians and University researchers have collected water, sediment, benthic invertebrates, zooplankton, and fish from 13 remote lakes that span 66 000 km2. Total and methyl mercury (MeHg) concentrations, chemistry (water, sediment), stable isotope ratios (fish), and growth rates (fish) have been analyzed from collected samples. Catchment attributes (e.g., vegetation cover, size, slope, etc) have also been quantified. Results indicate that the best proximate predictors of Hg concentrations in Northern Pike (Esox lucius) are fish growth rate and MeHg concentrations in prey. Results of a structural equation modeling exercise indicate that variability in these proximate drivers is best predicted by dissolved organic carbon concentrations in lake water and Hg concentrations in lake water and sediment, respectively. Abiotic chemistry variables are in turn predicted by catchment size, elevation, and vegetation composition. Our model explains >80% of among-lake variability in Hg concentrations in Northern Pike. Lake-specific rates of biomagnification explain additional variability. Results also indicate that littoral environments may be considerable sources of MeHg in these lakes. This unique comprehensive, long-term, community-driven, and ecosystem-scale study is revealing catchment-lake-fish interactions that inform predictions of effects of climate change.

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