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Abstract Title: Physiochemical Controls of Mercury in a Large, Sub-Arctic Lake and Its Tributaries
Presenter Name: Taylor Luu
Company/Institution: University of Toronto
Session: Mercury in Freshwater Ecosystems
Co-Authors: Taylor Luu,Brian Branfireun,Igor Lehnherr,Heidi Swanson

Abstract Information :

Freshwater lakes in the Arctic and sub-Arctic are an important source of food for northern communities. These ecosystems face several threats, including contamination by mercury (Hg) that is atmospherically transported long distances from industrial sources. In aquatic environments, Hg can be converted to the neurotoxin methylmercury (MeHg), which can bioaccumulate and biomagnify up food webs to attain elevated levels in top predators, including fish, that are concerning for human consumers. Mercury methylation and accumulation can be influenced by many factors, including the quantity and quality of dissolved organic matter (DOM) in glacial and freshwater inputs. Lh—?……n Mƒn (Kluane Lake) is a large sub-Arctic lake in the Yukon Territory and an important source of food and water for local Indigenous communities. In 2016, the lake lost its main source of glacial meltwater via a river diversion event, and now receives a fraction of its former input from smaller tributaries. While levels of Hg in fish in Lh—?……n Mƒn are currently extremely low, the loss of glacial meltwater could affect Hg delivery and accumulation in the lake. This deserves further study. We examined a pre-diversion 2015/16 physiochemical dataset of Lh—?……n Mƒn and its tributaries, focussing on Hg concentration and speciation as well as DOM concentration and quality. In the lake, the more productive northern sites exhibited distinctly different sediment Hg and dissolved carbon levels compared to the formerly glacially affected southern sites, while lake and tributary water MeHg levels were mostly below detection limits. Water THg was affected by catchment inputs: lake water THg was negatively correlated with sulfate, and tributary water THg was primarily bound to terrigenous DOM. These results will inform a future sampling campaign of a post-diversion dataset, which will help determine changes related to the loss of glacial inputs and possible effects on environmental and biotic Hg levels.

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