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Abstract Title: Spatiotemporal Variability and Climate Change Impacts on Methylmercury Cycling in an Arctic Catchment
Presenter Name: Igor Lehnherr
Company/Institution: University of Toronto
Session: Special Session - Climate-Driven Perturbations of Arctic Mercury Cycling
Co-Authors: Igor Lehnherr,Stephanie Varty,Kyra St. Pierre,Jane Kirk,Victoria Wisniewski

Abstract Information :

The presence of toxic methylmercury (MeHg) in Arctic freshwater ecosystems and foodwebs is a potential health concern for northern Indigenous people. Addressing this issue requires a better understanding of MeHg production, fate during transport, and uptake into foodwebs. We used methylation assays and spatiotemporal surveys of MeHg concentrations, during the ice-covered and open water seasons, across a hydrologic continuum (composed of thaw seeps, lake/ponds, and a wetland) to identify Hg methylation hotspots and seasonal differences in MeHg cycling unique to Arctic ecosystems. Ponds and saturated wetland soils support methylation hotspots during the open water season, but subsequent export of MeHg to downstream ecosystems is limited by particle settling, binding of MeHg on soil organic matter, and/or demethylation in drier wetland soils. During the ice-covered season, MeHg concentrations in lake waters were approximately ten-fold greater than in summer; however, zooplankton MeHg concentrations were paradoxically five times lower at that time. Despite limited evidence of snow-phase methylation, the snowpack is an important MeHg reservoir. The contrast between the ice/snow-covered and open water seasons, as well as the difference in meteorological and hydrologic conditions between sampling years, provide useful indications of how climate change will continue to alter MeHg cycling in non-glaciated Arctic catchments. Changes in ice-cover duration will alter MeHg production and bioaccumulation in lakes, while increased thaw and surface water flow will likely result in higher methylation rates at the aquatic?terrestrial interface and more efficient downstream transport of MeHg.

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