Heidi Swanson, Mike Low,George Low, Brian Branfireun, Leanne Baker (2022). Understanding mercury cycling in subarctic lakes in the Dehcho region. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

For mercury (Hg) to accumulate and magnify in aquatic ecosystems, it must be first be methylated to form methylmercury (MeHg). For the past several decades, we have focused on what we thought were the primary sites of methylation in lakes – that is, deep, profundal, anoxic sediments that support the sulphate-reducing and iron-reducing (among other types) bacteria known to methylate mercury. Recent work (last ~7 years) by leaders in the discipline have shown, however, that methylation may occur in a range of different habitats, including shallow littoral areas, and in biofilms and periphyton. This has profound implications for our understanding of how climate-induced changes to lake physicochemistry will affect mercury cycling and accumulation. In this talk, I will present results from subarctic and Arctic lakes in the Northwest Territories and Alaska that suggests that dominant or at least important sites of mercury methylation occur in what might be considered ‘unconventional’ habitats. Concentrations of mercury in water, benthic invertebrates, and sediments will be discussed, and placed in the context of results from recent structural equation modeling exercises that reveal how catchments are related to lake chemistry, fish ecology, and fish mercury concentrations in subarctic lakes in the Dehcho, NT. Findings from ~ 10 years of research in the Dehcho region inform our understanding of effects of warming water temperatures and changing catchments on mercury cycling in these ecosystems, and how to design future experiments and empirical studies. Links and knowledge gained from Indigenous Guardians and research partnerships will also be discussed.

First Author: Heidi Swanson, University of Waterloo
Additional Authors: Mike Low, Dehcho First Nations, George Low, Dehcho First Nations, Brian Branfireun, Western University, Leanne Baker, ERM Consultants