Long-term perspectives on aquatic ecosystem change with thawing permafrost

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Approximately 25% of all lakes globally are located in permafrost regions, and these lakes are among the most vulnerable to climate warming through accelerated rates of permafrost thaw. A long-term perspective is needed to understand how lake ecosystems are responding to permafrost degradation, in order to place recent changes in the context of natural ecosystem variability. My research will use lake sediment cores to reconstruct lake histories (centennial to millennial timescales), in order to address key knowledge gaps in our understanding of the responses of lake ecosystems to the transformative landscape changes occurring as a result of permafrost thaw. I will explore long-term aquatic ecosystem changes under two contrasting scenarios of thawing permafrost in Canada’s Northwest Territories. The first scenario focuses on lakes at the southern limit of permafrost (near Hay River), where thawing permafrost leads to the conversion of forested permafrost-supported peat plateaus into wetlands. These landscape changes alter terrestrial carbon run-off to lakes, which has implications for carbon and contaminant cycling, and ecological interactions among aquatic biota. The second scenario examines a spectacular form of permafrost degradation, retrogressive thaw slumps that form on the shorelines of lakes in areas of high ground-ice content, such as near Inuvik, NT. Thaw slump development releases large amounts of inorganic material (such as clay particles) to lakes, which scavenges organic carbon and nutrients out of the water column, and increases water clarity. The increase in water clarity following thaw slumping may increase the exposure of aquatic biota to harmful UV radiation, a potential stressor in slump-impacted lakes that has yet to be thoroughly investigated. The study of lake histories on millennial timescales, under both permafrost thaw scenarios, will allow me to reconstruct ecosystem conditions during past warm periods as a frame of reference from which to evaluate current conditions under recent human-induced climate warming. The north hosts an abundance of freshwater resources, and permafrost thaw will continue to intensify as a stressor on these ecosystems. By examining lake responses to this stressor over varying temporal and spatial scales, my research will provide insights into the fate of aquatic food webs under future climate warming, contributing to the protection of healthy and diverse aquatic ecosystems in northern Canada.