The impacts of permafrost thaw slump events on limnological variables in upland tundra lakes, Mackenzie Delta region

Thawing permafrost is widespread in Canada's western Arctic. In upland tundra situated north of Inuvik (NWT), ice-rich permafrost is thawing to form retrogressive thaw slumps, a process that transports large volumes of previously frozen inorganic material to adjacent lakes. Prior studies have indicated base water chemistry changes in slump-affected lakes, including lower dissolved organic carbon (DOC) and increased major ion concentrations. Here we demonstrate significant reductions in DOC and colour, and increases in water clarity as a function of the percent of catchment area disturbed by slumping. The influx of thawed sediments and solutes leads to ionic enrichment, and direct loading of several trace metals, including uranium, strontium, and lithium. The influx of ion-rich sediments from thaw slumps is associated with higher pH, and lower concentrations of several biologically important metals, including Fe, Mn, and Al, in the water column. The sedimentation of organics and particulates from the water column is a probable driver for the removal of major nutrients (N and P) leading to significantly lower planktonic chlorophyll-a (Chl-a) concentrations in thaw slump affected lakes by as much as two thirds when comparing the most thaw slump affected lakes to reference lakes. Both phytoplanktonic and periphytic algal measurements indicate greater reductions in primary production in active slump-affected lakes as opposed to stabilized slump-affected lakes. We also highlight the slump-driven reduction in Chl-a concentrations relative to 11 other studies across Canada's low Arctic as well as other ecotypes. In these already nutrient-poor systems, future warming-accelerated thaw slumping will likely reduce overall primary production and alter the limnological characteristics in similar tundra systems.