Impacts of retrogressive thaw slump disturbances on biological structure and function in Arctic streams, Peel Plateau, NWT
University of New Brunswick
The northwestern Canadian Arctic has undergone a period of rapid warming which has promoted the formation of thermokarst across the region. Among the most dramatic thermokarst features are retrogressive thaw slumps - large depressions of melted permafrost that form on the landscape. Thaw slumps often flow into nearby streams, driving increases in sediments, nutrients, and major ions. The Peel Plateau, Northwest Territories has seen an increase in the size and frequency of thaw slumps associated with increases in precipitation and warmer air temperatures. Thus, it is important to evaluate the impacts of thaw slump disturbance on the structure and function of biological communities as they are strongly linked to water quality. Chin et al. (2016)1 performed an extensive survey of thaw slump impacts on benthic macroinvertebrate (BMI) communities in the Peel Plateau and found a negative relationship between thaw slump disturbance and abundance, but were lacking information on minimally-disturbed sites. The aim of the present research was to build on Chin et al. (2016) by evaluating primary production and decomposition and looking at patterns in BMI community structure and function at undisturbed and minimally-disturbed sites in the same region. Minimally-disturbed sites showed stronger nutrient effects than the highly-disturbed sites sampled in Chin et al. (2016), but sediments were still the main drivers of change in impacted streams. Total suspended solids strongly reduced primary production and BMI abundance, while decomposition was driven by nutrients, temperature and pH. Finally, BMI drift densities were lower at thaw-slump impacted sites, but the proportion of drifting BMIs increased with higher rates of settling sediments. The present study suggests that thaw slumps are non-selective and chronic stressors of stream food webs in the Peel Plateau, NWT.