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Tracking changes in permafrost thaw slumps between 2005 and 2017 on lakes in the Mackenzie Delta Uplands

Tracking changes in permafrost thaw slumps between 2005 and 2017 on lakes in the Mackenzie Delta Uplands

Claire O'Hagan

The Arctic is warming at more than double the global rate, increasing stress on landscapes and ecosystems. Permafrost, defined as ground that is continuously below 0°C for at least two consecutive years, is degrading rapidly in response to warming air temperatures and altered precipitation regimes, representing a formidable threat to the Arctic landscape.  Claire O’Hagan, a 4th year Geography student, was awarded an NSERC Undergraduate Student Research Award to study permafrost thaw in the Mackenzie Delta Region (Northwest Territories, Canada) under the supervision of EUC Prof. Jennifer Korosi.

Claire’s research focuses on a dramatic type of permafrost thaw referred to as thermokarst. Thermokarst refers to processes and landforms arising from land surface collapse, as a result of melting ground ice. Specifically, Claire is researching decadal-scale trends in retrogressive thaw slump activity on lake shorelines in the uplands east of the Mackenzie Delta. Retrogressive thaw slumps are a mass wasting (i.e. landslide) features that occur as a result of melting of ground ice. They are visible as C-shaped scars on the shorelines of lakes that cause mud to erode downslope into the adjacent lake, resulting in water quality degradation

Claire used remote sensing to document the presence and size of retrogressive thaw slumps on 66 lakes based on 2017 SPOT (1.5-m resolution) satellite imagery and compared it against slump mapping data available for the same lakes from 2005. Her research aims to determine how slump size and frequency of slumps changed between 2005 and 2017, and whether thaw slump activity intensified since 2005 in response to continued climate warming. Lakes were categorized as: (1) active slumps, where the slump continues to grow; (2) stable slumps, where the slump is no longer growing, and revegetation of the slump scar is evident; (3) ancient slumps that have been stable long enough to have fully revegetated scars; and (4) reference lakes that have no history of thaw slumping. Claire also measured slumps in hectares and as percent of the catchment impacted by slumping.  

Examples of retrogressive thaw slumps.

Claire found that there were there were 11 active slumps, and 22 stable slumps in 2017 compared to 20 active slumps, and 13 stable slumps in 2005. Between 2005 and 2017, 4 stable slumps reinitiated, 2 reference lakes developed slumps, and 6 active slumps stabilized. Slumps that were active in both 2005 and 2017 showed an increase in slump size from 0.41% up to 10.8% of the catchment. 16 of the 66 study lakes had slumps that were stable in both 2005 and 2017.

The overall number of active slumps was less in 2017 compared to 2005, indicating slump activity has not intensified; however, the re-initiation of stable slumps and the formation of slumps on lakes where they weren’t present before indicates that retrogressive thaw slump activity remains high, driving continued changes to the topography and water quality of the region.

Claire’s research supports ongoing work by EUC professors Jennifer Korosi and Joshua Thienpont to understand the impacts of retrogressive thaw slumps on lake water quality and ecosystem health. For example, her lake classifications are being used to identify candidate study lakes to examine lake recovery trajectories and timelines following slump stabilizations. With permafrost thaw rates expected to accelerate in future decades, continued monitoring and research is critical for understanding the cascading impacts to Arctic freshwater ecosystems.