Assessing Spatial Patterns and Temporal Trends in Lake Response to Rapid Permafrost Thaw in the Scotty Creek Basin (Northwest Territories, Canada)

Abstract

Aquatic ecosystems at the southern limit of permafrost are highly sensitive to climate warming, including dramatic alterations of the landscape resulting from thawing of permafrost. In the southern Northwest Territories (NT), permafrost is typically restricted to forested peat plateaus, that are elevated above the surrounding wetland complex. As mean annual air temperatures approach 0°C, permafrost thaw can result in collapsed peat plateaus and waterlogged trees. These landscape changes can alter the connections between water bodies and the amount of terrestrial organic matter that enters these ecosystems, potentially contributing to the “browning” of lakes. Understanding how lakes in the southern NT have been responding to the acceleration of permafrost degradation is challenged by the scarcity of monitoring records. The Scotty Creek basin, southern NT, is an ideal location to study linkages among shallow lake limnology, landscape hydrology, and landscape change in thawing permafrost peatlands as three decades of field research has provided a unique long-term perspective on watershed changes rarely available for remote regions. For this dissertation, paleolimnological methods were applied to indirectly reconstruct long-term environmental change, using chemical and biological proxy data preserved in lake sediments from lakes in or near the Scotty Creek basin. Modern diatom ecology was assessed to improve diatom-based paleolimnological inferences of changes over time, and applied in a multi-proxy paleolimnological approach to investigate regional lake ecosystem changes over the past few hundred years. Two key findings emerged from the research: (1) dissolved organic carbon (DOC) quality, rather than DOC quantity, was a key driver of spatio-temporal variability in lake change; and (2) most lakes experienced only modest changes despite the widespread prevalence of permafrost degradation. This research presents a necessary step for integrating lakes into the ecohydrological research network at the Scotty Creek Research Station.