TRACKING PEAT SUBSIDENCE AND AQUATIC ECOSYSTEM CHANGE IN THE DISCONTINUOUS SPORADIC PERMAFROST ZONE (NORTHWEST TERRITORIES, CANADA) USING ORGANIC BIOMARKERS PRESERVED IN LAKE SEDIMENT CORES

Northern boreal ecoregions globally are experiencing a rapid loss of permafrost in response to climate warming, with many implications for aquatic ecosystems. In particular, permafrost thaw in these organic-rich landscapes is expected to increase the transport of allochthonous carbon and catchment-derived contaminants such as mercury to lakes. In the Great Slave lowlands region of the southern Northwest Territories, the subsidence of permafrost-supported peat plateaus can cause pronounced hydrological changes that alter run-off of terrestrial organic matter from the catchment to aquatic ecosystems. Aquatic ecosystems are greatly influenced by terrestrial organic matter inputs, which influences many lake processes, such as the depth of light penetration, thermal stratification, and the bioavailability of contaminants. Consequently, understanding the long-term trajectory of changes in terrestrial organic matter inputs to boreal lake ecosystems has been highlighted as an important avenue for future research. In this study, we analyzed plant biomarkers and other geochemical proxies in sediment cores from two lakes in the southern Northwest Territories that have documented extensive peat subsidence in the catchment in recent years, to provide a long-term perspective on permafrost thaw and allochthonous carbon inputs. We observed changes in the quantity and source of terrestrial organic matter entering lakes, and documented relationships between allochthonous carbon inputs and mercury accumulation in the sediments. In one lake, an increase in terrestrial organic matter inputs was associated with ecological changes in aquatic biota indicative of decreased water clarity. This research demonstrates how the use of organic biomarkers can advance our understanding of the transformative changes occurring in watersheds in permafrost-supported northern boreal forests as a result of climate warming.