Examining Responses of Thermokarst Lake Water Chemistry to Climate and Landscape-Driven Influences in Old Crow Flats, Yukon, Canada

Lake-rich permafrost landscapes are sensitive to climate change, which has intensified during recent decades. Old Crow Flats (OCF), Yukon, Canada, a 14,500-km2 watershed containing over 8700 thermokarst lakes and ponds, is the traditional territory of the Vuntut Gwitchin First Nation who are concerned with how landscape changes are altering lake ecosystems and downstream environments. Recent research shows that lakes in OCF are receiving more rainfall during recent years in response to lengthened thaw seasons. This may be altering carbon (C) cycling, which is important to investigate given potential implications for downstream environments and climate change feedbacks. Using a 15-year water chemistry record and 5-year carbon isotope (δ13C-DOC and δ13C-DIC) record, we evaluate relations among hydrological change, catchment properties, and C cycling in 14 long-term monitoring lakes. Since 2007, spring dissolved organic carbon (DOC) concentrations significantly decreased in 2 lakes while dissolved inorganic carbon (DIC) concentrations significantly increased for 3 lakes and decreased for 2 lakes. The significant change in DOC and DIC concentrations were likely due to changes in flow paths (i.e., catchment surface versus subsurface inputs). Stable isotope ratios of C help to explain these differences by source identification. For spring samples, a weak significant positive relationship exists for δ13C-DIC and lake area to catchment area ratio (LA/CA), which is likely due to greater inputs of biogenic C from the larger catchments. Lakes occupying larger portions of their catchments showed greater average seasonal declines in δ13C-DIC from -3.4‰ to -6.4‰ indicating increased portion of δ13C-DIC from atmospheric CO2 and mineral weathering over the ice-free season. This research underscores the complexity of C cycling and the need to maintain long-term monitoring of relations among climate, landscape characteristics, and surface water across important permafrost landscapes. The application of stable isotope techniques provides insight into temporal trends that cannot be explained by concentration alone.