The hydrology of northern boreal lakes in the Taiga Shield and Plains, Northwest Territories and the importance of catchment characteristics in mediating responses to climate

Abstract

Freshwater lakes are prominent features across northern boreal regions and are sensitive to changing climate conditions. This study, spanning the 2017-18 ice-free seasons, broadens our understanding of how variable climate and landscape conditions influence subarctic lake hydrology in the North Slave Region near Yellowknife, Northwest Territories (NT), Canada. We studied 20 lakes located within the Taiga Shield and Taiga Plains ecozones through an integrated approach, utilizing water isotope tracers (δ2H and δ18O), lake level changes, local meteorological conditions and remotely sensed catchment data. Lake water isotope data were obtained twice during the ice-free season (May and August) and evaporation/inflow (E/I) ratios were calculated to identify the relative importance of catchment hydrological controls. Hydrological data were compared to measured and modelled catchment characteristics, including relative lake/catchment size, slope, land cover and recent wildfire burn area. Overall, precipitation was a major driver of seasonal and interannual lake hydrological change, while evaporation was a major driver of summer water loss. Relative catchment size (lake area to catchment area (LA/CA)) was found to be an important driver of lake hydrology, however, this relationship is complicated by storage deficits associated with variable meteorological conditions. During wet conditions (e.g., freshet and periods of high rainfall), lakes with larger catchments (low LA/CA) had more positive water balances than lakes with high LA/CA. Under drier conditions, lake catchment size and associated fill-and-spill hydrological connectivity was reduced. Lake basins with high LA/CA (particularly those with shallower depth and greater surface area) were more prone to evaporative water loss. Lake hydrological conditions were less influenced by catchment land cover compositions, including burn area. Findings presented here highlight important drivers of lake water balances in subarctic boreal regions, which are sensitive to ongoing changes in climate. This study is part of a broader research project funded and supported by NWT Cumulative Impact Monitoring Program (CIMP), which is using a multi-proxy, paleo-ecological approach to determine long-term (i.e., 2,000 years) records of hydrology, drought, fire and water quality to inform future policy planning.