Evan Wilcox, Brent B. Wolfe, Philip Marsh (2022). Exploring Variability in Thermokarst Lake Water Balances in the Inuvik-Tuktoyaktuk Region using Isotope Tracers. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

Arctic warming is causing precipitation to shift from snowfall to rainfall, permafrost thaw, which is altering the hydrological connectivity of lake watersheds, longer ice-free periods that increase evaporation, and increased vegetation growth, which changes snow redistribution and snowmelt timing. All of these changes are altering thermokarst lake water balances, however the response of lakes to these changes will depend on how watershed properties influence the response lake water balances to varying meteorological conditions. We evaluated how lake and watershed properties and meteorological conditions affected lake water balances by applying water isotope (18O and 2H) methods to water samples from taken 25 thermokarst lakes along the Inuvik-Tuktoyaktuk Highway, Northwest Territories from May-September 2018. Water isotope data was used to estimate the average isotope composition of input waters (dI), and the ratio of evaporation to inflow (E/I). We identified four distinct water balance phases as lakes reacted to changing meteorological conditions. During the freshet phase from May 1 to June 15, the median E/I ratio of lakes reduced from a median of 0.20 to 0.13 in response to freshet runoff and limited evaporation due to lake ice presence. The following warm, dry, and ice-free period from June 15 to July 26, which we designated the evaporation phase, saw E/I increase to a median of 0.19. During the soil wetting phase, E/I did not respond to initial rainfall between July 26 and August 2, as soils absorbed most of the precipitation and contributed minimal runoff to lakes. E/I ratios had reduced to a median of 0.11 after an unseasonably cool and rainy August, which we dubbed the recharge phase. Throughout the sampling period dI remained relatively stable and most lakes contained a greater amount of rainfall-sourced water than snow-sourced water, even after the freshet phase, as a result of snowmelt bypass. The range of average E/I ratios we observed at lakes (-0.01 – 0.43) was relatively small compared to other regions of thermokarst lakes, likely owing to the larger ratios of watershed area to lake area (WA/LA), efficient preferential flow pathways for runoff, and shorter ice-free season present in this region. WA/LA strongly predicted the average E/I ratio of a lake (R2= 0.74), as lakes with smaller WA/LA tended to have higher E/I ratios because they received relatively less inflow. If future permafrost thaw and warming cause less runoff to flow into lakes, we expect that lakes with smaller WA/LA will be more influenced by increasing evaporation.

AOSM2022 NWF First Author: Evan Wilcox Additional Authors: Brent B. Wolfe, Wilfrid Laurier University, Philip Marsh, Wilfrid Laurier University