Isotopic constraints on water balance of tundra lakes and watersheds affected by permafrost degradation, Mackenzie Delta region, Northwest Territories, Canada

Chengwei Wan; John J Gibson; Daniel L Peters

doi:10.1016/j.scitotenv.2020.139176

Isotopic constraints on water balance of tundra lakes and watersheds affected by permafrost degradation, Mackenzie Delta region, Northwest Territories, Canada

Sci Total Environ. 2020 Aug 20:731:139176. doi: 10.1016/j.scitotenv.2020.139176. Epub 2020 May 5.

Authors

Chengwei Wan¹, John J Gibson², Daniel L Peters³

Affiliations

¹ State Key Laboratory of Hydrology - Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China; Department of Geography, University of Victoria, P.O. Box 3060 STN CSC, Victoria, BC 11 V8W 2Y2, Canada; InnoTech Alberta, 3- 4476 Markham Street, Victoria, BC V8Z 7X8, Canada.
² Department of Geography, University of Victoria, P.O. Box 3060 STN CSC, Victoria, BC 11 V8W 2Y2, Canada; InnoTech Alberta, 3- 4476 Markham Street, Victoria, BC V8Z 7X8, Canada. Electronic address: jjgibson@uvic.ca.
³ Department of Geography, University of Victoria, P.O. Box 3060 STN CSC, Victoria, BC 11 V8W 2Y2, Canada; Watershed Hydrology & Ecology Research Division, Water Science and Technology Directorate, Environment and Climate Change Canada, University of Victoria, P.O. Box 3060 STN CSC, Victoria, BC 11 V8W 3R4, Canada.

PMID: 32428755
DOI: 10.1016/j.scitotenv.2020.139176

Abstract

Widespread permafrost degradation in Canada's western Arctic has led to formation of shoreline retrogressive thaw slumps (SRTS), a process influential in modifying water and biogeochemical balances of tundra lakes. To investigate hydrological effects of SRTS, water sampling campaigns were conducted in 2004, 2005, and 2008 for paired lakes (undisturbed vs SRTS) in the upland region adjacent to the Mackenzie Delta, Northwest Territories, Canada. An isotope mass balance model to estimate evaporation/inflow, precipitation/inflow, water yield, and runoff ratio was developed incorporating seasonal evaporative drawdown effects and a mixing model to simulate gradients in marine-continental atmospheric moisture. Site-specific water balance results revealed systematically higher evaporation/inflow and precipitation/inflow for lakes with active SRTS compared to undisturbed lakes, and typically higher ratios of these indicators associated with stabilized versus active SRTS. Water yields were higher for active SRTS sites compared to undisturbed and stabilized SRTS sites, suggesting that slumping is an initial but not a sustained source of water delivery to lakes. Catchments with wildfire history were found to have lower water yields, attributed to reduced permafrost influence on runoff generation. Conceptually, we define a permafrost thaw trajectory whereby undisturbed sites, active SRTS, stabilized SRTS, and ancient SRTS represent progressive stages of permafrost thaw. We postulate that release of additional runoff is mainly due to permafrost thaw in active SRTS, which also promotes lake expansion, talik formation, and subsurface connectivity. Eventual stabilization of slumps and reduced runoff is expected once permafrost thaw sources are exhausted, at which time lakes may become more reliant on replenishment by direct precipitation. The effect of snow catch in slumps appears to be subordinate to permafrost thaw sources based on eventual decline in runoff once thaw slumps stabilize. Improved, site-specific hydrologic understanding is expected to assist with ongoing research into carbon cycling and biogeochemical feedbacks in the region.

Keywords: Isotope mass balance; Mackenzie delta region; Permafrost; Thaw slumps; Thermokarst lakes.