Contrasting Responses of Carbon Dioxide and Methane Fluxes Following Thermokarst Erosion Across Tundra‐Lake Interfaces in the Western Canadian Arctic

Abstract

Erosion from ice‐rich permafrost thaw (“thermokarst”) alters tundra vegetation cover and soil moisture, and laterally transports organic material into lakes, altering net fluxes of carbon dioxide (F _CO2 ), methane (F _CH4 ), and nitrous oxide (F _N2O ). Tundra and lakes are rarely examined together, although a joint view is necessary to understand their coupled biogeochemical responses to widespread thermokarst erosion. We aimed to understand the impact of thermokarst erosion on F _CO2 , F _CH4 and F _N2O and their underlying biogeochemical controls across the tundra‐lake interface. We conducted weekly plot‐scale measurements during the growing season (June–August 2022 and 2023) in stable and eroding tundra and adjacent lakes in the Inuvialuit Settlement Region, NT, Canada. Counterintuitively, eroding tundra absorbed more CO ₂ than stable tundra (−64.0 ± 79.7 mg C m ⁻²  h ⁻¹ , n  = 85, vs. −26.7 ± 84.2 mg C m ⁻²  h ⁻¹ , n  = 98; mean ± standard deviation), driven by increased photosynthetic activity and higher soil moisture in vegetated eroding tundra. Stable tundra was a net CH ₄ sink (−0.024 ± 0.027 mg C m ⁻²  h ⁻¹ , n  = 108). This sink capacity increased with an increase in temperature and deepening frost table, but decreased with erosion. Lake F _CH4 was significantly higher from eroding lake shores (2.56 ± 5.65 mg C m ⁻²  h ⁻¹ , n  = 88) compared to stable lake shores (1.05 ± 3.61 mg C m ⁻²  h ⁻¹ , n  = 90). Tundra and lake F _N2O were generally negligible. The contrasting responses of CO ₂ and CH ₄ fluxes highlight the complex effects of thermokarst erosion across the tundra‐lake continuum.