Dissolved Organic Carbon Mobilization and Degradation Patterns in Retrogressive Thaw Slumps of the Peel Plateau, Northwest Territories, Canada

Abstract

Anthropogenic climate change has affected the Canadian Arctic cryosphere, accelerating the development of retrogressive thaw slumps (RTS) across the Peel Plateau, NWT, Canada. RTS result from the thawing of ice-rich permafrost and develop due to ablation of ground ice exposed in the slump headwall. RTS provide pathways for dissolved organic carbon (DOC), previously inaccessible when stored in permafrost, to become available for biologically or photochemically-mediated degradation; creating a relatively novel input source to the global carbon cycle. The Peel Plateau, which is comprised of ice-rich glaciogenic materials and soils that are rich in inorganic materials, exhibits a high occurrence of RTS activity. RTS activity in the Peel Plateau is predicted to alter the carbon dynamics of receiving waters in ways that contrast with the effects of permafrost slumping in Arctic regions containing organic-rich soils. Here, we explore the environmental drivers and absolute magnitude of DOC delivery to impacted stream systems, and the susceptibility of this DOC to biological degradation. This work determined that temperature and precipitation are the main drivers of DOC mobilization across the Peel Plateau; environmental variables that are predicted to increase considerably across Arctic regions. Pristine streams demonstrated higher concentrations of DOC than streams impacted by slump runoff, an effect that seems likely to occur as a results of DOC adsorption to slump particles. DOC from RTS streams was more susceptible to bacterial degradation, though at lower rates than those found in other thermokarst impacted regions. Spectral and isotopic characteristics of RTS-affected and pristine streamwater were examined to explore how differences in DOC origin and composition relate to decomposition. Permafrost DOC response to climate change has been identified as one of the key knowledge gaps in predicting how integrated Arctic systems will function in the future. This work aimed to close this gap through the monitoring of the flux and fate of DOC mobilized from slump features in an understudied region.