The Impacts of Thermokarst and Burn History on the Composition of Dissolved Organic Matter in the Yukon Kuskokwim Delta

Permafrost thaw from rapid warming across the Arctic can cause ground collapse, significantly altering the geomorphology of the landscape. Evolving conditions from rapid warming have also increased the frequency, severity, and magnitude of tundra wildfires. While prior studies have enhanced our understanding of the singular impacts of permafrost thaw and wildfires, the combined impact of these two disturbances on carbon cycling are not well understood. To assess the joint effects of thermokarst processes and wildfire on carbon processing, we examined the concentrations, composition (CDOM), and biolability of dissolved organic carbon (DOC) leached from soils from thermokarst exposures and undisturbed control sites within a recent burn (2015), an older burn (1972), and unburned areas in the Yukon-Kuskokwim Delta, AK. Biolability was measured as the percent loss of DOC throughout a 28 day incubation in dark, oxic conditions. We hypothesize that water flowing through the active layer of these regions can be impacted by the combined effects of thermokarst processes and burn history. If we find that biolability is higher in thermokarst areas, thus indicating faster processing of the higher concentrations of dissolved organic matter (DOM) found in these soils, it could lead to the potential increased flux of carbon to the ecosystem. This would be compounded in thermokarst soils from burned regions, as there is more DOC present from fire history, and this DOC would have high lability. This increased flux of carbon can have substantial implications for landscape stability regionally and future climate trends globally. It is crucial to further examine the relationship between wildfire, thermokarst, and the carbon cycle.