High ebullitive, millennial‐aged greenhouse gas emissions from thermokarst expansion of peatland lakes in boreal western Canada

Abstract

Methane (CH4) and carbon dioxide (CO2) emissions from small peatland lakes may be highly sensitive to climate warming and thermokarst expansion caused by permafrost thaw. We studied effects of thermokarst expansion on ebullitive CH4 and CO2 fluxes and diffusive CH4 fluxes from a peatland thaw lake in boreal western Canada. Ebullitive CH4 fluxes from the thaw edge (236 ± 61 mg CH4 m−2 d−1) were double and quadruple that of the stable lake edge and center, respectively. Modeled diffusive CH4 fluxes did not differ between the thawing and stable edges (~ 50 mg CH4 m−2 d−1) but were double that of the center. Radiocarbon (14C) analysis of CH4 and CO2 bubbles from the thaw edge was older (~ 1211 and 1420 14C yr BP) than from the stable edge and the center (modern to ~ 102 and 50 14C yr BP, respectively). Incubations indicated that deep, old peat sediment was more labile along the thaw edge than in the center. While our study suggested increase CH4 emissions partly derived from millennial‐aged carbon along the thaw edge, accounting for these emissions only increased the estimated total lake CH4 emissions by ~ 10%, which is a much smaller contribution than measured from thermokarst lakes in yedoma regions. Our study suggests that it is important to account for landscape history and lake types when studying the processes that govern the sensitivity of lake greenhouse gas emissions to climate change.

Nitrous Oxide Fluxes in Permafrost Peatlands Remain Negligible After Wildfire and Thermokarst Disturbance

“…In our study, four of five ponds had minor N 2 O uptake similar to the peatland stages. We also found no differences in N 2 O exchange between thermokarst and stable edges, despite previous studies on these ponds found higher CH 4 emissions from thermokarst edges (Kuhn et al, 2022), suggesting different controls on CH 4 and N 2 O emissions in boreal ponds.…”

“…Boreal peatland ponds have been identified as potential hot spots for N 2 O, CH 4 , and CO 2 emissions (Huttunen et al., 2002; Kortelainen et al., 2020; Kuhn et al., 2021) with thermokarst activity enhancing CH 4 and CO 2 emissions (Kuhn et al., 2022). In our study, four of five ponds had minor N 2 O uptake similar to the peatland stages.…”

“…The surroundings of pond L2 were burned in 2007 and L2 was the only pond with a beaver lodge. All ponds had thick organic sediments, up to 4 m depth above the underlying mineral sediment (Kuhn et al., 2022).…”