Persistent net release of carbon dioxide and methane from an Alaskan lowland boreal peatland complex

Abstract

Permafrost degradation in peatlands is altering vegetation and soil properties and impacting net carbon storage. We studied four adjacent sites in Alaska with varied permafrost regimes, including a black spruce forest on a peat plateau with permafrost, two collapse scar bogs of different ages formed following thermokarst, and a rich fen without permafrost. Measurements included year‐round eddy covariance estimates of net carbon dioxide (CO2), mid‐April to October methane (CH4) emissions, and environmental variables. From 2011 to 2022, annual rainfall was above the historical average, snow water equivalent increased, and snow‐season duration shortened due to later snow return. Seasonally thawed active layer depths also increased. During this period, all ecosystems acted as slight annual sources of CO2 (13–59 g C m−2 year−1) and stronger sources of CH4 (11–14 g CH4 m−2 from ~April to October). The interannual variability of net ecosystem exchange was high, approximately ±100 g C m−2 year−1, or twice what has been previously reported across other boreal sites. Net CO2 release was positively related to increased summer rainfall and winter snow water equivalent and later snow return. Controls over CH4 emissions were related to increased soil moisture and inundation status. The dominant emitter of carbon was the rich fen, which, in addition to being a source of CO2, was also the largest CH4 emitter. These results suggest that the future carbon‐source strength of boreal lowlands in Interior Alaska may be determined by the area occupied by minerotrophic fens, which are expected to become more abundant as permafrost thaw increases hydrologic connectivity. Since our measurements occur within close proximity of each other (≤1 km2), this study also has implications for the spatial scale and data used in benchmarking carbon cycle models and emphasizes the necessity of long‐term measurements to identify carbon cycle process changes in a warming climate.

Changing climatic controls on the greenhouse gas balance of thermokarst bogs during succession after permafrost thaw

“…Due to decreasing air temperatures late in the growing season and the high thermal diffusivity of saturated peat (Arkhangelskaya & Gvozdkova, 2019), soil temperature at 5 cm in the wetter young bog decrease earlier S1) e.g., potentially accounting for greater cumulative mature bog GPP. While the mature bog had higher cumulative GPP, the range of annual GPP observed across the thermokarst bog stages (−105 to −383 g C-CO 2 m −2 year −1 ) was lower than previously reported annual GPP estimates from thermokarst bogs in Alaska (−569 to −574 g C-CO 2 m −2 year −1 ; Euskirchen et al, 2024), and wetlands across the boreal region (−406 g C-CO 2 m −2 year −1 ; Virkkala et al, 2021). Our lower annual estimates of GPP in the young and intermediate bogs may be due to surface inundation conditions present at our site, which were rarely found in Alaskan thermokarst sites (Euskirchen et al, 2024).…”

WetCH4: A Machine Learning-based Upscaling of Methane Fluxes of Northern Wetlands during 2016–2022

“…Gaps in winter SMAP data were filled with zero values to represent frozen soils for upscaling. Soil moisture has been identified as one of the important, controlling factors of freshwater wetland CH4 fluxes (Euskirchen et al, 2024;Voigt et al, 2023). Passive microwave radiometermeasured brightness temperature was merged with estimates from the GEOS Catchment Land Surface and Microwave Radiative Transfer Model in a soil moisture data assimilation system, to generate global products of surface and rootzone soil moisture (Reichle et al, 2017).…”

Thermal and hydrological limitations on modeling carbon dynamics at wetland sites of discontinuous and continuous permafrost extent

“…Sites in Alaska, fitting these criteria, were found through the ABCFlux database (Virkkala et al 2021) shown in Figure 1. The pair of moist and wet sites in discontinuous permafrost belong to the Alaskan Peatland EXperiment (Turetsky et al 2023;Euskirchen et al 2024)…”