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 similar to 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 km(2)), 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.

How methane (CH4) fluxes from alpine peatlands, especially during freeze-thaw cycles, affect the global CH4 budget is poorly understood. The present research combined the eddy covariance method, incubation experiments and high-throughput sequencing to observe CH4 flux from an alpine fen during thawing-freezing periods over a period of four years. The response of CH4 production potential and methanogenic archaea to climate change was analyzed. We found a relatively high mean annual cumulative CH4 emission of 37.7 g CH4-C m(-2). The dominant contributor to CH4 emission was the thawing period: warmer, longer thawing periods contributed 69.1-88.6% to the annual CH4 budget. Non-thawing periods also contributed, with shorter frozen-thawing periods accounting for up to 18.5% and shorter thawing-freezing periods accounting for up to 8.8%. Over the course of a year, emission peaked in the peak growing season and at onset of thawing and freezing. In contrast, emission did not vary substantially during the frozen period. Daily mean emission was highest during the thawing period and lowest during the frozen period. Diurnal patterns of CH4 emission were similar among the four periods, with peaks ranging from 12:00 to 18:00 and the lowest emission around 00:00. Water table and temperature were the dominant factors controlling CH4 emissions during different thawing-freezing periods. Our results suggest that CH4 emission from peatland will change substantially as CH4 production, microbial composition, and patterns of thawing-freezing cycles change with global warming. Therefore, frequent monitoring of CH4 fluxes in more peatlands and in situ monitoring of methanogenesis and related microbes are needed to provide a clear picture of CH4 fluxes and the thawing-freezing processes that affect them.

Arctic wetlands are currently net sources of atmospheric CH4. Due to their complex biogeochemical controls and high spatial and temporal variability, current net CH4 emissions and gross CH4 processes have been difficult to quantify, and their predicted responses to climate change remain uncertain. We investigated CH4 production, oxidation, and surface emissions in Arctic polygon tundra, across a wet-to-dry permafrost degradation gradient from low-centered ( intact) to flat-and high-centered ( degraded) polygons. From 3 microtopographic positions ( polygon centers, rims, and troughs) along the permafrost degradation gradient, we measured surface CH4 and CO2 fluxes, concentrations and stable isotope compositions of CH4 and DIC at three depths in the soil, and soil moisture and temperature. More degraded sites had lower CH4 emissions, a different primary methanogenic pathway, and greater CH4 oxidation than did intact permafrost sites, to a greater degree than soil moisture or temperature could explain. Surface CH4 flux decreased from 64 nmol m(-2) s(-1) in intact polygons to 7 nmol m(-2) s(-1) in degraded polygons, and stable isotope signatures of CH4 and DIC showed that acetate cleavage dominated CH4 production in low-centered polygons, while CO2 reduction was the primary pathway in degraded polygons. We see evidence that differences in water flow and vegetation between intact and degraded polygons contributed to these observations. In contrast to many previous studies, these findings document a mechanism whereby permafrost degradation can lead to local decreases in tundra CH4 emissions.

Methane (CH4) emissions from Arctic tundra are an important feedback to global climate. Currently, modelling and predicting CH4 fluxes at broader scales are limited by the challenge of upscaling plot-scale measurements in spatially heterogeneous landscapes, and by uncertainties regarding key controls of CH4 emissions. In this study, CH4 and CO2 fluxes were measured together with a range of environmental variables and detailed vegetation analysis at four sites spanning 300 km latitude from Barrow to Ivotuk (Alaska). We used multiple regression modelling to identify drivers of CH4 flux, and to examine relationships between gross primary productivity (GPP), dissolved organic carbon (DOC) and CH4 fluxes. We found that a highly simplified vegetation classification consisting of just three vegetation types (wet sedge, tussock sedge and other) explained 54% of the variation in CH4 fluxes across the entire transect, performing almost as well as a more complex model including water table, sedge height and soil moisture (explaining 58% of the variation in CH4 fluxes). Substantial CH4 emissions were recorded from tussock sedges in locations even when the water table was lower than 40 cm below the surface, demonstrating the importance of plant-mediated transport. We also found no relationship between instantaneous GPP and CH4 fluxes, suggesting that models should be cautious in assuming a direct relationship between primary production and CH4 emissions. Our findings demonstrate the importance of vegetation as an integrator of processes controlling CH4 emissions in Arctic ecosystems, and provide a simplified framework for upscaling plot scale CH4 flux measurements from Arctic ecosystems.