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.

Boreal forest regions are a focal point for investigations of coupled water and biogeochemical fluxes in response to wildfire disturbances, climate warming, and permafrost thaw. Soil hydraulic, physical, and thermal property measurements for mineral soils in permafrost regions are limited, despite substantial influences on cryohydrogeologic model results. This work expands mineral soil property quantification in cold regions through soil characterization from the discontinuous permafrost zone of interior Alaska, USA. Values extend beyond the range of prior measurement magnitudes in analogous regions, highlighting the importance of this data set. Rocky and silty upland soil landscape classifications and wildfire disturbance provided guiding frameworks for the sampling and analysis for potential implications for the hydrologic response to thawing permafrost. Bulk density (rho(b)), soil organic matter, soil-particle size distributions (sand, silt, and gravel fractions), and soil hydraulic properties of van Genuchten parameters alpha and N had moderate evidence of differences between silty and rocky classifications. Burned and unburned sites had only moderate evidence of differences for silt fraction. Field-saturated hydraulic conductivity (K-fs) was more variable at burned sites compared to unburned sites, which corresponded to observations of greater rooting depths at burned sites and observations of root paths in soil cores for K-fs measurement. Soil thermal properties suggested that gravel content may reduce the accuracy of commonly used estimation methods for thermal conductivity. This work provides soil parameter constraints necessary for hypothesis testing and site-specific prediction with cryohydrogeologic models to examine controls on active layer and permafrost dynamics in upland boreal forests.

The effect of thawing permafrost on boreal ecosystem water cycling represents a significant knowledge gap of how climate change will affect northern landscapes. Evapotranspiration, particularly transpiration, may be changing in response to changes in permafrost conditions, vegetation, and climate. This study focuses on the effect of permafrost thaw on boreal plant transpiration over two summers with contrasting weather conditions. We quantified the response of stomatal conductance (gs), from which transpiration was calculated, of deciduous and evergreen plants to soil environmental factors that permafrost thaw affects: soil water content (S), depth of seasonal thaw (D), and soil temperature (T). We found that gs was least sensitive to T compared with S and D at both sites and across both years. At the thawing site, gs was more sensitive to S in a dry year (2009) and to D in a wet year (2010). In the wet year, S of similar to 50cm represented a threshold wherein the sensitivity of gs to T and D switched between positive (S50cm). However, the sensitivities to T and D were negative when S was consistently less than 50cm in the dry year. This is one of the first studies to explore the effect of permafrost thaw on boreal plant gs and transpiration, and our model predicted higher transpiration rates from deciduous plants located on thawing permafrost. Copyright (c) 2013 John Wiley & Sons, Ltd.