Assessment of winter fluxes of CO2 and CH4 in boreal forest soils of central Alaska estimated by the profile method and the chamber method: a diagnosis of methane emission and implications for the regional carbon budget

This research was carried out to estimate the winter fluxes of CO2 and CH4 using the concentration profile method and the chamber method in black spruce forest soils in central Alaska during the winter of 2004/5. The average winter fluxes of CO2 and CH4 by chamber and profile methods were 0.24 ± 0.06 (SE; standard error) and 0.21 ± 0.06 gCO2-C/m2/d, and 21.4 ± 5.6 and 21.4 ± 14 μgCH4-C/m2/hr. This suggests that the fluxes estimated by the two methods are not significantly different based on a one-way ANOVA with a 95% confidence level. The hypothesis on the processes of CH4 transport/production/emission in underlying snow-covered boreal forest soils is proven by the pressure differences between air and in soil at 30 cm depth. The winter CO2 emission corresponds to 23% of the annual CO2 emitted from Alaska black spruce forest soils, which resulted in the sum of mainly root respiration and microbial respiration during the winter based on the δ13CO2 of −22.5‰. The average wintertime emissions of CO2 and CH4 were 49 ± 13 gCO2-C/m2/season and 0.11 ± 0.07 gCH4-C/m2/season, respectively. This implies that winter emissions of CO2 and CH4 are an important part of the annual carbon budget in seasonally snow-covered terrain of typical boreal forest soils. 1. Introduction