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

ABSTRACT

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.