Diurnal dynamics of CH₄ from a boreal peatland during snowmelt

ABSTRACT

Peatlands are one of the major natural sources of methane (CH₄), but the quantification of efflux is uncertain especially during winter, fall and the highly dynamic spring thaw period. Here, we report pronounced diurnal variations in CH₄ fluxes (F_CH4), measured using the eddy-covariance technique during the snow-thawing period at a boreal peatland in north-western Russia. Following the background winter emission of ∼0.5 mg m⁻² h⁻¹, strong diurnal variability in CH₄ fluxes from 21 April to 3 May was apparently controlled by changes in surface temperature (T_sur) and near-surface turbulence as indicated by the friction velocity (u*). CH₄ fluxes were ∼0.8 mg m⁻² h⁻¹ during night and ∼3 mg m⁻² h⁻¹ during peak efflux. Primarily, the freeze-thaw cycle of an ice layer observed at the wet peatland microforms due to surface temperatures oscillating between >0°C during the days and <0°C during the nights appeared to strongly influence diurnal variability. Once the ice layer was melted, increases in wind speed seemed to enhance CH₄ efflux, possibly by increased mixing of the water surface. Apparently, a combination of physical factors is influencing the gas transport processes of CH₄ efflux during the highly dynamic spring thaw period.