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 (FCH4), 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 ∼0.5mgm−2 h−1, strong diurnal variability in CH4 fluxes from 21 April to 3 May was apparently controlled by changes in surface temperature (Tsur) and near-surface turbulence as indicated by the friction velocity (u*).CH4 fluxeswere∼0.8mgm−2 h−1 during night and∼3mgm−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.