Diurnal and seasonal variation in methane emissions in a northern Canadian peatland measured by eddy covariance

Abstract

AbstractEddy covariance measurements of methane (CH4) net flux were made in a boreal fen, typical of the most abundant peatlands in western Canada during May–September 2007. The objectives of this study were to determine: (i) the magnitude of diurnal and seasonal variation in CH4 net flux, (ii) the relationship between the temporally varying flux rates and associated changes in controlling biotic and abiotic factors, and (iii) the contribution of CH4 emission to the ecosystem growing season carbon budget. There was significant diurnal variation in CH4 emission during the peak of the growing season that was strongly correlated with associated changes in solar radiation, latent heat flux, air temperature and ecosystem conductance to water vapor. During days 181–215, nighttime average CH4 efflux was only 47% of the average midday values. The peak value for daily average CH4 emission rate was approximately 80 nmol m−2 s−1 (4.6 mg CH4 m−2 h−1), and seasonal variation in CH4 flux was strongly correlated with changes in soil temperature. Integrated over the entire measurement period [days 144–269 (late May–late September)], the total CH4 emission was 3.2 g CH4 m−2, which was quite low relative to other wetland ecosystems and to the simultaneous high rate of ecosystem net CO2 sequestration that was measured (18.1 mol CO2 m−2 or 217 g C m−2). We estimate that the negative radiative forcing (cooling) associated with net carbon storage over the life of the peatland (approximately 2200 years) was at least twice the value of positive radiative forcing (warming) caused by net CH4 emission over the last 50 years.