Abstract
Eddy covariance measurements of methane (CH 4 ) 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 CH 4 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 CH 4 emission to the ecosystem growing season carbon budget. There was significant diurnal variation in CH 4 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 CH 4 efflux was only 47% of the average midday values. The peak value for daily average CH 4 emission rate was approximately 80 nmol m −2 s −1 (4.6 mg CH 4 m −2 h −1 ), and seasonal variation in CH 4 flux was strongly correlated with changes in soil temperature. Integrated over the entire measurement period [days 144–269 (late May–late September)], the total CH 4 emission was 3.2 g CH 4 m −2 , which was quite low relative to other wetland ecosystems and to the simultaneous high rate of ecosystem net CO 2 sequestration that was measured (18.1 mol CO 2 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 CH 4 emission over the last 50 years.