Near-zero methane emission from an abandoned boreal peatland pasture based on eddy covariance measurements

Although estimates of the annual methane (CH(4)) flux from agriculturally managed peatlands exist, knowledge of controls over the variation of CH(4) at different time-scales is limited due to the lack of high temporal-resolution data. Here we present CH(4) fluxes measured from May 2014 to April 2016 using the eddy covariance technique at an abandoned peatland pasture in western Newfoundland, Canada. The goals of the study were to identify the controls on the seasonal variations in CH(4) flux and to quantify the annual CH(4) flux. The seasonal variation in daily CH(4) flux was not strong in the two study years, however a few periods of pronounced emissions occurred in the late growing season. The daily average CH(4) flux was small relative to other studies, ranging from -4.1 to 9.9 nmol m(-2) s(-1) in 2014–15 and from -7.1 to 12.1 nmol m(-2) s(-1) in 2015–16. Stepwise multiple regression was used to investigate controls on CH(4) flux and this analysis found shifting controls on CH(4) flux at different periods of the growing season. During the early growing season CH(4) flux was closely related to carbon dioxide fixation rates, suggesting substrate availability was the main control. The peak growing season CH(4) flux was principally controlled by the CH(4) oxidation in 2014, where the CH(4) flux decreased and increased with soil temperature at 50 cm and soil water content at 10 cm, but a contrasting temperature-CH(4) relation was found in 2015. The late growing season CH(4) flux was found to be regulated by the variation in water table level and air temperature in 2014. The annual CH(4) emission was near zero in both study years (0.36 ± 0.30 g CH(4) m(-2) yr(-1) in 2014–15 and 0.13 ± 0.38 g CH(4) m(-2) yr(-1) in 2015–16), but fell within the range of CH(4) emissions reported for agriculturally managed peatlands elsewhere.