Scales of temporal variability in episodic CH4 emissions: from hours to seasons

Despite leading to potentially significant positive climate feedbacks, the processes controlling temperate and northern peatland methane fluxes remain relatively poorly understood. In order to gain a better process understanding of the net efflux of methane, automated gas flux chambers were operated continuously in a temperate peatland site to quantify the timing and magnitude of methane ebullition, one of the three pathways for wetland methane flux. The resulting datasets offer high temporal coverage of both components (timing and magnitude) of this flux pathway, allowing for the first analysis of ebullition variability on seasonal, synoptic and diel timescales. The seasonal peak in ebullition occurred in August, likely due to higher methane production rates and lower methane solubility, both driven by temperature. Synoptic scale variability was controlled by changes in hydrostatic pressure due to water table position, while no clear atmospheric pressure relationship was observed. A daily pattern in ebullition was identified, with nighttime peaks most distinct during summer and autumn months. Several potential mechanisms for this pattern were explored, including atmospheric turbulence and PAR/NEE. The cumulative contribution of episodic ebullition to total methane flux at our site during the summer of 2009 was estimated to be 2 - 12%.