Falling atmospheric pressure as a trigger for methane ebullition from peatland

Abstract

Peatlands are widely regarded as a significant source of atmospheric CH4, a potent greenhouse gas. At present, most of the information on environmental emissions of CH4 comes from infrequent, temporally discontinuous ground-based flux measurements. Enormous efforts have been made to extrapolate measured emission rates to establish seasonal or annual averages using relevant biogeochemical factors, such as water table positions or peat temperatures, by assuming that the flux was stationary during a substantial nonsampling period. However, this assumption has not been explicitly verified, and little is known about the continuous variation of the CH4 flux in a timescale of individual flux measurement. In this study, we show an abrupt change in the CH4 emission rate associated with falling atmospheric pressure. We found that the CH4 flux can change by 2 orders of magnitude within a matter of tens of minutes owing to the release of free-phase CH4 triggered by a drop in air pressure. The contribution of the ebullition to the total CH4 flux during the measurements was significant (50-64%). These results clearly indicated that field campaigns must be designed to cover this rapid temporal variability caused by ebullition, which may be especially important in intemperate weather. Process-based CH4 emission models should also be modified to include air pressure as a key factor for the control of ebullient CH4 release from peatland. Copyright 2007 by the American Geophysical Union.