Title

Episodic CH4 emissions from a temperate fen

Abstract

Wetlands are the largest natural source of atmospheric methane (CH4). Since CH4 flux from wetlands is controlled by peat and air temperature, water table and substrate availability, it is sensitive to forcing by climate and weather. Large uncertainties in annual CH4 flux estimates exist due to high spatial and temporal variability. To gain a better quantitative and process understanding of the temporal variability in net CH4 emissions, automated chambers were employed at Sallie’s Fen (43°12.5’ N, 71°3.5’ W), a temperate peatland site. The resulting datasets offer high temporal coverage of the continuous release of CH4 and the frequency and magnitude of ebullitive release. Measured fluxes ranged between 7-2000 mg CH4 m-2 d-1 from April 27 to December 19, 2009. Episodic release of CH4 via ebullition (bubbling) was frequently observed - 2,727 ebullition events were identified from chamber closures during the study period (i.e., ~55 events m-2 d-1). The seasonal peak in non-ebullitive flux occurred during the week of August 16th while the ebullitive peak also occurred in August, likely due to high CH4 production rates and low CH4 solubility, both driven by temperature. Synoptic scale variability in ebullitive loss was driven by hydrostatic pressure variations due to water table position, while no clear atmospheric pressure relationship was observed. A daily pattern in ebullition was identified, with peaks at night. Several potential mechanisms for this pattern were explored, including atmospheric turbulence and vegetation productivity.

These data are the first analysis of ebullition variability on seasonal, synoptic and diel timescales. The derived empirical relationships between ebullition frequency and magnitude and environmental variables, combined with a biogeochemical process-based model for CH4 emissions from wetlands, will help reduce uncertainties in annual CH4 emissions and will inform the predictive capability of these kinds of models.

Publication Date

1-2011

Journal Title

North American Carbon Program Meeting

Publisher

North American Carbon Program

Document Type

Conference Proceeding