Comparison of closed-chamber and Bowen-Ratio methods for determining methane flux from peatland surfaces

Methane (CH4) is an important greenhouse gas, and it has been estimated that 50% of annual CH4 comes from terrestrial systems. Better and more accurate methods are needed to quantify CH4 flux from terrestrial environments. Two general methods commonly applied to measure trace gas fluxes are soil cover (chamber) techniques, and micrometeorology methods. Both of these methods has advantages and disadvantages, get little information is available concerning the relative performance of the techniques. This study was conducted to compare CH4 flux measurements obtained by using a closed-chamber soil cover technique and a micrometeorological method (Bowen-ratio Energy Balance [BREB]). Methane flux rates obtained by both methods were compared using nine time points over 3 d at a peatland site in north central Minnesota. Mean CH4 fluxes obtained by both methods were of the same magnitude (2.43-5.88 mg CH4 m(-2) h(-1)); however, differences were observed in the magnitudes of temporal variability as well as the detection sensitivities (minimum detectable flux). The minimum detectable flux for the closed-chamber method was 9.32 x 10(-2) mg CH4 m(-2) h(-1), while the minimum detectable flux for the BREB method ranged from 2.16 to 25.5 mg CH4 m(-2) h(-1). Due to analytical uncertainties associated with gas chromatographic determination of CH4 gradients, the BREB is not recommended.