Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 1997
Publication Date: N/A
Interpretive Summary: Methane is an important greenhouse gas that has been implicated in contributing to global warming. In order to better understand the factors controlling methane emissions from terrestrial systems, better methods are needed to measure rates of methane transfer to and from the atmosphere. This study compares two different methods for measuring methane emission from terrestrial ecosystems. It as found that a simple, inexpensive technique employing soil chambers was a sensitive method for measuring methane emission; however, the spatial variability was high and many replicate measurements are required. A more complicated meteorological technique provided a better spatial average but was less sensitive. This information will allow researchers to select the appropriate methodology for measuring methane emissions from different terrestrial ecosystems.
Technical Abstract: Methane 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. This study was done to compare the CH4 flux measurements obtained by using a closed-chamber soil cover technique and a micro-meteorological method (Bowen-ratio Energy Balance or BREB method). Methane flux rates obtained by both methods were compared using 9 time points over a 3-day period at a peatland site in north central Minnesota. Mean CH4 fluxes obtained by both methods were of the same magnitude (2.4 to 5.09 mg CH4 m**-2 h**-1); however, differences were observed in the magnitudes of spatial and temporal variability as well as the detection sensitivities (minimum detectable flux). Spatial variability associated with the closed-chamber flux determinations was high. Spatial variability of the Bowen-ratio method could not be assessed because only one Bowen-ratio station was used. Temporal variations for CH4 were found to be large using the Bowen-ratio method, but were low for the chamber method. 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 Bowen-ratio 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.