Spatial variability of CH4 uptake in a Danish forest soil and its relation to different measurement techniques

We measured CH4 uptake in a Danish beech forest soil using traditional closed chambers (0.0078 m2) with gas chromatographic analysis of headspace CH4 and a megachamber (64 m2) with Fourier transform infrared (FTIR) spectroscopy for CH4 analysis. The two techniques gave uptake rates of 22.5 and 21.8 μg CH4 m2 h−1, respectively. CH4 uptake rates from 122 small chambers were normally distributed. Geostatistical analysis of uptake rates indicated that a megachamber covering 10–12 m will encompass most of the spatial variability. Thus, the 29 × 2.2 m megachamber would cover most of the variability, and this explains the similar uptake rates obtained by this technique and the 0.0078 m2 chambers. In a parallel study, 0.0078 and 0.49 m2 closed chambers showed similar CH4 uptake rates indicating that both chamber sizes are adequate for estimating CH4 uptake.