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

We measured CH, uptake in a Danish beech forest soil using traditional closed chambers (0.0078 m(2)) with gas chromatographic analysis of headspace CH4 and a megachamber (64 m(2)) with Fourier transform infrared (FTIR) spectroscopy for CH4 analysis. The two techniques gave uptake rates of 22.5 and 21.8 mu g CH4 m(2)h(-1), respectively. CH4 uptake rates from 122 small chambers were normally distributed. Geostatistical analysis of uptake rates indicated that a megachamber covering 10-12m will encompass most of the spatial variability. Thus, the 29 x 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 m(2) chambers. In a parallel study, 0.0078 and 0.49 m(2) closed chambers showed similar CH4 uptake rates indicating that both chamber sizes are adequate for estimating CHI uptake.