Methane and carbon dioxide production in, transport through, and efflux from a peatland

Abstract

The top 5-50 cm of a peat deposit above the water table are predominantly oxic while below that the peat is anoxic. The concentrations of CH 4 and CO 2 in the peat below 50 cm do not change with the seasons. The concentrations are greatest at or near the base of the peat and decrease quadratically upwards, consistent with a gas production rate (CH 4 + CO 2 ) of 0.03 μ mol cm -3 a -1 and movement by diffusion. The upward efflux of CH 4 , calculated from the concentration profile in deep peat, is 1, and of CO 2 is 17 μ mol m -2 h -1 . Just below the water table there is a small peak in CH 4 concentration. The peak concentrations are greater in summer than in winter. This indicates a second, seasonal and local, but not yet quantified source of CH 4 . Effluxes of CH 4 from the peatland surface range from ordinary summer maxima of about 200 down to winter values less than 10 μ mol m -2 h -1 , and at times negative values. The efflux from hummocks is usually about a third of that from hollows. These results indicate that methane oxidation may be important in hummocks.