SOIL TEXTURE PARAMETERIZATION OF THE METHANE UPTAKE IN AERATED SOILS

Long-term records of the methane uptake by five different aerated soils in South-West Germany and spot measurements in Western Europe, North America, and North-West Africa are presented. A good correlation between the methane uptake rate and soil permeability, obtained from parallel Radon-222 flux and concentration measurements of methane and Radon-222 in soil air indicates, that methane consumption in aerated soils is mainly controlled by the gas transport resistance within the soil. Soil temperature is found to be of minor influence on the methane flux from the atmosphere into the soil. The soils investigated were classified with respect to the three major soil texture classes - coarse, medium, and fine - representing soils with low, medium, and high gas transport resistance, respectively. Average methane uptake rates for each soil texture class were determined and extrapolated to fit into the scheme of the NASA-GISS global digital data set of soil types (Staub et al., 1987). Assuming that the observed relation between methane uptake rate and soil permeability (soil texture) is valid for all kinds of aerated soils, methane uptake rates are estimated on a regional and global scale. From this parameterization we calculate a global CH4 soil sink in the range of 9.0 to 55.9 Tg CH4/a with a best estimate of 28.7 Tg CH4/a. This corresponds to about 7% of the total global destruction rate by OH radicals.