CONSUMPTION OF ATMOSPHERIC METHANE BY DESERT SOILS

ATMOSPHERIC concentrations of methane, a greenhouse gas, are increasing at a rate of about 1% yr-1 (refs 1-4). Oxidation by methylotrophic bacteria in soil is the largest terrestrial sink for atmospheric CH4, and is estimated to consume about 30 x 10(12) g CH4 yr-1 (refs 4-6). Spatial and temporal variability in the rate of soil CH4 consumption are incompletely understood 6-19, as are the apparent inhibitory 12,13,18 or enhancing 20 effects of changes in land use. Dry deserts, which constitute 20% of total land surface, are not currently included in global soil uptake estimates. Here we describe measurements of the rate of uptake of atmospheric CH4 by undisturbed desert soils. We observed rates as great as 4.38 mg CH4 m-2 day-1; 50% of the measured rates were between 0.24 and 0.92 mg CH4 m-2 d-1. Uptake of CH4 by desert soil is enhanced by rainfall after an initial soil-drainage period-opposite to the response of temperate forest soils 12. Methane is consumed to a depth of about 2 m, allowing for deep removal of atmospheric CH4 if near-surface conditions are unfavourable for consumption. On the basis of an annual average CH4 consumption rate of 0.66 Mg CH4 m-2 d-1, we estimate that the global CH4 sink term needs to be increased by about 7 x 10(12) g yr-1 to account for the contribution of desert soils.