Consumption of atmospheric methane by desert soils

Abstract

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 10¹² 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^12,13,18or enhancing²⁰ 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 CH₄m^-2d^-1. Uptake of CH⁴ by desert soil is enhanced by rainfall after an initial soil-drainage period—opposite to the response of temperate forest soils¹². Methane is consumed to a depth of about 2 m, allowing for deep removal of atmospheric CH₄if 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 10¹² g yr^-1 to account for the contribution of desert soils.