Methanotrophic activity in a diffusive methane/oxygen counter-gradient in an unsaturated porous medium.

Microbial methane (CH4) oxidation is a main control on emissions of this important greenhouse gas from ecosystems such as contaminated aquifers or wetlands under aerobic onditions. Due to a lack of suitable model systems, we designed a laboratory column to study this process in diffusional CH4/O2 counter-gradients in unsaturated porous media. Analysis and simulations of the steady-state CH4, CO2 and O2 gas profiles showed that in a 15-cm-deep active zone, CH4 oxidation followed first-order kinetics with respect to CH4 with a high apparent first-order rate constant of approximately 30 h(-1).