Supplementary file 1_Methane consumption by a landfill cover soil under variable soil moisture and temperature conditions.docx

At each temperature and moisture combination, CH₄ was spiked into the headspace through multiple consecutive injections, and headspace CH₄ and CO₂ concentrations were measured to calculate CH₄ consumption and CO₂ efflux rates. The maximum CH₄ consumption rate was observed at the moderate soil moisture and temperature conditions (330 ± 12.3 nmol h^-1 g DW^-1 at 60% WFPS and 25 °C), while the maximum CO₂ efflux rate was observed at the maximal WFPS and temperature conditions of the experiment (652 ± 85.0 nmol h^-1 g DW^-1 at 100% WFPS and 35 °C).

A diffusion-reaction model was fit to the observed data to represent the effects of temperature and soil moisture on the CH₄ consumption and CO₂ efflux rates. The model predicted similar optimal conditions as those observed for both the CH₄ consumption and the CO₂ efflux rates. The modeling and experimental results show that the dominant controls on the optimal soil moisture for CH₄ consumption are the interactive effects of moisture limitation of microbial activity and of gas (CH₄ and oxygen) diffusion, whereas for the CO₂ effluxes, the dominant controls were the interactive effects of moisture limitation of gas (oxygen) diffusion and solute mobility.

These results provide insight into how seasonal changes in soil moisture and temperature could impact CH₄ oxidation rates, and therefore also net CH₄ emissions, in landfill cover soils and other environments.</p>