Methane oxidation in a neutral landfill cover soil: Influence of moisture content, temperature, and nitrogen-turnover

Well-managed, aerated cover soils can have a mitigating effect on methane emission from landfills. The influence of moisture content, soil temperature, and N on the methane uptake capacity of a neutral landfill cover soil was examined. A soil moisture content of 15% w/w gave the maximum CH4 oxidation rate (2.36 ng CH4 h(-1) g(-1) soil). When wetter, CH4 consumption was slower (e.g., 1.6 ng CH4 h(-1) g(-1) at 30% w/w) because of a limited gas diffusion. At lower soil moisture, microbial activity was reduced and consequently the oxidation capacity decreased (e.g., 0.84 ng CH4 h(-1) g(-1) at 5% w/w). Optimum temperature was between 25 and 30 degrees C. The calculated activation energy of the CH4 oxidation was 56.5 kJ K-1 mol(-1). After NH4+ addition, a negative linear correlation was found between the methane oxidation rate and the nitrous oxide flux (R(2) = 0.96, Y1 = 2.7 - 0.44 x Y2). Addition of NO3- had no significant effect on CH4 oxidation. The effect of organic residue amendments depended on their C/N ratios. Crop residues with a high C/N ratio (wheat [Triticum sativum L.] and maize [Zea mays L.] straw) stimulated N-immobilization and did not affect the methane-oxidizing capacity. On the other hand, addition of crop residues with low CIN ratios (potato [Solanum tuberosum L.] and sugar beet [Beta vulgaris cv. Altissima] leaves) stimulated N-mineralization, resulting in a strong inhibition of the methane oxidation.