Methane emission from a landfill and the methane oxidising capacity of its covering soil

Methane emission from a small covered landfill site showed, seasonally varying fluxes, ranging from -5.9 to 914.3 mg CH4 m-2 d-1. The moisture content of the CH4-oxidising cover soil was thought to cause this variation. Comparing gross and net CH4 emission rates, it was found that the cover soil, due to its CH4 oxidising capacity, had a large mitigating effect on the CH4 emission. In laboratory experiments the effects of soil moisture, temperature and different ammonium amendments on CH4 oxidation were investigated. When the moisture content and temperature were combined, CH4 oxidation rates between 0.88 and 10.86 ng CH4 g-1 h-1 were observed. The optimum moisture content ranged between 15.6 and 18.8% w/w (+/- 1/2 WHC). The optimum incubation temperature (30-20 degrees C) decreased with increasing moisture contents. For the oxidation rates at 10 and 20 degrees C, we found an average Q10 value of 1.88 +/- 0.14. The activation energy for moisture contents between 5 and 25% was 83.0 +/- 4.4 kJ mol-1. Increased ammonium additions reduced the CH4-oxidising capacity. This reduction decreased with increasing moisture contents. A high correlation (R2>0.98) was found between the moisture content and the reduction of the CH4 uptake rate mg-1 NH4+-N kg-1 added. Because the nitrification rate was also lower at higher moisture contents, it was thought that the CH4 oxidation rate was more closely connected with the NH4+ turnover rate than with its actual concentration. Multiple linear regression analysis of the CH4 oxidation rates under the different incubation conditions showed the following decreasing effect on the CH4-oxidising capacity of the soil: amount of NH4+ added > moisture content > incubation temperature.