METHANE EMISSION FROM A LANDFILL AND THE METHANE-OXIDIZING 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 mo isture content of the CH4-oxidising cover soil was thought to cause th is variation. Comparing gross and net CH4 emission rates, it was found that the cover soil, due to its CH4 oxidising capacity, had a large m itigating effect on the CH4 emission. In laboratory experiments the ef fects of soil moisture, temperature and different ammonium amendments on CH4 oxidation were investigated. When the moisture content and temp erature were combined, CH4 oxidation rates between 0.88 and 10.86 ng C H4 g(-1) h(-1) were observed. The optimum moisture content ranged betw een 15.6 and 18.8% w/w (+/-1/2 WHC). The optimum incubation temperatur e (30-20 degrees C) decreased with increasing moisture contents. For t he oxidation rates at 10 and 20 degrees C, we found an average Q(10) v alue of 1.88 +/- 0.14. The activation energy for moisture contents bet ween 5 and 25% was 83.0 +/- 4.4 kJ mol(-1). Increased ammonium additio ns reduced the CH4-oxidising capacity. This reduction decreased with i ncreasing moisture contents. A high correlation (R(2)>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 lo wer al 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 t he following decreasing effect on the CH4-oxidising capacity of the so il: amount of NH4+ added, moisture content > incubation temperature. C opyright (C) 1996 Elsevier Science Ltd