Temporal and spatial variability of the CH4 dynamics of landfill cover soils

Landfills are regarded as important sources of the atmospheric methane (CH₄), one of the major greenhouse gases. In this study we investigated the CH₄ dynamics of landfill cover soils in a long‐term field experiment. The CH₄ emission rates were low, mostly ranging from —100 to 100 μmol m^—2 h^—1, with prevailing negative values. Higher values of up to 130,000 μmol m^—2 h^—1, obtained concurrently, were due to mice burrows, connecting the reduced soil sections with the aerated ones. Thus, the appearance of spatial dissimilarity was the most important factor influencing temporal variability. Reducing the soil cover from 120 cm to at least 60 cm caused a tendency of increased CH₄ emission. The oxidation rates were also low and differed with low temporal variability from 1.0—11.9 nmol g^—1 h^—1 in 0—10 cm soil depth and 0—5.3 nmol g^—1 h^—1 in 40—50 cm, respectively. Highest rates were obtained at 25—30 % soil water content. A mapping of CH₄ concentrations over the whole landfill showed a large spatial variation with values of 3.1—343 nmol g^—1. Subsequent CH₄ emission rates were between —0.2 and 120,000 mmol m^—2 d^—1 and showed a positive correlation to the CH₄ concentrations (r = 0.993, P < 0.05). Thus, by a large scale mapping of CH₄ concentrations a low‐cost procedure is proposed to identify the hot spots of CH₄ release which should be treated with additional thick and well aerated cover soil materials.