The Effect of Vegetation on Microbial Methane Oxidation

Basically, the activity of the methane oxidizing bacteria is limited by the availability of oxygen in the landfill cover soil. Enforced by the use of fine-grained soils like silt, the surface tends to crust due to vertical erosion, blocking pores required for gas exchange. A column study was carried out to examine the impact of vegetation on improving the aeration of critical soil material and supporting the oxidation process. Oxidation potential was strongly diminished in the bare control column filled with clayey silt even at low CH4-loads. In contrast, the planted clayey silt showed ahigh oxidation potential of 91 % at a CH4-load of 5.6 l CH4 m h. It was shown, that spreading root system forms secondary macro-pores, and hence amplifies the air diffusivity and sustains the oxygen supply to the bacteria. Water produced during methane oxidation was reduced by evapotranspiration, and more water-free pores are availabel for gas diffusion. Leguminous plants support the enrichment of soil with nitrogen compounds, which benefit the oxidation process. In conclusion, vegetation is relevant to the increase of oxygen diffusion into soil and subsequently enhances effective methane oxidation in landfill cover soils.