Methane oxidation in landfill cover soils, as revealed by potential oxidation measurements and phospholipid fatty acid analyses

Landfills account for ca. 10% of the annual global burden of atmospheric methane. Part of the efflux is mitigated by means of biological methane oxidation in the landfill covers. In this study, two types of landfill cover soils (mineral soil and sewage sludge) were compared with respect to methane emissions as well as potential methane oxidation capacity and the PLFA (phospholipid fatty acid) content of soil samples. Methane fluxes were lowest at a landfill site where wastes were covered with old sewage sludge. This site consumed atmospheric methane on most occasions. In incubated soil samples from the landfill cover composed of mineral soil, potential methane oxidation was most strongly correlated with the concentration of PLFA 18:1ω8, which is typical for type-II methanotrophic bacteria. In contrast, in samples from a landfill cover composed of fresh sewage sludge, methane oxidation was most strongly correlated with 16:1-PLFAs, indicating that type-I methanotrophs predominated, probably owing to nutritional conditions being more favourable in the sludge. The results also indicate that it takes a long time, i.e. several years, for methanotrophs to get well established in landfill cover soils.