The biogeochemical controls of N 2 O production and emission in landfill cover soils: the role of methanotrophs in the nitrogen cycle

Abstract

Emissions of N 2 O from cover soils of both abandoned (> 30 years) and active landfills greatly exceed the maximum fluxes previously reported for tropical soils, suggesting high microbial activities for N 2 O production. Low soil matrix potentials ( 2 O formation during most of the time of sampling. Soil moisture had a strong influence on N 2 O emissions. The production of N 2 O was stimulated by as much as 20 times during laboratory incubations, when moisture was increased from −2.0 MPa to −0.6 MPa. Additional evidence from incubation experiments and δ 13 C analyses of fatty acids (18:1) diagnostic of methanotrophs suggests that N 2 O is formed in these soils by nitrification via methanotrophic bacteria. In a NH 3(g) ‐amended landfill soil, the rate of N 2 O production was significantly increased when incubated with 100 ppmv methane compared with 1.8 ppmv (atmospheric) methane. Preincubation of a landfill soil with 1% CH 4 for 2 weeks resulted in higher rates of N 2 O production when subsequently amended with NH 3(g) relative to a control soil preincubated without CH 4 . At one location, at the soil depth (9–16 cm) of maximum methane consumption and N 2 O production, we observe elevated concentrations of organic carbon and nitrogen and distinct minima in δ 15 N (+1.0‰) and δ 13 C (−33.8‰) values for organic nitrogen and organic carbon respectively. A δ 13 C value of −39.3‰ was measured for 18:1 carbon fatty acids in this soil, diagnostic of type II methanotrophs. The low δ 15 N value for organic nitrogen is consistent with N 2 fixation by type II methanotrophs. These observations all point to a methanotrophic origin for the organic matter at this depth. The results of this study corroborate previous reports of methanotrophic nitrification and N 2 O formation in aqueous and soil environments and suggest a predominance of type II rather than type I or type X methanotrophs in this landfill soil.

Bibliographic Information