The biogeochemical controls of the delta N-15 and delta O-18 of N2O produced in landfill cover soils

We document an enrichment of both the delta(18)O(Atm.O2) and delta(15)N(Atm .N2) values of soil-derived N2O collected from landfill cover soils relativ e to tropospheric N2O. The isotopic values of N2O vary from -5.1 parts per thousand to +19.4 parts per thousand and from +19.0 parts per thousand to 33.5 parts per thousand for delta(15)N(Atm.N2) and delta(18)O(Atm.O2), resp ectively. A tight linear correlation for delta(18)O(Atm.O2) versus delta(15 )N(Atm.N2) is apparent, reflecting coupled microbial processes that produce N2O that may be isotopically enriched or depleted in relation to troposphe ric N2O, Several explanations are provided to explain this correlation, inc luding evidence for NH3 limitation during nitrification, which would be exp ected to diminish isotopic fractionation and consequently result in more en riched isotopic values of N2O. Desiccation effects on nitrification were al so observed, which contribute to NH3 limitation and thus could influence th e isotopic signature of N2O. Our results indicate that the N2O isotopic com position from soils may vary greatly depending on the season and soil moist ure conditions and may at times be enriched in N-15 and O-18 relative to tr opospheric N2O.