Abiotic nitrous oxide production

Chemodenitrification is generally considered to encompass all non-biological processes that produce NO, N2O or N2. Its occurrence in terrestrial systems is rarely considered, and no attempts have been made to include the process in studies aiming to discriminate between all sources of N2O. Chemodenitri-fication is thought to occur when NO2~ accumulates and reacts with organic compounds (thought to be phenolics) to produce NO and N2O (Bremner, 1997), and may be a significant source of N2O in acid soils <pH 5.5 where the NO2:HNO2 equilibrium shifts in favour of nitrous acid (HNO2), which either self-decomposes to form NO, HNO3 and H2O, or reacts with constituents of soil organic matter to form N2, N2O and CH3ONO (Chalk and Smith, 1983; Van Cleemput and Samater, 1996; Venterea and Rolston, 2000). Under acidic conditions chemodenitrification may be a more significant source of NO than N2O (Nelson, 1982; Yamulki et al, 1997). The occurrence of chemodenitri-fication is generally verified in sterilized soils, assuming complete inactivation of the microbial population, and thereby the impossibility of microbial production of N2O (Yamulki et al, 1997; Clough et al, 2001; Morkved et al, 2007). For example, Morkved et al (2007) measured a 0.4 per cent conversion of NO2~ to N2O in sterilized peat soil at pH 4.1-4.2, which they attributed to chemodenitrification.

Nitrite may also in some environments be reduced to NO and/or N2O, where Fe(II) is used as an electron donor. Cooper et al (2003) observed an eightfold increase in N2O emissions in the presence of Fe(II) in a wastewater treatment, and whilst Parkes et al (2007) stated that such reactions may have contributed to nitrogen removal in a municipal waste leachate treatment facility, similar relationships have yet to be observed in soils.

0 0

Post a comment