Chemo-nitrification

In models in which bacteria are not modelled explicitly, nitrification is modelled as oxidation of ammonium without explicit description of growth of the chemolitho-trophic bacteria that perform the oxidation. This process is shown in Table 16.15. Other oxidation processes undertaken by chemo-lithotrophic bacteria are modelled similarly. When omitting the growth of chemolitho-trophic bacteria, organic phosphorus is not affected by these processes. 

Soils inclnding wetland soils are important sonrces of atmospheric nitrous oxide. A wide range of processes may produce nitrous oxide, as well as minor amounts of NO, but not all of these seem to be fully understood. The main biological processes of nitrous oxide formation in soils are shown in Figure 16.5. They include nitrification, denitrification, the dissimilatory reduction of nitrate to ammonium, and the assimilatory reduction of nitrate wherein N is incorporated in the cell biomass. Additionally, some NO and nitrous oxide may be released due to chemo-denitrification and pyro-denitrification. Of these processes, nitrification and denitrification are the most important with respect to nitrous oxide production. 

Micro-organisms are mainly responsible for the processes of N-fixation, nitrification and denitrification and contribute largely towards immobilization, But not all processes involving N fixation are biological and within the soil N cycle, abiotic processes contribute towards mineralisation and volatilization of ammonia, although chemo-denitrification leads to the loss of nitrite as N O. 

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