Conditions Required
Denitrification takes place under special conditions in both terrestrial and marine ecosystems. In general, it occurs where oxygen, a more energetically favourable electron acceptor, is depleted, and bacteria respire nitrate as a substitute terminal electron acceptor. Due to the high concentration of oxygen in our atmosphere denitrification only takes place in anaerobic environments where oxygen consumption exceeds the oxygen supply and where sufficient quantities of nitrate are present. These environments may include certain soils and groundwater, wetlands, oil reservoirs, poorly ventilated corners of the ocean, and in seafloor sediments.
Denitrification generally proceeds through some combination of the following intermediate forms:
- NO3− → NO2− → NO + N2O → N2 (g)
The complete denitrification process can be expressed as a redox reaction:
- 2 NO3− + 10 e− + 12 H+ → N2 + 6 H2O
This reaction shows a fractionation in isotope composition. Lighter isotopes of nitrogen are preferred in the reaction, leaving the heavier nitrogen isotopes in the residual matter. The process can cause delta-values of up to −40, where delta is a representation of the difference in isotopic composition. This can be used to identify denitrification processes in nature.
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