Nitrification

Nitrification is a key microbial process in the environmental nitrogen cycle that links the oxidation of ammonia (produced from the degradation of organic matter) to the loss of fixed nitrogen in the form of dinitrogen gas. It is performed by ammonia-oxidizing bacteria and archaea, and nitrite-oxidizing bacteria. These microbes are all aerobes and are predominantly autotrophic. Nitrification is very important in agriculture, where it determines the availability of fertilizer nitrogen, and in wastewater treatment systems, where it participates in the removal of excess nitrogen. Nitrification is coupled to denitrification and anammox (anaerobic ammonium-oxidation) in low-oxygen waters and in sediments, where it is an important oxygen sink. Nitrifying bacteria and archaea are involved in the production of the greenhouse gas, nitrous oxide. In natural systems, nitrification rates are influenced by environmental factors such as substrate concentration, salinity, temperature, oxygen, and pH.