Nitrogen

NO3- (+5) —> nitrate

NH4+ (-3) —> ammonium

NO2- (+3) —> nitrite

N2O (+1) —> nitrous oxide

—> all nitrogen species except N2

1. (1)  Assimilation: preferentially taken up by phytoplankton/microorganisms as it is a readily available N source. NH3/NH4+ already has an oxidation number of -III (same as in PON)→easy incorporation, easy transformation to glutamate (for further use)

2. (2)  Nitrification: microbially mediated slow oxidation to Nitrate, autotrophic, yields energy for ATP production (but only little)

   NH3 -> Nitrosomonas -> NO2- -> Nitrobacter -> NO3-

3. (3)  Denitrification: dissimilatory nitrite reduction to N2, serves as an electron acceptor for heterotrophs; yet: more likely to happen to/ or in combination with NO3- it is a Nitrogen loss process NO2- -> (N2O) -> N2

   Anammox: anaerobic ammonium oxidation to N2 in anoxic environments, synproportionation. It is a nitrogen loss process NH4+ + NO2– → N2 + H2O

   DNRA: dissimilatory nitrate (nitrite) reduction to ammonium, anaerobic respiration process of heterotrophs using nitrate as an electron acceptor (NO3- ->) NO2- -> NH4+

4. N2 fixation: diazotrophic bacteria fixate gaseous N2 to NH3/NH4+ with the enzyme nitrogenase heavily energy dependent and high Fe requirement N2 + 8H+ + E -> 2NH4+

2NO3- + 12H+ + 10e- —> N2 + H2O

Denitrification is the process that converts nitrate into nitrogen gas. This is an anarobic process that is carried out by procaryotes in sediments or OMZs.

Yes, by the Haber-Bosch process including high temperature, high pressure and use of H2 as well as an Fe-catalyst.