Editing Fen (section)

==== Nitrogen ====
Fens play an important role in the global [[nitrogen cycle]] due to the anaerobic conditions found in their soils, which facilitate the oxidation or reduction of one form of nitrogen to another.<ref name=":23" /> Most nitrogen arrives in wetlands as nitrate from [[Surface runoff|runoff]], in organic matter from other areas, or by [[nitrogen fixation]] in the wetland.<ref name=":23" /> There are three main forms of nitrogen found in wetlands: nitrogen in organic matter, oxidized nitrogen ([[nitrate]] or [[nitrite]]), and [[ammonium]].<ref name=":63" />

Nitrogen is abundant in peat.<ref name=":63" /> When the organic matter in peat is decomposed in the absence of oxygen, ammonium is produced via [[ammonification]].<ref name=":23" /> In the oxidized surface layer of the wetland, this ammonium is oxidized to nitrite and nitrate by [[nitrification]].<ref name=":23" /> The production of ammonium in the reduced layer and its consumption in the top oxidized layer drives upward [[diffusion]] of ammonium.<ref name=":23" /> Likewise, nitrate production in the oxidized layer and nitrate consumption in the reduced layer by denitrification drives downward diffusion of nitrate.<ref name=":23" /> [[Denitrification]] in the reduced layer produces nitrogen gas and some [[nitrous oxide]], which then exit the wetland to the atmosphere.<ref name=":23" /> Nitrous oxide is a potent greenhouse gas whose production is limited by nitrate and nitrite concentrations in fens.<ref>{{Cite journal|last1=Palmer|first1=Katharina|last2=Horn|first2=Marcus A.|date=2015-04-10|title=Denitrification Activity of a Remarkably Diverse Fen Denitrifier Community in Finnish Lapland Is N-Oxide Limited |journal=PLOS ONE|language=en|volume=10|issue=4|pages=e0123123|doi=10.1371/journal.pone.0123123 |doi-access=free|issn=1932-6203|pmc=4393310|pmid=25860353|bibcode=2015PLoSO..1023123P}}</ref>

Nitrogen, along with phosphorus, controls how fertile a wetland is.<ref name=":23" />