Nitrogen cycle

Global cycling of reactive nitrogen [1] including industrial fertilizer production,[2] nitrogen fixed by natural ecosystems,[3] nitrogen fixed by oceans,[4] nitrogen fixed by agricultural crops,[5] NOx emitted by biomass burning,[6] NOx emitted from soil,[7] nitrogen fixed by lightning,[8] NH3 emitted by terrestrial ecosystems,[9] deposition of nitrogen to terrestrial surfaces and oceans,[10][11] NH3 emitted from oceans,[12][13][11] ocean NO2 emissions from the atmosphere,[14] denitrification in oceans,[4][15][11] and reactive nitrogen burial in oceans.[5]

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen,[16] making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.

The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle.[17][18][19] Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health.[20][21]

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  21. ^ Cite error: The named reference Kim 2017 was invoked but never defined (see the help page).