Editing Nitrogen cycle (section)

== Human influences on the nitrogen cycle ==
[[File:Global - Global Fertilizer and Manure, Version 1 Nitrogen Fertilizer Application (6074011960).jpg|thumb|Nitrogen fertilizer application]]
[[File:Global Global Fertilizer and Manure, Version 1 Nitrogen in Manure Production (6173194512).jpg|thumb|Nitrogen in manure production]]
{{Main|Human impact on the nitrogen cycle}}
As a result of extensive cultivation of legumes (particularly [[soy]], [[alfalfa]], and [[clover]]), growing use of the [[Haber–Bosch process]] in the production of chemical [[fertilizer]]s, and pollution emitted by vehicles and industrial plants, human beings have more than doubled the annual transfer of nitrogen into biologically available forms.<ref name="Vitousek 1997" /> In addition, humans have significantly contributed to the transfer of nitrogen trace gases from Earth to the atmosphere and from the land to aquatic systems. Human alterations to the global nitrogen cycle are most intense in developed countries and in Asia, where vehicle emissions and [[industrial agriculture]] are highest.<ref name="Holland 1999" />

Generation of Nr, [[reactive nitrogen]], has increased over 10 fold in the past century due to global [[industrialisation]].<ref name="Galloway 2008" /><ref name="Gu 2012 dup?" /> This form of nitrogen follows a cascade through the [[biosphere]] via a variety of mechanisms, and is accumulating as the rate of its generation is greater than the rate of [[denitrification]].<ref name="Cosby 2003" /> Nr burial in lakes and oceans has been increasing in tandem with anthropogenic input, now double the Nr burial flux pre-[[Industrial Revolution|industrial revolution]]. Reactive nitrogen can be denitrified in water or buried in sediments to accumulate. This buried Nr lies latent until its sediments are disturbed through events like [[Storm|storms]] or [[Flood|floods]], when large amounts of nitrogen are reintroduced to the water where it can be denitrified and impact the environment.<ref>{{Cite journal |last1=Wang |first1=Mei |last2=Houlton |first2=Benjamin Z. |last3=Wang |first3=Sitong |last4=Ren |first4=Chenchen |last5=van Grinsven |first5=Hans J. M. |last6=Chen |first6=Deli |last7=Xu |first7=Jianming |last8=Gu |first8=Baojing |date=2021-11-28 |title=Human-caused increases in reactive nitrogen burial in sediment of global lakes |url=https://www.sciencedirect.com/science/article/pii/S2666675821000837 |journal=The Innovation |volume=2 |issue=4 |pages=100158 |doi=10.1016/j.xinn.2021.100158 |pmid=34704084 |bibcode=2021Innov...200158W |issn=2666-6758|pmc=8527044 }}</ref>

[[Nitrous oxide]] ({{chem|N|2|O}}) has risen in the atmosphere as a result of agricultural fertilization, biomass burning, cattle and feedlots, and industrial sources.<ref name="Chapin 2002" /> {{chem|N|2|O}} has deleterious effects in the [[stratosphere]], where it breaks down and acts as a [[catalyst]] in the destruction of atmospheric [[ozone]]. Nitrous oxide is also a [[greenhouse gas]] and is currently the third largest contributor to [[global warming]], after [[carbon dioxide]] and [[methane]]. While not as abundant in the atmosphere as carbon dioxide, it is, for an equivalent mass, nearly 300 times more potent in its ability to warm the planet.<ref name="Howarth 2009" />

[[Ammonia]] ({{chem|NH|3}}) in the atmosphere has tripled as the result of human activities. It is a reactant in the atmosphere, where it acts as an [[aerosol]], decreasing air quality and clinging to water droplets, eventually resulting in [[nitric acid]] ([[Hydrogen|H]][[nitrate|NO<sub>3</sub>]]) that produces [[acid rain]]. Atmospheric ammonia and nitric acid also damage respiratory systems.

The very high temperature of lightning naturally produces small amounts of {{chem|NO|x}}, {{chem|NH|3}}, and {{chem|HNO|3}}, but high-temperature [[combustion]] has contributed to a 6- or 7-fold increase in the flux of {{chem|NO|x}} to the atmosphere. Its production is a function of combustion temperature - the higher the temperature, the more {{chem|NO|x}} is produced. [[Fossil fuel]] combustion is a primary contributor, but so are biofuels and even the burning of hydrogen. However, the rate that hydrogen is directly injected into the combustion chambers of internal combustion engines can be controlled to prevent the higher combustion temperatures that produce {{chem|NO|x}}.

Ammonia and nitrous oxides actively alter [[atmospheric chemistry]]. They are precursors of [[troposphere|tropospheric]] (lower atmosphere) ozone production, which contributes to [[smog]] and [[acid rain]], damages [[plant]]s and increases nitrogen inputs to ecosystems. [[Ecosystem]] processes can increase with [[nitrogen fertilization]], but [[human impact on the environment|anthropogenic]] input can also result in nitrogen saturation, which weakens productivity and can damage the health of plants, animals, fish, and humans.<ref name="Vitousek 1997" />

Decreases in [[biodiversity]] can also result if higher nitrogen availability increases nitrogen-demanding grasses, causing a degradation of nitrogen-poor, species-diverse [[Heath (habitat)|heathlands]].<ref name="Aerts 1988" />