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Reactive nitrogen ("Nr"), also known as fixed nitrogen, refers to all forms of nitrogen present in the environment except for molecular nitrogen (). While nitrogen is an essential element for life on Earth, molecular nitrogen is comparatively unreactive, and must be converted to other chemical forms via 
Reactive nitrogen ("Nr"), also known as fixed nitrogen, refers to all forms of nitrogen present in the environment except for molecular nitrogen (). While nitrogen is an essential element for life on Earth, molecular nitrogen is comparatively unreactive, and must be converted to other chemical forms via nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
before it can be used for growth. Common Nr species include nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:
Charge-neutral
*Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide
*Nitrogen dioxide (), nitrogen(IV) oxide
* Nitrogen trioxide (), or ...
(), ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
(), nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and ha ...
(), as well as the anion nitrate ().
Biologically, nitrogen is "fixed" mainly by the microbes (eg., Bacteria and Archaea) of the soil that fix N2 into mainly NH3 but also other species. Legumes, a type of plant in the Fabacae family, are symbionts to some of these microbes that fix N2. NH3 is a building block to Amino acids and proteins amongst other things essential for life. However, just over half of all reactive nitrogen entering the biosphere is attributable to anthropogenic activity such as industrial fertilizer production. While reactive nitrogen is eventually converted back into molecular nitrogen via denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
, an excess of reactive nitrogen can lead to problems such as eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
in marine ecosystems.
Reactive nitrogen compounds
In the environmental context, reactive nitrogen compounds include the following classes: *oxide gases: nitric oxide,nitrogen dioxide
Nitrogen dioxide is a chemical compound with the formula . It is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the productio ...
, nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and ha ...
. Containing oxidized nitrogen, mainly the result of industrial processes and internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
s.
*anions: nitrate, nitrite. Nitrate is a common component of fertilizers, e.g. ammonium nitrate
Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
.
*amine derivatives: ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
and ammonium salts, urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
. Containing reduced nitrogen, these compounds are components of fertilizers.
All of these compounds enter into the nitrogen cycle.
As a consequence, an excess of Nr can affect the environment relatively quickly. This also means that nitrogen-related problems need to be looked at in an integrated manner.http://international.vrom.nl/pagina.html?id=37594
See also
*Human impact on the nitrogen cycle
Human impact on the nitrogen cycle is diverse. Agricultural and industrial nitrogen (N) inputs to the environment currently exceed inputs from natural N fixation. As a consequence of anthropogenic inputs, the global nitrogen cycle (Fig. 1) has b ...
References
;Citations ;General references * * {{refend Cycle Biogeochemical cycle Soil biology Nitrogen cycle Metabolism Biogeography Intensive farming