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Review
. 2013 May 27;368(1621):20130164.
doi: 10.1098/rstb.2013.0164. Print 2013 Jul 5.

The global nitrogen cycle in the twenty-first century

David Fowler  1 , Mhairi Coyle, Ute Skiba, Mark A Sutton, J Neil Cape, Stefan Reis, Lucy J Sheppard, Alan Jenkins, Bruna Grizzetti, James N Galloway, Peter Vitousek, Allison Leach, Alexander F Bouwman, Klaus Butterbach-Bahl, Frank Dentener, David Stevenson, Marcus Amann, Maren Voss
Affiliations
Review

The global nitrogen cycle in the twenty-first century

David Fowler et al. Philos Trans R Soc Lond B Biol Sci. .

Abstract

Global nitrogen fixation contributes 413 Tg of reactive nitrogen (Nr) to terrestrial and marine ecosystems annually of which anthropogenic activities are responsible for half, 210 Tg N. The majority of the transformations of anthropogenic Nr are on land (240 Tg N yr(-1)) within soils and vegetation where reduced Nr contributes most of the input through the use of fertilizer nitrogen in agriculture. Leakages from the use of fertilizer Nr contribute to nitrate (NO3(-)) in drainage waters from agricultural land and emissions of trace Nr compounds to the atmosphere. Emissions, mainly of ammonia (NH3) from land together with combustion related emissions of nitrogen oxides (NOx), contribute 100 Tg N yr(-1) to the atmosphere, which are transported between countries and processed within the atmosphere, generating secondary pollutants, including ozone and other photochemical oxidants and aerosols, especially ammonium nitrate (NH4NO3) and ammonium sulfate (NH4)2SO4. Leaching and riverine transport of NO3 contribute 40-70 Tg N yr(-1) to coastal waters and the open ocean, which together with the 30 Tg input to oceans from atmospheric deposition combine with marine biological nitrogen fixation (140 Tg N yr(-1)) to double the ocean processing of Nr. Some of the marine Nr is buried in sediments, the remainder being denitrified back to the atmosphere as N2 or N2O. The marine processing is of a similar magnitude to that in terrestrial soils and vegetation, but has a larger fraction of natural origin. The lifetime of Nr in the atmosphere, with the exception of N2O, is only a few weeks, while in terrestrial ecosystems, with the exception of peatlands (where it can be 10(2)-10(3) years), the lifetime is a few decades. In the ocean, the lifetime of Nr is less well known but seems to be longer than in terrestrial ecosystems and may represent an important long-term source of N2O that will respond very slowly to control measures on the sources of Nr from which it is produced.

Keywords: denitrification; deposition; emissions; global budgets; nitrogen fixation.

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Figures

Figure 1.
Figure 1.
Global nitrogen fixation, natural and anthropogenic in both oxidized and reduced forms through combustion, biological fixation, lightning and fertilizer and industrial production through the Haber–Bosch process for 2010. The arrows indicate a transfer from the atmospheric N2 reservoir to terrestrial and marine ecosystems, regardless of the subsequent fate of the Nr. Green arrows represent natural sources, purple arrows represent anthropogenic sources.
Figure 2.
Figure 2.
The processing and fluxes of reactive nitrogen in terrestrial and marine systems and in the atmosphere (Tg N yr−1), showing the dominant forms of the Nr in the exchanges and the magnitude of the boundary fluxes, and approximate lifetimes, integrated over global scales.
Figure 3.
Figure 3.
The global atmospheric processing of reactive nitrogen, illustrating the main sources, the main chemical pathways and products and the magnitudes of the fluxes (units Tg yr−1). The emission flux values in black are the total fluxes while the red values indicate the anthropogenic contribution.
Figure 4.
Figure 4.
The nitrogen cycle within the EU-27 showing natural fluxes (Tg N) in green, (intentional) anthropogenic fluxes as blue and (unintentional) as orange adapted from the ENA [69]. The terrestrial component of the cycle is delineated by the dotted ellipse.
Figure 5.
Figure 5.
A simplified schematic of nitrogen cycling in the global oceans (adapted and simplified from [17]). The fluxes are as detailed in the text to be consistent with figure 2.
See this image and copyright information in PMC

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