Also shown is the tight coupling between the nitrogen

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Unformatted text preview: Biological’ phosphorus Figure 1 | Depiction of the global nitrogen cycle on land and in the ocean. Major processes that transform molecular nitrogen into reactive nitrogen, and back, are shown. Also shown is the tight coupling between the nitrogen cycles on land and in the ocean with those of carbon and 25 Burial ‘Biological’ phosphorus phosphorus. Blue fluxes denote ‘natural’ (unperturbed) fluxes; orange fluxes denote anthropogenic perturbation. The numbers (in Tg N per year) are values for the 1990s (refs 13, 21). Few of these flux estimates are known to better than ±20%, and many have uncertainties of ±50% and larger13,21. 294 Gruber & Galloway, Nature, 2008 Nitrogen Sources to soils •  Important atmospheric phases (NH4+, NO3- , NOx, N2O, N2) •  Main sources: –  N- fixa:on of atmos. N2 (human or microbial) –  Decomposi:on of organic maSer releases N (NH4+; NO3- ) Losses to rivers –  Par:culate N (minor) •  Organic N –  Dissolved N (major) •  Organic N •  Inorganic N –  Major: nitrate ion (NO3- ) »  mobile anion easily l...
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