FIGURE 1. Depiction of the global nitrogen cycle on land and in the ocean.

From the following article:

An Earth-system perspective of the global nitrogen cycle

Nicolas Gruber & James N. Galloway

Nature 451, 293-296(17 January 2008)

doi:10.1038/nature06592

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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 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 plusminus20%, and many have uncertainties of plusminus50% and larger13, 21.

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