Nitrogen fluxes from the landscape are controlled by net anthropogenic nitrogen inputs and by climate
Frontiers in Ecology and the Environment, 2011.
In a nutshell:• Nitrogen (N) pollution is one of the primary threats to the ecological integrity of estuaries and other coastal marine ecosystems• Although synthetic fertilizer is the main source of N pollution in many areas, other sources – such as atmospheric deposition and the movement of N in food and animal feeds – contribute, and are sometimes dominant
• N fluxes in rivers to coastal ecosystems increase as the “net anthropogenic nitrogen inputs” (NANI) to the landscape
increase
• NANI provides a powerful approach for estimating these N fluxes and for determining
Article abstract
The flux of nitrogen (N) to coastal marine ecosystems is strongly correlated with the “net anthropogenic nitrogen inputs” (NANI) to the landscape across 154 watersheds, ranging in size from 16 km² to 279 000 km², in the US and Europe. When NANI values are greater than 1070 kg N km–2 yr–1, an average of 25% of the NANI is exported from those watersheds in rivers.
Our analysis suggests a possible threshold at lower NANI levels, with a smaller fraction exported when NANI values are below 1070 kg N km–2 yr–1. Synthetic fertilizer is the largest portion of NANI in many watersheds, but other inputs also contribute substantially to the N fluxes; in some regions, atmospheric deposition of N is the major component. The flux of N to coastal areas is controlled in part by climate, and a higher percentage of NANI is exported in rivers, from watersheds that have higher freshwater discharge.
Available online December 2011
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