Linking Anthropogenic Reactive N Release to Localized Environmental Pollution: Reactive N Spatial Intensity.

Nitrogen (N) footprint has been developed as an indicator to quantify the release of reactive nitrogen (Nr; all species of nitrogen except N₂) to the environment from anthropogenic food production and consumption, and energy use, on a per capita basis. However, the Nr release on a per capita basis may not be proportionate to its impact on the environment, which is governed by the intensity of the Nr release on a per area basis. This means a large N footprint may represent little environmental pollution, and vice versa. In that regard we developed an indicator of Nr release spatial intensity (NrSI) that links human activities with localized environmental pollution for eight countries which have quantified their N footprints. We found that vegetable and dairy production were the hot-spots of Nr release, with the NRI values ranging from 124-457 and 4-537 kg N ha^-1 yr^-1, respectively. Urban areas were also hot-spots of Nr release because of intense food and energy consumption. Among the eight countries, Australia had the lowest NRI (7 kg N ha^-1 yr^-1) while Japan and the Netherlands had nearly equal largest values (around 330 kg N ha^-1 yr^-1). This follows an opposite trend to that of the N footprint of these countries. The development of NRI complements the current N footprint framework in spatially linking anthropogenic Nr release with environmental pollution for effective mitigation of Nr release.