Reactive Nitrogen in the Environment: Too Much or Too Little of a Good Thing

About 40% of the human population depends upon food production made possible by synthetic nitrogen fertilizers. Combustion of fossil fuels adds more reactive nitrogen to air, water and soil. This distortion of the global nitrogen cycle, while raising agricultural yields, causes degradation of water and air quality, biodiversity, ecosystem services and human health. This review examines the impacts of reactive nitrogen on the environment, human health and economies from local to global scales.