Executive summary
Nitrogen is an essential, fundamental building block for life. It is the most plentiful element in the earth’s atmosphere, yet in its molecular form (N2), it is unusable by the vast majority of living organisms. It must be transformed, or fixed, into other forms, collectively known as reactive nitrogen (See Glossary), before it can be used by most plants and animals. Without an adequate supply of nitrogen, crops do not thrive and fail to reach their maximum production potential. In many ecosystems, nitrogen is the limiting element for growth. However, when present in excess, reactive nitrogen causes a range of negative environmental effects, poses risks to human health and consequently can have negative economic and social consequences. This nontechnical review seeks to convey an understanding of the effects of reactive nitrogen in the environment, focusing mainly on those caused by excesses of reactive nitrogen. It also examines experience with some policies developed to address those effects, and offers recommendations to advance understanding and policy responses to them.
