The Nitrogen Cascade

TLDR

Human food and energy production breaks atmospheric N₂ into reactive nitrogen, which circulates through air, water, and ecosystems, causing diverse environmental and health impacts. The study defines the nitrogen cascade and proposes that converting reactive nitrogen back to N₂ is the only way to halt its accumulation. The cascade proceeds independently of the nitrogen source once it enters the system. The cascade rate varies across systems, with some reservoirs accumulating reactive nitrogen and creating lag times that amplify its environmental effects.

Abstract

Human production of food and energy is the dominant continental process that breaks the triple bond in molecular nitrogen (N2) and creates reactive nitrogen (Nr) species. Circulation of anthropogenic Nr in Earth’s atmosphere, hydrosphere, and biosphere has a wide variety of consequences, which are magnified with time as Nr moves along its biogeochemical pathway. The same atom of Nr can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health. We call this sequence of effects the nitrogen cascade. As the cascade progresses, the origin of Nr becomes unimportant. Reactive nitrogen does not cascade at the same rate through all environmental systems; some systems have the ability to accumulate Nr, which leads to lag times in the continuation of the cascade. These lags slow the cascade and result in Nr accumulation in certain reservoirs, which in turn can enhance the effects of Nr on that environment. The only way to eliminate Nr accumulation and stop the cascade is to convert Nr back to nonreactive N2.