The same atom of reactive nitrogen (Nr) can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems; reactive nitrogen also has effects 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 non-reactive N2.
Source: Galloway et al. (2003) The nitrogen cascade. Bioscience 53: 341-356
This nitrogen cascade makes finding solutions to problems associated with Nr a difficult task. For this reason it is necessary that different sectors in society, such as the agriculture and industry to cooperate. The most effective actions in this respect aim at preventing the formation of Nr. Furthermore, policy actions should not move the problem from one place to the other or lead to the transformation of one form of Nr into the other. For example, reducing ammonia emissions from animal houses results in more Nr in the manure available for spreading, which in turn leads to more nitrate, ammonia, nitrous oxide or nitric oxide emissions.
International effort needed
The problems associated with reactive nitrogen (Nr) largely occur at the international level. For example, export of nitrogen in the form of animal feedstuffs and transport of nitrogen through air and water is a transboundary problem. International agreements are needed to combat these problems, since a less stringent policy for Nr in a country other than a neighboring one could bring economic advantages. One example of international agreement and regulation is evident in the Nitrate Directive in the European Union. The need for international cooperation is also expressed in frequent international scientific and policy conferences on nitrogen.
International nitrogen conferences dealing specifically with nitrogen in all its scientific and policy dimensions, are organized for this purpose. The first was held in 1998 in the Netherlands. The aim of these conferences is to exchange knowledge and bridge the gap between science and policy so as to encourage the formulation of policy actions based on the latest scientific facts.
The third international nitrogen conference, held in Nanjing, China in 2004, was marked by signing of the Nanjing declaration on nitrogen management. Global nitrogen balances and efficiency of nitrogen use in agricultural systems formed the topic of an invited PBL (formerly MNP) presentation.
- Third international nitrogen conference
- Nanjing declaration (PDF)
- Presentation: Surface N balances and reactive N loss from global intensive agricultural production systems for the period 1970-2030 (PDF)
The fourth international nitrogen conference was held in Brazil in October 2007. During this meeting a policy agenda for nitrogen based on the Millennium Development Goals was prepared for the period up to 2025. In this way the problems and proposed policy actions will receive due attention at the international level. During this conference PBL (formerly MNP) prepared a presentation on nitrogen cascade effects of biofuels and the production of energy crops.
- Fourth international nitrogen conference in Brazil
- Presentation: Consequences of the cultivation of energy crops for the global nitrogen cycle (PDF)