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GEO Year Book 2003  
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More than was bargained for

Reactive nitrogen does not cascade at the same rate through all sectors of the environment. Some systems (most notably forest and grassland soils) are able to slow down the continuation of the cascade by accumulating reactive nitrogen and therefore acting as reservoirs. However, most systems have a finite capacity to accumulate reactive nitrogen. As a system becomes saturated, more and more reactive nitrogen moves from these storage reservoirs to systems downwind or downstream. Table 1 shows those systems that have large accumulation potential and those from which reactive nitrogen is most readily transferred. It also shows where reactive nitrogen is likely to move to, and some potential effects of excess nitrogen within each system.

Table 1. Characteristics of different systems in relation to the nitrogen cascade

System

Accumulation potential Transfer potential Links to other systems Effects potential
Atmosphere Low Very high All but groundwater Human and ecosystem health, climate change
Agroecosystems Low to moderate Very high All Human and ecosystem health, climate change
Forests High Moderate, high in places All Biodiversity, net primary productivity, plant mortality, groundwater
Grasslands High Moderate, high in places All Biodiversity, net primary productivity, groundwater
Groundwater Moderate Moderate Surface water, atmosphere Human and ecosystem health, climate change
Wetlands, streams, lakes, rivers Low to moderate Very high Atmosphere, marine coastal systems Biodiversity, ecological structure, eutrophication, harmful algal blooms
Marine coastal regions Low to moderate Moderate Atmosphere Biodiversity, ecological structure, fish, eutrophication, harmful algal blooms, hypoxia
Source: Galloway and others 2003 

With more anthropogenic reactive nitrogen present in the environment, it is likely to be increasingly mobilized from storage reservoirs, compounding the consequences on people and ecosystems. However, just as anthropogenic activities have substantially increased the rate of reactive nitrogen formation, so is it possible to intervene at critical points along the nitrogen cascade and make reactive nitrogen less abundant. This can be done in two ways – decreasing the rate of reactive nitrogen creation during energy and food production, or converting reactive nitrogen back to N2 after it has been created and used.


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