Global Nitrogen Overload

Nitrogen is one of the primary soil nutrients needed by plants, and in some (particularly agricultural) ecosystems it is a limiting factor for vigorous plant growth. As nitrogen in the form of nitrates or ammonia is deposited on the soil from anthropogenic releases, the excess nitrogen will be taken up by plants until the natural removal rate is reached. Different land use categories (plant types) have different capacities for removing nitrogen. For instance, boreal forests can remove about 15 kg/ha/y whereas arable farm land or rich pasture can remove 40 kg/ha/y or more.

A recent research summary by Anne Simon Moffat (Science 279, 988-989) points out the critical nature of a global overload of nitrogen compounds. Fixed nitrogen (ammonia, nitrogen oxides) is beginning to overwhelm a wide range of forest, lake, river, and coastal ecosystems. One "ecological service" of natural ecosystems is to absorb or breakdown these compounds, but the increased volume of nitrogen compounds is increasingly overwhelming these natural systems.

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