AN ENCYCLOPEDIA OF SUSTAINABILITY
Heading: Environment Topic: Nitrogen
Human activities have more than doubled the cycling of nitrogen in the earth's system. As much as 70 % of reactive nitrogen in the atmosphere, soil and seas has come from human activities, and represents an environmental threat and risk to human health probably more serious than the carbon causing climate change (Hooper, 2006). Four-fifths of nitric oxide emissions worldwide now come from human activities such as the combustion of fossil fuels, cultivation of certain crops, and especially the manufacture of nitrogen-rich fertilisers. The amount of industrially-fixed nitrogen applied to crops during the decade from 1980 to 1990 more than equals all that applied previously in human history (Pearce, 1997). Nitrogen oxides from fossil fuel combustion cause ground-level ozone, and ammonia from agriculture, are both lung irritants and cause asthma. Nitrous oxide has reached almost the same atmospheric concentration as carbon dioxide, but is 300 times as potent as a greenhouse gas (Hooper, 2006). Nitrogen saturation causes eutrophication in coastal waters, urban smog, the death of trees, acidification of rivers and lakes, the leaching of nutrients from soils and the loss of fragile heaths. Symptoms of eutrophication (the process of over-fertilization whereby an aquatic or marine ecosystem may lose much of its natural capacity to support a wide variety of vegetation and wildlife) include toxic algal blooms, loss of fish habitat, hypoxia and anoxia, changes in species composition of plankton, elimination of entire food chains, and the death of fish and shellfish (Sea Technology, Dec 1996 & Jan 1997).
There are now calls for a global convention on nitrogen similar to that for climate change (Hooper, 2006). Since nitrogen emissions are so closely linked to fossil fuels and intensive agriculture, the only sustainable solution is less consumptive lifestyles.
REFERENCES AND SOURCES
Based partly on materials originally prepared for UN System-wide Earthwatch