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The effects of urbanization and agriculture
on water quality: Nitrogen

Nitrogen, in the forms of nitrate, nitrite, or ammonium, is a nutrient needed for plant growth. About 78% of the air that we breathe is composed of nitrogen gas, and in some areas of the United States, particularly the northeast, certain forms of nitrogen are commonly deposited in acid rain. Although nitrogen is abundant naturally in the environment, it is also introduced through sewage and fertilizers. Chemical fertilizers or animal manure is commonly applied to crops to add nutrients. It may be difficult or expensive to retain on site all nitrogen brought on to farms for feed or fertilizer and generated by animal manure. Unless specialized structures have been built on the farms, heavy rains can generate runoff containing these materials into nearby streams and lakes. Wastewater-treatment facilities that do not specifically remove nitrogen can also lead to excess levels of nitrogen in surface or ground water. Two of the major problems with excess levels of nitrogen in the environment are:

• Excess nitrogen can cause overstimulation of growth of aquatic plants and algae. Excessive growth of these organisms, in turn, can clog water intakes, use up dissolved oxygen as they decompose, and block light to deeper waters. This seriously affects the respiration of fish and aquatic invertebrates, leads to a decrease in animal and plant diversity, and affects our use of the water for fishing, swimming, and boating.
• Too much nitrate in drinking water can be harmful to young infants or young livestock.

For information on the status and trends of nitrogen and phosphorus in the nation's surface and ground water, visit the USGS site Nutrients in the Nation's Waters--Too Much of a Good Thing? (http://water.usgs.gov/nawqa/CIRC-1136.html). This USGS circular was produced by the National Water-Quality Assessment (NAWQA) Program, which was designed to describe the status and trends in the quality of the Nation's ground- and surface-water resources and to provide a sound understanding of the natural and human factors that affect the quality of these resources.

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U.S. Department of the Interior | U.S. Geological Survey
URL: http://ga.water.usgs.gov/edu/urbannitrogen.html
Page Contact Information: Howard Perlman
Page Last Modified: Friday, 07-Nov-2008 15:46:28 EST