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:
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.
• Nutrients in the Nation's Waters--Too Much of a Good Thing?: USGS Circular 1136
• The Quality of our Nation's Waters: USGS Circular 1225
• USGS National Water-Quality Assessment (NAWQA) Program