National Water-Quality Assessment (NAWQA) Program
U.S. Geological Survey
Water-Resources Investigations Report 94-4001
Nonpoint and Point Sources of Nitrogen in Major Watersheds
of the United States
By Larry J. Puckett
Estimates of nonpoint and point sources of nitrogen were made for 107
watersheds located in the U.S. Geological Survey's National Water-Quality
Assessment Program study units throughout the conterminous United States.
The proportions of nitrogen originating from fertilizer, manure, atmospheric
deposition, sewage, and industrial sources were found to vary with
climate, hydrologic conditions, land use, population, and physiography.
Fertilizer sources of nitrogen are proportionally
greater in agricultural areas of the West and the Midwest than in other
parts of the Nation. Animal manure contributes large proportions of
nitrogen in the South and parts of the Northeast. Atmospheric
deposition of nitrogen is generally greatest in areas of greatest
precipitation, such as the Northeast. Point sources (sewage and industrial)
generally are predominant in watersheds near cities, where they may account
for large proportions of the nitrogen in streams. The transport of nitrogen
in streams increases as amounts of precipitation and runoff increase and is
greatest in the Northeastern United States. Because no single nonpoint
nitrogen source is dominant everywhere, approaches to control nitrogen must
vary throughout the Nation. Watershed-based approaches to understanding
nonpoint and point sources of contamination, as used by the National
Water-Quality Assessment Program, will aid water-quality and environmental
managers to devise methods to reduce nitrogen pollution.
Table of Contents
- Why be concerned about nitrogen?
- What are the major sources of nitrogen?
- Animal Manure
- Atmospheric Deposition
- Point Sources
- Proportions of nonpoint and point
sources of nitrogen
- What are the implications
for national water-quality programs?
- The National Water-Quality Assessment
- References cited
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