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 Program
References cited

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For further information about this report, contact the National Water-Quality Assessment Program office.

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