National Water-Quality Assessment (NAWQA) Program

U.S. Geological Survey
Circular 1136

Nutrients in the Nation's Waters--Too Much of a Good Thing?

By David K. Mueller and Dennis R. Helsel

photo - Fir Creek near Brightwood, OR, drains old growth forest before
becoming drinking water for the city of Portland. (Photo by Dennis Wentz.) (798K GIF)


Nutrients are essential for plant and animal growth and nourishment, but the overabundance of certain nutrients in water can cause a number of adverse health and ecological effects. To determine the extent of nutrient and other types of contamination in the Nation's streams and ground water, we analyzed data from about 12,000 ground-water samples and more than 22,000 surface-water samples collected at more than 300 sites between October 1979 and September 1990. Most samples had been collected within NAWQA study units. Nutrient concentrations in water generally are related to land use in the upstream watershed or the area overlying a ground-water aquifer. Nitrate concentrations were generally higher in ground water than in streams. Concentrations were highest in the Northeast, Great Plains, and along the West Coast. Drinking water from public-supply wells and domestic-supply wells outside of agricultural areas is not likely to have high levels of nitrate. Domestic-supply wells in agricultural areas are more prone to increased concentrations. Ammonia and phosphorus concentrations in surface water are highest downstream from urban areas. Where these concentrations are high, they warrant concerns about decreased oxygen in the water, toxicity to fish, and accelerated eutrophication.

Table of Contents

Major findings
What parts of the Nation are most affected?
What are nutrients?
Are drinking-water supplies affected?
Ground water
Surface water
What information can science provide for policy decisions?
What are the concerns about nutrients in water?
What are the sources of nutrients in water?
Sewage effluent
How large are natural concentrations of nutrients in water?
What are the major influences on nutrients concentrations in water?
Land use
Soil drainage
Depth to ground water
Is the nutrient situation getting better or worse?
Ground water
Surface water
Where can I get more information?
Other publications referred to in the report
A coordinated effort
Publications of the National Water-Quality Assessment (NAWQA) Program related to data used in this report

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

FirstGov button  Take Pride in America button