News Release

High levels of nitrate found in agricultural areas

Nitrate concentrations in ground water and surface water are higher in agricultural areas than in urban or forested areas in the Lower Susquehanna River Basin, according to a new report by the U.S. Geological Survey (USGS), which is conducting a multi-year study of water quality in the Lower Susquehanna River Basin as part of a program called the National Water-Quality Assessment (NAWQA). Nitrate is of major concern in drinking water because of its potential effects on human health. Also, excessive amounts of nitrate can cause undesirable growth of aquatic plants in surface water.

One of the priority topics for the Lower Susquehanna River Basin NAWQA study was to determine the occurrence and distribution of nitrate, a chemical form of nitrogen, in ground and surface water and to explain, to the extent possible, the natural and human factors that affect nitrate concentrations. According to Hydrologist Bruce Lindsey, "The human activities on the land surface, such as application of fertilizers and manure on croplands, have a significant effect on the concentration of nitrate that ends up in the ground water or streams." "Nitrate concentrations are highest in ground water in agricultural areas underlain by limestone bedrock. Forty-five percent of the wells sampled in agricultural areas underlain by limestone had water with nitrate concentrations that exceeded the U.S. Environmental Protection Agency Maximum Contaminant Level for drinking water of 10 milligrams per liter." Lindsey explained, "The limestone bedrock has features such as large fractures, caverns, and sinkholes that allow nitrate to move rapidly from the surface to the ground water."

Nitrate concentrations in small streams vary throughout the year; the highest concentrations were detected in the fall and winter. The study also showed differences among various source areas for nitrate that flows into the Chesapeake Bay from the Lower Susquehanna River Basin. Lindsey explained, "The Lower Susquehanna River Basin has some areas where manure from animal operations contains much more nitrogen than crops can use; the excess runs off into streams or infiltrates into the ground water and eventually much of it ends up in the Chesapeake Bay." According to the study, the manure application rate may be the most important factor controlling nitrate concentrations in surface water in agricultural basins.

The report is based on data collected from 161 wells and 156 streams from 1993 to 1995, prior to full implementation of the Pennsylvania nutrient management law requiring management plans for fertilizer and manure. Follow up studies, scheduled to begin in 2001, may provide insight into how effective nutrient management legislation has been at reducing nitrogen in ground water and streams of the Lower Susquehanna River Basin.

The report, "Nitrate in Ground Water and Stream Base Flow in the Lower Susquehanna River Basin, Pennsylvania and Maryland," by Bruce D. Lindsey, Connie A. Loper, and Robert A. Hainly, is published as Water-Resources Investigations Report 97-4146. Copies of the report are available at the USGS office at 215 Limekiln Road New Cumberland, PA 17070-2424; telephone (717) 730-6900.

Copies can be purchased from:

U.S. Geological Survey
Branch of Information Services
Box 25286
Denver, Colorado 80225-0286
Telephone: (303) 202-4700

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