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Instream wetland
In-stream wetland, Herrings Marsh Run watershed, Duplin county, N.C.

In-Stream Wetlands Can Improve Water Quality

By Hank Becker
June 30, 1998

Cleaning up excess nitrogen and other nutrients in soil before they run off and enter bodies of water is becoming a major concern in the eastern United States. Scientists recently found that constructing a wetland in a stream can remove nitrogen that otherwise would continue traveling downstream.

Scientists with USDA’s Agricultural Research Service and North Carolina State University-Raleigh tested an 8-acre in-stream wetland as a water quality improvement practice. The work was part of a USDA Water Quality Demonstration Project in Herrings Marsh Run watershed in North Carolina. The scientists created the in-stream wetland by stabilizing the wall of an old dam.

Water in the wetland was 6 feet deep at the lower end, but in most places it was less than 2 feet deep. About 40 percent of the wetland was covered by aquatic weeds; another 40 percent was mainly trees.

The wetland’s area was less than 1 percent of the area of the watershed that drained through it. But the wetland lowered the amount of nitrogen in the stream by about 40 percent.

The reduction was greatest in warm months. During these times, water high in nitrogen as nitrate--about 7 parts per million as it entered the wetland--left it carrying less than 1 ppm. The nitrate was taken up by plants or changed to gaseous nitrogen by beneficial bacteria.

The ARS scientists in the project are based at the agency’s Coastal Plains Soil, Water and Plant Research Center in Florence, S.C.

An article on the wetland project appears in the June issue of Agricultural Research, the monthly publication of ARS. The article is also on the World Wide Web at:


Scientific contact: Patrick G. Hunt, ARS Coastal Plains Soil, Water and Plant Research Center, Florence, S.C., phone (803) 669-5203, fax (803) 669-6970,

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