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Individual Highlight

Changes in Water Quality Last More Than 30 Years After Clear Cutting

Photo of Watershed 7 following harvest using timber cutting and yarding with mobile cable system January 1977–June 1978. Wayne Swank, U.S. Department of Agriculture Forest Service.Watershed 7 following harvest using timber cutting and yarding with mobile cable system January 1977–June 1978. Wayne Swank, U.S. Department of Agriculture Forest Service.Snapshot : Evidence from 36 years of data following experimental clear-cut logging at Coweeta Hydrologic Laboratory, N.C., suggests that forest disturbance in the southern Appalachian mountains can cause elevation of nitrogen in streamflow. These elevated nitrogen levels an last decades or perhaps longer.

Principal Investigators(s) :
Knoepp, Jennifer D. 
Research Location : Coweeta Hydrologic Lab, Otto, N.C.
Research Station : Southern Research Station (SRS)
Year : 2016
Highlight ID : 1087

Summary

After disturbances, healthy ecosystems are usually resilient enough to return to a pre-disturbance state; however, some disturbances are extreme enough to permanently shift an ecosystem, a phenomenon known as a regime shift. In a study of the effects of clear-cut logging, Forest Service scientists found surprising effects on water chemistry, effects that persisted almost 40 years after the experimental clearcut. In the clearcut watershed, dissolved nitrogen was higher, and the seasonal spike in nitrogen concentration had shifted from summer to winter. Nitrogen enters the forest via several pathways and, in the studied watershed, one of the most important sources was black locust. Black locust dominated the clearcut watershed for the first 10 years after the cut. The species, which is native to the southern Appalachians, has nitrogen-fixing bacteria in its roots. The bacteria can convert atmospheric nitrogen to a form that plants can use for growth. The scientists suggest that the long-term elevation of stream nitrogen concentration and export along with the changes in seasonality of nitrogen export and the relationship between concentration and discharge represent a functional regime shift initiated by forest disturbance. This regime shift was not predicted, nor would it have been understood without the long-term and large-scale experimentation possible in FS Experimental Forests.

Forest Service Partners

External Partners

  • Nantahala Ranger District
  • National Science Foundation Long-Term Ecological Research Program
  • Virginia Polytechnic State and University