BLACKSBURG, Va.Preliminary research results on the hyporheic zones of streamsthe region in which stream and ground waters mixin different types of environments show that hyporheic activity accounted for up to 70 percent of stream respiration as oxygen demand and 10 percent to 50 percent of nitrate uptake. The results suggest that the retention of nitrate in the stream increases with the size of the hyporheic zone. Steven A. Thomas, a research scientist in biology at Virginia Tech, and colleagues at Virginia Tech, the University of New Mexico, and the Environmental Science Division at Oak Ridge National Laboratory have been examining the hyporheic zone beneath streams, where surface and subsurface waters mix. This region is a "hot spot," Thomas said, because biological activity there may be a significant player in stream nitrogen dynamics.
Thomas and his fellow researchers are midway through a three-year grant from the National Science Foundation, and their results tend to show that about half the nitrogen retained in streams occurs in the hyporheic zones. They are examining the ability of such areas to take the nitrogen out of the water. "Streams that have high amounts of surface-subsurface exchange tend to retain more nitrogen," Thomas said.
While retention might be temporary, it is ultimately desirable that the nitrogen be returned to a gaseous dinitrogen, he said. Retention delays the sweeping of the materials downstream, but if denitrification does not occur, the material will be transported downstream, where it may alter environmental conditions. "We're trying to determine whether hyporheic zones are important denitrification areas and therefore important in the global nitrogen cycle," he said.
For example, agricultural areas often use fertilizer, containing nitrogen and phosphorous, which ultimately runs off into nearby streams. This process results in higher levels of nitrogen than naturally occur in the streams and may cause species shifts, or
Contact: Steven A. Thomas