"The bottom line is streams have an impact. They can remove as much as 50 percent of the inorganic nitrogen. So anything we do to streams to modify them will impact the nitrogen that reaches rivers, lakes, bays and oceans," says Webster. The finding could have important consequences for land-use policies.
What happens to the nitrogen that is removed from streams? The Science article reports that some of the nitrogen is converted to nitrogen gas through denitrification processes and the rest becomes nutrition for algae, bacteria and fungi, which then become food for aquatic insects and fish. As the plant or organism dies, the nitrogen can then end up as slowly decomposing materials that settle in the stream or lake sediments, Webster says.
He explains that plant life, particularly algae, is a very important nitrogen-user in some streams -- such as in Alaska, Arizona and Kansas, where there are few trees to block the sun. Alternatively, in forested streams, such as those in Oregon and North Carolina, nitrogen is removed by fungi and bacteria, which do not photosynthesize, but decompose dead organic material settled on the stream bottom, also a food resource for some aquatic insects.
"The smaller the stream, the more quickly nitrogen can be removed and the less distance it will be transported down the stream," Peterson says. Thus, taking greater care to insure that small streams can work effectively to clean the water will reduce the overall nitrogen load that makes its way into larger bodies of water. "It doesn't m
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Contact: Bruce Peterson
peterson@mbl.edu
508-289-7484
Virginia Tech
5-Apr-2001