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Small streams remove up to 50 percent of the nitrogen that enters their waters, a new study by researchers from more than a dozen institutions reveals in the April 6 issue of Science. The finding could have important consequences for land use policies.
Researchers studied streams from Puerto Rico to Alaska during a two-year period.
The study revealed that some of the nitrogen removed from streams is converted to nitrogen gas, 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 end up as decomposing materials that settle in stream or lake sediments.
Human activities, such as fertilizer application and the burning of fossil fuels, result in excess nitrogen entering streams, changing water quality downstream such as in the Chesapeake Bay or Gulf of Mexico. Excess nitrogen has led to so called dead zones in these areas, where the decomposition of algae removes oxygen from the water, suffocating fish and other species.
Efforts to minimize nitrogen in these waterways have focused on the land, since the process of nitrogen uptake and release in streams has been unclear. But breakthroughs in nitrogen tracers and computer models have allowed scientists to track nitrogen through streams.
"The smaller the stream, the more quickly nitrogen can be removed and the less distance it will be transported down the stream," said Bruce Peterson of the Marine Biological Laboratory in Woods Hole, Mass.
Taking greater care to insure that small streams can work to clean the water will reduce the overall nitrogen load that makes its way into larger bodies of water, he noted.
"It doesn't mean that you can ignore your sewage treatment plants, but if we can do better with our small streams and do some restoration activities, it's going to have some benefits," Peterson said.