Small Streams, Big Impact

A new study finds that healthy streams—even very small ones—play a significant role in keeping pollutants from ending up in lakes and oceans

• Hannah Schardt
• Apr 01, 2008

WHEN IT COMES to the cleaning power of waterways, size doesn't always matter. A new study published in the journal Nature finds that healthy streams--even very small ones--play a significant role in keeping pollutants such as nitrogen from ending up in lakes and oceans. Excess nitrogen, often found in runoff from farms, can wreak havoc downstream by stimulating algae blooms and depleting the water of oxygen, situations that threaten many important fisheries.

Researchers added small amounts of a harmless nitrogen isotope in 72 streams in the United States and Puerto Rico, then traced the isotope's movement through the waterways. They found that in small to moderate amounts, the nitrate was effectively removed by the streams, either by algae and other tiny organisms or by denitrification, which occurs when microbes convert nitrate to nitrogen gas, allowing it to return, inert, to the atmosphere. In much higher amounts, that effectiveness disappeared.

Based on their findings, the researchers recommend that even small stream ecosystems should be protected and restored--and not overused as a means of filtering pollutants. "Our results show streams can help us use natural resources, but this capacity has its limits," says study coauthor Stuart E.G. Finlay of the Cary Institute of Ecosystem Studies in Millbrook, New York.