Small Streams Help Clean Big Waterways

(The following is an excerpt from a news release issued by the National Science Foundation.)

Small streams remove more nutrients such as nitrogen from water than do their larger counterparts, according to researchers who have applied sampling methods developed in a National Science Foundation (NSF) Arctic area ecological study to waterways across the nation. The finding could have important implications for land-use policies in watersheds from the Chesapeake Bay on the East Coast to Puget Sound in the West.

The findings, published in Science* magazine, are based on data collected initially from streams in NSF’s Arctic Tundra Long-Term Ecological Research site in Alaska. Excess nitrogen can cause ecologically damaging effects, including algae blooms, in large waterways because the nutrients are transported downstream and collect there.

“There’s a very strong relationship between the size of a stream and how rapidly that stream removes nutrients,” said Bruce Peterson of the Ecosystems Center at the Marine Biological Laboratory in Woods Hole, Massachusetts. “The smaller the stream, the more quickly nitrogen can be removed and the less distance it will be transported down the stream.” He noted that the findings are unique because research teams working in a coordinated and identical fashion nationwide under the same research protocol produced them.

“In terms of ecosystems studies it’s very rare to get people from this many sites to agree to do this kind of controlled experiment,” Peterson said. “Many people study nitrogen cycling, but they all tend to do their own experiments. Collaboration is the key to developing a general understanding of ecosystems.”

Peterson notes that, collectively, the new studies provide a radically different picture of the role of small streams in contributing to existing nutrient loading. “Traditionally streams have been thought of as transport systems moving substances from catchments to downstream points,” he said. “It’s been difficult to understand how dynamic the stream system itself is.”

By placing tracers in smaller streams, the researchers discovered how quickly nutrients were assimilated and processed by organisms that live on the stream beds.

The findings could have important implications for land use policies. In many agricultural areas, for example, small streams are often covered to allow ease of access for tilling and working fields. The covering, in effect, creates a dark pipe that inhibits the stream’s ability to scrub excess nutrients.

While excess nitrogen has many sources, including runoff from residential lawns and byproducts of automobile combustion, 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 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. “What it means is that you have to take care of the streams on the landscape.”

* Science 2001 April 6; 292: 86-90, American Association for the Advancement of Science.

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