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Little Streams, Big Impact

EPA researchers have been traversing Oregon to develop a small stream classification system that will help states protect water bodies far downstream.

Overhead image of a stream

Water flows. The water that fills the lakes, rivers, and other large water bodies might have begun flowing in the far, upper reaches of a watershed, in small streams that hydrologists and others specialists refer to as “headwaters.” Fed by sources such as rainfall, runoff, and underground waters, these small, sometimes intermittent natural ecosystems can be easy to overlook.

But despite their obscurity, headwater streams may play a critical role both sustaining local plants and animals and in maintaining water quality even far downstream.

EPA researchers are working to develop a classification system that will help state officials and other resource managers identify headwaters that should be protected under the Clean Water Act (CWA).

The researchers have been traversing Oregon to develop a classification system that will predict just what kind of an impact headwater streams have on rivers, lakes, and other large water resources.

A broad range of diverse geographical features and watersheds makes Oregon the perfect state in which to develop an initial stream classification system.

“We’ve developed [a classification system] for Oregon, but we think it has potential for a nation-wide application,” says EPA scientist Jim Wigington, who is studying headwater streams.

This study will help to determine what types of small streams have a large impact on downstream rivers and lakes.

Unfortunately, headwaters and their unique ecosystems are threatened.  Due to urban expansion, mountain-top mining, farming practices, and various other economic and agricultural ventures, hundreds of headwater streams have become buried or polluted, disrupting and destroying headwater ecology.  Also, headwaters at high risk from local pollutant sources impose a high risk on the water quality downstream.

A Supreme Court Decision (Rapanos v. United States) in 2006 developed two requirements to be met in order for small headwater streams to be protected by the CWA.  First, the water body must show permanence, maintaining a wet and flowing nature.  Second, the stream must have a significant connection to and impact on larger, recognized water resources.  Therefore, in order for a headwater stream to be protected under the Act, it must present continual water flow or have a significant impact on downstream waters.

The Oregon headwaters research project focuses on the second of these two requirements.  EPA researchers are categorizing different headwater streams based on environmental details of the streams’ locations. 

“The outcome is that we would use this research to be able to evaluate how small streams and wetlands in different landscapes influence downstream waters,” explains Wigington.

The research team has developed a framework that uses factors such as rock type, land type, and climate to classify different groups of headwater streams.

Research has also been done to quantify the impact each headwater stream group has on larger waters.  Some headwater streams are more likely to carry nutrients and sediments, some house populations of fish, and some provide a significant amount of water to the downstream river network.  All of these factors help researchers to determine the impact a stream in each classification group has on larger waters.

In order to test their classification system, researchers analyzed existing stream-flow data from 30 different streams.  By comparing that data to their predictions from the classification system, researchers found a strong correspondence.  The outcome of this study directly supports their research.

The results of the EPA research effort could make it easier to define the impact of a certain headwater stream.  For example, based on the category of a given stream, one could estimate how large an impact that stream has on downstream waters.  If the impact is considered significant, that water has a chance of being protected under the CWA.

Consequently, this research could play a fundamental role in the protection of headwaters. “It provides a cost-effective way of how to answer this policy question about what difference these small streams and wetlands make on rivers,” says Wigington.  “It’s also an objective way.  It gives you some basis for making a policy or regulatory decision.”

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