Scientific Report Shows Strong Connection between Wetlands, Streams, Rivers and Estuaries

By Lek Kadeli

You may have noticed along a favorite hiking trail that some streams only appear after rainfall, or maybe you’ve seen wetlands far from the nearest river. You probably didn’t think about the importance of those smaller water bodies. But a new scientific report we’re releasing today shows that small streams and wetlands play an important role in the health of larger downstream waterways like rivers and lakes.

Our researchers conducted an extensive, thorough review of more than 1,200 peer-reviewed, published scientific studies to learn how small streams and wetlands connect to larger, downstream water bodies. The results of their work are being released today. The report, Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence, is a state-of-the-science report that presents findings on the connectivity of streams and wetlands to larger water bodies.

So, what did the researchers find?

  1. The scientific literature clearly demonstrates that streams, regardless of their size or frequency of flow, are connected to downstream waters in ways that strongly influence their function.
  2. The literature also shows that wetlands and open waters in riparian areas (transition areas or zones between terrestrial and aquatic ecosystems) and floodplains are integrated with streams and rivers, and help protect downstream waters from pollution.
  3. There is ample evidence illustrating that many wetlands and open waters located outside of riparian areas and floodplains provide functions that could benefit rivers, lakes, and other downstream waters, even where they lack surface water connections. Some potential benefits of these wetlands, in fact, are due to their isolation, rather than their connectivity.
  4. Connectivity between waters occurs in gradients determined by the physical, chemical and biological environment.
  5. The incremental contributions of individual streams and wetlands are cumulative across entire watersheds.

Before finalizing these conclusions, our researchers subjected early drafts of the report to rigorous scientific review. Reviewers came from academia, consultation groups, and other federal agencies, including the U.S. Geological Survey, U.S. Department of Agriculture, the Department of the Interior, and the U.S. Army Corps of Engineers. Our Science Advisory Board reviewed the September 2013 draft of the report and comments were received from members of the public on that draft.

Based on both the extensive, state-of-the-science report and the rigorous peer review process it received, this report makes it clear: What happens in these streams and wetlands has a significant impact on downstream water bodies, including our nation’s largest waterways.

About the Author: Lek Kadeli is the Acting Assistant Administrator in EPA’s Office of Research and Development.