The U.S. Environmental Protection Agency (EPA) released a report in January 2015 assessing stream and wetland connectivity. The report, Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientifc Evidence, analyzes over one thousand peer-reviewed publications in an effort to achieve a comprehensive understanding of the connectivity and mechanisms by which streams and wetlands, separately or cumulatively, affect the physical, biological, and chemical integrity of downstream waters. In particular, the research focused on the effects of small or temporary streams, non-tidal wetlands, and open waters on larger waters downstream, such as rivers, lakes, rivers, and estuaries, through the presence of surface and subsurface connections. 

 The report comes to five major conclusions:

1. Regardless of size or frequency of flow, streams are connected to downstream waters and strongly influence their function.
2. Floodplains and transitional zones between land and water, such as riparian areas, are integrated with rivers via physical, chemical, and/or biological functions that improve downstream water quality.
3. Wetlands and open waters outside of riparian areas and floodplains benefit downstream water integrity, even when surface water connections are absent.
4. The degree of connectivity between streams and wetlands to downstream waters varies depending on the physical, chemical, and biological environment, and by human activities. 
5. The additive effects of individual streams and wetlands are cumulative across whole watersheds, and should be evaluated within the context of other streams and wetlands in the watershed.

The EPA hopes these findings will inform rulemaking by the U.S. Army Corps of Engineers (USACE) and the EPA on the definition of “waters of the U.S.” under the Clean Water Act, including the Clean Water Rule which was advanced to the Obama administration on April 6, 2015 for review. Known as the Clean Water Rule, the 370 page rule would change the definition of waters of the U.S. EPA Administrator Gina McCarthy and Assistant Secretary of the Army to Civil Works Jo-Ellen Darcy said a key part of the rule is protecting water bodies that have a “significant nexus” to downstream waters.

Want to learn more? A FAQ about the proposed rule is available on the EPA’s website.