Streams and Wetlands Affect Downstream Waters


USEPA Report Concludes Streams and Wetlands Affect Downstream Waters

According to the United States Environmental Protection Agency (USEPA) report released on January 15, 2015, Connectivity of Streams and Wetlands to Downstream Waters:  A Review and Synthesis of the Scientific Evidence, streams, wetlands, and other open waters influence the health of downstream waters.  This report was conducted to support USEPA and the Army Corps of Engineers’ joint proposed rule to define Waters of the United States under the Clean Water Act (CWA), first proposed in spring 2014.  The proposal is intended to reduce confusion about the types of waters that are covered under the CWA; however, landowners, industry, and others have concerns over the rulemaking.

Based on peer-reviewed publications, the report summarizes the current understanding about the connectivity and mechanisms by which streams and wetlands affect the physical, chemical, and biological integrity of downstream waters.  USEPA focused on surface and shallow subsurface connections by which small or temporary streams, non-tidal wetlands, and open waters affect larger waters such as rivers, lakes, reservoirs, and estuaries.

The report makes five major conclusions:

    1. Streams, regardless of their size or frequency of flow, are connected to downstream waters and strongly influence their function.
    2. Wetlands and open waters in riparian areas (transitional areas between terrestrial and aquatic ecosystems) and floodplains are physically, chemically, and biologically integrated with rivers via functions that improve downstream water quality.  These systems act as effective buffers to protect downstream waters from pollution and are essential components of river food webs.
    3. Many wetlands and open waters located outside of riparian areas and floodplains, even when lacking surface water connections, provide physical, chemical, and biological functions that could affect the integrity of downstream waters.  Some potential benefits of these wetlands are due to their isolation rather than their connectivity.  Evaluations of the connectivity and effects of individual wetlands or groups of wetlands are possible through case-by-case analysis.
    4. Variations in the degree of connectivity are determined by the physical, chemical and biological environment, and by human activities. These variations support a range of stream and wetland functions that affect the integrity and sustainability of downstream waters.
    5. The incremental contributions of individual streams and wetlands are cumulative across entire watersheds, and their effects on downstream waters should be evaluated within the context of other streams and wetlands in that watershed.

This report was developed to inform rulemaking by the USEPA and the U.S. Army Corps of Engineers on the definition of “waters of the United States” under the CWA.  However, because the report is a technical review of peer-reviewed scientific literature, it does not set forth legal standards for CWA jurisdiction or establish USEPA policy.

The USEPA is currently finalizing the proposed rule to clarify which waters are considered “waters of the United States” and therefore eligible for CWA protections.  The rule under consideration is expected to restore protections to certain smaller streams and wetlands.  EHS Support will be on top of this controversial final legislation, which is anticipated in April 2015.


For more information on the Connectivity of Streams and Wetlands to Downstream Waters report, please contact our Compliance Service Line Leader, Amy Bauer.

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