Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (Final Report)

Notice

EPA announces the availability of the final report "Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence" in a January 15, 2015 Federal Register Notice. The purpose of this report is to summarize the current understanding about the connectivity and mechanisms by which streams and wetlands affect the physical, chemical, and biological integrity of downstream waters.


Abstract

Cover of Waters of the US Connectivity of Streams Final Report The U.S. Environmental Protection Agency's (USEPA) Office of Research and Development has finalized the report Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence. The report reviews more than 1,200 peer-reviewed publications and summarizes current scientific understanding about the connectivity and mechanisms by which streams and wetlands, singly or in aggregate, affect the physical, chemical, and biological integrity of downstream waters. The focus of the report is on surface and shallow subsurface connections by which small or temporary streams, nontidal wetlands, and open waters affect larger waters such as rivers, lakes, reservoirs, and estuaries.

This report represents the state-of-the-science on the connectivity and isolation of waters in the United States. It makes five major conclusions, summarized below, that are drawn from a broad range of peer reviewed scientific literature.
  • The scientific literature unequivocally demonstrates that streams, regardless of their size or frequency of flow, are connected to downstream waters and strongly influence their function.

  • The scientific literature clearly shows that 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.

  • There is ample evidence that 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.

  • 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.

  • The literature strongly supports the conclusion that 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 U.S. EPA and the U.S. Army Corps of Engineers on the definition of "waters of the United States" under the Clean Water Act (CWA). Because this report is a technical review of peer-reviewed scientific literature, it neither considers nor sets forth legal standards for CWA jurisdiction, nor does it establish EPA policy.

The report summarizes current scientific understanding about the connectivity of streams and wetlands to downstream waters. EPA has conducted a thorough review of the literature – more than 1,200 peer-reviewed and published documents – on the scientific evidence regarding the effects that streams, nontidal wetlands, and open -waters have on larger downstream waters such as rivers, lakes, estuaries, and oceans. The focus of the report is on surface and shallow subsurface connections by which small or temporary streams, nontidal wetlands, and open waters affect larger waters such as rivers, lakes, reservoirs, and estuaries. EPA, along with other federal agencies and states, can use this scientific report to inform policy and regulatory decisions, including the Clean Water Rule being developed by EPA and the U.S. Army Corps of Engineers.

Citation

U.S. EPA. Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-14/475F, 2015.

History/Chronology

Jan 2012EPA’s peer review contractor conducted an external independent peer review by scientist from federal agencies, academia, and consulting groups of the draft report titled Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence.
Sep 2013EPA released the draft report titled Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (EPA/600/R-11/098B) for external public review (via the Science Advisory Board) and invited submission of public comments for consideration by the Science Advisory Panel [Federal Register Notice Sep 24, 2013]
Oct 2014Science Advisory Board completed a peer review of the draft report and posted their final report on the SAB website.
Jan 2015EPA released the final report titled Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (EPA/600/R-14/475F) and EPA’s Response to Peer Review Comments document. [Federal Register Notice Jan 15, 2015]
May 2015EPA released an update to the report with an errata sheet.

Additional Information

Note: Due to the large size of this attachment, we recommend that you save the file to your computer rather than opening it directly from the web site. If you are still having problems please contact EPA for assistance with retrieving the report(s).

This download(s) is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by EPA. It does not represent and should not be construed to represent any Agency determination or policy.