The Finalized Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence Report Released

Swamp Stomp

Volume 15, Issue 4

The Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence report serves as the scientific basis for the new Waters of the U.S. rules. Now final, the 408 page scientific report can be used to inform future policy and regulatory decisions, including the proposed Clean Water Rule being developed by EPA’s Office of Water and the U.S. Army Corps of Engineers.  The significance of this release is that this report was the final item that needed to be in place before the proposed Waters of the US rules (WoUS) could be implemented.  What remains is the final publication of the WoUS rules in the Federal Register.  This is expected soon.  Once that happens the new WoUS rules will be the “law of the land.”

According the EPA, the report summarizes “the 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.” More specifically, however, the report focuses on “shallow subsurface connections by which small or temporary streams, nontidal wetlands, and open waters affect larger waters such as rivers, lakes, reservoirs, and estuaries.” It is able to do so by addressing the following three questions pertaining to connectivity:

  • What are the physical, chemical, and biological connections to, and effects of, ephemeral, intermittent, and perennial stream on downstream waters?
  • What are the physical, chemical, and biological connections to, and effects of, riparian or floodplain wetlands and open waters on downstream waters?
  • What are the physical, chemical, and biological connections to, and the effects of, wetlands and open waters in non-floodplain settings on downstream waters?

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In order to answer these questions, the EPA reviewed over 1,200 peer-reviewed publications in scientific literature. Subsequently, the final report lists the following five major conclusions:

  • 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.
  • 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.

A major sticking point regarding the definition of wetlands was brought up in the public comments to this report.  Namely, the use of the 1979, US Fish and Wildlife’s one parameter approach to identifying wetlands.  There were many who questioned the wisdom for using this method as opposed to the US Army Corps Federal 3 parameter definition.  The EPA has decided to stick with the 1979 definition and only requires the presence of soil, vegetation OR hydrology to define a wetland for the purposes of its study.  This report is enjoined in the proposed WoUS rules by reference and as such its recommendations carry forward into the new rules.  Consequently, one could extrapolate that a wetland need only meet one criteria to be deemed jurisdictional.  It remains to be seen if this will carry forward into the new rules.

This report is one of the last steps before the EPA and U.S. Army Corps of Engineers will implement new rules for the “waters of the U.S.” under the Clean Water Act. Now that the report has been finalized, we can expect to see the new rules published in their final form very soon.

The full report can be found on EPA’s website at: http://ofmpub.epa.gov/eims/eimscomm.getfile?p_download_id=521415