EPA Agrees: We All Live Downstream

In a draft scientific report the U.S. Environmental Protection Agency (EPA) has confirmed what many of us already know:  That small streams – and many wetlands — substantially affect the physical, chemical and biological makeup of rivers downstream.

This seemingly simple concept has big implications.  For years, environmentalists, trade associations, citizens and government agencies have argued over just which waters EPA and the U.S. Army Corps of Engineers can regulate under the Clean Water Act (CWA).   Many developers and farm groups maintain that CWA doesn’t apply to wetlands and intermittent or ephemeral streams, because the law only applies to “navigable waters.”  Many environmentalists and sportsmen call for a broader interpretation that would capture all waters.  Supreme Court cases in recent years have only added to the confusion.  In a 2006 case, (Rapanos v. United States) Justice Antonin Scalia wrote that CWA applied only to waters “with a continuous surface connection” to navigable water.  But Justice Anthony Kennedy concluded in the same case that CWA applied to any water with a “significant nexus” with navigable waters, such that they “significantly affect the chemical, physical, and biological integrity of other covered waters.”

Headwater streams are the smallest parts of river and stream networks, but make up the majority of river miles in the United States.

With no clear guidance and uncertain whether it could claim jurisdiction, EPA enforcement levels dropped after that according to a congressional  investigation in 2008 and an EPA Inspector General report in 2009.  But since then, EPA has marshaled its scientific resources to answer Justice Kennedy’s question; namely, when do waters significantly affect other waters?  EPA’s team of aquatic scientists reviewed more than 1,000 papers in the scientific literature and, in their draft report, reached three major conclusions.

  1. All streams are connected to rivers downstream.  In short, the draft report states that all tributary streams, including perennial, intermittent or ephemeral streams are physically, chemically and biologically connected to downstream rivers.   They report that headwater streams are the most abundant stream type in most river networks, and supply most of the water in rivers.  Streams also transport sediment, wood, organic matter, nutrients, chemical contaminants and many of the organisms found in rivers.  And they connect with downstream waters through processes such as nutrient spiraling, in which streams assimilate nitrogen and other nutrients that would otherwise increase nutrient loading downstream.  EPA’s map of drinking water sources highlights the importance of headwater and ephemeral streams:  More than one-third of the U.S. population gets some or all of its drinking water from these sources.  (You can read about headwater streams in the Potomac River watershed on The Downstream Project blog here.)
  2. Wetlands and open waters in riparian areas and floodplains are connected to rivers.   Wetlands adjacent to rivers remove excess nutrients such as nitrogen and phosphorus; provide habitat for insects and fish; and store floodwaters, sediment and nutrients that otherwise would flow downstream.
  3. Other wetlands, such as prairie potholes, vernal pools and playa lakes, can improve downstream water quality and integrity.  Wetlands with an obvious surface connection or a shallow subsurface connection to other waters provide clear benefits:  They hold floodwaters; retain (and transform) pollutants such as nutrients, metals and pesticides; and recharge groundwater that forms the base flow of rivers.  When wetlands have no obvious connection to other waters, their value varies.  The team couldn’t draw general conclusions about these wetlands.

EPA stresses that the report is only a draft and doesn’t reflect agency policy – at least not yet.  Its external Scientific Advisory Committee will review the report at a public meeting December 16 -18  and is accepting public comments before then.  But EPA and the Corps already have sent a draft rule based on the report to the White House’s Office of Management and Budget for review.   The timing and final makeup of the rule is unknown, but the intent is clear:  Broad jurisdiction to protect U.S. waters under the CWA.


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