Scientific Importance of Small Streams and Wetlands

Our nation’s rivers, from the Shenandoah to the Sacramento, owe their very existence to the seemingly insignificant rivulets and seeps that scientists call headwater streams. Although 19th century explorers often searched for the headwaters of rivers, the birthplace of most rivers cannot be pinpointed. The origins of rivers are many anonymous tiny rills that can be straddled by a 10-year-old child, and no one trickle can reasonably be said to be “the” start of that river. Rather, rivers arise from a network of streamlets and wetlands whose waters join together above and below ground as they flow downstream. As other tributaries join them, creeks grow larger, eventually earning the title “river.” The character of any river is shaped by the quality and type of the numerous tributaries that flow into it. Each of the tributaries is, in turn, the creation of the upstream waters that joined to form it.

The ultimate sources of a river often appear insignificant. They could be a drizzle of snowmelt that runs down a mountainside crease, a small spring-fed pond, or a depression in the ground that fills with water after every rain and overflows into the creek below. Such water sources, which scientists refer to as headwater streams and wetlands, are often unnamed and rarely appear on maps. Yet the health of these small streams and wetlands is critical to the health of the entire river network. The rivers and lakes downstream from degraded headwater streams and wetlands may have less consistent flow, nuisance algal growth, more frequent and/or higher floods, poorer water quality, and less diverse flora and fauna.

Historically, federal agencies, in their regulations, have interpreted the protections of the Clean Water Act to cover all the waters of the United States, including small streams and wetlands. More recently, federal agencies and the courts have examined whether such streams and wetlands merit protection. In January, 2003, the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers announced an “advance notice of proposed rulemaking” to solicit public comments on whether and how to exclude “isolated,” intrastate, and non-navigable waters from the scope of the Clean Water Act. Many small streams and wetlands, including headwater streams, could fall into one or more of those categories. While the proposed rulemaking was withdrawn, the agencies meanwhile instructed their field staff not to enforce the law to protect such waters, sometimes requiring case-by-case approval from agency headquarters before enforcing the Act. The result of this policy guidance is that thousands of our nation’s waters have been denied protections under the Clean Water Act.

More recently, the Supreme Court issued a splintered decision in two cases (Rapanos and Carabell ) about the scope of the Clean Water Act that leaves small streams and wetlands vulnerable to further loss of protections. Although there is no majority support for diminishing the Clean Water Act’s application to wetlands and streams, the Court’s ruling creates additional uncertainty as to which waters remain protected. The ruling places a burden on the EPA and the Corps of Engineers to show that upstream waters have a “significant nexus” to downstream waters. The “case-by-case” analysis required creates extra layers of work to prove what we already know scientifically: water flows downstream and bodies of water are integrally connected with each other. There is great concern that this decision will lead to more confusion and legal challenges and a loss of protection for many of our nation’s waters.

Small streams and wetlands provide crucial linkages between aquatic and terrestrial ecosystems and also between upstream watersheds and tributaries and the downstream rivers and lakes. Since the initial publication of this document in 2003, scientific research has continued to bolster the significance of these connections. Based on the most recent research, this paper summarizes the scientific basis of understanding how small streams and wetlands mitigate flooding, maintain water quality and quantity, recycle nutrients, create habitat for plants and animals, and provide other benefits.

Resources

Report:  Where Rivers Are Born: The Scientific Imperative for Defending Small Streams and Wetlands