The nation’s network of rivers, lakes and streams originates from myriad small streams and wetlands. Extensive scientific studies document the significance of these small systems. Yet these headwater streams and wetlands exert critical influences on the character and quality of downstream waters. Historically, federal agencies have interpreted the protections of the Clean Water Act to cover all the waters of the United States, including small streams and wetlands. The extent to which small streams and wetlands should remain under the protection of the Clean Water Act is currently under consideration in federal agencies and Congress. This paper summarizes the scientific basis for understanding that the health and productivity of rivers and lakes depends upon intact small streams and wetlands.
We know from local/regional studies that small, or headwater, streams make up at least 80 percent of the nation’s stream network. However, the ability of scientists to extend these local and regional studies to provide a national perspective is hindered by the absence of a comprehensive database that catalogs the full extent of streams in the United States. The topographic maps most commonly used to trace stream networks do not show most of the nation’s headwater streams and wetlands. Thus, such maps do not provide detailed enough information to serve as a basis for stream protection and management.
The natural processes that occur in such headwater systems benefit humans by mitigating flooding, maintaining water quality and quantity, recycling nutrients, providing an enormous array of habitats for plant, animal and microbial life, and sustaining the biological productivity of downstream rivers, lakes and estuaries. These ecosystem services are provided by seasonal as well as perennial streams and wetlands. Many species depend on small streams and wetlands at some point in their life history, for food and shelter from predators, spawning sites and nursery areas, and travel corridors through the landscape. Even when such systems have no visible overland connections to the stream network, small streams and wetlands are usually linked to the larger network through groundwater.
Despite these benefits, many of these ecosystems have been destroyed by agriculture, mining, development and other human activities and, as a result, the unique and diverse biota of headwater systems is increasingly imperiled. Human-induced changes to such waters, including filling streams and wetlands, water pollution, and the introduction of exotic species, can diminish the biological diversity of such small freshwater systems, thereby also affecting downstream rivers and streams. For example, changes in surrounding vegetation, development that paves and hardens soil surfaces, and the total elimination of some small streams reduces the amount of rainwater, runoff and snowmelt the stream network can absorb before flooding. The increased volume of water in small streams scours stream channels, changing them in a way that promotes further flooding. Such altered channels have bigger and more frequent floods. The altered channels are also less effective at recharging groundwater, trapping sediment, and recycling nutrients. As a result, downstream lakes and rivers have poorer water quality, less reliable water flows, and less diverse aquatic life. Algal blooms and fish kills can become more common, causing problems for commercial and sport fisheries, and recreational uses may be compromised. In addition, the excess sediment can be costly, requiring additional dredging to clear navigational channels and harbors and increasing water filtration costs for municipalities and industry.
Scientific research shows that healthy headwater systems are critical to the healthy functioning of downstream streams, rivers, lakes and estuaries. To provide the ecosystem services that sustain the health of our nation’s waters, the hydrological, geological, and biological characteristics of small streams and wetlands require protection.