vide are becoming common wisdom (Malanson, 1993). For example, rivers buffer and attenuate flood peaks by storing water in their floodplains. Attendant sediment deposition replenishes floodplain soils, and within the floodplains, microbes help to efficiently process and recycle nutrients. Additionally, the sediment remaining in the river is transported downstream where it replenishes beaches and deltas.
Viewed from a scientific perspective, American society is conducting a great, uncontrolled experiment on the interconnected river systems of the nation, and human activities have profoundly changed the nature of our nation’s rivers. Today, few rivers are pristine or free flowing. Beginning with deforestation by European settlers for agricultural land use in the 1700s and continuing with urbanization, floodplain cultivation, dam and levee construction, and channelization, human activities have dramatically altered natural flow regimes. These changes have often exacerbated natural flooding, such as when spring snowmelt on the Red, Mississippi, and Missouri Rivers covered large swaths of the continental interior with attendant loss of life and property damage (Barry, 1997; Shelby, 2003). Enhanced sediment erosion and transport often accompany such floods, and in the process, rivers become incised and ecological diversity is lost. Modifications to natural flow regimes have led to declines in commercial river fishing in California, New England, the Southeast, the upper Midwest, and most recently the Northwest where human activities have disrupted the life cycle of salmon (NRC, 2004a).
The introduction of non-native species has decimated native fish populations in some cases (USGS, 1998). Water quality has suffered from deforestation, tillage, and urbanization. Industrial, domestic, and agricultural wastes frequently contaminate rivers. Trace metals, arsenic, organic contaminants, excessive loads of nitrogen and phosphorus, human pathogens, and thermal discharges from power plants are present in the nation’s surface waters. Overall, the degradation of rivers and their riparian ecosystems has impacted flood storage, aesthetics, fisheries, clean water, and other river-related goods and services that the nation has come to value and depend upon.
River goods and services, and thus the conditions of rivers and riparian ecosystems, are important at local, regional, national, and international levels. Rivers cross state and international boundaries, and actions in one state have impacts elsewhere. Therefore, not surprisingly, there has been a long-standing national interest in river systems.
In the past, the national interest was focused on the human utilization of river resources. In 1851 the Supreme Court defined navigable waterways for federal responsibility as streams that served interstate or international commerce, and subsequent rulings were very liberal in defining navigation. As early as