As a result of a 2001 Supreme Court decision (Solid Waste Agency of Northern Cook County vs. U.S. Army Corps of Engineers, 2001), some wetlands and other waters that are considered "geographically isolated" from navigable waters no longer fall under the jurisdiction of the Clean Water Act. Scientific assessments of the potential impacts of the court's decision are needed to provide guidance to the federal agencies, states, tribes and local governments that will have responsibility for protecting these valuable resources.
In this study we sought to assess potential impacts of the court's decision on the nation's biological diversity. To do so, we first used a nationally standardized classification of wetland ecological systems. We then established a working definition to categorize types as "geographically isolated," and using expert knowledge of these wetland types, we narrowed the national list of wetland ecological systems to those that tend to occur "geographically isolated" from navigable waters. Through review of scientific literature, input from regional experts, and compilation of existing location data for at-risk species (those species considered rare, imperiled or critically imperiled using NatureServe's standard criteria) we identified those at-risk species and plant communities that are supported by these isolated wetland types throughout the United States.
This assessment used the best currently available information. Because comprehensive wetland maps are unavailable nationally, this study focuses on documenting the number, or diversity, of isolated wetland types, rather than on the acreage these wetland types occupy. These analyses could be significantly augmented in the future with the collection of additional data on the occurrence of isolated wetland types, their spatial extent, and their associated species and communities.