Biodiversity Values of Geographically Isolated Wetlands: An Analysis of 20 States

From NatureServe’s Datamanager listserv http://lists.natureserve.org/mailman/listinfo/datamanager

Some of the wetlands and other waters that are "isolated" from navigable waters are no longer under the jurisdiction of the Clean Water Act as a result of a recent Supreme Court decision (Solid Waste Agency of Northern Cook County vs. U.S. Army Corps of Engineers (SWANCC), 2001). NatureServe has recently completed an assessment of the potential impacts of the SWANCC decision on the at-risk species and communities that are associated with these isolated wetland systems in 20 U.S. states. The information and analyses contained in this study are designed to assist policymakers and land managers at federal, state, and local levels to better understand the biodiversity value of isolated wetlands in their jurisdiction and plan for their protection.

The report and supporting data are available for viewing and download on NatureServe's website (http://www.natureserve.org/ ). A limited number of hard copies are also available on request. Contact Meghann Gili (meghann_gili@natureserve.org or (703) 908-1881) to request a hard copy of the report.

A summary of the report is provided below.

Biodiversity Values of Geographically Isolated Wetlands: An Analysis of 20 States

Some of the wetlands and other waters that are "isolated" from navigable waters are no longer under the jurisdiction of the Clean Water Act as a result of a recent Supreme Court decision (Solid Waste Agency of Northern Cook County vs. U.S. Army Corps of Engineers, 2001). The loss of protections afforded these isolated wetlands is of considerable concern to federal, state, and local policymakers, land managers, and the public. Scientific assessments of the potential impacts of the court's decision are needed to provide guidance to federal agencies charged with implementing the decision, as well as to the states, tribes, and local governments that have responsibility for most land use decisions in the United States.

In this study we assess the potential biodiversity impacts of the court's decision. To do so, we first established a working (non-jurisdictional) definition of "geographically isolated" wetlands, and using a nationally standardized classification of wetland types, developed a list of isolated wetland ecological systems. Through literature and expert review and analysis of the best available occurrence data, we identified those at-risk species and ecological communities that are supported by these wetland habitats in 20 coastal and Upper Great Lakes states. We also conducted more detailed county-level analyses in three states ( Oregon , Michigan , and South Carolina ) designed to better understand the land use and environmental settings within which these wetland types occur. This study is an assessment of the best currently available information. It is likely that additional occurrences of isolated wetlands and their associated at-risk species will be documented as inventory, mapping and classification efforts continue.

Key Findings

Of the approximately 177 wetland types found in our 20-state study area, 68 (38%) met our definition of 'isolated' and may no longer be protected under the Clean Water Act. More than 80% of these isolated wetlands were classified as "partially" rather than "strictly" isolated. Their treatment under the Clean Water Act will therefore largely be determined by how lawmakers, regulators, and the courts choose to interpret the term 'isolated.'

This study documents that isolated wetland ecological systems support high levels of biodiversity, including significant numbers of species and ecological communities of conservation concern. For example:

• Half of isolated wetland types support species listed under the U.S. Endangered Species Act. Isolated wetlands within the 20-state study area harbor a total of 66 federally listed species, of which nearly two-thirds (42) are completely dependent on isolated wetland habitats for their survival.
• Isolated wetlands support a total of 264 plant and animal species classified by NatureServe as imperiled or vulnerable. Nearly half (129) of these at-risk species appear to be restricted to isolated wetlands, with nearly three-quarters of at-risk animals dependent on these habitats.
• Two to fourteen percent of all the at-risk plants in a given state occur in isolated wetlands.
• About 10% of vegetation associations classified by NatureServe as imperiled or vulnerable are characteristic of isolated wetlands, with 83% of these at-risk vegetation types not supported by any other habitats.

Significant loss of isolated wetland habitats could have a serious impact on the survival of the many rare or endangered species and ecological communities that depend on them. While an unknown but potentially significant number of these isolated wetland systems are likely to lose protection under the Clean Water Act, some may continue to receive protection through other regulatory or incentive mechanisms. In particular, the Endangered Species Act and the U.S. Department of Agriculture's SwampBuster incentive program may afford some protection to isolated wetlands and the biodiversity they sustain. Lacking federal protections, states, tribes and local governments will increasingly be in a position to decide the fate of many of these wetlands. The information and analyses contained in this study are designed to assist policymakers and land managers at federal, state, and local levels to better understand the biodiversity value of isolated wetlands and plan for their protection.

Contributing Authors

Patrick Comer, Kathy Goodin, Geoff Hammerson, Shannon Menard, Milo Pyne, Marion Reid, Marcos Robles, Mary Russo, Lesley Sneddon, Kristin Snow, Adele Tomaino, Michael Tuffly

We wish to express our sincere appreciation to biologists and ecologists from the 20 natural heritage programs that contributed expertise, review and data. The extensive field experience represented by this network of scientists and their close working partners form the basis for this analysis.

We are grateful for the financial assistance provided by the U.S. Environmental Protection Agency (EPA), Office of Wetlands, Oceans and Watershed - Wetlands Division through a Wetlands Program Development Grant.