Isolated wetlands: State-of-the-science and future directions

Abstract

In Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC), the U.S. Supreme Court held that isolated, intrastate, non-navigable waters could not be protected under the Clean Water Act based solely on their use by migratory birds. The SWANCC decision has created a need to compile and make available scientific information for post-SWANCC policy development. In response, this article reviews the state of our scientific understanding of isolated wetlands, based on the major findings of papers contributed to this special issue of Wetlands. Because the term “isolated wetland” has not been used consistently in the scientific literature, we recommend that geographically isolated wetlands be defined as “wetlands that are completely surrounded by upland,” as proposed by Tiner, for the purposes of scientific studies. Geographically isolated wetlands are not homogeneous but have a broad range of functional response, partly due to their occurrence over a wide range of climatic and geologic settings. One major question addressed through this special issue is the role that isolation plays in the function of geographically isolated wetlands. It appears that isolation is not a primary factor and that many of the functions performed by isolated wetlands are also performed by non-isolated wetlands and non-wetland ecosystems. Variability in moisture conditions plays an important role in the function of many geographically isolated wetlands. However, hydrologic isolation may affect moisture conditions, and biotic isolation could be important for certain populations. Depending on the factor being considered, geographically isolated wetlands are not entirely isolated but are better viewed as occurring within an isolation-connectivity continuum that has both hydrologic and biotic expressions. The juxtaposition of isolation and connectivity occurring in geographically isolated wetlands may represent a semi-isolated state that uniquely shapes these wetlands and their functions. Comprehensive data, designating the number, total area, and functional classification of isolated wetlands, would provide the foundation for monitoring impacts to isolated wetlands. Studies are needed to examine and quantify how isolated wetlands, wetland complexes, and other potentially impacted waters contribute hydrologically, chemically, and biologically to waters of the U.S. Methods to assess and map the degree of connectivity between geographically isolated wetlands and waters of the U.S., based on ground-water travel time, recurrence frequency of intermittent surface-water connections, and home ranges of species that require both types of waters, could be useful for regulators. Whatever policies are developed, scientific input and technical information will continue to play a crucial role in the policy and regulatory arena. Maintaining and enhancing the dialogue among wetland scientists, policy-makers, and regulators will ensure that critical information is developed and communicated and also continue to invigorate wetland science.