Science informs policy: How life history, dispersal, and population genetic structure provide evidence of “biological connectivity” under the Clean Water Act

Background/Question/Methods Wetlands and streams that lack permanent surface water connections may be excluded from protection under the U.S. Clean Water Act (CWA) unless they can be shown to influence the physical, chemical, or biological condition of an indisputable “water of the United States.”  Legal decisions to protect individual streams and wetlands are currently made case-by-case from (1) evidence of physical, chemical, or biological connectivity, AND (2) evidence that the connectivity has important, measurable effects on downstream condition. While many decisions are based on connectivity and effects of streams and wetlands via flow of water, substantial potential exists to use biological data for similar purposes. We reviewed the scientific literature for examples of biological data likely to be applicable to the question of legal protections of small streams and wetlands under the CWA. 

Results/Conclusions We will describe several of the few data sets that we did find, including life history and demographic studies of aquatic invertebrates and migratory, commercially important fish. We suggest additional types of studies that would bolster relevant evidence of biological connectivity and effects. For instance, studies of dispersal and population genetic structure in aquatic and semi-aquatic plants, invertebrates, and fish that utilize small streams or wetlands and large rivers could provide insight into the frequency and magnitude of biological connections between those bodies of water. Studies of organisms dependent on these various aquatic environments for the completion of their life cycles are also likely pertinent, and have the potential to confirm not only connectivity, but also effects on biological condition of downstream waters. Finally, we begin to develop a conceptual framework with which to organize and understand how biological and ecological study can help inform this important policy question.