Evaluating ecosystem responses to dam re-operations across the United States

Freshwater ecosystems in rivers and estuaries and on floodplains harbor much of the biological diversity that is threatened by human activities. Dams and their operation for flood control, hydropower, and water supply have far-reaching ecological effects on material transport, water quality, migration of aquatic organisms, and the physical conditions of aquatic and riparian habitat. Unlike many human activities, dam operations are feasible to revise in the short term to restore some components of the natural hydrograph. The Sustainable Rivers Project, a national partnership between The Nature Conservancy and US Army Corps of Engineers, has a goal of changing water management at Corps projects for environmental objectives in addition to the projects' authorized purposes. The partnership currently has eight demonstration basins around the US including five where the Corps water managers have modified dam operations to implement environmental flow prescriptions. Evaluation of the ecosystem responses to dam re-operation is essential for the success of this conservation strategy because environmental flow prescriptions represent only partial restoration of a river's hydrograph, dams influence many other factors that are not restored by their re-operation, and other human activities may have persistent and overwhelming impacts on biodiversity. Nonetheless, environmental flows are likely a necessary component for restoring and protecting freshwater ecosystems. Investigations must span a range from those focused on the direct and immediate responses to environmental flows, which typically address physical habitat conditions and organism behavior, to those that account for the longer term status of conservation targets such as populations of species of concern or community composition and structure. Despite the challenges of large-scale, in-situ ecological investigations, SRP sites provide an opportunity to use an experimental approach in such investigations.