Barrier Removal in the 21st Century: Context, Generalities, and Potential Trade Offs

Anthropogenic barriers are pervasive and have a variety of impacts on river and upland ecosystems. In particular, many migratory fish populations are imperiled, largely owing to migratory barriers.  In recent years, there have been a few opportunities to remove or  circumvent migratory barriers; however, the ecological costs and benefits of barrier removals generally are not well quantified.  Based on these few case-studies, the costs and benefits of barrier removal are often portrayed as context specific. While there are some reasonably well-established benefits of allowing a river to evolve back to a “more natural” (i.e., less perturbed) state, additional threats (exotic species, pollutants, etc.) within these systems may pose trade-offs associated with barrier removal. Many, if not most, river systems with anthropogenic barriers have been modified by additional anthropogenic changes so that when a barrier removal reconnects a stream, it does so in a system that is much different than what existed before the barrier was constructed, resulting in potentially unexpected costs and benefits. Therefore, the challenges for restoration practitioners and scientists are vast, underscoring the need for collaboration across agencies, universities, countries, and continents. In this symposium we will present some case studies from different continents that may shed light on general patterns of costs and benefits to these seemingly context-specific examples. Our goalis to bring together restoration scientists and practitioners with relevant case studies to explore the costs and benefits of barrier removal with a view toward generating some over-arching “lessons learned” to date.