Process-based principles for restoring river ecosystems

Process-based restoration aims to re-establish natural rates and magnitudes of physical, chemical, and biological processes that sustain river and floodplain ecosystems, thereby moving ecosystem conditions (physical, chemical, and biological) into the range of natural potential conditions at any site. Ecosystem conditions at any site are governed by hierarchical regional, watershed, and reach-scale processes, identifying restoration actions that are necessary to restore ecosystem function should include analyses that answer two main questions: (1) How have changes in riverine habitats affected biota?, and (2) What are the ultimate causes of changes in riverine habitats? Answers to these questions identify habitat types or areas that are most in need of restoration or will contribute most to biological recovery, as well as the causes of degradation that must be addressed to achieve restoration goals. Watershed analyses therefore include assessments of processes controlling hydrologic and sediment regimes, floodplain and aquatic habitat dynamics, and riparian and aquatic biota. Four process-based principles help guide river restoration toward sustainable actions: (1) address root causes of degradation, (2) make sure actions are consistent with the physical and biological potential of the site, (3) the scale of restoration should match the scale of environmental problems, and (4) restoration actions should have clearly articulated expected outcomes for ecosystem dynamics. Applying these principles will help avoid common pitfalls in river restoration, such as creating habitat types that are outside the range of a site’s natural potential, attempting to build static habitats in dynamic environments, or constructing habitat features that are ultimately overwhelmed by untreated system drivers.