Wetlands restoration and mitigation

For decades, scientists, managers, policy makers, and practitioners have sought to improve the design and performance of mitigated and restored wetlands. Progress has been made, but further improvements are needed. In this chapter, we provide a historical context, review the mitigation process, summarize the literature on mitigation and restoration of wetlands, and make the case for using natural reference wetlands as templates for designing mitigation and restoring projects and assessing their performance. Two case studies conducted by Riparia at Penn State are used to demonstrate the value of a reference-based approach. A comparison of scores from Habitat Suitability Index models between reference and created wetlands shows that the latter are either not equivalent, with created sites scoring lower, or habitats are shifted toward species in the wildlife community that favor open water or emergent conditions. In the second study, scores of hydrogeomorphic (HGM) functional models are compared between reference wetlands and mitigation sites, showing that average performance is often significantly lower for several functions across multiple HGM types. Finally, we describe how a set of variables from Riparia's database of reference wetlands can be used to improve the outcome of mitigation and restoration projects.