Evaluating restored tidal freshwater wetlands

Abstract

As restoration of tidal freshwater wetlands has progressed in North America and Eurasia, research findings have continued to emerge on the postrestoration success of these ecosystems. The most common approaches used to restore tidal freshwater wetlands involve excavation or placement of dredged sediment to restore tidal hydrology compatible with vegetation establishment and managed realignment or diversion, which involves reconnecting former wetlands to tides by breaching dikes or levees. Postconstruction monitoring of tidal freshwater wetland restoration projects commonly includes not only studies of hydrology, soil, and vegetation but also geomorphology, microbial communities, seed banks, fish, birds, and invertebrates. Based on a review of assessment approaches and monitoring studies, we present criteria for evaluating tidal freshwater wetland restoration projects. In a case study, we apply these criteria to evaluate restored tidal freshwater wetlands in the highly urbanized Anacostia River watershed (Washington, DC, USA). We conclude that restoration can create tidal freshwater wetlands worldwide that share some structural or functional aspects with natural systems. Soil organic matter and microbial communities may be the slowest components to develop, and watershed urbanizationimposes strong constraints that prevent development of tidal freshwater wetlands similar to those in rural settings.