Tidal wetlands are a hallmark feature of the Delaware Estuary and span a salinity gradient from salt water at the mouth of the bay to fresh water in the upper reaches. W etland loss and interest in conserving ecological function of shorelines has increased attention on nature-based solutions such as living shorelines . Living shorelines are techniques that incorporate natural materials to protect shorelines and provide ecological uplift while retaining connectivity between subtidal and higher elevation areas. Until recently, living shorelines have typically been applied in saltwater environments to help mitigate wave attenuation and erosion and to positively enhance environmental conditions . Additionally, s ome living shoreline structures have been shown to attract recruitment of sessile bivalves such as oysters and ribbed mussels, which promotes both structural resilience and diverse ecological benefits.
To date, living shoreline approaches have not been applied to freshwater habitats. In April, 2021, a pilot living shoreline project was installed along a degraded section of the lower Schuylkill River in southeast Pennsylvania, USA in freshwater tidal zone situated in an urban landscape with diverse anthropogenic stressors , with a goal to test whether native species of freshwater mussels could be incorporated into a multi-habitat mosaic type of living shoreline that will eventually include other targeted biota such as submerged aquatic vegetation . The approach was to install benthic stabilization structures to enhance habitat suitability for mussels, which are infaunal benthic animals sensitive to erosion. Structures of varying shapes (Fig. 1) were constructed using gabions filled with recycled and aged oyster shell, and the native freshwater mussel Utterbackiana implicata was stocked within and outside of structures in replicate cohorts of similar number and size.
The monitoring framework developed by the Delaware Estuary Living Shoreline Initiative was then adapted for this project, including changes in sediment grain size, bathymetry, and mussel retention, survival, and growth. Despite record flooding from the remnants of Hurricane Ida in August, 2021, the living shoreline structures and deployed mussels survived, and considerable sediment was trapped in and around the structures. Contingent on continued success, these results suggest that living shoreline approaches can be adapted for tidal freshwater conditions in degraded and vulnerable urban landscapes .