Raising elevation with sediment addition is a potential strategy to enhance tidal marsh resilience in the face of rising seas. A diverse team of state and national coastal managers and scientists reached consensus on recommendations for the use of thin-layer placement (TLP) of sediments in tidal marshes. Here, we share these recommendations, as well as guidance from the team on navigating the permitting processes for TLP and the design of scientific monitoring plans to track success of TLP projects. We also report on findings from greenhouse experiments led by Drexel University examining how different marsh plant species respond to varying sediment conditions, which informs understanding of marsh response to TLP. Finally, we describe a coordinated restoration experiment conducted across eight National Estuarine Research Reserves on US East and West Coasts. We tested TLP as a restoration strategy for decreasing bare cover in drowning low marshes and for increasing representation of rare high marsh species at high marsh elevations. We compared two thicknesses of sediment addition, and compared TLP plots to controls and reference plots. Overall, we found the potential of TLP to achieve restoration goals varied significantly by site and elevation, highlighting the importance of local data for decision-making, and the value of coordinated experiments for seeking generality across systems.
Presented by: Kerstin Wasson (Elkhorn Slough NERR), Beth Watson (Drexel University), and Kenny Raposa (Narragansett Bay NERR)
Kerstin Wasson has served as the Research Coordinator at the Elkhorn Slough National Estuarine Research Reserve for 20 years. She is passionate about restoration of native oysters and salt marshes, and conducts experiments to inform restoration strategies. In addition to local, place-based work at Elkhorn Slough, Kerstin has led major collaborative projects across the network of National Estuarine Reserve Reserves.
Beth Watson is an environmental science faculty member at Drexel University, in Philadelphia, where she teaches classes about climate change, restoration, wetlands, biogeochemistry, and ecology, and conducts research focused on coastal ecosystem change. Beth has contributed to 50 peer-reviewed publications on various topics related to human impacts to coastal wetlands, sediment transport, and water quality, and works closely with stakeholders to ensure that her research promotes informed coastal management. Beth was a 2019 Fulbright Scholar in Mexico, where she studied historic changes in seagrass distribution in Baja California lagoons.
Kenny Raposa has been the Research Coordinator at the Narragansett Bay NERR in Rhode Island for over 19 years. Trained as a salt marsh ecologist, his research now focuses on examining marsh resilience to climate change and sea-level rise and evaluating different adaptation strategies aimed at building resilience. Kenny is currently involved with multiple large-scale thin-layer sediment placement projects in southern RI and is co-lead of the NERR field experiment evaluating TLP in replicated experimental field plots.