Tidal marshes provide key ecosystem services, but are threatened by sea level rise. For these ecosystems to survive, it will require active management to increase tidal marsh resilience. Researchers at the Narragansett Bay and Elkhorn Slough National Estuarine Research Reserves recently led the first national assessment of tidal marsh resilience to sea level rise to monitor coastal reserve sites across the continental United States. In this project, the group took the next step to test a strategy that can enhance tidal marsh resilience. Thin-layer placement (TLP) is an emergent climate adaptation strategy that mimics natural deposition processes in tidal marshes by adding a small amount of sediment on top of marsh in order to maintain elevation relative to sea level rise. It is one of the only viable strategies to protect tidal marshes in their current footprint.
This project conducted coordinated restoration experiments at eight National Estuarine Research Reserves across the East and West Coasts to test the use of thin-layer placement across diverse marsh plant communities. The team assessed the impact of elevation, sediment type, and layer thickness on the success of this marsh adaptation technique. Greenhouse experiments exploring the effect of sediment texture and the addition of biochar as a soil amendment complemented these field studies. To support future use of thin-layer placement, the project team and an advisory committee of coastal managers at state and federal agencies and nonprofit groups created a suite of guidance documents including a consensus statement on thin-layer placement in tidal marsh ecosystems. These project outcomes represent significant progress toward a national framework to enhance tidal marsh resilience through broadly applicable adaptation strategies.