Graham Sustainability Institute

Thin-layer Sediment Placement: Evaluating an Adaptation Strategy to Enhance Coastal Marsh Resilience

March 2018

Tidal marshes provide key ecosystem services—and they are increasingly threatened by sea level rise. Narragansett Bay and Elkhorn Slough National Estuarine Research Reserves recently led the first national assessment of tidal marsh resilience to sea level rise by developing and applying multi-metric indices to 16 reserve sites. Now the group is moving beyond marsh resilience monitoring and assessment efforts to actively test strategies to enhance resilience.

Through this project, replicated restoration experiments are being conducted at several reserve sites across the nation, with the purpose of examining the effectiveness of thin-layer sediment placement as a marsh adaptation strategy. Novel aspects of the project include the broad distribution of sites, the examination of the effectiveness of thin-layer sediment placement at different marsh elevations, a standardized monitoring protocol, and the incorporation of biochar (carbon material produced through the conversion of biomass in an oxygen limited environment) to improve soils and plant health.

Beneficial use of dredged sediment to enhance coastal resilience is of interest to, and already being applied in, many coastal states. At project conception, the team interviewed and surveyed end users involved in funding, permitting, implementation, and monitoring of thin-layer sediment projects. This project will address the needs end users identified, including a vetted monitoring protocol to assess restoration success after thin-layer sediment placement, a synopsis of associated permitting issues, and an evaluation of effectiveness of different treatments detailed in a technical report and summarized in a brochure and webinar.