Award: OCE-1426896

Nearly half of the world's population lives within 100 km of the coast, the area ranked as the most vulnerable to climate-driven sea-level rise (SLR). Salt marshes are intertidal habitats that provide a buffer for coastal communities to SLR and are also valued for many other ecosystem services, including wildlife habitat, nutrient cycling, carbon sequestration, aesthetics, and tourism. They are highly dynamic systems that have kept pace with changes in sea level over millennia. However, projected rates of SLR and increased human modification of coastal watersheds and shorelines may push marshes past a tipping point beyond which they are lost. This project examined the comparative vulnerability of salt marshes to SLR in three U.S. Atlantic coastal sites that vary with respect to sediment supply, tidal range and human impacts. It leveraged the long-term data, experiments and modeling tools at three Atlantic Coast Long-Term Ecological Research sites (in MA, VA, GA), and addressed the broad interdisciplinary question "How will feedbacks between marsh response to SLR and human adaptation responses to potential marsh loss affect the overall sustainability of the combined socio-ecological systems?" As a sub-contract to this project, researchers at the University of Georgia used historical aerial photographs to measure changes in the marsh shoreline as well as the extent of vegetated marsh over approximately 70 years at each of the study sites. We also collected sediment cores (16 per site) to quantify historic rates of sediment accumulation for use in models to project marsh vulnerability to current and projected SLR. We found that the marsh/bay boundary was the most dynamic part of the marsh, with net erosion at the marshes in VA and MA and accretion in GA. When combined with internal channel edges, only MA showed evidence for net erosion, demonstrating the importance of considering change across the entire marsh. Historical changes in marsh features (channels, mud flats and ponds, and the location of both the seaward and marsh-upland border) were also different at the 3 sites. At the GA study site losses in vegetated marsh, which were primarily due to channel widening, were largely offset by channel contraction in other areas, such that there was little to no net change over the study period. The study marsh in VA experienced extensive vegetated marsh loss to interior mud flat expansion, which occurred largely in low-lying areas. However, this loss was counterbalanced by marsh gain due to migration onto the upland, resulting in a net increase in vegetated marsh area over time. Vegetated marsh in MA decreased over time due to losses from ponding, channel widening, and erosion at the open fetch marsh edge. This analysis, which has been submitted for publication, provided insight into what factors are important in controlling marsh dynamics and can serve as a guide to potential management actions for marsh protection. This research involved 1 MA student and 2 undergraduates, and was also part of a teacher training workshop. The results were presented at a salt marsh and sea-level rise workshop organized for this project, as well as in multiple public and academic venues. Data from the project are available in the GCE Data Catalog (http://gce-lter.marsci.uga.edu/public/app/data_catalog.asp) and through BCO-DMO. Last Modified: 03/02/2020 Submitted by: Merryl Alber