Quantifying coastal protection ecosystem services of salt marshes

Salt marshes are known for providing several essential ecosystem services, including coastal protection via wave attenuation and sediment stabilization. Despite their value, the global extent of salt marshes is decreasing due to human pressures, such as land reclamation, climate change and eutrophication, which are primary drivers of change in salt marsh ecosystems. We determined the factors affecting resistance to erosion in salt marshes of the Italian Northern Adriatic coast by subjecting salt marsh sediment cores to simulated wave treatment in wave mesocosms and estimating volume loss with novel photogrammetry techniques. In our first experiment investigating the influence of vegetation and sediment properties on erosion, our results showed that Spartina spp. salt marsh vegetation, and its root biomass in particular, enhances resistance to erosion, and this effect is stronger in sandy compared to silty soils. In a second experiment, we investigated the impacts of increased eutrophication on resistance to erosion by manipulating nutrients in one of our study sites (Grado Lagoon). Spartina spp. below-ground biomass significantly reduced erosion in nutrienttreated plots. Species composition in fertilized plots also shifted from Spartina spp. to Salicornia spp. succulents. Our study demonstrates the critical role of salt marsh vegetation in resistance to erosion, and how the effect of vegetation is mediated by sediment and nutrient conditions, raising important considerations for management of salt marshes for coastal protection.