The role of living shorelines as a resilience strategy for nutrient reduction in estuarine systems

IntroductionTidal salt marshes provide critical ecosystem services in estuaries including the removal, storage, and transformation of nutrients, improving water quality and aquatic habitat. As tidal marshes drown from sea level rise, this service is lost, impacting estuarine resilience and leading to degradation of water quality. Living shorelines are a strategy to protect shorelines, while restoring some capacity to improve water quality. MethodsIn this study, we examine the magnitude of different nutrient storage and removal pathways in living shorelines, which range from short-term storage of nutrients (weeks-months) to permanent removals. ResultsWe found that all variables (plant and algal biomass, soil characteristics and sediment nutrient fluxes) varied significantly across sites emphasizing the variability in living shoreline functions. Plant biomass, benthic microalgae biomass, soil %C, soil %N, and denitrification (net N2 fluxes) were significantly different by season. Marsh age was only significantly correlated with phosphate fluxes from the sediment, so it was not an important driver of variability in function between living shorelines.DiscussionDespite the spatial variability, we found that nutrient storage and removal pathways were generally similar to those in natural marshes, reinforcing the assumption that these systems are replacements for natural marshes and an important component of resilience efforts. However, we found the short-term storage of nitrogen and phosphorus through uptake by benthic microalgae and the permanent removal of nitrogen through denitrification (both higher in living shorelines) suggests that living shorelines could maintain or improve estuarine water quality, contributing to coastal resilience.