Living Shorelines Assessment

Coastal marshes are among the most degraded and threatened habitats in the world because of their sensitivity to coastal erosion from sea-level rise or storms, and increasing direct (e.g., development, in-filling, excavation) and indirect (e.g., sediment supply alterations, nutrient cycling changes, altered natural resource extraction) impacts from anthropogenic activities. Coastal marshes are highly valued because they offer storm and flood protection, habitat for many wildlife species, carbon sequestration, nutrient regulation, water quality improvement, shoreline stabilization, and other ecosystem services. Although marsh loss through the process of coastal erosion is natural, human activities such as water-front construction of homes, boating, and dredging can accelerate this process. It is expected that shoreline hardening, including construction of docks, seawalls, bulkheads and revetments, to protect built structures from eroding coastlines will continue to intensify, causing undesirable ecological consequences to nearshore coastal environments.

Hardened shorelines have been the leading method against shoreline erosion. Living shorelines, however, have longer sustainability and provide an ecosystem similar to a natural marsh. The living shoreline method often combines native vegetation and a wave dampener just offshore. We compared hardened, natural, and living shorelines and their success at mitigating erosion under different wave energy and fetch exposure. Comparisons of these three shoreline types was conducted at six field sites in Mississippi and Alabama. The field data was collected in winter and summer of 2020 using wave gages, water quality sondes, sediment cores, and vegetation quadrats. Google Earth satellite imagery was used to calculate shoreline erosion rates and fetch. 

The coastline and its shape were influenced by the energy exerted, with the high energy coastlines eroding quicker. Hardened shorelines were found to have little to no erosion, while natural shorelines had the greatest amount of erosion. Living shorelines lessened the rate of erosion. However, natural and living shorelines were similar in slope and sediment parameters, while hardened shorelines had steep slopes and higher sand content. Living and natural shorelines had similar vegetation diversity, while hardened shorelines differed with often very little vegetation.  Living shorelines with a combination of vegetation and a wave dampener decreased the impact of erosion to create a more natural ecosystem, especially at low energy sites. This data on different exposure and wave energies will help managers and landowners to decide the best method to protect their property from erosion while maintaining a healthy ecosystem.