Prevalence and impending ecological consequences of shoreline hardening along US coasts

Background/Question/Methods

Human population growth and development are major global threats to coastal ecosystems, with roughly one third of the world’s population living within 100km of a coastline. The consequences of anthropogenic climate change, particularly a rise in sea level and increases in storminess (i.e. hurricanes), have the potential to drown and erode coastal habitats, resulting in unprecedented losses. As sea level and storms threaten developed coastal property, individuals and communities often resort to hardening the shoreline with bulkheads or seawalls. Shoreline hardening severs the connection between intertidal and upland habitats and will likely prevent upslope transgression of salt marshes, mangroves, and intertidal oyster reefs with rising sea levels.

We determined the prevalence and potential future impact of shoreline hardening on United States (U.S.) estuarine habitats by coalescing existing national datasets and using regression trees to relate factors such as population density, population growth, storminess, and shoreline geomorphology to total km of hardened shoreline within every coastal county in the U.S. We also evaluated current threats and looming risks of salt marsh loss as a result of sea-level rise and shoreline hardening.

Results/Conclusions

Our analyses revealed that 20,076 km of U.S. shoreline (14%) has been hardened, 66% of which is along the south-Atlantic and Gulf coasts. These coasts contain most of the U.S. salt marshes and are also most vulnerable to sea level rise, storm events, and future development (based on the physical characteristics of the shoreline, storm frequency, and current population growth rates). This is the first analysis to quantify the total amount of hardened shoreline in the U.S. and to determine the vulnerability of salt marsh to future coastal development and sea level rise. Federal and state agencies could use the results of this study to inform new shoreline protection policies and coastal management practices.