Marshes and Wetlands Beat Seawalls When It Comes to Protecting People and Wildlife
As the United States’ coastal population surges, it is battening down the hatches, building seawalls, bulkheads, and breakwaters to protect people from rising seas and ever-stronger storms. The result: 14 percent of the nation’s tidal shoreline has been “hardened.” By the end of the century, a third of the coast could be armored if the trend continues.
But new research finds that wetlands, marshes, and other natural barriers are more effective than concrete at protecting coasts.
“Nature knows best, in the sense that natural shorelines are resilient to erosion and storm events,” said Rachel Gittman, a marine ecologist at Northeastern University and the author of a trio of new papers about living shorelines.
Gittman said hardened vertical structures made of concrete, rock, wood, or vinyl are typically flat surfaces rather than the complex salt marshes or low-sloping rocky areas they often replace. That results in fewer habitats for a diverse set of marine life, including fish, crabs, and other creatures.
“Sea level rises and falls over time, and marshes have persisted through those changes,” Gittman said. “What you’re doing [with a barrier] is essentially stopping that transgression.”
In one study in press at the journal Ecological Applications, Gittman and her colleagues looked at a natural coastline, a bare bulkhead shoreline, and a hybrid coastline made of rocks and marsh plantings, comparing the abundance of juvenile fish and crustaceans. They were surprised to find that the hybrid rock and marsh grass shorelines had the highest diversity and abundance of marine life.
In another study, the researchers used Hurricane Irene, which struck the East Coast in August 2011, to test how different types of shorelines fare in big storms. Gittman collected data on shorelines before the storm made landfall and did damage assessment afterward on some of the hardest-hit shorelines.
In the central Outer Banks of North Carolina, Irene damaged 76 percent of bulkheads surveyed. Across marsh sites within 15 miles of the hurricane’s landfall, the storm had no effect on marsh surface elevations. Although the storm temporarily reduced the density of vegetation at those sites, the plants recovered to pre-hurricane levels within a year.
Gittman isn’t alone in her interest in making shorelines more natural. The National Oceanographic and Atmospheric Administration has a Web page dedicated to helping people figure out how living shorelines can help them. Living shorelines can include materials such as sand, wetland plants, oyster reefs, submerged aquatic vegetation, and stones.
Homeowners should know that they don’t always need to build a giant bulkhead, Gittman said: “Natural shorelines in combination with engineering solutions in moderation can be better than bulkheads to stabilize the shoreline. Using natural components can lead to better results in both the long-term protection of shoreline and ecologic resources we value.”