Article: Davis JL, Currin CA, O’Brien C, Raffenburg C, Davis A (2015). “Living Shorelines: Coastal Resilience with a Blue Carbon Benefit”. PLoS ONE 10 (11): e0142595. DOI:10.1371/journal.pone.0142595
Protecting our Shorelines
We have all seen pictures of shoreline erosion caused by the combined strength of coastal storms, flooding, and sea level rise, and if you haven’t, take a peek at Figure 1 (1). This erosion and subsequent damage is particularly bad if you happen to live near a coast or enjoy a day at the beach! Obviously, for the safety of life and property, we are very interested in protecting our shorelines.
Methods to Reduce Coastal Erosion
Generally speaking, there are two approaches to protect shorelines from coastal erosion: built and natural infrastructure.
Built infrastructure, also called hardened shoreline or shoreline armoring, employs concrete-like structures such as a seawall or bulkhead (Figure 2). These structures help protect shorelines, but also take away valuable habitat. Bulkheads may actually reduce seagrass coverage (2), which is a vital habitat for organisms including the blue crab.
Living shorelines are an alternative and natural infrastructure option which uses native vegetation. These green infrastructures are typically planted and/or restored fringed marshes that thinly border the coast in widths <30 meters, which is much narrower than an established marsh. Most living shorelines also employ natural structures such as oyster shell to help reduce waves. In many cases, such as in Davis et al., these shells can become living oyster reefs!
In some cases, living shorelines may be more resilient to storm impacts than bulkheads. For example, after hurricane Irene, a homeowner in North Carolina saw their property turned into a mudflat when waves crashed over the bulkhead while a homeowner less than 650 ft away protected by a living shoreline was left little damage (3).
Living shorelines also provide numerous ecosystem services that are lost when bulkheads are used. Marshes, rock sills, and oyster beds (all living shoreline types) also act as fish nursery areas, trap sediments and nutrients which improve water quality, and decrease the power of crashing waves (4). This study by Davis et al., looked at one more ecosystem service: carbon sequestration.
Can Living Shorelines trap carbon?
Marsh preservation and restoration has been fueled by the ability of coastal vegetation to store carbon. But what about these smaller, fringe marshes used to protect shorelines?
The researchers in this study looked at 8 different coastal marshes in the Newport River Estuary in North Carolina. Three marshes were natural, old, and fully established. The other 5 marshes were planted or restored (young) marshes with 2 of those created to be living shorelines. The environmental conditions (temperature, tidal range, storms) should all be the same since these 8 marshes were all near each other.
In marshes, most carbon storage occurs below-ground. Carbon is considered to be sequestered when the below-ground production (the creation of carbon by photsynthesis) is greater than the remineratization (the loss of carbon due to respiration).
The older, established marshes, had a lower rate of carbon sequestration (Figure 3). But do not be deceived! The higher rate of carbon sequestration in the restored marshes are likely “inflated.” Much of the sequestered carbon in these young marshes is likely labile, meaning that some of this carbon will end up being respired back into the atmosphere. The carbon sequestered by the older marshes, although at a slower rate, is likely more refractory, or “unappetizing”, to microbes. In other words, these mature marshes are have a long-term carbon trapping potential (Figure 4).
However, it should not be lost that the living shorelines are also sequestering carbon, and the long term storage of that carbon will likely increase as the marsh ages.
Traditional best management practices have used built structures, such as bulkheads, to protect shorelines. However, living shorelines not only help reduce coastal erosion, but can also trap and store carbon. However, most homeowners still prefer bulkheads. In moving forward, more research is needed on living shorelines to understand the long-term benefits (and flaws). Living shorelines may not always be the best option, but should be considered as an option when protecting our coasts.
Additional Citations and Good Reads
(1) Wigand, Cathleen, Thomas Ardito, Caitlin Chaffee, Wenley Ferguson, Suzanne Paton, Kenneth Raposa, Charles Vandemoer, and Elizabeth Watson. “A climate change adaptation strategy for management of coastal marsh systems.” Estuaries and Coasts (2015): 1-12. DOI: 10.1007/s12237-015-0003-y
(2) Patrick, Christopher J., Donald E. Weller, and Micah Ryder. “The Relationship Between Shoreline Armoring and Adjacent Submerged Aquatic Vegetation in Chesapeake Bay and Nearby Atlantic Coastal Bays.” Estuaries and Coasts 39, no. 1 (2016): 158-170. DOI: 10.1007/s12237-015-9970-2
(3) Popkin, Gabriel, and Dylan Ray. “Breaking the waves.” Science (New York, NY) 350, no. 6262 (2015): 756-759.
(4) Currin, C. A., W. S. Chappell, and A. Deaton. “Developing alternative shoreline armoring strategies: the living shoreline approach in North Carolina.” (2010): 91-102.