HOST: Welcome to Diving Deeper, I’m your host Kate Nielsen. For today’s episode we’ll explore what a living shoreline is and why they’re so important. Joining us today by phone from Pivers Island, North Carolina, is Carolyn Currin, a biologist from NOAA’s National Centers for Coastal Ocean Science.
Hi Carolyn, thanks for joining us today!
CAROLYN CURRIN: Hi Kate.
HOST: Carolyn, can you start off by explaining what a living shoreline is?
CAROLYN CURRIN: A living shoreline is a term that is used to describe an alternative approach to shoreline stabilization—an approach that uses natural vegetation and native habitats instead of hardened materials such as bulkhead, a rip rap, or a sea wall. The reason that the living shorelines approach was developed is that we’ve learned over time that those hardened shorelines have some adverse impacts to the estuarine ecosystem. So, a move was developed to see if we can do something better, that’s better for the ecosystem, that’s better for property owners, something that’s more resilient, and something that may be more cost effective in the long run.
Some of the problems with the traditional hardened approach to shoreline stabilization is that they don’t absorb wave energy, they reflect it and so you end up getting scour offshore of the system, you get deepening of the water, you lose vegetation that may have been present offshore, and in that process you lose some of the things vegetative habitat provide such as fish habitat, improving water quality, and those kinds of things. So, living shorelines try to protect those habitats at the same time as offering property owners some shoreline stabilization advantages.
HOST: Thanks Carolyn, so what are some examples of a living shoreline? You’re saying it could be like a salt marsh?
CAROLYN CURRIN: Yeah, salt marshes are frequently a major feature of a living shoreline approach especially on the Atlantic and Gulf coasts. In this case, a fringe of salt marsh, 25 to 50 feet wide perhaps, running parallel to the shoreline. Offshore of that shoreline may be another structure, either a low rock fill, particularly if there’s a little bit lower wave energy, maybe oyster reef . Landward of that salt marsh would just be a gradual transition into the upland or into a lawn. In other parts of the world, some other approaches could be used in more tropical environments, a living shoreline might be mangrove or coral reef. On the West Coast, where you have much higher energy estuarine settings, you might incorporate sediment bluffs with logs or sandier gravel beaches to provide a more natural shoreline habitat.
HOST: Are there places where our listeners may have seen a living shoreline? Are these common?
CAROLYN CURRIN: Yes, they may have. They’re not as common as I wish they were quite yet. The living shoreline term really originated in the Chesapeake Bay area where people developed this alternative idea to shoreline stabilization, and they’re quite a few places in Chesapeake Bay where you might see one, including for example the NOAA lab in Oxford, Maryland; the Virginia Institute of Marine Sciences. But if you’re not around the Chesapeake Bay area or you’re not familiar with local living shorelines, we’re going to give you some links on the notes with this podcast that will give you some places on the Internet where there’s some really great resources that have pictures of living shorelines, more information about them, and where you can go to see them.
HOST: Carolyn, how do communities decide what type of living shoreline is best for them or even if a living shoreline is right for them? What are some of the factors they need to consider?
CAROLYN CURRIN: Yes, a living shoreline can be a great solution in many cases, but it won’t work everywhere. The primary factor determining the kind of living shoreline one might be able to use is the wave energy of the site. So salt marshes do occupy estuarine shorelines across a pretty wide range of wave energies, but there is a limit to where a salt marsh can be sustainable. The other is the slope of the site. Salt marshes require a rather gentle slope so steep sediment bluffs may not be easily adaptable to the salt marsh version of a living shoreline.
If there’s really deep water offshore of the site, that also kind of makes the living shoreline a little bit more difficult to put in. These are the primary factors one would consider, but there’s a range of approaches where you can incorporate some hardened structure, as I mentioned earlier the stone fill can provide some additional protection from wave energy for the marsh in higher energy settings.
HOST: Do communities ever need to replant or replace a salt marsh? How long do they typically last?
CAROLYN CURRIN: The marsh can take a couple of years to develop, so it may require some initial replantings, once its established, its very resilient and requires very little care. Another thing that we’ve learned in some recent studies is that these living shorelines are very resilient to storm events. There’ve been some studies recently looking at the impact of, for example, Hurricane Irene, which passed over North Carolina a couple of years ago and several living shoreline sites were shown to have come through it very well and that in contrast, adjacent bulkheads sometimes suffered damages that storm surge came up over the bulkhead and then it receded and it actually caused the bulkhead to have damage. So really our experience is that after a couple of years, they are well established and they can provide really effective shoreline stabilization.
HOST: Carolyn, what are some of the benefits of living shorelines?
CAROLYN CURRIN: Well, living shorelines provide many of the benefits that salt marshes do and there’s a number of them including fish habitat, which most people are probably very familiar with and also they do attenuate wave energy and they also trap sediments. The fish habitat that salt marshes provide is not only in providing food, so they support the food web that supports food and shellfish production, but salt marshes also provide refuge and in not only providing that for large fish but the most crucial part of salt marshes is that they provide really important nursery habitat and that’s almost more refuge than food. So if you’re a larval or juvenile fish you need shallow water where big fish can’t come and eat you. And so that’s one of the reasons why we want to maintain a shallow sloping shoreline and a vegetated shoreline to provide refuge and nursery habitat for larval and juvenile fish.
I mentioned also marsh’s ability to attenuate waves. So salt marshes have these hollow, stiff stems and as a wave comes into a salt marsh, those stems absorb that wave energy, dampen that wave energy, and so over a fairly remarkably short distance—20 or 30 feet—you can watch a wave come into a salt marsh, knock those stems back and forth and then by the time you get to the end of the salt marsh, the wave has disappeared, so they’re really effective at attenuating wave energy.
As they’re doing that, the sediment that comes in, as most people know there’s a lot of suspended sediment in estuarine waters, as that tidal water comes in and there’s sediments in that water suspended by that wave energy is that that wave energy decreases, the sediment falls out and those sediments become part of the marsh and actually build the surface elevation of the marsh up. So the marsh is increasing its elevation which is especially important in enabling the marsh to maintain its position relative to sea level rise. So the marsh is trapping sediments which not only increases resiliency of that shoreline by increasing its elevation, it also improves water quality by removing sediments from that system.
Another quality that salt marshes have and another benefit that they have is that whole process of trapping sediments and this high rates of primary production that the marsh has, results in a removal of carbon dioxide from the atmosphere and transferring it into the sediment in the salt marsh where it’s sequestered. So there’s a net removal of CO2 which as we know is a greenhouse gas, so salt marshes also play an important role in climate adaptation and mitigation of greenhouse gas in the atmosphere.
HOST: So it seems with all of these benefits, a living shoreline is a great decision to help with local erosion control. Are there disadvantages or limitations to living shorelines?
CAROLYN CURRIN: Well, I think there are some limitations, I’m not sure if there’s any disadvantages. The limitations as I mentioned before are primarily in terms of the physical setting of the site. It has to be a wave energy setting in which a marsh can sustain itself. And I should mention here that it’s not just wind-generated waves that are of concern, it’s also boat wakes. So proximity to navigation channels can sometimes be a problem. And then as I also said, if the site doesn’t have the proper slope to support a salt marsh, it can be difficult.
In terms of disadvantages, one thing I’ve learned in talking to people is that it can be an aesthetic issue. Some people really like a neat, trim straight line at the edge of their lawns and maybe don’t like the more fuzzy, ragged appearance of a salt marsh. I think part of this process is once people understand all of the great things that salt marsh shoreline is providing them, maybe they’ll have a different take on its not as neat look as the bulkhead.
HOST: Carolyn, what is NOAA’s role with respect to living shorelines?
CAROLYN CURRIN: NOAA has several roles. First, NOAA has a mandate to provide regulatory protection to both vegetated habitats and what we call essential fish habitat which is described as nursery grounds for larval and juvenile fish. So in the permitting process for living shorelines, NOAA plays a role in making sure that the design will protect those habitats. NOAA also has an advisory role and builds partnerships with a number of groups. NOAA, for example, works with the National Estuarine Research Reserve Coastal Training Program to provide information to state and local governments, marine contractors, real estate agents, just a whole variety of stakeholders and NOAA develops a lot of advisory material in support of that effort.
NOAA provides funding for community-based and coastal resilience projects, so a lot of the living shorelines that I’m familiar with were constructed with NOAA funds by other groups. Finally, NOAA has a research role, these are relatively new solutions to shoreline stabilization. We’re still learning a lot about where they can work, how they can work. So NOAA funds both internal and external research to help provide guidance and assess the effectiveness of living shorelines.
HOST: Is there a good living shorelines example, maybe a success story that you can share with us today?
CAROLYN CURRIN: Yeah, one of my favorite stories is right here on Pivers Island. In the 90s, we had a series of hurricanes come through North Carolina—Bonnie, Fran, Floyd, Dennis, etc., etc., and Pivers Island is home to both NOAA and Duke Marine Lab, and we unfortunately have one stretch of beach left on this island, the rest has been bulkheaded. And these hurricanes created about a 20-foot erosion event, removed some upland shrubs, undercut a maintenance area and really knocked that sandy beach/unhardened shoreline back. And so the facility managers initially said, “OK, we’re going to connect the sea wall, there’s a sea wall at Duke, there’s a sea wall at NOAA, we’re just going to put a sea wall along this last bit of natural shoreline.” And we said, “well let’s try planting some salt marsh in there, can we do that,” and they allowed us to, this was about the year 2000. We planted four rows of Spartina, we then had the Division of Marine Fisheries come and spray some oyster shell off their barge in front of the marsh, this is about a 500-600 foot stretch of property here, and allowed the thing to grow and over time, it’s just become a beautiful salt marsh with a live oyster reef that’s spread and built in front of it. We’ve completely eliminated all erosion of the lawn. It’s just a beautiful marsh. We see birds out there. We see fish out there all the time. And so it was really a great process and showed us how effective these approaches can be in stabilizing a shoreline and providing all these other services as well.
HOST: Carolyn, I like to ask our guests to share with us a little bit about themselves, how you got to NOAA and in particular how you got to the position that you’re in today?
CAROLYN CURRIN: Well, I first arrived in Beaufort in 1983 for a 700 hour summer job, I had just graduated from college and the 700 hour summer job at the beach sounded a lot better than any of the other job offers I had, so I came down here as a research technician and just fell in love with the area and fell in love with marine research. I ended up going back to graduate school and came back to the NOAA lab after going to the University of North Carolina and got a permanent position here at NOAA in the 90s. And over time, I’ve kind of gone from looking at salt marsh restoration, how salt marshes provide food for fish, to now how salt marshes can help communities in stabilizing shorelines.
And I guess to answer the question of how I get a position here today, I think the great thing about working for NOAA is it really is applied science. You work closely with communities, state and federal governments to hear what the current problems are and kind of target your research in that direction and that’s been a really enjoyable process for me.
HOST: Do you have any final, closing words to leave our listeners with today?
CAROLYN CURRIN: Yeah, I like to live near the coast as does over 40% of the U.S. population, but these are really dynamic environments. And as recent events have shown us, coastal communities are vulnerable to sea level rise, storms, and coastal erosion. And so this living shoreline concept is part of a larger thought process about how coastal communities can be resilient to these changes and storm events, which are just part of being on the coast, and to be both resilient and protect themselves but also protect the natural resources which is why everyone wants to live here. I think as we mentioned before, there is a lot of information out there on the living shorelines approach. There are a lot of state/local/federal government resources targeted towards promoting this approach as well as a lot of environmental groups. And so I really think and hope that we’re at a point where this is really going to be embraced widely by coastal communities and provide a great service to not only homeowners and property owners, but also to the public who enjoys these coastal ecosystems so much.
HOST: Thanks Carolyn for joining us on Diving Deeper to talk with us about living shorelines. For our listeners, you can find more information in our show notes. That’s all for today’s show. We hope you’ll tune in again!