10/15/2021

Save The Wetlands, Save The World

17:30 minutes

illustrated stack of books with text "scifri book club"

This story is a part of our fall Book Club conversation about ‘Rising: Dispatches From the New American Shore.’  Check out our main landing page for more about how to join the conversation.


In Rising, the Science Friday Book Club pick for this fall, author Elizabeth Rush writes frequently of marshes, starting with Jacob’s Point on the Rhode Island Coast.

“Jacob’s Point, like all tidal marshes, contains three distinct zones: low marsh, high marsh, and an upland area at its farthest inland edge. Every day the low marsh is covered in salt water twice, and also uncovered twice; the high marsh slips beneath the salt only in storms. Which is to say, along the point’s seaward edge, plants and animals have adapted to live with the tides while upland the opposite is true. Think of a tidal marsh as—like all wetlands—a transitional region where distinctions blur and the entirely wet world morphs into the almost entirely dry one. It is a liminal ribbon. An in-between. A spit of land at the edge of things, where the governing laws change four times a day.”

a coastal marshland with small mountains in the distance
Coastal marsh land in San Francisco Bay at high tide. This photo was taken at Baylands Nature Preserve in Palo Alto, California. Credit: Shutterstock

Rush goes on to explore the disappearing wetlands of Louisiana’s hurricane-battered coast, the San Francisco Bay Estuary, Staten Island’s newly abandoned flood zones, and other marshes around the country. But why, scientifically speaking, are wetlands such a feature of the conversation around coastal resilience to climate change and rising seas.

In a recording with a ‘live’ Zoom audience, SciFri producer Christie Taylor speaks with wetland ecologists Marcelo Ardón and Letitia Grenier about the resilience and adaptability of marshland, how climate change and sea level rise threatens them, and why protecting and restoring tidelands is good for everyone.


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Segment Guests

Letitia Grenier

Letitia Grenier is a senior scientist and program director of the Resilient Landscapes Program at the San Francisco Estuary Institute in San Francisco, California.

Marcelo Ardón

Marcelo Ardón is an associate professor in the College of Natural Resources at North Carolina State University in Raleigh, North Carolina.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. It’s book club season, and that means Book Club Captain Christie Taylor is here to modulate the medium, and shepherd the conversations we’ve been having about the climate change-centered book, Rising– Dispatches From the New American Shore by Elizabeth Rush. Hey there, Christie.

CHRISTIE TAYLOR: Hey there, Ira.

IRA FLATOW: OK. What are we going to talk about today?

CHRISTIE TAYLOR: Ira, I have just one word for you, and that’s marshes.

IRA FLATOW: Marshes, marshes, marshes– reminds me of that old sitcom. You know what I mean?

CHRISTIE TAYLOR: [LAUGHS] I have that problem too. But we really need to talk more about marshes, specifically, coastal wetlands. Just like the ones we heard about in Long Island. In Rising, Elizabeth Rush talks a lot about them– how they collect and sequester carbon, how sea level rise makes them rot and disappear, and how we need them to protect the coast from flooding.

IRA FLATOW: You know, anyone who’s ever lived through a hurricane has an appreciation already. And I can attest to that.

CHRISTIE TAYLOR: Yeah. For sure. And the thing is, a coastal marsh is also really complex. Here’s a short excerpt from the book about a marsh in Rhode Island. It gives you a good idea of how much there actually is to understand about these ecosystems.

Elizabeth writes, “Jacob’s Point, like all tidal marshes, contains three distinct zones: low marsh, high marsh, and an upland area at its farthest inland edge. Every day the low marsh is covered in saltwater twice, and also uncovered twice. The high marsh slips beneath the salt only in storms. Along the point’s seaward edge, plants and animals have adapted to live with the tides. While upland, the opposite is true. Think of a tidal marsh as, like all wetlands, a transitional region where distinctions blur, and the entirely wet world morphs into the almost entirely dry one.”

IRA FLATOW: Wow. That’s a great quote. Great–

CHRISTIE TAYLOR: Yeah. It really is. So to wade in, as they say, to marsh science, I grabbed some experts from opposite coasts. Marcelo Ardon, an Assistant Professor at North Carolina State University, and Letitia Grenier, a scientist with the San Francisco Estuary Institute’s Resilient Landscapes program.

And just a quick note that this interview was recorded in front of a live Zoom audience. You’ll hear a couple of audience questions along the way.

But first, I asked Letitia to tell us more about the specific marsh ecosystem she worked in, and what exactly makes it tick.

LETITIA GRENIER: Tidal marshes are the most important ecosystem you’ve never heard of. Often we drive by them, if you live near the coast, and so many of us do. And you don’t even think about them. They’re pretty flat. And what’s really important about them is they do so many things for people, and also for nature and Wildlife.

They lie between high tide and low tide. So they actually are tidal. The tide goes in and out of them every day. And it comes via this network of channels, that’s a lot like the arteries bringing blood into your body, and muscles, and then taking it away.

So they’re very connected to the ocean, and to the land. They’re really half of each. And what they do for us are things like sequester and store carbon. So they’re actually helping mitigate climate change. But they also protect the shorelines.

So they’re helping us adapt to climate change by absorbing water, reducing erosion– if you have a big tidal marsh in front of your shoreline, you can actually have a much smaller levee behind it than you would need to have if you didn’t have that marsh there.

They also have lots of important species in them– endangered species, especially, in California. And they make food. That’s a huge thing. They make tons and tons of food which feeds fish and other kinds of sea life. And that feeds people, and even more wildlife. So I think of them as the refrigerators of California where we work.

CHRISTIE TAYLOR: And Marcelo, meanwhile in North Carolina, you’re working in a very different kind of coastal wetland. It’s actually a Freshwater ecosystem. But tell us about your area of study.

MARCELO ARDON: Yeah. So I love that description that you just read from the book, talking about the low marsh, the high marsh, and the upland. We started studying upland forested wetlands– and here, when we say upland, they just mean they’re a little higher elevation. And so we don’t have the influences of those tides that you have in the marshes. But what we’ve been seeing is that line that separates the forest and the marsh has been shifting.

We’ve been getting– sea levels are rising. The soils– these wetlands are getting saltier. And then we’re having more storms as well.

And so we’re having these forested wetlands are turning into marshes in some cases. And in some other cases, we don’t really have that marsh state. Basically, these forested wetlands get swallowed by the, in our case, the sounds, the estuaries.

So we have a loss of all of these ecosystem services. So if forest wetland turns into a marsh, maybe that’s not as big of a deal. But when you have a forested wetland turn into open water, then you’re definitely losing a lot of those ecosystem services.

CHRISTIE TAYLOR: Well and you’re already referring to something that Elizabeth talks about in this book, which is the migration and transitions of marshes and wetlands to different kinds of marshes and wetlands and ecosystems. And I wonder if you could talk more about that process, both how a marsh can change under rising seas, but also, how, in some ways, that change isn’t always bad, perhaps.

MARCELO ARDON: I guess one way that I like to think about it is these marshes, and these wetlands, and the sea level, are kind of dance– right? They’re kind of doing this back and forth.

If you look over a long enough period of time, we know that sea levels have been higher in the past than they are now. They have retreated. And now they’re kind of moving back up again.

And so you could imagine these marshes and these wetlands dancing, and going back and forth as these changes have been happening.

So these changes are not new. What I think it’s important to remember is that sea levels are rising at rates that are faster than at least the last 2,000 years.

And so when you have these changes happening at a faster rate, it means that these wetlands don’t have the time to migrate as they migrated in the past. And the other problem is that we’ve put barriers that prevent this movement, as well.

We’ve built roads. We put agricultural fields, we’ve put golf courses, marinas, all these different things. So change is happening faster, and we’re preventing or restricting the ability of these ecosystems to change or to adapt to this. Which kind of gives it a double whammy. And we end up with dead trees standing in the water.

CHRISTIE TAYLOR: Letitia, anything to add there?

LETITIA GRENIER: What’s amazing about tidal marshes, in addition to all the things I said before, is that they are super resilient. So if they have enough material– remember those arteries I was talking about, where the tide comes in and goes out of the marsh?

That will actually bring in sediment. So dirt in water is sediment. So it will bring in that mud. And as the tide gets to the high tide, and then it turns around it has to stop– if you think about it, the tide comes all the way up to high tide. It stops, and then turns around goes out.

And in that moment of stopping, the water velocity is zero. And the sediment falls out of the water and lands on the marsh.

And so if there is enough sediment in your water, your marsh can build itself up quite rapidly with sea level rise. The challenge is, where are you going to get that sediment?

And actually a piece of that is the marsh plants can actually make their own sediment, which is very cool. But in our estuary, and along most of the California coast, and really most of the coast of the world, we do need that inorganic sediment, that mud, to build up the marshes.

And the issue is that we’ve interrupted a lot of how sediment flows through our ecosystems, with our dams, and our other water projects that have changed how sediment moves. And so we don’t have enough.

So we’ve actually done the research here in San Francisco Bay to figure that out. And we only have 40% of what we need for our marshes to last until 2100.

But there are many things we can do to create enough material for the marshes to build up. But it takes, really, decades with all of our environmental regulations and landscape modification to get the sediment in the right place to be able to do that. So that’s why we have to plan ahead.

CHRISTIE TAYLOR: We have another question from John in Forks, Washington. And John, why don’t you go ahead and ask that question.

JOHN: Here in the Northwest and in Alaska, we have ghost forests that formed as the result of subduction zone earthquakes. This is the extreme of rapid, if infrequent change. Do they provide any insight into the ability of habitats to respond to such changes?

MARCELO ARDON: Yeah. That’s a great question. So, yeah. So what we mean by ghost forests are these– basically, a place where you had a forest, and for some reason you’ve had rapid mortality of the trees there.

In some cases, you have the marsh vegetation coming in. And so you can see the dead trees, and the spartina, or the cord grass coming in. In some other cases, you just have the water coming in.

I’ve read about these ghost forests in Alaska that have to do because of the earthquake and subduction. Honestly, I don’t know that much about them. They seem really interesting. And it might be a good place to study what, as you say, a very rapid change– because the changes that we’re seeing, for example, here in North Carolina, that change happens a little bit slower than what is probably happening in Alaska and other places in the Northwest.

But absolutely. That’s a great question. And I would love to fly over there to check those out.

CHRISTIE TAYLOR: We have another question from our audience from K. Go ahead K.

K: Hi my name is [INAUDIBLE], and what I wanted to know is that– I had read, a couple of days ago, that there was a major oil spill off the coast of California. Are there land stewardship policies in place right now to protect and restore a marsh? I can understand reforestation projects. But how do you protect the marsh?

LETITIA GRENIER: Yeah. –A great question. There’s a lot of activity in California preventing for further drilling on the coast, for exactly this reason. Despite everybody’s best efforts, accidents happen. And the more infrastructure you have out there that’s got oil moving around, the more problems you could have.

In terms of marsh restoration, historically it was a pretty easy process. You would go to a place that’s at the right elevation and has tide. And you would simply open it up to the tide. Most of these places have been diked for agriculture.

And if you open a place that’s at that right elevation, and the tide comes in, honestly, nature does the rest. It’s kind of amazing.

The seeds are often there or they get brought by the tide. The sediment builds up. The animals come.

We’ve had wildlife returning to restored marshes in five years– endangered species– in these marshes very, very quickly.

Now that was the past, when sea level wasn’t rising so fast. In the future, we’re going to have to think about how to bring enough sediment to those marshes to keep them around.

CHRISTIE TAYLOR: Marcelo, there’s restoration happening on the East Coast too. How is that going? Is that something where we can see a difference between the quote “original marshes” and the restored marshes, in terms of how they function?

MARCELO ARDON: There’s a fair amount of restoration in the East Coast as well. And a lot of the things that Letitia was talking about are things that we’re facing as well.

There’s been a fair amount of restoration of marshes that have happened in the coast of North Carolina, and South Carolina, and Georgia. I’ve been involved in restoration of forested wetlands as well. And again, it’s hard to do, but it’s definitely not impossible.

We’ve also been working on restoring wetlands that we have here in North Carolina called pocosin wetlands, which are also forested wetlands. They’re peat wetlands. Their soil is very carbon rich. They have been drained.

And what we’re working on is just raising the water table. So it’s relatively minor restoration in that all you’re doing is putting water control structures– and by raising the water table, you decrease the greenhouse gas emissions, again, helping to mitigate climate change.

So there’s definitely lots of opportunities for restoration, and lots of benefits that can come from–

CHRISTIE TAYLOR: Just a quick reminder that this is Science Friday from WNYC Studios.

We were talking earlier about how marshes can adapt and migrate as long as there are no barriers in the way of them moving. Listener Rebecca has a question, though, about those barriers. Go ahead, Rebecca.

REBECCA: Hi. I was wondering– is there at least a conversation about dismantling some of these? Is it happening? Or is it even being contemplated?

LETITIA GRENIER: That’s a good question. I think there are areas that are being improved. So in a lot of cases where you’ve got a man-made barrier, it’s eroding, or falling apart, or it needs improvement. And usually, what’s behind it, people aren’t ready to let it go yet.

So certainly we’ve gotten rid of barriers. When it’s time to restore the wetland behind that and turn it into tidal marsh, then we might take down that levee entirely. And that’s certainly happening.

But where there’s a Walmart parking lot behind it, and certainly if there’s a neighborhood, or a road, or the footing to a bridge, or a sewage treatment plant, or Google, those are all things that are right behind the levees in San Francisco Bay.

People aren’t ready to have that be a more natural space. So what we can do, though, is replace that with what we call hybrid structures. Instead of all gray they’re green gray. And so they may have maybe a levee with a very shallow slope. And that slope can have a wetland on it.

Sometimes we put treated wastewater to feed that wetland, and the water gets cleaned up. And we’ve got a wetland that’s supporting wildlife and sequestering carbon. So there’s these new ideas about how we can make these sort of hybrid measures around the shoreline. There is quite a lot of talk about managed retreat, which is people actually moving back away from sea level rise.

And there is one instance of that happening in San Francisco, where they’re having really intense erosion around a piece of the water treatment system. And they’re actually going to move everything back, and let nature take its course, and change the shoreline in that area.

That’s pretty rare. There’s a little bit of that that’s happened in Louisiana, where there’s some real extreme examples of wetland loss, and– Mostly, people aren’t ready yet to let go of land.

On the other hand, I think thinking ahead is really important here. And the way I think of it is we retreat when we restore wetlands. So we know how to do that. Maybe we can start retreating for parking lots, and places that people aren’t emotionally attached to.

And then we could use that space for these really beneficial ecosystems that would really benefit everyone behind them. And then, way down the road, we can think about the places that are really harder for us to deal with. Because it is very painful to think about moving a neighborhood, for example.

CHRISTIE TAYLOR: So as we wrap up, Letitia, Marcelo, is there anything that you still want from lawmakers– from policy?

LETITIA GRENIER: I think we need to regulate sediment. It’s a precious commodity that we’re giving away for free. It’s not good. And we need to actually be able to regulate that migration space. So the place where the ocean and the wetlands want to go, as sea level rises, there’s no government regulation of that space.

And that’s a huge problem. Because it can be developed. It’s actually just as precious as the wetlands themselves at this point. So we do need some legislative change.

MARCELO ARDON: Yeah. That’s a great answer. I think I– got to fully agree. A lot of these wetlands in North Carolina are sediment starved. We don’t have enough sediment. So that’s why our marshes and our forested wetlands aren’t keeping up.

And we don’t have good ways to either regulate, or just even think about how these things are changing, and how they’re likely to change in the coming decades.

And so we need better ways to think about it. You know, I’m not– I don’t interact as much with policy. Right? I do think there’s a philosophical change of how we think about these systems. It’s hard when the US legislative system has a lot about how to control land. It has less about how to control water. Wetlands are stuck in between. So that’s why we need to think more about how do we legislate these systems that are in between, and that they’re changing.

CHRISTIE TAYLOR: Well, thank you both. That is all the time we have. Letitia Grenier co-directs the Resilient Landscapes Program at the San Francisco Estuary Institute. And Marcelo Ardon is Associate Professor at the College of Natural Resources at North Carolina State University. Thank you both for being here today.

MARCELO ARDON: Thank you. This was great.

LETITIA GRENIER: Thank you so much.

CHRISTIE TAYLOR: And thanks so much to all of our listeners for coming here today. And all of your really amazing questions– we had far too many to actually ask. We would be here for 17 hours if we did. But thank you all so much. I’m Christie Taylor.

IRA FLATOW: Thank you, Christie. That really was a terrific story. For the full video of that event, or to sign up for one of our upcoming live tapings on Zoom, visit our website sciencefriday.com/livestream.

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Christie Taylor is a producer for Science Friday. Her day involves diligent research, too many phone calls for an introvert, and asking scientists if they have any audio of that narwhal heartbeat.

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