American Scientist

As the Earth’s climate continues to warm, scientists are searching for ways to reduce greenhouse gases in the atmosphere. Ecosystem ecologist and biogeochemist Ariana Sutton-Grier says that it will take every tool at our disposal to combat climate change, including capitalizing on natural ecosystems that absorb carbon. These environments are known as carbon sinks, and Sutton-Grier says that coastal wetlands are the best carbon sink you’ve never heard of. The University of Maryland visiting associate research professor and 2019 Sigma Xi Young Investigator Award recipient spoke with American Scientists’s Robert Frederick about why saltwater marshes and other coastal environments should be a big part of climate change policy and discussed why their importance may often be overlooked.

Why do you think coastal wetlands have been left out of much of the climate change policy discussions?

Wetlands scientists have been studying carbon in wetlands for several decades at least; however, their focus was not necessarily the policy implications of that carbon in these wetlands. It was more to understand how different wetlands were separated from one another. Which ones had more carbon, which ones had less? How did that affect the biogeochemistry of the wetlands? How did it affect the plant growth, perhaps? Now that we are very much concerned with climate change mitigation and understanding natural carbon sinks, it puts a whole new lens on trying to better understand carbon in wetlands.

What also helped was taking a focus on comparing the carbon in these wetlands to other systems we already knew were natural climate sinks, such as forests. And without that comparison, it was very hard to make blue carbon [carbon stored in oceans and coastal systems] policy-relevant. Once that comparison started to be put forward, suddenly there was a new interest in the potential of wetlands carbon.

You’ve said that proper policies and management of coastal wetlands are among the best, overlooked climate change solutions. Why are these ecosystems a climate change solution?

Climate change is a socioenvironmental problem. It has environmental impacts, but it also has the human dimension—the socio piece, if you will. The human dimension is really important. Humans are a part of what is going on, humans are affected by it, and humans have to make the decisions about what we do about climate change.

There are a lot of options for how to tackle climate change. Quite honestly, in my opinion, we’re likely to need every single one of them. So yes, it includes renewable energy, and it includes, maybe in the future, something like fusion. It definitely includes thinking about energy efficiency and also how to reduce emissions by lots of different means. But the pieces that I focus on in my research are the natural climate solutions—the part of the puzzle that our ecosystems can play.

One thing I think people often don’t think about is that we already have a technology, if you will, for removing carbon dioxide from the atmosphere via photosynthesis. Plants take carbon dioxide from the atmosphere and turn it into plant biomass, some of which makes its way into soils and soil storage, and some of which stays in plant biomass. We already have this amazing system that does this, so my colleagues and I have been asking, “How much is happening through those natural mechanisms? How much more could we potentially do if we changed some of our management?”

We have other opportunities for management that will help us increase the ability of those natural systems to sequester this carbon, to take it out of the atmosphere and store it for the long term: for example, by doing things like increasing the amount of reforestation, trying to limit the conversion of natural systems, halting deforestation, and halting other land uses that are not sustainable, such as destroying coastal wetlands. And “long term” can mean anything from—ideally we’re looking for at least 50 to 100 years. In some cases we’re talking about hundreds to thousands of years that these systems are storing carbon.

When saltwater marshes are cut off from the ocean, particularly by human building projects such as roads, they are often inundated with fresh water, and as a result become huge emitters of methane, a powerful greenhouse gas. Why is that?

Saltwater marshes have sulfate present in that salt water. And when you have sulfate present, the microbes in the soil that do sulfate reduction can out-compete the microbes that produce methane—meaning the sulfate-reduction microbes can get to the carbon faster, and they can use their process of metabolism faster. So when you have sulfate present, you tend to have very low or no methane production.

When you introduce fresh water, which has no sulfate in it, you remove that ability of the sulfate reducers in the soil to outcompete those methane-producing microbes, and as a result more methane is produced. Methane is a natural part of freshwater wetlands. Always has been, probably always will be. So for a normal freshwater wetland, that’s just part of its natural biogeochemistry.

In a coastal setting where we humans have put in a road, a railroad line, or sometimes a bridge, one that has a very narrow culvert—there’s a little bit of tidal exchange, but not what used to be there before the human obstruction. Suddenly the amount of sulfate present in the water, which was limiting that methane, is gone. Now you have those methane-producing microbes that can go ahead and do their thing, naturally of course. They do what they’re supposed to do, and you get methane produced.

My colleague Kevin Kroeger with the U.S. Geological Survey found that one of the biggest opportunities for wetlands restoration in the United States—and this is actually true for many developed countries—is to start removing those tidal restrictions. They are working on the Herring River Tidal Restoration Project in Massachusetts, which will take a very small culvert and turn it into a large culvert with three separate openings to restore that tidal flushing. Almost immediately when those openings are created, you will get a drop in the methane and you’ll have a greenhouse gas benefit. The second you change the biogeochemical environment for those microbes, you’ll stop that methane production. It’s very exciting as a restoration opportunity.

On a per-unit-area basis, coastal wetlands are a much bigger carbon sink than forests. You get a lot of bang for your buck if you protect or restore coastal wetlands.

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Why do you think coastal wetlands have been overlooked as an opportunity for greenhouse gas reduction?

People are more likely to have heard about the importance of forests as a natural climate sink. We can see the carbon in those systems. It’s in the trees. It’s in the trunks. Most of it is above ground. And so it’s very natural that people would think of forests as a carbon sink.

The carbon in these wetlands is almost entirely below ground. You don’t see it. But coastal wetlands are very impressive carbon sinks per unit area. They tend to be better carbon sinks than forests. Now, on the planet, we do have far more acres of forest than of coastal wetlands, but on a per-unit-area basis, they are a much bigger carbon sink. You get a lot of bang for your buck if you protect or restore coastal wetlands. That’s why they need to be a part of our solution. Not the only thing, but a big part of our natural climate solutions.

What’s it going to take for communities to adopt coastal wetlands restoration policies?

Coastal states and communities have started to recognize the benefits that coastal ecosystems provide. (See “Renewed Hope for Coastal Marshes in Louisiana.”) There’s already a growing interest in, “How do we do resilience, but using natural and nature-based features?”

One of the challenges with natural and nature-based features is that there is no one-size-fits-all solution. Green infrastructure, as it’s also sometimes called, can be a lot of different things depending on the geologic or geographic setting. And then it also depends on what the community wants from their shoreline. Do they want recreational opportunities? Do they want more fishing habitat?

We need to take time and help communities figure out what works for them. We then need to monitor those natural and nature-based features when the next storm hits to figure out what worked really well. What maybe didn’t work as well as we hoped, and we should modify and test again? We need to have that research and monitoring framework for these natural and nature-based features, because we all need to learn and to get better at this so that we can help communities have more options.

How do you see your work fitting into the larger picture of policy making and advocacy?

I consider my work as science to support policy making and decision making. When your research is relevant to human decisions, societal challenges, and societal decisions, you want to make that research known. You want to do the science, and you need to publish the research. But then you need to do the translation that helps people who are not in the science community figure out what it means and why it might be relevant.

At no time in my papers do I ever say, “We must adopt policy Y written in this exact language.” I will say, “We should be considering the use of natural and nature-based features in our coastal resilience strategies.” That’s what all the research is suggesting, that these ecosystems can and should be a part of what we consider when we’re thinking about coastal resilience, because of their ability to attenuate waves and slow erosion. But I am never advocating one particular policy, one particular route. To me it’s the difference being policy-relevant and societally useful—that’s use-inspired research, if you will—versus advocacy.

Some scientists get hung up because they are concerned that by saying anything about their research, they will be immediately labeled as doing advocacy. And I think that’s a huge drawback, because it means that relevant research that could be very useful may never make it to the light of day on a policy-maker’s desk.

There’s this fantasy that somehow a policy maker is just going to see the paper we got published and immediately know what it means, how it’s useful to them, and how to translate it into the policy they’re working on. But policy makers don’t have the time. They’re not looking at the journals. They’re hoping that somebody on staff has some science training and is doing that for them and bringing them anything useful. But there’s no reason that a scientist can’t do that as well and say, “I’m going to publish this research in a science journal, and then I’m going to figure out how to talk about it to another audience.”

For example, when I talk about blue carbon, I talk about “carbon banks.” You have an input of carbon each year that’s like your salary, and then you have your savings, which is what’s in the soil. I use a metaphor to help people understand what I’m trying to say, what I’ve learned, and then let them get to the point of, “Oh, this might mean we should have policy X.”

That piece is where it moves to the advocacy and the specific policy part. Scientists can play a very important role there, too. My research has always been on the front end of making sure that whatever new science is happening is translated, available, and relevant to the policy makers and decision makers that I’ve been working with. But that’s not advocacy, in my opinion.