S5 E9 – Foundational Research on Rebalancing with Blue Carbon

Air Date: March 29, 2023

About This Episode

Coastal ecosystems provide an essential part of the solution to global climate change, along with multiple benefits. Among other things, coastal ecosystems sequester and store “blue carbon”—carbon that’s stored in coastal and marine ecosystems. We’re talking with leading scientists about their foundational research into how blue carbon is helping to address climate change. Hosts Sarah Thorne and Jeff King, National Lead of the Engineering With Nature® Program, are joined by Lisa Chambers, Associate Professor of Biological Sciences at the University of Central Florida; Jenny Davis, Research Ecologist with the National Centers for Coastal Ocean Science (NCCOS), in the Beaufort Lab, Marine Spatial Ecology Division of the National Oceanic and Atmospheric Administration (NOAA); and Jacob Berkowitz, a Research Soil Scientist and Lead of the Wetland Team with the Engineer Research Development Center (ERDC), US Army Corps of Engineers (USACE).

As Lisa explains, blue carbon refers to carbon stored in vegetated coastal ecosystems such as marshes, mangroves, and seagrasses. The “blue” term differentiates it from carbon stored in other ecosystems such as terrestrial forests. Lisa notes that coastal ecosystems actually sequester significantly more carbon than most terrestrial forests. And importantly, they store it for long periods of time below the ground in the soils. In addition to storing this carbon, coastal ecosystems provide co-benefits, including wildlife habitat and shoreline protection.

Rhizophora mangle (red mangroves) in Islamorada, FL, USA. Source: EWN Podcast S1 E4

There’s increasing interest by the US Department of the Defense (DoD) and across US federal agencies in understanding carbon dynamics and identifying opportunities to increase the sequestration of carbon. As Jacob explains, he and Lisa were asked by the EWN Program to investigate blue carbon within the context of the Corps’s ecosystem restoration and navigation programs, including beneficial use of dredge material to restore and create coastal habitats. “We’ve been looking at blue carbon within an applied research context to see where opportunities exist to maximize the storage of carbon within these coastal systems.”

Lisa notes, “It takes a long time for carbon to naturally accumulate in wetlands, but not all carbon is created equal. There are different types of carbon with different stability that accumulate in blue carbon systems. We’ve found that some of the most persistent and long-lasting forms of carbon are associated with fine silts and clays, which, as it turns out, dredge material often provides. This provided us an opportunity to see if by engineering with nature, we could actually improve not just carbon storage in blue carbon ecosystems but also the stability of that carbon.”

This research is important because, as Jeff notes, it links to EWN’s of objective of creating environmental and social benefits, in addition to the Corps’ navigation-related mission objectives. “On average, USACE produces about 200 million cubic yards of dredge sediment every year. The idea that we could use this dredge sediment to out-compete sea level rise and replenish salt marsh systems while increasing the potential to sequester carbon is a very good thing. I’m really excited about this work.”

Jenny’s work focuses on studying what happens when you restore a system with dredge material. “We can understand the carbon budget of a marsh in its natural state, but what happens when you add dredge material to preserve that marsh, to build it up in the tidal frame so that it has some resilience against sea level rise? How have you changed that budget overall?”

Blue carbon ecosystems are threatened by climate change and development. Lisa notes the shift in sea level rise and talks about the critical importance of mangroves to the sustainability of coastal ecosystems. “They serve as a major barrier for communities, they help prevent erosion, and they provide extremely important habitat for commercial and recreational fisheries.”

Mangroves providing coastal protection. Source: The Role of Mangroves in Coastal Protection.

Historically, in the US, more than half of the wetlands have been converted to other uses or otherwise degraded. As Jacob describes it, “When we lose these coastal wetland areas, we also lose the blue carbon that’s stored there. We lose the ability to take carbon out of the atmosphere and store it in these long-term, protected forms beneath the ground where it’s protected not only from release to the environment but also from threats like wildfire that we anticipate will increase over time. In many of these coastal systems, we have very deep, oftentimes several meters or multiple yards of material that has very high organic carbon content. These tidal ecosystems represent a relatively small portion of the earth’s surface, but they store much more carbon than twice that of all the forests on the planet. So, it really is just a massive store of carbon and a really incredible resource. Plus, we also see benefits to the homes and communities that are behind these systems, as well as opportunities for recreation or for fisheries and other habitat.”

Why does carbon storage matter? Jacob explains: “Coastal ecosystems really play a key role in helping to regulate the global climate because there’s a balance between carbon stored in the soil, in the atmosphere, and in the ocean. When that system becomes out of balance, that’s when we induce the type of climate changes that we’re increasingly beginning to see—more disruptive storms and an increased likelihood of multiple storms hitting our coastlines in the same year.” He adds, “Taking carbon out of the atmosphere and storing it for long periods in the soil can help us to essentially rebalance the carbon system. But we have to recognize it is going to take a lot of work and a long time to achieve a more balanced carbon budget.”

When these valuable coastal ecosystems are degraded, much of the stored carbon appears to be released into the atmosphere. Lisa notes, “We’ve done some research in Louisiana and are seeing high rates of coastal wetland loss as a result of submergence due to subsidence and sea level rise. What is the fate of that missing carbon? Does it cycle back into the atmosphere where it can contribute to climate change? Our work shows that, unfortunately, it seems to. A lot of that carbon gets mineralized by microbes and released back into the atmosphere as CO2. So, we need to keep that carbon sequestered in the soil so it is not contributing to climate change.”

Restoring these ecosystems and protecting these old stores of carbon are critical. Jenny explains: “When we take core samples down in those deep marsh sediments, in some cases a couple of meters, we can use radiocarbon isotopes to date when that material was deposited. In some cases, it’s 2,000 to 3,000 years ago, which is a really cool realization when you’re standing there looking at that material. It’s important to think about how long it took to build that store of rich carbon and, if you lose it, how long it’s going to take to replace it. It’s really important to preserve it.”

Left: Jenny taking a 3-meter core sample in a marsh. Source: Jenny Davis, NOAA. Right: Jenny Davis (NCCOS) inspects a peat core from Swan Island (Chesapeake Bay) that will be analyzed for carbon content prior to and after dredge sediment placement, 2022. Credit: NOAA. Source: coastalscience.noaa.gov

“Whenever we can get USACE and NOAA collaborating on these kinds of topics, it really does accelerate our understanding of these complex systems and processes,” Jeff says. The goal is that this foundational research Jenny, Jacob, and Lisa are conducting will ultimately lead to actionable beneficial use of sediments guidance for practitioners in the field. Jeff adds, “Everybody’s thinking about this, and we’re seeing entities like Department of the Navy or Army including blue carbon or carbon sequestration in their climate-action strategies and plans. That’s a pivotal shift in how the DoD is thinking about the opportunity here and how they’re going to manage installations and all that land that they’re responsible for. The work you’re doing now will really contribute to what

Episode Guests

Research Soil Scientist, Environmental Laboratory, ERDC

Associate Professor of Biological Sciences, University of Central Florida

Research Ecologist Beaufort Lab, Marine Spatial Ecology Division National Centers for Coastal Ocean Science National Oceanic and Atmospheric Administration

National Lead, USACE EWN Program


Engineering With Nature; EWN; N-EWN; natural and nature-based features; NNBF; nature-based solutions; NBS; natural infrastructure; coastal erosion; coastal storm risk management; CSRM; flood risk management; ecosystem restoration; ecological engineering; ecosystem services; climate change; collaboration; extreme weather events; stakeholder engagement; community resilience; coastal resiliency

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