North Carolina's wetlands emit lots of climate-warming methane gas. Is that bad? – StarNewsOnline.com


A large stormwater wetland at Wade Park in Wilmington. Although freshwater wetlands produce methane, a powerful greenhouse gas, officials say wetlands support many other economic, environmental and community benefits.

When Duke Energy unveiled its plans to meet North Carolina’s aggressive carbon-cutting goals, attention quickly focused on the utility giant’s plan to replace much of the energy produced by its pollution-spewing coal-fired power plants with new natural gas-powered facilities.

The reason was while natural gas is a cleaner-burning fuel than coal, it is still a fossil fuel that releases climate-warming greenhouse gases, namely methane, into the atmosphere through the burning of the gas and leakages from pipes and the plants themselves. Duke said natural gas offered a cleaner way than coal to provide a reliable, affordable and secure power source to its customers. Environmentalists argued it was simply replacing one fossil fuel with another and locking North Carolina and its customers into a “dirty” energy future for decades to come when renewable energy sources could meet the power need in a cleaner, cheaper way.

Methane has a much bigger impact than carbon dioxide on global warming − an impact 25 times greater, according to researchers. Since pre-industrial times, increases in atmospheric methane have contributed to a quarter of the climate-warming effect from greenhouse gases.

That’s prompted increased efforts to control methane releases from sources like landfills, agriculture and fossil fuels, including natural gas plants. Many scientists also are studying ways to remove methane from the atmosphere. That’s because methane is 81 times more potent in terms of warming the climate over the first 20 years after its release, and about 27 times more potent over a century, according to two 2021 Stanford University-led studies.

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Natural methane pumps

But there’s a dirty little secret about methane that can be seen all across North Carolina, especially in the boggy and wet eastern portions of the state. Natural wetlands emit between 30% and 40% of global methane emissions. The water‐logged soils in wetlands are ideal for producing methane as microbes in the soil decompose organic matter like dead plants, and the patterns and intensity of these emissions are likely to increase as the planet warms and gets wetter in many places, according to the U.S. Geological Survey.

This means that global warming is driving greater wetland methane emissions. This process is called the “wetland methane feedback”.

Adam Gold

According to the state’s 2022 greenhouse gas inventory report, methane emissions accounted for approximately 11% of North Carolina’s total greenhouse gas emissions.

So does that make wetlands pollution-spewing machines that need to be mitigated or controlled in some way just like power plants, concentrated animal farms and vehicles that are helping warm the planet?

Not so fast, researchers say.

“Wetlands provide many co-benefits that help us in many different ways, from flood mitigation to ecological enhancements, that we’re really only learning how to maximize and enhance,” said Adam Gold, manager of the climate resilient coasts and watersheds program in North Carolina and Virginia for the Environmental Defense Fund.

Gold said protecting and enhancing this “green infrastructure”, especially in urban areas, is key to producing more resilient communities that are better able to handle the heavy rain events that climate change is forecast to bring to North Carolina in the coming decades.

Hurricanes Matthew and Florence, which brought historic levels of flooding to much of Eastern North Carolina in 2016 and 2018, respectively, highlighted how our draining of wetlands and channeling of natural water systems created an environment where communities weren’t able to handle the massive volumes of water that were dumped on them.

Gold said restoring floodplains and allowing wetlands to fill their historic roles of slowing water flows and improving water quality offers economic, community and environment-wide benefits.

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A large area east of Burgaw is experiencing severe flooding from the Northeast Cape Fear River due to the rains from Hurricane Florence in Burgaw, N.C., Wednesday, September 19, 2018.

“We need to manage that natural infrastructure to take advantage of all the co-benefits these wetlands can offer us,” he said.

That concept took a big step forward late last year with the launch of North Carolina’s “Flood resiliency Blueprint,” a statewide initiative aimed at helping flood-prone communities in the state’s river basins develop flood resiliency planning and strategies. The program also will help the state and communities prioritize flood mitigation projects.

The blueprint is funded through a $20 million appropriation from the N.C. General Assembly to the N.C. Department of Environmental Quality.

“This program is going to provide information that’s accurate with cutting-edge modeling and make it available to everyone,” Gold said. “It’s going to provide that planning capacity to communities that might otherwise not have access to it.”

But what about the methane problem?

While scientists don’t shy away from wetlands emitting lots of methane, they caution that we need to take a look at the holistic picture of all the benefits wetlands bring to the table.

That includes removing and sequestering carbon from the atmosphere in the soil and vegetation itself rather than allowing it to further warm the planet.

These wetland “carbon sinks” work especially well when wetlands are allowed to mimic their role created for them by Mother Nature, whether by being kept as natural wetlands or restored in a way that mirrors their natural function rather than maintained in a degraded state.

A wetland mitigation site constructed by the NCDOT as part of the Martin Luther King Jr. Parkway project in Wilmington.

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An October 2022 study by researchers from N.C. State University found overall greenhouse gas emissions from a restored coastal wetland in northeastern North Carolina, restored by raising the groundwater in the pocosin wetlands that had been drained for farmland, were significantly reduced.

By effectively reflooding the fields, the scientists reduced the decomposition rate of the plant material in the soil.

“Despite the increases in (methane) and (nitrous oxide), the higher magnitude of fluxes and large decline in (carbon dioxide) lead to an overall lowering of greenhouse gas emissions after hydrologic restoration,” stated the research paper published in the journal Wetlands. “Our results suggest that raising the water table in this shrub bog peatland decreased overall greenhouse gas emissions, illustrating that hydrologic restoration of peatlands can be a valuable climate mitigation practice.”

Ghost forests like this one in Wilmington, N.C. in June 2022, increasingly appear along coasts as rising sea levels intrude landward.

Another impact from climate change, sea-level rise, is also helping reduce the emission of methane gas from freshwater wetlands near the coast − although it’s not necessarily a welcome impact.

When salt water enters former freshwater wetlands, it eats away at the carbon-based soils, leaving behind “ghost forests” and degrading the marshes first to grass and then eventually open water. While the process does stop the production of methane, it allows all the carbon that had been sequestered in the soils and vegetation to escape − further adding to the pressures on global temperatures.

Gold said in the big picture, the production of methane by wetlands is a small price to pay for all of the other benefits they bring to the table.

“From flood storage and improving water quality to providing important ecosystem values and roles as carbon sinks, they really do offer a host of co-benefits,” he said. “We just have to manage and design these natural infrastructure projects so we can take advantage of all of these benefits.”

Tundra swans are just some of the animals that take advantage of North Carolina's extensive wetlands.

Reporter Gareth McGrath can be reached at GMcGrath@Gannett.com or @GarethMcGrathSN on Twitter. This story was produced with financial support from 1Earth Fund and the Prentice Foundation. The USA TODAY Network maintains full  editorial control of the work. 


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