The ecosystem of the Great Dismal Swamp has changed over the past several hundred years.
Humans have transformed it through draining and ditching, and several natural disasters tore through the area in recent years. The effects of all these changes include less habitat and biodiversity in the swamp.
In new research by the U.S. Geological Survey, scientists outline another major impact: the swamp has released about 50 million metric tons of carbon dioxide into the atmosphere since the colonial era.
That’s roughly equivalent to running about 15% of the country’s cars for a year, said lead author Miriam Jones, a USGS research geologist.
“Maybe in the grand scheme of things that doesn't sound that great,” she said. “But when you put land use change of wetlands all together across the country or even across the world, it is a very large source of carbon to the atmosphere that can impact global climate and exacerbate climate change.”
The research is a window into how changing conditions even in protected natural areas can speed up climate change.
The Great Dismal Swamp National Wildlife Refuge is the last vestige of a swamp that once covered more than a million acres, including almost all of Hampton Roads and stretching south to North Carolina’s Albemarle Sound.
Humans’ major impacts on the swamp trace back to the 1700s, when George Washington arrived with his timber company.
They saw the wide expanse as a huge business opportunity. Washington’s Dismal Swamp Company cut down juniper and cypress trees to turn into shingles and drained sections of swamp to make way for farmland, Jones said.
Draining and ditching at the swamp continued for many years, helping support the creation of communities in surrounding Chesapeake and Suffolk.
Jones’ research team found direct links between the spots where this happened most, and the highest amounts of carbon loss.
There are several types of ecosystems worldwide that act as what are called carbon sinks, naturally storing carbon underground for hundreds or thousands of years when undisturbed. That includes soil, seagrasses and forests.
Peat or bog, which forms the basis of swampland, is another big carbon sink.
It’s made of “basically any kind of litter that falls on the surface of this wetland and accumulates over time,” Jones said.
Water that stays close to the surface of the bog contains little oxygen and traps partially decayed organic matter, she said. That prevents it from fully decomposing and releasing gases like carbon dioxide and methane, she said.
Over tens of thousands of years, the peat slowly grows by several feet. If left alone, the process makes peat a huge reservoir of unreleased carbon. But that’s not the case at the Great Dismal.
Human activity hasn’t just reduced the amount of peat at the swamp. The species of vegetation has also been changing, replacing native species like bald cypress with trees and shrubs that favor a drier climate.
Natural disasters have also played a role.
In 2008 and 2011, massive wildfires tore through the swamp, burning up to a meter of peat: “hundreds to thousands of years of peat accumulation gone in three months,” Jones said.
A tornado during Hurricane Isaias in 2020 also devastated hundreds of acres in the swamp. Researchers at Old Dominion University have been studying how the ecosystem rebounds, and some species don’t seem to be coming back.
As the peat dwindles, it releases carbon dioxide into the atmosphere, which then contributes to global warming.
It may sound counterintuitive that important natural features like wetlands contribute to climate change. It’s a vicious cycle: humans continue to burn fossil fuels that warm the planet; climate change impacts systems like wetlands, which then release even more greenhouse gases as they recede.
The Washington Post reported this month that wetlands have become a major source of the world’s emissions of methane, a potent greenhouse gas. As the world warms, permafrost is also melting, releasing gases that were long trapped underground.
The USGS, which partnered with the U.S. Fish and Wildlife Service on the recent research, wrote that officials should invest in “aggressive mitigation methods” to return the Great Dismal Swamp to being a carbon sink.
Jones said that can include installing more water control structures around the swamp to slow or stop further declines through the drainage ditches. The National Wildlife Refuge has already begun this work, but it depends on funding, she said.
“The thing that kind of is eye-opening is that we think of something like the Great Dismal Swamp, which is a protected refuge, as this natural system,” Jones said.
“But it's important to think about it in the long term context of all of the land use change that's happened over the last 200 years. What we see today is actually not what the swamp was.”
