Turning a marsh into a climate change laboratory with heat lamps and CO2 pumps

This Chesapeake Bay wetland could be an environmental crystal ball.

With infrared lamps pointed down at marsh grasses — and heating cables placed beneath them — the environment is 5.1 degrees Celsius hotter than the surrounding area, simulating a future world warmed by climate change.

In nearby sections of marsh, carbon dioxide is pumped into structures that look like mini, open-air greenhouses.

“You’re never going to get a warmer world without also having higher CO2 in the atmosphere,” said Genevieve Noyce, a senior scientist at the Smithsonian Environmental Research Center, which runs the wetland site.

The wetland is just a few miles from the Research Center’s headquarters in Edgewater, nestled in a crook of the Rhode River. And it has become a hotbed — pun intended — for several experiments that mimic global warming.

The latest research to emerge from the Global Change Research Wetland, or GCREW, was published last week in Science Advances, a peer-reviewed journal. That study captured data for five years, focused not on the wetland’s growth, but on its emissions.

But one of the experiments here has been going since 1987, leading the center to pronounce that it’s likely the world’s longest-running field experiment simulating carbon dioxide elevation.

The researchers found that adding carbon dioxide stimulated the wetland’s growth by about 30% — and allowed its long grasses to start growing earlier in the springtime and stay green farther into the fall. Some years, the grasses can make it until December before they turn entirely brown, said Andrew Peresta, the site’s operations manager.

But nearly 40 years after the experiment’s beginning, Mother Nature is playing scientist, and adding new conditions to the simulation, Peresta said. Rising water levels, a handful of millimeters each year, have begun to change the story, slowing the rate of increased grass growth.

“All of these plants are adapted to grow with their roots in wet soil. But if it’s too wet — if the sea level comes up too fast — and they can’t keep up, then they start struggling,” Noyce said.

The study’s long time horizon has allowed scientists to document the marsh’s changes over time, including incursions by invasive phragmites, Peresta said.

“A lot of projects are only two to three years long,” Peresta said. “You might not learn as much as you do with this.”

Collectively, coastal wetland environments are among the world’s greatest carbon sinks. According to a National Oceanic and Atmospheric Administration webpage, they annually trap carbon at a rate 10 times greater than mature tropical forests, preventing the harmful gases from reaching the atmosphere, where they contribute to warming.

But wetlands also release methane, a greenhouse gas that is about 28 times more potent than carbon dioxide when it comes to trapping heat in the atmosphere, according to the Environmental Protection Agency.

Traditionally, wetlands have been considered minor producers of the gas. But the Smithsonian researchers have discovered that raising the temperature of the wetland, with the submerged heaters and overhead lamps, speeds up methane production by about four times, compared to the undisturbed wetlands close by, Noyce said.

The same was true when researchers added carbon dioxide to the equation, except the increase was less dramatic — about 1.5 times. In other words, if climate change gets worse, it could tip off a domino effect in the wetlands, yielding more emissions that further worsen global warming.

“We knew there was something with adding elevated CO2 to reduce the amount of methane coming out of the plots. But we didn’t really know why,” Noyce said.

So the researchers looked to the microbial community in the soil beneath the wetland. There, some microbes produce methane, but others consume it.

Climate change seems to change the fine balance between these two types of microbes, increasing the methane that is released, said Jaehyun Lee, who was the study’s lead author as a post-doctoral researcher at the Smithsonian Center.

When carbon dioxide was added to the plots, it stimulated root growth, increasing the amount of oxygen in the soil. This gave more fuel to the microbes that consume methane by oxidizing it, Lee said. Their activity canceled out some of the effect from hotter temperatures, which spurred the methane-producing microbes, causing methane emissions to spike.

Even with the increased methane emissions, it seems likely that wetlands will still store more globe-warming emissions than they release, Lee said. But the research proves that the balance is delicate, and could potentially flip in the other direction, said Lee, who is now a senior researcher at the Korea Institute of Science and Technology in South Korea.

Since 2016, experiments in Noyce’s section of the wetland, known as SMARTX, or the Salt Marsh Accretion Response to Temperature Experiment, have been funded by the U.S. Department of Energy. It remains unclear whether the funding will be impacted by recent Trump administration cuts to scientific research, particularly that which focuses on climate change.

The wetland receives three years of funding at a time, and is currently in its last year of the cycle, Noyce said. The team just applied for another three years, she said.

The 1987 project is funded by a National Science Foundation grant for long-term research in environmental biology, she said.

The new data could help improve the accuracy of climate change modeling, as researchers attempt to predict the amount of globe-warming gases that will be emitted, Lee said.

“When we set the the goal for carbon reduction in the future, to slow down the temperature rise, we also have to consider these types of changes in methane emissions,” Lee said. Otherwise, governments could struggle to reach their carbon reduction goals, he said.

The findings, released Wednesday, could also inform wetland plantings and restoration efforts, Noyce said.

“If you can start understanding which plant communities are going to respond in different ways under global change, then you can say: ‘Oh, maybe this plant community is going to be better. It might reduce the amount of methane coming out of this sort of ecosystem,’” Noyce said.