With their sluggish, oxygen-starved waters and buffets of organic muck, wetlands are ideal habitats for anaerobic microbes that produce methane, a potent greenhouse gas. In a menacing feedback, a warming climate seems to be turbocharging that microbial activity, helping drive a global surge in methanewhich leads to more warming. To interrupt it, some researchers are exploring an exotic idea: hacking the swamps.
Starting this year, an effort called Feedback Research and Action on Methane Emissions (FRAMES) plans to treat wetland microbial ecosystems with chemicals that could curb their methane releases, first in the lab and later in small field trials. The researchers stress that this new kind of geoengineering could have unforeseen consequences; understanding them is a primary reason for the work. This is delicate, says Brian Buma, who co-leads the Climate Innovation Initiative at the Environmental Defense Fund, the U.S. nonprofit backing the effort. Were in uncharted waters.
Methane levels have risen by nearly 10% in the past 2 decades, and the gas is thought to be responsible for one-third of overall global warming. Researchers know the main source of the rising methane levels isnt the oil and gas industry, because atmospheric methane has become more enriched in carbon-12, a light isotope favored by biology.
The growth of cattle ranching and landfills is certainly playing a role, but in recent years, researchers have realized that emissions from wetlands are also rising. Global warming is shifting rainfall patterns, expanding swamps in some regions and thawing permafrost to create new ones. The warming also favors methanogens: Heat speeds up their metabolisms, and warmer waters hold less dissolved oxygen, making it easier for the anaerobic organisms to dominate ecologically.
Last year, a team of U.S. Department of Energy scientists found that methane emissions from wetlands across northern Eurasia and North America increased 9% from 2002 to 2021. And by carefully examining shifts in the seasonal ebb and flow of methane at long-term monitoring sites, a study published in May in Nature found that global wetland emissions have been increasing since the 1980s. Both studies tied the trend to global warming. Its inescapable that this is all happening, says Paul Palmer, an atmospheric chemist at the University of Edinburgh.
The best way to stanch the methane emissions would be to stop the wetlands from warming in the first place. That means burning less fossil fuels, says Emily Ury, an ecologist at Colgate University who published a review last year with Buma laying out ideas for how the wetland feedback could be mitigated. But absent such action, its worth at least studying artificial interventions, she says.
One well-known way to curb wetland methane comes from an earlier environmental crisis. Last century, coal-fired power plants spewed huge amounts of sulfur into the air, creating acid rain. These emissions damaged human and ecosystem health alike. But the acid rain also caused a notable decline in the methane produced by swamps. The extra sulfate in the system, researchers found, allowed sulfate-consuming bacteria to outcompete methanogens, starving them out.
Today that lesson plays out in the rice paddies of East Asia, where farmers have unintentionally reduced methane emissions by adding sulfate-rich gypsum to alleviate salt stresses on the plants. Other additives, such as nitrate, iron, and biochara form of charcoal used as a soil conditionerare also promising.
As part of FRAMES, Ury and Meredith Holgerson, an ecologist at Cornell University, are establishing an array of soil coreswetlands in a jarto test these options. Wetlands are so variable that even if a treatment is successful on one type, it might totally fail on another, Ury says. We want to do these experiments in a really reproducible way.
Field trials of sulfate could also come as soon as this year. Irena Creed, a hydrologist at the University of Toronto, says one of her partners, the conservation organization Ducks Unlimited, is eager to see whether it can stanch methane emissions from restored wetlands it oversees in Canada. Such a trial would involve a baseline study of the chemistry and microbiology of the swamp and its greenhouse gas emissions, followed by careful monitoring after the sulfate treatment. Creed also works on wetlands in the cities and farmland of the Prairie Pothole region of western Canada, and hopes to start trials there in the next 18 months.
When these chemicals are deployed, the emphasis will be on monitoring for potential negative consequences to the ecosystem, Creed says. For example, sulfates have been shown to boost the rate at which microbes convert mercury from pollution into methylmercury, a toxin that can bioaccumulate in aquatic species. We cant just apply [an additive] for 12 hours and move on, Creed says.
There are other ways to reduce a swamps methane emissions, notes Danielle Potocek, a biogeochemist at Spark Climate Solutions, a small nonprofit focused on methane mitigation. You can dig a channel to reconnect a coastal marsh to the sulfate-rich ocean. Or you could raise a swamps water levels, helping prevent methane from escaping to the atmosphere. Vegetation type is also critical: Hollow sedges and grasses act like straws for methane, speeding up its escape. Aquatic ferns, meanwhile, are known to promote oxygenation in wetland soils, reducing methanogen populations.
As with many geoengineering proposals, scale is the problem, Potocek adds. Regularly adding huge amounts of chemicals to wetlands would be costly and logistically infeasible, and no one wants to tamper with the vast unmanaged wetlands in Africa or South America, where much of the methane feedback could play out.
Perhaps a small way to start would be to incorporate the ideas into wetland restoration, a surging field worldwide, Buma says. Even if just a few projects prioritized methane, he says, you could get a huge amount of additional climate benefit.
