A vast African peatland once thought stable is now leaking carbon thousands of years old.
Tropical swamps and peatlands are major components of Earth’s carbon system and play a significant role in regulating the climate. Regions such as the Amazon Basin, the Congo Basin, and the wetlands of Southeast Asia steadily build up thick layers of partially decomposed plant material. Over time, these landscapes trap enormous amounts of carbon, storing an estimated 100 gigatonnes in total.
In Central Africa, the Congo Basin contains one of the largest and most important of these carbon reserves. While its peatlands and swamps make up only 0.3 percent of the Earth’s land surface, they hold roughly one third of all carbon stored in tropical peatlands.
Despite their global importance, these ecosystems remain understudied. Much of the central Congo Basin is difficult to access, and travel to remote lakes and swamps often depends on boats or traditional pirogues. This remoteness has limited scientific understanding of how strongly these peatlands influence the global carbon cycle and climate.
Congo Basin Blackwater Lakes Reveal Surprises
Over the past decade, researchers led by ETH Zurich have conducted extensive fieldwork in the Congo Basin. Their investigations have already uncovered unexpected features, including the Ruki River, one of the darkest blackwater rivers in the world.
In a new study published in Nature Geoscience, the team focused on two darkly stained lakes shaped by organic runoff from surrounding forests: Lac Mai Ndombe, Africa’s largest blackwater lake, and its smaller neighbor, Lac Tumba. Once again, the findings were surprising.
Lac Mai Ndombe covers an area more than four times the size of Lake Constance. Its waters resemble strong black tea due to dissolved organic material washed in from nearby swamp forests and largely untouched lowland rainforest growing on deep peat soils. As plant debris and soil matter break down and flow into the lake, they give the water its rich brown color.
Ancient Carbon Emissions From Congo Lakes
Measurements from both lakes show that substantial amounts of carbon dioxide are escaping into the atmosphere. What surprised researchers was the age of some of that carbon.
Not all of the CO2 comes from recently grown plants. Up to 40 percent originates from peat that accumulated thousands of years ago in the surrounding wetlands. Scientists determined this by analyzing the age of dissolved carbon dioxide using radiocarbon dating (radiocarbon dating).
“We were surprised to find that ancient carbon is being released via the lake,” explains lead author Travis Drake, a scientist in the Sustainable Agroecosystem (SAE) group led by ETH Professor Johan Six. “The carbon reservoir has a leak, so to speak, from which ancient carbon is escaping,” adds co-author Matti Barthel, research technician in SAE.
How Is Ancient Peat Carbon Being Released?
Until now, researchers generally assumed that carbon locked in Congo Basin peat would remain stable for very long periods and would only be released under specific circumstances, such as extended drought.
Exactly how this old carbon is being freed from layers of undecomposed plant material remains unclear. Scientists also do not yet know the precise routes by which it moves from peat soils into lake water.
A key question is whether this release represents a destabilizing shift in the ecosystem or a natural process that is balanced by the formation of new peat over time.
Climate Change and Peatland Drying Risks
The presence of ancient carbon in lake emissions may signal broader environmental changes linked to climate change.
If regional conditions become drier, peat soils could dry out more often and for longer stretches. As peat dries, oxygen can penetrate deeper into the soil, stimulating microorganisms that break down organic matter that was previously stable. This process can release additional CO2 into the atmosphere from what has long been a vast carbon store.
“Our results help to improve global climate models, because tropical lakes and wetlands have been underrepresented in these models so far,” as Six stated.
Water Levels and Methane Emissions
The researchers also examined emissions of other greenhouse gases from Lake Mai Ndombe, including nitrous oxide and methane. In a parallel study published in the Journal of Geophysical Research, they found that lake water levels strongly influence how much methane escapes.
When water levels are high, microorganisms are more effective at consuming methane before it reaches the air. During periods of lower water levels, such as the dry season, methane is broken down less efficiently and larger amounts are released into the atmosphere.
“Our fear is that climate change will also upset this balance. If droughts become longer and more intense, the blackwater lakes in this region could become significant sources of methane that impact on the global climate,” says ETH Professor Jordon Hemingway. “At present, we do not know when the tipping point will be reached.”
Deforestation and Land Use Pressures in the Congo Basin
Climate change is not the only concern. Shifts in land use could have even more serious consequences. The population of the Democratic Republic of Congo is projected to triple by 2050, increasing demand for farmland and leading to further forest clearing.
Deforestation can intensify drought conditions, potentially keeping lake levels persistently low. “We all know the analogy whereby forests are the green lungs of the Earth,” says Barthel. “They are not only responsible for gas exchange like our lungs, but they also evaporate water through their leaves, thereby enriching the atmosphere with water vapour. This promotes cloud formation and precipitation, which in turn feeds rivers and lakes.”
Why Congo Peatlands Matter for Global Climate
These findings clarify the role that tropical peatlands and blackwater lakes play in shaping global climate patterns. They also underscore the importance of protecting wetlands in the Congo Basin and other equatorial regions while developing strategies to limit greenhouse gas emissions.
Reference: “Millennial-aged peat carbon outgassed by large humic lakes in the Congo Basin” by Travis W. Drake, Jordon D. Hemingway, Matti Barthel, Antoine de Clippele, Negar Haghipour, Jose N. Wabakanghanzi, Kristof Van Oost and Johan Six, 23 February 2026, Nature Geoscience.
DOI: 10.1038/s41561-026-01924-3
The research was carried out as part of the TropSEDs project led by ETH Zurich and funded by the Swiss National Science Foundation, in collaboration with scientists from the University of Louvain in Belgium and the Democratic Republic of Congo.
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.
4 Comments
Population of DR Congo is now 113 million; by 2050, 25 years time it will be 339 million? The world can’t afford the USA, PR China, India, Pakistan, Europe, Japan and no doubt many other countries at present. That’s most of us alive today.
rob, your unstated assumption is that the increase in population in the DR Congo in the recent past is a good predictor of the near future. Extrapolations are always fraught with problems of both the known influences and the unknown influences. It stretches credulity to believe that a country with a weak central government, widespread political violence, subsistence living that requires children to work for the family to survive, rare access to refrigeration to keep food from spoiling, restricted access to medical care, and almost no infrastructure, can increase its population to that of the USA without running into some significant barriers. Even the USA has problems with adequately housing and feeding all of its people, and we don’t have the problems of poor sanitation, endemic malaria, and other diseases more common in tropical climes than a country where Winter snows kill many pathogens. The DR Congo will be unlikely to achieve the kind of growth you suggest, in my opinion.
“The presence of ancient carbon in lake emissions MAY signal broader environmental changes linked to climate change.”
Once again the ubiquitous lawyer words of “may” and “could” are used in an attempt to support conjecture. “May” implies a future scenario of unspecified probability and “could” really only says that a particular event is not impossible, but again doesn’t specify a probability. At best, both words speak to ambiguous but low-probability future events.
While they mention methane, they didn’t mention that is has a lifetime in the atmosphere of about a decade, after which it remains as CO2, which may not last much longer than the methane did.
Where are the historical measurements that demonstrate even a trend, let alone a functional relationship between the variables? The authors appear to be trying to stimulate interest to obtain funding. They say it best themselves: “… these ecosystems remain understudied. …. This remoteness has limited scientific understanding of how strongly these peatlands influence the global carbon cycle and climate.” They further say, “Exactly how this old carbon is being freed from layers of undecomposed plant material remains unclear. Scientists also do not yet know the precise routes by which it moves from peat soils into lake water. … A key question is whether this release represents a destabilizing shift in the ecosystem or a natural process that is balanced by the formation of new peat over time.” Thus, it become obvious this is an appeal for support to explore their conjectures.
These are probably legitimate concerns. However, there are political forces at work that are reluctant to support the research because it has the potential to reduce the alarm about anthropogenic forces.
We are indeed living in “interesting times.”
With the concern raised here in this article, and the recently published https://scitechdaily.com/wildfires-in-the-arctic-may-be-releasing-far-more-carbon-than-we-thought/ and https://scitechdaily.com/why-are-the-worlds-forests-changing-the-way-they-breathe/ , I think we should also be concerned about whether we are deluding ourselves in blaming anthropogenic emissions for the recent warming. The proposed solution to prevent, or at least slow, warming may be ineffectual, yet, we are risking de-stabilizing the world economy and triggering unintended consequences. In fact, I have made the case that the empirical evidence doesn’t support the claim that reduced anthro’ emissions will lead to our salvation: https://wattsupwiththat.com/2022/03/22/anthropogenic-co2-and-the-expected-results-from-eliminating-it/ .
We should keep an open mind about how everything in the Carbon Cycle works, and question claims that the natural driver(s) for warming over the last 20,000-years are less powerful or important than the small, constant human emissions. Focusing on fossil fuels and calcining of limestone, without thoroughly understanding the Carbon Cycle, is equivalent to taking your eyes off the hands of the guy shuffling the walnut shells that supposedly have a pea under one of them.