In the Congo Basin, lakes release carbon from thousands of years ago

The peatlands of the Congo Basin, which have been accumulating carbon for thousands of years, are now releasing some of this buried carbon, according to a study conducted by UCLouvain and ETH Zurich.

Contrary to popular belief, peatlands and blackwater lakes are not simply carbon sinks that store CO₂: they are vectors for the transfer of ancient carbon from peatlands to the atmosphere, with impacts on the regional carbon balance and global climate. 

Scientists from UCLouvain (professor and researcher Kristof Van Oost's team, Earth and Life Institute, School of Geography) and ETH Zurich have recently highlighted a previously unknown phenomenon: in the Congo Basin, certain large lakes located in the heart of tropical peatlands are releasing carbon stored for thousands of years into the atmosphere.

This major discovery, published in the journal Nature Geoscience, highlights the potential vulnerability of one of the planet's largest carbon reservoirs to environmental change.

To conduct this research, the scientists spent six weeks aboard a boat in the Kasai Basin, in the heart of the Congo Basin, collecting samples and observing these ecosystems, which have been little studied to date. 

The peatlands of the Congo Basin, located in the heart of Africa, are one of the world's largest natural carbon reservoirs. Although they cover only a tiny fraction of the Earth's surface, they contain nearly one-third of the carbon stored in tropical peatlands.

This carbon has accumulated over thousands of years in the form of poorly decomposed plant matter trapped in waterlogged soils, which until now were thought to be relatively stable. 

Huge quantities of carbon dating back thousands of years

By analyzing water from Lake Mai-Ndombe, the largest lake in the region, and Lake Tumba, scientists measured the age of dissolved carbon dioxide using isotopic dating techniques.

Their results show that up to 40% of the CO₂ released into the atmosphere comes from ancient peat bogs, some of which are thousands of years old, and not just from recent vegetation.

These observations reveal that lakes act as transfer vectors: they receive ancient carbon from surrounding peatlands and facilitate its release into the atmosphere.

The challenge now is to determine whether this phenomenon corresponds to a natural balance or whether it reflects a gradual weakening of these ecosystems.

Climate change and human activities exacerbate the process

The results also suggest that climate change could exacerbate this process. Longer periods of drought are likely to dry out peatlands, promoting the decomposition of organic matter and the release of CO₂.

Analyses also show that lower water levels promote emissions of methane, a particularly powerful greenhouse gas. 

In addition to these climatic effects, there is growing pressure from human activities. Deforestation, particularly linked to the expansion of agricultural land, disrupts the water cycle and exacerbates the drying up of soils and lakes.

Ultimately, these changes could further accelerate the release of carbon that has been stored for thousands of years.

A better understanding of the Congo Basin

Through this research, UCLouvain confirms its commitment to studying major global environmental issues.

By combining fieldwork in demanding conditions, cutting-edge analysis, and international collaboration, its scientists are contributing to a better understanding of the Congo Basin, a key ecosystem for the planet's climate balance. 

References

Drake, T.W., Hemingway, J.D., Barthel, M. et al. Millennial-aged peat carbon outgassed by large humic lakes in the Congo Basin. Nat. Geosci. (2026). https://doi.org/10.1038/s41561-026-01924-3 

Discover the fascinating complete report “Why does the Kasaï basin matter?”, with numerous explanations and figures, and breathtaking photos. 

This article was originally written in French by the AREC team of UCLouvain. It is available to be read here. 

Photo credits: photographer Matti Barthel, photographer Travis W Drake, and researcher Kristof Van Oost.