Congo peatlands found venting ancient carbon

Vast peatlands beneath the Congo Basin’s blackwater lakes are releasing carbon that has been locked away for millennia, according to new scientific findings that raise fresh concerns about the stability of one of the planet’s largest tropical carbon stores.

Researchers studying Africa’s most extensive tropical peat complex have identified that a notable share of carbon dioxide escaping from the region’s dark, tannin-rich lakes originates from ancient peat deposits rather than only from contemporary vegetation. The discovery suggests that carbon once considered safely stored over thousands of years may be entering the atmosphere under changing environmental conditions.

The Congo Basin, spanning six countries in Central Africa, contains the world’s largest tropical peatland complex. Mapping efforts published over the past decade have estimated that these peatlands store around 30 billion tonnes of carbon, an amount comparable to several years of global fossil fuel emissions. Much of this carbon has accumulated slowly in waterlogged forest soils where decaying plant material is preserved in oxygen-poor conditions.

Blackwater lakes, common across the basin, are characterised by their dark colour from dissolved organic matter. Scientists have long known that such lakes release carbon dioxide as microbes break down organic material. What is new, researchers say, is evidence that the carbon in some emissions is far older than previously assumed.

Using radiocarbon dating techniques to analyse dissolved carbon and gases bubbling from lake surfaces, the team found that part of the carbon dioxide being emitted predates modern vegetation by centuries or even millennia. That indicates that peat layers buried beneath forests and wetlands are being mobilised and decomposed, rather than emissions arising solely from fresh plant litter.

This finding carries implications for global climate projections. Tropical peatlands are widely regarded as critical carbon sinks because they accumulate organic matter faster than it decomposes. If conditions shift in ways that accelerate peat breakdown, these ecosystems could transition from net carbon sinks to carbon sources.

Scientists involved in peatland research have pointed to several possible drivers. Seasonal drought, rising temperatures and subtle hydrological changes can lower water tables, exposing peat to oxygen and stimulating microbial activity. Even minor alterations in flooding patterns may increase the movement of dissolved carbon from soils into nearby lakes and rivers, where it can be converted into carbon dioxide and released to the atmosphere.

The Congo Basin has so far experienced less extensive drainage and industrial peatland conversion than regions such as Southeast Asia. In countries including Indonesia, large-scale drainage for agriculture and forestry has led to peat oxidation, fires and substantial carbon emissions. By contrast, Central African peatlands remain comparatively intact, though logging, oil exploration and infrastructure expansion are expanding.

Climate variability poses an additional risk. Studies over the past decade have shown that parts of Central Africa have undergone shifts in rainfall patterns. Extended dry periods can expose peat surfaces, while intense rainfall may flush dissolved organic carbon into aquatic systems. Researchers caution that even without large-scale land conversion, climatic stress could destabilise long-stored carbon.

Carbon fluxes from inland waters have gained increasing attention in climate science. Rivers, wetlands and lakes are now recognised as active components of the global carbon cycle rather than passive conduits. Globally, inland waters are estimated to emit significant quantities of carbon dioxide annually, though the proportion derived from ancient carbon stores varies by region.

The Congo Basin’s scale makes it especially significant. Its peatlands cover an area roughly the size of England and are concentrated largely in the Cuvette Centrale, a vast low-lying swamp forest straddling the Republic of Congo and the Democratic Republic of Congo. These ecosystems not only store carbon but also support biodiversity and livelihoods for local communities.

Policy frameworks aimed at conserving tropical forests, including REDD+ mechanisms under the United Nations climate process, have focused heavily on above-ground biomass. Peat carbon, which is stored below ground, has often received less attention in Central Africa. The new findings add weight to calls for more detailed monitoring of peat hydrology and carbon dynamics.

Researchers emphasise that the presence of ancient carbon in lake emissions does not automatically signal widespread peat collapse. The proportion of old carbon detected varies among sites, and further fieldwork is required to determine how extensive the phenomenon is across the basin. Long-term measurements are also needed to assess whether emissions are increasing over time or represent a relatively stable background flux.

Nonetheless, the study underscores the vulnerability of tropical peat systems. Unlike mineral soils, peat accumulates over thousands of years but can degrade far more rapidly if environmental conditions shift. Once oxidised, that carbon cannot be readily restored on human timescales.