The Congo Basin’s vast peatlands have long been regarded as stable, long-term carbon stores — a counterweight to tropical deforestation. New field measurements challenge that assumption directly.
A study published Feb. 23 in Nature Geoscience finds that blackwater lakes and rivers in the Cuvette Centrale, a 56,000-square-mile (145,000 square kilometer) region of forests and swamps in the Democratic Republic of the Congo, are releasing carbon dioxide that is between 2,170 and 3,500 years old. The source of that ancient carbon, according to the research, is the peat itself — not modern vegetation or surface runoff as previously assumed.
The Cuvette Centrale holds Earth’s largest known tropical peatland complex. Within it, two large blackwater lakes — Lake Mai Ndombe and Lake Tumba — and the Ruki River carry high concentrations of dissolved organic carbon from decomposing plant material, giving the water its characteristic dark color. That organic load, combined with direct CO₂ inputs from surrounding swamps and forests, creates supersaturated concentrations of carbon dioxide in these water bodies, which then emit large quantities of the gas into the atmosphere. Until now, scientists believed the ancient peat deposits beneath the region remained inert, protected by oxygen-depleted, waterlogged conditions.
What the Measurements Show
Travis Drake, a carbon biogeochemist at the Swiss Federal Institute of Technology Zurich (ETH Zurich) and the study’s lead author, and his colleagues conducted three research expeditions to the basin over four years, taking measurements at Lake Mai Ndombe in 2022 and 2024, and at Lake Tumba and the Ruki River in 2025. The team accessed remote sampling sites by small dinghy boats — difficult work given strong winds that nearly capsized them at Lake Mai Ndombe — because most locations are unreachable by land.
Their analysis found that a significant proportion of the CO₂ escaping these blackwater systems originates from peat carbon thousands of years old. “We were very surprised because we fully expected the carbon dioxide to be modern,” Drake said, according to the report.
A 30-Million-Tonne Question
The finding directly contradicts the long-held view that old peat carbon stays locked underground. If the ancient deposits are already releasing carbon under current, relatively undisturbed conditions — Drake described the ecosystems as “relatively pristine,” with only sparse settlements around Lake Mai Ndombe — the implications for climate projections tied to tropical peatland stability are significant.
The researchers stop short of declaring a crisis, but they frame the uncertainty in precise terms. “We are now faced with a 30-million-tonne question: we need to determine if this is just a small, natural leakage of ancient carbon, or the onset of broadscale destabilization,” Drake said. That figure refers to the scale of carbon at stake in the Cuvette Centrale, and the study calls for further work to establish whether the observed emissions reflect a minor, chronic process or an accelerating shift that could flip tropical peatlands from net carbon sinks to net carbon sources.
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