Africa’s rivers are doing far more to slow climate change than scientists previously realised, thanks to the vast flooded forests that surround many of them, according to a new study published in Science Advances.
Researchers found that rivers connected to flooded forests remove large amounts of methane—a greenhouse gas more than 80 times more powerful than carbon dioxide over a 20-year period—before it escapes into the atmosphere.
The international team of researchers analysed 262 methane oxidation measurements from rivers across Africa and Europe and found that African rivers consistently outperformed their European counterparts in naturally removing methane from the water.
“Methane oxidation was highest in African rivers connected to flooded forests, highlighting the critical role of wetlands in regulating greenhouse gases,” the researchers in the study.
Methane is naturally produced in river sediments and surrounding wetlands. While some of it escapes into the atmosphere, specialised bacteria consume part of the gas through a process known as methane oxidation, reducing the amount released into the air.
The study found that this natural filtering process becomes increasingly important in larger rivers. In Africa, methane oxidation accounted for an average of 37% of dissolved methane removal, compared with only 9% in European rivers.
“As rivers become larger, methane oxidation becomes a more important pathway for removing dissolved methane than its direct release into the atmosphere,” the authors write.
The findings suggest that Africa’s extensive flooded forests, particularly those in the Congo Basin and other tropical river systems, provide conditions that allow methane-eating microbes to thrive, making these ecosystems important but often overlooked allies in the fight against global warming.
The researchers also discovered that geography matters more than chemistry. Contrary to expectations from laboratory experiments, common water quality factors such as pH, nutrient levels and suspended sediments were poor predictors of methane oxidation rates.
Instead, “river size and connectivity with flooded forests—not water chemistry alone—were the strongest predictors of methane oxidation rates,” the study found.
The results underscore the importance of protecting Africa’s wetlands and flooded forests, many of which are increasingly threatened by deforestation, agriculture, mining, dam construction and climate change.
Scientists say these ecosystems provide benefits beyond supporting wildlife and local communities. They also help regulate the Earth’s climate by limiting methane emissions from rivers.
The findings can also improve climate models. Although rivers are recognised as important natural sources of methane, scientists have struggled to predict how much of the gas is removed before reaching the atmosphere.
“Understanding what controls methane oxidation is essential for predicting how river methane emissions may respond to climate change and increasing nutrient pollution,” the researchers note.
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