In the tropics, rivers and lakes emit less GHGs than previously thought
A large-scale international study, to which FNRS researcher Alberto Borges from the University of Liège contributed, reveals that greenhouse gas emissions from tropical and subtropical rivers and lakes are lower than previously thought. Published in the journal Nature Water, this synthesis challenges the idea that the tropics are systematically a major hotspot for emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O).
L
akes and rivers play a key role in the carbon and nitrogen cycles. They receive, transform and release large quantities of greenhouse gases (GHGs) into the atmosphere. Until now, due to a lack of sufficient data, global estimates have tended to overestimate the importance of tropical regions. To fill this gap, a team of thirty researchers from twenty countries compiled more than 22,000 concentration measurements and 16,000 GHG flux measurements corresponding to (sub)tropical regions between latitudes 34°N and 34°S.
Alberto Borges, a biogeochemical oceanographer and FNRS research director at ULiège, played an important role in this research by providing extensive data collected from African rivers and lakes and coordinating the synthesis of lake emissions.
"This study illustrates the importance of integrating the diversity of tropical landscapes and hydrological regimes, rather than considering them as a homogeneous block," the researcher points out.
Nuanced and promising results
The study shows that small tropical rivers, particularly headwaters, account for most river emissions. It also highlights that large lakes and reservoirs contribute significantly to emissions, but with marked variability depending on climate zones. Overall, the revised emissions are 29 to 72% lower than previous estimates. This downward revision changes the way global greenhouse gas balances are calculated and calls for adjustments to climate models, both in terms of source attribution and future trajectory projections. Finally, it implies a reorientation of observation efforts towards small tropical systems, while taking into account the regional contrasts that characterize the influence of large bodies of water.
This downward revision has direct implications for global GHG balances and climate models.
While this synthesis marks a turning point, the authors point out that there are still some grey areas. "Arid regions, certain large lakes, and tropical drainage channels and s remain poorly studied," says Alberto Borges. "New measurements will be needed to refine the estimates."
By providing a new and more accurate perspective, this research highlights the importance of tropical and subtropical diversity in assessing GHG emissions. "These results do not minimise the role of tropics, but allow us to adjust our global models to better anticipate the evolution of global warming."
Scientific reference
Reference: Duvert C., Borges A.V. et al., Hydroclimate and landscape diversity drive highly variable greenhouse gas emissions from (sub)tropical inland waters, Nature Water (2025). doi.org/10.1038/s44221-025-00522-8
