Substantial methane emissions from central Congo’s wetlands

The Congo Basin is home to the world’s largest tropical peatland complex storing 29 PgC across 16.7 million ha, which poses a major unconstrained source of global wetland CH₄. Key controls over their spatio-temporal variability remain unclear, limiting our ability to assess responses to future environmental change. Here, we present the first time series of in situ measurements from four intensive locations covering peat, seasonally flooded and terra firma forest ecosystems. Measurements were done every month for two years and additional widespread in situ CH₄ flux measurements from the peat surface and from tree stems, across 12 transects distributed across the region. The intensive sites show a substantial CH₄ source from hardwood and palm dominated peat swamp forest respectively, representing the most substantial emissions from peat swamp forests globally. These emissions were accompanied by substantial emissions from non-peat forming seasonally flooded forests while emissions were close to zero from the terra firme sites. Temporal variation in emissions were coincident with seasonal variation in the water levels with greater emissions during the wet seasons and little during the dry season. We demonstrate large spatial variation in net CH₄ emissions across the region and that net emissions are dominated by peat emissions with only a small overall contribution of tree emissions. The emissions followed an exponential relationship with water levels and higher CH₄ emissions occurred in areas closer to the nearest river and in areas with greater river water rather than rainwater inputs. Taken together, our findings demonstrates that the Congo wetlands have the capacity to produce large amounts of CH₄ with distinct differences between dominant vegetation communities, and water levels and sources representing a key control over dynamics.