GHG emissions from African lakes and headwaters of the Amazon River

We collected CO2, CH4 and N2O data in 24 African lakes that accounted for 49% of total lacustrine surface area of the African continent and covered a wide range of morphology and productivity. The surface water concentrations of dissolved CO2 were much lower than values attributed in current literature to tropical lakes, and lower than in boreal systems due to a higher productivity. In contrast, surface water dissolved CH4 concentrations were generally higher than in boreal systems. The lowest CO2 and the highest CH4 concentrations were observed in the more shallow and productive lakes. Emissions of CO2 may likely have been substantially overestimated by a factor between 9 and 18 in African lakes and between 6 and 26 in pan-tropical lakes.
We collected CO2, CH4 and N2O data in Andean headwater and piedmont streams in the Napo River basin in Ecuador, part of the Amazon River catchment. Concentrations increased exponentially with elevation decrease between 3990 and 175 m above sea level and scaled with catchment slope. We estimate river emissions across the whole Amazon basin using existing data for the lowland Central Amazon. We find that Andean mountainous headwater and piedmont streams are hotspots of CO2 and CH4 emission representing 35% CO2 and 72% CH4 of basin scale integrated fluvial diffusive emissions. Data collected in 15 Ecuadorian mountainous lakes was combined with published data from lowland lakes, allowing to compute CO2 and CH4 lacustrine emissions at the scale of the Amazon basin using the HydroLAKES spatial data set. Total CO2 and CH4 emissions from lakes represented a small fraction (8.6%) of total lentic and lotic CO2 and CH4 emissions at the scale of the Amazon basin