GHG emissions from African lakes and headwaters of the Amazon River

The Chemical Oceanography Unit of the University of Liège studies the exchange of greenhouse gases (CO2, CH4 and N2O) with the atmosphere in the cryosphere, oceans and inland waters (lakes and rivers). We will present the results from two studies in African lakes and the Andean mountainous streams in Ecuador.
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. Concentration changes scaled with catchment slope, and were attributed to variations in gas transfer velocity, forest cover, inundation extent, and water temperature. 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, with respective areal fluxes being 1.7 and 4.5 higher in headwater streams, and 1.2 and 6.6 higher in piedmont streams than in lowland streams. Together, Andean mountainous headwater and piedmont streams and rivers represented 35% CO2 and 72% CH4 of basin scale integrated fluvial diffusive emissions. Conversely, N2O emissions from headwater and piedmont streams were low compared to lowland streams.