Abstract
Carbon dioxide emissions to the atmosphere from inland waters—streams, rivers, lakes and reservoirs—are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly affect greenhouse-gas emissions from African inland waters.
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Acknowledgements
This work was funded by the European Research Council (ERC-StG 240002 AFRIVAL), the Fonds National de la Recherche Scientifique (FNRS, CAKI 2.4.598.07, TransCongo, 14711103), the Belgian Federal Science Policy (BELSPO) (projects COBAFISH SD/AR/05A and EAGLES SD/AR/02A), the Research Foundation Flanders (FWO-Vlaanderen), the Research Council of the KU Leuven, the IRD and INSU/CNRS (SOERE BVET and LIMON projects). The Boyekoli-Ebale-Congo Expedition (2010) was funded by the Belgian Development Cooperation, BELSPO, and Belgian National Lottery. A.V.B. and T.L. are a senior research associate and a postdoctoral researcher at the FNRS, respectively. We are very grateful for help in sampling from A. Yambélé (Direction de la Météorologie Nationale, Central African Republic), J.-D. Mbega (Institut de Recherches Agronomiques et Forestières, Gabon), B. Alhou (Université de Niamey, Niger), F. C. Nyoni and I. Nyambe (University of Zambia, Zambia), B. Ogwoka (Kenya Wildlife Service, Kenya), T. Mambo Baba and E. Tambwe Lukosha (Université de Kisangani, DRC), T. Kisekelwa (Institut Supérieur Pédagogique de Bukavu, DRC), J. N. Wabakanghanzi (Congo Atomic Energy Commission, DRC), C. M. Balagizi (Goma Volcano Observatory, DRC) and J. L. Boeglin (Géosciences Environnement Toulouse – GET, France), for analytical support from M.-V. Commarieu, S. Hoornaert, S. Petrovic (University of Liège (ULg)) and C. Deshmukh (GET), for advice and help in setting up the GCs at ULg from J. Barnes, G. Abril, B. Delille and W. Champenois, and for feedback and input on modelled basin-wide k values from P. Raymond.
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A.V.B. and S.B. conceived and designed the study and coordinated the project and fieldwork. Field data collection was carried out by all co-authors. T.L. carried out the geographical system information (GIS) analysis. A.V.B. drafted the manuscript, which was substantially commented upon and amended by S.B., C.R.T., T.R.M., N.G., T.L. and F.G. All co-authors approved the manuscript.
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Borges, A., Darchambeau, F., Teodoru, C. et al. Globally significant greenhouse-gas emissions from African inland waters. Nature Geosci 8, 637–642 (2015). https://doi.org/10.1038/ngeo2486
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DOI: https://doi.org/10.1038/ngeo2486
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