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Globally significant greenhouse-gas emissions from African inland waters

Nature Geoscience volume 8, pages 637–642 (2015)Cite this article

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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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Figure 1: The 12 studied rivers cover a wide range of discharge, catchment size and land cover.
Figure 2: Complex interplay of biogeochemical processes is revealed by GHGs property–property relations.
Figure 3: Wetland presence drives the pattern of GHGs and O2 in the Congo River.
Figure 4: Wetland presence drives the pattern of CO2 and CH4 concentrations across sub-Saharan African Rivers.

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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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Authors and Affiliations

  1. Université de Liège, Unité d’Océanographie Chimique, Institut de Physique (B5), B-4000, Belgium

    Alberto V. Borges, François Darchambeau & Thibault Lambert

  2. Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200E, B-3001 Leuven, Belgium,

    Cristian R. Teodoru, Trent R. Marwick, Fredrick Tamooh, Naomi Geeraert, Fredrick O. Omengo, Cédric Morana, Eric Okuku & Steven Bouillon

  3. Department of Zoological Sciences, Kenyatta University, PO Box 16778-80100 Mombasa, Kenya,

    Fredrick Tamooh

  4. Geosciences Environnement Toulouse UMR 5563 & UR 234 IRD, Université Paul-Sabatier, Avenue Edouard Belin 14, F-31400 Toulouse, France,

    Frédéric Guérin

  5. Kenya Marine and Fisheries Research Institute, PO Box 81651 Mombasa-80100, Kenya,

    Eric Okuku

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  1. Alberto V. Borges
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Contributions

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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Correspondence to Alberto V. Borges.

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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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