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Abstract

River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle1. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems2. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream3,4. Three-quarters of the world’s flooded land consists of temporary wetlands5, but the contribution of these productive ecosystems6 to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems1,7. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains8. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

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Acknowledgements

This research is a contribution to the CARBAMA project, funded by the French National Agency for Research (grant number 08-BLAN-0221), the French INSU national programme EC2CO, and the National Council of Research and Development (CNPq), Brazil (Universal Program number 477655/2010-6). It was conducted under the auspices of the Environmental Research Observatory Hydrology and Geochemistry of the Amazon Basin (HYBAM), supported by the INSU and the IRD (Institute for Research and Development, France). F.R. was supported by CNPq and a Brazilian ‘Excellent Researcher’ fellowship. We thank all the participants of the CARBAMA cruises.

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Affiliations

  1. Laboratoire Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), CNRS, Université Bordeaux 1, Avenue des Facultés, 33405 Talence, France

    • Gwenaël Abril
    • , Nicolas Savoye
    •  & Jonathan Deborde
  2. Laboratoire Géosciences et Environnement de Toulouse, Institut de Recherche pour le Développement, Université Paul Sabatier, 14 avenue Edouard Belin, 31400 Toulouse, France

    • Gwenaël Abril
    • , Jean-Michel Martinez
    •  & Patricia Moreira-Turcq
  3. Laboratoire d’Océanologie et Géosciences, CNRS, Université du Littoral Côte d’Opale, 32 avenue Foch, 62930 Wimereux, France

    • L. Felipe Artigas
  4. Equipe Géochimie des Eaux, Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, 35 rue Hélène Brion, 75205 Paris Cedex 13, France

    • Marc F. Benedetti
  5. Laboratório de Ecologia Aquática, Departamento de Biologia, Universidade Federal de Juiz de Fora, Rua José Lourenço Kelmer, MG 36036-900 Juiz de Fora, Brazil

    • Luciana Vidal
    •  & Fabio Roland
  6. Laboratoire Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Muséum National d’Histoire Naturelle, CNRS, IRD, UPMC, 61 rue Buffon, 75005, Paris, France

    • Tarik Meziane
  7. NIOZ (Royal Netherlands Institute for Sea Research), Department of Marine Organic Biogeochemistry, Texel, 1790 AB Den Burg, The Netherlands

    • Jung-Hyun Kim
  8. Programa de Geoquímica, Universidade Federal Fluminense, Outeiro São João Batista, RJ 24020015 Niterói, Brazil

    • Marcelo C. Bernardes
  9. Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, DF 70.910-900 Brasília, Brazil

    • Edivaldo Lima Souza
  10. Institut des Sciences de la Terre d’Orléans, 1A rue de la Férollerie, 45071 Orléans Cedex 2, France

    • Patrick Albéric
  11. Laboratório de Oceanografia Química, Universidade Estadual de Santa Cruz, Rodovia Ilhéus-Itabuna, 45662-900 Ilhéus, Bahia, Brazil

    • Marcelo F. Landim de Souza

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Contributions

G.A., J.-M.M., P.M.-T., L.F.A., T.M. and M.F.B. conceived and designed the study. G.A. coordinated project and fieldwork. G.A., J.D., M.F.L.d.S. and N.S. performed the pco2 measurements. J.-M.M. and E.L.S. analysed the remote sensing data. L.F.A. measured Chl a and fluorescence. L.V. and F.R. measured respiration. All authors contributed to the interpretation of the data. G.A. wrote the manuscript, J.-M.M., L.F.A. and F.R. contributed to manuscript writing and P.M.-T., L.V., T.M., J.-H.K., M.C.B., N.S. and M.F.B. commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Gwenaël Abril.

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https://doi.org/10.1038/nature12797

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