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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/esd-2020-3
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esd-2020-3
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  11 Mar 2020

11 Mar 2020

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A revised version of this preprint is currently under review for the journal ESD.

Historical and future contributions of inland waters to the Congo basin carbon balance

Adam Hastie1,2, Ronny Lauerwald2,3, Philippe Ciais3, Fabrice Papa4,5, and Pierre Regnier2 Adam Hastie et al.
  • 1School of GeoSciences, University of Edinburgh, EH9 3FF, Edinburgh, Scotland, UK
  • 2Biogeochemistry and Earth System Modelling, Department of Geoscience, Environment and Society, Universite Librede Bruxelles, Bruxelles, 1050, Belgium
  • 3Laboratoire des Sciences du Climat et de l'Environnement (LSCE), CEA CNRS UVSQ, Gif-sur-Yvette 91191, France
  • 4Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, Centre National de la Recherche Scientifique–Institut de recherche pour le développement–Université Toulouse Paul Sabatier–Centre national d’études spatiales, 31400 Toulouse, France
  • 5Indo-French Cell for Water Sciences, International Joint Laboratory Institut de Recherche pour le Développement and Indian Institute of Science, Indian Institute of Science, 560012 Bangalore, India

Abstract. As the second largest area of contiguous tropical rainforest and second largest river basin in the world, the Congo basin has a significant role to play in the global carbon (C) cycle. Inventories suggest that terrestrial net primary productivity (NPP) and C storage in tree biomass has increased in recent decades in intact forests of tropical Africa, due in large part to a combination of increasing atmospheric CO2 concentrations and climate change, while rotational agriculture and logging have caused C losses. For the present day, it has been shown that a significant proportion of global terrestrial NPP is transferred laterally to the land-ocean aquatic continuum (LOAC) as dissolved CO2, dissolved organic carbon (DOC) and particulate organic carbon (POC). Whilst the importance of LOAC fluxes in the Congo basin has been demonstrated for the present day, it is not known to what extent these fluxes have been perturbed historically, how they are likely to change under future climate change and land use scenarios, and in turn what impact these changes might have on the overall C cycle of the basin. Here we apply the ORCHILEAK model to the Congo basin and show that 4% of terrestrial NPP (NPP = 5,800 ± 166 Tg C yr−1) is currently exported from soils to inland waters. Further, we found that aquatic C fluxes have undergone considerable perturbation since 1861 to the present day, with aquatic CO2 evasion and C export to the coast increasing by 26 % (186 ± 41 Tg C yr−1 to 235 ± 54 Tg C yr−1) and 25 % (12 ± 3 Tg C yr−1 to 15 ± 4 Tg C yr−1) respectively, largely because of rising atmospheric CO2 concentrations. Moreover, under climate scenario RCP 6.0 we predict that this perturbation will continue; over the full simulation period (1861–2099), we estimate that aquatic CO2 evasion and C export to the coast will increase by 79 % and 67 % respectively. Finally, we show that the proportion of terrestrial NPP lost to the LOAC also increases from approximately 3 % to 5 % from 1861–2099 as a result of increasing atmospheric CO2 concentrations and climate change.

Adam Hastie et al.

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Adam Hastie et al.

Model code and software

ORCHILEAK source code R. Lauerwald, P. Regnier, M. Camino-Serrano, B. Guenet, M. Guimberteau, A. Ducharne, J. Polcher, and P. Ciais https://doi.org/10.5194/gmd-10-3821-2017-supplement

Adam Hastie et al.

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Short summary
We used a model of the Congo basin to investigate the transfer of carbon (C) from land (vegetation and soils) to inland waters. We find that leaching of C to inland waters, emissions of CO2 from the water surface, and the export of C to the coast have all increased over the last century, driven by increasing atmospheric CO2 levels and climate change. We predict that these trends will continue through the 21st century with potential implications for pH levels and the ecology of the Congo River.
We used a model of the Congo basin to investigate the transfer of carbon (C) from land...
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