Aquatic Sciences

, 80:19 | Cite as

Seasonal and inter-annual variations in carbon fluxes in a tropical river system (Tana River, Kenya)

  • Naomi Geeraert
  • Fred O. Omengo
  • Fredrick Tamooh
  • Trent R. Marwick
  • Alberto V. Borges
  • Gerard Govers
  • Steven Bouillon
Research Article


The hydrological status of river systems is expected to change due to dam operations and climate change. This will affect the riverine fluxes of sediment and carbon (C). In rivers with strong seasonal and inter-annual variability, quantification and extrapolation of sediment and C fluxes can be a challenge as measurement periods are often too short to cover all hydrological conditions. We studied the dynamics of the Tana River (Kenya) from 2012 to 2014 through daily monitoring of sediment concentrations at three sites (Garissa, Tana River Primate Reserve and Garsen) and daily monitoring of C concentrations in Garissa and Garsen during three distinct seasons. A bootstrap method was applied to calculate the range of sediment and C fluxes as a function of annual discharge by using daily discharge data (1942–2014). Overall, we estimated that on average, sediment and carbon were retained in this 600 km long river section between Garissa to Garsen over the 73 years (i.e., fluxes were higher at the upstream site than downstream): integration over all simulations resulted in an average net retention of sediment (~ 2.9 Mt year− 1), POC (~ 18,000 tC year− 1), DOC (~ 920 tC year− 1) and DIC (~ 1200 tC year− 1). To assess the impact of hydrological variations, we constructed four different hydrological scenarios over the same period. Although there was significant non-linearity and difference between the C species, our estimates generally predicted a net increase of C retention between the upstream and downstream site when the annual discharge would decrease, for example caused by an increase of irrigation with reservoir water. When simulating an increase in the annual discharge, e.g. as a potential effect of climate change, we predicted a decrease in C retention.


Carbon fluxes Tropical rivers Inter-annual variability Intra-annual variability Long term simulations Carbon retention 



Funding was provided by the KU Leuven Special Research Fund, the Research Foundation Flanders (FWO–Vlaanderen, project G024012N), and an ERC Starting Grant (240002, AFRIVAL). We are grateful to the Kenya Wildlife Service (KWS) for assistance during field experiments and to the Water Resources Management Authority (WRMA) for assistance during the ADCP measurements and for sharing discharge data. AVB is a senior research associate at the FRS-FNRS

Author contributions

S. Bouillon, N. Geeraert, T. Marwick, F.O. Omengo and F. Tamooh were involved in the data collection. N. Geeraert prepared the manuscript with contributions from all co-authors.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Naomi Geeraert
    • 1
  • Fred O. Omengo
    • 1
    • 2
  • Fredrick Tamooh
    • 1
    • 3
  • Trent R. Marwick
    • 1
  • Alberto V. Borges
    • 4
  • Gerard Govers
    • 1
  • Steven Bouillon
    • 1
  1. 1.Department of Earth and Environmental SciencesKU LeuvenLouvainBelgium
  2. 2.Kenya Wildlife ServiceNairobiKenya
  3. 3.Department of Zoological SciencesKenyatta UniversityMombasaKenya
  4. 4.Unité d’Océanographie Chimique, Institut de Physique (B5)Université de LiègeLiègeBelgium

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