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Riverine fluxes of sediments and carbon in the lower Tana River: the importance of floodplain retention

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Academic year: 2021

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Sediment and carbon transport in the lower Tana River (Kenya): the regulating role of floodplains

Fredrick Tamooh1,2, *, Filip J. R. Meysman3,4, Alberto V. Borges5, Trent R. Marwick1, Karel Van Den Meersche 3,4, Frank Dehairs3, Roel Merckx1, & Steven Bouillon1

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

(2) Kenya Wildlife Service, P.O. Box 82144-80100, Mombasa, Kenya.

(3) Vrije Universiteit Brussel, Department of Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussel, Belgium.

(4) Royal Netherlands Institute of Sea Research (NIOZ), Korringaweg 7, 4401 NT Yerseke, The Netherlands.

(5) Université de Liège, Unité d’Océanographie Chimique, Allée du 6 Août, 17, B-4000, Belgium.

* Corresponding author.

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Abstract

We estimated annual fluxes of suspended sediments and different carbon species at three sites along the lower Tana River (Kenya), based on monthly sampling between January 2009 and December 2011. Floodplains are present along large stretches of the lower Tana River. Total suspended matter (TSM), concentrations of particulate and dissolved organic and inorganic carbon (POC, DOC and DIC), as well as their stable isotope composition were determined. Both TSM (24 to 9386 mg L-1) and POC (0.8 to 141.9 mg C L-1)concentrations were highly variable. DOC and DIC concentrations ranged from 0.8 to 5.2 mg C L-1 and 7.1 to 23.5 mg C L-1, respectively, but their seasonal variations were not systematic. A strong shift in the origin of POC was observed, being dominated by C3-derived carbon (C) during dry conditions (low δ13

CPOC signatures between -28‰ and -25‰), but with significant C4 contributions during

higher flow events (δ13CPOC up to -19.5 ‰). On average, annual suspended sediment fluxes

ranged from 3.1 Tg y-1 to 8.7 Tg y-1. Mean annual C fluxes ranged from 36.6 Gg C y-1 to 104.9 Gg C y-1, 6.0 Gg C y-1 to 13.9 Gg C y-1 and 50.6 Gg C y-1 to 63.6 Gg C y-1 for POC, DOC and DIC, respectively. Tana River floodplains play a critical role in regulating the transport of sediments and organic carbon as reflected by a significant reduction in the sediment, POC and DOC (ranging between 34% and 65% for the 3-year study period).

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