Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 11 2009 10.5194/bg-6-2475-2009 http://www.biogeosciences.net/6/2475/2009/ http://www.biogeosciences.net/6/2475/2009/bg-6-2475-2009.html http://www.biogeosciences.net/6/2475/2009/bg-6-2475-2009.pdf 2475 2493 2009-11-05 Distribution, origin and cycling of carbon in the Tana River (Kenya): a dry season basin-scale survey from headwaters to the delta S. Bouillon steven.bouillon@ees.kuleuven.be G. Abril A. V. Borges F. Dehairs G. Govers H. J. Hughes R. Merckx F. J. R. Meysman J. Nyunja C. Osburn J. J. Middelburg Katholieke Universiteit Leuven, Dept. of Earth & Environmental Sciences, Kasteelpark Arenberg 20, 3001 Leuven, Belgium Dept. of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Belgium Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology, Yerseke, The Netherlands Environnements et Paléoenvironnements Océaniques, Université Bordeaux 1, France Unité d'Océanographie Chimique, Université de Liège, Belgium Royal Museum for Central Africa, Dept. of Geology, Tervuren, Belgium Kenya Wildlife Service, P.O. Box 40241-00100, Nairobi, Kenya Department of Marine, Earth & Atmospheric Sciences, NC State University, Raleigh, USA Faculty of Geosciences, Utrecht University, PO Box 80021, 3508 TA Utrecht, The Netherlands The Tana River basin (TRB) is the largest in Kenya (~120 000 km²). We conducted a survey during the dry season throughout the TRB, analyzing a broad suite of biogeochemical parameters. Biogeochemical signatures in headwater streams were highly variable. Along the middle and lower river course, total suspended matter (TSM) concentrations increased more than 30-fold despite the absence of tributary inputs, indicating important resuspension events of internally stored sediment. These resuspended sediment inputs were characterized by a lower and ¹⁴C-depleted OC content, suggesting selective degradation of more recent material during sediment retention. Masinga Dam (a large reservoir on the upper river) induced a strong nutrient retention (~50% for inorganic N, ~72% for inorganic phosphate, and ~40% for dissolved silicate). 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