Preprints
https://doi.org/10.5194/bg-2017-31
https://doi.org/10.5194/bg-2017-31
10 Feb 2017
 | 10 Feb 2017
Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.

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, and Steven Bouillon

Abstract. Quantification of sediment and carbon (C) fluxes in rivers with strong seasonal and inter-annual variability presents a challenge for global flux estimates 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. In wet seasons, C fluxes were dominated by particulate organic C (POC) and decreased downstream. Dry season fluxes of dissolved inorganic C (DIC) and POC had a similar share in total C flux at both locations while POC fluxes increased downstream. The dissolved organic C (DOC) flux did not show strong spatial nor temporal variations. The construction of constituent rating curves with a bootstrap method in combination with daily discharge data (1942–2014) provided potential sediment and C flux ranges as a function of annual discharge. At low annual discharge, our estimates generally predict a net decrease of sediment and C storage between the upstream and downstream site. As the annual discharge increases, our simulations shift toward net retention. This analysis allowed us to infer how variations in discharge regime, related to climate or human impacts, may affect riverine fluxes. Overall, we estimate that retention was dominant: integration over all simulations resulted in an average net retention of sediment (~2.9 Mt yr−1), POC (~18000 tC yr−1), DOC (~920 tC yr−1) and DIC (~1200 tC yr−1) over the 73 years of discharge measurements.

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Naomi Geeraert, Fred O. Omengo, Fredrick Tamooh, Trent R. Marwick, Alberto V. Borges, Gerard Govers, and Steven Bouillon
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Naomi Geeraert, Fred O. Omengo, Fredrick Tamooh, Trent R. Marwick, Alberto V. Borges, Gerard Govers, and Steven Bouillon
Naomi Geeraert, Fred O. Omengo, Fredrick Tamooh, Trent R. Marwick, Alberto V. Borges, Gerard Govers, and Steven Bouillon

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Short summary
We observed that the relationship between the concentrations and the water discharge in the Tana River changed in wet seasons with and without flooding. Detailed sampling in those seasons is required in order to construct several rating curves and to obtain reliable flux estimates. The sediment and carbon fluxes in function of discharge will help us to asses the flux changes that can be expected when the hydrology changes due to climate change or human impact.
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