Effect of evapotranspiration on dissolved inorganic carbon and stable carbon isotopic evolution in rivers in semi-arid climates: The Okavango Delta in North West Botswana

Journal article

Authors / Editors

Molwalefhe, Loago

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Publication Details

Author list: Atekwana EA, Molwalefhe L, Kgaodi O, Cruse AM

Publisher: Elsevier: Creative Commons Licenses / Elsevier

Place: AMSTERDAM

Publication year: 2016

Journal: Journal of Hydrology: Regional Studies (2214-5818)

Journal acronym: J HYDROL-REG STUD

Volume number: 7

Start page: 1

End page: 13

Number of pages: 13

ISSN: 2214-5818

Languages: English-Great Britain (EN-GB)

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Abstract

Study region: Okavango Delta, Middle Kalahari, NW Botswana.Study focus: We investigated the effect of evapotranspiration on the evolution of dissolved inorganic carbon (DIC) and stable carbon isotopes of DIC (delta C-13(DIC)) in the Okavango River. We measured the DIC concentrations and the delta C-13(DIC) for samples collected over a 400 km reach of the river in the Okavango Delta during flood conditions and non-flood conditions. In addition, we incubated river samples collected from the proximal portion (Mohembo) and the distal portion (Maun) of the Delta and subsequently evaporated the samples by similar to 90% under ambient conditions.New hydrological insights: We found a 379% and 500% increase in the DIC concentrations and a delta C-13(DIC) increase of 3.9%. and 6.1 parts per thousand. in the river during the flood non-flood conditions, respectively. The DIC concentrations of evaporated river samples increased by 535% for the Mohembo and by 850% for the Maun samples. The increase in the delta C-13(DIC) of the evaporated river samples resulted from CO2(g) loss during chemical equilibrium with atmospheric CO2(g) followed by carbon exchange between DIC and atmospheric CO2(g). Although the delta C-13(DIC) increased spatially for the Okavango River, it never reached the value of similar to 0 parts per thousand expected for equilibration of river DIC with atmospheric CO2(g). The results of the evaporated river samples suggest that isotopic enrichment from equilibration in Okavango River was balanced by respiration and photo-oxidation of carbon-depleted dissolved organic matter. (C) 2016 The Authors. Published by Elsevier B.V.

Keywords

Dissolved inorganic carbon, Evapoconcentration, Okavango delta, Semiarid environment, Stable carbon isotopes

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