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

Eliot A. Atekwana, Loago Molwalefhe, Oratile Kgaodi, Anna M. Cruse

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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 (δ13CDIC) in the Okavango River. We measured the DIC concentrations and the δ13CDIC 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 ~90% under ambient conditions. New hydrological insights: We found a 379% and 500% increase in the DIC concentrations and a δ13CDIC increase of 3.9‰ and 6.1‰ 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 δ13CDIC 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 δ13CDIC increased spatially for the Okavango River, it never reached the value of ~0‰ 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.

Original languageEnglish
Pages (from-to)1-13
Number of pages13
JournalJournal of Hydrology: Regional Studies
Publication statusPublished - Sep 1 2016


All Science Journal Classification (ASJC) codes

  • Water Science and Technology
  • Earth and Planetary Sciences (miscellaneous)

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