Hydrochemical characterization of complex volcanic aquifers in a continental rifted zone: the Middle Awash basin, Ethiopia |
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Authors: | Wakgari Furi Moumtaz Razack Tamiru Alemayehu Abiye Seifu Kebede Dagnachew Legesse |
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Institution: | 1. Department of Hydrogeology, University de Poitiers, 86000, Poitiers, France 2. School of Geosciences, University of the Witwatersrand, Wits, 2050, Johannesburg, South Africa 3. Department of Earth Sciences, Addis Ababa University, P.O.Box 1176, Addis Ababa, Ethiopia
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Abstract: | The Middle Awash basin is an arid region in Ethiopia where surface waters are scarce and local communities are dependent on groundwater resources for water supply. The complex hydrogeological system of this basin has been conceptualized. Multivariate statistical analysis of hydrochemical variables and water isotopes were used to study the rock?Cwater interaction, geochemical reaction processes and the hydrological link between aquifers. Groundwaters from aquifers of the high-rainfall plateau bounding the rift are slightly mineralized, as well as depleted in ??18O and ??D, and contain 3H above 0.8?TU. This suggests a low degree of rock?Cwater interaction and that groundwater is under recharge from heavy rain that falls on surrounding highlands. On the other hand, groundwaters from aquifers of the rift floor are highly mineralized and show slight enrichment in ??18O and ??D with positive oxygen shift, but contain 3H below 0.8?TU. The positive oxygen shift in rift floor groundwaters may be caused by the isotopic exchange of oxygen between groundwater and aquifer materials during rock?Cwater interaction, whereas the low 3H content could be due to the decay of tritium along relatively long flow paths. The approach utilized in this study may be applicable to understanding hydrogeochemical processes in other complex volcanic terrains. |
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