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| Titel |
Hydrochemical and isotopic characterisation of deep groundwater reservoirs in the Sahara desert |
| VerfasserIn |
R. Abdalla, A. Leis, M. Dietzel, S. J. Köhler, M. E. Böttcher, J. Savarino, S. Morin |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027032
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| Zusammenfassung |
| Large sedimentary basins are extended over hundreds of square kilometres cross the Libyan
Sahara. These basins consist of several aquifer systems, which belong to various geological
ages. Most common are Quaternary, Mesozoic and Palaeozoic aquifers. The Jabal
Hasouna well fields are located about 700 km south of Tripoli and are part of the Great
Man-Made River Project for water supply to the coastal areas. The well field area
extends over 4000 km2 with 440 production and 44 standby wells. In this region the
main Cambro-Ordovician Sandstone aquifer is overlain by a shallow carbonate
aquifer with a basal aquitard, predominantly composed of marly limestone, clay and
shale.
Hydrochemical investigations involving collection and analysis of numerous deep
groundwater samples from Hasouna well fields have been carried out to evaluate the regional
groundwater quality and origin. Therefore, the groundwater samples were analyzed for major
ions, trace elements, and environmental isotopes. Additionally, soil and rock samples were
collected and characterized using XRD and XRF for mineralogical and chemical
composition, respectively.
The groundwater can be classified in Na-Ca-Cl-SO4, Na-Ca-Cl-SO4-HCO3,
Ca-Na-Cl-SO4-HCO3 and Na-Ca-Mg-Cl-SO4 types with moderate to high salinity. Most
solutions indicate elevated ion concentrations of chloride, sodium, sulphate and nitrate. In
some parts of the investigation area the respective ion concentrations in the groundwater
exceed the WHO quality limits.
Stable hydrogen and oxygen isotopic composition of the H2O show that the groundwater
composition typically falls below the Global Meteoric Water Line and are far away from the
Mediterranean Meteoric Water Line. Accordingly, the groundwaters were recharged in a
climate different from that of the recent Mediterranean. The relationship between stable
hydrogen and oxygen isotope ratios indicate that the ancient groundwater was recharged
under cooler climate conditions. In order to verify the source of dissolved nitrate and
sulphate, selected samples were analysed for nitrogen (δ15N) and oxygen isotopes (δ17O,
δ18O) and sulphur (δ34S) and oxygen (δ18O) isotopes in NO3-and SO42-, respectively. |
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