Abstract form

Geological conditions of the salinization in case of two irrigated fields
in Central and South Sahara, Libya
Bashir H. MAHDI 1 , János KALMÁR* 2
1 Industrial Research Institute, Tripoli, Libya
2 Geological Institute of Hungary, Stefánia út 14, Budapest, Hungary
Presenting the environmental problems of the mapped Saharian region, two significative
areas were studied: the first area, situated in Wāw al Kabir oasis (NG 33-12 sheet) and
the second one, near to Rabiyanah village (NG 34-15 sheet). Both areas are located in
the driest zone of the African continent, consequently plant production is possible only
by irrigation, in so called Agricultural Projects.
In Wāw al Kabir, an ancient Islamic eremite site, during a long historical time the sandy
soil was irrigated from 5-8 m deep wells, using with care the groundwater found in
disaggregated Paleogene rocks and in the gravels from the base of the Quaternary
deposits, with ~2000 mg/l total salinity. Boring a few hydrogeological wells, an artesian
water, below 500 mg/l was obtained, but because of the accidental mixing with
groundwater in the northern part of the oasis, in a few years the soil became saline, with
2-5% NaCl.
In Rabiyana, a large Pleistocene proluvial fan, with silty-sandy or clayey-silty deposits
were irrigated with low saline (500-700 mg/l.) water from the Cretaceous aquifer.
Unfortunately, the clay retained more and more salts, resulting, after 15 years of
irrigation, the total salinization of the soil, with 2-10 mm thick halite lenses, in which all
of vegetation has disappeared.
The paper is illustrated with tables and graphics of analytical data, with X-ray diagrams
and optic and SEM micrographs of the salinized soil samples as well.
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