Salinisation origin and hydrogeochemical behaviour of the Djerid oasis water table aquifer (southern Tunisia)
- PDF / 1,692,007 Bytes
- 15 Pages / 595.276 x 790.866 pts Page_size
- 55 Downloads / 199 Views
ORIGINAL PAPER
Salinisation origin and hydrogeochemical behaviour of the Djerid oasis water table aquifer (southern Tunisia) Samir Kamel
Received: 26 August 2011 / Accepted: 2 December 2011 # Saudi Society for Geosciences 2011
Abstract The shallow Plio-Quaternary (PQ) water table, present over almost the whole Djerid and Chott El Gharsa basins (southern Tunisia), is used as a complement of oases irrigation, especially in summer season. The simplicity of the Plio-Quaternary lithology is confronted to the complexity of the mineralisation mechanisms and the water origin in this aquifer. An approach combining the use of water-dissolved chemical species and isotopic contents has been used to better understand the PQ behaviour under severe increasing exploitation and to determinate the origin of its different water bodies. In southern Tunisia, the aquifer system is composed of the upper unconfined PQ aquifer, the intermediate semiconfined/confined Complexe Terminal (CT) and the deeper confined Continental Intercalaire (CI). Chemical analyses highlighted an origin of mineralisation in close relationship to the dissolution of both sulphated salts (MgSO4 and Na2SO4) and chlorinated salts (NaCl and MgCl) abundant in the surface and subsurface gypsum crust. Positive correlations between gypsum anhydrite, mirabilite, thenardite and halite saturation indexes with respective mineral species, confirm evaporites dissolutions. Isotopic data showed that in addition of sporadic rainfall events, there is a contribution from the CI and the CT Saharan groundwaters, recharging the PQ aquifer in the study area. Return flow irrigation is partly affected by evaporation, before recharging the shallow aquifer, in oases limits. Keywords Oases . Water table aquifer . Evaporation . Dissolution . Crust . Vertical leakage . Stable isotopes . Tunisia
S. Kamel (*) Institut Supérieur des Sciences et Techniques des Eaux de Gabès, Cité Erriadh, Campus Universitaire, Zrig, Gabès 6072, Tunisia e-mail: [email protected]
Introduction At the beginning, the oases have been created around the artesian springs, forming assembly points of desert nomads. Based on landform, oases, in southern Tunisia, can be classified as alluvial plain (Chott Djerid and Chott el Gharsa margins), mountains (Metlaoui-Gafsa and Northern Chotts range piedmonts) and coastal (around Gulf of Gabes) (Coque 1962). Saharan hot strong winds and sands, serious soil salinisation and water insufficiency are the natural causes for the disappearance of some ancient oases (Mamou and Kassah 2002). The study area is located in southwestern Tunisia between longitude 7°30′–8°30′ east and latitude 33°30′–34°30′ north. It is limited in the west by the Algerian frontier, in the north by the Metlaoui Chain, in the east by the gulf of Gabes and in the south by the Chott Djerid depression (Fig. 1). The study area is famous in Tunisia for production dates and known as the “Djerid” region. The development and evolution of oases is mainly decided by the human utilisation of water resources. The
Data Loading...
