The oases of the Algerian Sahara, between hydric excess and salinity: Example of the oasis of Ouargla

Abstract

To speak about water surpluses in a desert medium can appear wrong at first sight. It is however a current reality that has been present for many years already in most of the oases of the Algerian Sahara. This problem has become today a true threat for the environment and the consequences are evident in urban areas as well as in their periphery. Increased discharges of urban wastewater and water from agricultural drainage have induced a significant rise in the level of the shallow aquifer waters in most urban areas of the Algerian Sahara. These raised water levels have promoted the degradation of environmental conditions and have severely disrupted the natural balance in the Saharan oases, already weakened by extreme climatic conditions and topographic features that do not facilitate evacuation of excess water. In fact, the oases of the Algerian Sahara are mostly located in sedimentary basins. These oases, which had previously functioned as well-balanced hydraulic systems, are currently suffering from water excess. The present study describes through a particular case, that of Ouargla, this phenomenon of hydric excess and highlights its consequences, in particular, the salinization of oasis soils. The results of physicochemical analyses showed that the electrical conductivities of the different soils of the Ouargla basin are excessively high, up to 5000 mS*m-1 in surface horizons during the summer season. This over-salinization is mainly influenced not only by the unfavorable geological and climatic contexts, but also by the very high salinity of the shallow aquifer, in which the electrical conductivity exceeds 7000 mS m-1.