EVOLUTION SPATIALE DES CARACTERISTIQUES PHYSICO-CHIMIQUES DES EAUX DU LAC OUBEIRA IMPOSE PAR LES CONDITIONS SEVERES DE LA SECHERESSE (EXTREME NE ALGERIEN)

Abstract

The endoreic lake Oubeira, vast lake located in Algeria (36°51' N- 8°23' E), at an altitude of 23 m, is subject to severe natural and anthropic constraints during the dry season, which generally begins in April and is completed in October. Due to its geometrical configuration and wind exposure, the water of the lake is well brewed within the entire water column. The first results, covering all the shallow water level, show the average mineralisation of hot moderate water, which releases CO2 in the atmosphere, an alkaline pH, higher than 8, related to intense evaporation and biological activity, in particular photosynthesis and calcite precipitation. Physicochemical measurements brought a considerable contribution to identify the individualization of two distinct water masses, one in the East and the other in the West, and the absence of limnologic layers. The conditions of the environment make organic particles degraded in the water column. Conservation of organic remains in the reducing environment, represented by the mud, is much reduced. Almost circular, the lake Oubeira has a flat bottom, generally covered with greyish mud, because of the presence of reduced iron, less than 2 m thick. The thickness of the water blade hardly exceeds 1.50 m and the maximum depth, between the surface of the lake and the substratum is about 3.50 m, in period of dryness.