Geochemistry of saline soils in two arid zones of the Mediterranean basin. I. geochemistry of the chott melghir‐mehrouane watershed in Algeria

An endoreic region in South Algeria was studied, which included the southern slopes of the Aurès, the Biskra and Touggourt areas, and the Melghir and Merouane chotts, which are large depressions located below sea level. The chemistry of surface waters and groundwater and the mineralogy of efflorescences were studied along a 100‐km‐long toposequence. The ionic strength of natural solutions varied from 22 × 10‐3 in the Aures Mountains to over 5.0 in the chotts. Thermodynamic equilibrium models indicated that solutions were controlled by the following precipitation sequence: calcite > gypsum > mirabilite = bloedite > halite. This sequence, confirmed by X‐ray diffraction of efflorescences, indicated that the landscape had behaved as a Chromatographic separator. Chemical composition variations related to this separation were consistent with generalized residual alkalinity, thereby indicating that a single chemical family was present in the study area, which suggests that a single hydrologic system was also present. Gradual concentration and precipitation of minerals in the downstream direction accounted for most of the chemical facies variations. This study provided a chance to test successfully a new extension to the Debye‐Hückel law for chlorurated sodic brines.