THE Sr /Ca RATIO, A GOOD INDICATOR OF THE ORIGIN OF WATER SALINITY: THE CASE OF THE TABLES OF EL MALABIOD, TEBBESSA AND AL AOUINET (UNDER THE BASIN OF THE OUED MELLAGUE- EASTERN ALGERIAN)

Abstract

Algeria is characterized by an important outcrop of evaporite formations that may be of economic interest. For this purpose geological studies have been conducted showing that Algeria ranks third in the world in terms of Gypsum reserves. However, in contact with water, the evaporite formations (gypsum, halite) cause an increase in the salinity of the groundwater making their use limited. The study area is characterized by large outcrops of gypsiferous formations that can lead to the observed salinity. To highlight the probable link between salinity and outcrop formations, we used the Sr2 ⁺ / Ca2 ⁺ ratio, as well as Leaching. The ratio Sr2 ⁺ / Ca2 ⁺ shows values exceeding the threshold of 3‰, which suggests a direct influence of the gypsiferous formations on the salinity of the waters. This influence is corroborated by the leaching carried out according to the following protocol: drawing of soil sediments belonging to the three targeted zones, these were deposited in demineralized water, we carried out five leachings, distributed as follows: 24 hours, 48 hours, 7 days, 30 days and 90 days. The analyzes carried out on the leachates show after 24h and 90 days of reaction, an increase in the value of the ratio Sr 2⁺ / Ca 2⁺, especially for the points, El Aouinet 4, El Ma Labiod plain Cement, Djebissa 9, whose values did not exceed the threshold value of 3 ‰, in the beginning, acquire values exceeding 3‰, thus highlighting the salt contribution by dissolving the evaporite formations24 hours, 48 hours, 30 days and 3 months. The spatio temporal analysis carried out that the three zones studied does not react in the same way. In this respect, the regions of Djebissa and El Ma Labiod, show a cause-and-effect relationship between mineralization and dissolution, while the El Aouinet region shows a variable evolution that is limited in time. These trends are generated by the positions of the evaporitic formations vis-à-vis the water bodies. Indeed in Tebessa and El Ma Labiod, the Triassic is upstream and therefore influences the chemical composition of the waters. In El Aouinet, on the other hand, the outcrop of the Triassic is scattered, thus explaining the values obtained.