Assessment of the hydrogeochemical and isotopic characterization and hydraulic behavior of the Izeh complex karstic area, Khuzestan province, southwest Iran

Proper water resources management requires recognizing and evaluating the factors that affect the quantity and quality of water resources. The Ilam-Sarvak (Upper Cretaceous) and Asmari (Oligocene to Miocene) limestone- dolomite formations in the Zagros structural belt have formed a promising karst groundwater horizon. In the present study, the hydraulic relationship between the karst structures of the Izeh territory in the northeast of Khuzestan province was investigated using hydrogeochemical and isotopic information of springs and wells. The results enabled to understand various components influencing the recharge of water resources. In this study, samples were collected from the karst springs and wells of Mongasht, Shavish-Tanosh and Kamarderaz anticlines and Naal-e-Asbi (Horseshoe) syncline and meteoric water to understand the hydrochemical and isotopic characterization, and hydrogeological and hydraulic behavior of the Izeh karst system. The meteoric and groundwater samples were analyzed to determine major and minor ion concentrations and δ18O and δ2H isotope ratios. Isotopic content ranged from -31.6 to -2.9‰ and from -6.32 to -1.87‰ for δ2H and δ18O, respectively, and d-excess values were high and positive. The study of the isotopic content of water samples of springs and wells in the region shows three groups of water sources. The first group, related to the Mongasht anticline springs, has lower isotopic values, indicating that it is recharged by rainfall at high altitudes and snow melting. The isotopic value of the second group is richer than that of the first group, indicating rainfall recharge as well as groundwater mixing (ex­amples of Naal-e-Asbi syncline and Shavish-Tanosh anticline). The highest value in the third group (samples of Kamarderaz anticline) is attributed to evaporation and longer distance from the recharge site to the discharge point, as well as to the diffu­sion system. The trend of decrease in Sr+2 and increase in Ba+2 in the samples of dolomitic limestone formations (Shavish Ta­nosh and Mongasht anticlines) compared to the water samples of Kamarderaz anticline and Naal-e-Asbi syncline indicates the possibility that karst aquifers of the region are recharged from the Mongasht anticline and that there is a hydraulic relation­ship between these structures. D-excess and δ18O show a linear trend, illustrating the effect of altitude difference on isotopic content and recharge sources. The major and minor changes in the concentration of ions, the isotopic content of groundwa­ter and the relationship between TDS and δ18O and d-excess and δ18O indicate the mixing and recharging of karst aquifers (Shavish-Tanosh, Kamarderaz and Naal-e-Asbi aquifers) from the Mongasht karst aquifer and their hydraulic connection.