Isotopic evidence to characterize the sources of sulfate ions in the carbonate aquifer system in Aleppo basin (North Syria)

Abstract

Sulfur and oxygen isotopic compositions of sulfate (δ34SSO4, δ18OSO4) and δ18OH2O, δ13CDIC have been used in conjunction with chemical data to constrain sulfate sources and geochemical processes in carbonate aquifers of the Aleppo basin in north Syria. The Aleppo basin comprises two limestone aquifers: the first one is shallow unconfined of Paleogene age and the second is deep confined of Upper Cretaceous age. The chemical data indicate that dissolution of carbonate and evaporites is the main process controlling groundwater quality. In the mainly unconfined modern groundwater, the wide range of δ34SSO4 values (10.39–17.6 ‰) indicates a variety of input sources. The likely sources of sulfur include meteoric precipitation and sewage waters which recharge the aquifer through Qweik River crossing the area. These waters have low SO42− concentration ( 20 mg/L). Sulfate increases in deep confined groundwater in some of which gypsum saturation is reached. The δ34SSO4 and δ18OSO4 are relatively constant with mean values of 18.5 and 13.5 ‰, respectively. This indicates that gypsum and anhydrite dissolution are the primary sources of sulfate. This water is associated with higher depleted value of δ18OH2O. The heavier δ13CDIC with mean value −1.8 ‰ and high Mg2+ concentration (~100 mg/L) in the high sulfate deep groundwater, indicates that the de-dolomitization reactions dominate along flow paths where sulfate concentrations increase.