Environmental isotope study of groundwater discharge from the large karst springs in West Syria: a case study of Figeh and Al-sin springs

Environmental isotopes (δ¹⁸O, δD and ³H) in precipitation and groundwater were integrated for the description of groundwater discharge from the large karst springs of Figeh and Al-sin located in West Syria. The two springs are considered as the most important springs in this Middle East country due to their huge discharge. The δ¹⁸O values are −8.91 and −6.49‰ for Figeh and Al-sin, respectively. The regression line for both precipitation and groundwater is described by the equation: δD = 7.9δ¹⁸O + 19.7, which shows no evaporation during precipitation and suggests that the groundwater is mainly from direct infiltration of precipitation. The altitude gradients in the precipitation were estimated to be −0.23‰/100 m for δ¹⁸O. The main recharge areas are 2,100 and 750 m.a.s.l., for Figeh and Al-sin springs, respectively. The tritium concentrations in groundwater are low and very close to the rainfall values of 4.5 and 3.5 TU for Bloudan and Kadmous meteoric stations, respectively. Adopting a model with exponential time distribution, the main residence time of groundwater in Figeh and Al-sin springs was evaluated to be 50–60 years. A value of around 3.9 and 4.2 billion m³ was obtained for Figeh and Al-sin, respectively, as the maximum groundwater reservoir size.