An in-depth understanding of complex karstic system evolutions of northwest Iran using stable isotopes (δ18O, δ2H, and δ13C) and hydrochemical techniques

In this study, main characteristics controlling the evolution of groundwater chemistry were assessed by employing hydrochemical methods along with environmental stable isotope (δ18O, δ2H, and δ13C) techniques in major and complex karstic resources in Paveh–Javanrud (PV─JR) area, northwest (NW) of Iran. Thirty-four water samples from caves, springs, and wells were collected during two seasons for major ions (cations and anions) as well as stable isotope investigations on December 2014 (wet season) and October 2015 (dry season). Additionally, nine samples were also acquired from monthly precipitation (January 2015 till November 2015) for isotopic analyses from PV climatology station. Determining meteoric water line of Paveh (PMWL, δ2H = 6.9 δ18O + 11.9, R2 = 0.97) indicates that the origination of air masses of the region was found to be Mediterranean Sea. Hydrogeochemical investigations, on the other hand, indicated that three major formations including a pure limestone, Bistoun formation (JKb), and two limestones with some sort of impurities, i.e., Ilam–Sarvak (KIl-KSv) and Goru (Gr.) affected the water resources of the region. Regarding δ18O and δ2H results, most of karstic resources are plotted near PMWL and represent depleted isotopic values due to recharging from high altitudes. Finally, carbon isotope investigation was also utilized to determine the main source of carbon which was found to be carbonate dissolution and C4 plants. Furthermore, the karst development type (less-, moderate-, and well-developed) of all formations were identified. Providing that isotopic findings are complementary to hydrochemical features, this study gives an in-depth understanding of vulnerable karstic terrains in NW Iran, which are highly important frameworks for effective water management.