Investigating the Origin and Interaction between Karstic and Alluvial Aquifers in NW of Zagros Mountain Range, Iran, Using Isotopic and Geochemical Tools

Zagros mountain range (ZMR) contains the most karst carbonate formations in Iran. Because of the broad expansion of folded and fractured carbonate rocks, well-developed karstic aquifers occur in NW of ZMR which is reflected in the existence of many karstic springs with large discharge (up to 6 m3/s). These important karstic formations in Paveh (PV), Javanrood (JR), Ravansar (RS) and Sarpol Zahab (PZ) study areas supply water for residents and may be a recharge source for the adjacent alluvial aquifers. Recognizing the recharge areas of these karstic springs and aquifers are very important for protection of water resources. A narrow range of isotopic compositions in JR (δ18O values of -7.5 to -7.0‰ and δ2H values of -38 to -35‰) and PV regions (δ8O values of -7.5 to -6.3‰ and δ2H values of -40 to -34‰) indicates the same origin for water for springs and rivers in these areas. The wider isotopic range of δ18O (-8.1 to -5.6‰) and δ2H (-46 to -26‰) in RS and PZ regions (δ18O values of -6.8 to -3.9‰ and δ2H values of -36 to -22‰), indicate the existence of different recharge areas for the aquifers in these areas. PZ is the only study area that has 5 alluvial springs and their isotopic compositions indicate the alluvial aquifer is fed by discharge from the underneath karstic aquifer. The good correlation between altitude and isotopic composition in springs indicates that the altitude of recharge is the main factor controlling the isotopic composition of the water in the study areas