Spatial Variation and Controlling Parameters of δ18O and δ2H Signatures in Surface Water Resources Across Iran

Surface water beside groundwater is dominant in providing water supply in Iran. Hence, for better management of surface water bodies in Iran, the stable isotope technique as an accurate method has been used to study these valuable water resources. The influence of moisture sources on surface water has been reviewed by comparing stable isotope signatures in surface water resources with Iran's MWLs, GMWL, and EMMWL. In addition, the contribution percentage of each air mass (precipitation events originate from each air mass) in the recharge of main rivers across Iran was calculated using the mixing model "Simmr-package" in R. In the Southern Zagros region, the role of cT air mass was dominant, while in the Western Zagros, the role of cP air mass was significant. However, the roles of cP and mP air masses were dominant in the North of Iran. Besides moisture origin, the evaporation effect on surface water resources was also studied. Plotting the average stable isotope content of surface water resources in each mega basin on Iran meteoric water line (IMWL) showed that surface water sources belonging to the Caspian Sea and Urmia lake basins had the most depleted isotope values. However, the surface water resources in the Persian Gulf and the Oman Sea basin as well as the Eastern border basin showed enriched stable isotope values and deviation from IMWL due to the extreme evaporation effect. In conclusion, stable isotopes in surface water resources across Iran were affected simultaneously by evaporation and precipitation moisture source variations.