Spatial distribution of stable isotopes (18O and 2H) in precipitation and groundwater in Iran

Iran is a semi-arid and arid country which always faces a water shortage crisis. Thus, the water resources in Iran should be studied by accurate methods such as stable isotope techniques. In precipitation sampling stations across Iran, the δ18O (ranges from −16.3 to −0.3 ‰, −4.9 ‰ average), δ2H (−114 to –13 ‰, −24.2 ‰ average) and d-excess (−2.1 to –22.7, 16.5 ‰ average) values are higher compared to δ18O (ranges from −10.9 to −3.1 ‰, −6.7 ‰ average), δ2H (−71 to −6 ‰, −37.4 ‰ average) and d-excess (1.0 to –21.6 ‰, 14.9 ‰ average) values in groundwater stations. Stable isotope distribution maps in precipitation and groundwater were also developed for Iran. The stepwise technique was used to study the role of parameters influencing stable isotopes in Iran precipitation. Results show the dominant role of temperature, elevation and latitude as well as ‘cP and MedT’ air masses mixture on stable isotope values in precipitation. Furthermore, the contribution percentage of each air mass which influences Iran in groundwater resources recharge was studied using ‘Simmr’ package in R programming language. Finally, the accuracy of the developed stable isotope distribution maps was validated.伊朗属于半干旱与干旱国家，长期面临水资源短缺危机。因此，需借助稳定同位素技术（stable isotope techniques）这类精准方法开展伊朗水资源相关研究。伊朗全境降水采样站的δ¹⁸O值（范围为-16.3‰至-0.3‰，平均值为-4.9‰）、δ²H值（范围为-114‰至-13‰，平均值为-24.2‰）及氘盈余（d-excess）值（范围为-2.1‰至-22.7‰，平均值为16.5‰），均高于地下水采样站的δ¹⁸O值（范围为-10.9‰至-3.1‰，平均值为-6.7‰）、δ²H值（范围为-71‰至-6‰，平均值为-37.4‰）及氘盈余值（范围为1.0‰至-21.6‰，平均值为14.9‰）。本研究还针对伊朗绘制了降水与地下水的稳定同位素分布图。采用逐步分析法（stepwise technique）探究了影响伊朗降水中稳定同位素分布的参数作用机制。结果显示，气温、海拔、纬度以及cP与MedT气团的混合作用，是调控降水中稳定同位素值的主导因素。此外，本研究借助R编程语言（R programming language）中的"Simmr"包，分析了影响伊朗地下水资源补给的各气团贡献率。最终，对所绘制的稳定同位素分布图的精度进行了验证。