Ecohydrological processes are often evaluated by studying the fate of stable water isotopes. However, isotopic fractionation during evaporation is often ignored or simplified in current models, resulting in simulation errors that may be propagated into practical applications of stable isotope tracing. In this study, we adapted and tested the HYDRUS-1D model, a numerical model widely used to simulate variably-saturated water flow and solute transport in porous media, by including an option to simulate isotope fate and transport while accounting for evaporation fractionation. The numerical results obtained by the adapted model were in excellent agreement with existing analytical solutions. Additional plausibility tests and field evaluation further demonstrated the adapted model's accuracy. A simple particle tracking algorithm was also implemented to calculate soil water's transit times and further validate the modified model's results. Transit times calculated by the particle tracking module (PTM) were similar to those estimated by the isotope peak displacement method, validating the applicability of the PTM. The developed model represents a comprehensive tool to numerically investigate many important research problems involving isotope transport processes in the critical zone.

生态水文过程通常通过研究稳定水同位素的归宿来评估。然而，蒸发过程中的同位素分馏在当前模型中经常被忽略或简化，导致模拟错误可能会传播到稳定同位素示踪的实际应用中。在这项研究中，我们调整并测试了 HYDRUS-1D 模型，这是一种广泛用于模拟多孔介质中可变饱和水流和溶质传输的数值模型，包括在考虑蒸发分馏的同时模拟同位素归宿和传输的选项。调整后的模型获得的数值结果与现有的解析解非常吻合。额外的合理性测试和现场评估进一步证明了适应模型的准确性。还实施了一个简单的粒子跟踪算法来计算土壤水的传输时间并进一步验证修改后的模型的结果。粒子跟踪模块 (PTM) 计算的传输时间与同位素峰值位移法估计的传输时间相似，验证了 PTM 的适用性。开发的模型代表了一种综合工具，可以对涉及临界区同位素传输过程的许多重要研究问题进行数值研究。