Determining variations in groundwater replenishment over a variety of time scales remains a challenge in the management and protection of groundwater resources. Specifically, capacity to use hydraulic data collected in small windows of time to infer long‐term changes can be limited by system responses. Groundwater ages offer an alternative approach as they represent the time since recharge occurred. Here we use spatial variations in groundwater ages and environmental tracer concentrations to infer temporal variations in groundwater recharge and apply the method to a mine site in northwest Australia, where a stream has been modified from ephemeral to perennial, resulting in enhanced recharge to groundwater. Measurements of ¹⁴C and CFC‐12 at five transects along an ephemeral stream were interpreted with the new model to identify recharge rates and the proportion of recharge attributable to enhanced versus natural recharge from flood events. Enhanced recharge varied between 0.03 and 0.66 m/year compared to flood‐generated recharge values ranging between 0.07 and 1.3 m/year. Our results show that spatial variations of groundwater ages and environmental tracer concentrations preserve information about past flow regimes. While our study has demonstrated decadal variations in recharge, application of the method on larger scales could infer much greater extent of temporal variability in recharge, with the potential for significant insight into climate effects on groundwater.

中文翻译：

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利用地下水年龄的空间变化评估地下水补给量的时间变化

在各种时间范围内确定地下水补给量的变化仍然是管理和保护地下水资源的挑战。特别是，使用系统在较小的时间范围内收集的水力数据来推断长期变化的能力可能受到限制。地下水年龄提供了一种替代方法，因为它们代表补给发生的时间。在这里，我们使用地下水年龄和环境示踪剂浓度的空间变化来推断地下水补给量的时间变化，并将该方法应用于澳大利亚西北部的一个矿山，该矿山的水流已从短暂过渡到多年生，从而增强了对地下水的补给。三围¹⁴使用新模型解释了沿短暂河流的五个断面处的C和CFC-12，以识别补给率以及可归因于洪水事件的补给量与自然补给量的补给比例。相比于洪水产生的补给值介于0.07和1.3 m /年之间，增强的补给在0.03和0.66 m /年之间变化。我们的结果表明，地下水年龄和环境示踪剂浓度的空间变化保留了有关过去流态的信息。尽管我们的研究表明补给量存在年代际变化，但该方法在较大规模上的应用可能会推断补给量的时间变化程度更大，并且有可能深入了解气候对地下水的影响。