Uncertainties in tritium mass balance models for groundwater recharge estimation
Uncertainties in tritium mass balance models for groundwater recharge estimation
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DOI：
10.1016/j.jhydrol.2019.01.030
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发表时间：
2019-04
影响因子：
6.4
通讯作者：
Zhi Li;S. Jasechko;B. Si
中科院分区：
文献类型：
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作者：
Zhi Li;S. Jasechko;B. Si
了解水穿过包气带所需的时间对于量化地下水补给率和评估含水层受污染的脆弱性很重要。氚质量平衡模型提供了测量驱动的土壤水速度估计，但这些地下水补给估计中包含的不确定性很少被研究。在这里，我们分析了从中国所在的黄土高原厚的非饱和带中收集的6个15m氚剖面，并比较了不同计算方法得到的补给率。根据非饱和区数据估算补给量的模型包括氚峰值法和氚储存法；利用饱和区数据估算补给量的模型包括现代地下水法和一种假定地下水在含水层中混合良好的方法。氚峰法提供了可靠的补给；然而，氚储存方法的补给是氚峰法的两倍。混合良好的水库方法高估了地下水的更新率，因为地下水在含水层中混合良好的隐含假设是不现实的。对于潜在补给量，降水氚重建带来了相当大的不确定性；而对于实际补给量估计，不确定性来自于模型假设与当地特征之间的补给机制不匹配。选择合适的氚质量平衡模型是估算补给量的关键。
Understanding the time that water takes to traverse the vadose zone is important to quantify groundwater recharge rates and to assess the vulnerability of aquifers to contamination. Tritium mass balance models provide measurement-driven estimates of soil water velocities, yet uncertainties embedded in these groundwater recharge estimates are rarely investigated. Here we analyze six >15-m tritium profiles collected from thick unsaturated zones located on China’s Loess Plateau and compare recharge rates obtained from various calculation approaches. Models used to estimate recharge based on unsaturated zone data include the tritium peak method and the tritium storage method; models used to estimate recharge using saturated zone data include the ‘modern groundwater’ method and a method that assumes groundwater is well-mixed in the aquifer. The tritium peak method presents reliable recharge; however, the recharge from the tritium storage method is two times of that from the tritium peak method. The well-mixed reservoir method overestimates groundwater renewal rates because the implicit assumption that groundwater is well-mixed in aquifers is not realistic. For potential recharge, considerable uncertainties arise from precipitation tritium reconstruction; while for actual recharge estimation, uncertainties come from the mismatched recharge mechanism between the model assumption and local characteristics. Selection of appropriate tritium mass balance models is of utmost importance for recharge estimation.