The nature and extent of bomb tritium remaining in deep vadose zones: A synthesis and prognosis

Tritium present in deep vadose zones is a useful tracer for estimating groundwater recharge, but its full utility is constrained by not knowing where and for how long the tritium tracing method remains applicable. We obtained 44 tritium profiles from 17 globally distributed sites with vadose zone thicknesses of 13−624 m and used transport models to estimate the number of years that tritium may still be useful. Results show that the method may still be usable for 26 of 44 soil profiles surveyed, mainly in China, Australia, USA, South Africa, and Senegal, with a remaining useful period of between 6 and 83 years. We also developed a statistical model that uses outputs from a hydrological model to predict the applicability of the tritium tracing method. Global implementation of the statistical model showed that the method remains usable at 20% of Earth’s land mass (excluding Antarctica and Greenland) over the next few decades.

Methods
The dataset – soil water tritium profiles (n = 40) – was compiled from the peer-reviewed literature (see Text S2 in manuscript). This was supplemented with 4 profiles from study sites in Changwu, Shaanxi Province, China.

The dataset was compiled by co-authors Yanan Huang ([e-mail]) and Zhi Li ([e-mail]) of Northwest A&F University.

深包气带（deep vadose zone）中的氚（tritium）是估算地下水补给（groundwater recharge）的有效示踪剂（tracer），但其全部应用潜力受限于无法明确氚示踪法的适用范围与持续时长。我们从全球17个分布站点获取了44条氚剖面，这些站点的包气带厚度介于13−624米，并利用溶质运移模型（transport models）估算了氚示踪法仍可发挥作用的年限。结果显示，44条土壤剖面中有26条仍可适用该方法，主要分布在中国、澳大利亚、美国、南非与塞内加尔，剩余有效时长为6至83年。我们还构建了一套统计模型，该模型借助水文模型（hydrological model）的输出结果来预测氚示踪法的适用性。对该统计模型的全球应用结果表明，未来数十年内，全球20%的陆地面积（不含南极洲与格陵兰岛）仍可使用该方法。

方法
本数据集包含土壤水氚剖面（n=40），从同行评议文献中汇编得到（详见稿件文本S2），并补充了中国陕西省长武地区研究站点的4条剖面。
本数据集由西北农林科技大学的黄亚南（[e-mail]）与李智（[e-mail]）两位共同作者汇编完成。