Groundwater age determination using 85Kr and multiple age tracers (SF6, CFCs, and 3H) to elucidate regional groundwater flow systems
Groundwater age determination using 85Kr and multiple age tracers (SF6, CFCs, and 3H) to elucidate regional groundwater flow systems
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DOI：
10.1016/j.ejrh.2017.05.003
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发表时间：
2017-08
期刊：
影响因子：
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通讯作者：
M. Kagabu;Midori Matsunaga;K. Ide;N. Momoshima;J. Shimada
中科院分区：
文献类型：
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作者：
M. Kagabu;Midori Matsunaga;K. Ide;N. Momoshima;J. Shimada
研究区域日本南部的熊本地区（945平方公里），几乎100%的饮用水依赖地下水。研究重点在熊本地区对地下水测年示踪剂（85Kr、氯氟碳化合物[CFCs]、六氟化硫[SF6]和3H）进行同步测量，以阐明区域地下水流动系统并获得改进的地下水年龄估计。地下水年龄是根据三个区域九个地点的 85Kr 浓度估算的：沿着两条主要地下水流线（A-A' 和 B-B'）；该地区的新水文见解无法使用 CFC 或 SF6 估算地下水年龄，特别是在城市地区，因为几乎整个研究区域的浓度都被人为添加。然而，即使在这些区域情况下，根据 85Kr 测量，A-A’线上的三个位置（分别是地下水补给区、排放区和地下水停滞区）也获得了大约 16 年、36 年和不少于 55 年的表观年龄。使用 3H 观测时间序列的集总参数模型分析也支持了这一趋势。相比之下，沿着B-B'线，包括补给排放区在内的三个地点的地下水年龄不低于55年，其中未检测到CFC和SF6，这意味着旧地下水：这也是发生反硝化的区域。在C区，从浅水区获得了非常年轻的地下水，并且在更深的地方检测到了较古老的地下水，这得到了地下水中NO3−N浓度的长期波动的支持。本研究结果可以有效地作为研究区地下水可持续利用和地下水水质保护的“时间轴”，该地区地下水几乎占饮用水资源的100%。
Study regionThe Kumamoto area (945 km2) in the south of Japan, where almost 100% of the drinking water is dependent on groundwater.Study focusSimultaneous measurement of groundwater dating tracers (85Kr, chlorofluorocarbons [CFCs], sulphur hexafluoride [SF6], and3H) was performed in the Kumamoto area, to elucidate the regional groundwater flow system and obtain improved estimates of groundwater ages. The groundwater ages were estimated from the85Kr concentrations in nine locations from three areas: along two major groundwater flow lines (A–A’ and B–B’); and a high-nitrate-input recharge area (C area).New hydrological insights for the regionThe groundwater ages could not be estimated using CFCs or SF6, particularly in the urban areas because of artificial additions to the concentration over almost the entire study area. However, even in these regional circumstances, apparent ages of approximately 16, 36, and not less than 55 years were obtained for three locations on the A–A’ line (recharge area, discharge area, and stagnant zone of groundwater, respectively) from85Kr measurements. This trend was also supported by lumped parameter model analysis using a time series of3H observations. In contrast, along the B–B’ line, the groundwater age of not less than 55 years at three locations, including the recharge to discharge area, where CFCs and SF6were not detected, implies old groundwater: this is also the area in which denitrification occurs. In the C area, very young groundwater was obtained from shallow water and older groundwater was detected at greater depths, as supported by the long-term fluctuations of the NO3−–N concentration in the groundwater. The results of this study can be effectively used as a “time axis” for sustainable groundwater use and protection of groundwater quality in the study area, where groundwater accounts for almost 100% of the drinking water resources.