Water 2011, 3(1), 64-78; doi:10.3390/w3010064
Article

Distribution of 36Cl in the Yoro River Basin, Central Japan, and Its Relation to the Residence Time of the Regional Groundwater Flow System

Received: 10 December 2010; in revised form: 22 December 2010 / Accepted: 24 December 2010 / Published: 6 January 2011
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: This study investigates the potential of 36Cl in tracing young groundwater with residence times of up to ~50 years. Groundwater samples were obtained from 16 irrigation wells in paddy fields located within an upland–lowland system in the Yoro River basin, Central Japan. The 36Cl/Cl ratios were in the range of 17 to 362 × 10−15. Among the samples with higher Cl concentrations (>10 mg/L), two samples showed high nitrate concentrations as well (>30 mg/L). Except for these samples, the distribution of 36Cl in groundwater was essentially consistent with previous tritium concentration data measured in 1982 and 1994, considering the time that has elapsed since these earlier measurements were performed. 36Cl/Cl values were less than 30 × 10−15 in lowland areas, with higher values in and around upland areas. The results indicate longer residence times in the regional groundwater flow system (>50 years) than those estimated in previous studies, especially in the area west of the Yoro River. The results demonstrate the ability of 36Cl to trace young groundwater flow, particularly because high values of bomb-derived 36Cl/Cl are easily discriminated from pre-bomb water with low 36Cl/Cl values. Because of its very long half-life (3.01 × 105 years), 36Cl remains even after tritium is no longer available.
Keywords: groundwater flow system; residence time; environmental tracer; 36Cl; accelerator mass spectrometry (AMS)
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MDPI and ACS Style

Tosaki, Y.; Tase, N.; Kondoh, A.; Sasa, K.; Takahashi, T.; Nagashima, Y. Distribution of 36Cl in the Yoro River Basin, Central Japan, and Its Relation to the Residence Time of the Regional Groundwater Flow System. Water 2011, 3, 64-78.

AMA Style

Tosaki Y, Tase N, Kondoh A, Sasa K, Takahashi T, Nagashima Y. Distribution of 36Cl in the Yoro River Basin, Central Japan, and Its Relation to the Residence Time of the Regional Groundwater Flow System. Water. 2011; 3(1):64-78.

Chicago/Turabian Style

Tosaki, Yuki; Tase, Norio; Kondoh, Akihiko; Sasa, Kimikazu; Takahashi, Tsutomu; Nagashima, Yasuo. 2011. "Distribution of 36Cl in the Yoro River Basin, Central Japan, and Its Relation to the Residence Time of the Regional Groundwater Flow System." Water 3, no. 1: 64-78.

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