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

Water

Yuki Tosaki⁴  Norio Tase³  Akihiko Kondoh²  Kimikazu Sasa¹  Tsutomu Takahashi¹ 

[1] Tandem Accelerator Complex, Research Facility Center for Science and Technology, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan; E-Mails:;Center for Environmental Remote Sensing (CEReS), Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan; E-Mail:;Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan; E-Mail:;Crustal Fluid Research Group, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan

关键词: groundwater flow system;    residence time;    environmental tracer;    ³⁶Cl;    accelerator mass spectrometry (AMS);   

DOI  :  10.3390/w3010064

来源: mdpi

【 摘 要 】

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.

【 授权许可】

CC BY   
© 2011 by the authors; licensee MDPI, Basel, Switzerland.