[AHW24-P05] On concentration and origin of chloride ion in small rivers in Jyoboji area, Fujioka, Gunma, Japan
Keywords:stream water, chloride ion, dissolved load, stable isotopes of water, Yasio mineral springs, deep-seated fluid
The concentration of chloride ion of Yashio mineral springs were between 4,798 mg/L and 11,892 mg/L in August, and between 5,162 mg/L and 11,032 mg/L in December. The concentration of chloride ion was very high in the streams; for example, in Minamizawa-gawa, the maximum concentration of chloride ion ranged up to 632.5 mg/L in July, while up to 213.7 mg/L in December. The load of chloride ion in Minamizawa-gawa was calculated to be as much as 45 kg/day in December, accounting for 90 % of the total load of chloride ion transported by these ten streams. In spite of being a short stream 1 km long, the hydrogen (δD) and oxygen (δ18O) isotopic ratios of Minamizawa-gawa in December showed a sharp increase from -54.5 ‰ and -8.0 ‰ in headwaters to -46.7 ‰ and -7.3 ‰ at a downstream end portion, respectively. In addition, the Li/Cl ratio of Minamisawa-gawa was found to be more than 0.001 for most of its watercourse with a maximum ratio of 0.0018 at a downstream end portion. These characteristics of the chloride ion, δD and δ18O isotopes, and Li/Cl ratio are attributed to the deep-seated fluid which flows upward through the Sambagawa crystalline schists and mixes with shallow water bodies.