Water quality classification and vertical distribution of hot springs using hydrochemical methods and multivariate analysis at the Beppu hydrothermal area, Japan

Abstract

To evaluate changes in hot spring water quality and estimate the flow paths from its vertical distribution, multivariate analysis (Hierarchical cluster analysis and Factor analysis) and hydrological analysis were conducted using 52 hot spring wells in the Beppu hydrothermal area, Japan. Hot spring water quality was classified by five groups (G1, G2a, G2b, G2c, and G3). G1 and G2a are distributed in the Kamegawa thermal zone, and G3 and G2c are mainly found in the Beppu thermal zone. G2b is observed in both thermal zones. The water types of the hot springs were almost consistent with those in the 1980s but changed from Cl to HCO₃ type in the Beppu thermal zone. The vertical distribution of the hot springs implies that there are two distinct flow paths in the Beppu thermal zone, and confirmed the seawater mixing in the well located near the shore. The mixing rate between the seawater and hot spring water was calculated by Cl^－ concentration, which was 12% of seawater.