“…Multivariate principal component analysis (PCA) was undertaken to examine major trends and interrelationships in the analysis results for each sample. The approach has been applied in many studies comparing the qualities of AMD, groundwater, and river water in mine areas [38][39][40]. Here, PCA was performed using the multivariate analysis software IBM SPSS Statistics 25 (IBM Japan, Ltd., Tokyo, Japan), and it was applied to four variables measured in situ (temperature, pH, EC, and Eh), the concentrations of seven major ions (Na + , K + , Ca 2+ , Mg 2+ , Cl − , HCO 3 − , SO 4 2− , and NO 3 − ), Si, three heavy metals (total Fe, Cu, Zn), and the isotopic ratios of δD and δ 18 O.…”