HYDROGEOCHEMICAL RECONNAISSANCE OF ARSENIC CYCLING IN HYDROTHERMAL SYSTEMS OF TAIWAN

The distribution of major and minor solutes (including arsenic (As)) was studied in hydrothermal systems of Taiwan to understand the elemental cycling, arsenic fate and transport and their potential impact to ambient surface hydrological systems. Water samples were collected from sixteen hydrothermal springs that are located in the various geological settings of Taiwan. While, many of the springs were analyzed to be strongly acidic (pH<3), and of H-SO4 type (e.g. springs at Taipu, Beitou and Yangmingshan). Hydrothermal springs at the locations of Jiben, Antung and Kuantzeling are slightly to medium alkaline in nature (pH>8). In contrast, many hydrothermal springs (e.g. Wulai, Hongye, Taitung and Hualien, Rueisuei, Chunglun and Biolai) are found to be circum-neutral (pH 6.47-7.41). These springs are mostly of Na-HCO₃ and Na-Cl-HCO₃ type. The spring water is mainly enriched with alkali metal and alkali earth metal. All of the sampled locations were found to be enriched with As, with the highest concentration found at Beitou (1.456 mg/L). Most of the sampled locations have the hydrothermal spring waters dominated by As(III). The mean±sd of As concentrations in hydrothermal spring of igneous rock region exhibit higher concentrations (0.69±0.71 mg/L) followed by a decreasing order in sedimentary (0.16±0.14 mg/L) and metamorphic (0.06±0.02 mg/L) terrains.