| Summary: | 碩士 === 國立中正大學 === 應用地球物理研究所 === 102 === Diel changes in concentration of trace elements were investigated in North Huanghsi River, which is located at Tatun Volcanic Group and drains the volcanic geothermal spring water northward to the coastal area. A 24-h sampling procedure was conducted at two sites: BY (the upstream site) and SH (the downstream site).
According to the results of chemical analysis, only Fe, As and V show considerable diel concentration cycle while the others including rare earth elements demonstrate insignificant diel change. Along with the increase of pH value at night, the concentration of Fe decreases due to the transformation from Fe2+ (higher solubility) to Fe3+ (much lower solubility). Therefore, iron hydroxide would be significantly generated at night and would probably dominate the adsorption behavior of ions. In general, iron hydroxide is in the form of positive charged ion under the low pH environment. On the contrary, As is an anionic complex. It is expected that As can be adsorbed and consequently precipitated with iron hydroxide in the form of negative charged ion. Therefore, a lower concentration of As was observed in the late afternoon in this study. In addition, it is interesting that V demonstrates an opposite behavior with As during the diel cycle. This implies that V is in the form of positive charged ionic complex under the low pH environment and shows a quite different cycle from As.
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