本研究試圖應用地下水體離子地球化學來探討火山地區之地下水行為，並討論火山活動對地下水之可能影響。本研究自2017年9月至2018年12月，採集大屯火山群南、北磺溪流域之地下水體，共採集348個樣品，分析其水體中陰陽離子濃度，結果顯示大屯火山地區北磺溪流域地下水體以馬槽溪為界，主要和火山氣體作用程度有關；南磺溪流域地下水離子濃度則自上游往下游遞增，與流徑長度有關。南、北磺溪流域離子化學特徵分別受到降雨雨量、水體的酸鹼度(pH)和溫度影響，雨季時，因降雨的稀釋作用使離子濃度下降，溫度高時，使離子濃度增高尤其是陽離子，酸鹼度減少硫酸根陰離子增加。而圍岩的岩性種類並不會造成任何差異。
本研究利用水體地球化學組成，將火山地區地下水體分類，發現大屯火山群地區地下水水體皆屬於熱液地下水，此外，北磺溪流域之大多地下水體陰離子SO42-含量高，顯示水體受到火山氣體影響，顯示該地區地層中裂隙較多，能提供火山氣體至地表逸散的路徑。
This study aims to use ion geochemistry of groundwater to explore the recharge mechanism of groundwater in the Tatun volcanic area and investigate the relationship between volcanic activities and groundwater. 348 water samples were collected and analyzed from the Northern and Sulfur Creeks watersheds during the period of September 2017 to December 2018. We found the concentrations of anion and cation of groundwater are clearly divided by the Macao Creek which is mainly attribute to volcanic gas emitting through fracture to the groundwater system in the Northern Sulfur Creek watershed. On the other hand, the spatial distribution of concentrations of anion and cation in groundwater of Southern Sulfur Creek watershed display an increase trend from the upstream area to the downstream region This distribution is associated with distances of water flow or the mean residence time. In general, the concentrations of ion in the Northern and Southern Sulfur Creeks watersheds are affected by rainfall amount, pH value and temperature of groundwater. However, no relationship can be established between host rock types and geochemistry of groundwater.
We have characterized all groundwaters in the study area as hydrothermal groundwater (HG) type according to their ion characteristics. However the HG in the Tatun volcano Group do exhibit an additional high concentrations of SO42- in particular area which may imply that the presence of highly fractured zone under. It may be worth testing to use this as an indicator of fractures by assistance with fully understood regional groundwater characteristics particular the mean residence time and recharge mechanism.
