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年度	99	專案性質	實驗性質
專案類別	研究專案	研究主題	調查
申請機構	國立中正大學	申請系所	地球與環境科學系
專案主持人	呂學諭	職等/職稱	副教授
專案中文名稱	嘉南平原曾文溪流域含水層與地下水間之水-岩反應系統
中文關鍵字	嘉南平原；土壤連續萃取
專案英文名稱	Water-rock interaction between groundwater and soil in Cengwen River watershed, Chianan Plain
英文關鍵字	Chianan Plain；Soil Sequential Extraction Procedures
執行金額
執行期間	2010/12/29 至 2011/12/28
計畫中文摘要	台灣大量利用地下水做為飲用水之水源，但這些地下水中 Fe、Mn 以 及許多重金屬離子含量常有過高的趨勢，除人為污染的來源外，重金屬元 素多源自於天然地下水與圍岩之間的水－岩反應。常久以來，泥質沉積物 被認為是這些污染物的主要供應者，因此，由土壤釋出重金屬元素的研究 相形重要。本研究藉天然示蹤劑的概念做為探討這些議題的手段，並以曾 文溪流域做為研究地區。地下水質分析結果顯示，此區地下水以末次冰期 為界限，分為淺層含水層及深層含水層，淺層含水層因潟湖環境具有較高 的鹽度，但 As 與重金屬含量均低，深層含水層則因陸相沉積環境具有較 低的鹽度，但 As 與重金屬含量均高。藉由 BCR 溶出試驗之分析結果，主 要元素、Mn 與 Sr 在可交換相中含量較高，可能代表在 pH 值大於 8 且略 微氧化的環境； Fe、As 與其他重金屬元素以鐵錳氧化物形態存在；在有 機物相中富集的元素僅有 Th 與 Li。分層結果顯示，As 在深層含水層中的 平均含量約為淺層的 1.7 倍，但其他重金屬元素則約略相等或反序，此與 地下水質的分布有明顯差異。由稀土族元素的分析結果顯示，地下水含 As 量高者，幾乎沒有 Ce 負異常的現象。Ce 負異常指示水體曾發生過強烈的 氧化反應，顯示地下水體的 As 含量與氧化作用的發生有直接的關係。
計畫英文摘要	Groundwater is one of the major sources for supplying daily usage water of residents. However, the contaminants, such as Fe, Mn and heavy metals, are still a major issue in the coming years. These pollutants are generally recognized as being released by natural soils due to the water-rock interaction. In this study, a concept of natural tracer will be utilized to establish the water chemical model. Some ultra-trace metal elements, such as rare earth elements, are very suitable to be the natural tracers. The hydrochemistry of groundwater demonstrates that the shallow groundwater is salty but arsenic and heavy metals is depleted. On the contrary, the deep groundwater is enriched with arsenic and heavy metals.The results of BCR (European Community Bureau of Reference) sequential extraction procedure show that most of heavy metals are extracted from the phase of Fe-Mn oxides while Li and Th are enriched in the phase of organic matter. Alkali and calc-alkali elements are mainly extracted from exchangeable phase in shallow aquifer. They represent the quality of pore water. It is worth to notice that the heavy metals of the BCR extracted solutions from sediments do not have the corresponding distribution in spite of As. However, arsenic in deep aquifer is almost twice the concentration in shallow aquifer. This implies that the enrichment of arsenic in sediments is not the only factor to cause high arsenic in groundwater. Some other chemical reactions are significantly involved in the water-rock interaction system. The results of rare earth elements demonstrate an interesting fact that the groundwater samples with top three arsenic concentrations do not have considerable Ce negative anomaly. On the contrary, the groundwaters with bottom three arsenic concentrations show strong Ce negative anomaly. In general, Ce negative anomaly is an excellent indicator of oxidation in aquatic system, which means that the oxidation reaction is responsible to result in minimum arsenic concentration in groundwater.