以天然示蹤劑之端點混合分析法驗證農業用水之循環性—以彰化扇頂區為例

Abstract

本研究利用以氫氧同位素及氯離子建構而成的端點水源混合分析技術，進行彰化扇頂區地下水及八卦山地下水之補注來源分析。進一步，本研究探究濁水溪溪水、八卦山地下水與彰化扇頂區地下水三者間之關聯。結果顯示，八卦山地下水約有47% 來自雨水入滲，53% 來自引來的濁水溪溪水。濁水溪溪水是彰化平原地下水之主要補注源，約占總補注量的68%；其中，約有38% 來自河床溪水直接補注，另外30% 來自八卦山上來自濁水溪的灌溉水。也就是說，濁水溪溪水可被引至八卦山進行農業灌溉，之後灌溉水入滲形成地下水進而形成彰化平原地下水的補注水源。本水源分析研究不僅半定量證明濁水溪溪水對彰化平原地下水的重要性，也驗證了農業灌溉水的循環性。 This study employed the end member mixing analysis (EMMA) approach constructed with hydrogen/oxygen isotopes (δ18O/δ2H) and chloride-ion (Cl-) concentration to study the sources of groundwater in proximal-fan region and Bagua Tableland in Changhua County, Taiwan. This study also depicted the relationship among Zhuoshuixi stream water, Bagua Tableland groundwater, and plain groundwater in the proximal-fan region. The results indicate that approximately 47% of Bagua-Tableland groundwater comes from rainwater infiltration, and the remaining 53% from Zhuoshuixi stream water. The Zhuoshuixi stream water is the main source recharging groundwater in Changhua Plain, accounting for 68% of the total recharge of the proximal-fan groundwater. Of 68%, approximately 38% comes from direct recharge via the riverbed, and other 30% comes from the Bagua Tableland groundwater containing the stream water derived from the Zhuoshuixi. In other words, Zhuoshuixi stream water can be streamed to Bagua Tableland for irrigation. Thereafter, part of and the irrigation water may percolate to form groundwater of the Bagua Tableland, which then recharges groundwater in the Changhua Plain. This study not only semi-quantitatively confirms the importance of stream water of Zhuoshuixi to groundwater of Changhua Plain, but also verifies the circularity of agricultural irrigation water.