利用氮氧同位素鑑別地下水中硝酸鹽之來源與轉化：以南投農業區地下水為例

Abstract

本報告整理南投名間農作區與城鎮區地下水的 NO3-濃度及其氮、氧同位素組成，以說明 此地區地下水 NO3-污染狀況及探討地下水中 NO3-的來源及轉化。本報告區約有 54 %水樣之 NO3-濃度高於飲用水標準，主要發生在農作區內。由氮、氧同位素證據顯示，這些超標地下水中的 NO3-主要來自土壤有機物和化學肥料。同位素證據同時顯示農作區地下水中並未發生造成 NO3-濃度降低之脫氮或同化作用；反之，城鎮區之地下水則很明顯曾受到同位素分化作用。 This report integrated the concentration, and nitrogen and oxygen isotope compositions of groundwater’s NO3- in agricultural and urban regions of Ming-Jian, Nantou to illustrate the situation of NO3- pollution and the NO3- sources and transformation. The results indicate that nearly 54 % of NO3- determinations exceeded the criterion of drinking water, especially in agricultural region. The polluted groundwater mainly source NO3- from soil nitrogen and chemical fertilizer. The results also indicate the denitrification/assimilation that will reduce the NO3- concentration is ambiguous in groundwater of agricultural region, but the assimilation is significant in urban groundwater.