為了解合歡山臺灣冷杉 (Abies kawakamii) 林冠與降雨化學交互作用，本研究於 2011年1月至12月一年期間，收集合歡山臺灣冷杉林外降雨、林內穿落水與幹流水雙週水 樣，進行水化學分析。研究結果顯示，合歡山降雨年平均電導度僅為 3.3 ± 4.6 μS/cm，平 + 均酸鹼值為5.78 ± 0.61，呈弱酸性。雨水中陽離子平均濃度以NH4 之5.64 ± 14.92 μeq/L為最 2+ + + 2+ - 高，其它依次為Ca > Na > K ，Mg 則低於檢測低限。而陰離子平均濃度以HCO 之32.20 3 ± 14.21 μeq//L 為最高，其它依次為SO 2- > NO - > Cl-。此些結果顯示合歡山降雨溶解離子濃 4 3 度偏低，明顯低於其它臺灣中低海拔森林降雨溶解離子濃度。合歡山臺灣冷杉林內穿落水 與幹流水中年平均電導度略微增加，平均酸鹼值略微降低，仍呈弱酸性。穿落水與幹流水 + 中陰、陽離子平均濃度皆較雨水中各項離子濃度增加許多，其中陽離子以K 濃度增加最 2 + 2 + - 為明顯，其次為Mg 與Ca ；陰離子則以HCO3濃度增加最為明顯，顯示合歡山臺灣冷杉林 冠與雨水之交互作用以此些離子交換為主。合歡山臺灣冷杉林外降雨、林內穿落水與幹流 + 2 + 2 + 水化學雙週變化亦顯示，臺灣冷杉林冠與降雨之化學交互作用陽離子以K 、Ca 與Mg 交 - 2- - 換為主，陰離子則以HCO3 交換為主，而SO4 與NO3 於冬春季濃度較高現象，可能顯示境 外遠程傳輸的影響。

In order to understand interactions between canopy of Taiwanese fir (Abies kawakamii) and rainfall, rainfall, throughfall and stemflow samples were collected bi-weekly and analyzed for major ions, from January to December, 2011 at Mt. He-Huan area. Results showed that average conductivity of rainfall was only 3.3±4.6 μS/cm, average pH was 5.78±0.61 and classified as weakly acidic, in the alpine region. The highest average cation concentration of rainfall was NH + (5.64±14.92 μeq/L), followed by Ca2+ > Na+ > K+, and Mg2+ was non-detectable. 4 The highest average anion concentration was HCO - (32.20±14.21μeq/L), followed by SO 2- > 3 4 NO - > Cl-. These results showed that rainfall was relatively low in ionic concentration and less 3 affected by pollution in this alpine ecosystem, and ionic concentration was lower than that in forested ecosystems at lower altitudes of Taiwan. These phenomena were possibly due to greater distance of Mt. He-Huan site to pollution sources, and also possibly due to releasing effects as cloud uplifting toward the central mountain range. Compared to that of rainfall, average conductivity of througfall and stemflow were slightly increased, while average pH decreased slightly, and average cation and anion concentrations of throughfall and stemflow also showed an increase, indicating canopy interactions between rainfall and Taiwanese fir forest. The biggest increase in cation concentration of throughfall and stemflow was K+, followed by Mg2+ and Ca2+, while the biggest increase in anion concentration was HCO -, indicating major interaction were 3 caused by exchange of these species. Changes in bi-weekly water chemistry of rainfall, throughfall and stemflow also showed that interactions between rainfall and Taiwanese fir canopy were mainly caused by exchanges of K+、Ca2+ and Mg2+ for cations, and HCO - for anions. 3 Nevertheless, higher concentration of SO 2- and NO - in rainfall, throughfall and stemflow in 4 3 winter/spring could be affected by long distance atmospheric deposition.