中台灣竹山至溪頭雨水化學的時空變異

全球氮量沉降的不斷增加，是當前重要的環境議題。台灣屬高氮沉降地區之一，但氮的沉降並非均質的，而是具有空間和時間上的差異。本研究選擇在竹山溪頭地區，從最接近農業和工業區域海拔100 m竹山樣區，沿海拔梯度上升至最高處1800 m的豬彎樣區，共選擇七個樣區，架設雨量收集桶收集雨水，分析雨水中的陽離子 (K+、Na+、Ca2+、Mg2+和NH4+)、陰離子 (Cl-、SO42-、NO3-和HCO3-)、pH值及電導度，主要目的為了解雨水化學組成及海拔如何影響氮沉降。本研究於2016年至2017年，研究期間內，竹山溪頭地區不同海拔年雨量為2632 - 3,406 mm，雨水pH介於5.12至7.18之間，呈弱酸性至中性。雨水中離子以HCO3-、NH4+、Ca2+、NO3-與SO42-為主要組成。雨水的離子濃度有季節性的變化，3-4月以春季鋒面為主要降雨型態，受到乾沉降累積及農業活動等影響，各離子濃度高；5-6月之梅雨所帶來的雨量多，造成離子的稀釋，雨水中各離子濃度低；雷陣雨和西南季風是7-9月的主要降雨型態，此時雨水離子濃度亦較低；颱風雨水受到海洋影響，Cl-、Na+濃度高；10-2月為乾季，受到降雨間隔長且雨量少等因素，各離子濃度高。海拔上的變異方面，Cl-、Na+受到距海遠近的影響，離子濃度隨海拔增加而減少；雨水中的Mg2+、Ca2+、K+、HCO3-和小範圍的自然或人為活動有關，與海拔的關係較低；NO3-、SO42-、NH4+，隨海拔增加，人為活動的減少而離子濃度降低。2016年至2017年竹山溪頭地區總無機氮沉降量為14.6 - 40.9 kg N ha-1 yr-1，總硫沉降量為5.4 - 13.2 kg S ha-1 yr-1，屬於高氮、硫沉降區，且氮、硫沉降量隨海拔增加而下降。

關鍵字

氮沉降；海拔；雨水化學；時間變異；空間變異

並列摘要

Increasing nitrogen deposition is one of important environmental issues worldwide. Taiwan is one of the areas that affected with have high nitrogen deposition. However, the nitrogen deposition might vary with spatial and temporal factors. In this study, we collected precipitation along an elevation gradient ranged from 100 m which was closest to the agricultural and industrial areas to 1800 m which was located in the mid-elevation mountainous regions to identify how elevation affects nitrogen deposition under an annual determination. Cations (K+, Na+, Ca2+, Mg2+, and NH4+), anions (Cl-, SO42-, NO3- and HCO3-), pH and electric conductance (EC) of precipitation water were analyzed. During the study period, the annual rainfall is between 2,632 and 3,406 mm at Zhushan-Xitou area, and the rainwater pH ranged from 5.12 to 7.18. The ions in rainwater are mainly composed of HCO3-, NH4+, Ca2+, NO3- and SO42-. The concentration of ions in rainwater has a seasonal change. We found the ions concentration from March to April is high, which is affected by dry deposition and agricultural activities. Ions concentration from May to June is low, due to high rainfall amount, which causes the ions to dilute. The thunderstorm and the southwest monsoon are the main rainfall patterns from July to September. At this time, the rain ion concentration is also low. The rainfall during typhoon events is mainly influenced by the ocean with high Na+ and Cl- concentration. The dry season is from October to February, and the concentration of each ion is high due to factors such as long rain interval and low rainfall amount. Regarding the altitudinal effect, Na+ and Cl- are affected by the distance from the sea, and the ion concentration decreases with the elevation. Mg2+, Ca2+, K+ and HCO3- has a low relationship with altitude, which associated with a small range of natural or man-made activities and; NO3-, SO42- and NH4+ concentration decreases with the elevation. The depositions of nitrogen and sulfur in 2016 and 2017 were 14.6 - 40.9 kg N ha-1 yr-1and 5.4 - 13.2 kg S ha-1 yr-1, respectively.