合歡高山降雨與溪水化學初探

PRELIMINARY STUDY ON THE WATER CHEMISTRY OF RAINFALL AND STREAMFLOW AT THE ALPINE AREA OF HE-HUAN MT.

高世俊(Shih-Jiun Gao) ； 王立志(Lih-Jih Wang)

《中華林學季刊》 49卷4期 (2016/12) Pp. 365-377

摘要

為初探合歡高山地區降雨與二溪流水化學性質，本研究於2007年3月至2008年2月間，收集合歡山高山降雨，並於合歡山武嶺溪及小風口溪瓢取水樣，進行水化學分析。初步結果顯示，合歡山高山降雨年平均電導度僅為4.4±2.9 μS/cm，平均酸鹼值為5.05±0.47，呈弱酸性。水中陽離子平均濃度以Na^+ 之0.21±0.15 mg/L為最高，其它依次為NH_4^+ ＞ Ca^(2+) ＞ K^+，Mg^(2+) 則低於檢測低限。而陰離子平均濃度以HCO_3^- 之0.89±1.01 mg/L 為最高，其它依次為NO_3^- ＞ SO_4^(2-) ＞ Cl^-。此些結果顯示合歡山高山降雨溶解離子濃度偏低，尤其與臺灣中低海拔森林集水區降雨溶解離子濃度比較明顯更低，推測合歡山區離汙染源較遠，且雲雨氣團因地形抬升時，大部分溶解離子隨雨水降落所致。合歡山高山降雨化學月變化顯示，雨水酸鹼值以冬春季2-4月較低，其餘月份多高於5.0；電導度也以冬春季略高，其餘月份皆低，此現象顯示冬春季雨中離子含量較多，致酸離子SO_4^(2-) 與NO_3^- 濃度也以冬春季較高，是否因合歡山生態系位處於高山地區，但仍受遠程傳送酸性沉降影響，有待未來研究確定。而一年之中春季雨水中NH_4^+ 濃度則相對偏高，是否受當地農業施肥影響也有待未來研究了解。而研究期間雨水與溪流二者間水化學特性亦有顯著差異，小風口溪水化學與武嶺溪水化學亦明顯不同。小風口溪水平均電導度179.1±14.7 μS/cm，平均酸鹼值為7.48±0.49，呈中性，該溪水之陽離子平均濃度以Ca^(2+)之23.69±6.27 mg/L為最高，其它依次為Mg^(2+) ＞ Na^+，NH_4^+則低於檢測低限。而陰離子平均濃度以HCO_3^-之123.72±11.38 mg/L 為最高，其它依次為SO_4^(2-) ＞ NO_3^- ＞ Cl^-。武嶺溪水平均電導度61.9±9.6μS/cm，平均酸鹼值為7.08±0.40，亦呈中性。水中陽離子平均濃度以Ca^(2+)之9.89±3.03 mg/L為最高，其它依次為Mg^(2+) ＞ Na^+ ＞K^+ ＞ NH_4^+。而陰離子平均濃度也以HCO_3^-之36.34±5.20mg/L 為最高，其它依次為SO_4^(2-) ＞ NO_3^- ＞ Cl^-。武嶺溪水中陰陽離子濃度皆較小風口溪之離子濃度為低，可能因二溪流集水區地質、土壤及植群差異所致。至於合歡山小風口溪及武嶺溪水化學月變化呈現相同趨勢，其中，K^+與NO_3^-之濃度明顯於8月受颱風引起地表淋洗影響而濃度增高；但Ca^(2+)、Mg^(2+)與SO_4^(2-)、HCO_3^- 等則在高流量時因稀釋作用而呈現濃度較低現象。

關鍵字

合歡高山 ； 降雨 ； 溪水 ； 水化學

並列摘要

In order to understand the chemical characteristics of both rainfall and streamflow in the alpine ecosystem of Mt. He-Huan area, rainfall and streamflow samples were collected and analyzed for major ions, from March, 2007 to February, 2008. Preliminary results showed that the average conductivity of rainfall in the alpine region was only 4.4±2.9 μS/cm, the average pH was 5.05±0.47 and classified as weakly acidic, in the alpine region. The highest average cation concentration of rainfall was Na^+ (0.21±0.15 mg/L), followed by NH_4^+ ＞ Ca^(2+) ＞ K^+, and Mg^(2+), and non-detectable; while the highest average anion concentration was HCO_3^- (0.89±1.01 mg/L), followed by NO_3^- ＞ SO_4^(2-) ＞ Cl^-. These results showed that rainfall was relative low in ionic concentration and less affected by pollution in this alpine ecosystem, and lower in ionic concentration than that in forested ecosystems in lower elevations of Taiwan. These phenomenona were possibly due to the greater distance of the Mt. He-Huan site to the pollution sources, also possibly due to releasing effects as cloud uplifting toward the central mountain range. Changes in monthly water chemistry of rainfall showed there were pH values were lower than 5.0, higher conductivities and SO_4^(2-), NO_3^- concentration in the period from February to April. Whether it is affected by remote acidic deposition and long distance transportation, needs further study. Besides, the higher NH_4^+ concentrations were also observed in the spring rainfall. Could these be caused by local agricultural fertilization? It also needs further monitoring. There were significant differences in water chemistry between rainfall and streamflow during the studied period. Significant differences in water chemistry also existed between stream water of Siao-Fon-Ko and Wu-Ling streams. In the Siao-Fon-Ko stream, the average conductivity was 179.1±14.7 μS/cm, average pH, 7.48±0.49, and classified as neutral, and the highest average cation concentration was Ca^(2+) (23.69±6.27 mg/L), followed by Mg^(2+) ＞ Na^+ ＞ K^+, and NH_4^+, and non-detectable; while the highest average anion concentration was HCO_3^- (123.72±11.38 mg/L), followed by SO_4^(2-) ＞ NO_3^- ＞ Cl^-. In the Wu-Ling stream, the average conductivity was 61.9±9.6 μS/cm, average pH, 7.08±0.49 and classifies as neutral, and the highest average cation concentration was Ca^(2+) (9.89±3.03 mg/L), followed by Mg^(2+) ＞ Na^+ ＞ K^+ ＞ NH_4^+; while the highest average anion concentration was HCO_3^- (36.34±5.20 mg/L), followed by SO_4^(2-) ＞ NO_3^- ＞ Cl^-. Some ionic concentrations were lower than those in the Siao-Fon-Ko stream, possibly resulted from differences in geological, soils and vegetation characteristics of these two watersheds. Monthly chemical changes in both streamflow showed similar tendency. Nevertheless, the higher K^+ and NO_3^- concentrations (possibly due to the leaching effects during the typhoon period), and the lower Ca^(2+), Mg^(2+), SO_4^(2-) and HCO_3^- concentrations (possibly due to the dilution effects) during the high discharge period which generally is the highest in August.

並列關鍵字

Alpine area of He-Huan Mt. ； Rainfall ； Streamflow ； Water chemistry