鳥石坑地區18年生台灣杉人工林雨水之質量組成

Throughfall, Stemflow, Rainfall Interception, and Their Ionic Fluxes at a 18-year Taiwan-fir (Taiwania cryptomerioides) Plantation in the Wushyrkeng Area of Central Taiwan

本研究於1998年2月到1999年5月收集烏石坑地區18年生台灣杉人工林降雨並分析其水質以瞭解其穿落水、幹流和截留量及化學組成之改變。試驗期間烏石坑之年降雨量為2,050 mm，台灣杉人工林穿落水量為1,771 mm，幹流量為23.5 mm，截留量為255.6 mm，各占降雨量之86.4%、1.1%和12.5%。分析結果顯示穿落水及幹流均與降雨強度呈顯著線性迴歸。雨水流經台灣杉時電導度及大部分離子濃度自林外雨、穿落水及幹流逐漸增加，只有pH值及HCO3（上標 -）呈現穿落水＞林外雨＞幹流。穿落水增多係數由1.18（Na（上標 +））到21.89（K（上標 +）），幹流的增多係數由1.83（F（上標 -））到90.41（K（上標 +）），顯示幹流中離子濃度變化較穿落水高。林內雨之年輸入量（穿落水加幹流），在陽離了中以Ca（上標 2+）最高（44.38 kg／ha）,K（上標 +）（36.22 kg／ha）及NH4（上標 +）（11.04 kg／ha）次之；陰離子依序為HCO3（上標 -）、（85.13 kg／ha）、NO3（上標 -）（48.49 kg／ha）及HCO3（上標 -）（36.01 kg／ha）。穿落水的pH值與SO4（上標 2-）、HCO3（上標 -）有顯著相關，幹流的pH值則與NO3（上標 -）、SO4（上標 2-）及HCO3（上標 -）有顯著相關。整體而言，林內雨H（上標 +）淨輸入量為-003 kg／ha／year，HCO3（上標 -）淨輸入量為53.23 kg／ha／year，台灣杉冠層保留部分的H（上標 +）並增加HCO3（上標 -）的量，對於酸沉降具有中和能力。 Throughfall, stemflow and rainfall interception were collected and their ionic concentrations were analyzed for each of the rainfall events at a 18 year-old Taiwan-fir (Taiwania cryptomerioides) plantation in the Wushyrkeng area of central Taiwan, February 1998 to May 1999. The total annual flow were 1,771 mm for throughflow, 23.5 mm for stemflow, and 255.6 mm for rainfall interception, representing, respectively, 86.39%, 1.15% and 12.46% of the total annual rainfall of 2,050 mm. Annual fluxes of main cations from throughfall and stemflow were 44.38 kg/ha for Ca(superscript 2+), 36.22 kg/ha for K(superscript +), and 11.04 kg/ha for NH4(superscript +), while the fluxes of main anions were 85.13 kg/ha for HCO3(superscript -), 48.49 kg/ha for NO3(superscript -), and 36.01 kg/ha for SO4(superscript 2-). The pH-values were significantly correlated to SO4(superscript 2-) and HCO3(superscript -) for throughfall but to NO3(superscript -), SO4(superscript 2-)and HCO3(superscript -) for stemflow. The annual stemflow flux of H(superscript +) was negative -0.03 kg/ha but positive 53.23 kg/ha for HCO3(superscript -), indicating that some of the H(superscript +) ions were retained by the forest canopies. This suggested that the Taiwan-fir plantation functions as a buffer for acid rain.