2001年桃芝颱風蓮華池人工林及天然林集水區溪流水化學之比較

Abstract

2001年7月30日侵台之桃芝颱風(Typhoon Toraji)為近10年來對蓮華池地區影響最大颱風之一。本文探討桃芝颱風期間，蓮華池4號（杉木人工林）與5號（天然闊葉林）兩試驗集水區溪流水化學之變動。桃芝颱風期間，蓮華池試驗林累積雨量為390mm，分別於4號與5號試驗集水區溪流中形成1,440及1,792 LPS之最大洪峰流量。颱風期間蓮華池溪流水化學變化可歸納為下列三種形式：(1)與流量成負相關，即濃度隨流量升高而下降，如電導度、pH、Ca(上標 2+)、Mg(上標 2+)、Na(上標 +)、Cl(上標 -)、SO4(上標 2-)、HCO3(上標 -)等；(2)與流量成正相關，即濃度隨流量升高而上升，如懸浮質及NO3(上標 -)；(3)與流量無顯著相關，即濃度沒有明顯之變化趨勢，如NH4(上標 +)、K(上標 +)等。颱風期間4號集水區溪水中Ca(上標 2+)、Mg(上標 2+)、SO4(上標 2-)及HCO3(上標 -)的平均濃度分別為5號集水區的4.6、1.7、2.0及4.5倍，可能顯示與林相變更有關。

Typhoon Toraji in 2001 was the most influential typhoon event in central Taiwan during recent decades. The purpose of this paper was to compare with streamwater chemistry between Lien-hua-chi watershed No. 4 and No. 5 during the typhoon Toraji. The area of watershed No. 4 is 5.86 ha with China-fir plantation, while the area of watershed No. 5 is 8.39 ha with natural broadleaf forests. Total rainfall was 390 mm during typhoon Toraji event, and the highest peak flow rates were 1, 440 and 1, 792 LPS in watershed No. 4 and No. 5, respectively. Results showed that conductivity, pH, and concentrations of Mg(superscript 2+), Na(superscript +), Cl(superscript -), SO4(superscript 2-) and HCO3(superscript -) in streamwater decreased with increasing discharge. However, suspended solid and concentration of NO3(superscript -) increased with increasing discharge. Ionic concentrations of Ca(superscript 2+), Mg(superscript 2+), SO4(superscript 2-) and HCO3(superscript -) in watershed No. 4 were obviously higher than those in watershed No. 5 indicating possible influence from the last forest alternation.