森林流出水の水質についての広域的考察 (1)

Abstract

森林流出水の水質分析を日本全国34ヵ所の集水域で行った。流出水のpHはほぼ中性であり, 電気伝導度は温暖乾燥の地点で高く寒冷温潤の地点で低かった。Ca, Mg, Na, Cl, SO_4, NO_3-Nは電気伝導度と正の相関があった (r＞0. 6)。NO_3-N濃度とSO_4濃度は瀬戸内の岡山, 香川でとくに高かった。Na濃度とCl濃度は沖縄と多雪地の山形で高かった。一方, 標高1000m以上にあって, 寒冷湿潤な気候条件下にある岐阜, 長野では, 全ての物質の濃度が低かった。気候条件の等しい隣接集水域のなかでは, 老齢林のNO_3-N濃度が若齢林のそれよりも高かった。

Chemistry of forest run-off water was monthly studied for thirty-four watersheds in various regions from Hokkaido to Okinawa in Japan. The pH values of forest run-off water were around 6.8 and did not differ among the watersheds. EC (Electric Conductivity) of water was higher in warm and dry, than cool and wet regions. EC was correlated with concentrations of Ca, Mg, Na, Cl, NO3-N and SO4 in water(r>0.6). Concentrations of NO3-N and SO4 were especially high in Okayama and Kagawa where Warmth Indexes were high and Humidity Indexes were low. Concentrations of Na and Cl were high in Okinawa which is located near the sea, and in Yamagata which has much snowfall. Concentrations of all elements were low in Gifu and Nagano pref., where the watersheds are located at a higher altitude of 1000 meter above the sea level and in cool and wet climate. Among the watersheds in same climatic conditions, run-off water from old-aged forest had higher concentrations of NO3-N than that from younger-aged forest.