森林立地学会誌　森林立地45(1), 2003, 21～27

森林立地学会誌　森林立地45(1),2003,21～27

Jpn.J.For.Environment 45(1),21-27 2003

御岳山における７年間の降雨･降雪のpH, ECと溶存成分の特性

酒井寿夫^＊・森澤　猛^＊＊・仙石鐵也^＊＊＊

^＊森林総合研究所北海道支所・^＊＊森林総合研究所東北支所・^＊＊＊長野県松本市中山

長野県の御岳山（標高2,120m）で降水および降雪のpH，ECと溶存成分濃度を測定した。７年間のpH，ECの加重平均値はそれぞれ5.04, 5.7μS/cmであった。溶存成分濃度は他の山岳地域と比較して低いレベルにあった。降雪期（12～3月）におけるECは降雨期（6～１0月）に比べて高かったが，これはすべての溶存成分の濃度が12～1月に高いためであった。御岳において，降雨期と降雪期の溶存成分濃度を比較すると，海塩起源の比率が高いと考えられるNa⁺，K⁺，Ca²⁺，Mg²⁺，Cl^-，ss-SO₄^2-のそれぞれの濃度は降雪期の方が明らかに高かった。一方，非海塩起源のNH₄⁺，NO₃^-，nss-SO₄^2-の濃度も高い傾向にあった。したがって，降雪期における溶存成分濃度の増加は，海塩とそれ以外のものを起源とする複合的な要因によるものと推定された。

降雪期にNa⁺，K⁺，Ca²⁺，Mg²⁺，Cl^-，ss-SO₄^2-の濃度が高い傾向は、比較した5つの観測地点（輪島，八方尾根，立山，犬山，名古屋）でも見られた。しかし，御岳におけるこれらの成分の濃度比（降雪期／降雨期）は、日本海側の輪島，八方尾根，立山ほど高くなく，太平洋側の犬山，名古屋と同程度であった。一方，御岳ではNH₄⁺，NO₃^-，nss-SO₄^2-の濃度比（降雪期／降雨期）も高くなっており，同じ傾向が日本海側の輪島と八方尾根で明らかに見られた。御岳における降雪期のNH₄⁺，NO₃^-，nss-SO₄^2-濃度増加は，藤田ら（2001）が西日本で観測した現象（降水中のnss-Ca，NH₄⁺，NO₃^-，nss-SO₄^2-濃度が10～3月に濃度が高くなる現象）と非常に似ていた。

Hisao Sakai, Takeshi Morisawa, Tetusya Sengoku: Characteristics of pH, EC values and ionic components in rain and snow for 7 years at Mt. Ontake, Central Japan

pH, EC and ion concentration in rain and snow were measured at Mt. Ontake (2,120m above sea level), Nagano Prefecture. The average of pH, EC for 7 years were 5.04, 5.7μS/cm. Ion concentrations were low level in comparison with that in other mountain areas. EC value in snow period (Dec.-Mar.) was higher than that in rain period (Jun.-Oct.) because the concentration of all ions was high in December and January. The concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^- and ss-SO₄^2-, which most are the sea salt origin, were clearly high. On the other hand, the concentrations of NH₄⁺, NO₃^-, nss-SO₄^2- in snow period, which are the non-sea salt origin, were high tendency compared with that in rain period. Therefore, it was estimated that increase of ion concentration in snow period was caused by two (or more) compound factors.

Ion concentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, ss-SO₄^2- were high tendency at the five comparison observation sites (Wajima, Happou-one, Tateyama, Inuyama, Nagoya), too. However, the concentration ratio of snow period ageinst rain period about Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, ss-SO₄^2- in Ontake was not so high as that in Wajima, Happou-one and Tateyama in the Japan Sea side, was almost the same as that in Inuyama and Nagoya in the Paciffic Ocean side. On the other hand, the concentration ratio of snow period against rain period about NH₄⁺, NO₃^-, nss-SO₄^2- were high in Ontake, the similar tendency was seen in Wajima and Happou-one in the Japan Sea side. This phenomenon that was observed in Ontake was similar to the phenomenon observed by Fujita et al. that the ion concentrations of nss-Ca²⁺, NH₄⁺, NO₃^- and nss-SO₄^2- were high in the periods from Oct. to Mar. from 1987 to 1996 in west Japan areas.

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