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地すべりの発生と侵食作用 : 奥羽山系を例として
Get PDFテクニカルレポートはじめに ｢地すべり｣というと,一般には災害の一種で,防災の対象として扱われることが多い. しかし,山地の形成史といった長い時間の中では,地すべりは侵食現象の1つとして重要な役割を演じていたのではなかろうか. また,地史的な時間の中で生じた地すべりは,その多くが現在ではほとんど動きを停止している.こうした地すべりは,それがなぜ発生し,そしてどうして止ったかを知ることができれば,現在動いている地すべりの止め方に何らかの指針を与えてくれるはずである.小論は奥羽山系の山地に残された地すべり地形を解析し,斜面の形成と地すべりの発生との関係を史的に解釈しようと試みたものである.すなわち,まず奥羽山系の西側の斜面(乱川流域)に残されている地すべり地形を空中写真の判読により求め,さらに現地調査による観察を加えるといった調査を行った.それらを整理し,考察を加えた結果,乱川流域の侵食は,約50万年前に始った｢村山変動｣と称する激しい構造運動と共に生じ,その後の侵食の最盛期には,地すべりなどの急激な侵食作用が主体となっていたであろうことが推定できた.そして,現在見られる地すべり地形は,侵食の最盛期の末期に形成されたもので,それが侵食の衰退期を経て,今日に至るも,削り残されているものであることなどを指摘することができた
Effects of canopy on the distribution of seedlings and saplings in a successional forest on Mt. Bandai
Get PDF論文(Article)Summary : The relationship between the spatial distribution of seedlings and saplings and the overhead canopy structure was examined in a successional forest on Mt.Bandai. The total density of seedlings and saplings was high under the canopy of Pinus densiflora, and low under that of Betula maximowicziana, both making up the tree layer. This total density was also low under gaps in the canopy. The relevance of these results to the replacement of woody species in successional forests is discussed
Trophic State and Hypolimnetic Nitrogen Metabolism of Lake Hibara
Get PDF論文(Article)Abstract : This is the first attempt to elucidate the seasonal changes in some physical and chemical parameters in a water column of Lake Hibara. The observation extended from spring to early winter of 1991. In the hypolimnion, nitrification started between 13 June and 10 July. The nitrification rate in this period was 0.21 - 0.44 μg atom N・1~-1・day~-1. The dissolved oxygen (DO) level of about 0.6 - 0.7 mg・1~-1 appeared critical in impeding efficient nitrification. The gross ammonia production rate was estimated to be 0.05 - 0.15 μg atom N・1~-1・day~-1. Denitrification seems to have taken place in the lower hypolimnion and / or on the surface of the bottom sediment when DO decreased to 2 - 3% (0.2 - 0.3 mg・1~-1). The levels of TN, TP, Chl. a and transparency in the autumn circulation period indicate that the lake is on the boundary between oligo- and mesotrophic, though the epilimnetic water in summer was oligotrophic. The relative areal oxygen deficit in the hypolimnion (0.055 - 0.061 mg・cm~-2・day~-1) was at the lower limit of eutrophy. The question of why, in spite of the lake's overlying oligotrophic epilimnion, the hypolimnetic DO consumption rate was at a eutrophic level remained to be solved. The hypolimnetic DO consumption rate seems to have been accelerating for the last 20 years. To elucidate the extent of the fluctuation of the hypolimnetic processes from year to year is important for future study. Key words : Lake Hibara, trophic state, oxygen consumption, nitrogen metabolism
