On the Seasonal Change of the Water Temperature, Oxygen Content and the pH of Lake Nakatuna, Nagano Prefecture, Japan
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概要
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This paper refers to the results of twenty five regular observations made during the period from January to December, 1931. Importance has been attached to the study of seasonal change of the factors. The investigation revealed that the highest temperatures of the surface and bottom were 27.8° (Aug. 26) and 10.9° (Oct. 5-15) respectively, while the lowest temperatures of these layers were respectively 1.0° (Jan. 30) and 3.7° (Jan. 30). The layer of discontinuity ranged at first between 6 meters and 12 meters from late May onwards, its uppermost limit reaching, in August, the two meter layer. The lowest limit of the layer of discontinuity reached bottom by mid-September, showing that there is no hypolimnion in this lake. According to the oxygen estimation the water layer above 6-8 meter might be called a tropholytic layer. As is usually the case with eutrophic lakes the bottom water of this lake occasionally loses its oxygen during summer. Over saturation of 102% was found only once at the 6 meter layer in May, suggesting the vegetation of phytoplankton at that season. The pH of this lake ranged around 6.25-7.0 at all seasons and depths. As observed by MIYADI (1929) and YOSHIMURA (1931) in several of the lakes of Japan the vertical distribution of pH in this lake also showed a salient feature, i.e. in summer the pH of the bottom is slightly but steadily higher than that in the layer just above the bottom. For the reason of this phenomenon it is referred to the interpretations given by MIYADI (1929) and YOSHIMURA (1931).
- 社団法人 日本水産学会の論文