Reconnaissance of the Regional Limnology of the Lake surrounding Volcano Bandai, Hukusima (3)

Abstract

The author studied the regional limnology of several lakes lying at the northern foot of volcano Bandai and also of Lake Inawasiro at its southern foot during the summers of 1930 and 1931. In his second visits was accompanied by Mr. D., MIYADI, who made the soundings and collected the bottom fauna.
The lakes at the northern foot of the volcano were formed by the damming up of the valleys by the mud flow at the time of the famous eruption of Bandai in 1888. The morphology of the lakes that were studied by the writer, are as follows:
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Lake Akimoto, which was sounded in 1931 by MIYADI and the writer has many auxillary basins, which are interesting fields for comparative studies of the dissolved oxygen and also of the bottom fauna between the main and the auxillary basins.
Studies, both physico-chemical and biological, were made during their visits. As physical studies, the colour of the water, transparency, and water temperature were observed. The pH, CO₂, dissolved oxygen, H₂S, total residue, Na, Ca, Mg, Fe, Mn, SO₄, Cl, SiO₂, N, P, and also organic matter at various depths, of these lakes were analysed by the writer. The plankton was collected with a net. The bottom fauna was collected by means of an EKMAN-BIEGE bottom sampler (I).
From these data, the writer has attempted a classification of these lakes. From his studies of Japanese lakes, the author finds that the amounts of chemical constituents, such as N, P, pH, and organic matter best indicated the lake type from the point of view of NAUMANN-THIENEMANN These amounts are as follows:
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The amounts of these constituents in the lakes that were studied and the lake type established by these amounts are as follows:
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Lakes Yanagi, Ruri, Aka and Bisyamon (Gosiki Lake Group) received inflows of mineral water of high salinity from the explosion crater of Volcano Bandai. As their salinities fluctuate between 0.9 and 1.8 gr/1, they are salt-water lakes! Although their waters are very rich in calcium, they give an acid reaction.
Other characters that confirm the lake type above established are the forms of the basin, colour of the water, transparency, dissolved oxygen, the production and the quality of the littoral vegetation, plankton, bottom fauna, and the bottom deposits. Littoral vegetation cannot develop in Lakes Hibara, Onogawa, and Akimoto, since their annual range of water level is very great owing to artificial control. The bottom deposit of Lake Inawasiro is diatom-gyttja, while that of the Lakes Gosiki consists of sulphur, and the oxides of iron and manganese. Lacustrine deposits have not yet covered the bottoms of Lakes Hibara, Onogawa, and Akimoto, Further characters are as follows:
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With only two slight discrepancies, the lake type as established by chemical standards is closely confirmed by other characters. The oligotrophic lake Onogawa and the Terazawa Basin of Lake Akimoto, having lost the dissolved oxygen from their deepest bottom layer Corethra was the dominant species at the bottom. The other discrepancy is that Chironomus plumosus, which is regarded as the indicator of the eutrophic type, is the representative species in the oligotrophic lakes Hibara and Akimoto The production on benthos in Lake Inawasiro was rather rich, considering its ultraoligotrophic conditions. It may be said that the quality and the quantity of the bottom fauna is not always the best indicator of lake types in which the production of biological forms is great, as recently pointed out by NAUMANN (1932) and LANG (1931), since they are influenced by many factors which are not closely related to the trophic value of the lake.
The regional limnology of the district surrounding Volcano Bandai is characterised by edaphic conditions.