昭和八年夏期猪苗代湖調査の結果に就いて

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概要

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• Lake Inawasiro is located at the north latitude 37°30 and the east longitude 140°05 and is 514m high above the sea-level. It has the coast 56.09km long, the area of 103.64km2 and the maximum depth of 102m. On the occasion of the great explosion of the volcano Bandai in 1888, all the fishes in the lake were killed and the lake has become barren. Over twenty years after that time the Hukusima Fisheries Experimental Station made a chemical analysis of the lake water, which proved to be no more unusual. Since 1908 Hukusima Fisheris Experimental Station has taken charge of the fish cultual experiment of trouts (Oncorhynchus nerka and Salvelinus kundscha) in this lake, liberating to it 125, 300-3, 200, 000 young every year. Compared with these, however, only 550-1, 800 adults a year are caught in the rivers around the lake. Why is the productivity so poor as this? To answer this question, the present author made an investigation last summer (1933) on the chemical properties1) of the water and the distribution of plankton in this lake. The Nagase River, rising from the northern foot of Mt. Bandai, supplies the largest part of the inflow to this lake. It discharges water from the lakes of Hibara, Akimoto and Onogawa mixed with the highly acidic water of a branch called Su-gawa. By dint of inflow of the acidic water the whole mass of the lake water is markedly acidified showing the fall in pH-values to 2.8 at the inlet and 5.5 at the outlet (Fig. 1). In Fig. 1 the direction of the flow of this acidic water over the lake, inferred from the isolines of pH-values, is indicated by the arrows. The results of the chemical analysis of surface-samples from different positions are tabulated in Tab. 1. We know that the phosphate and the nitrate are extremely poor, while the sulphate is comparatively rich. The composition of the plankton in several parts of the lake collected by horizontal hauls through 400m in the surface-layer is shown in Tab. 2. The plankton is generally very poor in its density except at the stations XII, XIII, XIV and XV in the shallow littoral zone which is fed by the fresh water from the skirts of Mt. Bandai raising the pH-value to 6.0 to 8.0. The relation between the pH-values and the density of the plankton is given in Tab. 3, whence we can see that the zoo-plankton develops hardly at the pH-value of 5.3, while the phyto-plankton distributes in a wider range. Both the zoo-plankton and the phyto-plankton grow most favourably at pH of 7.0 to 8.0.

著者

• 山村 彌六郎

  水産講習所

関連論文

• 昭和八年夏期猪苗代湖調査の結果に就いて
• The Putrefactive Degree and the pH-value of Fish Muscle
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• Chemical Study of Food-Organism for Fish:II. Distribution of Aluminium

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