The lake Togo-ike with its area of 4. 1 km² and maximum depth of 5. 2 m. is a brackish lake and situated on the middle part of Tottori Prefecture. There are many hot springs such as Togo, Shin-Togo and Asazu in and around the lake. The authors studied the influence of the change of lake level due to polderling on the discharge of hot springs. The results obtained are summarized as follows :
(1) Togo hot spring group has the same chemical constituents and ground temperature, suggesting that they have the same origin under the ground.
(2) Some of these springs discharge through the lake bottom into the lake, but they give little influence on the quality of lake water.
(3) Factors which will affect the discharge of spring water are barometric pressure, rain-fall amount, lake level change, tidal change and pumping. Barometric change and tidal change are not separated. Distinguished effects of rain-fall and lake level upheaval are shown in Table 5. Pumping effect is also obvious.
(4) The effect of lake water level change on the spring discharge, dQ/dh is larger at Azusa than that of at Togo (Table 6). It suggests that change of lake water level affects directly to the discharge of hot spring.
The results above mentioned lead us to the conclusion that the polderling of this lake will cause the decrease of hot spring discharge.

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Yubara-ko is a man-made lake that lies in the northern part of Okayama Prefecture and stores water for the purpose of generating hydroelectric power. The writer investigated the limnological features of this lake on August 7-10, 1965, ten years after the water was impounded behind the dam in 1955. The stations at which the surveys were made are shown in Fig. 1.
The vertical distribution of water temperatures at each station is shown in Fig. 2. The metaliumion developed in the layers between 15-16m and 23m. The color of water is FOREL'S Nos. 6-9, the SECCHI'S disc transparency varying from 1. 5 to 4. 0m. The pH-values range from 7. 2 to 7. 4 in the surface and from 6. 0 to 7. 3 in the bottom water. The contents of dissolved oxygen vary 7. 88-10. 56 p. p. m. in the surface and 8. 67-10. 04 p. p. m. in the bottom water. The dissolved oxygen is supersaturated at nine stations except the Station No. 7. Table 1 shows the results obtained by chemical analyses of lake water. Total Fe is scarce as a whole, but 0. 004-0.048 p. p. m. were determined in the bottom water. The amount of NH₄-N is 0. 08 p. p. m., four times as much as that in 1958, as described in the first report (HIGUTI, M. 1960 : Limnological studies of a reservoir, Lake Yubara-ko, Okayama prefecture (1). Jap. J. Limnol., 21, 87-98). It seems that the nutrients in the water have become richer in the past ten years.
The individual numbers of net-plankton organisms in ten litre water sampled at each station are shown in Fig. 3. There are found thirty species of plankton animals and plants, 11 of which are the phytoplankters and 19 zooplankters. The plankton at the Station No. 2 are counted 5370/10l, which are the maximum numbers of all the stations surveyed, and 121/10l at the Station No. 5 are the minimum.

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(1). The species of the thiosulfate-oxidizing bacteria (Th. ferrooxidans) have been isolated from Frutobe mine water (Daikokuzawa, west, O. L, No. 3 loop).
(2). The iron oxidation rates by F. ferrooxidans were accelerated by increasing the size of the inoculum, at inoculum of one ml per 150 ml of medium converted to the ferric state about 70% of initial Fe²⁺ concentrations in 11 days of incubation and at inocula of 2 ml converted to the ferric state about 99%. By increasing the size of the inoculum, up to 410 ml per 150ml of medium, converted to the ferric state 9799% in 8 days of incubation.
(3). By breeding successive generations of F. ferrooxidans in culture media successively more concentrated in dissolved copper (CuSO₄, solu.), the tolerance of the bacteria was increased to approximately 25 grams of the copper per liter.
(4). The strain of F. ferrooxidans could oxidize elemental sulfur as well as ferrous iron, but the presence of the large amounts of elemental sulfur suppressed the iron oxidizing ability of this organism.
(5). On the studies of the influence of various organic substances on the oxidation of ferrous iron by F. ferrooxidans, urea and peptone retard the oxidation of iron and the growth of bacteria at concentrations greater than 0. 2%. Glucose was able to accelerate the growth of bacteria by increasing the amounts, but retarded the oxidation of iron at concentrations greater than 0. 1%.
(6). If was not evident that the strain of F. ferrooxidans utilizes thiosulfate, but Th. ferrooxidans was able to grow using thiosulfate as the energy source and Th. thiooxidans utilized a little thiosulfate.
(7). Th. ferrooxidans and F. ferrooxidans could utilize chalcopyrite as a source of energy.Th. ferrooxidans leached 86 % of the copper from chalcopyrite and F. ferrooxidans leached 68% in 50 days at 26 °C on a reciprocal shaker. Th. thiooxidans had no effect on the dissolution of copper from chalcopyrite.

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The Mamigasaki-gawa R., which is the second order tributary of the Mogami R., starts from the Zao Volcano. The upper reaches consists of two drainage systems, i. e., the Mamigasaki-gawa R. (main stream) and the Name-kawa R. The catchment area of the former is not only damaged by landslide to a great extent but also subjected partly to the sulfataric action of the volcano. Under the circumstances, the author has been interested in the transportation of dissolved minerals and suspension of the river. In this paper, such a hydrological problem is discussed comparing the river with the Name-kawa R.
Regarding the concentrations of dissolved ions, the Mamigasaki-gawa R. is larger than the Name-kawa R. with the exception of chloride ion. Especially, the sulfate ion content of the former is twice as much as that of the latter.
All the dissolved ions except chloride ion in the rivers mentioned above are mainly supplied with the channel scour while chloride ion is derived from the atmospheric salt. Accordingly, even at the season of rapid thaws, the concentration of the ion does not decrease but on the contrary the contents of the other ions become minimum at the same period.
The relationship between mineral discharge Qd and flow rate Q is expressed by the equation : Qd=αQn where 'α' and 'n' are constants dependent on the ion and the drainage system.
As for the transportation of suspension, the Mamigasaki-gawa R. exceeds the Name-kawa R. in its ability.

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Plankton collected from Lake Totsuru-numa, Hokkaido, in October, 1966 was studied.
Forty eight species of phytoplankton and six species of zooplankton were found in this lake, the abundant species being Melosira italica (diatom) and M. granulata (diatom).
Some species such as Anabaena Scheremetievi var. recta (blue-green algae), Coccomyxa dispar (green algae), Pediastrum aranaeosum var. ruglosum (green algae), Cymbella sumatrensis (diatom) are rare in Japan.
Rhynchotalona rostrata (Cladocera) was found for the first time in Japan.

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