Japanese Journal of Limnology (Rikusuigaku Zasshi)

In the summer of 1935 we made the hydrographic survey of a lake, Seseki-numa near Bettobu, Etorohu, Kurile Islands, and obtained the results shown in Table I. The lake lies 2 km from the sea coast and 10 m above the sea level, and has its maximum depth of 5.8 m. The bottom water of this lake has high salinity, yet its salt composition is much similar to that of the sea water. From the topographical features of the lake, the origin of the salt can not be considered to be due to the upstream invasion of the sea water. Moreover, the dissolved O₂ content of the bottom water is abnormally high, while N and P₂O₅ con ents, as well as KMnO₄ consumption are not so high. These facts show that bottom water is of rather fresh condition. Judging from the neutral or weak acid reaction of the water, and also rich free CO₂ content, we can not attribute the abundance of O₂ in the bottom water to algal assimilation.
We calculated the saturation percentage of dissolved O₂, and got the value of nearly 100% in the surface layer (0-4m), while it reaches as high as 148% in the bottom layer, and if the hydraulic pressure is taken in consideration, the so called absolute saturation percentage of O₂ in the bottom water is about 100%. Thus the only possible explanation for the condition of the bottom water is the existence of the underwater saline spring, having abundant dissolved O₂ (c.f. TABLE III).

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The monthly observations were made on the vertical changes in the temperature and the specific gravity of the water of Lake Saroma during the period from June 1933 to March 1937. Judging from the relations between the temperature of the lake water, that of the adjacent sca water, and the air temperature, as well as from the relations between the specific gravity of the lake water, that of the adjacent sea water, the precipitation and the evaporation, it is shown that this lake has the characteristics of a bay but not a lake.

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The quantity of phytoplankton (P) correlates with that of zooplankton (Z), as is expressed by the formula P=α Z^b, where a and b are constants, and always positive. Therefore, there occurs no inverse correlation between the quantities of the two plankton populations, whereas formula N=Cr^-k and P=C (1-γ) γ^-k apply to plankton of similiar character distributed in a given area, where N is the total number of plankton individuals and γ=Z/N. Since if γ falls, the phytoplankton increase in number, the inverse relation is considered to hold, although actually the quantity of zooplankton either increases or, at least, remains unchanged.

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During our stay at the Aso and Unzen National Parks all in Kyusyu, in October, 1936 and January, 1938, we made an excellent collection of thermophilous insects, etc. In the vicinity of Aso, there are many hot springs, e. g. Zigoku, Tarutama, Yunotani, Totinoki, and in Unzen there are Huruyu and Sinyu springs.
The following are represented in the collection.
In Zigoku (alum-vitriol spring), where the water temperature ranges from 33.8 to 60°C, and pH is 3.8, we found Chironomus thumnis KIEFFER and Scatella sp.
In Tarutama (iron and bitter), where the water temperature ranges from 29 to 36°C, and pH from 4.2 to 7.4, there are Cloeon dipterum LINN. and Scatella sp.
In Totinoki (iron-alum, bitter and saline), where the water temperature ranges from 27.9 to 36.4°C and pH is from 7.8 to 7.9, of the many creatures may be mentioned, Hirudo sp., Semisulcospira libertine GOULD, Gyrauluscompressus japonicus MARTENS, Lymnaeapervia MARTENS, Tabanidae, Hydropsych.e brevilineata IwATA, Orthotricha sp., Glossosoma sp. Ecdyonurus sp., Baetis sp., Microvelia sp., Laccobius oscillans SHARP, Ochthebius inermis SHARP, Berosus sp., and Bidessus japonicas SHARP.
Unzen (sulphrous springs) has a water temperature ranging from 32 to 34.4°C, and pH is from 3.7 to 3.9. There we found two species of insect larvae, Chironomus thumni Kieffer and Scatella sp.
It is notable that although the, adult of Cloeon dipterum LINN. appears in abundance in January and October, elsewhere it is usually found in July. Ochthebius inermis SHARP which has been described from Nevada (BnuEs, 1928) and the Sardinian hot springs (KRAUSE, 1913), was found in the Totinoki hot spring. It is rather surprising to meet with Chironomus and Scatella larvae in highly acidic hot springs.

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