Ref ID : 3102
Hada Yoshine and Kusuki Yosiaki; [Limnological Studies of Lake Toyoni, Hokkaido]. Jap.J.Limnol. 8(2):53-67, 1938
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Lake Toyoni is a single lake found in the Hidaka ranges which are very steep and non-volcanic. This lake which is situated on the north-eastern slope of Mt. Toyoni was probably made by slide damming a deep dale, judging from the heap of stones of the lake-shore. This is a small but deep, heart-shaped lake with the longest axis of about 300 m and the greatest depth of 18.55 m, and has neither inlet nor an outlet. Our hydrobiological observations and collections were made on September 12, 1936, and the following results were obtained. The thermal and chemical stratifications were observed, but the definite thermocline could not be found on account of slight stir of the surface layer by wind, though the metalimnion was distinct in the layer of 10-13 m. Dissolved oxygen was in the super-saturated condition in the epilimnion, but suddenly decreased in the metalimnion, then diminished in the upper layer of the hypolimnion and finally disappeared in the deep layer lying to the bottom. Free carbon dioxide and bicarbonate increased in the hypolimnion and a remarkable increase of iron and phosphate was also observed. Nitrate, nitrite and ammonia were detected only from water of the hypolimnion, while chloride and silicate gradually increased with the increase of depth. As the amounts of dissolved salts except silicate are very poor, this lake apparently belongs to a lake of the oligotrophic type. We could not see any aquatic vegetation on the stone and rocky shore of this lake. Only a species of fish rainbow trout, propagates; it was transferred from other lake in 1929. Two forms of Copepoda, four kinds of Cladoceran, seven species of Rotatoria, two Testacea, and larvae of aquatic insects and a mite were detected as the zooplankters from material. Of them, Acanthodiaptomus pacificus var. yamanacensis Brehm was most frequently found in off-shore plankton, but near the shore Alonella excisa (Fischer) most abundant. In the phytoplankton algae were very poor, but two species of Dinoflagellata were exceedingly abundant in the hypolimnion. The biological characterstics of this lake are as follows: the first is the vegetable bareness of the lake-shore, the second the richness of the flagellata as well as the scantiness of diatoms in spite of plentiful supply of dissolved silicate, the third the differences in the number and the composition of plankton between the central part and shore part, and the last the presence of the living Crustacea in the deep layers lacking in dissolved oxygen.