Ref ID : 3103
Hada Yoshine; [Studies on Bog Lakes I. Bog Lake at Tokotan (after parts)]. Jap.J.Limnol. 7(1):13-30, 1937
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There is a small bog lake by the fishery village to Tokotan situated 4 km from the Akkeshi Marine Biological Station on the coast of Akkeshi Bay. The lake is elongated elliptical, 150 m in length, 47 m in greatest width, and 3.5 m in greatest depth. It is surrounded by Sphagnum-moss and is connected by a short canal with Lake Tokotan which is larger than the former and not boggy. Floating lakeward margins are 2-6 m in width and mainly consist of a netwark of stems of Menyanthes trifoliata growing thick around the lake. Colour of water is deep brown. The transparency varies from 1.15 to 1.70 in meter and is changeable dependent upon the amount of zooplankton, especially Rotatoria which are the most important group in the plankton of this bog lake. Bottom deposits are generally composed of peat debris. Thermal stratification was observed during June-September in summer and during December-March in winter, and the spring overturn takes place in April and May and the autumn one in October and November. The surface of the lake is frozen through the winter stagnation period. The water of this lake is generally acid (smallest pH value, 6.05), but surface water is sometimes weakly alkaline (greatest pH value, 7.4). Dissolved oxygen is often free in a thin layer of deeper water immediately above the bottom during the summer stagnation period. From this bog lake and also from Lake Tokotan, have been known seven kinds of fishes, including Cyprinus carpio L., Carassius auratus (L.), and Hypomesus olidus (Pallas), etc. as useful fishes. Some of C. auratus are of reddish colour in natural propagation. Such naturally reddish coloured individuals inhabiting lakes are distributed on the Pacific coast of the eastern part of Hokkaido. There have been found in this lake 2 species of Mollusks, 2 of leeches, 1 of Isopoda, and several kinds of insect larvae from Menyanthes zone, and also found 2 species of Mollusks and one fresh water sponge from the next Equisetum-zone of 1-2 m wide. Zooplankton is considerably superior to phytoplankton in amount. The decrease of the latter seems to be mainly due to the fact that the latter becomes prey of the former. The following pelagic animals were detected in the plankton of this lake: 2 kinds of insect larvae, 1 Hydracarina, a single form of Copepoda, 3 Cladocera, 1 Nematoda, 21 species of Rotatoria, 1 Gastrotricha, 18 Ciliata, 8 Amoebina including some of Testacea, and 2 Heliozoa. Insect larvae belonging to bottom dwellers are common in deeper water, but Copepoda and Cladocera occur more frequently in surface collections of summer plankton. The Rotatoria are the most abundant among the zooplankton and richer in the surface layer than in the deeper one. The Ciliata are very rare in surface water, being abundant near the bottom where the amount of dissolved oxygen is scarce or free. The Amoebina are not found in surface collections, but found very rarely in deeper water only in summer. The Flagellata are the most excellent quantitatively in the phytoplankton of this lake, 21 species being secured, 23 forms of Chlorophyceae, 22 species of Bacillarieae, and 5 kinds of Myxophyceae, have been found. Most of these usually appear very rarely in deeper water of the lake. The small bog lake at Tokotan is of the distrophic type, but is not poor in production of zooplankton as compared with eutrophic lakes in Hokkaido.