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Volume 30, Issue 3
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Teruyoshi KAWAMURA1969 Volume 30 Issue 3 Pages 87-97
Published: October 28, 1969
Released on J-STAGE: October 16, 2009
JOURNAL FREE ACCESSLake Toya (Fig. 1) is a large caldera basin located in the Shiribeshi volcanic area of southwestern Hokkaido. The average and the maximum depth of the basin are approximately 117 m and 180 m respectively, the surface area being 69.6 km2 except three islands in the lake.
Since 1939, acidic water, deriving from two sulphur mines in the upper reaches of the Nagawa River (Osaru River), has penetrated into the lake through a tunnel to generate electric power, resulting in the decrease in pH value of the lake water, as low as pH 5.8 near the surface in recent year (Fig. 2). The species number of plankton organisms is extremely small in recent year, only 5 species (Fragilaria crotonensis, Fragilaria sp., Synedra pulchella, Oedogonium sp. and Peridinium sp.) of phytoplankton and only 2 species (Cyclops strenuus and Scaphoreberis mucronata) of zooplankton are remaining at present. The standing crop of phytoplankton in terms of amount of chlorophyll is 10. 24mgChl. a/m2 -6.01 mgChl. a/m2 in an euphotic zone, and it is an average of 0.43 mgChl. a/m3 -0.01 mg Chl. a/m3 through the euphotic zone.
An experiment was made to ascertain an influence of acidification of water on the photosynthetic activity of phytoplankton, Scenedesmus sp. cultured in the laboratory. Carbon fourteen technique was adopted to estimate photosynthesis on the experimental waters of three kinds of pH value under 1-10 klux of light intensity (Fig. 3). In the control water (pond water : pH 7. 4) photosynthesis is as high as 15 mgC/m3/h at the optimum light intensity of 6 klux, whereas in the water of pH 5.8 which mixed acidified lake water with pond water the rate is extremely low, being 2.5 mgC/m3/h in the optimum light intensity (4-10 klux). The light assimilation curve is similar to that of lake water of pH 4.2 which was sampled from the surface near the end of the tunnel. Experiments on the survival of two species of zooplankton, Cyclops strenuus and Daphnia pulex, in waters of various grades of pH value were made at the same time (Fig. 4). In waters below pH 5.0 all Daphnia died within four days. In pH 6.0 water the surviving number of Daphnia was 40% of a total of individuals on the fourth day. In contrast to the above fact, all Cyclops experimented upon survived in the water of pH 5.0 for four days.
Successive changes in the predominant species of zooplankton have been distinctly demonstrated since 1958. During the period from 1958 to 1960 Daphnia occurred very abundantly in the lake, but the leading rank of Daphnia was turned to Bosmina longirostris in 1962, continuing until 1967. Then, Bosmina suddenly dropped out of the rank in 1968, being replaced by Cyclops strenuus. Daphnia completely disappeared these last two and three years. Such successions in the leading species of zooplankton clearly correspond to the progress of acidificafion of lake water.View full abstractDownload PDF (1089K) -
Hiromu KOBAYASI, Fujiko YAMASHITA1969 Volume 30 Issue 3 Pages 98-107
Published: October 28, 1969
Released on J-STAGE: October 16, 2009
JOURNAL FREE ACCESSTaxonomical and floristical aspects of the diatoms from Sanpoji-ike Bog were already reported as a part of the report of the diatoms from ponds and pools in the vicinity of Tokyo (H. Kobayasi, 1968). In order to obtain more precise information on the diatom community, present investigations concerning the distribution and the ecological analysis were carried out.
Sanpoji-ike Bog is a small and shallow peaty bog located in the western district of Tokyo. It is about 300 m in length, 120 m in breadth and about 1 m in depth. At present, though it has no watersoaked bog margin or mat because of the construction of artificial promenade around the margin. There is a floating mat in the center and a considerable amount of peat deposits in the bottom.
As shown in Table 1, the pH value is about 6. 5, being slightly acidic as usual, except in a shorter period of mid-summer when it shifts to weakly alkaline side. Stations from which materials were collected are shown in Fig. 1.
Many species of Eunotia and Pinnularia and some species of Tabellaria and Frusturia which are considered to be peculiar to such acid waters were also found in this bog.
About 30% of the dominant or common species shown in Table 2, were recognizable as acidphilous forms.
Fragilaria was vigorous in the materials from the sunny St. 1, 2 and 3, whereas Eunotia was in the materials from St. 4, 5 and 6 where garden trees make them shady.View full abstractDownload PDF (4374K) -
Drastic change of temperature accompanied with the intrusion of deep waterIwao OKAMOTO, Kazushige YAGI1969 Volume 30 Issue 3 Pages 108-118
Published: October 28, 1969
Released on J-STAGE: October 16, 2009
JOURNAL FREE ACCESSA drastic change of water temperature which amounted up to 8°C in the bottom layer was by chance found in the southern basin of Lake Biwa-ko during the period of routine observation in August 1967. At the same time, an automatic recorder for water temperature installed at Biwa-ko Ohashi Bridge caught a remarkable variation of temperature.
On analyzing the records, two kinds of oscillatory change have been indicated. One of them, whose period is 4 hours, is caused by an ordinary seiche on the occasion of horizontal gradient of temperature existing in that region. The other, which has a period of 43 hours with an amplitude of 4°C, may be caused by an internal seiche in the northern basin, because its period is computed at 42 hours on assuming a free uninodal oscillation of two layers. Successive measurements of the water current performed at the fixed station have shown that the no-flow level between the upper layer flowing northwards and the lower layer flowing southwards has gradually ascended together with the rise of thermocline level.
A remarkable depression of temperature observed in the southern basin occurred owing to the intrusion of cold deep water of the northern basin accompanied with an internal seiche mentioned above. The water volume of the intrusion is calculated at 4×107m3, on the assumption of the conservation of water mass and of heat content.View full abstractDownload PDF (1035K)
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