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Volume 28, Issue 2
Displaying 1-4 of 4 articles from this issue
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Kiyoaki KOIDSUMI, Yoshio SAKURAI, Shinji KAWASHIMA1967 Volume 28 Issue 2 Pages 57-63
Published: July 28, 1967
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe following seven species of rooted aquatic plants were listed as dominant for Lake Suwa in 1966:
Emergent—Zizania latifolia (234), Nuphar japonicum (142), Phragmites communis (63); floating—Trapa natans (630); submerged—Hydrilla verticillata (597), Potamogeton malaianus (276), Vallisneria asiatica (16).
Figures in parentheses denote the estimated standing crop of each plant expressed in terms of ton of the wet weight for the total area of the lake.
The hydrophytes densely cover the water along the entire margins of the lake extending to the depths of about 2.3-2.5m, which are shallower than those recorded in 1911 (3.4-4.0m) and 1949 (2.5m) respectively.
The total area occupied by the plants was about 0.92km2 which constitutes 6.3% of the whole area of the lake, 14.53 km2.
The total standing yield of the plants in the lake amounted to about 1, 958 ton in wet weight and to about 220 ton in dry weight in the late summer of the year when the growth reached a maximum. The wet quantity is just twice as large in weight as that reported in 1949 (970 ton).
Ecological succession appeared in the hydrophytes was quite remarkable. It may generally be said that the submerged plants have decreased, and the floating as well as emerged ones have become luxurious, when compared with the conditions in the past. It appears that this phenomenon will have a close relation to the recent trend of eutrophication of the lake.View full abstractDownload PDF (257K) -
Hiroshi YAGI1967 Volume 28 Issue 2 Pages 64-67
Published: July 28, 1967
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSChemical analyses were made on the contents of nitrogen, phosphorus and carbon in the seven dominant species of higher aquatic plants of Lake Suwa collected on September 10, 1966, when their growth reached a maximum.
All the plants of the lake are larger in contents of nitrogen as compared with those of Lake Biwa. The contents are almost the same as those of the plants found in the water of a rice-field, rich in nutritive matters.
The rough estimates of total amount of each constituent calculated from the total standing crop of the plants are so large as 6, 076 kg in nitrogen, 1, 338 kg in phosphorus and 83, 511 kg in carbon.
The carbon-nitrogen ratio of the submerged and floating plants of the lake are smaller in value than that of the milk vetch. Similarly, the values of the emergent ones are much smaller as compared with those of straws of rice and wheat.
In their growth processes the larger plants remove temporarily these essential nutrients from the water and bottom deposits, and also from the air. These substances are not carried away from the lake but retained in the plant bodies, and finally returned to the water. This will no doubt play an important role in the eutrophication of the lake.View full abstractDownload PDF (160K) -
Yoshiyasu KANETSUNA1967 Volume 28 Issue 2 Pages 68-91
Published: July 28, 1967
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSThe diatom-and desmid-flora of the paddy-fields in the two valleys, Kiso-dani and Ina-dani were studied by the author in August 1956 and July 1963 respectively.
The results obtained in these surveys are as follows:
1. In these districts there were found 208 forms, 147 diatoms and 61 desmids.
2. The flora of both groups resembles well that of paddy-fields in some other parts of Japan in the presence of the dominant, subdominant and the widely-distributed species.
3. A few alpine diatoms, Eunotia parallela, Tetracyclus lacusrtis, Diatoma hiemale var. mesodon were found in the Ina district.
4. The author has no doubt that agricultural chemicals exert influence upon the distribution of desmids and diatoms in these paddy-fields.View full abstractDownload PDF (621K) -
Shiko SHIGA1967 Volume 28 Issue 2 Pages 92-102
Published: July 28, 1967
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSWater samples were obtained at the mouths of the Ono and the Oita rivers and also along the coast of the Beppu Bay, and soluble silica was determined by Iwasaki's method (1960). Soluble silica was defined as the part of the total silica which formed silicomolybdic acid in the part of ammonium molybdate and sulphuric acid.
When a river enters the sea, it would be expected that the high concentration of soluble silica in river water could be reduced by dilution with sea water of a low concentration of soluble silica. The data obtained, however, show that some removal of soluble silica from the river water other than dilution does occur in field samples. Several experiments were performed in the laboratory by mixing river water with Bay water showed similar results.
On the basis of the field data and the laboratory experiments the mechanism of inorganic removal of soluble silica has been proposed as follows.
(1) The removal of soluble silica from the river water is mainly caused by the process that soluble silica is reformed to colloidal silica during the mixing with Bay water. In the river water the initial percentage of soluble silica to total silica is over 95 per cent. This rate slightly drops with increasing chlorinity until 10gm Cl per litre but over this point the dropping rate becomes greater and when it is over 17mg Cl per litre, as in thesurface Bay water, the percentage drops down to 10-14. The difference between the concentrations of soluble and total silica indicates the amount of colloidal silica. Therefore, at a high value of chlorinity nearly all of the soluble silica change to colloidal silica by coagulation of them and are removed from the surface Bay water.
(2) In addition to the mechanism mentioned in (1), the other removal of soluble silica is caused partially by suspensions in river water. In this case increasing removal occurs when the chlorinity is increased and 50-60 per cent of soluble silica removed in maximum by suspended materials.
Other mechanism, i. e., removal of soluble silica due to biological uptake by diatoms and inorganic removal by electrolytes in Bay water are both negligible small.View full abstractDownload PDF (344K)
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