| Research Abstract |
The shallow water pollution has been caused by the transport or deposits of organic materials for breeding fish. In fact, the trend of entrophication by the bottom deposits is remarkable in semiclosed bay. The superannuation of water circumstance for fish culture has become serious recently. This field study has been examined in Kitanada semi-closed bay as following: 1. Examinations of water qualities and bottom deposits in the bay, 2. Bay topography, 3. Observation of tide and wind wave, 4. Information research for utilization of the bay, 5. Experiments on consumed oxygen by bottom deposit, 6. Analysis of bottom deposits for organic matter content, 7. Physical test of sediments and 8. Field research of benthos et al.
The results of studies has been proved that: 1. Getting worse of water qualities in summer are caused by the encouraged temperature densitocline by muddiness and by fresh water, which are accelerated by an phenomenon of DO flowout on density current, an increasing of fish
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food, decrease of exchange water on effective wave, death of benthos, influence of the bay lay and crowded fish culture. 2. Moist-pellets and dry-pellets for fish have made the effective improvement of water qualities. 3. Organic matters are not related to the consumed oxygen of bottom deposit during short period. Therefore, it is necessary to examine about the condition of bottom deposit by Eh measurement. 4. Eh has been related to the consumed oxygen of short period. Both BOD and Eh are to be a characteristic about the consumed oxygen together. 5. At the incipient stage, reducing condition of bottom deposit oxidation take place fairly fast, and then the Eh indexing go up too. 6. As compared with the results 12 years ago, the organic pollution spreaded out the whole area of Kitanada semi-closed bay. 7. The wave from NW direction wind only has been influenced in the bay current effectively. 8. The decreasing effects depended on tidal forces are useful to exchange of the bay water. 9. Consequently, it is necessary that the sea water's DO have to be kept over 4 ppm after sea water exchange, and that bottom deposit's Eh have to be kept over -150 mv. Less
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