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Results
In order to get a clear idea about the thermal environment of the tidal flats of the Ariake Sea, two study areas, Iida and Higashiyoka tidal flats were selected. By installing five nos. of thermocouple at different specified depths (0.10 m,0.20 m,0.50 m,1.0 m and 2.0 m) connected with data logger (TDS-530) were used to observe diurnal variation of temperature during the 1st April to 8th April, 2006 at Higashiyoka tidal flat. The measured temperature was stored automatically at 1 h interval in the data logger. To observe seasonal variation of temperature in different depths, temperature was measured by inserting the thermocouple at 0.10 m depths interval in the last week of every month at both study areas in the Ariake sea tidal flat. The diurnal temperature variation was more visible near the surface (0.10 m and 0.20 m) indicating the influence of solar radiation in that portion, however in the deeper region (1.0 m and 2.0 m depth) the temperature was dominated by thermal properties of the mud. From seasonal variation of temperature it was seen that during spring and summer heat was transferred from subsurface to the deeper area but during winter and autumn opposite phenomenon was observed. Finally, equations are proposed to get the temperature profile in the tidal flat mud in different seasons. INTRODUCTION The Ariake Sea which is situated in the south western part of Kyushu island, is one of the best-known semi-closed shallow seas in Japan. The vast muddy tidal flat of the Ariake sea, which is almost 40% of the total tidal flat area of Japan, is famous for its rich fishery products and Porphyra sp. (sea weed) cultivation. However, a dramatic decrease of catch of shells, such as Sinonovacula constricta, Atrina pectinata and Crassostrea gigas is observed in the tidal flat in the Ariake Sea for the last 3 decades.
Ariake Sea is famous for its various kinds of fisheries products and Porphyra sp. (sea weed) cultivations. But a dramatic decrease of catch of shells is observed for the last 3 decades in the Ariake Sea. The unfavorable geoenvironmental condition of the Ariake Sea is the most liable for this declination. In order to investigate the geoenvironmental condition of the Ariake Sea a regular monitoring was carried out both in the tidal flat area and inside the sea from 2002 to date. Some predetermined sampling points fixed by global positioning system (GPS), were selected for collecting the mud sample. The major geoenvironmental properties of the Ariake Sea mud such as sulphide content (SC), oxidation-reduction potential (ORP), pH, salinity were measured in different specified layers by using steel tube sampler (0.9 m long, 0.07 m diameter) regularly. The high sulphide content of the mud is found to be one of the most important causes for unfavorable geoenvironmental condition for the benthos in the Ariake Sea. A laboratory test was carried out by mixing the acid in different concentrations with mud and executed a survival test for Sinonovacula constricta and Ruditapes philippinarum shells. The deterioration of the mud quality was increased with increasing the concentration of the acid and no survival of both types of shells was observed after 10 days. The sulphide content seems to be decreasing annually but still it is above the favorable limit for the benthos living in the tidal flat mud. INTRODUCTION The Ariake Sea having a unique feature is one of the best-known semi-closed shallow seas in Japan. The total area of this sea is 1700 km with an extended 96 km of the bay axis and an average width of 18 km. The vast tidal flat mud of the Ariake Sea, which is almost 40% of the total tidal area of Japan, is famous for its rich fishery products and Porphyra sp. cultivation.
- Geology > Mineral (0.82)
- Geology > Sedimentary Geology > Depositional Environment > Transitional Environment > Tidal Flat Environment (0.79)