A limnological survey of Lake Shinsei, 1: Seasonal changes of water qualities
1981
Nozaki, T. (Kanagawa-ken. Environmental Center, Yokohama (Japan)) | Watanuki, T. | Sakamoto, T.
Seasonal changes of water qualities in Lake Shinsei, Kanagawa Prefecture, were surveyed from July 1978 to June. 1980. The seasonal changes could be divided into the stagnation and the whole circulation periods from the results of the vertical distribution of water temperatures. The thermocline was found to be kept stablely from June to September. Water qualities of the epilimnion considerably differed from the one of the hypolimnion especially in summer complete stagnation periods. In the epilimnion, the high values of pH and DO were observed and nutrients such as NH4-N,NO3-N and PO4-P were not detected. On the other hand, in the hypolimnion, the increase of concentration of nutrients, iron and manganese released from bottom sediments were observed under the conditions of pH6.8-7.0 and 0 micro m/l of DO. In whole circulation periods, water qualities were almost same from the surface layer to the bottom one. In summer complete stagnation periods, content of chlorophyll-a was changed as follows. The averaged value in May for two years was about 40 micro g/cubic m The maximum value from June to October in 1978 was 75.1 micro g/cubic m However in 1979, that value during this season was only 23.0 micro g/cubic m In the whole circulation periods, the average content of chlorophyll - a was 9.7 micro g/cubic m. These results showed that Lake Shinsei had characteristics of a deep eutrophic lake on flatland.
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