Abstract
As the Ohori, where the limnologicol observations have been made by us since March, 1931, is highly entrophied and in the warmer season abundantly populated by aquatic plants, PH rises to above 9, 6 due to the strong photosynthesis.
The seasonal variation of PH was fairly well correlated with that of the quantity of aquatic plants. PH was 9, 3 - 9, 5 and 9, 6 at 8h. and 16h. respectively during warmer season from the middle of May to August and then decreased suddenly to 7, 5 at 8h. on October 16, the bottom flora being decayed at the time. In the winter, PH maintained its value between 8, 0 and 8, 5 and the diurnal fluctuation was very small, if any, while at early spring PH rose to 8, 9 at 8h. and to 9, 5 at 16h.
The seasonal variation of PH ranged from 7, 5 to 9, 7, the amplitude being 2, 2; the greatest amplitude of the diurnal fluctuation in all seasons was 0, 8 observed on September 23, 1931, the range of variation being from 7, 6 to 8, 4.
The fact that PH in the Ohori does not show acidic reaction even in the winter is especially interesting as there is no record of the type of “Gypsotropher Fazies” in the fresh water of other places of Japan.
