1961 Volume 11 Issue 2 Pages 75-82
The type of seasonal change of water color in the ponds under consideration are classified into two categories from the chromatological point of view. I compared the ponds of type A with those of type B on the basis of seasonal change of phytoplankton-flora and its population. This classification of the types A and B was made on the basis of whether the locate point x, y, of the water color approaches to the Illuminant C in June. The plankton flora and its population in the period when the locate point of water color approaches to the Illuminant C is discussed below. This period is June and December in the ponds of type A and December in type B. (1) In both types of ponds, the population of Chlorophyceae was large and that of Cyanophyceae was small during the winter, and the plankton-flora consisting chiefly of Scenedesmus occurred continuously during this period. In the pond of type A, Chlorophyceae were dominant not only in winter but also in the middle or the end of June. It is, therefore, considered that the phenomenon, on which the chromaticity coordinates of water color approaches to the Illuminant C, was caused by the large increase of Chlorophyceae and the decrease of Cyanophyceae in all seasons. In such occasions, the water color becomes generally dark olive and the values of brightness and excitation purity of water color are always low ; this will be explained by the small plankton population in this period. After December, the water colors in both types of ponds become gradually bright olive and their locate points x, y, leave the Illuminant C accompanied with the rich production of Chlorophyceae. This fact that the locus of water color runs almost parallel with the isodominant wave-length's line on the C.I.E. Chromaticity diagram is, I think, caused by the change of quantity of Chlorophyceae, especially of Scenedesmus. When Chlorophyceae increases, the water color becomes bright olive ; when it decreases, the water color becomes dark olive. This phenomenon means that the seasonal change of water color in this period is caused by the change of its brightness and excitation purity within certain limits of the hue. (2) The locus of water color on the C.I.E. Chromaticity diagram during the period, with the exception of certain months mentioned in the above section (1), runs almost parallel with the spectralocus. This phenomenon is found during the period from May to November except June in the ponds of type A, and is found through the period from April to November in the ponds of type B. In this period, Aphanocapsa, Microcystis, Merismopedia, Lyngbya and Anabaena become dominant in all the gold-fish ponds, and populations of such blue-green algae are extremely large, and many of them become also neuston, floating in the upper layer of the water. There fore, the water color in this period is caused chiefly by the reflected light by neuston, so that the brightness and the excitation purity of water color in this period is always high. On the other hand, the hue of the water color in this period changes between yellowish green and olive by the change of quantity of Cyanophyceae. The above results show the following facts concerning the mechanism of the appearance of water color in the gold-fish ponds. (a) When Scenedesmus (Chlorophyceae) increases and becomes dominant, the locus of water color on the C.I.E. Chromaticity diagram runs almost parallel with the isodominant wavelength's line accompanied with the variability of its population. (b) When Cyanophyceae increases and Chlorophyceae decreases, the locus of the water color runs almost parallel with the spectralocus accompanied with the variability of Cyanophyceae population. (c) As the algal population increases in the ponds, the brightness and the excitation purity of water color become generally high. This tendency is remarkable in the period when Chlorophyceae increases. From both the chromatological a
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