Abstract
Twenty gold-fish ponds in Kita-Koriyama, Nara Prefecture were studied in March, 1955, concerning the relation between the water colors and plankton.
The water colors were measured by the method of YAMAZAKI and WATANABE (1955), in which the principle of additive color mixture by using a MAXWELL'S disc was applied, and the results were indicated by the C.I.E. color language (Table 1). As to obtain the quantitative values of plankton as exactly as possible, the author calculated the extinction values measured by photoelectric photometer with compensating circuit, and substituted those values for the quantity of plankton (Fig. 1).
The results are as follows :
a) The correlation between the luminosities (Y) and excitation purities (Pe) in the water colors is shown as Y=0. 267Pe+0. 4 ; and the correlation coefficient (r) is 0. 895.
b) In the ponds, in which the extinction value is above 0. 20, each dominant wavelength (λD) and luminosity (Y) in water colors shows a negative correlation, but in those below 0.20, such a correlation cannot be seen. Moreover, the water color in the former is determined by the composing percentage of Scenedesmuswhich is dominant in every pond, while in the latter it is considered that the water colors are not only determined by pigments of plankton but also by physical factors. (Fig 3, Fig. 4).
From the above facts, it is difficult to consider that the plankton density corresponding to the excitation value of about 0. 20 is a critical point in the relation between the water colors and plankton quantities in gold-fish ponds.
