Plankton Succession of Lake Nukabira, an Artificial Lake in Hokkaido, for Five Years after being Impounded

Abstract

1. Observations of plankton in Lake Nukabira in eastern Hokkaido, which was impounded as a reservoir in September 1955, were carried out five times during the period from 1957 to 1960.2. Plankton species identified were nine both on October 26, 1957 and on July 25, 1958, twenty one on November 11, 1959 and twenty four on July 15, 1960. 3. The succession of the predominant species of plankton from year to year was as follows :Synedra ulna→Asterionella formosa→Daphnia longispina→Asterionella formosa→Daphnia longispina→Dinobryon divergens→Mougeotia viridis8 months one year two years three years four years five years five years afterimpounding 4. The total number of plankton in the present lake is larger than that in other reservoirs, such as Lake Fusen (UENO, 1941, 1951; YAMAMOTO, 1941) and Lake Miure (YAMAGUTI & YAMAMOTO, 1958), and it is smaller than that of Lake Sagami (SHIRAISHI et al., 1953) and of Lake Arasawa (ABE et al., 1960).5. Asterionella formosa and Daphnia longispina predominated by turns in the present lake for four years after being filled with water, instead of Dinobryon which usually occurs in artificial lakes.6. The appearing of Polyphemus pediculus in 1960, which is a typical lake plankton, suggests that this lake is becoming similar in type to that of a large lake. 7. From general plankton association, this lake seems to be mesotrophy, but a vigorous thiving of Mougeotia viridis in monotonous composition in 1960 gave it an impression of oligotrophic nature.