Abstract
Forty-five dammed lakes have been investigated during the years 1972-1973, regarding particularly the animals inhabiting the bottom of them. Those lakes cover most of the representative dammed lakes constructed for various purposes in Japan. (Table 1). The vertical distributions of water temperature and oxygen amount dissolved in water are shown in Figs. 1-6. The oxygen curves, especially the hypolimnetic declines, as well as the indicatory species of phytoplankton were suggestive to the writer to establish a classification of the lakes in question on the basis of their benthonic animals.
Regarding the bottom-inhabiting animal taxa, the Oligochaeta and the Chironomidae (larvae) were the main components in most lakes, except a few lakes in which Asellus and Gammarus (both Crustacea) occurred.
In the lakes of the oligotrophic type, in which the quantities of hypolimnetic oxygen were enough to support benthonic animals, two subtypes can be distinguishable : the Tubifex sp. I. type and the Endochironomus type.
The lakes of the eutrophic type can be divided into the four subtypes, i. e., the Tubifex sp. II. type, Chironomus plumosus type, Chironomus plumosus-Tubifex sp. III. type, and the Chironomus plumosus-Chaoborus type. In most of such lakes dissolved oxygen in the hypolimnion entirely disappeared in mid-summer. Among the lakes of the latter three subtypes, all of which are characterized by the occurrence of Chironomus plumosus, eutrophication is progressing in various stages as the following order :
Chironomus plumosus type→Ch. plumosus-Tubifex sp. III. type→Ch. plumosus-Chaoborus type.
