びわ湖南東部に流入する河川の水生昆虫群集およびbiotic index
概要
The present paper deals with the ecological studies of the aquatic insect communities of Echi River, Hino River and Yasu River which flow into the southeastern part of the Lake Biwa. The biotic index of same rivers was determined based on the BECK-TSUDA method. The field study was made in early September in 1963. The results are summarized as follows : 1. Aquatic insect fauna was poor in the three rivers. Especially the middle and lower parts of those rivers had far smaller standing crop of aquatic insects than the rivers flowing into the northwestern part and the northeastern part of the Lake Biwa. The causes are probably due to the water pollution by wastes from a pulp plant, digging out the sand of the river bed for construction purposes and drying up of the river bed in some seasons. 2. The larger part of the standing crop of each station of the three rivers was occupied by the net-spinners and creepers with only a few exceptions. 3. The biotic index of the three rivers are shown in Fig. 4. The biotic index of the middle and lower parts of the same rivers is small for various reasons.