AQUATIC INSECT COMMUNITIES AND THE BIOTIC INDEX OF THE RIVERS WHICH FLOW INTO THE NORTHEASTERN PART OF THE LAKE BIWA

Abstract

The present paper deals with the ecological studies of aquatic communities of Okawa River, Yogo River, Ane River and Seri River which flow into the northeastern part of the Lake Biwa. The biotic index of the same rivers was determined based on the BECK-TSUDA method. The field study was made in spring (Seri River) and summer (other rivers) in 1963. The results are summarized as follows : 1. Okawa River and Yogo River had more standing crops of aquatic insects than Ane River and Seri River. But the mouth of Yogo River had less standing crop, the river being polluted by drainages of paddy fields and sewages. The lower part of Ane River which is polluted by wastes from a paper mill, had small standing crop. The lower part of Seri River which is polluted by sewages of Hikone City and besides dried up in winter, had also small standing crop. 2. The standing crop of each life form of aquatic insects is shown in Fig. 3. 3. The biotic indexes of the four rivers are shown in Fig. 4. In the lower parts of those rivers, a low biotic index is obtained because of various ill-effects.