Aquatic inset communities of the Niu River before and after the construction of a dam

Abstract

The aquatic insect communities in the Niu River, Nara Prefecture, were investigated concerning the conditions before and after a dam was constructed at Kurobuchi in the course of that river. The results obtained are as follows:
1. In May 1954, before the construction of the Kurobuchi dam, there were found rich insect communities in the river. For example, the standing crops of all the stations (Jodo, Kurobuchi, Wada, Obusu) were estimated 4.5-7.7g in wet samples per 0.25m2. The net-spinning caddis worms were dominant, and the communities were in climax in succession of the aquatic insect communities of rapids.
2. In May 1960, after the construction of the dam, the lake formed behind the dam has become to have bottom deposits, such as: 1) gravel and sand in the upper part, 2) sand with mud in the middle part, and 3) mud in the lower part. The dominant species found in this investigation are as follows:
1. Ecdyonurus yoshidae 2. Potamanthus kamonis 3. Limnodrilus sp. The dominant life forms are: a creeping form (1 & 2) and a burrowing form (3).
3. The lower reaches of the river from the Kurobuchi dam has a very poor fauna, consisting of creeping forms as dominant life forms.
4. At Wada, on the 2. 5 km lower from the dam, the dominant life forms are swimming and creeping ones.
5. A rich insect fauna was found at Obusu, 4 km lower from Wada, where the dominant life forms were net-spinners.