Evaluation of river improvement works based on benthic animal fauna

根据岩手县的雪谷川和宫森川的水质和水生昆虫，对河川整治工程进行了评价。河道整治后，水生昆虫的个体数和类群数都很少，以潜穴型为主，其次为织网型。结果表明，只要河床条件、支流来水量和水生昆虫爬高等条件安排得当，水生昆虫群落结构在几个月内即可恢复。结果表明，河道整治工程引起的高浊度水体对水生昆虫生物区系的危害并不严重，位于宫森河上、中游的河岸林增加了流动有机质的通量和河床中有机质的含量，从而使水生昆虫的个体数和类群数增加。粉碎器的个体数与粒径大于3.35 mm的流动有机物通量具有较好的相关性，增加了水生昆虫Shannon多样性指数。可见河岸林对河流水环境的重要性。

Evaluation of river improvement works was conducted based on the water quality and water insects obtained in the River Yukiya and the River Miyamori in Iwate prefecture. Immediately after the river improvement work the number of individuals and taxa of aquatic insects was very small and the burrowing type of insects was predominant and then the net-spinning type. It was found that the community structure of aquatic insect could recover in several months if the condition of riverbed, inflow of tributary and runup of aquatic insects were arranged well. It was shown that the high turbidity water caused by river improvement works did not damage the biota of aquatic insects seriously.The riparian forest located in the upper and middle water regions in the River Miyamori increased the flux of flowing organic matter and the amount of organic matter in the riverbed, resulting in an increase in the number of individuals and taxa of aquatic insects. The individual number of shredder and the flux of flowing organic matter with a size of more than 3.35 mm had a good correlation and the value of Shannon Diversity Index of aquatic insect was increased. The importance of riparian forest on river water environment was clearly shown.