Abnormal water temperature downstream dam construction and its effects on river biota in some Japanese rivers.

在日本天龙河、静冈河、岐阜河和熊本河等河流中，研究了大坝建设对下游生物群的影响。在初级生产者的物种组成方面，研究了上游水库的低温水源对淡水红藻分布的影响。河床中附着藻类的生物量在靠近大坝建设的夏季有所增加，但在没有大坝建设的参考河流中，藻类生物量在冬季达到最大。除摇蚊科(双翅目)外，下游堤坝蓄水的水生昆虫密度全年均低于参照河。来自大坝蓄水的颗粒物有机质的浓度和负荷量沿河流纵向迅速下降。根据毛翅目昆虫的优势度和肠道含量的观察，水生昆虫的摄食有助于有机物的减少，以附着藻类为食的高山毛翅目鱼类肠道中藻类的种类组成在有堤坝的河流和没有堤坝的河流中有显著差异。分别检测了丝状蓝藻，特别是简氏同源藻和硅藻。参考河流高山对虾的体脂指数(体重/(体长)^3×1,000)大于建坝河流。

Effects of dam construction on biota in its lower reaches were studied in some Japanese rivers such as the Tenryu,(Shizuoka Pref.), the Hida (Gifu Pref) and the Kuma (Kumamoto Pref) Rivers.For species composition of primary producer, effects of low temperature water originating from upper dam impoundment on distribution of freshwater Rhodophyta was detected. Biomass of attached algae in riverbed was increased in summer just downstream dam construction, though maximum algal biomass was recorded in winter in reference rivers without such constructions. On the other hand, no significant difference of primary production rate was detected between rivers with dams and without such constructions.Density of aquatic insects, except for Chironomidae (diptera), down reaches dam impoundments was low through the year in contrast with reference rivers. Both concentration and loading of particulate organic matte originated from dam impoundment were rapidly decreased longitudinally along the stream. Based on the observations of dominance of Trichoptera with net and of the content of their guts, consumption by aquatic insects contributed to decrease of organic matter.The species composition of algae in guts of P1aoglossus altivelis which feed on attached algae showed significant difference between rivers with dam and that without such constructions. Filamentous Cyanophyta especially Homeothrix janthina in former and diatoms in latter were detected respectively Index of fatness (weight/(body lengths)^3 X 1,000) of P. altivelis in reference rivers were larger than that in a river with dam constructions.