| Stream and river biotic integrity had decreased due to the change of natural flow and sediment regimes、 water quality degradation altered by landscape utilization and direct alteration of channel structure. Several rehabilitation methodos had been introduced previously in the world's rivers but its biological assessment was done very poorly. In urban rivers、 previous studies conducted were still inadequate despite the biological invasion of tolerant and exotic aquatic species. This study designed two rehabilitation methods: partial river widening (RW) resulting to slow flow area and Groyne (GR) resulting to high flow area. The two methods were assessed on both native and exotic aquatic species. After rehabilitation、 the heterogeneity and diversity of river morphology、 substrate composition and water velocity were enhanced both in RW and GR areas. The low flow zone in backwater pool was formed by sand bar evolution in the RW area、 and the high flow zone of riffle widened in the GR area. The environmental diversities increased both abundance and species richness on the aquatic creatures. Positive effects were: presence of new captures of fishes such as Plecoglossus altivelis altivelis、 Misgurnus anguillicaudatus、 Silurus asotus、 ans Macrobrachium nipponense、 and increased presence of endagered Oryzias latipes and native Carassius sp. And Cyprinidae sp. (larvae). Negative effects were inhabitation of exotic fish species: Micropterus salmoides、 Gambusia affinis and Lepomis macrochirus、 which increased in the backwater、 andd proliferation of G. a. contributiong th the recudtion of biodiversity. Statistical models indicated tha faster current velocity of 5 cm/sec was effective in the prevention of exotic species、 decreasing to 77% of G. a. and 89% of L. m. numbers in backwater zone. Research results suggested that creation of flowing water in the backwater by excavating the upper part of sand bars was effective in exotic species prevenntion and vative species preservation. |
