Page - 1011 - in Book of Full Papers - Symposium Hydro Engineering

guichenoti, Rhinogobio cylindricus, and Rhinogobio ventralis, migrated from the still-water sections of the reservoir area to the flowing-water river sections of the upper reaches of the river indication of the shrinking habitat space and an indirect cause of population reduction among these fish (Wu Qiang et al., 2007).SHRINKING POPULATION 4. INCREASED WATER POLLUTION AND LAKE EUTROPHICATION According to statistics, sewage discharge in the Yangtze River Basin has risen from 12.7 billion m3 in the early1980s to the current level of 15 billion m3, accounting for about 40% of the national total. Urban sewage treatment is inefficient, and a large amount of untreated sewage is discharged into various water bodies, causing varying pollution. The middle and lower reaches of the Yangtze River, 4, 000 lakes here are larger than 0.5km2. Five most famous freshwater lakes are located in the economic development zone in China. 5.6% are oligotrophic, 44.4% are mesotrophic, and 50% are eutrophic. More than half of them, especially those in suburban areas, have been affected by eutrophication. Taihu, Chaohu, and Dianchi Lakes are typical heavily polluted lakes (China Environmental Quality Report, 2011). For a vast majority of the lakes in the Yangtze River, sluices and embankments separate them from rivers. Poyang and Dongting Lakes are the only large lakes that are still linking to the River. 5. REDUCED RIVER AND LAKE CONNECTIVITY Today, it has a lake area of about 15,200km2 in Yangtze River, which accounts for 1/5 of the national area. Historically, more than 100 lakes larger than 10km2 originally connected with rivers. Since the 1950s, due to massive construction of water conservancy projects and artificial reclamation, the longitudinal, horizontal, and vertical connectivity of the river systems in the Yangtze River Basin has been, in varying degrees, damaged. 5.1. RECLAMATION AND SLUICES AFFECTED RIVER-LAKE CONNECTIVITY For a vast majority of the lakes in the Yangtze River, sluices and embankments separate them from rivers. Poyang and Dongting Lakes are the only large lakes that are still linking to the River Table 1 Factors Affecting the Connectivity between Lakes -Rivers in the Middle and Lower Yangtze River 1011