Analysis of the Ecological Environment of the Three Gorges Project during 15 Years’ Impounding

The Yangtze River is the third longest river in the world and the longest in China. The Three Gorges Project, started in 1994, with control basin area 1 million km2 and total storage capacity 39.3 billion m³, is a key project of Yangtze River, and the largest hydropower station in the world. In 1996, the government constructed the ecological and environmental monitoring system of TGP, focused in the reservoir area, extend to the middle stream and down stream and the estuary of Yangtze rive, involved of pollution sources, water environment, agriculture ecosystem, terrestrial ecosystem, aquatic ecosystem, local climate, geological disaster, earthquake, people health, and etc. Based on these data, the ecological environment before and after the water storage of TGP was compared by statistical analysis. Since the impounding of TGP, annual incoming suspended sediment discharge equivalents to 29% of the demonstration stage, sediment deposition amount in the past 15 years lower than forecast deposition amount in the first 10 years. The water quality of the main stream in the reservoir area remained in good condition and gradually improved, and the water quality of tributaries gradually improved too. There are 14 floods "water bloom" per year on average in 2003-2005, and "water bloom" founded in 7 to 22 tributaries per year in 2006-2017. From 1996 to 2017, the total natural fishing output of the fishery showed a gradual downward trend in the early stage and dropped to the lowest point in 2011, gradually rcovered since 2012. Since 1996, the runoff volume of fish fry of the four major Chinese carps in the monitoring area has decreased dramatically, and gradually became stable after 2003 ,began to recover gradually and stabilized to about 400 million after 2009. The reservoir-induced earthquakes are characterized by low intensity and high frequency of multi-cause earthquakes, but they do not break the normal situation. The maximum magnitude does not exceed the predicted range. On the whole, the ecological environment quality in the three gorges reservoir and related areas has been good in the past 15 years. The change of ecological environment is generally within the demonstration and feasibility studies.