Ecological And Hydrological Variability Of The Yangtze River And Its Influence On Fish

With the rapid development of social productivity and economy,China has made further new requirements for river ecological health and high-quality development of the Yangtze River Economic Belt.Therefore,to explore the characteristics of hydrological changes in the Yangtze River in a long time series,especially to study a series of hydrological changes in the Yangtze River and the resulting ecological effects after China gradually carried out different degrees of hydropower development in the upper,middle and lower reaches of the Yangtze River since the 1960 s.It is of great significance to the future ecological health protection and high-quality development of the Yangtze River.Based on this,this paper takes the Yangtze River as the research object,selects representative hydrological stations in the upper,middle and lower basins,and conducts research on the hydrological changes in the Yangtze River and the resulting ecological effects through the measurement and extraction of field flow data at each hydrological station.The main research contents and results are as follows:(1)According to the results of the Mann-Kendall test,it is concluded that the annual average precipitation in the Yangtze River basin shows a small fluctuation in the long-term series,and the overall trend shows a downward trend.The annual average flow of the hydrological station decreases with the increase of the distance from the estuary,and the annual average flow of each tributary tends to be stable.Combined with the cumulative anomaly method and the T-test method of mean difference,it is concluded that the year 1998 has obvious abrupt changes in the upper reaches of the Yangtze River,and the reasons are analyzed to be related to the construction of tributary hydropower projects,the great flood in 1998 and the construction of the Three Gorges Reservoir;the middle and lower reaches of the Yangtze River are affected by the Three Gorges.The impact of reservoir development and operation has an approximate abrupt year of 2003.Using the wavelet analysis method,it is concluded that the annual average flow in each basin of the Yangtze River has a cyclical change of 16-24 years with different time spans,and the annual average flow in the mainstream of the Yangtze River has a relatively uniform main period of 18 years.The annual average flow in each tributary basin varies greatly in cyclical changes,and there are generally multiple small cycles.(2)Using RVA method and RI method to quantitatively analyze the degree of change of hydrological regime before and after the construction of major hydropower projects,the results show that: the hydrological regime of the middle reaches of the Yangtze River has changed seriously.The hydrological regime of Jinsha River,Minjiang River,Wujiang River and Dongting Lake changed highly.The upper reaches of the Yangtze River,Jialing River and Hanjiang River had moderate changes.Poyang Lake and the lower reaches of the Yangtze River were slightly affected.The contribution rate of climate change and human activities to runoff change in different time periods was calculated by using the cumulant slope change rate method,which proves that human activities have a significant impact on runoff change.(3)Calculate and analyze the difference degree of hydrological regime and fish species similarity coefficient between each tributary watershed,and draw the correlation curve by using correlation analysis method.The lower the similarity of species,it proved that there is a correlation between the change of hydrological regime and the diversity of fish species.The grey relational analysis method was used to analyze the correlation between each hydrological index and the change of fish resources.The 12 hydrological indicators of daily average flow and average water rise rate have a greater impact on fry runoff,and the correlations are all above 0.9.Among them,the monthly average flow index in October has the greatest impact on the change of fry runoff.