Study On The Change Of Water Heat Regime In The Yangtze River And Its Influence On Fish

As an important index of water quality,water temperature reflects the thermal state of water.In recent years,affected by climate change and intensified human activities,the annual average temperature of the Yangtze River has increased significantly,which has a negative impact on river ecological health.Therefore,it is beneficial to the ecological protection and restoration of the Yangtze River to study the change of water potential and analyze its impact on fish in the Yangtze River.In this paper,the main stream of the Yangtze River as the research subject,qualitative and quantitative analysis of the Yangtze River hydrothermal regime change characteristics and laws,and the Yangtze River four major fish and Chinese sturgeon as the main target population,to explore the Yangtze River fish response mechanism to the hydrothermal regime change.The main results are as follows:(1)Based on the theory of ecological hydrology and river ecosystem,this paper discusses the theory of river water potential and ecological effect,expounds the theory of natural hydrological regime,summarizes the response relationship between the changes of river hydrological characteristic variables and water heat variables and river ecosystem,and the influence of river water heat regime changes on important fish in river system.(2)The trend analysis of water temperature shows that the average annual water temperature of the main stream of the Yangtze River is generally warming up;the abrupt analysis of water temperature shows that Cuntan station,Yichang station,Hankou station and Datong station have abrupt warming up in 2002,1995,2003 and 2004;the periodic analysis of water temperature shows that Cuntan station,Yichang station and Datong station all have 24-32 year main cycle.The analysis of water temperature variability shows that after 2003,the overall change degree of water temperature in Cuntan and Yichang reaches or approaches the height change.The influence of heat and cold stagnation caused by the impoundment of Three Gorges and other large reservoirs on the Yangtze River's hydrothermal regime is reflected in the increase of annual average water temperature and the increase of the number and duration of extreme water temperature events.(3)The RVA variability analysis of water temperature shows that the change degrees of the first group to the fifth group of 32 indexes in Cuntan station are 44.35%,69.37%,60.61%,74.55% and 100.00% respectively;the overall change degree of the32 indexes reaches 65.00%,which is a high change,indicating that the water temperature index of Cuntan station has changed significantly before and after 2002.The change degrees of the first group to the fifth group of 32 indexes in Yichang station are respectively 44.35%,69.37%,60.61%,74.55% and 100.00% The overall change degree of 32 indexes reached 61.02%,close to the high change degree,indicating that the water temperature of Yichang station changed significantly before and after 2003.The influence of heat and cooling hysteresis caused by the impoundment of Three Gorges and other large reservoirs on the Yangtze River water and heat situation is reflected in the increase of annual average water temperature and the number and duration of extreme water temperature events in the year.(4)The results show that the contribution rate of annual average temperature to annual average water temperature gradually decreases with the passage of time,while the upstream damming activities gradually intensify,and the contribution rate of human activities to annual average water temperature gradually increases,especially after the impoundment of the Three Gorges in 2003.(5)The results of principal component analysis showed that the water-saving temperature in winter and summer,the extreme water temperature events and their duration had a profound impact on the spawning of the four major fish.The main water temperature factors affecting the number of parent fish tails of Acipenser sinensis were water temperature from March to October,extreme water temperature events and their duration,as well as the number of water temperature reversals.The prediction model of water temperature factor and fish factor was obtained by principal component regression and multiple linear regression,and the simulation effect was ideal.The multiple linear regression fitting degree was very high,and the error was only 0.01%.