Study On The Evolution Of Water Ecological Environment In The Middle And Lower Reaches Of Hanjiang River

The Han River is the largest tributary of the Yangtze River.The middle and lower reaches of the Han River is an important area for the economic development of Hubei Province.The Han River water resources are the basis for the sustainable development of cities along the Yangtze River.The Middle Route of the South-to-North Water Transfer Project and the project of Diversion of Yangtze River to Hanjiang river have changed the spatial and temporal distribution of water resources in the middle and lower reaches of the Han River,which inevitably affects the water ecological environment in the middle and lower reaches of the Han River.The water ecological environment of Hanjiang river is mainly affected by factors such as climate,hydrology and water pollution.The paper analyzes the hydrological situation of the middle and lower reaches of the Hanjiang River,the spatial and temporal distribution of water quality,and the ecological evaluation of phytoplankton and environmental factors.A comprehensive analysis of environmental evolution has led to the following conclusions:(1)Through the Mann-Kendall method and the process line method,the hydrological data from 1990 to 2015 in Huangzhuang,Huangjiagang and Xiantao sites were analyzed.It was found that the precipitation of the three stations did not decrease significantly;after water transfer The distribution of runoffs of the three stations tends to be uniform throughout the year,and the unevenness coefficient of the Huangzhuang station is the largest;the flow of the middle and lower reaches of the Hanjiang River has changed in 2003 and 2014 due to the official flooding of the Danjiangkou Reservoir and the South-to-North Water Transfer Project.(2)Using the seasonal Kendal test method and Kendell analysis method,the 12-year monitoring data of five stations including Shenwan,Huangzhuang and Yujiahu in the Hanjiang River show that the total phosphorus in Shenwan station has a rising trend year by year;The total nitrogen in Yujiahu Station exceeded the standard value;the ammonia nitrogen of Huangzhuang Station was increased year by year;the permanganate index,total phosphorus and ammonia nitrogen of Luohanzha Station and Shilou Station showed a downward trend.The trends of water quality indicators in Luohanzha and Shilou station were almost the same,indicating that the water quality of these two stations is relatively stable;By analyzing the relationship between pollutant concentration and flow rate,it is found that the relationship between concentration and flow rate is not significant,indicating that the water quality change in the middle and lower reaches of the Hanjiang River is more affected by the source pollution source,and the water quality change has a greater impact on the water ecological environment change of the basin.(3)Using the sampling data of phytoplankton in the three periods of rainy season,intermediate season and dry season,the phytoplankton community in the middle and lower reaches of the Hanjiang River was dominated by diatoms and the trend of the transformation to the green algae;the RDA analysis of phytoplankton and environmental factors showed that the pH value is the main influencing factor affecting the distribution of phytoplankton community structure,and the main influencing factors have changed in different periods.