Assessment Of Ecological Environment Change Of Danjiangkou Reservoir Under The Influence Of Water Diversion Project

The Middle Route of the South-to-North Water Diversion Project is a strategic project to transfer water across river basins in China.Since it was officially opened in December 2014,it has effectively alleviated the water shortage in the north.Danjiangkou Reservoir is the water source of the middle route of the South-to-North Water Diversion Project.In order to meet the water diversion requirements,the dam has been raised from 162 m to 176.6m,which not only increases the reservoir capacity,but also brings a series of ecological and environmental problems,which has a profound impact on the whole basin.Therefore,it is of great value to evaluate the ecological environment change of the reservoir area under the influence of water diversion projects for guiding the ecological construction and development of the basin and scientific water diversion.Meanwhile,it also provides reference for the scientific identification of the response mechanism of the ecological environment of the basin under the influence of large-scale water conservancy projects.This article in danjiangkou reservoir and the upstream and downstream as the research object,using remote sensing images,land use,such as weather and statistical yearbook data,the variation characteristics of water diversion danjiangkou reservoir before and after,land use change situation of upstream and downstream of the reservoir and the reservoir ecosystem services value analysis,evaluation of danjiangkou reservoir changes in the environment under the influence of the water diversion project.The main conclusions are as follows:(1)From the interannual variation characteristics of Danjiangkou Reservoir,the water volume of Danjiangkou Reservoir presents an overall growth trend.Before water transfer,the growth trend is relatively gentle,mainly fluctuating around 10 billion m3,while after water transfer,the growth trend is significantly accelerated,maintaining more than 10 billion m3,the most direct reason is the dam height and the strengthening of water storage.On the whole,the monthly mean water quantity showed a trend of decreasing first and then increasing,gradually decreasing from January to May,greatly increasing from June to October,and basically unchanged from November to December.Moreover,the variance of the monthly mean water quantity variation is 17.87% of the annual average water quantity of Danjiangkou Reservoir,indicating that the water quantity is relatively stable between months.Under the conditions of climate and artificial regulation and storage,the fluctuation of Danjiangkou Reservoir does not change much.(2)Land use in the upper and lower reaches of Danjiangkou Reservoir decreased in the two stages before water diversion(2000-2015)and after water diversion(2015-2018),while water area and construction land increased;The forested and grassy land was first decreased and then increased,while the unused land was first increased and then decreased.Before and after water transfer,the land types with big changes were the same,and the changes before water transfer were greater than those after water transfer.From the danjiangkou reservoir upstream and downstream,upstream and downstream the reservoir before and after water diversion construction land area were increased,but the downstream area of construction land changes upstream significantly,suggesting a construction land in the rapid expansion of the reservoir,is a reflection of the accelerating urbanization process,and downstream of urbanization is more apparent,the upstream after water diversion construction land area changes tend to be gentle;After the water transfer project,the area of forest and grassland in the upper reaches of the reservoir began to increase,and the spatial distribution of forest and grassland gradually stabilized.The reason is that after the water transfer project was completed,the measures of returning farmland to forest and grassland,afforestation and fencing were implemented.From the perspective of transfer direction,cultivated land,woodland and water area are interconverted,while the construction land mainly comes from cultivated land and forest and grass land.(3)the danjiangkou reservoir on the whole ecosystem services value slightly growth trends,ecosystem services is relatively stable,single service value is sorted by size of the diversion water,climate regulation,tourism function,hydro,atmosphere regulation,organic production and scientific research and education,in which water diversion danjiangkou reservoir impoundment and climate regulation is the core functions of ecosystem service function,accounting for 97.02% of the total value of ecosystem services of danjiangkou reservoir.With the operation of the middle route of the south-to-north water transfer project,the Danjiangkou reservoir has an increasing trend in the aspects of water transfer and storage,climate regulation,tourism function and hydropower generation value,while the values of air regulation,organic production and scientific research and education have little fluctuation.