Ecosystem Functioning And Influencing Factors In The North Canal Basin Based On The Evolution Of Landscape Patterns

The Beijing Sub-center assumes the important mission of undertaking the non-capital functions of Beijing and promoting the integrated development of Beijing-Tianjin-Hebei.The North Canal water system is the main water system in the sub-center of Beijing,and it carries more than 80% of Beijing's population,economic scale,and nearly 90% of the discharge pressure of sewage and other pollutants.The North Canal water system has always suffered from serious shortages of water resources,serious pollution of the water environment,and insufficient water ecological functions.In the future,the high-standard and rapid construction of the sub-center will still need to carry a large number of population increments and ecological environmental burdens.To promote the collaborative development of ecological protection and social and economic integration in Beijing's sub-center and surrounding areas,and to enhance the function of the regional ecosystem,it is necessary to grasp the temporal and spatial change trends and key control elements of the ecosystem function of the North Canal.The landscape pattern affects the process,which in turn affects the function of the regional ecosystem.The study of the interaction between the watershed landscape pattern and process,and the function of the ecosystem will help the formulation of regional land use and ecological protection policies.Therefore,the 6th Landsat remote sensing image from 1995 to 2018 was selected as the basic data;and water quality indicators such as COD,TP,TN,ammonia nitrogen,and chlorophyll a were obtained.Collected many years of social-economic,climate,and hydrological historical data,combined with the field survey data for two consecutive years in 2019 and 2020,established an ecosystem function evaluation system using a comprehensive index method,and calculated the ecosystem function of the basin for the past 30 years.In addition,the influencing factors of the water ecosystem of the river basin are studied,and the correlation between the change of landscape pattern and the macro and micro ecosystem functions of the river basin and the relationship between them are analyzed.The main conclusions of the paper are as follows:(1)From 1995 to 2018,the ecosystem function status of the North Canal Basin showed obvious temporal and spatial differentiation.Except in 2000,the overall ecosystem function status of the North Canal Basin was basically in a general state.In2000,the overall ecosystem function status of the North Canal Basin was in a poor state;in terms of the ecological function status of the North Canal sub-basin,the upstream ecosystem function status was basically relatively good.The middle and lower reaches are good,and the ecosystem functions of the Shahe sub-basin and Bahe sub-basin are relatively good,while the Liangshuihe sub-basin,Wenyuhe sub-basin,and the Qinghe sub-basin are poor.Combining multiple methods,the key element of the watershed ecosystem function evaluation system is identified as aquatic habitat indicators.(2)From 1995 to 2018,the changes in the ecosystem functions of the North Canal Basin were jointly affected by a variety of factors.The inflection point of the changes in the ecosystem function of the North Canal Basin is roughly in 2005;the change trend of the ecosystem function in the North Canal Basin is similar to the change trend of multiple factors.The main influencing factors are the development of urbanization in the basin,and the social-economic development of the basin,such as population changes,Changes in GDP,etc.,natural endowments of the basin,such as vegetation coverage,water resources,etc.(3)There is a certain correlation between the functions of the river basin ecosystem and the landscape pattern.Changes in some landscape pattern indexes such as aggregation index,connectivity index,and sprawl index can explain the changes in watershed ecosystem functions from 1995 to 2018 to a certain extent;in addition,changes in watershed micro-ecosystem diversity have a certain impact on watershed landscape pattern changes.The correlation of,mainly is that the change of benthic fauna diversity has a certain correlation with the change of indexes such as connectivity in the landscape pattern index.In addition,the changes in the configuration of landscape elements also have a certain impact on the changes in ecological functions.The changes in the proportion of ecological sources in each sub-basin in the North Canal Basin have a certain correlation with the changes in sub-basin ecosystem functions.