Research On The Evolution Of Land Space Pattern And The Response Law Of Water Ecological Environment In The Three Gorges Reservoir Area

River basin is not only a natural space unit with water network as its vein,but also a social space unit of human production and life.With the continuous development of social economy,the evolution of the land space pattern in the Three Gorges Reservoir Area（TGRA）has led to the profound variation of nature-society dualistic water cycle,and the imbalance and disharmony of water environment and water ecological protection are prominent.At present,the management with water ecological environment protection has developed from local terminal regulation to systematic restoration and management.It is of great significance to explore the theoretical framework and technical system of watershed eco-environmental integrity research in line with China’s natural environment and socio-economic characteristics,so as to provide scientific supports for planning the strategic layout of the high-quality socio-economic development and high-level eco-environment protection in the basin.This paper constructed the assessment system of the spatial pattern evolution of urbanization,agriculture and ecology in the basin,and the integrated model of the land space pattern and water ecological environment,quantitatively revealed the evolution characteristics of the land space pattern and the response law of water environment in the TGRA,and analyzed the coordination degree and mutual feedback mechanism between the national land space pattern and water eco-environment health,the main research achievements are as follows:（1）The research progress of the evolution of the land space pattern,the response law of water environment and evaluation of their coupling coordination was reviewed.Integrating the dimension of‘space-product-population-function’to carry out a comprehensive assessment of the evolution of the national land space pattern,build an integrated model of the land space pattern and water ecological environment in the basin,revealing key areas and key periods of water ecological environment response to the evolution of land space pattern,and quantify the coordination degree between the land space pattern and water ecological environment health are the hotspot and difficulty of the present research.It is of great support value to carry out this kind of research in the TGRA.（2）A comprehensive assessment system with 2850 districts（counties）of 31provinces（municipalities or autonomous regions）as the basic unit for the evolution of the urbanization,agriculture and ecology land space pattern was constructed based on the multi-source heterogeneous data fusion technology,and the dynamic evolution characteristics of the land space pattern of 26 districts（counties）in the TGRA in 2000-2018 were quantified.Urban space is widely distributed at the left bank of the TGRA,the urban construction space of Nan’an District,Yubei District and Shapingba District increased significantly in 2005-2010,and the construction space of industrial and mining in Jiangbei District,South Bank district,Jiulongpo District increased significantly in 2010-2015,which were from agricultural production space and green ecological space.Agricultural production space is mostly distributed at the left bank of the TGRA,Jiangbei District,Nan’an District and Yubei District decreased significantly in 2010-2015,and mostly developed into green ecological space.Rural living space is dotted,increasing by 0.09%in 2000-2018 from agricultural production and green ecological space.Green Ecological Space is mostly distributed in the right bank of the TGRA,Jiangbei District,Dadukou District,Nanan District decreased a lot in 2010-2018.The capacity to provide industrial goods and service products,and the population agglomeration degree in Yuzhong District is the highest.The supply capacity of agricultural products in Kaizhou district increased significantly,and the supply capacity of ecological products in Jiangbei District,Nan’an District and Dadukou District decreased significantly.Urban function in the TGRA has been improved significantly,with an increase of 61.54%at the medium-high level,and the largest spatial difference was found at the end of the TGRA.The center of urban function pattern in the head,middle and tail of the reservoir moved to northeast,southwest and northwest respectively.The growth rate of agricultural function is obvious,with an increase of34.62%at the medium-high level.Agricultural function performs better at the end and in the middle of the TGRA than the head,and spatial difference of agricultural function at the end of the TGRA is prominent.The center of the agricultural pattern at the end of the reservoir shifted to the southwest,while the center and the head of the reservoir shifted to the southeast.Ecological function has improved by 7.38%after a reduction of 11.54%at the medium-high level,which showed a‘V’type change with the year of2010 as a turning point,and performs best in the Xingshan County.Spatial difference of ecological function widened from 2005 to 2010,with a prominent difference at the end of the TGRA.The focus of green ecological space has shifted to the southwest in the middle and the head,and to the southwest at the end of the TGRA.（3）The integrated model of the land space pattern and water ecological environment covering 23 tributaries of the TGRA was constructed,and the spatial scale conversion method based on area weighting was adopted to analyze the coupling of natural-social spatial units in the basin.LH-OAT method was used to analyze the sensitivity of parameters such as runoff,sediment,nitrogen and phosphorus.The monitoring data of daily runoff,monthly sediment,total nitrogen（TN）and total phosphorus（TP）from 10 hydrological stations and 8 water quality monitoring sections in the TGRA from 2010 to 2013 were selected for model calibration and validation.The determination coefficients（R²）and Nash-Sutcliffe efficiency coefficients(E_NS)of the monitoring value and the simulated value were almost higher than 0.5 for both calibration and validation period,indicating that the model had good applicability and could be used to quantify the response law of water ecological environment under the evolution of the land space pattern.（4）The response law of water environment under the evolution of the land space pattern of 26 districts（counties）in the TGRA was revealed quantitatively,and the spatial and temporal differentiation characteristics of water eco-environment health were comprehensively analyzed.The number of days of TN reaching the standard in Beibei District,Yubei District and Changshou District,Fuling District,Fengjie County and Wushan County decreased significantly from 2005 to 2010,the number of days of TP reaching the standard in Yuzhong District,Yubei District,Zhongxian County and Wanzhou District decreased significantly in 2000-2005.The number of days reaching the standard in the wet season（June to September）is less in the districts（counties）dominated by urban space,while and the number of qualified days in dry season（January to March and December）is less in the districts（counties）dominated by agricultural and ecological space.The water environmental capacity of TN and TP decreased significantly in 2005-2010 and 2000-2010,respectively.Water environment capacities of TN and TP were both higher in wet season than that in dry season.The areas with larger TN water environmental capacity are concentrated in the Wanzhou District,Zhongxian District and Fuling District,and the areas with smaller TN water environmental capacity include Xingshan County,Yiling District and Badong County.The areas with larger TP water environmental capacity are concentrated in Kaizhou District,Yunyang County and Wanzhou District,while the areas with smaller TP water environmental capacity are concentrated in Yuzhong District,Yubei district and Changshou District.Soil erosion increased significantly from 2010 to 2015,and decreased significantly from 2015 to 2018,and its amount was larger in the third quarter and high-water period.The area of soil erosion decreased by 4431.77 km² from 2000to 2008,and key development zones such as Beibei District,Yubei District and Kaizhou District were where the area of soil erosion was larger.Water ecological environment health of the key development areas and the key ecological function areas changed respectively from low to lower high,higher low to high.Xingshan County,Kaizhou district and Yubei district were obviously degraded in 2005-2010,and Jiangjin District,Dadukou District and Jiulongpo District were obviously improved in 2010-2018.（5）The coupling coordination degree between the land space pattern and water environment health in the TGRA was quantified with the coupling coordination degree model,and the driving mechanism on water environment health from the national land space pattern was explored.The number of districts（counties）belonging to the coordinated development category between urban function and water eco-environment health decreased by 15.39%from 2000 to 2018,and the coordination degree showed the characteristics of the key development areas>the key ecological function areas.Yuzhong District,Yubei District and Xingshan County belonged to the imbalanced and water eco-environment-declined category.The number of districts（counties）belonging to the coordinated development category between agricultural function and water eco-environment health decreased significantly by 15.38%from 2010 to 2015.The coordination degree showed the characteristics of the key development areas>the key ecological function areas.Yubei District,Yuzhong District and Xingshan County belonged to the imbalanced and water eco-environment-declined category.The number of districts（counties）belonging to the coordinated development category between ecological function and water eco-environment health increased by 26.92%from 2000to 2010.The coordination degree showed the characteristics of the key ecological function areas>the key development areas.Yuzhong District and Yubei District belonged to the imbalanced and water eco-environment-declined category.Water eco-environment health was significantly affected by the evolution of the national land space pattern.Systematic water environment management lagged significantly behind socio-economic construction in Yuzhong District,leading to the uncoordinated state between the national land space pattern and water eco-environment health.Kaizhou District pursued too much supply of agricultural products,leading to the prominent agricultural non-point source pollution and decreases of coordination degree.The ecological advantages of the Xingshan County in the head of the TGRA were prominent,but the relationship between its primary and secondary functions was not clear,which resulted in the decline of the coordination degree of urban function,agricultural function and water eco-environment health.