Spatial Heterogeneous Evolution And Optimized Simulation Of Landscape Pattern And Ecosystem Service In The Three Gorges Reservoir Area

Land use/cover changes and its ecological effects have become the research focus of global change.Land use/cover types can be divided into the natural landscape,semi-natural landscape and man-made landscape according to their attributes.The specific forms include forest landscape,grassland landscape,water landscape,urban landscape,farmland landscape,etc.Therefore,direct impact of land use/cover changes is the change of surface landscape pattern.The change of landscape pattern is affected by the natural ecosystem as well as by human activities.Human activities irreversibly alter the landscape pattern under consideration of"production-life-ecology"harmony.Such activities are primarily manifested in the area such as deforestation,land reclamation,returning farmland to forest and grassland,construction of nature reserves,land consolidation projects,permanent basic farmland delimitation,urbanization development,the construction of large-scale water conservancy and hydropower projects.Therefore,a comprehensive analysis to clarify the ecological effects caused by the"economy-society-ecology"ecosystem is needed.Since the 19th National Congress of the Communist Party of China,the state has formulated a strategic policy"to step up conservation of the Yangtze River and stop its over development"focusing on the sustainable development of the Yangtze River Basin and the comprehensive environmental management issues.In 2019,the Yangtze River Economic Belt accounted for 46.2%of the country's GDP,and it is an important"golden waterway"across the country.Therefore,how to coordinate ecological protection concepts with sustainable development strategies is the main goal of the region.The Three Gorges Reservoir(TGR)area is a typical river basin artificially formed by the construction of water conservancy projects,and is located in the upper and middle reaches of the Yangtze River.The Three Gorges Project(TGP)is a world-class water conservancy and hydropower project.TGP has attracted worldwide attention due to its enormous scale.The construction began in1994;the water level reached 175 m before the full operation in 2009.Due to the irreversibility of the project,the landscape pattern and ecological environment in this area have undergone tremendous changes.The China central government continuously monitors the TGR area because of fierce water and soil erosion.At the same time,TGR plays a vital role in the eastern part of the Chengdu-Chongqing urban agglomeration and serves as the economic channel for the middle and upper reaches of the Yangtze River Economic Belt.Indeed,the TGR burdens dual tasks:maintain ecological health and boost economic development.Therefore,the ecological effects of land use/cover changes in the TGR area should be valued,to analyze the formation mechanism of landscape patterns and ecological processes,and evaluate the comprehensive impact of changes in ecosystem services.Furthermore,it is recommended to propose optimization of landscape patterns based on economic and ecological benefits.The ultimate goal of the countermeasures is to provide a scientific basis for the adjustment and optimization of the industrial structure,the construction of ecological civilization and the sustainable development of the regional economy in the TGR area.Based on the above analysis,this research divides the research period into four sections:construction,intercepting,water storage,and operation.Each section took up five years,starting in1990 and finished in 2015.The study unravels different drives to natural ecosystems and further quantify the change in landscape pattern.The spatial features are integrated to evaluate the ecosystem service value and material provision capacity,which facilitates the understanding of the dynamic of landscape patterns and ecological evolution.The specific research process comprises four parts described below:1)Land use and land cover change data production.The tasks include preprocessing of Landsat TM/ETM+/OLI remote sensed image data,classification schema to perform land use and land cover mapping.Granularity analysis include a sensitivity test for different granularity,determine the optimum threshold,and identify the characteristics given various granularity.2)Measure coupled change between landscape pattern and ecosystem service value and to classify the spatial heterogeneity of ecosystem service value(ESV),this study uses the equivalent coefficients of ecosystem service value,G_i~*cold hot spot analysis technology,and GWR geographic weighted regression model.3)The CASA and In VEST model are used to quantify the three ecosystem services:organic matter production,carbon storage,and soil conservation.Besides,the partial correlation analysis and Geo DA spatial analysis are employed to model the trade-off and synergy between grid-scale and district scale.4)This study uses the FLUS model to simulate the spatial and quantitative features in 2030,and apply a multi-objective genetic algorithm to optimize the quantity structure and spatial configuration of different landscape types in the TGR area with multiple scenario settings.The simulation and optimization are transited into valid ecological and economic value,then produce the most suitable landscape scenario based on the ratio among various ecosystem services.The results showed that:(1)We measured the spatial granularity effect of landscape metrics and identified the characteristics of landscape transformation.The landscape metrics had a significant grain size effect.Choosing the proper grain size and landscape index aided in further analyzing the internal mechanisms driving landscape patterns and ecological processes in the TGR.Our results showed that some landscape indices are sensitive to Landsat data,so the grain size should be first determined before using these indices.Most turning points due to granularity appeared after 60 m,which suggests that the suitable grain size for analyzing landscape change in the TGR is 30 m�60 m.During the 4 TGP stages,the landscape pattern in the construction stage is reflected by farmland reclamation,at which time the farmland increased rapidly;at the stage of TGP cutting the Yangtze River,the increase of forest and water area is the most significant landscape dynamic pattern;at the inundation stage,the water area in the upper river increased fast,and land consolidation projects and forest protects projects were deployed in the more aggregative area;at the operation stage,Chongqing Central area and Yichang central area developed fast.These indices are highly relevant to the landscape change process are number of patch(NP),largest patch index(LPI),landscape shape index(LSI),effective mesh size(MESH),and patch density(PD),so that there are suitable for illustrating changes in landscape patterns in the TGR.These indices should be linked more comprehensively with urban development,hydro condition change,and land cover change.Experimental data in the next study could be applied to validate the landscape metric on a different scale to explore its ecological value in landscape dynamics.(2)We have identified the impact of landscape conversion on the spatial heterogeneity of ecosystem service value.In the study period,the change of landscape comprehensive dynamic degree in the TGR area is ordered as follows:impoundment phase(3.95%)>operation phase(2.27%)>construction phase(1.98%)>interception phase(1.46%).The built-up area increased by308.16%and water body increased by 43.99%,forest land increased by 1.38%,unused land decreased by 49.45%,grassland decreased by 18.82%,paddy field decreased by 5.40%,dry land decreased by 1.17%,among which urbanization development and hydropower station project had the greatest impact on the change of single landscape type in built-up area and water body.From the perspective of landscape type and ESV conversion,the increase of ESV in forest and water body is mainly affected by forest engineering and hydropower station engineering,which are also the main causes of ESV increase in the study area.ESV of 52.99�10~7 yuan is converted from local types to forest,ESV of 22.71�10~7 yuan is converted to water body,among which the main ESV sources of forest are grassland and dry land,with contribution degrees of 56.57%and 36.94%,respectively.The main sources of water body are grassland and dry land.The conversion sources of the water body are dry land(34.02%),forest(21.94%),paddy field(18.52%),grassland(15.69%)and built-up area(8.44%).The main reasons for the decrease of ESV in dry land and built-up area are the rapid development of urbanization and the implementation of land consolidation project,among which the land reclamation and the development of unused land and grassland cause the conversion of forest and grassland into dry land by 22.05�10~7 yuan and 21.95�10~7 yuan,with a contribution of-49.50%and-49.27%.The total ecological loss caused by urbanization is 8.03�10~7 yuan,including forest land contribution-47.56%,paddy field contribution-26.01%,dry land contribution-15.81%and grassland contribution-8.53%.The total ESVs in the TGR area has little change.In terms of service types,cultural services increased by 1.40%in the study period,while supporting services,regulating service and provision service decreased by 1.26%,0.35%and 0.07%respectively.From the perspective of single service,hydrological regulating service increased by 11.01�10~7 yuan or5.70%,which was the most growth type in the study period.The service of climate regulation decreased the most,ESV decreased 10.19�10~7 yuan or 1.91%.The decrease of food production service and soil conservation service are 5.26�10~7 yuan and 1.77�10~7 yuan,with a decrease of2.10%and 2.29%respectively.The spatial heterogeneity of ESV in the TGR area is obvious in the study period.Affected by urbanization and land improvement projects,the main urban area of Chongqing City,Yichang City,Kaizhou District and the northern Fengdu County are the main cold spots.Affected by forest engineering,the mountainous areas of Wulong District,Fengdu County and Shizhu County are the main hot spot distribution area.Zigui County,Fengjie County,Yunyang County,Wanzhou County,Kaizhou District and other places of the Yangtze River system and its tributaries are mainly affected by the TGP in the hot spots.(3)Estimation of the amount of material and their trade-off and synergy for the three types of ecosystem services.From 1995 to 2015,the total amount of carbon storage in the TGR area decreased.During the study period,it decreased by 5.74 Tg,a decline of about 1.06%,because the carbon storage function of dryland,paddy fields and grassland reduced.The total soil conservation decreased by 0.24�10~9t,a decline of about 2.8%,because the dryland and paddy fields reduced,and the forest project has restored the total soil conservation of forest.Furthermore,the production of organic matter decreased by 5.13 Tg,a decline of about 11.94%.Therefore,the reduction in organic matter production was mainly caused by the decrease of dryland's production function in the TGR area.As can be seen from the spatial distribution,the carbon storage and soil conservation were relatively high in Wushan County,Wuxi County,Badong County,Xingshan County,Zigui County,Yiling District,Shizhu District,Wulong District in the central reservoir and Jiangjin District in the tail area.Huaying Mountain,Jinyun Mountain,and Zhongliang Mountain have also become high value areas.There were high-value areas for organic matter production in the 9 districts of Chongqing,Yiling District,Kaizhou District,Wanzhou District,Wuxi County,Fengjie District,and Yunyang District in the central reservoir.The ecosystem service functions of these regions should be maintained and protected.Through the partial correlation analysis based on the trade-off and synergy,there was a distinct synergy between carbon storage and soil conservation,and between soil conservation and organic matter production.Furthermore,the relationship has been enhanced.There was a more obvious trade-off between carbon storage and organic matter production,and this relationship has also been strengthened.Therefore,the main ecological problem in the TGR area was the trade-off between organic matter production and carbon storage affected by human activities during the study period.Generally,the ecosystem services trade-off and synergy of the TGR have been spatially heterogeneous significantly in the past 20 years.Specifically,through the grid and county-scale trade-off and synergy analysis,the synergy areas were mainly located in Kaizhou District,Fengjie District,Yunyang District and Wuxi County in the northeast of the reservoir area.The agglomeration of forest and grassland made this regional synergy obvious.The trade-off areas were mainly located in the main urban area of Chongqing in the tail area,the surrounding Jiangjin District,Yichang and Yiling districts at the head of reservoir.The trade-off was mainly affected by urbanization and tended to strengthen.(4)The multi-objective genetic algorithm(MO-GA)optimizes the quantity structure and the FLUS model for space simulation coupling model construction.The quantity structure of landscape pattern-ecosystem services-social economy has been optimized and simulated in the TGR area.The model is preset by constraint conditions,the multi-objective genetic algorithm is used to optimize the landscape quantity structure,Markov chain calculates the conversion probability,and BP-ANN builds a suitable area.Finally,the cellular automata(CA)module in FLUS model is used to optimize and simulate the scenario.The optimal landscape type of the MO-GA is combined with the advantages of the FLUS model in space simulation,and it has the strong self-learning ability of the BP-ANN reverse neural network,which can realize the unity of quantity and space optimization.The landscape index suitable for the change of landscape pattern is applied to the training of the BP-ANN inverse neural network,and the suitable area layer constructed is used as the simulation sample,which can improve the simulation accuracy.The accuracy of corrected simulation data has been verified.The accuracy of the waterbody has increased by 13.86%,the accuracy of the built-up area has increased by 4.66%,and the overall landscape simulation accuracy has reached 95.98%.The Kappa coefficient is tested with the actual landscape type data in 2015,and the final Kappa coefficient is 0.94.Based on the GM(1,1)gray prediction model which can predict social and economic development and the value of ecosystem services,a comprehensive benefit evaluation method of"economic benefit target-ecological benefit target-ecological amount of material"is constructed.On the basis of constraint conditions and setting the conversion conditions expected in different scenarios,a MO-GA is used within the constraints to calculate the optimal landscape quantity structure for different modes.From a comprehensive comparison,the most suitable scenario for the TGR area is the development of ecological protection.On the basis of economic growth,the comprehensive ecological benefits are the highest.2015 is used as the base period to simulate and optimize the TGR area in 2030.From the perspective of spatial distribution,the optimization space is mainly located in the following three areas under the economic development scenario,including the main urban area of Chongqing as the center,the northern part of the surrounding Jiangjin District,the western part of Changshou District and the built-up area of Fuling District,the surrounding Yunyang District and the built-up area of Kaizhou District with Wanzhou District as the center,and Yiling District with Yichang as the center.The peripheral diffusion and internal filling of the built-up area are basically implemented.Under the economic-ecological development model,the optimization space is mainly concentrated in the northwestern part of Kaizhou,Wuxi County,the northern part of Wushan County and Xingshan County.They are mainly concentrated and contiguous mountainous areas,where the dryland is converted to grassland and forest.Under the ecological protection scenario similar to the economic-ecological development scenario,they are also mainly concentrated in the above areas,where the density is higher,the range is larger,and the dryland is mainly converted to forest.To sum up,the land area of the TGR area is mostly mountainous hills with the limited land resources.During the research period,this area is severely affected by human activities.How to optimize the allocation of land resources in this area has become the key to promote regional sustainable development and ecological civilization construction.The research reveals the spatial heterogeneity of the landscape pattern and ecosystem service evolution in the TGR area on a regional scale,and provides data information and decision support for the optimization of the landscape quantity structure and spatial optimization of the area,as well as the formulation of corresponding management policies.According to the division of ecological function space,for the areas seriously affected by urbanization,the boundary of urban growth should be defined;for the areas with the production function,the protection of permanent basic farmland should be strengthened;for the concentrated and contiguous high-value forest and grassland,the main ecosystem service function should be maintained by building natural reserves and other ways.It is necessary in order to strengthen the water quality monitoring of the main rivers in the periodic impoundment of the hydropower station,build the ecological barrier in the reservoir area,and prevent agricultural non-point source pollution and landslides caused by improper land use.With the progress of ecological planning concept and the improvement of data accuracy,the scientific significance of the application of ecosystem services in ecological planning will be further explored.In the future,we will continue to explore the evolution and analysis of multi-scale landscape patterns and ecological processes,and provide important ideas and data support for subsequent research work.