| The evolution of landscape pattern directly changed the characteristics of water resources utilization and pollutant emission process,especially the landscape elements of point source and non-point source pollution.Landscape element not only have direct influence on the integrity and coordination of surface water environmental purification system,but also cause great pressure on water environment carrying capacity.As an important ecological barrier in the upper reaches of the Yangtze River,the Chishui river basin covers three National Natural Reserves of the subtropical evergreen broad-leaved forest,the Chishui tree and the rare Endemic Fishes in the upper reaches of the Yangtze River.The water environment quality directly determines the balance of the ecosystem,the carrying capacity of the environment and the sustainable development level of the social economy.Study on the relationship between water environment and landscape pattern,putting forward the optimized strategy of landscape pattern based on water environmental protection subsequently,which is of great significance to the development,protection and scientific management of the Chishui River Basin,and to promote the construction of natural ecological barrier in the upper reaches of the Yangtze River.According to the influential mechanism of landscape pattern and water environment in the Chishui River Basin,this study combines the GIS and RS technology,taking the Landsat remote sensing images and water environment detection results of 2014 and 2017 as the basic data sources.The optimized strategy of landscape pattern is put forward based on the PLS and GWR model which simulate the relationship between landscape pattern index and water environment index.The results of the study show that:(1)Between 2014 and 2017,the grassland,arable land and construction land types in Chishui river basin changed significantly,concentrating on the urban fringe zone,forest-grass transition zone and forest-plow transition zone.The construction land in the Chishui River Basin has increased from 288.95km~2 in 2014 to 569.13km~2in 2017,with an average annual land-use growth area of 93.39km~2,which represents the most significant category of land-use change.Secondly,the area of forest land and cultivated land decreased significantly,both decreased by 364.79 km~2 and 206.3 km~2,respectively,and the annual average rate of decline was 1.36%and 2.31%.However,the areas of cultivated land and woodland reduction were all concentrated in the sub-basin Csh-3;There is no dramatic change in the spatial distribution and area of land use and water.(2)From 2014 to 2017,the patch edge density(ED),average shape index(SHAPE_MN)and Shannon index(SHDI)of each sub-basin increased,while the rest of the landscape indices varied from basin to basin.Among them,the area of construction land expands from point to linear,and the average annual growth rate of the minimum adjacent distance(LPI),average area(AREA_MN),edge density(ED),and patch density(PD)is 62.25%,,19.57%,13.27%,and 13.02%respectively.The average annual growth rate of grassland maximum patch area(LPI)was 6.15%,while the patch density decreased at an average annual rate of 3.89%,indicating that the grassland area increased and the number of patches,the marginal density and proximity index gradually decreased,resulting in a decrease in the fragmentation degree of the patch and an increase in the degree of aggregation;land use types in which the land of the forest land and cultivated land were significantly decreased.Compared with forest land,although the total area of cultivated land has decreased by203.3 km~2,its average patch area index has increased by 1.18 km~2,indicating that the extent of patch fragmentation has increased,and the degree of sprawl and connectivity index between patches has decreased year by year.(3)By comparing the single factor assessment method and the grey relational analysis method,the results of water environment safety assessment show that:the single factor assessment method is mainly based on Type I water quality(except for Class II water quality in the Chishui River and Liyu Creek sections in 2014)The results of the grey correlation analysis are based on Type II water quality.Only the2014 Songliao Stream and Maotai Section were Class I water quality,and the water environment quality of the river basin gradually deteriorated.By comparing the evaluation results of the single-factor evaluation method and the grey correlation analysis method,it can be seen that the trend of the changes in the water environment evaluated by the two is in the opposite direction,and the former has a higher evaluation result than the latter.Because the single-factor evaluation method is an interval classification principle,and the gray correlation analysis method uses the principle of membership,the gray correlation analysis method achieves the quantitative correlation between the test results and the evaluation grade and the difference between the grades,making the evaluation result more quantitative and accurate.(4)By comparing the regression equation residuals and R~2 values of the GWR and PLS models,it is found that the R~2 of the GWR model is mostly higher than that of the PLS model of the same period.The R~2 mean values of the GWR models in2014 and 2017 were 0.64 and 0.70,respectively,which were all higher than the 0.16year-on-year PLS model.In particular,the average R~2 regression coefficient of the GWR model landscape pattern and the water environment in 2017 was 0.702,which was 0.28 larger than that of the PLS model,and the mean value of the residual error was 0.082 lower than that of the PLS model,because the GWR model incorporated spatial information.It can realize the spatial difference measurement of the correlation between landscape pattern and water environment,and refine the spatial simulation of water environment.It also makes the regression analysis result more fitting and more in line with the actual situation.(5)The Countermeasures of landscape pattern optimization mainly include:1)In order to realize the sustainable development of the ecological environment and social economy,the contradiction between the construction land and the cultivated land need to be weakened,the construction land should be guided to the slope land and the woodland,and the spread and connectivity of the construction land can be reduced.2)To ensure the quality of cultivated land in high quality farming areas on the edge of the city,we should disperse the woodland and the arable land gap zone.3)as the wetland as the center of river network,lake reservoir and so on to construct the point source and the ecological prevention and control barrier of surface runoff,and optimize the land use structure and landscape characteristics of the River basin. |
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