Study On The Temporal And Spatial Differences Of The Impact Of Slope Landscape On River Water Quality In Chishui River Basi

The unique geographical conditions of the Chishui River basin create a highly heterogeneous surface landscape,which makes the relationship between it and water quality more complex and uncertain.In order to further study the impact of landscape features on water quality in such areas,this study takes the Chishui River basin in Southwest China as the research object,adopts the methods of field sampling test,subdivision,correlation analysis,Geo Detector and BP neural network model,and combines the data of water quality,land use and related environmental factors.The difference of water quality in different relief areas and the influence of landscape characteristics on water quality driven by environmental factors were studied quantitatively.The temporal and spatial differences of the effects of slope landscape characteristics on river water quality in Chishui River Basin were obtained.Establish a response model of "slope landscape-water quality" which is more suitable for the topographic and geomorphic features of the basin.The simulation and prediction of river water quality in different time and space can provide reference for non-point source pollution prevention,water resource protection and landscape planning in Chishui River basin.The main research results are as follows:(1)The characteristics of slope landscape in different relief areas are different.In terms of slope landscape composition,gentle slope landscape occupies the largest area(PL)among all landscape components,namely paddy field(64.9%),dry land(73.5%),forest land(59.3%),shrubbery(68.2%),grassland(70.9%)and construction land(58.9%).From small topographic relief(STR)to large topographic relief(LTR),the area of dry land,shrubbery and construction land decreased,while the area of forest land increased significantly.The gentle slope dry land and gentle slope shrubbery in STR are the dominant landscape.The dominant landscape in LTR is gentle slope forest land and steep slope forest land.The landscape pattern index of dominant landscape in STR and LTR are higher than that of other non-dominant landscape.The landscape intensity in STR is much greater than that LTR,indicating that the transformation degree of human activities on the surface landscape in STR is much greater than that in LTR.(2)The correlation between slope landscape characteristics and river water quality in different relief areas is different.In STR,the "source" landscape features,such as flat dry land,gentle slope dry land,gentle slope shrubbery,steep slope shrubbery and construction land,had a stronger positive correlation with water quality parameters,and had a negative impact on river water quality.In LTR,dry land,shrubbery and construction land are the "source" landscape,which has a negative impact on water quality.Forest land is a "convergence" landscape,which has a positive impact on water quality.The PL,patch density(PD)and edge density(ED)of dry land,shrubbery,grassland and construction land were highly positively correlated with water quality parameters.The PL,PD,ED,landscape shape index(LSI)and largest patch index(LPI)were highly negatively correlated with water quality parameters.(3)The explanatory power of slope landscape features to river water quality is different in time and space.The average explanatory power of slope landscape features to water quality in LTR(0.60 in wet season and 0.52 in dry season)was much higher than that in STR(0.36 in wet season and 0.33 in dry season).In the two types of relief areas of the two water periods,the slope landscape features with the strongest explanatory power for water quality were different.The wet season of STR is flat paddy field LSI(0.62),the dry season of STR is gentle slope dry land LPI(0.68),the wet season of LTR is steep slope dry land PL(0.84),the dry season of LTR is flat construction land PL(0.74).(4)The combined effects of slope landscape characteristics and environmental factors on river water quality are greater than the separate effects of each factor.In wet season of STR,the interaction of precipitation(0.52)and flat dry land PL(0.58)had an explanatory power of 0.92 for river water quality.In dry season of STR,the interaction of air temperature(0.49)and mean patch size of flat grassland(MPS,0.55)had an explanatory power of 0.98 for river water quality.In wet season of LTR,the interaction of precipitation(0.55)and steep slope dry land PL(0.84)had an explanatory power of 0.92 for river water quality.In dry season of LTR,the air temperature(0.55)and steep slope dry land PL(0.73)had an explanatory power of 0.97 for river water quality.Therefore,it is particularly important to consider the comprehensive effect of environmental factors and landscape characteristics on river water quality.(5)The response model of "slope landscape-water quality" was constructed.The decision coefficients of the "slope landscape-water quality" response model for the two types of relief areas in the two water periods are all above 80%,and the average absolute error is less than0.18.The model has good fitting effect and small error.The degree of fitting in dry season is slightly lower than that in wet season,and the degree of fitting in LTR is slightly lower than that in STR.The BP neural network model simulates the response of river water quality to landscape characteristics in different topographic and geomorphic areas of Chishui River Basin.The independent variables entered into the model were different.The dry land landscape characteristics in STR contributed more to the response model,while the forest land landscape characteristics and temperature in LTR contributed more to the response model.The contribution of dryland landscape characteristics and precipitation was greater in wet season,while the contribution of air temperature was greater in dry season.Based on the experimental results,the water environment protection strategies with specific slope landscape characteristics were proposed in different relief areas.