Multidimensional Evaluation Of Ecological Effects In Chishui River Basin And Its Relationship With Topographic Factors

The Chishui River Basin is a major tributary of the south bank of the Yangtze River.It not only has important strategic significance for biodiversity,water supply,and material and energy cycle of the ecosystem,but also contributes to the GDP of Guizhou Province.At the same time,Chishui River Basin is located in the transition slope area from Yunnan-Guizhou Plateau to Sichuan Basin,with large slope and fragmented landscape distribution.As an important factor restricting the change of watershed ecological pattern and land use allocation,the multi-dimensional evaluation of watershed ecological effect and the quantitative analysis of spatiotemporal change trend considering the characteristics of slope landscape are of great significance for land resource planning,ecological environment protection and the healthy development of ecosystem in the Chishui River Basin.This article from the Angle of spatial and temporal dynamic changes of land use and landscape pattern,combining the model of In VEST,ecosystem service value model and landscape ecological risk model of quantitative evaluation in three dimensions on the general slope in land cover,habitat quality,ecosystem service value of spatial and temporal variation characteristics and slope landscape ecological risk level,The topographic relief degree under the optimal window was extracted,and the relationship between the ecological effect indexes and topographic relief was analyzed,so as to reveal the spatial distribution law of different ecological effect indexes on topographic relief in the basin,providing scientific reference for the sustainable development of land use resources in the Chishui River Basin.The relevant results are as follows:(1)Land use types of sloping land in Chishui River Basin changed significantly in time and space.The surface landscape is mainly slope woodland,slope farmland and steep slope woodland.There was obvious bidirectional transformation between slope grassland,slope woodland and slope farmland.The proportion of water area and unused land decreased,while the construction land increased gradually.From 2000 to 2020,the conversion of farmland on flat land,slope land and steep slope land to construction land,slope forest land and steep slope forest land is the most obvious.Among them,113km~2was converted from sloping farmland to sloping woodland,and 28.87km~2 was converted from steep slope farmland to steep slope woodland,which were the two main conversion trends.The growth rate of construction land was the fastest from 2010 to2020,with a total increase of 66.37km~2.(2)The results of spatiotemporal variation of habitat quality in the study area showed that the habitat quality increased slightly from 2000 to 2020,and the level of biodiversity was very important.Spatially,forest land was the main land use type of grade IV(extremely important habitat).Class II(moderately important habitat)with cultivated land as the main land use type followed.The areas with higher habitat quality were mainly concentrated in Tongzi,Zunyi and Gulin counties in the middle reaches and Chishui and Xishui counties in the lower reaches.The areas with low habitat quality were mainly distributed in Zhenxiong County,Bijie City and Jinsha County in the upper reaches of the basin,Renhuai City in the middle reaches and the mouth of the Chishui River and the Yangtze River in Hejiang County in the lower reaches.(3)The ecosystem service value in the Chishui River Basin increased first and then decreased,and the overall ecosystem service value(ESV)increased by 1.473×10~8yuan.Among ESV of single land use type,forest land has the most ecological service value and is the main positive contribution land type.The cultivated land is the main type of negative contribution in the basin.Except for waste disposal,climate regulation and food production,all other functions are reported to be on the rise.(4)Based on GIS and Landscape ecology theory,this paper establishes a landscape ecological risk model of slope land in Chishui River Basin to conduct a quantitative analysis on the landscape ecological risk level of slope land in the study area.In general,the landscape fragmentation degree of Chishui River Basin decreased from 2000 to2020,and the"conversion of farmland to forest"of sloping farmland above 6°and steep slope farmland changed more obviously,while the dominance degree of sloping forest land and steep slope forest land increased.On the whole,the ecological risk level of slope landscape decreased from 0.682 to 0.667,and the area of medium risk area decreased,while the area of low risk and low risk area increased.In different periods,the risk level in the middle and upper reaches of the basin is high,while the risk level in the lower reaches is low.(5)The optimal analysis window of relief degree in Chishui River Basin is12×12.The main type of relief in the basin is small relief area(70-200m),which accounts for about 68%of the area.The spatial characteristics of the topographic relief degree and each ecological effect index under the optimal window were mainly shown as follows:the optimal fitting function of habitat quality was a logarithmic function,while the optimal fitting function type of slope landscape ecological risk was a power function,and the R~2 of both of them were more than 90%,and the greater the topographic relief degree was,The higher the habitat quality index was,the lower the landscape ecological risk level was.The small fluctuation area is the best region of ecological effect,which is dominated by low risk and low risk.The habitat quality index is higher and the ecosystem service value accounts for 70%of the total ESV,which is the main contribution region of the total ecosystem service value.