Impact Of Landscape Pattern Changes On Soil Conservation Services In The Nansihu Basi

Soil conservation service is defined as the capacity of the ecosystem to prevent soil erosion and retain sediment,which belongs to the scope of regulation services and has a significant impact on nutrient and carbon cycle,land productivity,and social and economic conditions.Clarifying the impact mechanism of landscape pattern changes on soil conservation services is the basis for scientific management of land resources and promoting the coordination of ecological protection and high-quality development.Therefore,based on meteorological data,land-use data,soil data,and elevation data,this paper selected the Nansi Lake Basin as the study area.Arc GIS10.2,Excel,and Fragstats4.2 were used to analyze the spatial and temporal changes of landscape pattern in the Nansi Lake Basin from 1990 to 2018.In VEST model was used to simulate the soil conservation service quality in Nansi Lake Basin and to analyze its evolution law;In the grid scale,taking the landscape index as the breakthrough point,using Person correlation coefficient and bivariate spatial autocorrelation analysis method,the influence of landscape index on soil conservation services was analyzed from the perspective of quantity and spatial statistics.The spatial agglomeration characteristics of soil conservation services in each landscape index domain were visualized.The spatial regression model was used to identify the main driving indexes of soil conservation services,and further to explore the driving mechanism of ecosystem services in natural and human environments.To provide theoretical reference for the optimal allocation of land resources,the improvement of ecosystem service ability,and the sustainable development of economy in Nansi Lake Basin.The main conclusions are as follows:(1)Change characteristics of land-use landscape structure in watersheds.Cultivated land was always the largest land-use type in watershed,widely distributed;the second was construction land,with the area increasing year by year,and the sum of the two accounts for more than 85.8%of the total area.From the land-use dynamics,the annual change rate of unutilized land from 1990 to 2018 was the largest,which was-2.85%,indicating that its area fluctuated greatly.Especially in 1990-1995 and 2015-2018,the land-use dynamics reached-13.22%and 11.44%,respectively.The second was water,with a dynamic of 2.27%,and 1990-1995 had a decisive impact on the entire research phase.From the perspective of land transfer,from 1990 to 2018,different land-use types in the basin were constantly changing,and the total transfer area was465956.37 hm~2.Especially,the land-use change was the most intense from 2005 to2010,which was 358162.29 hm~2,accounting for 76.87%of the total transfer area in 29years.From the perspective of gravity center migration,the gravity center of various land-use types shifted in different directions and distances in different periods,closely related to the change of land-use types in different periods.(2)Change characteristics of land-use landscape pattern in the watershed.From the perspective of landscape level,the number of patches(NP)and the aggregation index(AI)in the whole study period showed a fluctuating downward trend,while the edge density(ED),the Shannon’s diversity index(SHDI)and Shannon’s evenness index(SHEI)showed a fluctuating upward trend,indicating that the patch shape was more irregular and complex,the influence of human activities was intensified,the aggregation of landscape decreased,the diversity and evenness increased,and the landscape heterogeneity was enhanced.From the level of landscape types,the landscape index changes of different land-use types were different.The AI value of forest land was the lowest,indicating that the discrete distribution and connectivity between patches were poor,but they were improved.The AI value of cultivated land was the highest but decreased;the patches of arable cultivated land and construction land are complex.From the grid perspective,the landscape pattern of Shanting District and the eastern and surrounding areas of Zoucheng City in Nansi Lake Basin was relatively stable,with diverse and uniform distribution of landscape types,no dominant land types,large separation and high fragmentation.However,changes in landscape patterns in other regions were complex,especially in the spatial distribution of landscape indices during 2005-2010.(3)Temporal and spatial variation of soil conservation function in the watershed and differences in the effects of different land-use types on it.From the perspective of the whole study period,the watershed’s soil conservation service of the watershed experienced a weakening-enhancement-weakening-enhancement process.The total soil conservation in each year was 279.51×10~6 t,231.36×10~6 t,172.86×10~6 t,260.02×10~6 t,174.17×10~6 t,158.21×10~6 t,and 210.60×10~6 t,respectively,which decreased by 68.91×10~6 t on the whole.The high-value area of soil conservation intensity was mainly concentrated in the eastern region with high vegetation coverage;the low-value area was distributed in the central and western regions with cultivated land and construction land as the main types.The soil conservation service of differenttypes of ecosystems was also different.The soil conservation service of forest land was the strongest,followed by grassland.Although the sum of the two areas was only 5.88-8.00%of the total area,it played a decisive role in the total soil conservation in the watershed.(4)Influence of watershed landscape pattern change on soil conservation service and analysis of influence index.Based on the grid scale,each landscape pattern index has a quantitative and spatial correlation with soil conservation services;among them,at the level of P<0.01,the correlation with ED,the landscape division index(DIVISION),SHDI,and SHEI were positive;the correlation with the contagion(CONTAG),and AI were negative.The aggregation characteristics in the eastern part of the basin were relatively stable in each period,and the landscape indexes and soil retention intensity were mainly high-high clusters(HH)or high-low clusters(HL)areas.The aggregation types of landscape index and soil retention intensity in other regions were mainly low-low clusters(LL)or low-high clusters(LH),and the distribution was different in different periods.Soil conservation service had a positive spatial spillover effect on adjacent grids;ED,DIVISION,and SHDI were important landscape indicators affecting soil conservation services,and SHDI was the most prominent.