Trade-off Analyses Of Water-related Ecosystem Services Based On Land Use Change In The Xiangjiang River Basin

Ecosystem can directly or indirectly provide human with a variety of products and services,namely ecosystem services.As a bridge connecting human society and natural ecology,the sustainable supply of ecosystem services is the basis of human survival and development.In the context of global change,the most direct reflection of the impact of human activities on ecosystem structure is the change of land use,and the direction and degree of the change will have an important impact on the supply capacity of ecosystem services and the balances between services.Therefore,the study of land use change and the response of ecosystem services to land use change,as well as the correlation between ecosystem services,will be helpful to optimize ecological space management and guide policy formulation.The Xiangjiang River basin(XJRB),as the most important part of the Dongting Lake basin,is the core area of Hunan Province.Human activities in the XJRB have been changing the nature of land use in recent years.On the one hand,urbanization and agricultural expansion increased the supply pressure of the ecosystem;On the other hand,the implementation of policies such as afforestation and Grain for Green also enhanced the regulation ability of ecosystem.At present,there is still a lack of quantitative evaluation and characteristic analysis on the process of land use change and its ecosystem service benefits in the XJRB.In this study,the XJRB was used as the research area.(1)Firstly,the characteristics of land use change in the past 35 years in the XJRB are analyzed.According to the results,several major land use types in the basin experienced significant changes during 1980-2015.The farmland,built-up land and water area increased by 3.3%,2.36%and 0.34%respectively,while woodland and grassland decreased by 5.53%and 0.95%respectively.Bare land basically remained unchanged.The main changes of land use in the past 35 years in the XJRB are the interconversion of farmland,woodland and grassland,and the conversion of some farmland and woodland to built-up land and water area.(2)Secondly,the yield model and InVEST model were used to quantify four water-related ecosystem services(WRESs)in the XJRB,which includes food production,water yield,soil conservation,and water purification.In the past 35 years,food production in the basin has increased by 5.14 million tons;The change range of water yield was small,and the total amount of water yield increased by 1.23 billion m3.Sediment export was reduced by 809,100 tons,which mean soil conservation were significantly improved.However,urbanization and agricultural expansion in the XJRB lead to the increase of nitrogen and phosphorus export by 587.5 tons and 89.9 tons respectively,which mean water purification declined significantly.(3)Thirdly,Spearman correlation analysis was used to reveal the trade-offs and synergies among these four WRESs.Significant synergistic relationships were found between food production and water yield(r=0.21),soil conservation(r=0.36)in the XJRB.The synergistic relationship between water yield and soil conservation(r=0.04)was not obvious.Significant trade-offs mainly exist between water purification and food production,water yield and soil conservation.In the case of nutrient nitrogen,the correlation coefficients with the other three services are-0.83,-0.36 and-0.19,respectively.(4)Then,the multi-criteria decision-making method was used to evaluate the suitability of agricultural development in the XJRB.Based on the analysis results,four scenarios were set to explore the impact of different land management schemes on ecosystem services.Supply services(food production and water yield)or regulation services(soil conservation and water purification)can only be improved unilaterally in the XJRB under Agricultural Expansion and Grain for Green scenario.Buffer Zone of Woodland scenario can greatly alleviate the degradation of water purification caused by agricultural expansion,and reduce the export of nitrogen and phosphorus by 324.5 tons and 38.7 tons,respectively.However,under this scenario,soil conservation showed a downward trend.The Combine scenario reduced the total nitrogen and phosphorus export by 566.4 and 64.5 tons,respectively.This scenario can not only maximize the increase of water purification in the basin,but also maintain the increasing trend of water yield and soil conservation.(5)Finally,the root mean square error coefficient was introduced to quantitatively analyze the trade-off relationships under different land use development scenarios in the XJRB.According to the results of quantitative analysis,the trade-offs between water purification and food production and water yield can be significantly reduced under the Combine scenario.According to the quantitative analysis and trade-off analysis of WRESs in the XJRB,it can be seen that the degradation of water purification in the basin is serious,and it is necessary to improve the water purification by establishing riverbank vegetation buffer.The combined scenario proposed in this study can be used as a comprehensive development scheme for the XJRB,which can help decision-makers deal with the uncertainty of future land use and development,and provide reference for the sustainable management of land and water resources protection in the XJRB.