Study On Grassland Ecosystem Service And Its Trade-off And Synergy In The Yellow River Basin

The sustainability of ecosystem services is of great significance to regional and even global sustainable development and ecological security.The Yellow River Basin is an important area with ecological functions such as water conservation,wind prevention and sand fixation,biodiversity protection,etc.The ecological situation in this area is related to the ecological security of North China,Northwest China and even the whole country.In the past decades,the remarkable increase of human activities and the obvious warming of climate have had a profound and significant impact on its ecological environment.It is of great scientific value to explore the past changes,future trends and spatial heterogeneity of ecosystem service functions in the Yellow River Basin,revealing the trade-off synergy and scale effects of different service functions,and clarify the contribution of grassland ecosystem to the global ecosystem services.Based on the scientific relationship between land use/cover change and ecosystem service,this paper takes land use/cover change in watersheds as the starting point and takes1990,1995,2000,2005,2010 and 2018 as the research objects,using In VEST model and CASA model to quantitatively evaluate and analyze water yield,carbon storage,soil conservation,habitat quality and NPP,to clarify the temporal and spatial variation characteristics of five services of grassland ecosystem,to reveal the sensitivity of ecosystem services to grassland use change,to explore the balance synergy relationship and scale effect of ecosystem services,and to clarify the balance synergy mechanism and driving factors of five services of grassland ecosystem.Then,the CA-Markov model is used to predict the land use/cover change and the change of ecosystem service in the next 10 years,and the ecological function zoning of the Yellow River Basin is demarcated according to the spatial pattern characteristics of ecosystem service,the trade-off and synergy relationship among various functions and the future trend,and then the grassland ecosystem management countermeasures are put forward.The main conclusions are as follows:(1)The grassland area in the Yellow River Basin accounts for about 50% of the total area of the whole region,which is mainly composed of low-coverage grassland.From 1990 to2018,the area of medium and high-coverage grassland decreased while the area of low-coverage grassland increased,and the grassland degradation trend was obvious.Due to the implementation of the policy of returning farmland to forest and grassland,the area of woodland and low-coverage grassland increased.Various types of land use/cover change frequently in the whole basin,especially among grassland,woodland and cultivated land,and between cultivated land and construction land;In the past 30 years,the combination of land use cover/type in each secondary watershed is relatively stable,showing the obvious zonal law of "grassland(woodland)-cultivated land-construction land" from west to east.(2)During the past 28 years,the ecosystem service has not changed significantly in space.The upper reaches of the Yellow River can provide higher water production,carbon storage,biodiversity and soil conservation services,while the NPP service in the lower reaches is more prominent.All the ecosystem services show obvious spatial heterogeneity and are sensitive to the conversion between grassland and other land use and cover types,indicating the importance of grassland ecosystem in the whole ecosystem.(3)Grassland is the main contributor to the ecosystem service function of watershed,providing water yield accounting for 76.74%,soil conservation accounting for 49.44%,and carbon storage accounting for 33.56%.Compared with other land types,grassland habitat quality and NPP are higher.Similar to the global ecosystem service,the grassland ecosystem service shows strong spatial heterogeneity,which is mainly affected by the distribution and area of grassland.Meanwhile,the grassland ecosystem service has obvious topographic effect.(4)The relationships among the five ecosystem services in the Yellow River Basin were basically stable during the study period,and the synergistic relationships among soil conservation,habitat quality,carbon storage,and NPP services showed obvious spat ial heterogeneity.The trade-off relationship of ecosystem services has obvious scale effect.The trade-off relationship of ecosystem services in each secondary watershed is different from that in the whole region,and it is also different among the secondary watersheds.The whole ecosystem services show obvious watershed differences and obvious regional laws.The balance and synergy of the five ecosystem services of grassland have completely different results from that of the whole region,which shows that the five ecosystem services are synergistic in each study period,and also show spatial heterogeneity.(5)Regardless of ecological protection measures,cultivated land protection measures or natural changes in the future,water production services,soil conservation services and habitat quality in the Yellow River Basin will be weakened compared with 2018.However,the attenuation range is different in different scenarios.Under the ecological protection scenario,the above three services decrease the least,while the carbon storage service and NPP increase the most.The habitat quality and NPP of high-cover grassland are the highest under the ecological protection scenario;The soil conservation and carbon storage of middle cover grassland are the highest under the ecological protection scenario;The water yield of low coverage is the highest,and it is the highest under the natural change RCP8.5 scenario.(6)According to the spatial differentiation of ecosystem services and the balance of synergy,it can be divided into three ecological service leading functional areas.Area I is the leading functional area of water supply,carbon storage and habitat maintenance services,mainly distributed in Lanzhou and above the Yellow River Basin.Area II is the leading functional area of habitat maintenance and carbon storage services,mainly distributed in the Loess Plateau,Yinchuan Plain and Hetao area,and Area III is the leading functional area of net primary productivity(NPP)services,mainly distributed in the lower reaches of the Yellow River Basin On the basis of zoning,according to the spatial distribution pattern of grassland ecosystem services,one extremely important unit of grassland ecological protection,five core units of grassland individual ecological services and five units of grassland ecological service promotion were determined,and the protection and promotion countermeasures of each service function of grassland ecosystem were put forward respectively.The above results show that grassland is the most widely distributed and largest land use/cover type in the Yellow River Basin,and its ecosystem service function significantly affects the whole ecosystem service of the Yellow River Basin and the trade-off synergy among various ecosystem services.Different drainage basin will show obviously spatial heterogeneity in ecosystem services due to the size and distribution of grassland,which will lead to different leading ecosystem services in different regions.The high-quality development and ecological governance of the Yellow River Basin need to pay special attention to the importance of grassland ecosystem services.Meanwhile,we should weigh the complex relationship between ecosystem services and regional human well-being based on different time and space scales,and strengthen the convergence ability of policies at different levels.