Spatial-temporal Associations Among Ecosystem Services And Their Driving Mechanisms: A Case Study In The City Belt Along The Yellow River In Ningxia

Ecosystem service(ES),the benefits and goods that people derive from ecosystem,can effectively connect natural environment with human welfare,which has great importance in sustainable development and ecological security.In recent years,global warming and human activities have great impacts on the fragile ecosystem in the arid and semi-arid area in northwestern China,which is composed of mountains,deserts and oasis.Understanding the spatial-temporal change of multiple ESs,their associations and underlying socio-ecological contributing factors are critical for ES management.Using the city belt along the Yellow River in Ningxia as a case study,this study quantified the spatial distribution of six ESs(food production,carbon sequestration,carbon storage,nutrient retention,sand fixation and recreational opportunity),analyzed their spatial-temporal associations and underlying socio-ecological influence factors,explored the impacts of climate change and land use change on ESs.Then we predicted the potential change of ESs under five urban expansion scenarios and two climate change pathways through SLEUTH model and RCPs.The results can provide useful suggestions for urban planning and ES management.The main conclusions are as follows:(1)Significant differences exist in the spatial distribution of the six ESs in 2017.In the regional scale,synergy relations exited among food production,carbon sequestration,carbons storage and nutrient retention,and they were impacted by similar socio-ecological driving mechanisms,in which land use pattern and vegetation coverage had the largest impacts.Synergy also existed between sand fixation and recreational opportunity,but their driving mechanisms had significant differences.Sand fixation was more impacted by topographic factors,while recreational opportunity by the comprehensive impacts of land use pattern,topography,climate factors and socioeconomic factors.Trade-off relations were shown between ESs in these two groups,while the six ESs were classified into three bundles,the same with the results of driving mechanism.Thus,spatial associations among ESs can be predicted by their driving mechanisms.(2)Three bundles were detected among the six ESs: bundle 1,characterized by high supply of recreational opportunity and limited supply of other ESs,was located in the transitional region between the central plain and the fringe mountains,and mainly impacted by climate and proximity factors;bundle 2,characterized by high sand fixation,medium carbon storage and limited other ESs,was located in the northwestern and southern mountains and mostly impacted by climate and geography factors;bundle 3,characterized by high food production,carbon sequestration,carbon storage and medium nutrient retention and limited other two ESs,was located in the central plain and impacted by vegetation coverage and proximity factors.(3)In 1989-2017,ESs had suffered significant change in their spatial distribution,spatial associations and socio-ecological driving mechanisms.The impacts of land use pattern on food production and nutrient retention,the one of vegetation coverage and climate factors on carbon sequestration,the one of slope on sand fixation and the one of socio-economic condition on recreational opportunity all increased,while the impacts of other factors on each ES decreased.The rapid development of socioeconomic system had driven the hotspot of recreation opportunity transformed from mountain area to the transition region,which resulted in the decrease of correlations between sand fixation and recreational opportunity and their separation from one bundle into two bundles.(4)In 1989-2017,food production,nutrient retention and recreational opportunity kept increasing in their average value,carbon sequestration increased first and then decreased,while sand fixation increased first and then decreased.Climate change had larger impacts on sand fixation and carbon sequestration than land use change,while land use change had larger impacts on crop production,nutrient retention and recreational opportunity than climate change.In the central plain,land use pattern has more substantial impact,and cropland reclamation was the most significant land use transition process,which had resulted in the simultaneous increase of crop production,carbon sequestration and nutrient retention and the decrease of recreational opportunity.In the central and fringe parts of plain,urban expansion and the establishment of transportation network and tourism spots had resulted in the significant increase of recreational opportunity and decrease of nutrient retention.(5)In 2017-2045,climate change would have larger impacts on the temporal change of carbon sequestration and sand fixation,RCP 8.5 would result in the increase of sand fixation by 2.75 times and decrease in carbon sequestration by 1.62%,while the change under RCP 8.5 would be larger than under RCP 2.6.Land use change driven by different urban growth strategies would have larger impacts on the other three ESs.Urban expansion would result in the decrease of food production growth driven by technical development,the decrease of nutrient retention and increase of recreational opportunity.Encouraging compact urban growth,building riparian vegetation buffers and environment protection can effectively reduce the trade-offs and simultaneous losses among ESs.