Research On Water-Crop-Energy-Ecosystem Nexus In The Yarkant River Basin

The Yarkant River Basin（YRB）is a typical arid inland river basin.Its upstream areas are rich in hydropower resources,and its downstream areas are large agricultural irrigation areas in China.The YRB is located at an essential node of the Belt and Road Initiative.Its development has high strategic significance for maintaining long-term security and stability in the northwest frontier regions of China.The YRB has a dry climate,scarce water resources,fragile ecological background,and backward economic development.The level of sustainable development between humanity and nature is at the initial stage,and it is urgent to explore a sustainable collaborative management pattern between society and ecology.Therefore,this thesis takes the basin’s water-crop-energy-ecosystem nexus（Nexus）as the starting point.In this context,this study analyzed the interaction process of physical water and virtual water and the change characteristics of the environmental footprint in the Nexus.It revealed the quantitative relationship between resource occupation and environmental discharge in agricultural production.Through emergy analysis,the response of ecosystem service emergy to changes in local production activities and the suitable development scale of cultivated land in the river basin is comprehensively evaluated in combination with three-dimensional emergy ecological footprint.Then,this study analyzed the spatiotemporal fairness and driving force of the critical elements affecting the Nexus in the river basin.Combined with the above results,this study designed the sustainable coupling coordination and comprehensive evaluation system of the Nexus to establish the mutual feedback and co-evolution paradigm between multiple systems.Moreover,this study proposed the Cotton Hydropower Trade-Compensation Path Mechanism（TCP）,and discussed the future coordinated development plan of the Nexus in the YRB.The main research contents are as follows:（1）This study sorted out the critical theoretical support,boundary structure,and connotation of the coordinated development of the Nexus.Then,this study calculated the transformation law of physical water and the virtual water cycle in the Nexus leading industries under the historical time series of the YRB,and analyzed the actual occupation of water resources and environmental discharge pressure by the crop system.Moreover,this study explained the critical policy measures affecting the resource occupation and environmental discharge of Nexus leading industries.The results showed that the high demand for cotton products in the non-local markets directly contributed to the substantial increase in the local crop water footprints and the outflow of a large amount of virtual water.High inputs of chemical fertilizers,agricultural film,etc.,and soil N₂O emissions became the main incentives for increasing crop carbon footprint,resulting in growing water scarcity and environmental discharge pressures in the YRB.（2）This study analyzed the crop-ecosystem emergy flow in the YRB.Then,this study calculated the response process of the ecosystem’s positive and negative service emergy to human activities.Third,this study discriminated the natural capital stock and flow occupancy caused by emergy input and output,and assessed the appropriate scale for sustainable development of the crop system.The results showed that the emergy input of crop production is mainly non-renewable industrial auxiliary energy.The downstream agricultural production and ecological protection actions improved the service emergy values of product supply,carbon sequestration,and oxygen release,while the upstream pays more opportunity costs.The downstream areas had a stronger ability to collect emergy elements,which led to uneven economic development and resources distribution.The YRB has been in an increasing ecological deficit for a long time.The ecological footprint size and the ecological carrying capacity of cultivated land have been in a state of decoupling for a long time.Therefore,the suitable development scale of the YRB should be controlled between 70%and 82%of the actually cultivated land areas.（3）By analyzing the equity and spatiotemporal patterns of key environmental elements of the Nexus in the YRB,this study clarified the influence degree of the main driving force on the increase in local environmental emissions.The results reflected a spatial mismatch between crop carbon footprint and emergy ecological footprint.The spatiotemporal accumulation of water and land resources in the artificial oasis reduced the functionality of natural oasis ecosystem services.The sensitivity of changes in environmental elements in the upstream areas was higher than in the downstream areas.The water economic,emergy technology input and population-scale effects positively promoted the increase of environmental discharge in the river basin.In contrast,the energy consumption effects played a negative inhibitory role.The water resources systems were a stronger driver force of economic output in downstream areas,resulting in more energy consumption and environmental discharge.Improving the water productivity effects in the downstream areas can reduce the emergy technology input and the environmental emission intensity.More energy needs to be consumed in the upstream areas to achieve the same production level.（4）This study evaluated the coupling and coordinated development level of the Nexus system indicators in the river basin and identified the main obstacle indicators affecting its sustainability.Then,this study predicted the future development trend of the Nexus.Finally,this study discussed the viability of the TCP pattern.The results showed that the Nexus gradually developed from low-coupling to co-coupling.During the 13^th Five-Year Plan period,the policy implementation strengthened the coupling coordination between the water-crop-ecosystem in the YRB.The obstacles of socio-economic indicators to the Nexus sustainability were weakened,and the barriers to resource consumption and technological input were strengthened.It is expected that the Nexus will enter the stage of collaborative coupling after 2030,and policy investment will have a more significant influence on the Nexus in the future.The TCP pattern has practical value for promoting the sustainable and coordinated development of the Nexus in the future.the pattern is in line with the policies of the Communist Party of China on governing Xinjiang for the new era.In summary,this study preliminarily answered the scientific questions of promoting the sustainable and coordinated development of the Nexus based on the theoretical methods of resources,environmental management,and ecological economics in the YRB.Furthermore,this study provides scientific supports and decision-making recommendations for the cross-system cooperation and management of the YRB and other arid inland river basins.