Assessing the ecological security of the Three Gorges reservoir complex ecosystem based on the improved three-dimensional emergy ecological footprint model.

The ecological security (ES) of the reservoir complex ecosystem (RCE) is one of the critical components of watershed water security and sustainable development. Hence, accurately assessing the ES of the RCE is of utmost importance. This study proposed a novel ecological security assessment model based on the improved three-dimensional emergy ecological footprint (ESM-IEEF3D), which integrated various emergy flows during the RCE's construction and operation into a three-dimensional emergy ecological footprint (EEF3D) calculation account. The Three Gorges Project (TGP) is selected as a case study to evaluate the ES from 1993 to 2022 comprehensively. The results showed that the Three Gorges RCE mainly showed an ecological remainder state, and the inflow runoff enormously promoted the TGP's sustainability. The EEF3D indicated a fluctuation decrease trend with a mean value of 7.18 × 102 ha, illustrating that TGP's ecological security and sustainability levels are gradually improving. Regarding the ES evaluation indicators, the TGP's resource dependency and ecological pressure on the natural ecosystem and the external socio-economic system are steadily relieved. Furthermore, the Three Gorges RCE's resource utilization condition is safe, the structural characteristics are healthy, and the eco-economic coordination degree is continuously enlightening. Finally, applicable policy implications for improving the ecological security of Three Gorges RCE were provided. This study helps to understand the complex relationship between humans and ecosystems. It provides a novel framework to be used as an evaluation index and policy insights for hydropower ecological security and sustainable development.

An approach to complex transboundary water management in Central Asia: Evolutionary cooperation in transboundary basins under the water-energy-food-ecosystem nexus.

Water-related issues in transboundary basins are generally complicated by the challenges of climate change, the historical evolution of the basin characteristics, and the different interests of the riparian countries. Therefore, dealing with water-sharing and water cooperation problems among basin countries needs to be based on multi-factor system analysis in the context of regional water, energy, food (land) resources, and ecosystems. In the present study, the Aral Sea basin in Central Asia, where transboundary water problems are extremely prominent and complex, was selected as the research area. Firstly, the characteristics of the water-energy-food-ecosystem nexus of the Aral Sea basin are analyzed. Then, based on the game theory, a multi-objective game model is constructed, and the multi-objective evolutionary game process and evolutionary stable strategies (ESSs) of both the upstream and downstream countries are explored. Finally, the evolutionary stable strategy under the intervention of the basin commission is simulated. The results show that there are obvious reciprocal feedbacks among water, land, energy, and ecosystem in the Aral Sea basin, and the uneven distribution of natural resources, fragile ecosystems, and conflicting demands of multiple actors lead to the unstable evolution of the nexus. Driven by the maximization of upstream and downstream countries' respective interests, the optimal stabilization strategy of the system cannot be realized. Whereas, the introduction of the basin commission intervention and its restraint mechanism is conducive to promoting cooperation and maximizing the overall benefits of the basin. The incentives and penalties of the basin commission have significant effects on whether the system can reach Pareto optimality, and higher incentive coefficient and penalty coefficient help the system converge to the ideal state more quickly. The evolution of the water-energy-food-ecosystem nexus based on the perspective of the whole basin can provide theoretical support for dealing with the transboundary water conflicts, and the cooperation strategy aiming at maximizing the overall benefits of the basin can provide decision-making basis for promoting transboundary water cooperation and synergistic development of the water-energy-food-ecosystem nexus.

Emergy-based sustainability evaluation model of hydropower megaproject incorporating the social-economic-ecological losses.

The sustainable development of the hydropower megaproject (HM) is one of the critical components of sustainable water resources management. Hence, an accurate assessment of the impacts of social-economic-ecological losses (SEEL) on the sustainability of the HM system is of utmost importance. This study proposes an emergy-based sustainability evaluation model incorporating the social-economic-ecological losses (ESM-SEEL), which integrated the inputs and outputs during HM's construction and operation into an emergy calculation account. The Three Gorges Project (TGP) on the Yangtze River is selected as a case study to comprehensively evaluate the HM's sustainability from 1993 to 2020. Subsequently, the emergy-based indicators of TGP are compared with several hydropower projects in China and worldwide to analyze the multi-impacts of hydropower development. The results showed that the river chemical potential (2.35 E+24sej) and the emergy losses (L) (1.39 E+24sej) are the primary emergy inflow sections (U) of the TGP system, accounting for 51.1% and 30.4% of the U, respectively. The flood control function of the TGP produced tremendous socio-economic benefits (1.24 E+24sej), accounting for 37.8% of the total emergy yield. The resettlement and compensation, water pollution during operation, fish biodiversity loss, and sediment deposition are the main L of the TGP, accounting for 77.8%, 8.4%, 5.6%, and 2.6%, respectively. Based on the enhanced emergy-based indicators, the assessment reveals that the sustainability level of the TGP falls in the middle range compared to other hydropower projects. Thus, along with maximizing the benefits of the HM system, it is necessary to minimize the SEEL of the HM system, which is a critical approach to promote the coordinated development of the hydropower and ecological environment in the Yangtze River basin. This study helps to understand the complex relationship between human and water systems and provides a novel framework that can be used as an evaluation index and insights for hydropower sustainability assessment.

A Study of Strength Parameter Evolution and a Statistical Damage Constitutive Model of Cemented Sand and Gravel.

Cemented sand and gravel (CSG) has a wide range of applications in dam construction, and its properties are between rockfill and roller compacted concrete (RCC). A difference in gel content will result in a variance in CSG's structure and mechanical properties. To investigate the intricate structural mechanical properties of CSG, this study conducted a series of laboratory tests and associated discrete element analyses. Accordingly, the evolution law of the strength parameters of CSG is explored and a statistical damage constitutive model suitable for CSG is established. The main contributions of this study are as follows: (1) The failure mechanism of the CSG was described from the microscopic level, and the evolution law of the strength parameter cohesion and friction angle of the CSG was analyzed and summarized. (2) Based on the particle flow model, the energy development law and the spatiotemporal distribution law of acoustic emission (AE) provide illustrations of the strain hardening-softening transition features and the interaction between cohesion and friction of CSG. (3) The evolution function between the strength parameter and the strain softening parameter was built, and the critical strain softening parameter was determined by the microcrack evolution law of the particle flow model. (4) The accuracy of the evolution curve was confirmed by comparing it to experimental results. (5) Based on the relationship between cohesion loss and material damage, a statistical damage constitutive model was developed using the improved Mohr-Coulomb strength criterion as the micro strength function. The constitutive model can accurately describe the stress-strain curves of CSG with different gel content. Furthermore, the model reflects the strain hardening-softening properties of CSG and reveals the relationship between the weakening of cohesion and material damage at the microscopic level. These findings provide valuable guidelines for investigating the damage laws and microcosmic failure features of CSG and other relevant materials.

Coupling coordination and spatiotemporal dynamic evolution of the water-energy-food-land (WEFL) nexus in the Yangtze River Economic Belt, China.

The interrelationship between regional water, energy, food, and land systems is extremely complex. Hence, accurately assessing the coupling coordination relationship and identifying the influential factors of the water-energy-food-land nexus (WEFL nexus) are of utmost importance. This study proposes a novel analytical framework and evaluation index system for exploring interactions across the WEFL nexus. The comprehensive benefit evaluation index (CBEI), coupling coordination degree (CCD) model, and obstacle factor diagnosis model are integrated to assess and analyze the coupling coordination relationship and spatiotemporal dynamic evolution of the WEFL nexus in the Yangtze River Economic Belt (YREB) from 2006 to 2020. The results indicated that (1) the CBEI and CCD generally increased from 0.23 to 0.79 and 0.45 to 0.88, respectively, revealing the upward trend of the coordination development levels of the WEFL nexus in the YREB. (2) The lower reaches achieved a relatively higher coordination development degree than the upper and middle reaches of the YREB. (3) The findings of obstacle factors reveal that agricultural non-point source pollution control, waterlogging disaster prevention, industrial solid waste efficient treatment, and urban water-saving are the essential fields that need to be improved in YREB's future development. This study helps to understand the complex interrelation of the WEFL nexus at different spatial-temporal scales and provides a novel framework that can be used as an evaluation system and policy insights for a region's integrated resources, environmental management, and green sustainable development.

A quantitative review of the effects of biochar application on rice yield and nitrogen use efficiency in paddy fields: A meta-analysis.

Applying biochar to paddy fields is a helpful approach that potentially increases rice production and nitrogen use efficiency (NUE) to ensure food security and protect the ecological environment. Notwithstanding, reviewing most of the previous experimental studies on the impacts of biochar reveals a considerable inconsistency in the proposed results. The present study conducts a comprehensive meta-analysis on the literature published before February 2021 to investigate the impacts of biochar properties, experimental conditions, and soil properties on rice yield and NUE. The meta-analysis results show that biochar application increases rice yield and NUE by 10.73% and 12.04%, respectively. The most significant improvements in the soil properties are seen in alkaline soils and paddy soils with a fine-textured. In addition, the benefits of biochar are significantly enhanced when produced at 500-600 °C with livestock manure due to the existence of more nutrients compared to other feedstocks. Analysis of water management reveals that biochar application under water-saving irrigation is more effective in increasing rice productivity. In terms of application rates, the >20 t/ha biochar and 150-250 kg/ha nitrogen fertilizer are recommended for improving rice yield and NUE. Regardless of existing uncertainty due to the lack of long-term experimental data, those investigated factors have significant implications for biochar management strategies in rice growth systems.