Exploring the relationship between water-energy-food nexus sustainability and multiple ecosystem services at the urban agglomeration scale

The current perception of how ecosystem services (ES) affect the water-energy-food nexus sustainability (hereafter, nexus sustainability) is still unclear. Here, we proposed an analytical framework to explore the relationship between nexus sustainability and multiple ES. This study took the Yangtze River Delta Urban Agglomeration (YRDUA) as an example. Firstly, a nexus sustainability evaluation index system was established to evaluate the sustainability of water-energy-food nexus and its three subsystems. Then various models were utilized to quantify the four ES (water yield, carbon storage, soil retention, and food production). Finally, the coupling coordination degree model and correlation analysis were applied to explore the relationship between nexus sustainability and multiple ES. The results show that the coordination between nexus sustainability and water yield gradually improved, while that between nexus sustainability and food production declined significantly, especially in the southern regions of the YRDUA. There were obvious spatial heterogeneities in the coordination between nexus sustainability and carbon storage/soil retention, characterized by a coordination state in the southern regions and an incoordination state in the northern regions. A complex relationship between nexus sustainability and multiple ES existed. Water subsystem sustainability had significant and positive linear correlations with water yield/carbon storage, and a significant and positive nonlinear correlation with soil retention. There was also a significant and positive nonlinear correlation between food subsystem sustainability and food production. The nonlinear correlations between energy subsystem sustainability and four ES were not significant in most years. Therefore, relationship-based and location-based management measures, such as ecological protection and restoration, strictest water resources management and cross-city cooperation, were proposed to facilitate the sustainable and coordinated development of nexus sustainability and multiple ES. This study can also provide references for the coordinated development of nexus sustainability and multiple ES in other urban agglomerations within and beyond China.