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-IEEF), which integrated various emergy flows during the RCE's construction and operation into a three-dimensional emergy ecological footprint (EEF) 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 EEF indicated a fluctuation decrease trend with a mean value of 7.18 × 10 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.