Spatio-temporal dynamics of ecological environmental quality and drivers under a dual-constraint framework: a case study of the Luo River Basin.

Large-scale ecological engineering construction and socioeconomic development have profoundly influenced the ecological environmental quality (EEQ) of the Luo River Basin. Revealing the nonlinear responses and threshold effects of EEQ to multiple driving factors is essential for promoting the sustainable development of ecologically fragile basins. Previous studies have predominantly emphasized upper-bound constraints while overlooking the ecological degradation risks associated with lower-bound constraints. Based on Google Earth Engine platform, this study constructs the remote sensing ecological index (RSEI) to systematically reveal the spatiotemporal evolution characteristics of EEQ in the Luo River Basin from 2000 to 2022. By integrating the optimal parameter geographic detector with "dual-constraint" analysis, the dominant driving factors and nonlinear threshold effects of EEQ were identified. The findings show that the basin's overall RSEI displays a spatial pattern with high values in the southwest and low values in the northeast. Land use intensity is the dominant driver and shows a significant interaction with average annual evapotranspiration. RSEI is often positively impacted by natural factors, with upstream forested hilly regions showing the strongest effects. RSEI exhibits multiple nonlinear relationships with its driving factors. Anthropogenic interference causes the threshold points of certain factors to shift either forward or backward, resulting in a substantial attenuation of RSEI. The proposed "dual-constraint" framework concurrently integrates the upper constraint of ecological improvement potential and the lower constraint of ecological degradation risk. It reveals that EEQ is jointly regulated by natural factors and anthropogenic activities, providing a scientific basis for sustainable development and ecological restoration of watersheds.