Multi-scenario simulation of water transfer impacts on water quality and ecological responses in the three gorges reservoir

Inter-basin water transfer (IBWT) projects profoundly reshape hydrological and ecological processes, yet their integrated environmental impacts on large reservoir systems remain insufficiently quantified, particularly under low-flow conditions. Addressing this critical knowledge gap, this study develops the first integrated space–air–ground modeling framework that couples hydrodynamic, water quality, and hydrogeological modules to comprehensively assess the environmental responses of the Three Gorges Reservoir (TGR) to large-scale IBWT during dry periods. Multi-source satellite observations were assimilated into the MIKE 21 modeling system to simulate baseline (current), near-term (2030), and long-term (2050) scenarios. Results reveal that: (1) Pollutant concentrations at mainstream cross-sections (Cuntan, Wanzhou, Taipingxi) exhibited spatial heterogeneity but similar temporal dynamics, with peaks in July–August. The concentration gradients intensified proportionally with increasing water transfer scale; (2) In the eutrophic Xiaojiang River, the trophic level index (TLI) was highly sensitive to winter low-flow transfers, rising by 0.33 % (2030) and 0.95 % (2050) compared with current conditions, indicating elevated eutrophication risk; (3) Seasonal analysis identified summer (hot–low-flow) and winter (dry–low-flow) as critical ecological vulnerability windows, during which transfer-induced disturbances exert the strongest environmental pressures.This study advances the mechanistic understanding of IBWT-induced aquatic impacts and provides quantitative insights for adaptive water allocation and ecological protection in large reservoir systems. The proposed integrative framework is transferable to other large-scale water transfer projects, offering a robust reference for sustainable management of water–environment interactions under climate change.