Spatio-temporal characteristics and influencing factors of water quality in Xiangxi Bay under the operation of the three gorges reservoir

As the largest hydropower project in the world, the Three Gorges Reservoir (TGR) exerts significant backwater effects, leading to various water quality issues. The Xiangxi River, the largest tributary near the dam, has experienced algal bloom phenomena for several years. However, the characteristics and influencing factors of water quality during different operational periods of the reservoir remain unclear. This study analyzes 12 physical and chemical parameters of the Xiangxi Bay (XXB) from 2019 to 2023, employing a data-driven approach to explore the temporal and spatial characteristics of water quality under varying operational conditions of the TGR. It discusses the influencing factors and proposes countermeasures to address water quality challenges. The results indicate that: (1) Water quality parameters in XXB exhibit significant spatial and temporal variability, peaking in summer, with higher values observed in the middle and upper reaches. The Water Quality Index (WQI) indicates overall good water quality, while the Trophic Level Index (TLI) suggests medium eutrophication, particularly evident in spring and summer. (2) The backwater effects of the TGR have altered hydrodynamic conditions and mixing processes in XXB, significantly impacting water quality and promoting eutrophication. (3) Water quality is influenced by nutrient, organic matter, algae, and temperature, especially during low water levels in summer, with the middle and upper reaches being most affected. Key factors driving algal growth during this period include Total Nitrogen (TN), Transparency (SD), and Water Temperature (WT). (4) Effective control of eutrophication and algal blooms in XXB should focus on long-term upstream source management, close monitoring and prediction during spring and summer, and ecological operation of reservoir. This study enhances our understanding of the temporal and spatial characteristics of water quality in XXB under the operational dynamics of the TGR, providing guidance for eutrophication management and bloom prevention.