Water quality evolution of water-receiving lakes under the impact of multi-source water replenishments

Study region: The Baiyangdian Lake, Xiong'an New Area of Hebei Province, China. Study focus: The construction of water transfer projects provides feasible measures for lake space and ecology restoration, with a critical issue in this practice being how to efficiently utilize multiple sources of water replenishments to improve the water quality of the water-receiving lakes. This study developed a hydrodynamic and water quality model for the Baiyangdian Lake, which receives water from upstream reservoirs within its basin and from two water transfer projects in other basins. Simulation scenarios with varied proportions of this lake receiving water from these sources were set up in the model, and the optimal water replenishment scheme for the best improvement in water quality was determined. New hydrological insights for the region: The multi-source water replenishment can effectively enhance the environment of the water-receiving lakes, and water transported from other basins has a more positive effect than that released from the local basin; additionally, water quality was found to be more improved during non-flood seasons compared to flood seasons. Under the preferred water replenishment scheme, the average concentrations of ammonia, total nitrogen, and total phosphorus in the core areas all decreased by more than 10%. However, the water replenishment may induce divergence in water quality indicators and aquatic system evolutions in the water-receiving lakes, making the lake environment fragmented. This study proposes to further exploit the water quality improvement benefits of multi-source water replenishments while mitigating its potential risks by enhancing hydrological connectivity in the water-receiving areas and integrating water quality monitoring and mathematical modeling.