Evaluation of Water Quality Security Effectiveness in the Danjiangkou Reservoir and Its Upstream Watershed and Countermeasure Recommendations for the 15th Five-Year Plan Period

To systematically evaluate the effectiveness of water quality security in the water source area of the Middle Route of the South-to-North Water Diversion Project and to scientifically formulate governance strategies for the 15th Five-Year Plan period, this study takes the Danjiangkou Reservoir and its upstream watershed as the research object. Through field surveys and systematic analysis, an effectiveness evaluation and situation assessment were conducted focusing on key indicators such as the water quality compliance rate, the proportion of sections with water quality better than Class III, total nitrogen concentration, sewage treatment rate, newly added soil erosion control area, aquatic organism integrity index, reservoir trophic state, and regional green and high-quality development index. The results show that by 2025, the water quality compliance rate at national-controlled sections in the water source area remained at 100%, and the proportion of sections with water quality better than Class III reached 100%. The urban sewage treatment rate significantly increased, the newly added soil erosion control area exceeded the planned target, the reservoir was generally in a mesotrophic state, the total nitrogen concentration decreased significantly compared to the binding target, the aquatic organism integrity index steadily improved, and the regional green and high-quality development pattern began to take shape. However, challenges remain prominent, including excessive total phosphorus and abnormal algal proliferation in some tributaries and reservoir bays, insufficient intelligent monitoring coverage and capability, weak resilience of water supply security, and a lack of a long-term mechanism for funding guarantee. Looking ahead to the 15th Five-Year Plan period, the study proposes key countermeasures, including refined control of water quality risks, the construction of an integrated "space-air-ground-water-engineering" intelligent monitoring system, optimization of water resource regulation, the establishment of a diversified funding guarantee mechanism, and strengthening research on key technologies, thereby providing scientific and technological support to ensure a perpetual flow of clear water to the north.