Simulation study on impact of sediments on water quality in typical section of Middle Route of South-to-North Water Diversion Project

The Middle Route of the South-to-North Water Diversion Project is dedicated to ensuring the water quality safety of the receiving regions.However, long-term accumulation of sediments in localized stagnant areas of the main canal releases nutrients such as nitrogen and phosphorus into the overlying water, posing a persistent threat to the transferred water quality.Investigating the environmentally driven mechanisms of sediment-water interface material exchange in simulated sediment tank experiments of the Middle Route of the South-to-North Water Diversion Project is of great significance for revealing the release patterns of endogenous nutrients.To this end, a multi-factor coupled simulation experiment was systematically conducted to simulate the release process of sediment nutrients under conditions of light (with or without shading), temperature (15~40 ℃), and hydraulic disturbance (0~150 r/min).The results showed that mechanical disturbance enhanced sediment resuspension, increasing the total phosphorus release flux by 3.2 times, while nitrogen transformation exhibited significant nitrification-denitrification coupling characteristics.A temperature increase of 5 ℃ significantly accelerated the degradation rate of organic matter, leading to a substantial increase in the release of various nutrients (TN increased by 175%, TP by 561%, and TOC by 13.6%).Although shading did not alter the total amount of nutrients, it increased the proportion of ammonia nitrogen, revealing the inhibitory effect of light on denitrification.Based on the analysis of sediment release patterns, a management strategy of "in-situ stabilization, ecological dredging, and resource utilization" was proposed.This study can provide a theoretical reference for the dynamic regulation of sediment management in long-distance water diversion projects.