Restoring Shallow Lakes by Constructing Pollution Absorption Zone: Practices and Insights

Based on zonal management and engineering-ecological synergy, this study innovatively designed and constructed a "pollution absorption zone" (PAZ) system to restore shallow eutrophic lakes, in response to excessive external nitrogen and phosphorus loads and the degradation of aquatic vegetation. Using Lake Changdanghu (China's Yangtze River Basin) as a case study, a functionally synergistic PAZ integrating underwater shoals, bottom traps, prereservoirs, and flow-guiding channels was constructed. Three-year monitoring demonstrated that PAZ effectively attenuated wind wave by 72% via the underwater shoals, significantly reducing the concentration of suspended solids and increasing water transparency. The marked increase in transparency has successfully created a still, clear-water environment conducive to the recovery of aquatic vegetation. Simultaneously, the synergistic effect of the PAZ effectively intercepted and slowed polluted inflows, thereby creating favorable conditions for in situ pollutant purification. With the improved habitat conditions, the area, distribution range, biomass, and coverage of aquatic vegetation within the PAZ have all significantly increased, leading to the effective restoration of the ecosystem structure. These outcomes demonstrate PAZ effectively mitigate external nitrogen, phosphorus loads while restoring degraded habitats. This study provides a replicable, large-scale engineering solution for balancing environmental carrying capacity with nutrient pressure through coupled physical-ecological intervention.