Advances in Resources and Environmental Science

Human activities such as polder aquaculture have posed significant challenges to the ecological health of lakes, affecting the water quality stability of the water-carrying lake system along the Eastern Route of the South-to-North Water Diversion Project. The implementation of ecological restoration projects such as retreating polder holds promise for reconstructing and rehabilitating lake ecosystems. To systematically explore the impact of retreating polder on the aquatic ecosystem of water-carrying lakes along the Eastern Route, Lake Luoma—a typical water-carrying lake—was selected as the study area. This study comprehensively examined the spatial and temporal distribution characteristics of aquatic ecological elements under the influence of retreating polder and applied Canonical Correspondence Analysis (CCA) and Hierarchical Partitioning (HP) analysis to elucidate the response mechanisms and key influencing factors of the lake ecosystem. Based on these key factors, a Water Pollution Index (WPI) evaluation method was developed to quantify changes in aquatic ecological health under the influence of retreating polder. The results showed that following the retreating polder, water transparency in the polder-retreated area improved, but the permanganate index and ammonia nitrogen concentration increased. Meanwhile, chlorophyll-a concentration was significantly higher than in other regions (27.43 µg/L), with an overall high abundance of cyanobacteria, and severe algal blooms were observed at certain monitoring sites. Additionally, the aquatic biological community in this region exhibited signs of recovery, with relatively high diversity indices (1.78–2.66) and evenness values (0.60–0.67). Further analysis revealed significant differences in the regulatory effects of various environmental factors on aquatic biological communities. Overall, total nitrogen, ammonia nitrogen, the permanganate index, and dissolved oxygen were identified as key environmental factors influencing the ecological health of Lake Luoma. This study systematically elucidates the ecological evolution characteristics and mechanisms of water-carrying lakes under the influence of retreating polder, providing theoretical foundations and technical support for safeguarding water quality in lakes along the Eastern Route of the South-to-North Water Diversion Project.

Water-carrying lakes; Retreating polder; Water quality; Aquatic ecology; Ecological response