Phosphorus Fixation and Algal Inhibition Efficacy of Modified Sediment Coverage in Synergy with Submerged Plants

Submerged macrophytes can effectively reduce phosphorus content in water and sediments through absorption and adsorption, making them a highly efficient, safe and eco-friendly bioremediation technology. However, their remediation performance is restricted by growth cycle and environmental conditions, with limitations including low phosphorus immobilization efficiency, weak environmental adaptability and difficulty in achieving long-term phosphorus control. Therefore, in practical applications, they need to be combined with other technologies to optimize phosphorus pollution control and improve the long-term effectiveness and stability of remediation. In this study, lake sediments from Zhushan Bay were used as the matrix. Three modified phosphorus-fixation materials, namely Fe-sediment, Fe-Cu sediment and Cu-Fe sediment, were prepared via impregnation and high-temperature calcination. Simulated experiments on phosphorus removal by materials and on modified sediment-submerged macrophyte composite systems were conducted separately. The physicochemical properties of modified sediments were characterized using XRF, SEM and other methods. Changes in pH, DO, ORP, total organic carbon (TOC) and phosphorus fractions (DTP, SRP) in overlying water were systematically monitored during the experiments, and the transformation rules of total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), NaOH-P and HCl-P in sediments were analyzed. The results showed that Cu-Fe sediment exhibited excellent Fe and Cu loading efficiency, with Fe₂O₃ content of 12.627% and CuO content of 7.483%, and possessed the best phosphorus removal and immobilization performance. In the modified sediment-submerged macrophyte composite system experiments, the Cu-Fe sediment-submerged macrophyte system achieved the optimal phosphorus immobilization effect. In the experimental group containing Microcystis aeruginosa, the OD₆₈₀ value decreased rapidly, indicating significant inhibition of cyanobacterial growth. Microbial community analysis revealed that the dominant phyla were Pseudomonadota and Chloroflexota. Alpha diversity indices showed no significant difference before and after the experiment (p > 0.05), suggesting that combined remediation exerted complex but overall stable effects on microbial communities. This study confirms that the combined mode of modified sediment capping and submerged macrophytes can efficiently control internal phosphorus release in rivers and lakes, with additional algae-inhibiting effects, exhibiting favorable potential for engineering applications.