Integrated benefits of Ca/Al composites capping coupled with Vallisneria natans: Removal sediment phosphorus and optimization the different microbial functions of sediment and leaf biofilm

Sediment modification would contribute to better restoration and stabilization of submerged macrophytes (SM), which is vital for the ecological recovery of eutrophic shallow lakes. In this study, the remediation performance and mechanisms of simplified calcium‑aluminum composites (SCA), prepared via a simple method, in conjunction with Vallisneria natans on eutrophic sediments were investigated for the first time. And the responses of aquatic microbial communities were also explored. SCA exhibited a strong phosphate adsorption capacity of 92.26 mg P/g and demonstrated high affinity for phosphate. Compared to single approaches, the combined application of SM and SCA was more effective in removing interstitial P and nitrogen (N). Their combination exerted the transformation of sediment mobile P by SCA and the P uptake ability of V. natans, thereby mitigating the risk of sediment P release through the dual mechanisms of total P removal by 98.85 mg/kg and mobile P reduction by 8.7 %. Meanwhile, the joint remediation strategy altered the compositions of sediment microbial communities, optimized community structure, and enhanced the sediment's capacity to retain P, N, and carbon (C). This was complemented by the role of biofilms on leaf surfaces in promoting P uptake and the cycling and elimination of C and N, thus ultimately improving the removal rates of nutrients from the overlaying water. These results suggested that the combination of SCA and SM has the synergistic benefits of removing sediment P and optimizing the microbial functions differed between sediment and leaf biofilms, and has great potential for application in eutrophic sediment remediation.