Contrasting effects of MgAl- and MgFe-based layered double hydroxides on phosphorus mobilization and microbial communities in sediment.

The effects of two types of layered double hydroxides (LDH) in-situ treatment on sediment phosphorus (P) mobilization and microbial community's structure were studied comparatively. The results presented that magnesium/aluminum-based (MA) and magnesium/iron (MF)-based LDH displayed great phosphate uptake ability in aqueous solution in a broad pH range of 3-8. The maximum phosphate sorption capacity of MA was 64.89 mg/g, around four times greater than that of MF (14.32 mg/g). Most of phosphate bound by MA and MF is hard to re-liberate under reduction and ordinary pH (5-9) conditions. In the in-situ remediation, the MA and MF capping/amendment both prevented P migration from the sediment to the overlying water (OL-water) under long-term anaerobic conditions, and MA had a better interception efficiency compared to MF in the same application mode. MA amendment significantly reduced mobile P (Mob-P) content in sediment and could remain its stable Mob-P inactivation capacity over a wide pH range. On the contrary, MF amendment increased Mob-P content in sediment and exhibited a variable ability to inactivate Mob-P under elevated pH conditions. MF can decrease Mob-P content at pH of 7 and 11 but increase Mob-P content at pH of 8-10. Under resuspension conditions, MA and MF capping groups still maintained low P levels in OL-water, while MA capping simultaneously showed a certain degree of resistance to sediment resuspension, but it had a weaker stabilizing effect for sediment than MF. Microbial community analysis manifested neither MA nor MF addition observably altered the sediment microbial diversity, but impacted the functional microorganisms' abundance and reshaped the microbial community's structure, intervening the sediment-P stabilization. Viewed from environmental friendliness, control efficiency, stability of P fixation capacity, and application convenience, MA capping wrapped by fabric is more suitable for addressing internal P loading in eutrophic lakes and holds great potential application.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.