This study explored the performance and underlying mechanisms of multiple applications of lanthanum-modified palygorskite (LMP) for mitigating phosphorus (P) release from sediment to the overlying water under the condition of suspended particulate matter (SPM) input, with a further analysis of the impact of LMP dosing frequency on the control efficiency. The findings revealed that LMP possessed a strong phosphate adsorption capacity in water (maximum adsorption capacity at pH 7: 22.5 mg/g), with significantly higher lanthanum utilization efficiency than pure lanthanum hydroxide (LH) and commercial lanthanum-modified bentonite (LMB). Multiple applications of LMP effectively inhibited the release of sediment-derived P to the overlying water under SPM input conditions, with superior control efficiency compared to multiple applications of LMB. Average reduction efficiencies of SRP in the overlying water of 72.8 %, 76.2 %, and 76.5 % were achieved with six, eleven, and thirty-one applications of LMP, respectively. These multiple LMP applications also effectively suppressed internal P release from the upper sediment layer into the pore water, achieving higher control efficiency than LMB. Even with LMP application, the release of sedimentary P to the pore water continued through mechanisms involving iron-reducing bacteria (IRB)-driven dissimilatory Fe(III) reduction and chemical Fe(III) reduction mediated by sulfate-reducing bacteria (SRB)-driven sulfate reduction products. However, LMP effectively eliminated soluble reactive phosphorus (SRP) in the pore water through two pathways: adsorbing pore water SRP, and inactivating diffusive gradients in thin films (DGT)-labile P and mobile P in the upper sediment. This dual-pathway action constitutes the key mechanism by which multiple LMP applications control the release of sediment-derived P to the overlying water under SPM input conditions. Additionally, the frequency of LMP dosing in the multiple additions affected its efficacy in controlling sediment P release. Overall, multiple applications of LMP represent a highly promising method for controlling sediment P release in the presence of SPM inputs.
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