Revealing the effects and mechanisms of lake autochthonous dissolved organic matter on phosphorus sequestration by lanthanum-modified clay at the molecular level.

Presence of dissolved organic matter (DOM) significantly affects phosphorus (P) sequestration in lanthanum (La)-modified clay. However, the effects and mechanisms of different autochthonous DOM at the molecular level remained unclear. In this study, algae-derived DOM (AOM), macrophyte-derived DOM (MOM), and sediment-derived DOM (SOM) from eutrophic lakes were selected as representative autochthonous DOMs. The impacts and mechanisms of these DOMs on P sequestration by La-modified attapulgite (LMA) were elucidated at the molecular level using a combination of kinetic experiments, X-ray photoelectron spectrometry (XPS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The results indicated that the effects of three autochthonous DOMs on P sequestration by LMA differed significantly. The maximum P desorption ratio was highest under the influence of MOM (10.40 %), followed by AOM (8.13 %) and SOM (5.25 %) at a DOC concentration of 20 mg/L. The effects of autochthonous DOMs on P sequestration by LMA were jointly determined by the molecular heterogeneity of DOM and metal-bound P species affected in LMA. Proteins and lignin, particularly oxygen-, nitrogen-, and sulfur-rich molecules, played key roles in P desorption because of their high chemical reactivity. Further analysis revealed that compounds with molecular formulas consisted solely of C, H, and O (CHO) were identified as the primary influencing components in SOM, competing with P for adsorption sites on Fe oxides via C=C bonds. Compounds containing additional N (CHON) and S (CHOS) were the key components in MOM and AOM, respectively, facilitating the desorption of La-bound P through C-O bonds. These findings enhanced the understanding of how different autochthonous DOM influenced P sequestration by La-modified clay, providing valuable guidance for optimizing P pollution control in eutrophic lakes enriched with autochthonous DOM.