Taking the eutrophic sediment as the research object, the indoor culture experiment was carried out. From the perspective of environmental micro-interface, the effects of common submerged plant Vallisneria natans on the migration and transformation of As(Ⅲ) and As(Ⅴ) in interstitial water of sediment, the behavior of environmental micro-interface were explored, and the removal effect of Vallisneria natans on As in the sediment-water interface was accurately evaluated. The results showed that Vallisneria natans increased the penetration depth of dissolved oxygen in the sediment and decreased the pH, UV₂₅₄, dissolved As, As(Ⅴ), As(Ⅲ), dissolved Fe(Ⅱ) and dissolved Mn; three forms of As (dissolved As, As(Ⅴ) and As(Ⅲ)) were significantly correlated with dissolved Mn and UV₂₅₄, and were poorly correlated with dissolved Fe(Ⅱ); the removal effect of As(Ⅲ) (69.5%) was better than that of As(Ⅴ) (64.6%). The research can provide a scientific basis for the control of heavy metal pollution in sediments and the water ecological restoration.

In order to study the removal effect of lanthanum modified bentonite (LMB) and oxygenating agent CaO₂ on arsenic (As) pollution in the sediment of eutrophic lakes, and clarify the removal mechanism of combined technology on the sediment-water interface, a simulation test was carried out on the sediment of Meiliang Bay in Taihu Lake. The results show that the combined use of LMB and CaO₂ has a better removal effect on As in sediment than the use of LMB and CaO₂ alone. On the 45th day of the experiment, the maximum removal rate of dissolved As in sediment by the combination of LMB and CaO₂ was 39.31%. On the 90th day of the experiment, the combined use of LMB and CaO₂ showed poor removal efficiency for As. To achieve efficient removal of As in sediment, LMB and CaO₂ can be recovered after 45 days of adding covering agents. The main mechanism of As removal by the combination of LMB and CaO₂ is the complexation of La³⁺and Ca²⁺in LMB and CaO₂ with arsenate ions to form LaAsO₄ and Ca₃ (AsO₄) ₂ precipitates, as well as the synergistic adsorption of Fe (Ⅲ) and Mn (Ⅳ) oxides. The redox cycling of Fe and Mn plays a crucial role in controlling the release of As from sediment.