The RNG k-ε turbulence model was used to simulate and analyze the open channel flow with patchy distributed double-layer rigid vegetation. The flow velocity and turbulence parameters of the open channel flow with vegetation were statistically analyzed based on the double-average method of time and space. The results show that the open channel flow with patchy distributed vegetation can be divided into vegetation zone, gap zone, and mainstream zone, and the magnitude and distribution of time-averaged flow velocity vary in different zones. In the open channel flow with double-layer vegetation, the vertical distribution of time-averaged flow velocity exhibits inflection points near the bed surface, near the top of the low plants, and near the top of the high plants, and the maximum values of fluctuation intensity and turbulence kinetic energy occur near the top of the high plants.

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 influence of dry-wet cycles on the mechanical properties and microstructure of clay, a series of unconfined compressive strength tests and CT scanning tests were carried out to reveal the deterioration mechanism of clay caused by dry-wet cycles from macroscopic and microscopic perspectives. The following conclusions were drawn: With the increase of the times of dry-wet cycles, the compressive strength of clay maintained an exponential decline trend. After 4 cycles, the compressive strength lost about 40%, and after 8 cycles, the compressive strength basically reached the stable state. It can be seen that from the cross-section of CT scanning, during the dry-wet cycle, cracks start to develop around the sample and gradually expand inward. The width and length of cracks continue to increase, and the continuity also improves. With the increase of the times of dry-wet cycles, the porosity of each layer of the sample increased significantly and the porosity of the interface between different layers increased more significantly. The cracks between layers developed first, and vertical cracks also developed on the surface of sample. Besides, the number of connected pores increases while the number of isolated pores decreases. There is a negative exponential relationship between porosity and compressive strength of clay under different dry-wet cycles and when the number of dry-wet cycles reaches 4 times, the increase of porosity has less effect on the decrease of compressive strength.

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.