The migration and enrichment of heavy metals have great influence on environment and ecosystem due to the increasing biological toxicity, resulting in serious environmental risk. This paper focuses on the vertical distribution of heavy metals in the water environment system and the migration of heavy metals at the sediment-water interface. It aims to reveal the law of adsorption and desorption of heavy metals at the interface of different media under the influence of water quality factors and to propose an improvement method to describe the isothermal adsorption at the interface including time factor. Based on field investigation results in the Yangtze River Estuary, a series of soil column experiments were setup to analyze the distribution of heavy metal cadmium (Cd) affected by multi-water hydraulic factors (salinity, pH and hydrodynamic) and the adsorption and desorption mechanism at the sediment-water interface. The experimental results were fitted by two-constant rate model, Elovich model the pseudo-first-order kinetic model and the pseudo-second-order kinetic model to reproduce the isothermal desorption at the interface. Moreover, pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the adsorption and desorption of Cd under the influence of hydrodynamics, and the hysteresis mechanism of heavy metal desorption sequence under the influence of hydrodynamics is proposed. Finally, the hydrodynamic processes of adsorption and desorption of Cd at the sediment-water interface under the influence of salinity, pH and hydrodynamic factors were discussed, and a prediction curve was proposed. Results in this paper can be used as the verification and correction of desorption kinetics model, which can also provide effective information for the research of heavy metal migration, adsorption and desorption under complex conditions.
Wetland is the transitional area between terrestrial ecosystem and aquatic ecosystem, which is important for the environment and ecosystem. However, environmental pollution occurs more and more frequent recently due to the density of population and the increase of human activities, which lead to the degradation of wetland resources and cause serious damage to the ecological environment(Fan 2021). Since 1979, the area of natural wetlands in the Yangtze River Estuary in China has decreased by a total of 163km2(Sun et al. 2017; Zhang 2018). In addition, a large amount of industrial and municipal sewage is discharged into the inshore area of the Yangtze River Estuary every year, especially heavy metal pollutants including Hg, Cd, Pb, Cr, Cu and metal-like As. These heavy metals have high biological toxicity and strong accumulation, which are harmful to the ecological environment of the Yangtze Estuary wetland(Adugna 2020) and the regional environment(Zhang, 1999; Fan et al. 2020;Li et al. 2020). According to the field investigations, Cd is the main contributor to potential ecological risks in the Yangtze Estuary wetlands (Uthe et al. 1971; Wang et al. 2015; Han et al. 2017; Sun et al. 2018; He et al. 2018; Li et al. 2020; Wang et al. 2021; Zhanget al. 2021).
