Model-based kinetics of heavy metal enrichment in plants affected by hydrodynamics

Heavy metal contamination threatens aquatic ecosystems by degrading water quality, biodiversity, and ecological stability. However, the role of hydrodynamics in modulating metal distribution and biogeochemical cycling, particularly in water-sediment-plant systems, remains unclear. Therefore, circular flume experiments were integrated with multiphase kinetic modeling to unravel cadmium (Cd) kinetics in water-sediment-plant systems under flow conditions. Affected by hydrodynamics, the distribution of Cd surged within 2 h and the Cd distribution coefficients showed a desorption peak within 8 h from the start of the experiment followed by reabsorption, and the hydrodynamic strength was negatively correlated with the resorption degree. Plant enrichment of heavy metals under hydrodynamics was observed initially, reaching a peak at the end of the experiment with phyto-sediment distribution coefficients of 0.22-0.25. The pseudo-second-order kinetic model effectively simulated the desorption of Cd from water, with r² > 0.97. However, the Plant Enrichment Factor (PEF) failed to accurately describe the plant enrichment kinetics of the water-sediment-plant system under hydrodynamic conditions, with the r² of cumulative Cd uptake kinetic of plants based on PEF lower than 0.77. Consequently, the nonlinear relationship of Cd in a multi-medium distribution was identified using the Artificial Neural Network (ANN), and a modified PEF was proposed, with r² > 0.96. From the modified PEF, the competitive advantage of the phytobiological action was emphasized as the experiment proceeded. The modified model proposed in this study explains the physical process of Cd enrichment by plants in the water-sediment-plant system under hydrodynamics, providing a feasible tool for the study of pollutant transport in aquatic environments, and the results can contribute to theoretical support for optimizing wetland ecosystem protection strategies.