Contaminant transport in wetland flows: Different fate between the upper and bottom layers

Abstract

Abstract The mechanism of contaminant transport in wetland flows plays a central role in various applications. A two-zone model is applied to study the transport process. The significantly different fate of concentrations between the upper and bottom layers is characterized. This model provides a practicable and useful tool to quickly capture the evolution of contaminant concentration, being of particular importance in engineering science. The results agree well with the numerical solutions, which reveal that the concentrations in the fast-moving zone in the upper layer and in the slow-moving zone in the bottom layer perform quite different in the transient dispersion stage. The two concentrations respectively form a leading right-skewed Gaussian curve and a tailing left-skewed Gaussian one. Under the effect of vertical diffusion at the interface of two zones, the two concentrations gradually approach the depth-averaged mean, and all evolve to asymptotically Gaussian distribution finally. The concentration variation rate between the two zones reaches about 50 % as the process falls into the asymptotic Taylor dispersion stage at dimensionless time 1.0. And it remains about 10 % even at one order larger dimensionless time 10.0. The findings of the different fate of two concentrations will offer meaningful information to study the benthon and plankton in related areas.