The effect of solute release position on transient solute dispersion in floating wetlands: An analytical study

Abstract

Considering the stochastic and complex pollutant emissions in the application of floating wetlands, we investigate the effects of release position on the solute transport in this work. On the basis of the analytical expressions derived from concentration moments, the temporal evolutions of dispersion intensity, the cloud distortion, and the displacement of the cloud centroid at the preasymptotic stage are all analyzed. Owing to the nonhomogeneous flow field, the location of the point source determines the strength of the initial advection, diffusion, and velocity shear acting on a solute cloud, which in turn affects the dispersion process. As a result, the waiting time before the dispersion enters the anomalous regime, the dispersion mechanism, the normality of mean concentration distribution, and the form of spatial concentration distribution are all influenced by the initial condition. The time at which the Taylor dispersion model is capable to depict the mean concentration distribution is t = 0.3 for the line source case and t = 0.5 for point sources released in the outer shear layer, and t = 1 for point sources released in the canopy region and the bottom boundary layer. The point source releases below the internal canopy layer and the line source release cause the initial accumulation of solute in the bottom boundary layer, even for the cases with relatively strong longitudinal dispersion. The depende-