Environmental dispersion in a tidal wetland with sorption by vegetation

Abstract

Understanding of the solute transport mechanism under the effect of sorption by vegetation in tidal wetland gains its significance for environmental and ecological management. Presented in this paper is a theoretical analysis of effective environmental dispersion in a depth-dominated tidal wetland. Based on the transport in porous media, a linear sorption isotherm model is adopted to account for the sorption by vegetation, and two models for momentum and concentration transport in wetlands are given, respectively. The velocity of flow forced by oscillating pressure is derived, and the effect of dimensionless parameters on velocity pulsation is analyzed. The velocity direction may reverse in the case of pulsation amplitude larger than the mean velocity. Using Aris’s method of concentration moments, we investigate the effective environmental dispersivity and concentration distribution. The effective environmental dispersivity increases over time at the initial stage to attain a steady oscillating status, the growth rate of which depends on the distribution coefficient KD. The variations of concentration distribution with typical dimensionless parameters are determined, which turn out to be consistent with those of dispersivity. The sorption by vegetation leads to lowered concentration and delayed contaminant cloud, contributing to the dispersion.