Indicators for contaminant transport in wetlands

Wetlands provide significant ecological services for urban regions in terms of water supply, wastewater treatment, flood storage, drought resistance, etc. For wetland flows, it is crucial to understand the process of contaminant transport as it provides scientific support for applications associated with various urban services. Two indicators respectively as the critical length and duration are frequently adopted for risk assessment of incidental release of toxic or contaminant cloud. This paper presents a review on recent progresses in the analytical study of contaminant transport in wetland flows by Taylor dispersion at the phase-average scale. The method of concentration moments is introduced. Analytical procedures for determining the key quantity of Taylor dispersivity are given for typical wetlands with free water surface, respectively as the steady flow wetlands, tidal flow wetlands, and the two-layer flow wetlands. As an example of applications, critical length and duration of the contaminant cloud in the steady flow wetlands are analyzed based on the obtained Taylor dispersivity. Results show that in contrast to the temporary, localized influence of COD on water quality, the heavy metal Pb can give rise to more severe damage.