Author(s): Yan Wu; Roger A. Falconer; Binliang Lin
Keywords: Heavy metals; Sediments; Mathematical model; 2-d and 1-d coupling; Ultimate quickest scheme; Mersey estuary
Abstract: The resuspension of heavy contaminated bed sediments may release a great amount of heavy metals into a dissolved phase in a water body. This desorption of heavy metals from their particulate phase can impact significantly on the aquatic environment and its ecosystems. In this paper a new mathematical model of heavy metal transport has been proposed. In this new model the total heavy metal in the water column is first calculated using the advective-diffusion equation, governing the total heavy metal transport, instead of calculating the transport of the dissolved and particulate phases of heavy metal separately. The dissolved and particulate heavy metals are then separated from the total heavy metal according to a partition coefficient. An implicit coupling of a two-dimensional and a one-dimensional model to predict salt, cohesive sediment and heavy metal transport in estuarine and riverine waters is also described. The QUICKEST scheme has been included in the two-dimensional and one-dimensional advective-diffusion equations to achieve high accuracy, and a modified one-dimensional ULTIMATE algorithm has also been used to avoid unphysical numerical oscillations. The present model has been used to study the salt, cohesive sediment and heavy metal transport processes in the Mersey Estuary, UK. The hydrodynamic model was first calibrated against six sets of data collected in the Mersey Estuary. Then the water quality model was calibrated for the dispersion coefficients and critical shear stresses for erosion and deposition against six sets of field measured salinity and suspended sediment concentrations. Finally, the calibrated model was applied to simulate cadmium transport in the Mersey Estuary, with the partition coefficient between the dissolved and absorbed particulate phases being modelled as a function of salinity. Good agreement was obtained with the field-measured data.