Heavy metal distribution model under estuarine mixing

Abstract

In modelling the fate and transport of heavy metals, the sorption processes, through the distribution coefficient, are applied to determine the amount of sorbed and dissolved fractions. Usually, these distribution coefficients are assumed to depend only on suspended sediment interactions. In estuaries, however, observations indicate that dissolved concentrations increase with salinity. It is hypothesized that salt competes for binding sites, leading to lower distribution coefficients. To study the fate and transport of heavy metals in an estuarine environment, a two-dimensional finite volume, depth-averaged toxic transport model has been developed. The distribution coefficients are approximated as a function of sodium activity or salt concentration. Other model parameters are obtained from a recently developed hydrodynamic model, salt transport and cohesive sediment transport modules. The model has been applied to the Scheldt Estuary and the results for both sorbed and dissolved heavy metal concentrations agree fairly well with measured data, indicating that under estuarine mixing, salt concentration is an important factor affecting the fate and transport of heavy metals.