Modelling contaminant geochemistry in estuaries

A numerical model predicting the transport and fate of contaminants in estuaries has been developed and tested. The modelling framework allows for (1) advection and diffusion of contaminants in the dissolved phase, (2) partitioning of contaminants between the dissolved and adsorbed phases, (3) input of adsorbed contaminants to the water column due to the resuspension of bed sediment, (4) accumulation of contaminants in the bed sediment due to deposition of suspended sediment and (5) in the case of organic contaminants, losses due to volatilization and biodegradation. Particle-water interactions throughout the estuary are encoded using relationships between empirically-derived partition coefficients and salinity, which have been coupled to an established two-dimensional depth integrated hydrodynamic and sediment model configured for the Humber Estuary, England, to simulate the distributions and transport of cadmium and zinc. The model has been run for a range of tidal and river flow conditions, and has been calibrated against field measurements of hydrodynamic parameters, salinity, suspended sediment concentrations and dissolved trace metal conentrations, and validated using independent dissolved trace metal data sets. The application of the model is discussed to a wide range of estuaries where the fate of trace metal contaminants is of immediate concern.