MODELING CONTAMINANT GEOCHEMISTRY IN ESTUARIES

A numerical model predicting the transport and fate of contaminants in estuaries has been developed and tested. The modelling framework allo ws for (1) advection and diffusion of contaminants in the dissolved ph ase, (2) partitioning of contaminants between the dissolved and adsorb ed 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 bi odegradation. Particle-water interactions throughout the estuary are e ncoded using relationships between empirically-derived partition coeff icients and salinity, which have been coupled to an established two-di mensional depth integrated hydrodynamic and sediment model configured for the Humber Estuary, England, to simulate the distributions and tra nsport of cadmium and zinc. The model has been run for a range of tida l and river flow conditions, and has been calibrated against field mea surements of hydrodynamic parameters, salinity, suspended sediment con centrations and dissolved trace metal conentrations, and validated usi ng independent dissolved trace metal data sets. The application of the model is discussed to a wide range of estuaries where the fate of tra ce metal contaminants is of immediate concern.