Chemical speciation of dissolved trace metals in estuarine, coastal and open ocean waters: modelling based on humic type ligands

If water quality standards for estuaries and coastal areas are to be formulated on a site specific basis and based on chemical speciation concepts then there is a pressing need to validate chemical speciation models, which are widely used for terrestrial systems, for saltwater environments. We apply the chemical speciation model WHAM/Model VI to investigate the distribution of metal species (of Fe(III) and the divalent cations of Ni, Cu, Zn, Cd, Hg and Pb) in the water column of estuaries and coastal areas as well as open oceans. In doing this we compare, for the same sites, modelled results with experimentally measured values. The advantage to using a single model for a wide range of data sets, is that it can help to identify whether there are consistent trends in activities obtained using different analytical methods, i.e. relative to a consistent set of predictions. We show that in some cases, speciation of trace metals in brackish and seawater environments may be reasonably predicted using this model with its default parameter set, without any model fitting. Comparisons for several metals and different salinity environments will be presented.