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Dissolved trace metal speciation in estuarine and coastal waters: Comparison of WHAM/Model vii predictions with analytical results

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We apply the chemical speciation model WHAM/Model VII 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. We compare, for the same locations, measured and modelled free ion and organically bound metal concentrations. The modelled free ion calculations show varying levels of agreement with experimental measurements. Where only natural organic matter is considered as the organic ligand, for Ni, Cd and Pb, agreement within one order of magnitude is found in 122 of 128 comparisons. For Fe and Zn comparisons 12 of 34 (Fe) and 10 of 18 (Zn) agree to within one order of magnitude, the remaining modelled values being over one order of magnitude higher than measurements. Copper measurements agree within one order of magnitude of modelled values in 314 of 533 (59%) cases and are more than one order of magnitude lower than modelled values in 202 cases. There is a general tendency for agreement between modelled and measured values to improve with increasing total metal concentrations. There are substantial variations among different analysis techniques but no systematic bias from the model is observed across techniques. It would be beneficial to crossvalidate the different analytical methods, in combination with further modelling. We also assessed the effect of including an anthropogenic organic ligand (EDTA) in the modelling, given its known presence in some coastal environments. Except for Cd, all metals were sensitive to the presence of EDTA, even at a low concentration of 50 nM. This article is protected by copyright. All rights reserved

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