Application of three-dimensional mercury cycling model to coastal seas

The use of two-dimensional (2D) and three-dimensional (3D) hydrodynamic and pollutant-transport models is presented for two cases of mercury contamination, where field measurements are also available: the Gulf of Trieste (Northern Adriatic), where the source of contamination is a former mercury mine, and the well-known case of Minamata Bay/Yatsushiro Sea in Japan. The degree of Hg contamination of water and sediment is of the same order of magnitude in both bays. Simulations have shown, that the most important processes in both cases are physical, i.e. transport by currents, dispersion, and exchange with bottom sediment. Storm winds can displace mercury, mainly bound to suspended sediment, by tens of kilometres. One of the models also includes some chemical processes (methylation, demethylation, reduction), although it was only partly possible to verify the correctness of simulation of these processes. The mass-balance of total and methyl-mercury was also calculated for both bays, showing potential sources of Hg and their relative magnitudes. Possible reduction of Hg contamination in the Gulf of Trieste could be attained by prevention of conditions for methylation in the Gulf and/or dredging of the contaminated sediment in the catchment area. The mass-balance of mercury for Minamata Bay showed, that in the future no significant Hg contamination of the Yatsushiro Sea can be expected from Minamata Bay.