This diploma paper focuses on evasion of mercury in the Gulf of Trieste and its calculation which is made in two ways. Preliminary simulation was performed by the use of the Excel tool with measured mercury concentrations in the water and air of the Gulf of Trieste area. Modelling simulations were performed by a three-dimensional baroclinic mathematical model PCFLOW3D. Both calculations are based on Wanninkhof's gas exchange model (GEM). The PCFLOW3D model consists of modules which can calculate hydrodynamics, transport and dispersion of suspended sediment including resuspension and transport as well as the dispersion of mercury in its dissolved and particulate forms. In the biogeochemical module we can simulate some transformation processes. The exchange with the bottom sediment and the atmosphere, methylation, demethylation, reduction and oxidation can be taken into account. The data about temperature and salinity conditions, wind, deposition and mercury concentrations in the Gulf of Trieste as well as in the Soča River discharges, temperatures and concentrations of different mercury species were collected and interpreted. On the basis of the seasonally averaged parameters and values in a few shorter sequences, a scenario of one-year simulations was established. The agreement within a factor of two was achieved between the results of the model and the preliminary simulations. Both sets of results helped to improve the annual mercury mass balance of the Gulf of Trieste
