| In recent years, marine pollution is gradually attracting government and public’s attention. Understanding the characteristics of mass transport and pollutant evolution is the key of marine pollution problems. In the paper, taking the typical basin in coastal waters - Xiangshan Bay as the study area, several Lagriangian methods were introduced to describe water transport processes and which were compared by using the numerial simulation method. The comprehensive Lagrangian method on mass transport were developed. Then a marine water quality model consisting of Dissolved Oxygen (DO), Carbonaceous Biochemical Oxygen Demand (CBOD), Phytoplankton and nutrients were established to study the transport and fate of pollutants within the physical, chemical and biological processes. The data driven method were applied to optimize the parameters in the water quality model, and the model were successfully developed and applied in Xiangshan Bay.Based on three dimensional incompressible viscous fluid dynamics equations, finite volume method and the unstructured grid coastal ocean model FVCOM, the distribution of tidal, tidal current and temperature-salinity in the Xiangshan Bay were simulated. The tidal current, wind stress, surface heat flux and river runoff considered in the model. Comparison of the simulated results with the measured data and other studies, the results showed that the model could simulate well the hydrodynamic and the distribution of temperature-salinity. Based on the numerical results, the characteristics of the tidal, tidal current and temperature-salinity structures in the study area were analyzed in detail. The model provides accurately current for the further researches on the mass transport problems.A concept based on the dynamical systems theory, Lagrangian coherent structures (LCS) was introduced in the paper. Combined with LCS, Lagrangian particles tracking method, Lagrangian residual current and synoptic Lagrangian maps (SLMs), several Lagrangian methods were applied to sutdy the mass transport in the study area. The results from different description methods were analyzed and compared in detail. Then a comprehensive mass transport description method was proposed, which could uncover the mass transport characteristics in the typical bay from the mass transport and distribution, fluid region dividion with different advection characteristics, transport time scales and paths. It was useful for better understanding of the physical processes and mass transport.Residual current is the carrier of mass transport. Its structures and driven factors could describe the mass transport ability and characteristic. LCS and SLMs is a powerful tool to uncover the mass transport process and fate in the current. Using the comprehensive mass transport description method, the residual current, mass transport process and transport time scales in Xiangshan Bay were studied. The influences of tide, wind, thermohaline and extreme weather process on the mass transport were analyzed based on the numerical experiments. The conclusion helps to understand the main driven factors and the influenecs of the different factors.A water quality model involving phytoplankton kinetics, nitrogen and phosphorus cycles, DO and CBOD, was developed based on the three dimensional hydrodynamic model. The model can simulate not only the physical processes of the water quality variables, but also consider the chemical and biological processes. To resolve the difficulty in parameters selection and determination, the parameters optimization method based on data driven theory was developed. Then the parameters were selected and optimized based on the measured data. The simulated results matched well with the measured data and reproducted the spatial-temporal variation of the water quality variables in Xiangshan bay, which verified the effectiveness of the model parameters optimization method. Then the water quality model was applied to study the influence of pollutant discharges on the water quality in Xiangshan Bay. |
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