Research On The Migration Characteristics And Prediction Of Marine Microplastics In Xiamen Bay

Once the plastic waste enters the ocean,it will be decomposed into microplastics under the effects of photodegradation and other factors.Marine microplastics can migrate under the action of the complex hydrodynamic factors,posing a great threat to the marine ecosystem and marine economy.As an important city on the southeast coast of China,the rapid industrial development in Xiamen has put tremendous pressure on the coastal environment,and a large amount of plastic waste and microplastics are discharged into the Xiamen Bay.The migration of microplastics under ocean dynamic factors is an important factor affecting their diffusion and distribution.Therefore,investigation on the migration model of marine microplastics in the Xiamen Bay area can provide theoretical basis and reference for marine environmental governance.In this paper,a three-dimensional hydrodynamic model for Xiamen Bay is developed based on MIKE3,by taking into account the impact of runoff and wind speed into the sea,and verifying the hydrodynamic model through the measured data of tides and tidal currents.The results show that the accuracy of the model is more consistent with the measured value,which can reflect the three-dimensional hydrodynamic characteristics under the actual conditions and provide a dynamic field for the microplastic diffusion model.The article divides marine microplastics into floating microplastics,suspended microplastics and deposited microplastics according to their vertical distribution.According to different migration and distribution characteristics,the migration and diffusion models of floating and suspended microplastics were established,and the empirical formula for the flux change of sedimentary microplastics in Xiamen Bay was put forward.The distribution characteristics and migration laws of floating microplastics and suspended microplastics under different working wind conditions were simulated based on the verified models.The deposition and prediction of the abundance of microplastics are carried out,respectively.The results show that the migration of floating microplastics is closely related to the response of wind and current.Microplastics accumulate on the shoreline under the action of wind,and the microplastics will be more concentratedly distributed under unfavorable wind,normal wind direction and wind conditions with maximum wind.Different pollution sources have different contributions to the distribution of microplastics in Xiamen Bay.Floating microplastics released by pollution sources in open waters and strong currents diffuse faster.The vertical distribution of suspended microplastics presents an exponential decline from the sea surface,and the horizontal migration distribution is related to tidal movement.Where the flow velocity is small,microplastics are more likely to accumulate and increase the local concentration.The diffusion of suspended microplastics is related to the physical properties of microplastic particles.The time for microplastics with low sedimentation speed to be suspended in water longer and easier to be transmitted to places farther from the pollution source.The increase in the flux of deposited microplastics is approximately linear,which is related to the production of plastics in Xiamen and the hydrodynamic characteristics of Xiamen Bay.Through the empirical formula of deposited microplastics,it is predicted that the sediment flux of microplastics in Xiamen Bay will nearly reach 10~7items/m~2 in 2050.