Study On Land-Based Pollutant Distribution Characteristics And Marine Environment In The Coastal Zone Of Bohai New Area

With the rapid development of economy and society in coastal areas,human activities become more frequent,which leads to the increasingly serious problem of marine pollutant,the deterioration of water quality and the increase of water eutrophication,and triggers a series of marine pollutant events,such as the outbreak of blue algae,red tide and so on.According to the survey,land-based social and economic activities are the important source of marine pollutant.Therefore,from the perspective of pollutant sources to study the marine water environment is of great practical significance to marine water quality monitoring,treatment and water resources optimization.Taking the land-based pollutant into the sea as research object,this paper studies its total amount,migration and diffusion and its impact on the sea water environment in the coastal zone of Bohai New Area.The main work and achievements are as follows:(1)Taking the coastal zone of Bohai New Area as research area,the calculation model of the migration of land-based pollutant into the sea is proposed and established.The whole process of the generation,migration into the sea and diffusion of land-based pollutant are systematically studied.The model integrates land-based pollutant with sea water pollutant,and reflects the development concept of land-sea integrated.(2)On the basis of social and economic data collection and actual investigation of pollution,the land-based pollutant load estimation model of point source and non-point source is established to calculate the load of pollutant sources using the per ten thousand yuan production values method and export coefficient method,such as industrial enterprises,residents' life,livestock and poultry breeding,farmland fertilizer and aquaculture in Bohai New Area.Based on the surface runoff model,following the balance of pollutant amount,considering the residual and degradation of pollutant,the migration amount of pollutant with water flow and the source intensity into the sea are calculated,which provides data support for the study of pollutant in the sea area.(3)Based on Godunov scheme,a high-precision finite volume mathematical model is established to solve the problems of complex computational domain,irregular terrain,discontinuous flow and still water harmony in the numerical study of water flow.For the problem of still water false flow caused by using Roe's approximate Riemann solution operator method to calculate the convective numerical flux in hydrodynamic module,the bottom slope source term is modified by the method of eigenvalue decomposition equilibrium flux.For the pollutant transport module,the high-order upwind reconstruction method is used to deal with numerical convection flux to avoid numerical dissipation,and the second-order precision scheme is adopted to deal with diffusion flux.A series of classical examples are used to verify the accuracy and reliability of the model.It is indicated that the model has the ability to deal with all kinds of complex flow patterns and material transport processes.(4)Based on the high-precision finite volume numerical method,the hydrodynamic mathematical model of the Bohai Bay is established and validated.The results show that the model can reflect the real flow movement and hydrodynamic characteristics.On this basis,the mathematical model of pollutant migration and diffusion is established,and the contour distribution of pollutant concentration and the pollutant concentration at the measured point is validated.Although there is a certain deviation between the calculated and the measured value,the error is within the acceptable and the accuracy meets the requirements.The migration and diffusion processes of pollutant under different wind conditions are simulated,and the temporal and spatial distribution patterns and diffusion laws of pollutant are analyzed,which lays a foundation for the study of sea water environment.(5)Based on the distribution of pollutant source intensity along the coast,combined with the functional location of the coastal waters and distribution characteristics of pollutant migration,the method of the water environment zoning assessment in the coastal waters is proposed.The coastal waters in the new Bohai Sea area are divided into 20 zoning control units.Based on the method of over-standard rate,the assessment criteria of water environmental carrying capacity in coastal waters is established.The water environmental carrying capacity of each zoning unit is classified to determine the zoning unit with serious pollutant overload,which provides scientific basis for water quality monitoring and water environment control in coastal waters.