| Bohai Sea is an inland bay of China. Because Yellow River, Hai River and Liao Riverflow into the Bohai Sea, the amount of land sources pollution is very big. With theland on three sides, Bohai Sea is only linked with the north of the Huanghai Seathrough Bohai Strait, which lies in the southeast of Bohai Sea. So the water-exchangeability of Bohai Sea is very low. Once the water is polluted, it is hardly to getimproved. As the fast developing of the economy in near sea area, a great deal ofindustrial wastewater, domestic sewage and animal husbandry industry wastewaterflowed into Bohai Sea, which caused the continued accumulation of the nitrogen andphosphorous nutriment in Bohai Sea ecosystem. The eutrophication of Bohai Seawater body has become an increasingly grave issue. The sustainable development ofcoast economic is being threatened by frequently occurred red tides, sharp reductionof oxygen, decrease of biodiversity and fishery. Therefore, simulation of the pollutantin Bohai Sea (such as COD, the nitrogen and phosphorous nutriment and petroleumhydrocarbons) has important significance in controlling the pollutant effectively,protecting and recovering the Bohai Sea environment, coordinating and promoting theeconomic developing, developing and utilizing the marine resources rationally andrealizing economic sustainable development.The density of pollutants is an important indicator to measure the sea water pollutionlevels. In the bays and coastal water, tides play an important part in the pollutanttransport. Researchers often study the pollutant through convectio n diffusion model.Although many scholars have studied pollutant with several models, it isn’t goodenough in organic combination between observational data and numerical simulation,which can not meet people’s requirements in recognizing and describing the pollutantvariation. However, the adjoint assimilation method could use the measured sufficiently and the assimilation result is much closer to the reality.In this paper, a new Cressman method is used to calculate the distribution of totalnitrogens of May2009in Bohai Sea. As shown in the evaluation, this provedCressman method could get better results than the original Cressman method. Thenthe total nitrogen distribution of other seasons in2009and2010could be calculated.Based on the hydrodynamic model, a pollutant transportation model was establishedwith the consideration of the transport and diffusion of pollutant. Adjoint assimilationmethod was used to inverse the given initial fields respectively in Laizhou Bay, BohaiBay and Liaodong Bay on the basis of the spatial distribution of independent point.The cost function and the mean absolute error of observation point decrease a lot after100times of assimilation. Whether the distribution shows high in the middle and lowon on the sides or low in the middle and high on the sides, the distributioncharacteristics can all be inversed effectively. After this model has been verifriedthrough ideal experiments, it can be used in the practical experiments. Thedistribution of total nitrogen of May, August and October in2009and May andAugust in2010can be accurately inversed after1000times of assimilation. Exceptthe mean relative error (MRR) of May in2010only decreased by37.2%, the decreaseof MRR of other quarters range from60%to80%. The MRR of August in2010decreases by78.5%. The mean absoutely error (MAR) between observation andsimulation dropped to a range of between32%and49.2%. The monthly meandistribution of pollution can be calculated by the statistical method. It has importantpractical significance in monitoring and evaluation of the marine environmentalquality. |
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