Research On The Ocean Water Quality Model Based On Grey System Theory

Water quality model is an important method to study water environment simulation,prediction and evaluation.It is also an important part of water environment planning and management,comprehensive prevention and control of water pollution.Based on the review of water quality model,this paper introduced the development process of water quality model,several main non organic water quality models and their application research progress,recognized the objective facts of uncertainty in water environment system,and pointed out the limitations of organic water quality model in the application of water environment system in China.At present,the research of water quality model in China is mainly focused on inland waters?rivers,lakes,reservoirs,etc?,and the research on marine water quality model is less,and the existing practical application results are still limited to the more ideal mechanism water quality model,and the complexity and uncertainty of marine environment system are not considered enough.Therefore,this paper based on the uncertainty theory of grey system,attempted to build a scientific,practical and objective water quality model for application of water environment simulation,prediction and evaluation in Haizhou Bay.the main research work is as follows:?1?Water quality evaluation is actually a multi index decision making problem with incompatible evaluation indexes.In this paper,the grey correlation method was combined with the improved entropy weight method,and the nonlinear and uncertain factors of marine water quality evaluation were fully considered.The model was applied to the comprehensive evaluation of water quality of nineteen monitoring stations in the artificial reef area,near-shore contrast area and far-shore contrast area of Haizhou Bay Marine ranch in the autumn of 2019.The weight of water quality evaluation factors was determined by entropy weight method.On this basis,the gray correlation analysis was used to evaluate the overall water quality level of each monitoring station and region in Haizhou Bay.The results shows that in the autumn of2019,the water quality of all stations in the artificial reef area of Haizhou Bay was mostly class II,while that in the near-shore contrast area was mostly class III,and that in the far-shore contrast area was class II.It could be seen that the overall water quality in the sea area of Haizhou Bay in the autumn of 2019 was better.According to the principle of comparing the quality of water in different evaluation areas,The order of the overall water environment quality of each region was artificial reef area>far-shore contrast area>near-shore contrast area,which indicates that the construction of artificial reef has a certain restoration effect on the water environment of the sea area;the marine water quality evaluation model based on the improved entropy weight grey correlation method is simple and fast,and the evaluation result is objective and reasonable,which can be applied to the study of marine water quality evaluation?2?In order to simulate the relationship between marine transparency and environmental factors in Haizhou Bay.And consideres that the complexity of the internal relationship between marine environmental factors,the limitations of mathematical statistical analysis and the uncertainty of marine environmental information.In this paper,the slope correlation model of grey correlation analysis method was used as the analysis tool to analyze the environmental data of four areas of Haizhou Bay Marine ranch from 2014 spring?May?,summer?August?and autumn?October?,and retained six main correlation factors.Based on the grey GM?0,N?model,a water quality simulation model of different seasons'seawater transparency and main correlation factors was constructed,and used 2015-2016 Haizhou Bay environmental data to verify.The grey slope correlation analysis results shows that the grey correlation order is Water Temperature>DO>Water Color>Water Depth>Chlorophyll>Si O₃-S>SS>COD>PO₄-P>DIN,Water Temperature,DO and Water Depth are positively correlated,while Water Color,SS,Chlorophyll,COD,Si O₃-S,PO₄-P and DIN are negatively correlated.The grey correlation order of the four areas of Haizhou Bay is roughly the same,but the near-shore contrast area is the environmental factor with the highest correlation of water color;the GM?0,N?model has a good model for the simulation of seawater transparency and the main relevant factors Accuracy,the relative error between the estimated value of seawater transparency in actual inspection and the actual monitoring data from 2015 to 2016 is within 20%,which verifies the credibility of the model.?3?In this study,residual modified GM?1,1?model and grey topological prediction method were used to establish water quality prediction models based on monitoring data of Dissolved oxygen?DO?,chemical oxygen demand?COD?,biochemical oxygen demand?BOD₅?and dissolved inorganic nitrogen?DIN?in artificial reef area of Haizhou Bay in spring?May?and autumn?October?2007-2017and selected a model with higher accuracy to predict the trend of water concentration in 2018-2022.Finally,the forecast results are verified with the actual data of2018.The results shows that the grey topological model has better prediction accuracy for water quality data than the residual correction GM?1,1?.the predicted results is in good agreement with the actual values in 2018,and the model is reliable;According to the analysis of prediction results,the water quality indicators of DO and COD will maintain good water quality in 2018-2022.It can be seen that the construction of artificial reef areas has a certain role in the restoration of marine water environment,but BOD₅and DIN will have a certain risk of exceeding the standard;The improvement of the grey topology model still has a lot of research space,which needs to be further excavated.