Evaluation Method Of Seawater Eutrophication In Yangtze River Estuary Based On Fuzzy Comprehensive Evaluation Method

In recent decades,with the development of the Yangtze River basin economy,a large number of nutrients,organic pollutants,pesticides and chemical fertilizers,as the river flows into the mouth of the Yangtze River and its adjacent sea area,making the eutrophication of seawater become more and more serious.Seawater eutrophication is a complex process,which results from the interaction of various nutrients,hydrological conditions,meteorological conditions and physical and biochemical processes.Nutrient is mainly marked by DIN and DIP,and is the material basis of seawater eutrophication.The hydrometeorological conditions and the physical process of the Yangtze Estuary are the driving conditions for the biochemical results of the eurtrophication of the sea water,that is,the proliferation of phytoplankton and the outbreak of the red tide.In recent years,many experts and scholars have studied the eutrophication of the seawater in the Yangtze Estuary.However,due to the lack of data,they can only evaluate small areas and cannot comprehensively see the complete eutrophication of the sea in the larger region of the Yangtze River Estuary.In order to better meet the requirements of prediction and forecasting,this paper uses the fuzzy comprehensive evaluation method to evaluate the eutrophication status of the Yangtze River Estuary based on the measured data and the existing model data of the National Ocean Environment Prediction Center.First of all,the fuzzy comprehensive evaluation method is applied to the intersection of the Jiao Xi,and the rationality of the fuzzy comprehensive evaluation method is verified by the field data.The evaluation results showed that the eutrophication evaluation of the Yangtze Estuary in different seasons according to the seasonal characteristics of the Yangtze Estuary.The fuzzy comprehensive evaluation method(E)and the nutritional state quality method(NQI)can better evaluate the sea area of the Yangtze Estuary and highlight the sea area.In order to understand the key areas of seawater eutrophication in Yangtze River Estuary,14 stations in the red tide high-incidence areas of Yangtze River Estuary were analyzed by principal component analysis.The results of this study are as follows:1.The fuzzy comprehensive evaluation method,eutrophication index method(E),nutritional quality index method(NQI)comparison indicated:?E index method evaluation is too large,the final area calculated is relatively large;?NQI index method does not distinguished each water area very well.Apart from a small part of the estuary,the Yangtze River estuary is basically a medium-nutrient type,which is not practical and does not highlight the problem areas;?The fuzzy comprehensive assessment method makes the evaluation of the Yangtze River estuary more reasonable and can also highlight the problem areas.It is more practice and guidance in the problem areas.Comparing the fuzzy comprehensive evaluation results with the four factors involved in the evaluation,it was found that the method better reflects the chemical indicators(DIN,P04)and biological indicators(Chla,DO)in the assessment of seawater eutrophication,and the evaluation results are relatively satisfactory.2.In summer,the fresh water of the Yangtze River extends to the Northeast under the effect of 122 degree 30 'under the influence of the south wind,and the main shaft extends to the southeast direction,which makes the eutrophication level in the northeast direction higher than that in the May.In winter,due to the decrease of precipitation and the decrease of runoff in the Yangtze River Basin,the impact range of the fresh water is smaller and the rich region of the nutrient salt is concentrated in the small area of the Yangtze Estuary.Therefore,the three seasons in spring,summer and autumn in the area of the sea water eutrophication in the mouth of the sea are larger than those in winter.3.The fuzzy comprehensive evaluation of the estuary of Jiao Xi found that there are three level degree kinds of eutrophication quality monitoring water at each station in Jiao Xi,which is due to the monitoring station is located in the deep estuary of the river,and the real time exchange function of each station is poor.The transverse comparison of the evaluation results showed that the three level membership degree of the station was decreasing from the estuary inside to the outside,and the three level membership of the flood season was higher.The fuzzy comprehensive evaluation of the cross river estuary is consistent with the characteristics of Jiao Xi.4.the monitoring data of the red tide monitoring area of the Yangtze River Estuary was analyzed by principal component analysis.It was found that the main components of the CC09 site,Z1,Z2 and Z3,located near the 10m contour line were very large.It was believed that this was due to the CC09 station located at the edge of the suspended sand front of the Yangtze Estuary,which could get sufficient light,and it brought a lot of nutrition from the fresh water from the mouth to the estuary.According to the analysis,CC09 stations should be monitored.Through the evaluation of the eutrophication of the Yangtze River estuary,comparing the three methods:fuzzy comprehensive evaluation method,eutrophication index method(E),and nutritional quality method(NQI)found that:the fuzzy comprehensive evaluation method is a quantitative way to forecasting marine ecological and the fuzzy comprehensive evaluation method is more suitable for quantifying marine ecological forecast.