| Danjiangkou reservoir is the birthplace for the middle line of the South-to-North water diversion project.The quality of the water quality is directly related to the success or failure of the South-to-North Water Diversion Strategy and is also the main basis for the government departments in the region to formulate economic development strategies.Long-term monitoring data show that the main factors determining the quality of Danjiangkou reservoir water quality is the total nitrogen,total phosphorus,chemical oxygen demand and other indicators for the degree of eutrophication.This paper studied the water evaluation model and prediction model of Danjiangkou Reservoir basing on the indexes of total nitrogen,total phosphorus,chemical oxygen demand,biological oxygen demand and chlorophyll a.This paper mainly studies the water quality of Taocha in Danjiangkou reservoir.Firstly,the water evaluation model was constructed by the monitoring data of total nitrogen,total phosphorus,chemical oxygen demand,biological oxygen demand and chlorophyll a in Taocha from 2008 to 2013.The fuzzy comprehensive evaluation model was established by using the improved fuzzy membership function;The concept of principal component is used to analyze the weights of each evaluation index,and the gray relational degree model is established based on the weighted distance.The weight of each index is determined by the improved entropy method,and the set pair analysis model is established based on the five elements connection number.Secondly,the evaluation results of the above three models are calculated.It is found that the fuzzy comprehensive evaluation method is the most suitable for the assessment of water quality of Taocha from 2008 to 2013 with the least error.In view of the minimum amount of calculation by the fuzzy comprehensive evaluation method,Evaluation method Songgang,black chicken mouth,Wulongquan,Tumen four reservoir areas from 2008 to 2013 to make a comment on the water quality.Finally,taking the total N indicators of Taocha,Songgang,Heijizui,Wulongquan and Tumen as examples,the weights of the background values and the selection of the initial values were determined according to the monitoring data of each monitoring site from 2011 to 2016 Improvement,established the GM(1,1)model.Details are as follows:This paper established three kinds of evaluation model for water eutrophication including fuzzy comprehensive evaluation method,grey correlation method and set pair analysis method to evaluate the degree of water eutrophication for Taocha area from 2008 to 2013 respectively.For analyzing the advantages and disadvantages of the three models,getting the best model and completing the evaluation of water eutrophication for Song gang?Black chicken mouth?Five longquan and Tumen in reservoir area.In addition,the grey prediction model is used to grasp the temporal and spatial dynamic changes of water eutrophication indicators,which can effectively predict the water quality development of Danjiangkou reservoir in the next few years.The results show that:1.In view of the different extent for the importance of these indexes of total nitrogen,total phosphorus,COD,BOD and chlorophyll-a in Danjiangkou Reservoir for water quality evaluation,in order to determine the weight of each evaluation index in fuzzy comprehensive evaluation method In this paper,an improved analytic hierarchy process(AHP)is used to determine the weight.At the same time,considering the non-linear features of the index changes,the cosine function is constructed to determine the membership degree,and the comprehensive membership degree is obtained by combining the weight and the fuzzy membership degree.In this paper,according to the size of the integrated membership degree,the eutrophication degree of Tao Chai from 2008 to 2013 is obtained: 2010 <2009 <2011 <2012 <2013.2.The concept of principal component is introduced to determine the weight of gray relational model.The five evaluation indexes are transformed into two principal components that can represent most of the information,and the comprehensive score model of the principal component is obtained.The coefficient of the original evaluation index in the comprehensive score model is Weights.The weight is combined with the gray correlation coefficient to get the gray relational degree.The Lagrange function is constructed by introducing the degree of difference.The minimum difference corresponding to the minimum value of the function is obtained and the water quality level corresponding to the minimum difference is determined.In this paper,the degree of eutrophication of Tao Chai from 2008 to 2013 is judged according to the minimum degree of difference: 2010 <2008 <2011 <2009 <2012 <2013.3.As the information carried by each evaluation index is disorder,in order to reflect the different effects of different indicators in the comprehensive evaluation results,the entropy method is used to determine the weight of the set pair analysis model.The trophic degree of this article is divided into five levels,so that only pairwise analysis with same degree,degree of opposition and degree of variance is not suitable for this study.Therefore,this paper establishes a set-pair analysis model using five-element association number.Using the fiveelement connection number method,Taocha obtained from 2008 to 2013 all belong to the mid-nutrition.According to the average connection degree,the eutrophication degree of the water quality is given: 2011 <2012 <2013 <2013 <2009 <2010.4.Based on the water quality evaluation model,the eutrophication evaluation of other indexes after removing nitrogen in Taocha from 2008 to 2013 was greatly reduced.As a result,the eutrophication degree of Taocha,Songgang,Heijizui,Wulongquan,Soil nitrogen content,the use of improved GM(1,1)model for 2017~2021 for total nitrogen content prediction,and the residual value test for the prediction of the error analysis.The results show that the nitrogen content of all the reservoir areas shows a slow downward trend from 2017 to 2021. |
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