Comprehensive Evaluation Of River Water Quality Based On PCA-AHP Dimensionality Reduction Combined Weighting Model

The comprehensive evaluation of water quality for many rivers in a basin plays an important role in regional environmental protection,ecological balance of water resources,and ecological planning and management of river basins.Most of the river water quality assessment methods are mainly based on the evaluation objectives and water quality standards to achieve the analysis for a single river.It is difficult to achieve the quantification of water pollution indicators of multiple rivers within the basin.In addition,with the continuous development of water quality detection technology and analysis instruments,the types of water quality indicators are more and more diverse.The rapid,accurate and comprehensive water quality comprehensive evaluation model has important practical significance for the quantitative evaluation of the overall water quality in a basin.In order to quantitatively evaluate the detection data of 18 water quality indexes for 25sections belonged to five rivers in the middle reaches of Daqing River Basin,this paper proposes to combine principal component analysis?PCA?and analytic hierarchy process?AHP?to construct a comprehensive quantitative evaluation model of water quality with reduced dimension combination weighting of PCA-AHP.PCA can quickly screen and reduce the dimension of water quality parameters,and calculate the objective weight.AHP can carry out category analysis on the water quality parameters after dimension reduction,and calculate the subjective weight.The subjective and objective weights can be integrated by multiplication normalization method and realized by statistical analysis software R programming.The main research works and achievements list as the following:?1?The whole pollution situation of five rivers in the middle reaches of Daqing River Basin was investigated and sampled from July to August 2017.The results of 18 water quality indexes?Permanganate index,Chemical oxygen demand,Ammonia nitrogen,Total phosphorus,Total nitrogen,Copper,zinc,Fluoride,Selenium,Arsenic,Mercury,Cadmium,Chromium,Lead,Stone oil,Volatile phenol,Anion surface activity,Sulfide?were analyzed by pollution index method.Using the single factor index evaluation method,the results showed that the total nitrogen and total phosphorus in all rivers exceeded the standard seriously,the exceeding multiple was more than 5 times,the permanganate index and chemical oxygen demand generally exceeded the standard,and the exceeding multiple was between 1 and 3times.Using the Nemero composite index evaluation method,the results show that the order of pollution degree of the rivers from heavy to light is Baohe>Fuhe>Daqing River>Xiaoyi River>Baigou river.?2?In order to comprehensively,accurately and quickly evaluate the pollution situation of five rivers in the basin,and solve the problem that the weight of water quality index was not comprehensive,a comprehensive evaluation model of water quality with PCA-AHP dimension reduction combination is proposed.A set of running program code of water quality evaluation method was compiled by using statistical analysis software R programming operation.The comprehensive analysis data of river basin water quality can be obtained conveniently and quickly.?3?The water quality of five rivers in the middle reaches of Daqing River Basin was evaluated by using that PCA-AHP water quality evaluation model.PCA part could reduce the dimension of water quality parameters from 18 to 5,which were permanganate index,chemical oxygen demand,ammonia nitrogen,total phosphorus and total nitrogen,and the objective quantitative weights were 0.208,0.078,0.306,0.098 and 0.31,respectively.Taking water eutrophication as the overall objective,the analytic hierarchy process?AHP?model of five water quality parameters was constructed.The subjective quantitative weights of permanganate index,chemical oxygen demand,ammonia nitrogen,total phosphorus and total nitrogen were 0.11,0.22,0.13,0.27 and 0.27,respectively.Finally,the subjective and objective weights were combined by the multiplication normalization method,and the combined quantitative weights are TN?0.441?>NH₃-N?0.209?>TP?0.139?>COD_Mn?0.121?>COD?0.090?.The results have important reference value for water environment restoration and planning.