Application of a New Improved Weighting Method, ESO Method Combined with Fuzzy Synthetic Method, in Water Quality Evaluation of Chagan Lake

Wenbin Zhao,Changlai Xiao,Zhang Fang,Xiujuan Liang,Yunxu Chai,Xiaoya Feng

doi:10.3390/w13101424

Abstract

The existing weighting methods mainly comprise subjective and objective weighting and have a certain degree of subjectivity, with certain requirements for the professional ability of the users and unstable results. Therefore, an improved weighting method based on the entropy weight, over-standard multiple, and single-factor evaluation methods, referred to as the ESO method, is proposed. The advantages and advancements of the ESO method are demonstrated in this study by combining it with the fuzzy synthetic evaluation method to evaluate the water quality of Chagan Lake wetland from 2007 to 2016. The main conclusions of this study are as follows: 1. The ESO method has more comprehensive consideration factors, lower requirements for the professional ability of users, and more stable weighting results than the traditional weighting method. Therefore, it is highly suitable for beginners and frontline staff who are not professionally qualified and cannot accurately conduct subjective weighting. Meanwhile, owing to the amendment rule and emphasis on the local weight of the sample in the ESO method, it is applicable to time-series samples. 2. The ESO method better allocates the amendment weights to indicators with a higher degree of pollution; thus, the final comprehensive evaluation results are relatively conservative. However, in contrast to the single-factor evaluation, the conservatism of ESO method is the result of the comprehensive effect of all samples; thus, the conservative result of the ESO method is more reasonable. 3. The water quality of Chagan Lake in 2009 and 2015 was class IV, which did not meet the standard, while that in remaining the eight years was class III, which met the requirements of the national 13th Five-Year Plan. The results of this study can provide a new approach to weighting calculation methods and a basis for the protection and treatment of the ecological environment of the Chagan Lake wetland.

Highlights

IntroductionSingle-factor assessment and comprehensive evaluation methods are commonly used for water quality evaluation
The comprehensive evaluation method gives a certain weight value to each indicator through a weighting method; the final evaluation results comprehensively reflect the impact of each indicator, and the influence of indicators can be indicated by weight values, resulting in a good practicability and evaluation effect than single-factor assessment
The pollution degree of each factor was decreased in the following order: F and CODCr > CODMn, total nitrogen (TN), and total phosphorus (TP) > BOD5 > NH3 -N > dissolved oxygen (DO)

Summary

Introduction

Single-factor assessment and comprehensive evaluation methods are commonly used for water quality evaluation. The Chinese government uses the single-factor assessment method for water quality evaluation in its monitoring report; it only uses one of the most polluted indicators as the evaluation factor and ignores the impact of other evaluation indicators, resulting in conservative evaluation results and wasting large amounts of water resources that could have been used [1]. The comprehensive evaluation method gives a certain weight value to each indicator through a weighting method; the final evaluation results comprehensively reflect the impact of each indicator, and the influence of indicators can be indicated by weight values, resulting in a good practicability and evaluation effect than single-factor assessment.

Objectives

Methods

Results

Conclusion