Abstract: a more detailed understanding of spatiotemporal

Abstract: Giventhat results of traditional assessing methods presently used are extreme valuesand of poor resolution, a set pair analysis based on triangular fuzzy number isestablished and a new method of calculating weight is constructed by using the weightedaverage method. The case study shows that the method presents the evaluatinggrade as a confidence interval which makes it more feasible and suitable topractical conditions.Keywords: set pair analysis;triangular fuzzy number; super-standard multiple weight method; confidenceinterval; lake eutrophication.

1       Introduction   Sustainablemanagement of water resources requires a more detailed understanding of spatiotemporaltrends and differences in hydrological parameters; even though large improvementsin water quality have been achieved as a result of tieless efforts to reduce culturaleutrophication, nutrient enrichment continue to be the main cause of waterpollution for many freshwater ecosystems in the developing world 1. Consideringthat the demand for freshwater resources is expected to increase, protectingdiminishing water resources has become one of the most important watermanagement and pollution control issues 2.Waterquality assessment is the back-bone of lake water management and pollutioncontrol, it provides water resource managers with much needed information tounderstand the state of the water bodies in order to make sound decisions forproper management of this vital resource.

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Many credible water qualityassessment methods have been designed and used, including; single factorevaluation method, comprehensive water quality evaluation method, fuzzyevaluation method, grey evaluation method, artificial neural network method,parameter method, biological evaluation method and nutritional statusevaluation method, set pair analysis method etc 3. All of these methods werewidely used in water quality evaluations of individual water bodies, and ofwatersheds. These existing methods were used to provide information that formedan important foundation for promoting the rational development, planned use,and protection of water resources 4. In recent years the comprehensive evaluation methods are extensivelyused in China because the methods allows a more thorough investigation of waterquality and a more continuous depiction of the eutrophication processes,however,  several problems are inherentin these methods. These methods include the fuzzy comprehensive evaluation whichhas been proved effective in solving problems of fuzzy boundaries andcontrolling the effect of monitoring errors on assessment results 5.

However,there are still some limits when applying fuzzy comprehensive evaluation methodto water quality assessment; For example, when the method emphasizes extremevalue action, more information is lost and the scientific character of weightvalue is not clear etc 6. Set pair analysis model has higher objectivity andreliability compared with the traditional fuzzy comprehensive evaluation model7. Nevertheless; it does not deal with the weight of the evaluation index 8.  Weight plays a key role in the comprehensiveevaluation mathematical model, reflecting the position and role of each indexin the procedure of comprehensive decision making, and directly influencingthe result of the comprehensive evaluation. For the same measured data, the lowcontent and high standard allowable concentration largely affect the pollutioncomparatively 9.  It is difficult toestablish a unified evaluation model, which promotes the further study on thewater quality assessment methods 10. 


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