Research On Evaluation Of Lake Eutrophication By Set Pair Analysis Model Based On Entropy Weight

In recent years, with the rapid development of society and economy, environmentalpollution problems continued to emerge and the ecological environment status becameworse and worse. The human beings attach more and more importance to waterenvironment problems, and the waters eutrophication received more concern. At present,numerous lakes of our country have been eutrophicated or are eutrophicating, the lakeeutrophication problems have constituted a serious threat to the living environment ofhuman beings and the safety of drinking water, even held up the sustainable developmentof society economy and environment. Therefore, the research about lake eutrophicationshould be developed widely, and the research of lake eutrophication assessment must bepaid sufficient attention. In order to provide a basis for the prevention and cure of lakeeutrophication, scientific and effective methods should be adopted to make sure the statusof lake eutrophication.Research of lake eutrophication assessment was developed based on the fact thatnumerous lakes of our country have been eutrophicated. In view of the coexistence ofmultiple uncertainties for lake eutrophication the set pair analysis was adopted. Theconnection degree between the sanmples and evaluation indicators were preliminarilycalculated, then the samples were further ranked through the identity, difference andantagonism set pair analysis. The weights of the indicators were obtained from the entropy,then the set pair analysis model based on entropy weight was established. The confidencewas used to obtain the level of lake eutrophication. The new model was used to evaluatethe eutrophication of Baiyun Lake, the largest artificial lake in Guangzhou city. Theexternal pollution sources were abtained by investigating the surrounding of Baiyun Lake,meanwhile, tracking and monitoring the water quality for two years after establishingdrainage systems of the lake. Five indicators including chla, TN, TP, CODMn, SD wereselected as the assessment index of lake eutrophication according to the actual situation ofBaiyun Lake, then based on the National standard and the experience which the previousresearchers had in lake eutrophication area, the lake eutrophication and the five indicatorswere classfied(five levels including highly-oligotrophic, oligotrophic, mesotrophic,light-eutrophic and hyper-eutrophic), then the Baiyun Lake eutrophication assessmentindex system was establish. Afterwards, based on the monitoring data to evaluateeutrophication condition of Baiyun Lake, and the confidence was used to obtain the level of lake eutrophication. The evaluation results showed that the Baiyun Lake was severelyeutrophicated; in the time scale, the eutrophication status of the west lake was the mostserious in January,2011, which was severely eutrophicated; the eutrophication degree ofBaiyun Lake was reduced since April,2011; the eutrophication status of the west lake wasin more serious condition than that of the east lake from space；the eutrophication status ofBaiyun Lake in the wet period was better than that in the dry season. According to theevaluation results, in order to improve the eutrophication status of Baiyun Lake, threemethods were suggested including improving intercepting the pollution sourcescomprehensively, increasing the amounts of facilities for water quality improvement andstrengthening the construction of wetland ecological system around the Baiyun Lake andthe headrace.Besides, in order to verify the rationality of set pair analysis model based on theentropy, the evaluation result was compared to that of traditional assessment methods. Itshowed that the evaluation results of set pair analysis model based on the entropy andtraditional assessment methods are basically identical. Therefore, the set pair analysismodel based on the entropy method for determination of weight is accurate and workableon evaluating lake eutrophication, and is compatible with extended applications.