ZHANG Qian, LI Guoqiang, ZHUGE Yisi, YU Xiao, TAN Hongwu and DU Qiang

Abstract: The results of water quality assessment in Erhai using single factor evaluation, do not well re-flect the effect of water environment management in recent years. This paper collects the monitoring data of water quality of Erhai systematically in 1992-2016. Based on the improved fuzzy comprehensive evaluation method and several water quality indexes, the trend of water environmental change in Erhai was evaluated from the aspects of surface water quality standard and lake eutrophication, and the results were compared with those obtained by the single factor evaluation method. The results show that the surface water quality in Erhai gradually deteriorated between 1992 and 2003, since 2003, and the water quality of Erhai has been improved year by year and tends to be stable. The quality of Erhai in non-flood season is better than that in flood season (during June to October) during the year, and the water quality in the center of the lake is better than in the south and north. Overall, the eutrophication level of Erhai has gradually changed from oligotrophic to medium nutrition. Compared with the single factor evaluation method, the improved fuzzy comprehensive evaluation method can better reflect the dynamic change characteristics of water quality in Erhai in recent 20 years.

Keywords: water quality evaluation; eutrophication; improved fuzzy comprehensive evaluation method; single factor evaluation method; Erhai