Application of improved fuzzy comprehensive evaluation method in eutrophication assessment for tributary bays in the Three Gorges Reservoir, China

Since the operation of the Three Gorges Reservoir, its tributaries have been eutrophic and flooded many times, the prompt and accurate eutrophication assessment is the foundation of water environmental management for this area. To address the problems existing in the fuzzy comprehensive evaluation, a novel method is proposed to adjust the indicator weight by using the analytic hierarchy process-entropy weight method, improve the fuzzy operation method, and take the weighted average as the basis of comprehensive evaluation. Through this method, the information of each indicator can be comprehensively used, and the subjectivity and blindness of evaluation can be effectively reduced. Then the eutrophication status of Hanfeng Lake is analyzed by it, and compares the results with that of conventional methods. The results show that Hanfeng lake is greatly affected by TN and TP, and it is generally in mesotrophic to mildly eutrophication. Eutrophication degree is as follows: Nanhe River > Donghe River > Regulating dam, so the control measures should be strengthened in Nanhe area. Combined with the water pollution control measures proposed in this paper, it can provide guidance for the monitoring and treatment of eutrophication in the Three Gorges Reservoir area and ensure the safety of the water environment. Practitioner points This paper proposes to use the analytic hierarchy process-entropy weight method combined with the fuzzy operation method to assess the eutrophication status of tributaries of the Three Gorges Reservoir, in China. The results indicate that Hanfeng Lake is generally in a light eutrophication state, which is greatly affected by TN and TP, and the Nanhe River is in a relatively high degree of eutrophication, which need to be extra vigilant. The evaluation results are more conformable to reality than that of the traditional fuzzy comprehensive evaluation, which can provide guidance for comprehensive management of eutrophication.