Adaptation and application of the fuzzy synthetic evaluation (FSE) method for characterizing the trophic state of tropical semiarid reservoirs

Abstract

Eutrophication is a recurrent problem in water bodies, especially in tropical semiarid reservoirs. The Trophic State Index (TSI) is an important tool for the environmental management of aquatic systems. However, determining the TSI involves uncertainties that can affect decision making. This study aimed to adapt and apply the Fuzzy Synthetic Evaluation (FSE) to characterize the TSI considering the uncertainties of the reference eutrophication classi cation system. The Castanhão reservoir, the largest in the State of Ceará, Brazil, was taken as a case study. The results showed that: i) the uncertainty of the trophic classi cation system can be characterized by the triangular and trapezoidal membership functions; ii) the result matrix associates the global trophic level with a degree of certainty, providing greater con dence to the decision maker; iii) the eutrophication index (EI) is not an adequate tool for hierarchizing the trophic degree; and iv) the membership level of the global trophic state generated by the FSE method is a suitable alternative to the EI.