Eutrophication Level Analysis of Shirin- Darreh Dam Reservoir Using Entropy-Based Fuzzy Approach

Eutrophication is a natural process which can be increased by human interferences and finally lead to water quality degradation and reservoir aging, and always is one of the challenging problems of reservoir across the world. Since determining of the trophic status of the reservoir is a complex and intriguing process, this study used fuzzy synthetic evaluation method with entropy weighting technique to determine eutrophication level in the Shirin-darreh dam reservoir in the North Khorasan province for a one year period of time. To this end, fuzzified data of main variable including chlorophyll-a concentration, total phosphorous, saturation oxygen and total nitrogen were used to determine membership function and the Shannon entropy technique was used for weighting index variables. Finally, results of this approach was compared with the results of equal weighting technique and Carlson method. The results showed that from December to March the reservoir was in oligotrophic status, during November in mesotrophic status and during other months it experienced an eutrophic condition. Considering the capability of this approach to express the degree of certainty and intensity at different levels and months, it was observed that July, August and September have the highest eutrophication level with most degree of certainty. Also, this approach has reasonable and realistic results in comparing with Carlson method and equal weighting fuzzy technique.