Assessment of Carson Trophic Index in Dam Lake: a Case Study of Ekbatan Dam

Background and purpose: The study aimed to investigate the trophic state of Ekbatan Dam Lake. In the current research, the quality of water behind the dam was studied during the months July and January in order to compare the trophic state and zonation of the reservoir in two different seasons (dry and wet). Materials and Methods: 15 sites were selected in different points of Ekbatan Dam Lake and sampling was accomplished in July and January. To determine the rate of eutrophication in the reservoir, 30 samples (15 in July and 15 in January) were taken from the reservoir. In this study, secchi disk, nitrate, phosphate and chlorophyll-a were measured. Then, using Carlson’s Trophic State Index, the rate of eutrophication was estimated for all points. Also, using GIS zoning of water quality parameters and TSI (Trophic State Index), value was evaluated in two different seasons. Results: The findings of the current study showed that TSI varied between 35.7 and 50.7 in different stations of the lake in July. At the same time, it was documented to vary between 55.13 and 58.6 at different points in January. Also, the results revealed that the trophic state of the lake is oligotrophic to eutrophic in different stations in July while it was eutrophic for all points in January. Conclusion: Based on the estimated values of this index, the stations located at the entrance of the lake showed more eutrophic situation in July. Also, phosphorous was revealed to be the limiting nutrient in this system. The current research showed that eutrophication is a serious problem in Ekbatan reservoir.