| Eutrophication is considered as a serious problem in water reservoirs. Awareness about
the eutrophic status of each reservoir could help in providing a better understanding of the problem in a
global scale. The present study was conducted to assess temporal and spatial eutrophication index in a water
reservoir (Sahand dam) in the northwest of Iran. Physico-chemical parametres that are effective on eutrphic
condition occurrence were analyzed, and trophic state index was calculated on a scale of 0-100 by measuring
Secchi disk depth, chlorophyll a, total phosphorus, total nitrogen, total suspended solids, and phosphorus P/N
ratio. Moreover, using the overlapping, the reservoir was mapped based on the mentioned index. Seasonal
variation of dissolved solids in the reservoir was recorded due to precipitation and subsequent dilution and
evaporation. Thermal stratification was observed during the summer months. The total trophic state index
value was calculated as 55.5- 58.07, with minimum value belonging to P/N and maximum value belonging
to suspended solids for individual parameters. There were some spatial and temporal differences for trophic
state index in the reservoir. It was found that the whole area of the reservoir was in almost moderately
upper-mesotrophic condition and in some target stations it was very close to eutrophic condition. The worst
condition was observed in Qaranqu River as the main input to the reservoir. Due to the significant impact of
suspended particles resulting from erosion of the surrounding lands on TSI value, there is an urgent need for
mitigation measures to intercept eutrophication. |