Seasonal assessment of eutrophication potential and thermal stratification in Esteghlal reservoir

This study investigates the water quality dynamics of Esteghlal Reservoir over a five-year period, with a specific emphasis on evaluating its eutrophication potential. We employed a two-dimensional water quality model, CE-QUAL-W2, to simulate daily variations in key variables, including temperature, dissolved oxygen, algae, phosphate, ammonia, and nitrate, which influence nutrient conditions and eutrophication. Due to significant fluctuations in the reservoir's water volume, water quality analysis was conducted seasonally. The results reveal a complex dynamic pattern within the nutrient cycle in the reservoir. In spring and summer, temperatures vary throughout the water column, indicating strong thermal stratification. There is a notable difference in dissolved oxygen concentration between the epilimnion and hypolimnion due to factors such as oxygen consumption by algae, limited wind-induced mixing, thermal stratification, and an extended detention time. In autumn, a reduction in inflow during the summer and evaporation lead to a decrease in water volume. This, along with a reduction in temperature, weakens thermal stratification. With the influx of floods in winter, water volume increases, and complete mixing occurs due to cooling. This provides a suitable environment to improve dissolved oxygen levels. However, it also leads to an increase in nutrient input. Simulation results and an assessment of nutrient criteria underscore the presence of eutrophication potential in most months. A well-defined monitoring program with optimized sampling frequency and location, coupled with the control of nutrient input through watershed management and detention time adjustment, can be considered effective strategies for improving the reservoir's condition.