Determining the water quality of the Tajan River (Sari City) to select the release station for economic fish juveniles of the Caspian Sea (2022)

Globally, rivers are under tremendous anthropogenic stress caused by stream fragmentation, land use changes, and regulation and water quality has been widely declined. In a review of studies, the integrity of flowing water systems largely depends on their natural dynamic characteristics, which sustain habitat. In this study, the physical and chemical factors of the Tajan River water, which is the habitat of various fishes and where the release of some economic fishes of the Caspian Sea takes place, are investigated in 7 stations during the year 2022. The results of the physical and chemical parameters such as water temperature, pH, electrical conductivity, total suspended solids, turbidity, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, ammonium, nitrite, nitrate, phosphate, water quality index and comprehensive pollution index were recorded as 14.50-32.00 °C, 6.48-12.24, 562-10020 µs/cm, 2.35-185.71 mg/l, 1.8-328 NTU, 1.01-14.11, 0.58-16.05, 2.39-50.21, 0.020-1.028, 0.005-0.771, 0.49-58.56, 0.010-1.610 mg/l, 17.0-75.0 and 1.20-7.33, respectively. Based on the principal component analysis, the biochemical oxygen demand, nitrite, nitrate, and phosphate variables are in the first component, which is more important in the Tajan River. Also, based on the step-by-step regression analysis of the water quality index, the most effective variable was recorded biochemical oxygen demand, turbidity, and phosphate, and according to the comprehensive pollution index, the water quality of this river was dependent on the variables of phosphorus, phosphate, and nitrate. Finally, based on the physical and chemical parameters and various water use indicators, the Tajan River is unsuitable for fish life. Based on various indicators, station one (placed in a separate group in the cluster test) compared to other stations has more suitable conditions for releasing fish juveniles.