S. N. Motevalian - Faculty of Civil and Environmental Engineering, Shahid Beheshti University, Tehran, Iran
M. R. Majdzadeh Tabatabai - Assistant Professor of Civil, Water and Environmental Engineering Department, Shahid Beheshti University, Tehran, Iran

The aim of present study was to investigate the relationship between hydraulic and ecological variables of the studied span and to investigate changes in living conditions of phytoplankton (Amphora ovsalis and Navicula placentula). According to the measurements and analysis of habitat fit curves, it can be concluded that the highest frequency of Amphora ovsalis and Navicula placentula occurred and specified at flow rate of ۱۵.۸۲ and ۱۴.۹۴۲ m۳/s, respectively. As can be seen, the lowest frequency of Amphora ovsalis and Navicula placentula in this measurement occurred at flow rate of ۱۵.۳۵۵ and ۵.۲۸۹ m۳/s, respectively. The best habitat conditions for Amphora ovsalis and Navicula placentula are in the range of ۰.۱۸ -۰.۳۱ and ۰.۱۸ - ۰.۲۶۵ of Froude number range respectively. The highest density and abundance of Amphora ovsalis and Navicula placentula was observed in the range of ۰.۰۱۷ - ۰.۰۵۵ and ۰.۰۱۷ -۰.۰۳۹ mg/l of phosphate demonstrating that the best growth and living conditions are predisposed in this range for these species had suitable habitat conditions for life in this range. The highest frequency of Amphora ovsalis and Navicula placentula is in the range of ۰.۰۱۹ - ۰.۰۷۱ and ۰.۰۴۷-۰.۰۷۱ mg/l nitrite, respectively. Amphora ovsalis and Navicula placentula had the highest frequency when nitrate ranges ۴.۴۸ – ۵.۱۶ and ۴.۴۸- ۵.۳۷ mg/l. The best habitat conditions for Amphora ovsalis and Navicula placentula were between the mean velocity values in the range of ۱ -۱.۲ m/s.

Amphora ovsalis, Navicula placentula, phytoplankton, Tajan River