الفهرس 
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Abstract
El Rayah El Tawfiky is one of the main sources of water supply for 3 governments in Nile Delta, Egypt. Investigation was carried out on using phytoplankton as biological indicators through matching between quantitative, qualitative analysis of phytoplankton in water and results of the physicochemical parameter analyzed. In our study120 algal taxa belonging to five systematic algal divisions (Bacillariophycophyta, Chlorophycophyta, Cyanophycophyta, Euglenophycophyta and pyrrophycophyta) were detected. Qualitatively, Chlorophycophyta was the dominant division followed by Bacillariophycophyta, Cyanophycophyta, Euglenophycophyta and pyrrophycophyta. On the other hand, the quantitative study showed that Bacillariophycophyta was the most dominant division, followed by Chlorophycophyta, Pyrrophycophyta and Euglenophycophyta. The highest number of individuals was recorded during winter and the lowest number of individuals was recorded during spring and summer. Physico-chemical analysis of El Rayah El Tawfiky revealed that temperature at all studied stations during all seasons ranged from 16.7 to 31.6 °C. There were remarkable variations in the degree of the turbidity during seasons. Concerning the pH, the pH values of water in El Rayah El Tawfiky at all stations were slightly alkaline and alkaline. Chlorophyll a concentrations varied during seasons, the highest concentrations of Chl a were detected during winter and the lowest one were detected during spring.
In this study, there were different relationships between Physico-chemical analysis with phytoplankton compositions especially phytoplankton biomass. Results showed an increased concentration in Physico-chemical parameters (Chl a, temperature, turbidity, phosphate, nitrate, nitrite and heavy metals) has an impact on the density of phytoplankton. There were negative relationships between total algal biomass (as number of individuals/ L) with temperature, turbidity and heavy metals except some heavy metals (Cd, Co, Cr, V and Al) had positive relationships with total algal biomass or with some algal species. On the other hand, there were strong positive correlations between algal biomass with concentrations of Chl a, phosphate and nitrite. Some algal divisions had relationships with some Physico-chemical parameters as Cyanophycophyta had strong positive relationship with nitrate. Euglenophycophyta had strong positive relation with ammonium. According to Shannon-Weaver index, trophic status and saprobic status of the El Rayah El Tawfiky and the dominance of these diatom taxa in the water of the El Rayah El Tawfiky, it was regarded that water quality of the studied area was relatively medium to good along different stations. Quantitative, qualitative analysis of Phytoplankton is regarded as an easy and useful indicator means to assess the quality of freshwater ecosystems.