Variation of water quality and phytoplankton along different zones of Aswan High Dam Reservoir

Abstract

his study was carried out at Aswan High Dam Reservoir and focused on the spatial variation of water quality parameters and phytoplankton composition. Water samples were collected from eighteen sampling stations, where six stations for each of the different zones were selected to represent the lacustrine, transition and riverine zones of the reservoir during 2007 and 2008. The results of the environmental factors showed wide variations in their concentrations along the different zones of the reservoir. In this study, chlorophyll a concentration was lower in the lacustrine zone than in the riverine, although turbidity and secchi depth values were all optimal for light availability. This result was influenced by higher abundances in the reservoir phytoplankton assemblages where riverine conditions predominate, by species tolerant to turbulent conditions and typical high mineral turbidity. Calculation of the trophic state index showed that riverine and transition zones are classified as eutrophic, while lacustrine zone is mesotrophic. Phytoplankton composition recorded thirty nine species belonging to Chlorophyceae (19 species), Cyanophyceae (10 species), Bacillariophyceae (7 species), and rare groups including Dinophyceae (2 species) and Eugelnophceae (1 species). Cyanophyceae were the most encountered group in the lacustrine and transition zones, while Bacillariophyceae were most encountered group in the riverine zone. This is due to that Cyanophyceae prefer the steady, transparent and low nutrients water (lacustrine), while Bacillariophyceae prefer flowing, turbid and nutrient-rich water (riverine). Statistical analysis showed that certain environmental factors do affect the phytoplankton growth. The results of the one-way ANOVA revealed that the different environmental factors (DO, water temperature, secchi depth, water velocity, turbidity, nitrate, phosphorus, magnesium, total dissolved solids, and trophic state index) and biotic factors (such as chlorophyll a and phytoplankton groups) were significantly different at the three zones of Aswan High Dam Reservoir (p<0.05). This result supports the speculation of variation in water quality and phytoplankton along the different zones of the reservoir.