Impact of Summer Thermal Stratification on Depth Profile of Phytoplankton Productivity, Biomass, Density and Photosynthetic Capacity in Lake Nasser (Egypt)

Lake Nasser is a headwater of Nile River in Egyptian territory. In wintertime, there is a complete upwelling in the water body whereas it is clearly thermally stratified in summer. Depth profile of summer stratification at the upper 15 m was investigated in four different sites. Temperature amplitude reached about 10 °C whereas oxygen concentration was about 7.491 mgO_2 1^(-1). Epilimnion layer was extended to 10 m depth whereas metalimnion underwnt from about 10 to 15 m and hypolimnion was initiated down. Bands of stratification were affected with the inflow of River Nile at the south. Peak maximum of chlorophyll a, phaeophytin, and standing crop was recorded at 10 m. Net primary productivity was irregular along the depth profile. Superficial water had climax photosynthetic capacity and declined downward. Integrated column productivity was correlated with that equivalent concentration of chlorophyll a. Khore Korosko exhibited the highest integrated productivity rate (315.9 mgC m^(-2) h^(-1) and photosynthetic capacity (24.4 mgC mgChl^(-1) h^(-1) among the studied sites. Layering width of water stratification and its temporal occurrence were affected with currant and physics of flooded water. So epilimnion is usually shallow in the north section while it becomes deeper toward the inflow of Nile floodwater at the south.