Fragilaria construens var. venter had higher tendency
toward conductivity (426 lS/cm) and ammonium-nitrogen
(445 lg/L). F. construens is known as eutrophic species, oligosaprobous
and alkaliphilous (Van dam et al., 1994). Navicula
atomus had higher optimum conductivity of 450 lS/cm and
is reported as hypereutrophic species, meso-polysaprobous,
water quality of class III-IV, needs continuously elevated concentrations
of organically bound nitrogen (Van dam et al.,
1994). In contradict with our results, in River Nile, Belal
(2012) found that Navicula atomus had lower optimum of
ammonium and conductivity. Nitzschia gracilis had higher
optimum conductivity of 488 lS/cm. Van dam et al. (1994)