Seasonal patterns in phytoplankton growth, composition, and predominance in relation to water quality at Northwest El-Manzala Lake, Egypt

The physicochemical properties and phytoplankton community structure were investigated seasonally at four stations representing Northwest El-Manzala Lake, Egypt, during 2019. Results indicated wide local and seasonal variations in the concentrations of various physicochemical parameters. There was a noticeable variation in levels of nitrogen and phosphorus forms; higher ammonia, nitrite, and nitrate contents of 11.6 (in autumn), 2.28 (in winter), and 2.32 mg L^-1 (in autumn), respectively, were detected at Shatt Greba (site IV). Total-P and ortho-P exhibited higher levels of 7.14 and 0.96 mg L⁻¹, respectively, at site IV in summer. The greatest amounts of sodium, potassium, calcium, barium, and lithium were 102.88 g L⁻¹, 9.12 g L⁻¹, 8.56 g L⁻¹, 345.8 mg L⁻¹, and 1.62 mg L⁻¹, respectively, during summer. Two-way ANOVA presented a highly significant local and seasonal effect of physicochemical parameters on phytoplankton biomass. There were high levels of autumn algal biomass (65.96 mg L⁻¹) and low levels of winter algal biomass (32.28 mg L⁻¹). Cyanophyta, Chlorophyta, and Pyrrophyta dominated in the autumn, whereas Bacillariophyta dominated in the winter. Cyanophyta and Pyrrophyta biomass showed high local variations in contrast to Bacillariophyta and Chlorophyta. The species diversity index revealed that the study area was mildly to moderately polluted water.