Influence of Phosphorus on Phytoplankton Diversity in a Shallow Eutrophic Reservoir

Seasonal changes in the algal diversity with respect to phosphorus load from sewage and dyeing effluent in a small eutrophic reservoir was investigated for a year with monthly samplings. An increase in phytoplankton count was observed (R² = 0. 6) with rise in Phosphate concentrations. Maximum algal diversity (Shannon Simpsons diversity indices, richness, and evenness) was observed during summer, April to July, when phosphate concentrations were at moderate level (0.074-0.163 mgL^-1). Excessive phosphate influx (1.060-1.170 mgL^-1) during rainy season, September to November, caused blooms of nonheterocystous assemblage of desmids, particularly of Cosmarium sp and myxophycean species, and a general decrease in algal diversity indices was observed.