Study of phytoplankton flora and its use as a biomonitoring tool to determine the water quality of Krishnasayar lake, Burdwan, West Bengal, India

The present study focused on biomonitoring approaches involving the phytoplankton composition, density and diversity, and their relationships, with changes in environmental variables, and to determine the pollution status of Krishnasayar Lake in the Burdwan District of West Bengal, India. A total of 29 phytoplankton taxa belonging to Chlorophyceae (13), Cyanophyceae (9), Bacillariophyceae (5) and Euglenophyceae (2) were observed. The phytoplankton density exhibited a maximum value of 12,633 cells/litre in the post‐monsoon season and a minimum value of 7,266 cells/litre in the pre‐monsoon season. The results of two multivariate proficiencies (cluster analysis; CCA) indicated the distribution of phytoplankton groups are influenced by pH, electrical conductivity, and the nitrate, phosphate, potassium and dissolved oxygen concentrations. Various diversity indices, including the Shannon–Wiener Diversity Index, Gleason Species Richness Index, Pielou Evenness Index and Naughton Dominance Index, were explored to illustrate the seasonal phytoplankton fluctuations. The Shannon–Wiener Diversity Index values (2.524, 2.331 and 2.666, respectively, for the pre‐monsoon, monsoon and post‐monsoon seasons) indicate the moderation level of pollution status of the lake. The present study also highlights biomonitoring is a reasonable technique for establishing ecological conditions of lakes by considering the organisms within them, including planktonic algae, macrophytes, benthic macroinvertebrates, crustaceans and fishes on the basis of a single indicator species or a combination thereof. The present study used planktonic algae to determine changes in surrounding environmental conditions. As some of the studied phytoplankton species exhibit specific ecological preferences, their presence can indicate the health of that system. As examples, Coelastrum microporum, Pandorina morum and Euglena viridis indicate high levels of organic pollution. Krishnasayar Lake is integrated with the Krishnasayar ecological park, being affected by large levels of anthropogenic disturbance attributable mostly to uncontrolled and careless activities of some visitors, annual cultural activities, other programmes, etc., meaning relevant management activities are needed to protect the lake from further degradation.