Seasonal Variation of Phytoplankton Diversity in Relation to Eutrophication of Mathura Beel, a Floodplain Lake in West Bengal, India

Current study deals with the phytoplankton structure and seasonal variation in Mathura Beel (wetland), a floodplain lake in Gangetic plane of West Bengal, India. The generic composition of phytoplankton was studied monthly during August 2008 to February 2011. All the relevant calculations were done according to three seasons viz. pre-monsoon, monsoon and post-monsoon. A total of 96 species belonging to 87 genera were identified under six algal classes. Chlorophyceae showed their maximum species diversity with 45% whereas the Cyanophycean algae showed maximum relative density i.e. 93.11% throughout the study period with Microcystis aeruginosa (45.08%) followed by Aphanocapsa rosena (15.53%). Phytoplankton species of Bacillariophyceae, Euglenophyceae, Xanthophyceae and Dinophyceae were negligible in number. Maximum and minimum phytoplankton diversity was found in post- monsoon (H. = 0.38) and pre-monsoon (H. = 0.09) respectively. Cyanophycean algae (D = 0.97) dominated in pre-monsoon season. The temperature increased upto 2 degrees C in pre-monsoon season during the study period. Dominance of cyanophycean algae (Microcystis sp.) has been found to be the main reason of eutrophication in Mathura beel.