ABSTRACT
A study was carried out in Chatla floodplain lake, Barak Valley, Assam, North East India on phytoplankton diversity, density and distribution in different seasons and their correlations with physico-chemical properties of water. A total of 34 phytoplankton taxa belonging to Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae were recorded. Highest number of species was present in pre-monsoon (29) and lowest in winter (23). Members of Chlorophyceae were present in a reasonable number throughout the year while being most abundant in pre-monsoon and monsoon. Bacillariophycae and Cyanophyceae populations did not show much seasonal variation. Percentage composition of Euglenophyceae showed clear seasonal change, being most dominant in post monsoon, moderate in pre- monsoon and winter and nearly absent in monsoon. Total phytoplankton density showed highly significant positive correlation with transparency (p< 0.01) and significant positive correlation with total suspended solids, total hardness and calcium (p < 0.05). Shannon-Wiener diversity index (H/) value (2.66) was found to be the highest during pre-monsoon while the highest evenness (J/) value (0.89) was recorded during winter. Berger-Parker index of dominance (0.45) was highest in post- monsoon. Our study revealed that the growth of phytoplankton is governed by transparency, total suspended solids, calcium and total hardness. These types of studies are prerequisites for evolving fish culture programmes and management of water resources.