An experiment was conducted to assess seasonal variations of some physico-chemical parameters and plankton community of the Atrai River in Dinajpur district from August 2017 to July 2018. Summer (May to July), autumn (August to October) winter (November to January) and spring (February to April) were the four seasons of the study. Samples were collected monthly from three sampling sites namely, Vushi, Birga and Jhanjira assigned as site-1, site-2 and site-3, respectively. Physico-chemical parameters and plankton abundance did not vary significantly (P>0.05) among the sites but varied significantly (P<0.05) among the seasons. However, all physico-chemical parameters were within acceptable limits, except transparency. A total 28 genera of phytoplankton comprising Chlorophyceae (11), Bacillariophyceae (11), Cyanophyceae (4) and Euglenophyceae 2) and 9 genera of zooplankton comprising Rotifera (3), Cladocera (3), Copepoda (2) and Nauplius (1) were identified. The highest mean value of total phytoplankton was observed in winter season with a peak in November and January at Site 1 whereas, the lowest mean value was observed in July of summer season at Site 3. The highest mean value of total zooplankton was observed in autumn season with a peak in September in Site 1 while, the lowest mean value was in March of spring season in Site 2. However, total plankton density was the maximum in winter and the minimum in summer where, phytoplankton (79%) dominated over zooplankton (21%). Therefore, the existing water quality and plankton density of the Atrai River would be contributed significantly to enhance the ecosystem productivity.
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