Author(s): Sumaiya Ahmed, Dulon Roy, Haraj Uddin, Shibananda Shil and Md. Sagir Ahmed

Abstract: Present study was conducted to compare phytoplankton diversity and their seasonal abundance in relation to some physico-chemical parameters from January to December 2001 in the river Buriganga. Among various chemical parameters dissolved oxygen content was found very low, range from 0.3-5.3 mg/l which is very alarming for aquatic lives in the river. In contrast, free CO₂ was high and ranged from 2.1-183.6 mg/l. The river water was alkaline and hard throughout the period of investigation (p^H 7.4 to 9.5, Hardness 145 to 380 mg/l and alkalinity 57 mg/l to 322 mg/l). About 59 species of algae belonging to 35 genera was identified during one year investigation. In the algal community the highest number of taxa belong to Chlorophyta (45.77%), followed by Cyanophyta (18.65%), Euglenophyta (18.65%) and Chrysophyta (16.95%). The dominant groups of algae like Melosira spp. (2779.16 indiv/l) were found throughout the year; other genus Microcystis spp. (2.8x106 cells/l) and Oscillatoria spp. (2520 indiv/l) were found dominant in July. The relationship between physico-chemical and biological parameter; temperature and phytoplankton were observed. Some species of phytoplankton have positive relationship with low oxygen content as well as nitrogen and some phytoplanktons have negative relationship. Diversity index of phytoplankton was carried out and ranged in between 0.279 to 1.296 and evenness index ranged from 0.1 to 0.9.The results indicated that the water of the river Buriganga was highly polluted and plankton diversity index was moderately rich and evenly distributed.

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