Seasonality and composition of epipelic diatom community were studied for two years in two wetlands of Bangladesh namely, Joysagar and Sitlai Beel. A total 73 diatom taxa were recorded. The average density of epipelic diatom was higher in Sitlai Beel (52.97  10 4 /g sediment) than in the Joysagar (3.92 10 4 /g sediment). The epipelic diatom community of Joysagar was dominated by the species of Melosira, Synedra, Navicula, Pinnularia, Gomphonema, and Nitzschia, whereas Melosira, Navicula, Pinnularia, Cymbella and Gomphonema dominated in Sitlai Beel. Melosira granulata, Navicula americana, Pinnularia major, and Gomphonema lanceolatum were dominant and expressed distinct seasonality in both wetlands. The concentration of soluble reactive silicate of water and the average density of epipelic diatom did not express any significant relation in both of the water bodies. The concentration of phytoplankton chl a had a positive relationship with epipelic diatoms and was significant in Sitlai Beel.

Samad Nagar pond situated in Jatrabari, Dhaka showed mean air temperature 20 - 30 °C and water temperature 19 - 28°C. Secchi depth (Zs) varied from 28.67 - 44.5 cm and pH 6.6 - 8.8. The mean DO and alkalinity ranged 5.34 - 10.00 mg/1 and 0.58 - 1.08 meq/1, respectively. Free C02, SRP and SRS ranged 1.31 - 4.21 mg/1, 158.39 - 635.70 pg/1 and 13.32 - 28.65 mg/I, respectively. During the study period, seasonal mean values of transparency was higher in monsoon and lower in winter. pH, alkalinity remained higher in winter but lower in monsoon. From aquatic plant communities of the pond, phytoplankton represented by 33 species of which 54.55% belonged to Chlorophyceae (54.55%) followed by Bacillariophyceae (13.64%), Cyanophyceae (13.64%), Euglenophyceae (13.64%) and Dinophyceae (4.55%). The population density of phytoplankton community ranged 6.16 - 25.96><1 06 ind/1. Benthic diatom density varied from 2.64- 11 .00 x 1 06 ind/1. Benthic diatom population was the highest (I lxlO6 ind/1) in late October and lowest in early September (2.64 xio6 ind/1). Chi a and phaeophytin concentration varied 5.10 - 228.51 pg/1 and 2.05 - 1513.36 pg/1, respectively. Aquatic macrophyte communities were represented by 23 species where Eichhornia crassipes (Mart.) Solms. , Ipomoea aquatica Forsk, Ipomoea fistulosa Mart., Telanthera philoxeroides Moq., Rumex maritimus L., Eclipta prostata (L.) L. and Salvinia natans L. were observed all over the study period. Asiat. Soc. Bangladesh, Sci. 41(2): 253-262, December 2015

A total 9 diatoms taxa newly reported from the sediments of Joysagar and Sitlai Beel has been reported. These are Navicula cuspidata var. heribaudii Peragallo, N. grimmei Krabke, Navicula americana Ehr, Pinnulara major (Kutz.) Cleve, P. braunii (Grun.) Cleve. P. brevicosta Cleve, P. divergens, P. acrosphaeria Brebisson, P. stauroptera (Grun.) Cleve and P. hemiptera (Kutz.) Cleve. Asiat. Soc. Bangladesh, Sci. 44(1): 1-6, June 2018

A total of 11 diatom taxa have been newly recorded and illustrated from the sediments of Joysagar and Sitlai Beel in the district of Sirajganj, Bangladesh. These are Frustulia rhomboides (Ehr.) de Toni, Diploneis smithii (de Breb.) Cl., Stauroneis pygmaea Krieger, S. schroederi Hust., Navicula bicontracta Oestrup, N. gottlandica Grun., N. neoventricosa Hust., Caloneis ventricosa (Ehr.) Meister var. minuta (Grun.) Mills, Pinnularia acuminata W. Smith, P. acrosphaeria de Breb. and Nitzschia tryblionella Hantzsch var. subsalina Grun. (syn. Nitzschia tryblionella Hantzsch var. debilis (Arnott) A. Meyer).