Seasonality and Diversity of Epipelic Diatoms in Two Wetlands of Bangladesh

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/g sediment) than in the Joysagar (3.92 10/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. Introduction Epipelic diatoms are important primary producers and key food source for benthic organisms (Daume et al. 1999, Beltrones and Romero 2001) in shallow aquatic environments. Moreover, they contribute in carbon cycling (Hecky and Hesslein 1995, Barranguet 1997). Several variables such as sediment type (Amspoker and McIntire 1986), nutrient availability (Agatz et al. 1999), salinity (Underwood et al. 1998) of a water body can affect the distribution and diversity of epipelic diatom communities. Compared to benthic macroinvertebrates, diatoms are considered more sensitive indicator of water chemistry owing to their shorter life cycle and nature as primary producer (Steinberg and Schiefele 1988). They have been found to be useful for river monitoring purposes (Eloranta and Andersson 1998). Seasonality and water quality alterations have been linked to changes in aquatic biota and each species of diatom has a specific distribution range and tolerance for environmental variables. Bangladesh possesses enormous area of wetlands and those have an ecological, socio-cultural, and economical importance. The haors, baors, beels and jheels are of fluvial origin and are commonly identified as freshwater wetlands and regarded as valuable fish and wild life habitats. The ecology of epipelic diatoms is less well understood than their pelagic counterparts in various limnological study of Bangladesh. The present study includes spatial and temporal variations in species composition of epipelic diatoms of Joysagar pond and Sitlai Beel Materials and Methods Two wetlands, namely Joysagar pond and Sitlai Beel in the district of Sirajganj, Bangladesh were selected for this study. Joysagar pond (24°28 ′ 40 ′′ 24°28 ′ 50 ′′ E and 89°25 ′ 24 ′′ 89°25 ′ 42 ′′ N) is about 0.226 km 2 in area and up to 2.13 m deep during monsoon. On the other hand, Sitlai Beel (24°28 ′ 10 ′′ E and 89°26 ′ 30 ′′ N) has an area of 0.04 km 2 . Fertilization is done by chemical fertilizer in *Corresponding author. Department of Botany, Jagannath University, Dhaka, Bangladesh. Institute of Freshwater Ecology and Inland Fisheries, 301, Müggelseedam, 12587 Berlin, Germany.