Quantitative and qualitative assessment of plankton: some ecological aspect and water quality parameters of the river Meghna, Bangladesh

Investigation on the seasonal distribution and abundance of various major taxa of phyto and zooplankton and the corresponding physico-chemical characteristics were carried out in four selected stations between the latitude 22°35.494N N-23°23.987 N and longitude 90°35.793 E- 90°49.061 E of the Meghna river system, Bangladesh. Drop count method was followed for the qualitative and quantitative analysis of both phyto- and zooplankton. A total of 41 phytoplankton genera belonging to 17 families and 13 zooplankton genera belonging to 11 families were recorded. Zooplankton growth cycle was noticeably less (3.0%) than the phytoplankton abundance almost throughout the study period. Quantity of plankton registered to increase chronologically from the upper to lower stretches of the river. During summer investigation the load of phytoplankton was recorded maximum (11,300-51,850 No/1). Ratio-wise quantitative difference between zoo- and phytoplankton in composition of the total standing crop fluctuated between 1.0:5.5 and 1:1037. Among the phytoplanktonic groups, Chlorophyceae was found to be dominating (95.0%) in all sampling stations. Protococcus, a single genus of Chlorophyceae played a unique role during summer, contributing the highest density of about 74.0%. The pattern of qualitative and quantitative difference of plankton standing crop in different sampling sites can be attributed to the existing physico-chemical characteristics, mainly water temperature, pH and hardness

Ecology of Shakla heel (Brahmanbaria), Bangladesh

The bed Shakla, comprising an average area of 75.0 ha is located in the northeastern region (Brahmanbaria district) of Bangladesh. The study was carried out to assess the ecological aspects of bed ecosystem. Surface run-off and increase inflow of rain water from the upper stretch during monsoon cause inundation and resumption of connection between beel and parent rivers. The range of dissolved oxygen (DO) content ( 4.5-8.9 mg/L) was found congenial for aquatic life. pH was in the alkaline range (7.3-8.5) and free C02 was reletavely high. Lower values of total hardness and total alkalinity indicated less nutrients in the beel water. A wide variation (1.4-27.2 x 103 ceHs/L) in the standing crop of total plankton was recorded during study period of which phytoplankton alone contributed about 90%. Phytoplankton diversity in the beel represented by three groups viz. Chlorophyceae, Myxophyceae and Bacillariophyceae in order of abundance. A total of 52 fish species belonging to 36 genera, 20 families and 1 species of prawn were identified so far from the beel. About l3 types of fishing method were found in operation. Seine nets (moshari berja, ghono berjal) and gill net (current jal) were identified as detrimental gear killing juveniles of different species during post spawning period. Kua fishing was also found harmful due to dewatering nature. A total of 11 species belonging to 11 genera and 10 families of aquatic weeds were identified from the beet The eggs of Macrobrachium Jamarrei were identified into the Najas najas vegetation during April-September