Phytoplankton biomass in relation to some environmental and nutritional parameters at Watch Tower Station of Tanguar and Rauar Station has been studied. Since the Haor is a Ramsar Site, it is a globally important aquatic ecosystem. In the present investigation, the structure of the phytoplankton and the water quality factors were worked out and the data were compared Rauar Station with having the same ecosystem. Though weaker, a difference among alkalinity, total dissolved solids (TDS), conductivity, dissolved oxygen (DO), Secchi disc transparency, soluble reactive phosphorous (SRP), soluble reactive silicate (SRS), NO3-N, NH4+, chlorophyll-a and phytoplankton population density was found between the Watch Tower and the Rauar Station of Tanguar Haor. The mean values of the aforsaid parameters were found to some extent higher in the Watch Tower Station. The Watch Tower Station was deeper and perennial, where the depth of water varied from 3.0 - 9.5 m annually with a mean of 6.72 m. In the studied station, air and water temperature varied from 22.6 - 30.6 and 22.7 - 30.3°C, respectively. Water transparency ranged from 2.08 - 3.0 m. From December to March the pH remained 8.1-9.7 and alkalinity from 0.73 - 1.35 meq/l. However, from April to September these two parameters ranged from 7.5 - 7.7 and 0.33 - 1.35 meq/l, respectively. Dissolved oxygen (DO) and free CO2 concentration ranged from 2.5 - 6.09 and 0.084 - 0.087 mg/l, respectively. During April to September the Chlorophyll-a value ranged from 5.5 - 7.5 μg/l while the range of SRP was 24.23 - 30.05 μg/l during the same period. At the latter part of the study year i.e., during the dry period (December to March) those two parameters were relatively low in concentration. In April a high concentration of NH4+ (1380 μg/l) was reported from the haor, at other times this parameter ranged from 690 - 820 μg/l. The NO3-N ranged from 0.25 - 0.75 mg/l. High density of phytoplankton population (2690 ind./l) was reported at the time of high concentration of SRP (30.05 μg/l ) of the haor water. The chlorophyll-a value (7.5 μg/l) was also highest at that time. So, it could be said that SRP concentration in Tanguar haor has been playing a vital role in regulating the standing crop of phytoplankton. To find the variation on a spatial scale, the data of the present investigation were compared with another study station of the haor namely, Rauar Station. No significant difference was observed among the concentrations of different parameters. However, a slight increasing trend in the concentrations of DO, alkalinity, SRP, NO3-N, SRS, NH4+ and total phytoplankton density was observed in the Watch Tower Station compared to Rauar Station. Watch Tower Station is also relatively deeper with an improved light climate as it had been revealed by the mean value of the Secchi depth. The water quality of Tanguar Haor has been classified as mesotrophic. Dhaka Univ. J. Biol. Sci. 29(1): 9-18, 2020 (January)

The qualitative and quantitative aspects of phytoplankton population belonging to the green algae (Chlorophyta) from Watch Tower and Rauar Station of Tanguar Haor, Sunamganj were studied. In the study, a total of 39 species of three Orders under the algal Division Chlorophyta was worked out. Their photomicrographs and individual densities in the pelagic community of phytoplankton over a study year of 2016 and 2017 are discussed. In Volvocales, Volvox carteri Stein, in Chlorococcales, Coelastrum microporum Nägeli and in Zygnematales, Staurastrum paradoxum Meyen represented the highest number of population in the community. Rauar Station was found to contain the lesser number of phytoplankton densities compared to Watch Tower Station. J. Biodivers. Conserv. Bioresour. Manag. 2019, 5(2): 101-106

In the present study, physicochemical and biological variables related to the water quality of Hakaluki Haor were studied. Three study stations viz. Bakshimul, Jalabeel and Dudhai were investigated because of an event of mass scale of dead fish and other aquatic organisms were reported. The stations had water depths from 2.74 - 5.13 m and Secchi Disc Transparency were 0.74 - 1.91 m. The air and water temperature among the three stations ranged from 28.2 - 30.4°C and 21.8 - 28.8°C, respectively. TDS ranged from 35 - 42 mg/l, while the electric conductivity of water showed 40 - 50 μS/cm. SRP, nitrate and SRS ranged from 10.68 - 12.32 μg/l, 0.116 - 0.122 mg/l and, 16.08 - 35.42 mg/l, respectively. The concentration of DO was very poor which ranged from 2.8 - 5.4 mg/l. In all the three studied stations, the free CO2 concentration was 0.096 mg/l. Chlorophyll-a value was moderate in all the three stations (ranged within 34.67 and 40.60 μg/l). The phaeopigment concentration was low and ranged from 1.51- 8.72 μg/l among the studied stations. Concentration of ammonia was much higher (1.03 - 1.72 mg/l) than the standard value for Bangladesh (0.5 mg/l). From this analysis, it is observed that during fish kill event the concentration of ammonia was higher with low DO content which might have resulted because of the decomposition of upper foliar parts of the rice plant due to the sudden inundation. Gross α and β counts were found to be 0.01 and 0.10 Bq/l in the Haor water at the time of fish kill. From the planktonic community, 16 phytoplanktons from green algae, 14 euglenoids, 5 diatoms, 5 dinoflagellates and 12 zooplankton species were recorded. A shift in the pH of the Haor water from acidic to alkaline might have occurred during the last 3 decades. A detailed limnological study covering the climatic seasons of Bangladesh has been recommended to be carried out for Hakaluki Haor. Dhaka Univ. J. Biol. Sci. 30(1): 69-78, 2021 (January)

The Balu River is a peripheral river of Dhaka Metropolis and like other rivers its water quality is also highly vulnerable towards pollution. In the present study, effects of water quality parameters on the phytoplankton biomass have been studied for six climatic seasons of the year. The results obtained were compared with two other rivers of Dhaka Metropolis namely, Buriganga and Turag. Balu River showed water quality characters almost comparable with two other rivers. The phytoplankton biomass as chlorophyll a (chl-a) was found to be correlated directly with air and water temperature and alkalinity of the water. However, a weak positive correlation was obtained between chl-a and Secchi depth and free CO2 concentration. Nitrate nitrogen showed weak negative correlation with chl-a and phaeopigment and phytoplankton total density. High fluctuation was observed in the concentration of DO (0.20 - 4.50 mg/l) and free CO2 (0.06 - 2.90 mg/l) throughout the seasons. Soluble reactive phosphorus ranged from 30 - 1248 μg/l and chl-a ranged from 6.77 - 32.60 μg/l. Phytoplankton density ranged 1178 - 7409×103 ind./l over the study year. Water color ranged from light blue to dark black. The depth of visibility as Secchi depth varied from 15.24 - 81.28 cm whilst the water depth of the studied station Paschim Gaon of Balu River ranged from 4.57 - 7.92 m. Air and water temperature ranged from 25.4 - 36.5°C and 23.4 - 32.3°C, respectively. J. Biodivers. Conserv. Bioresour. Manag. 2020, 6(1): 37-46

The section of Sitalakhsya River near heavily industrial zone of the District of Narayanganj has been studied for its water quality and potamoplankton dynamics. One year bimonthly sampling from DakhshinRupshi Station of the river was carried out. The air and water temperature of the river ranged from 25.6 - 34.0°C and 26.5 - 32.8°C, respectively. The temperature of water was lower than air by ca. 2.0°C. Water depth at the study station did not vary much but fluctuated only between 6.09 and 7.92 m. The Secchi disc transparency (Zs) varied from 0.2 - 0.6 m showing the lowest in March. Total dissolved Solids (TDS) load in water was 85 - 663 mg/l but the electrical conductivity varied from 110 - 910 μS/cm being the month of March as highest record. pH was alkaline and the fluctuations were negligible (7.2 - 7.4). Alkalinity peaked in March (6.65 meq/l) which dropped to 1.00 meq/l in August and October. Both dissolved oxygen (DO) and free carbon dioxide levels were low which varied from 0.37 - 2.43 and 0.04 - 1.93 mg/l, respectively. Among dissolved nutrients, soluble reactive phosphorus (SRP) showed a low value from May to December (89.48 - 127.70 μg/l). It, however, peaked during March (1265.94 μg/l). Soluble reactive silicate (SRS) concentration ranged from 7.01 - 82.11 mg/l, while the concentration of NO3-N ranged from 0.19 - 1.29 mg/l. The potamoplankton biomass as chl-a ranged from 3.38 - 24.52 μg/l, while its degraded product phaeopigment varied from 1.97 - 11.13 μg/l. The total density of potamoplankton showed their highest growth during December to March (2223 - 4293 ×103) and the lowest from May to October (181 - 785 ×103). The ranges of water quality and planktonic parameters recorded from the Sitalakhsya River are quite comparable with three other peripheral rivers of Dhaka Metropolitan City (DMC) namely, Balu, Turag, and Buriganga. But, low DO and poor transparency along with higher load of TDS made this river water quality relatively lower grading compared to others. Dhaka Univ. J. Biol. Sci. 30(3 CSI): 487-497, 2022 (June)