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Phytoplankton in Relation to Water Quality of Tanguar Haor Ecosystem, Bangladesh: I. Rauar Station

Mohammad Azmal Hossain Bhuiyan
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

S. A. M. Shariar Islam
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Abu Kowser
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Md. Rasikul Islam
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Shahina Akter Kakoly
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Khandoker Asaduzzaman
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Moniruzzaman Khondker
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The water quality at Rauar station of Tanguar Haor, Sunamganj was assessed studying phytoplankton and associated environmental variables. The environmental variables were monitored over a period of one year, collecting samples at two months interval between March, 2017 and March, 2018. Air temperature, rainfall, and humidity ranged from 22.6 - 32.1°C, 48 - 76% and 8 - 930 mm, respectively. Air temperature showed a direct relationship with water temperature which varied from 22.4 - 31.0°C during the study period. The water transparency remained relatively constant throughout the year having a mean Secchi depth (Zs) value of 2.48 m. Total dissolved solids (TDS), conductivity, and pH of the water ranged from 51 - 85 mg/l, 60 - 110 µS/cm, and 7.2 - 9.7, respectively. In December, because of a temperature fall, the dissolved oxygen (DO) concentration of the water reached its maximum value of 6.09 mg/l. In the rest of the period, the concentration remained between 2.44 and 4.80 mg/l. The value of alkalinity ranged from 0.43 - 1.35 meq/l. Among the nutrients, soluble reactive phosphorus (SRP), soluble reactive silicate (SRS), and NO_3-N ranged from 5.43 - 36.43 µg/l, 4 - 14.58 mg/l, and 0.06 - 0.31 mg/l, respectively. The concentration of NH₄⁺ ranged from 238 - 1230 µg/l. The highest concentrations (905 and 1230 µg/l) occurred between September and December, 2017. This might be attributed to the higher density of migratory birds during that period. The phytoplanktonic biomass expressed as chlorophyll-a (Chl-a) ranged from 1.35 - 8.45 µg/l while its degraded product phaeophytin concentration ranged from 0.08 - 3.5 µg/l. The standing crop of phytoplankton ranged from 397 - 2480 × 103 individuals/l of haor water exhibiting its maximum abundance in September. This parameter showed a highly significant positive correlation with SRP. From the correlation analysis, the degradation of chl-a to phaeophytin was found to be temperature dependent. Considering the different physicochemical and biological water quality data, it could be said that the Tanguar Haor is still free from organic pollution. However, the range of soluble reactive phosphorus data (5.43 - 36.43 µg/l) show that the Haor has been passing a meso-eutrophic state.

Keywords: Physical factors, Chemical factors, Phytoplankton standing crop, Chlorophylla, Tanguar Haor, Rauar station

Location: Rauar station of Tanguar Haor, Sunamganj, Bangladesh

Start Date: 00-03-2017

End Date: 00-03-2018

Program Area: Crop-Soil-Water Management

Commodity: Water quality

Objectives:

To study the community structure of pelagic plankton population and some of the key governing water quality factors at the study site, Rauar station of Tanguar Haor, Sunamganj.

Methodology:

The presently studied site Rauar station of Tanguar Haor is situated within 25°06'- 25°11' N and 91°01'- 91°06' E and approximately 2 km north of the Watch Tower of the Forest Department. The geographical location of Rauar station of Tanguar Haor in Sunamganj district and the location of Sunamganj district in Bangladesh. Detailed information on the physiographic and morphometric features of Tanguar Haor is available in IUCN and Mamun (3,4). The samples were collected mostly between 11:00 and 12:00 a.m. Air and water temperature were measured using an alcoholic thermometer. A field multimeter (Hanna Multi Instruments, Code - HI 9813-6, S/ND0108196, Romania) was used to measure pH, electrical conductivity and total dissolved solids (TDS) in situ. The depth of water was measured with the help of a graduated rope weighted at the end. A Secchi disc was used to measure the depth of transparency. Samples of dissolved oxygen were fixed in BOD bottles (Pyrex, clear glass-stoppered, 125 ml capacity) by adding the requisite amount of manganous sulfate and alkaline iodide solution. The bottles were carried to Dhaka for titration. An integrated water sample from the depth of 0 - 0.5 m was collected with the help of a Schindler’s sampler. The water was carried to the laboratory in a black carboy (5 liter capacity). Plankton collection was carried out following two methods. Firstly, one liter of lake water from a suitable depth was poured into a glass bottle with Lugol’s solution to obtain sediment of concentrated plankton. Another composite concentrated sample of plankton was obtained through sieving 100 liters of Haor water via plankton net (Nitex, mesh width of 55 μm). All the samples were transported to the laboratory keeping them in an ice box. From the collected 5-liter water sample of the Haor, 300 ml were filtered through a Whatman GF/C filter paper (circle dia. 48 mm, pore diam. 1.4 µm) using a Sartorius filtration device. After filtration, the filter paper was used to extract chl-a and phaeopigment(6). The filtrate was used to determine the concentration of soluble reactive phosphorus (SRP) and nitrate-nitrogen (NO_3-N) following Murphey and Riley and Müller and Wiedeman (7-8), respectively. The same water was used to measure the concentration of soluble reactive silicate (SRS) following the method of Wetzel and Likens(9). Unfiltered water sample was used for measuring NH₄⁺ and alkalinity. Kjeldhal microdistillation method was used to determine the concentration of NH₄⁺. Alkalinity was measured according to Mackereth et al. (10) and Wetzel and Likens(9). All the measurements were done in triplicate and the mean value was recorded. The meteorological data for Sunamganj district was obtained from the website of Bangladesh Meteorological department, Dhaka, Bangladesh. Quantification of phytoplankton population from the collected concentrate was done by using a Helber Bacterial Counting Chamber (Thoma, UK). Pearson’s correlation analysis was done to see the interrelationships among the water quality factors and the phytoplankton biomass of the studied station of Tanguar Haor.

Source of Information: Dhaka Univ. J. Biol. Sci. 28(2): 131-138, 2019 (July)

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Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

DO showed correlations with most of the variables. It showed a negative correlation with NO_3-N, but positive with conductivity, pH and phaeopigment. Phaeopigment also showed positive correlation with water temperature. The density of phytoplankton in the studied station of Tanguar Haor showed highly significant positive correlation with SRP. It means the system is limited by the supply of phosphorus. The concentration of SRP and chl-a show that the water body has been passing its meso-eutrophic state in terms of trophic state. Therefore, even though the high concentration of ammonia is a recurring phenomenon in the study area, the Haor cannot be termed as polluted as such.

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