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Phytoplankton Assemblage with Relation to Water Quality in Turag River of Bangladesh

Mostarina Khatun*
Department of Environmental Sciences, Jahangirnagar University, Dhaka- 1342, Bangladesh

A.K.M. Rashidul Alam
Department of Environmental Sciences, Jahangirnagar University, Dhaka- 1342, Bangladesh

Abstract/ Executive Summary:

The study was performed to evaluate phytoplankton assemblage, physical and chemical characteristics of water, interrelationship between phytoplankton assemblage and physical/chemical characteristics of water and to evaluate water quality index during November, 2015 - September, 2016 for Turag River that is located on the north-eastern side of Dhaka city, Bangladesh. Water samples were collected during winter (November - January/2015-2016), summer (March-May/2016) and rainy season (July - September/2016). During the study, the overall phytoplankton assemblage exhibited the following pattern: Bascillariophyceae (40.33%) > Chlorophyceae (32.90%) > Euglenophyceae (14.56%) > Cyanophyceae (12.20%). Fragillaria crotonensis, Navicula grimmei, Phacus circulatus, Euglena agilis, Chlorococcus minutum and Trachelomonas goossensii were dominant phytoplankton species. The average values of water temperature, total dissolved solids (TDS), electric conductivity (EC), pH, dissolved oxygen (DO), biological oxygen demand (BOD5), total nitrogen (TN) and dissolved phosphorus (DP) were 25.94°C, 273.46 mg L^-1 , 489.71µS cm^-1 , 6.81, 2.89 mg L ^-1 , 3.85 mg L^-1 , 8.55 mg L ^-1 and 0.62 mg L^-1 , respectively. Euglenophyceae displayed significant negative correlation with DO in winter while TDS in rainy season. Chlorophyceae exhibited significant negative correlation with DP in rainy season. Shannon-Weaver’s (H') and Simpson’s (D) diversity indices ranged between 2.58-3.01 and 0.91-0.95, respectively. In summer, the value of H' (3.01) indicated slight pollution. In winter and rainy seasons, the values of H' were 2.58 and 2.98, respectively displaying light pollution in Turag river. Measured water quality index (WQI) values were 229.71, 171.23 and 74.18 in winter, summer and rainy season, respectively exhibiting that water was unsuitable for drinking purposes in winter and summer and also very poor water quality in rainy season, respectively. The implication of these findings can be used to monitor health of riverine ecosystems which provide ecosystem services for society.

Keywords: Diversity Index, Phytoplankton, Pollution, Turag River, Water Quality Index (WQI).

Location: Turag River is situated on the northeastern side of Dhaka city.

Start Date: 00-10-2015

End Date: 00-09-2016

Program Area: Conservation and Biodiversity

Commodity: Plankton

Objectives:

The study was undertaken to evaluate phytoplankton assemblage, physical and chemical characteristics of water, interrelationship between phytoplankton assemblage and physical/ chemical characteristics of water and to evaluate water quality index.

Methodology:

Study area Turag River is situated on the northeastern side of Dhaka city. It is the upper tributary of the Buriganga River (Chowdhury & Chowdhury 2004). This river has a multipart river system that supports diversity of usages such as domestic and industrial usages. The study area falls in between latitude N = 23°78'66" and longitude E = 90°39'92" and its total length is 24 km. To perform the investigation, this study area was divided into five sampling sites at Gabtoli (A), Birulia (B), Ashulia (C), Kamarpara (D) and Abdullahpur (E). The recorded GPS location of study area and anthropogenic activities observed adjacent to the study sites are presented in Table 1. Study duration The investigation was carried out from November 2015 to September 2016. This period was divided into three seasons: winter (November 2015-January 2016), summer (March 2016-May 2016) and rainy season (July 2016- September 2016). Collection of water samples Water samples were collected from the five sites to evaluate phytoplankton assemblage, physical and chemical characteristics of water. From each site, four water samples were collected (5 × 4 = 20 samples) from 25 cm depth of the river surface in early morning between 6.30-8.30 AM. Before sampling, the bottles were pre-sterilized and dried. After sampling, bottles were screwed carefully and marked. 1 L of sample from each site was used for determination of phytoplankton assemblage and was preserved by 5% Lugol’s iodine solution. Another 1 L sample was acidified immediately with 1 mL HCl for determination of physical and chemical characteristics. However, fresh samples were used to determine pH immediately after sampling. Determination of phytoplankton composition 20 mL of sediment plankton layer was taken carefully after sedimentation in each sample bottle. For qualitative analysis, the concentrated plankton was observed on a glass slide under compound microscope (Olympus B × 43, Japan) fitted with camera. For quantitative analysis, 1mL of concentrated plankton was taken in a Sedgewick Rafter Counting Cell (SRCC) followed by counting method described by Boyd (1979). Related texts were consulted to identify the phytoplankton species at least up to generic level (Prescott 1984; Alam et al. 2004; Ahmed et al. 2007; Alam 2017). Determination of physical and chemical properties Physical and chemical characteristics of water were determined including temperature, total dissolved solids (TDS), electric conductivity (EC), pH, dissolved oxygen (DO), biological oxygen demand (BOD5), total nitrogen (TN) and dissolved phosphorus (DP). Temperature, pH and DO were measured on the site in the time of sample collection by digital thermometer, pH meter (Model: pH eP, Hanna) and DO meter (Model: DO 31P: TAO DK). EC was determined by EC meter (Model: Conductivity meter HI 8033: Hanna inst.), TDS by TDS meter (Model: ppm DiST1: Hanna), BOD5 by Winkler’s method (De 1993), TN by Micro-kjeldahl’s distillation method (Jackson 1973) and DP colorimetrically by ascorbic acid blue color method (Murphy & Riley 1962). Data analysis Assessment of diversity index for phytoplankton composition The diversity index of phytoplankton species was determined following Simpson’s diversity index (1949), Shannon-Weaver’s diversity index (1949); Hmax, richness was measured by Margalef’s richness index (1951), evenness by Pielou’s evenness index (1969) and similarity between species by Czeckanovsky’s similarity index (1934).

Source of Information: Caspian J. Environ. Sci. Vol. 18 No. 1 pp. 31~45

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Turag is one of the major rivers of Bangladesh. This river plays a multidimensional role as it is one of the main sources of freshwater of adjacent area as well as Dhaka city. Its water is used for irrigation, agriculture, domestic, industrial and navigation purposes. Now this river becomes narrow day by day and its flow is decreasing. Throughout this research, Bascillariophyceae found always high in percent composition. All observed physical and chemical parameters found within the permissible range except water pH (= 5.4) in rainy season. Nitzschia acicularis, Nitzschia clausii, Navicula grimmei, Chlorella sp. and Gloeocapsa alpina were observed as indicators of acidic aquatic environment in rainy season. Diversity indices exhibited more or less moderate phytoplankton diversity in the river. Measured water quality index (WQI) displayed unsuitable for drinking purposes in winter and summer, while very poor quality in rainy season. However, water of Turag River was more polluted in summer than in winter and rainy season. The implication of these findings can be used to monitor health of riverine ecosystems which provide ecosystem services for society.

Knowledge Management: Journal