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Limnology of Lake Ashura, Dinajpur, Bangladesh

MD ALMUJADDADE ALFASANE
Department of Botany, University of Dhaka, Dhaka

MD ATAUL GANI
Department of Botany, University of Dhaka, Dhaka

MD SHAFIQUL ISLAM
Department of Botany, University of Dhaka, Dhaka

MONIRUZZAMAN KHONDKER
Department of Botany, University of Dhaka, Dhaka

Abstract/ Executive Summary:

Results of limnological investigation of lake Ashura showed that air and water temperatures were 31.5 ± 0.25ºC and 30.0 ± 0.45ºC, respectively in the month of April, 2011. pH, alkalinity, conductivity, dissolved oxygen and TDS of water were 7.11 ± 0.02, 2.96 ± 0.58 meq/l, 760.67 ± 8.08 μS/cm, 7.72 ± 0.41 mg/l and 104.67 ± 1.53 mg/l, respectively. The concentration of NO₃-N, SRP and SRS were 63.33 ± 25.16 μg/l, 11.60 ± 1.60 μg/l and 14.36 ± 0.25 mg/l, respectively. Phytoplankton biomass as chl a and concentration of phaeopigment were 5.33 and 3.41 μg/l, respectively. The density of phytoplankton was 552.84 × 103 ind/l. A total of 35 species of phytoplankton were recorded of which 15 belonged to Euglenophyceae, followed by Chlorophyceae (8), Bacillariophyceae (7), Cyanophyceae (4) and Cryptophyceae (1). Macrophyte flora was represented by 31 species. The dominant species were Eichhornia crassipes (Mart.) Solms, Ludwigia adscendens (L.) Hara. and Oryza sativa L.

Keywords: Limnology, Macrophyte, Phytoplankton

Location:

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity:

Objectives:

The present attempt was made to investigate the water quality along with phytoplankton and macrophyte flora of Lake Ashura.

Methodology:

Water sample was collected from the south eastern fringe of the lake in April, 2011. A one liter capacity plastic bottle was dipped manually under the surface to collect water sample for physicochemical analysis. A total of two liter water sample was collected and from it, one liter was fixed by using Lugol’s Iodine and sediment for concentrating plankton. The second one liter sample was transported in a Cool Box to the Laboratory for analysis. The time necessary to transport the sample was 18 hours after collection. Field meters were used to measure conductivity, TDS and pH in situ (HANNA Instruments HI 9033, 9044 and). Triplicate BOD bottles (120 ml cap., Jena Schott) were filled with sample water from the lake and fixed in situ for DO analysis. Macrophyte population was estimated by applying one meter quadrat. Chlorophyll a (chl a), soluble reactive phosphorus (SRP), soluble reactive silicate (SRS), dissolved oxygen (DO) and alkalinity were determined on the same day after reaching Dhaka following standard methods (Marker et al. 1980, Murphy and Riley 1962, Wetzel and Likens 1979). However, an overnight digestion of samples for the analysis of nitrate nitrogen was required (Müller and Wiedemann 1955). Hence, nitrate determination was completed after 48 hours. Phytoplankton cell number was counted using a Hawksley microplankton counting chamber with improved Neubauer Ruling (Hawksley Ltd., Lancing, England) under a Nikon compound microscope (Japan) at a magnification of 400×.

Source of Information: Bangladesh J. Bot. 41(1): 43-48, 2012 (June)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In Lake Ashura, percentage composition among different genera shows that Chlorophyta dominates and occupied 33.33% followed by Chrysophyta (23.81%), Cyanophyta and Euglenophyta (19.05%) and Cryptophyta (4.76%). Cryptophyta can be treated as minor group. Maximum number of species (42.86%) among the phytoplankton population was represented by Euglenophyta. Next was Chlorophyta followed by Chrysophyta, Cyanophyta and Cryptophyta. The proportion (%) of recorded species of Cyanophyceae, Chlorophyceae and Cryptophyceae was lower in Lake Ashura than Lake Bogakain. Recorded species of Euglenophyceae in Bogakain is lower where diversity is highest in Lake Ashura. Members of Dinophyceae were absent in Lake Ashura. On the other hand, two members of Dinophyceae were present in Bogakain. However, the total number of taxa recorded in Lake Ashura is closer to Lake Bogakain (Lake Ashura, 35 taxa; Bogakain, 39 taxa of phytoplankton. Class wise distribution of the species of Lake Ashura were Euglenophyceae 15, Chlorophyceae 8, Bacillariophyceae 7, Cyanophyceae 4 and Cryptophyceae 1. A total of 40 species of phytoplankton were recorded from the lake Bogakain of which 21 belonged to Chlorophyceae followed by Cynaophyceae (5), Bacillariophyceae (4), Cryptophyceae (4), Euglenophyceae (3), Dinophyceae (2) and Chrysophyceae (1). On the other hand lake Bogakain occupied a few members of macrophytes like Nymphaea nouchali, Egeria densa, Potamogeton crispus and Polygonum sp. Lake Ashura, the third natural lake of Bangladesh has a different limnology compared to another natural lake namely, Bogakain. River Karotoa has a direct influence on Lake Ashura as the water from the former flows through the latter during rainy season. The lake holds a riverine character rather than a lacustrine one, shape elongated and overall area large and water depth is highly variable (0-10 m. About 30 cm thick and soft mud in the littoral was evident because of high densities of macrophyte population. The ionic load of water was also higher with a low value of phytoplankton chl a. The total number of phytoplankton species recorded in Lake Ashura is slightly lower than Lake Bogakain. Qualitatively, the phytoplankton flora of Lake Ashura has been found to be dominated by euglenoid algae whereas in Lake Bogakain green algae were predominant.

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