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Lemna Perpusilla: Screening on Habitat Limnology

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

A. K.M. Nurul Islam
Department of Botany, University of Dhaka. Dhaka 1000, Bangladesh

Atika DUR-E Makhnun
Department of Botany, University of Dhaka. Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Data of water quality recorded from three habitats of Lemna perpusilla the temperature, 15-28 °C; pH, 6.9-7.8; electrolytic conductivity. 200- 890 µS cm-¹: alkaltnity, 0.84-7.42 meq 1^-1; DO, 0-6.45 mg 1-¹; DO % saturation, 0- 79.43%, COD, 2.56-22.80 mgl^-1; SRS. 2.33-72.45 mg 1^-1; SRP. 0.10-3.94 mg 1^-1; N0₃-N, 0.04-0.33 mg 1^-1; chl a, 0-1.17 mg 1^-1 and phaeoptgment 0-0.04 mg 1^-1. The Lemnabiomass ranged from 13.2-148.52 g m^-2,which showed significant positive correlation with SRS (r=0.45. n = 28. P<0.05) and negative correlation with temperature (r = - 0.53, n = 28. P<0.01) and DO(r=0.43,n=p<0.01)

Keywords: Lemna petpusilla, Habitat limnology, Bio-Indicator value

Location: Department of Botany, University of Dhaka

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Contamination

Objectives:

To assess the bio-Indicator value and nutrient removal capacity from the contaminated water by Lemna sp.

Methodology:

Due to strong human influence in almost every part of the Dhaka Metropolis, it was very difficult to continue sampling in a single chosen habitat where Lemna used to grow naturally. The problem sometimes appeared at such a great stake that it finally forced the authors to abandon many interesting habitats. The work at last could be completed in three habitats. Out of the three studied habitats the biomass of Lemna was recorded at Station 1 in between 13 September and 27 December. 1990. Here the work was discontinued due to human interference. But at Stations 2 and 3 the biomass was recorded until May, 1991. The sampling was carried out at 15 days interval in all the habitats mentioned. The time of visit was in between 7:30 and 10:40 a.m. The water temperature was noted with the help of a mercury thermometer. Then duplicate BOD bottles (125 ml capacity) were filled with water and fixed for the determination of dissolved oxygen content. A one litre capacity opaque plastic bottle was then lowered underneath the Lemna cover to collect water sample for chemical analysis. A circular wire meshed seive (1 mm² pore size and 139 cm² in diameter) with handle was used for biomass collection. At first the sieve was dipped into the water and pushed in a horizontal manner to reach underneath of a certain undisturbed Lemna cover and then at the place the sieve was raised up collecting all the Lemna fronds fell into the sieve. The fronds were then carefully transferred into a polythene bag with traces of water from the sampling place. The biomass sampling was done in triplicate. Then average was calculated and recorded. A portion of the unfiltered water sample was used for the determination of pH (TOA MH 5S electric pH meter), conductivity (AL-52), alkalinity and chemical oxygen demand. The rest of the water sample was filtered through Whatman GF / C (7.5 cm circles) filter paper and the filtrate was used for the determination of soluble reactive phosphorus, soluble reactive silicate and nitrate-nitrogen (N0₃-N, Muller and Wiedemann 1955). Samples for biomass determination were first carefully transferred into a plastic bowl containing tap water. Portions of debris and other plants were screened. The fresh fronds were sieved again and transferred onto a petridish (10 cm dia.) where the sample was let air dried for few hours. After that it was put in an oven (Eyela NDS-450D.600D) having set at a temperature of 105⁰C previously. The biomass was dried for 24 hours and after that the samples were transferred to a desiccator. Finally, the biomass was transferred to a preweighed small polythene bags where it was sealed off and weighed with the help of an electronic balance (AND, FR-200MK 11).

Source of Information: Bangladesh J. Bot. 23 (1): 99-106. 1994 (june)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Indicates that the formation of Lemna blankets perpetuates well in small ditches and slowly flowing drains. Water- quality status of such habitats are mostly above eutrophic level. The plant found to tolerate high ranges of nutrient at least when compared with a free floating Ptertdophyta, Salvinia (N0₃: 0-0.2 mg I-¹ and Po₄: 0-l.21 mg I-^I; Gaudet 1973). Although, some effects of low temperature, ions and nutrients on the biomass have been noticed, but as a whole a clear dtstmctton.between causal effects and consequences is not yet possible. Detailed cultural studies under controlled environment may help to find the threshold effects of various water quality parameters on the biomass of Lemna perpusilla.

Knowledge Management: Journal