INTRODUCTION:

Aquatic ecosystem is the most diverse ecosystem in the world which includes rivers and streams, ponds and lakes, oceans and bays, and swamps and marshes, and their associated animals. Each aquatic species is unique and has an important role in making our lives easier, healthier, and more productive. It is not the size, but the genetic composition of plants and animals that makes all life forms special. Each species has its own inherent genetic library that codes its ability to survive in changing environments.

The phytoplankton are floating microscopic autotrophs whose movements are more or less dependent on water currents. They are the primary producers in an aquatic ecosystem. They are good indicators of water quality and capacity of water to sustain heterotrophic communities. Phytoplankton plays an important role in the biosynthesis of organic matter in aquatic systems, which directly or indirectly serves all the living organisms of the water body as food¹. Generally, different Planktonic species can tolerate different ranges of temperature as well as light and nutrient limitations. In a multi species algal community, the growth of different species is likely to be limited by the resources, including different nutrients².

The structure of aquatic communities is important in monitoring the water quality. Planktons also strongly influence certain non-biological aspects of water quality such as pH, colour, taste and odour³. These organisms along with other aquatic and terrestrial plants make up biodiversity and also sustain life by providing food, shelter, oxygen and play a fundamental role in regulating global climate⁴. The density and diversity of phytoplankton and their association with biological indicators are very crucial for the assessment of water quality.

MATERIALS AND METHODS:

Plankton samples were collected from sub-surface at all stations and preserved simultaneously, while taking samples for physico-chemical analysis. Planktons were collected by means of samples from the reservoir and filtered through bolting silk net (No. 25). The net was conically designed having a diameter of 30 cm and length of 60 cm. In the lower narrow part of the net, a transparent plastic tube of 50 ml capacity was fixed. Sixty litres of the reservoir water was carefully passed through net.

The filtrate was transferred carefully to plankton collection tube of 50 ml capacity and preserved with 5% formaline and brought to laboratory. The collected samples were concentrated by centrifugation at about 2500 rpm using table top centrifuge. The supernatant was removed carefully by dropper and 3 drops of glycerine were added. Only 5 ml was kept as final volume.

The quantitative and qualitative analysis of plankton was made under a microscope in Sedgwick-Rafter Counting Cell and calculated according to Welch⁵ as n = (a×1000) C/litre; where n = number of plankton per litre of original water (unit litre-1), a = average number of planktons in all counts in counting unit of 1 cu mm capacity, c = volume of original concentration in CC (counting cell) and l = Volume of original water expressed in liters.

Identification of plankters was made from Ward and Whipple⁶ and Needham & Needham⁷ methods. The plants collected from reservoir were stored out, labeled and preserved in 10 % formalin. The Water sampled was analyzed in the fit field as well as in the laboratory after following the methodology given in APHA⁸.

RESULTS AND OBSERVATIONS:

The phytoplankton population density varied in selected sites of Taj Baj pond as minimum at site 1 and maximum at site 3 with high value in summer and lower in winter season during the study period. The phytoplankton density also varied temporally and showed high density in summer and low density in winter season in the investigation period (Figure 1).

Figure 1: Mean phyoplankton at pond during study period.

(I). Density of Chlorophyta: The Chlorophyta density was recorded maximum in summer at site 3 and minimum in winter at at site 1 with high value in monsoon at site 2 corresponds winter and summer at site 3 during the study period (Table 1). It was also observed variation in preceding years of investigation as maximum in summer 2018-19, monsoon 2019-20 and 2020-21, whereas minimum in winter during the investigation period (Figure 2).

Figure 2: Mean Chlorophyta at pond during study period.

Table 1: Mean Seasonal Chlorophyta during study period.

Season	2018-19	2019-20	2020-21	Mean
Monsoon	368	364	371	368
Winter	228	227	232	229
Summer	385	322	388	365

(II). Density of Cyanophyta: The Cyanophyta density was recorded maximum in summer at site 3 and minimum in winter at at site 1 with high value in monsoon at site 3 corresponds winter at site 2 and summer at site 3 during the study period (Table 2).

Table 2: Mean Seasonal Cyanophyta during study period.

Season	2018-19	2019-20	2020-21	Mean
Monsoon	368	364	371	368
Winter	228	227	232	229
Summer	385	322	388	365

It was also observed variation in preceding years of investigation as maximum in summer, monsoon and winter 2020-21, whereas minimum in winter during the investigation period (Figure 3).

Figure 3: Mean Cyanophyta at pond during study period.

(III). Density of Bacillariophyta: The Bacillariophyta density was recorded maximum in summer at site 3 and minimum in winter at at site 1 with high value in monsoon at site 2 corresponds winter and summer at site 3 during the study period (Figure 4; Table 4).

Figure 4: Mean Bacillariophyta at pond during study period.

It was also observed variation in preceding years of investigation as maximum in summer 2018-19, monsoon 2019-20 and 2020-21, whereas minimum in winter during the investigation period (Figure 4).

Table 4: Seasonal Bacillariophyta during study period.

Season	2018-19	2019-20	2020-21	Mean
Monsoon	368	364	371	368
Winter	228	227	232	229
Summer	385	322	388	365

DISCUSSIONS:

In the present investigation it was observed that phytoplankton community was far less diverse from the zooplankton from this pond and mainly Chlorophyta and Cyanophyta are dominant during the study period. The phytoplanktons usually showed seasonal qualitative and quantitative fluctuations. Certain planktonic populations apparently disappear at specified periods due to the species concerned either became too scarce or occur as spores, resting eggs etc. which are not easily detectable. The phytoplankton population density varied in selected sites of Taj Baj pond as minimum at site 1 and maximum at site 3 with high value in summer and lower in winter season during the study period. The phytoplankton density also varied temporally and showed high density in summer and low density in winter season in the investigation period.

Most of the workers have suggested that total phytoplankton population of algae reached their maximum development during summer and minimum during the winter months. In present study, the general trend of increase in algae population was observed from January to May and again it increased from October. This might be due to increase in temperature from January onwards. In monsoon the population was decreased considerably due to floods except in second year¹.

The phytoplankton community of the Taj Baj pond belonged to four major groups and ranked Cyanophyceae>Chlorophyceae (green-algae)>Bacillariophyceae (diatoms) >Euglenophyta during the study period. It is further apparent from the data that the minimum number of species of phytoplankton was recorded during the rainy season, while the total density of phytoplankton was found to be less during winter. It is known that during winter, low algal growth is due to low water temperature. The nutrients are least available to algae and diatom for their growth and development during low light intensity and low temperature of winter season. These probably are responsible for comparatively lower phytoplankton population in winter months. However, in summer, the rise in temperature enhances the release of nutrients from sediments through bacterial decomposition.

The present study showed that in the pond concentrations of nitrate and phosphorus is liable to phytoplankton abundance during the study period. It can be pointed out that the phytoplankton peaks were followed by nutrient peaks. It may be suggested that nutrient enrichment enhances the growth of phytoplankton in summer season. Increasing phytoplankton population utilizes these nutrients by active absorption, resulting lower concentration of nutrient in next season. On the other hand, heavy grazing by zooplankton on phytoplankton may also be responsible for the lower density of phytoplankton during monsoon season¹².

The present study shows that in the Taj Baj pond both nitrogen and phosphate enhances the growth of phytoplankton in summer season. Increasing phytoplankton population utilizes these nutrients by active absorption, resulting lower concentration of nutrient in next season. On the other hand, heavy grazing by zooplankton on phytoplankton may also be responsible for the lower density of phytoplankton during monsoon season.

CONCLUSION:

Phytoplankton forms the major segment of primary producers in fresh water ecosystems. Phytoplankton plays a phenomenal role in the biosynthesis of organic material. It is well established that composition and abundance of phytoplankton is greatly regulated by the zooplankton. In the present investigation it was observed that phytoplankton community was far less diverse from the zooplankton from this pond and mainly Chlorophyta and Cyanophyta are dominant during the study period. The phytoplanktons usually showed seasonal qualitative and quantitative fluctuations. In present study, the general trend of increase in algae population was observed from January to May and again it increased from October. This might be due to increase in temperature from January onwards.

The phytoplankton community of the Taj Baj pond belonged to four major groups and ranked Cyanophyceae>Chlorophyceae (green algae) > Bacillariophyceae (diatoms) >Euglenophyta during the study period. The present study showed that in the pond concentrations of nitrate and phosphorus is liable to phytoplankton abundance during the study period. It can be pointed out that the phytoplankton peaks were followed by nutrient peaks. Low density of Bacillariophyceae in summer season may be due to the influences of temperature and grazing behavior of zooplankton on diatoms because zooplankton density was found very low in winter.

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Received on 27.07.2023 Modified on 31.08.2023

Research J. Science and Tech. 2024; 16(1):24-28.

DOI: 10.52711/2349-2988.2024.00005