INTRODUCTION:

Since planktons are very delicate and extremely sensitive in nature, they are the first ones to get hurt from water pollution among all the floating community. Any unwelcome change in pond ecosystem affects the biomass as well as diversity of planktons. The evaluation of plankton’s productivity illustrates the realization of conservation ratio at different trophic levels and resources as mandatory information for appropriate handling of the freshwater ecosystem. There are couples of noteworthy investigations on diversity of phytoplankton and zooplankton in Indian ponds and lakes lead by various groups^1-5.

The ecosystem of a floodplain is mainly governed by the planktonic community and physicochemical parameters of water. Phytoplankton is one of the initial biological components from which the energy is transferred to higher organism through food chain. Brraich and Kaur⁶ also revealed that phytoplankton act as primary producer, food for various aquatic organisms and bio-indicator for water quality. Zooplankton community distribution depends on some of the complex factors such as, change of climatic conditions, physical and chemical parameters and vegetation cover. Most of the planktonic organisms are cosmopolitan in distribution⁷.

This study presents the very first report on the status and diversity of phytoplanktons and zooplanktons in the Gandak floodplains of Gopalganj (Bihar) during study period.

MATERIALS AND METHODS:

Planktonic Analysis:

The water samples were collected from the surface, littoral region and the bottom mud of the floodplains to analyze planktonic population and their distribution in the pond. The qualitative analysis was carried out by collecting plankton samples through repeated towing of Hensen's standard plankton net with uniform speed. The Hensen's standard plankton net was made up of bolting silk (number 25). The as collected planktonic samples were fixed using 70% ethanol solution. The quantitative evaluation of the zooplanktons were carried out by filtering almost 50 L of surface water through a plankton net of material bolting silk number 25. From this, subsamples of volume 10 ml were taken to the counting chamber and the counting of zooplanktons were performed under a Carl Zeiss Inverted microscope. The identification of the zooplanktons and phytoplanktons were done following the guidelines^7-11and their numbers were presented as individuals per litre. The primary productivity in the selected pond was evaluated by adopting light and dark bottle method^12,13.

RESULTS AND OBSERVATION:

Phytoplanktons in Gandak floodplains:

The major members are Spirogyra, Ankistrodesmum, Tetraspora and Chlamydomonas under Chlorophyceae; Oscillatoria, Nostoc, Tetrapedia and Coelosphaerium under Mycophyceae and Protococcus, Desmids, Gonatozynon and Closterium under Pleurococcaceae family. Spirogyra was peak in summer and low in monsoon, Oscillatoria peak in summer and winter and low in monsoon, Nostoc peak in summer and monsoon and low in winter season, where as diatoms, Chlamydomonas and Tetraspora were minimum in number. These algae were disappeared in January and February month and reappear in March and April, again disappear in June and July and again reappear in August and September month.

The phytoplankton population density varied with their local niche such as high at site 3, moderate at site 2 and low at site 1 during the study period. It showed a high density of phytoplankton only at site with eutrophication and weed abundance at proposed sites. The density ranged 120-270, 140-280 and 270-320 No./litre at site 1, 2 and 3 with low in summer and high in monsoon season during the investigation period (Figure 1).

Figure 1: Phytoplankton density at Gandak floodplain sites.

The species richness in phytoplanktons showed seasonal variation as well as spatial heterogeneity affected by abiotic and biotic factors revealed during the investigation.

Figure 2: Phytoplankton species richness at Gandak floodplain sites.

The species richness is maximum at at site 3, moderate at site 1 and minimum at site 2 due to topographic conditions and niche overlap during investigation period and also through predation pressure which might be helpful to species diversification under drastic conditions of phytoplankton survival and growth with expected tolerance capacity (Figure 2).

The quantitative study for zooplankton was carried out during the study period. The site 1 showed total of 22 species of zooplankton in which 8 species of rotifer belong to 5 families showed dominance over other groups of zooplanktons.

There site 2 presented 19 species of zooplankton groups recorded in which rotifers are dominant with 5 species belongs to 02 families during the study period. The study of site 3 revealed 22 species of various zooplankton communities in which rotifer consist of 6 species belongs to 5 families during the study period (Figure 3).

Figure 3: Percent population of zooplanktons at floodplain sites

DISCUSSIONS:

Phytoplankton forms the major segment of primary producers in fresh water ecosystems. Phytoplankton plays a phenomenal role in the biosynthesis of organic material. The study of phytoplankton abundance in Gandak floodplain sites revealed marked monthly and seasonal variations. The high abundance of phytoplankton observed during July to September, seemed to be due to variations in the nutrient input of the Gandak floodplain through rain water runoff which deviated from the normal pattern. 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 year.

The increased nutrients brought in by rain water resulted in the sudden rise of phytoplankton which subsequently diminished due to lack of continuous nutrient supply. The gradual settlement of the suspended matter, leading to high light penetration, along with unused nutrients and increasing water temperature had led to high proliferation of plankton in the pre-monsoon period. This was followed by an abrupt fall in plankton density with the onset of rainy season. Replenishment occurred in August - September, resulting in another peak in plankton abundance, which culminated in November with the onset of north - east monsoon. Similar findings have been reported by Reid et al.¹⁴ and Barua et al.¹⁵

From the present data, it may be deduced that 9 species were at Site 1 and 7 species to Site 2, which was the highest of all local and regional sites^16,17. This phenomenon could be attributed to the unique combination of macrophytes present at these selected sites. The Gandak floodplain sites exhibited "Tropic-centered genera” as Brachionus and Lecania were most diversely found in the current investigation whereas the “temperate-centered genera” like Keratella species coincides with observations made by Pradhan et al¹⁸, Arora and Mehra¹⁹ and Sharma²⁰.

CONCLUSIONS:

The planktons are vital for aquaculture ponds for multiple reasons. First and foremost, they make a huge pool of nutritious food and fish mostly feed on them particularly during their larval stage. The planktonic algae also contribute in enriching water with dissolved oxygen by their photosynthetic activity during daytime. The rate of production of dissolved oxygen via photosynthesis is always much faster than the rate of diffusion of atmospheric oxygen into water.

As evident from the obtained results, the studied Ujain pond is found rich in biodiversity of phytoplanktons, zooplanktons, and fishes. This indicates that the pond is still in good condition for fish culture after unorganized fishing till date, and by employing organized and scientific means of pisciculture better yield can be obtained. This also necessitates the need for protecting the pond from becoming eutrophic in order to be benefitted from prolonged sustainable fish-farming.

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Received on 05.07.2024 Modified on 20.07.2024

Research J. Science and Tech. 2024; 16(3):189-192.

DOI: 10.52711/2349-2988.2024.00028