INTRODUCTION:

The water quality is the measure of its resource relative to the requirements of the biotic species and human needs. It is defined as the physical, chemical biological and organoleptic characteristics of water ¹. The water quality is vital for an aquatic ecosystem as it maintains the ecological processes that support biodiversity. The physico-chemical condition of an aquatic system directly affects its biological production and thus can be used to estimate trophic status and fisheries resource potential ². The water parameters induce several alterations in biota in order to develop regular productivity and play major role in pond metabolism. Limnological studies are aimed to understand the interaction among different physico-chemical parameters which collectively governs the productivity of aquatic ecosystems ^3-5.

The ecosystem of a fishpond is mainly governed by the physicochemical parameters of water. In general, man-made fishponds are shallow water bodies and their physicochemical, spatial, temporal, and biological characteristics greatly influence the fish population and diversity.

Ponds serve as the smallest unit of freshwater ecosystem rich in biodiversity. The Duraundha block of Siwan district, Bihar is blessed with couple of ponds located in and around village Ujain which is also site of large religious gatherings during various Indian festivals for prolonged durations. The subjected pond is the largest among all the ponds and functions as the source of water, commercial fishing and water born fruits (water chestnut) for the visitors as well as local population. The current investigation presents a thorough study on the limnological characteristic and trophic status of the subjected pond, which is very significant for its conservation and optimum utilization for pisciculture. The present study also discuss the relationships among different limnological parameters in the subjected pond of Duraundha (Bihar) observed during the two annual cycles 2017-18, and 2018-19 of this study.

MATERIALS AND METHODS:

This eutrophic pond was located at 26°13'10” N and 84°21'23” E with a total catchment area of about 3161.60 m². The subjected pond is quite old with untraceable origin, and with a total catchment area of about 3161.60 m². The water samples were gathered at seasonal intervals in two annual cycles 2017-18 and 2018-19. The water samples were collected in clean polyethylene bottle of volume 1 L and stored in refrigerator for the analysis of physico-chemical variables of water from the pre-assigned ponds. Different parameters important for the quality assessment of water like temperature at the air-water interface and inside water; alkalinity of water due to carbonate and bicarbonate; hydrogen ion concentration (pH); dissolved oxygen level and depth of visibility were estimated onsite. Water temperature was measured using LCD digital multistem thermometer of range -50°C to 150°C, pH was measured using digital pH meter HANNA-pHep. The depth of visibility inside pond was measured using a standard Secchi disc of diameter 20 cm. A digital (Hold) TDS meter was used to figure out total dissolved solids in the pond water and are presented in ppm or mg/l. The measurement of fluorides, silicates, orthophosphate, nitrate nitrogen and electrical conductivity were done in the laboratory within 24 h of sample collection. The concentration of fluoride ions in the collected water was estimated using ELICO ion analyser LI 126. The Systronics direct reading conductivity meter (308) was used to measure the conductivity. All the physico-chemical characteristics of the selected water body were evaluated following standard protocol ^{6, 7}.

RESULTS AND OBSERVATIONS:

Water temperature:

The obtained values of different limnological parameters are tabulated in table 1.

Table 1: Physico-chemical parameters in Ujain pond, Duroandha, Siwan

S. N.	Parameters	2017-18			2018-19
S. N.	Parameters	Winter	Summer	Monsoon	Winter	Summer	Monsoon
1.	Water Temp (°C)	22.6	28.3	24.7	22.2	28.2	24.3
2.	DO (mg/l)	11.41	6.71	9.76	11.39	6.73	9.78
3.	BOD (mg/l)	0.56	1.56	1.16	0.59	1.64	1.21
4.	Free CO2 (mg/l)	3.63	7.34	4.25	3.65	7.42	4.31
5.	pH	7.72	8.53	8.0	7.71	8.55	8.1
6.	Alkalinity (mg/l)	140	202	170	138	210	173
7.	Hardness (mg/l)	83	158	95	82	160	93
8.	Phosphates (mg/l)	0.24	0.47	0.35	0.23	0.49	0.36
9.	Nitrates (mg/l)	0.015	0.049	0.042	0.018	0.054	0.043

The variation in water temperature was from 22.6°C in winter to 28.3°C in summer of 2017-18 which has changed to 22.2°C and 28.2°C in winter and summer of 2018-19 respectively. The water temperature was found to be maximum (28.3°C) during summer of 2017-18 and minimum (22.2°C) during winter of 2018-19 (Figure 1). The gross average value of water temperature was 25.05°C respectively (Figure 1).

Figure 1: Water temperature at Ujain pond, Duroandha, Siwan.

Dissolved oxygen:

As per the data obtained in this study, the ponds of Ujain were marked with moderate to high levels of dissolved oxygen having average value of 9.29 mg/l. The lowest value of dissolved oxygen was observed in summer season of 2017-18 with value 6.71 mg/ml, and the highest oxygen level of 11.41 mg/l was observed in winter 2017-18 (Figure 2).

Figure 2: Dissolved Oxygen at Ujain pond, Duroandha, Siwan.

Biological oxygen demand:

In this study, the highest value of BOD was observed to be 1.64 mg/l in the summer of 2018-19, and the lowest 0.56 mg/l in the winter of 2017-18 (Figure 3).

Figure 3: Biological oxygen demand at Ujain pond, Duroandha, Siwan.

The highest BOD in late summer or, early rainy season is ascribed to the increase in the metabolic activity of microbes with an increase in organic content in pond water with surface water run-off. Also, high temperature accelerates the rate of oxidation, thus favors decomposition. The high value of BOD in monsoon season is again linked with high organic matter in water.

Free carbon dioxide:

The maximum and minimum values of free CO₂ were observed in the summer (2018-19) and winter (2017-18) seasons as 7.42 mg/l and 3.63 mg/l respectively, during this biannual study period (Figure 4).

Figure 4: Free carbon dioxide at Ujain pond, Duroandha, Siwan.

pH:

It is evident from the data that, the pH of the pond water was recorded in the range of 7.71 to 8.55. The minimum and maximum value of pH was observed in winter and summer of 2018-19 respectively. The average pH value of the pond was estimated as 8.10 (Figure 5).

Figure 5: pH at Ujain pond, Duroandha, Siwan.

Alkalinity:

During the course of this study, the total alkalinity of water sample was found to be highest in summer of 2018-19, and lowest in winter of 2018-19, with the values 210 mg/l and 138 mg/l respectively (Figure 6).

Figure 6: Alkalinity at Ujain pond, Duroandha, Siwan.

Hardness:

The average value of total hardness was observed as 111.83 mg/l, with lowest during winter of 2018-19 (82 mg/l) and highest as 160 mg/l during summer of 2018-19 (Figure 7).

Figure 7: Hardness at Ujain pond, Duroandha, Siwan.

After observation of the pond for two annual cycles, the water appears to be moderately hard for most of the year except peak summer when the water becomes hard by a slight margin.

Nitrates and phosphates:

In this study, we observed that, the pond water contained limited amount of nitrates, with maximum of 0.054 mg/l in the summer of 2018-19, and minimum of 0.015 mg/l in the winter of 2017-18 (Figure 8).

Figure 8: Nitrate at Ujain pond, Duroandha, Siwan.

Figure 9: Phosphate at Ujain pond, Duroandha, Siwan.

This study noticed the highest phosphate concentration of 0.49 mg/l in the summer, and minimum of 0.23 mg/l in the winter of 2018-19, respectively (Figure 9).

DISCUSSIONS:

Temperature is an important factor and contributes significantly in proper functioning of pond ecosystem (8, 9). In this study, seasonal variation in atmospheric and water temperature was observed. The recorded temperatures in winter, summer and monsoon seasons are well within the suitable temperature ranges for fish culture (10).

Dissolved oxygen is an essential component for the metabolism of aquatic organisms that respire aerobically, including fishes. It also influences the solubility of several other nutrients and thus, the periodicity of pond ecosystem ¹¹. The similar seasonal behavior of dissolved oxygen during winter was also observed by many other research groups ^12-15. Higher value of dissolved oxygen during winter can be linked with rise in phytoplanktonic population, high water-solubility of oxygen at low temperatures, and reduced degeneration of organic matters ¹⁶.

Biological oxygen demand (BOD) is the amount of dissolved oxygen needed by the microorganisms in order to decompose the organic matter of water body aerobically. Therefore, BOD also establishes the extent of water pollution by the organic matter. The BOD of unpolluted, moderately polluted, and heavily polluted water is established as <1 mg/l, 2-9 mg/l, and >10 mg/l respectively. As the value of BOD in the present study is fluctuated seasonally between 0.56-1.64 mg/l, with overall average of 1.12 mg/l throughout this study period suggests that the organic matter contamination in the pond is still very less and it is between unpolluted and moderately polluted.

A distinguished seasonal variation in the values of free carbon dioxide has been observed in the studied pond. In freshwater ecosystem, the primary sources of CO₂ are atmospheric diffusion, biotic respiration, and microbial decomposition of decaying matter. Dissolved CO₂ also affects the pH of water, as higher concentrations of dissolved CO₂ (means lower concentration of free CO₂) tend to lower the pH value making the water more acidic.

pH is one of the limiting factor of pond ecosystem and functions as an index of pond environment. The pH value of the ponds revealed alkaline trend. The slightly alkaline pH of pond water is very much suitable for fish culture. The alkaline water was also reported as the best for culturing fresh water fishes by other groups ^{10, 17}. The increase in total hardness of pond water during summer season was caused by increased photosynthetic activity, leading to utilization of available free carbon dioxide and conversion of bicarbonates into carbonates, which eventually got precipitated as calcium/magnesium salts and thereby increasing the hardness ¹⁸.

Alkalinity is directly linked with the productivity of pond ecosystem as it controls the pH and free carbon dioxide of pond water. The alkalinity of a fresh water body is mainly contributed by carbonates and bicarbonates, as their salts get hydrolyzed in water releasing hydroxyl ions ^{10, 19}. This indicates that, the pond water is rich in nutrients and also highly productive. The richness of nutrients establishes the pond favorable for fish culture.

Hardness of water is mainly caused by the carbonates and sulphates salts of Ca²⁺ and Mg²⁺ ions. The water can be classified based on the degree of hardness as soft (< 75 mg/l), moderately hard (75-150 mg/l), hard (150-300 mg/l), and very hard (> 300 mg/l). Similar observation was found by other groups ²⁰.

In the fresh water pond located in non-industrial area, nitrates are mainly contributed due to runoff from agricultural fields. The higher values of phosphate during summer season in other ponds of Siwan and Chapara districts of Bihar are also reported by other groups ^{21, 22}. Both nitrate and phosphate are key indicators of trophic state of water body as their higher concentration support algal blooms ²³. The high concentration in monsoon is due to the addition of rain water coming from agricultural fields and human settlement area loaded with organic waste and fertilizers. The decrease in concentration of nitrates and phosphates during winter is linked to their consumption in macrophytic growth. The elevated temperature in summer increases the evaporation rate resulting into decreased water volume, and also promotes the release of nutrients via decomposition activities, which leads to increase in nitrate and phosphate concentrations.

CONCLUSIONS:

The limnological characteristic of an aquatic ecosystem affects both flora and fauna. The present work reveals that the studied Ujain pond limnology is quite suitable for the commercially viable pisciculture and chestnut farming. Therefore, this pond needs to be conserved from eutrophication via all possible means in order to utilize maximum production potential of the pond water. As per the data obtained for BOD of the pond, with the slightest margin it falls under moderately polluted category, which needs to be take care in order to prevent further eutrophication and improve productivity in future.

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Received on 06.02.2023 Modified on 21.02.2023

Research J. Science and Tech. 2023; 15(1):8-14.

DOI: 10.52711/2349-2988.2023.00002