BIBECHANA Vol. 20, No. 2, August 2023, 200–204 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Chemical and microbial evaluation of water of Rupa lake Kamal Prasad Dhungana1, Akkal Dev Mishra2,∗, Kalpana Gautam Adhikari3 1Department of Chemistry, Prithvi Narayan Campus, Pokhara 2Central Department of Chemistry, Tribhuvan University, Kathmandu 3Department of Microbiology, Janapriya Campus, Pokhara ∗Corresponding author. Email: mishraad71@gmail.com Abstract Analysis of chemical and microbial features of Rupa lake water was carried out in summer season by adopting accepted analytical techniques. Water samples were collected at 28°C, and on-site observations were made for features like colour, odour, pH, transparency, dissolved oxygen, and free carbon dioxide. In the laboratory, the concentration of prominent min- eral ions and microbial contamination were measured using accepted analytical techniques. Transparency of lake water was noted 91cm and electrical conductivity 41 µs/cm indicat- ing the presence of suspended particulate at moderately higher concentration. This water is slightly alkaline with pH of 7.2 that is accounted by domination of alkali and alkaline metal ions. Presence of nitrogenous species mainly ammonium and nitrate in excess amount has detected to be major reason for rapid eutrophication in the lake. Analysis of Rupa lake wa- ter has shown the considerable presence of phosphate and sulphate which have added to the hardness 130 mg/L of the water as well. On the top of this fairly higher concentration of free carbon dioxide indicates presence of organic wastes in association with decaying matters. Domestic sewage discharge, the use of pesticides and fertilizers in agricultural areas, as well as other solid waste dumps has caused microbial contamination and the biggest dangers to the viability of Rupa lake. The risk of contamination and the eutrophication process needs to be managed by creating public awareness [1].The study shows that water quality of Rupa lake is contaminated for drinking but adequately suitable for all aquatic life and ecological balance. Keywords Chemical features, rock weathering, eutrophication, ecological balance, microbial contamination. Article information Manuscript received: June 22, 2023; Accepted: July 11, 2023 DOI https://doi.org/10.3126/bibechana.v20i2.56526 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 1 Introduction Lakes have diverse physical and chemical character- istics, making them valuable ecosystems for drink- ing water, fisheries, recreational activities, and eco- logical studies. The lake ecosystems are consid- ered as one of the valuable ecosystems in the world [2]. Water quality is vital for developing a healthy ecosystem, as both non-living and living factors de- pend on each other [3]. Rivers, lakes and oceans 200 http://nepjol.info/index.php/BIBECHANA mishraad71@gmail.com https://doi.org/10.3126/bibechana.v20i2.56526 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ K. P. Dhungana et al./ BIBECHANA 20 (2023) 200-204 201 greatly facilitated the world wide spread of the pop- ulation and commerce, springs, waterfall, glaciers and snow fields. About 97% of the total available water on earth is contained in Ocean, and remaining 3% is available as fresh water. Among fresh water, 2% is contained in ice in accusable region and 0.7% as ground water. Out of the total fresh water avail- able on Earth, only 0.25% exists in lakes and rivers at any given time, with the rest being stored in ice in inaccessible regions and groundwater [4]. The surface water is the form of oceans, rivers, lakes, ponds and streams on the earth's surface. There are about 5000 lakes in Nepal Out of them; ten are listed in the list of Ramsar site. The water from the lakes is the source of drinking and for various house- hold uses for rural and urban people [5]. Water quality and suitability for use are determined by its taste, odour, colour, and Concentration of organic and inorganic matters. Contaminants in the water can affect the water quality and on the health of the people. Most of the lakes of Nepal are situated in the hilly region. Among hill districts, the Kaski district contains the largest number of lakes and all of them are located to the Pokhara Valley. Pokhara valleyis Known as the "city of lakes’ ’. Phewa lake, Begnas lake, Rupa lake, Maidi lake, khaste lake, Dipang lake, Nyureni lake, Gude lake are the most popular lakes of Pokhara valley [6]. Physical characteristics such as light, temper- ature, transparency, pressure, water current and conductivity whereas chemical properties like dis- solved oxygen, carbon dioxide, pH, alkalinity, hard- ness, etc. of the lake water are some of the key factors to evaluate water quality [7]. Pollutants present like Pb, As, Hg, Cd, U, etc in the wa- ter may cause serious health hazards. Rupa Lake has become tourism attraction spot and provides enough spaceforboating and recreation.Farmers in the Kaski district have formed the Rupa Lake Re- habilitation and Fisheries Cooperatives limited to help protect the watershed [8]. The concentration of all minerals is related to two main factors are the abundance of chemical elements in the earth crust and the solubility of their compounds. The main anions contained in natural water are C1−, SO4 2−, HCO− 3 and CO2− 3 and the main cations are Ca2+, Na+, Mg2+, K+ etc [9]. All natural water contains dissolved gases but they differs in their origins such as volcanic pro- cess and degassing of the earth's mantle supply oxides and dioxides of carbon, methane, ammo- nia, hydrogen sulfide, hydrogen chloride, sulfurous gas [10]. Some other gasesmayappearand dissolve in waterasresult ofultravioletradiation, thunderstorm discharge sulfurous gas, vapour of iodine, ammo- nia, carbonic acid, etc. Biogenic substance these include compound of silicon, nitrogen, phosphorus, iron, etc. Organic matters are composed of organic compound that have come from remains of organ- ism such as plants and animals and their waste products in the environment [11]. Main objective of present study is to exam- ine Rupa lake water for mineral ions and microbes which determine water quality for drinking, irriga- tion, animals and aquatic creatures as compared to WHO standards. This study will help in creating public awareness to safeguard lake water, conserve the lake area and maintain local ecosystem. 2 Methods and Materials The study area, Rupa Lake, is a freshwater lake lo- cated in the border of Pokhara Metropolitan and Rupa Rural Municipality of Kaski District, Nepal. It is the third-largest lake in the Pokhara valley, covering an area of about 1.35 km2, with an av- erage water depth of 3 m and a maximum depth of 6 m. The lake is elongated north to south and is fed by perennial streams. Its watershed area is 30 km2 where the main inflow of water is from Talbesi stream, whereas Dhovan khola is the feeder stream with its outlet Tal khola at Sistani ghat. It supports a number of floral and faunal species. A total of 36 species of water birds have been recorded in the lake which represents about 19 percent of the total 193 wetland-dependent birds found in Nepal [12]. Rupa lake is the third largest lake in the clus- ter of Pokhara which is located at latitude of 28007’- 28012’N and longitude of 84005’-84010’ E. The lake is surrounded by dense forests over humus soils with hard rocks. The physical and chemical parameters such as temperature, transparency, dissolved oxygen, car- bon dioxide, pH, alkalinity, hardness, dissolved solids, chloride, calcium, and magnesium were eval- uated using various methods. Some of other param- eters such as Sulphate, Phosphate (PO4 3-), Nitrate (NO3 -), Ammonium (NH4 +), Iron (Fe2+/Fe3+) were studied with the help of spectrophotometer. The concentration of Potassium (K+) was esti- mated by Flame Photometer and electrical con- ductivity by conductivity meter [13]. All the so- lutions of the reagents to be used were prepared in 0.01M concentration in distilled water for titration and other reactions. Spectrophotometric absorp- tion was observed at 396 mµ-512 mµ for the detec- tion of Fe2+/Fe3+ ions simultaneously. Similarly, K+ ions gave purple emission with 760 nm in flame photometry at about 18000C. K. P. Dhungana et al./ BIBECHANA 20 (2023) 200-204 202 Table 1: Methods applied for evaluating the Physico-chemical features of water. Parameters Methods employed Transparency (cm) Secchi disc method Temperature (0C) Standard mercury thermometer Dissolved Oxygen (mg/L) Winkler’s iodometric titration Method Hydrogen Ion Concentration Microprocessor pH meter Total Alkalinity (mg/L) Titration Method Total hardness (mg/L) EDTA Titration Method Total Solid (mg/L) Evaporation Method Total dissolved Solid (mg/L) Filtration Method Calcium (mg/L) Titration Method Magnesium (mg/L) Titration Method Chloride (mg/L) Titration Method In addition to this, the microbial contamination in the lake was analyzed by Most Probable Num- ber (MPN) method [14]. Preliminary test was done by inserting Durham’s tube containing lake water into MacConky broth in inverted form. The change in colour into yellow indicates the presence of col- iform bacteria in water and formation of colony at 37 gives its confirmation. The number of positive tubes were counted and compared with standard chart to find MPN of 100 ml water sample. Figure 1: Overview of Rupa lake. 3 Results and Discussion Transparency was measured at 28°C using a Secchi disk method. The transparency of Rupa Lake was found to be 91 cm, which suggests that the pres- ence of organic and inorganic suspended particles, silts, sediments, and debris could affect the water quality. An increase in temperature might result in a drop in the quality of water as the organic matter composition decays more quickly due to the warmer water. Rupa Lake has a slightly alkaline pH value of 7.2, indicating the presence of carbonates and bi- carbonates of alkali and alkaline earth metals. The concentration of dissolved oxygen (DO) observed in this study is 4.2 mg/L, which is lower than the stan- dard value of 5.0 mg/L, indicating poor suitability for aquatic life. Presence of carbonates, bicarbon- ates and hydroxides of alkali metals and alkaline earth metals like Na, K, Mg, Ca, accounts for total alkalinity water. The lake water's total alkalinity is 52 mg/L, making it slightly alkaline, and the to- tal hardness is 130 mg/L, which is a bit high and might impact the biotic components of the lake. The electrical conductivity (EC) of the lake water is 41 µs/cm, suggesting higher dissolved ion concen- trations or high total dissolved solids (TDS) values. The TDS measures the amount of chemical weath- ering in the watershed. Its amount in Rupa lake in present study is found to be 50 mg/L. The variety of natural and human induced pollutant causes in- K. P. Dhungana et al./ BIBECHANA 20 (2023) 200-204 203 crease in TDS. The lake water's total solid matter is 136 mg/L, indicating a high level of solid materi- als, including dissolved and suspended solids, clay, plankton, organic waste, and inorganic precipitates. The chloride concentration of Rupa lake is 14 mg/L. The primary sources of chlorine in lakes and ponds are domestic sewage and faecal deposits. It lies within the standard value prescribed by WHO. Calcium and magnesium concentration observed are 24 mg/L and 13mg/L respectively that exceed the normal acceptable level. However the concen- tration of phosphate is 0.04mg\L which lies above WHO guideline for drinking water. The observed concentrations of nitrates, ammonia, and sulfates in Rupa Lake are slightly higher, possibly due to domestic runoff, industrial discharge, agricultural runoff, and natural degradation of organic matter, as well as sewage contamination. These nitroge- nous sources are responsible for eutrophication in water bodies. Nitrate is 0.61 mg/L, ammonia was 1.8 mg\L and sulphate is 2.6 mg\L in Rupa lake water respectively. The potassium concentration of lake water sample was 1.6 mg\L. The concentration of iron in the lake water is 0.5 mg/L, which exceeds the standard value of 0.3 mg/L. The higher iron concentration may be due to weathering of ferrous and ferric ions from surrounding rocks and min- erals. Higher concentration of iron in lake water becomes rusty red or brown in colour that causes health hazards. It may be due to the weathering of ferrous and ferric irons from surrounding rocks and minerals. The observation of microbiological anal- ysis performed by most probable number method revealed that the lake water contains coliform bac- teria. Table 2: Observations of various parameters of Rupa lake water. Parameters Rupa lake WHO standards (2020) Parameters Rupa lake WHO standards (2020) Transparency (cm) 91 100.0 Calcium (mg\L) 24 10.0 Temperature (0c) 28 12-25 Magnesium (mg\L) 13 5.0 Electrical conductance (µs/cm) 41 40.0 Phosphate(mg\L) 0.04 0.02 Total alkalinity (mg/L) 52 100.0 Nitrate (mg\L) 0.61 0.50 Total dissolved solids (mg/L) 50 45.0 Ammonia (mg\L) 1.8 1.5 Total solids (mg/L) 136 120.0 Iron (mg\L) 0.5 0.3 Dissolved oxygen (mg\L) 4.2 5.0 Sulphate (mg\L) 2.6 2.5 pH 7.2 6.5-8.5 Potassium (mg\L) 1.6 2.0 Chloride (mg\L) 14 20.0 Free CO2 (mg\L) 3.0 1.5 Total hardness (mg\L) 130 50.0 4 Conclusion The study of chemical and microbial features of Rupa lake revealed that the water is slightly alka- line with higher concentration of suspended and dis- solved minerals as compared to WHO water quality standards. On the top of this, the water is contami- nated with coliform bacteria. The water is not suit- able for drinking purposes however it is acceptable for aquaculture and irrigation. Rapid eutrophica- tion may be caused by household and industrial dis- charge along with decomposition of organic matters is posing severe danger to the sustainability of Rupa lake. This study has indicated another challenge to the sustainability of this lake like encroachment accompanied with deforestation and sedimentation due to weathering of soils and rocks from catchment areas. Right now it has become essential to con- serve the lake by strict monitoring and safeguarding aquatic environment and watershed areas by creat- ing public awareness towards local ecosystem and health hazards. Acknowldgement Authors would like to express sincere thanks to the Department of Chemistry, Prithvi Narayan Cam- pus, Tribhuvan University, for providing the labo- ratory facility to conduct this research work. The University grants commission of Nepal deserves thanks for financial support to carry out this re- search work. K. P. Dhungana et al./ BIBECHANA 20 (2023) 200-204 204 References [1] B. 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