Introduction

Lakes, a precious resource on our planet, are subjected to continuous chemical change due to the inflow and outflow of materials. Reduced mobility and increased sedimentation contribute to high biological activity¹. These lakes hold significant economic value, providing food through fish and aquatic products ². Bangalore, the capital city of Karnataka in southern India, was renowned for its serene lakes and landscapes. However, the city’s unplanned development has caused a gradual decline of these wetlands that play a significant role in supplying water for irrigation and drinking, supporting fish culture, replenishing groundwater, and mitigating natural calamities³. A balanced environment maintains the effectiveness of the water quality, encompassing the physical, chemical, and biological variables within these inland water resources⁴. Rapid urbanization, anthropogenic activities, and dumping of untreated sewage and waste have led to the degradation of lakes, reducing them into cesspools⁵.  The weathering of rocks generates ions within the catchment area that serve as natural pollutants⁶. Lake chemistry is reflected in the seasons and catchment characters⁷. These wetlands quickly pile pollutants from various industrial and domestic sources, leading to the deterioration of water quality and loss of biodiversity, making them a fragile ecosystem⁸.

The limnological approach to assess physical, chemical, and biological variables comprehends a region’s water quality and seasonal landscape^9,10. Declining water quality causes increased waterborne diseases and disrupts the sustenance of an ecosystem^11,12. Solid waste disposal causes havoc in water percolation and impacts groundwater recharge¹³. Population outbreaks, sewage discharge, and agricultural practices have resulted in the inflow of nutrients within these lakes, causing drastic eutrophication and creating an imbalance in natural functioning^{14, 15}. Variations in water quality parameters compromise the ecological health of these wetlands and signify the influence of urbanization¹⁶. Parameters such as Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), and Chemical Oxygen Demand (COD) help researchers understand the pollution levels of lakes¹⁷. In addition, the Most Probable Number analysis focuses on microbial ecology¹⁸. Overgrowth of aquatic weeds like Eichorrnia crassipes has degraded these inland water resources¹⁹. These indicate the threatened survival of lakes and call for immediate conservation efforts²⁰. Physico-chemical and microbial analysis of a few lakes in Bangalore emphasizes immediate conservation¹³.

Using the vertebrate model system, zebrafish (Danio rerio) provides valuable insights to assess the ecological health of a water body¹⁰. Organic and inorganic pollutants accumulate within the fish organs, leading to structural abnormalities^{21, 22, 23}. Thus, ecological responses and their influence on heart rate, behavior, physiology, and neurotransmission can be assessed^{24, 25, 26}. The integration of limnological analysis and D. rerio assessments has proven to be a valuable tool in monitoring the ecological health of a lake and has alerted sustainable water management ²⁴. In this context, the present research aims to understand the water chemistry, its influence over seasons, and its impact on a biotic system focusing on three grab sampling stations named Open surface (O), Deposit (D), and Inlet (I) over a time frame of one year in the distinct setting of Lingadheeranahalli Lake located in north Bangalore.

Materials and Methods

Study area – Lingadheeranahalli Lake

Lingadheeranahalli Lake is a small wetland near the D group employee’s layout in Bangalore North. It is 870 meters long and located at 13.0035° N latitude and 77.4827° E longitude. The lake offers walkers a pathway and a serene landscape for nearby residents. Mongooses, peacocks, and snakes are frequent sights in and around the lake.

Limnological Assessments

Water samples were collected, and limnological sampling was conducted between June 2022 and July 2023. Three sample stations were marked within the lake, namely, Open Surface (O), characterized by its direct atmospheric exposure and minimal obstruction at 13.003° N latitude and 77.482° E longitude. Deposit (D) station marked for high sedimentation and plant growth with coordinates 13.002° N latitude, 77.482° E longitude, and Inlet (I) station where treated water is discharged into the water body located at 13.002° N latitude, 77.483° E longitude. Water samples were analyzed in triplicates, and the mean value was considered. Temperature, humidity, and pH were measured on-site, and dissolved oxygen (DO) was fixed at the site. Water samples were collected in sterilized bottles and further transported to the laboratory for subsequent analysis of chemical and biological parameters. American Public Health Association ²⁷ standard procedures were followed to analyze various parameters.

Physical Parameters

Physical parameters such as pH, temperature, atmospheric humidity, turbidity, and conductivity were measured using calibrated instruments such as a pH meter, thermometer, hygrometer, turbidimeter, and conductivity meter. The total dissolved solids were measured using a TDS meter.

Chemical Parameters

Dissolved oxygen (DO) was fixed at the site using manganous sulfate and measured using a DO meter. Biochemical oxygen demand (BOD) was determined via the DO meter and Winkler’s method. The ferrous ammonium sulfate method was used to measure Chemical oxygen demand (COD). Alkalinity, total hardness, calcium, and magnesium levels were determined using titration. Sodium and potassium were measured using a flame photometer. The silver chloride method was used to detect chlorides, the barium chloride method was used to quantify sulfate, phosphate concentration was analyzed using the Fiske Subbarow method, and a UV spectrophotometer was used to screen nitrates. Prescribed techniques outlined in APHA 2017 were followed.

Most Probable Number (MPN) Analysis

MPN analysis was conducted to detect the presence of coliforms in the water sample utilizing standardized techniques ²⁸.

Statistical Validation

Descriptive statistics, mean and standard deviation, were determined for the physical, chemical, and biological parameters. Data distribution was measured using the Shapiro-Wilk and Kruskal-Wallis tests, following which the post-hoc analysis was conducted using the Dwass-Steel-Critchlow-Fligner (DSCF) comparison.

Zebra Fish Analysis

Aquaculture and Spawning

D. rerio and its embryos were chosen as the model organism and its embryos because of their genetic relatability to humans and the advantage of having transparent embryos ²⁶. Healthy D. rerio was maintained in temperature-regulated aquarium tanks with good ventilation and lighting.  Spawning was facilitated during the day with a male and three female fishes confined in breeding tanks equipped with a mesh ²⁹. Fresh embryos collected were used for developmental assessments and to count the heartbeat.

Experimental Setup

Three embryos were introduced into small glass tanks with Reverse osmosis (RO) water; like-wise, three were introduced into the lake water samples from the three stations. Embryos treated within the RO water setup were considered a control sample.

Embryo Analysis

Vital characteristics, such as tube formation, somite development, and overall embryo structure, were examined using a compound microscope in the control and test sample setups. Heartbeat was counted during the torpedo stages ^{30, 25}.

Results

Seasonal pH, temperature, humidity, and alkalinity variation for the three sampling stations are recorded in Table 1.

Table 1: Seasonal variation in pH, temperature, humidity, and alkalinity for the sampling station Open Surface water, Deposit, and Inlet sampled between June 2022 and July 2023

The mean values for limnological parameters and the standard deviation for various seasons and sampling stations are represented in Figures 1- 4, respectively.

Figure 1: Graphs representing turbidity, conductivity, and total dissolved solids for the sampling station Open Surface water, Deposit, and Inlet sampled between June 2022 and July 2023 Click here to view Figure

Figure 2: Graphs representing dissolved oxygen, biochemical oxygen demand, and chemical oxygen demand for the sampling station open surface water, deposit, and inlet sampled between June 2022 and July 2023 Click here to view Figure

Figure 3: Graphs representing total hardness, dissolved oxygen saturation percentage, calcium, and magnesium for the sampling station open surface water, deposit, and inlet sampled between June 2022 and July 2023 Click here to view Figure

Figure 4: Graphs representing anions for the sampling station open surface water, deposit, and inlet sampled between June 2022 and July 2023 Click here to view Figure

Data statistically validated through the Kruskal Wallis test for turbidity and MPN showing significance for the sampling stations are depicted in Table 2.

Table 2: Kruskal Wallis Statistics indicating significance for Turbidity and Most Probable Number MPN Test *p<0.05

Table 3 represents pair-wise comparisons done through the Dwass Steel Critchlow Fligner (DSCF) post hoc test for turbidity and MPN index analysis between sampling stations.

Table 3: Dwass-Steel-Critchlow-Fligner pairwise comparisons for Turbidity and MPN Index *p<0.05

Table 4 depicts significant data **p<0.001 and *p<0.05 for seasons through the Kruskal Wallis test for various limnological parameters. Table 5 represents pairwise season comparisons for various limnological parameters done through DSCF post hoc analysis **p<0.001 and *p<0.05. Table 6 represents the somite embryonic development stage of D. rerio. Figure 5 graphically represents the heartbeat changes recorded in D. rerio.

Table 4: Kruskal Wallis Statistics indicating significance for various limnological parameters **p<0.001 and *p<0.05

Table 5: Dwass-Steel-Critchlow-Fligner pairwise comparisons for various limnological parameters **p<0.001 and *p<0.05

The pH of the lake water showed significant seasonal variations; a low pH of 5.73 ± 0.60 was recorded in the inlet station during the monsoon, while the highest was observed in the spring (6.88 ± 0.30). The pH remained slightly acidic throughout the year. The temperature of the study site that is deposit recorded the lowest temperature of 21.55 ± 0.21°C due to high plant growth, while the open water station recorded the maximum temperature of 30.33 ± 1.02°C. A usual seasonal trend in temperature was observed across all stations. The lowest humidity of 35.60 ± 2.89 was recorded during the winter in the open station, while the highest of 73 ± 7.07 was recorded during the autumn in the inlet. The water remained turbid throughout, and the lowest and highest levels were noticed during winter. 1.00 ± 7.23 NTU was recorded in the open station, and the inlet was recorded with 80 ± 36.77 NTU. The conductivity of water highlights salinity and dissolved ion concentration; the lowest conductivity was recorded during the winter in the inlet station (340 ± 70.71 µS/cm), while the highest (1314 ± 528.92 µS/cm) was also in the inlet during the spring.

The inlet recorded the lowest DO of 0.53 ± 0.92 mg/L during the monsoon, while the open station showed 5.50±0.28 mg/L during the spring. Overall, the DO of the wetland was found to be lesser than the APHA standard values. The saturation percentage of DO is represented in Figure 4; the percentage of DO saturation fluctuates across seasons and sampling stations, Peaking in spring (67.9%) and dipping in autumn (42.83%) in the open station. An increase in DO was seen during the winter (60.91%). It was low during the autumn (14.44%) in the deposit station, while in the inlet station, the highest was in summer (68.02%) and the lowest was during the monsoon (6.54%). BOD significantly varied within the lake. High organic pollution and high microbial activity were observed. A negative BOD was seen in all three stations during the autumn, indicating oxygen surplus due to microbial load, while a high BOD of 3.10 ± 3.28 mg/L was recorded in the inlet station. All stations recorded a very high COD exceeding the permissible limits, indicating pollution throughout all seasons. High COD was observed during the spring, while the highest of 384 ± 45.25 mg/L was recorded with the inlet station during winter. Alkalinity due to hydroxides was zero across all seasons and stations; carbonate alkalinity was recorded in the open 5.00±7.07 mg/L and inlet 15±21.21 mg/L stations during the spring, 16.00±27.71 mg/ L was recorded during the summers in the deposit station. Majorly, alkalinity was due to bicarbonates across seasons, with the highest range between 122.67±76.04 – 127.33±50.21 mg/L during the monsoon and summer in the inlet station. At the same time, low values were recorded during the winter.

The total hardness was within the permissible range during the winter, spring, and summer. In contrast, it increased during the monsoon and autumn. 324±31.75 mg/L was the highest value recorded in the inlet station. TDS was within the permissible value in the open and deposit station, while in the inlet, it surpassed the permissibility with values ranging between 171±32.53 mg/l and 658±265.87 mg/L. High values were recorded during the spring across all stations. Calcium ions increased during the spring and summer, with the highest value of 93.33±38.44 mg/L recorded in the open station and the lowest of 9.20±1.70 mg/L recorded in Deposit and inlet stations. 50mg/L being the permissible limit as per APHA, the wetland recorded very high magnesium content during the monsoon and the autumn, with values ranging from 172.13±42.20 to 290.40±11.78 mg/L. Sodium and potassium levels remained consistently low across all seasons. Chloride concentrations were within the APHA standards; values increased during the spring. 83.09±0.98 mg/L was the maximum value recorded in the inlet station, while the lowest of 28.16±29.79 mg/L was seen in the deposit. Sulfate concentrations ranged between 8.32±6.98 mg/L and 34.92±25.38 mg/L, within the permissible limit (400 mg/L) as per APHA.

Nitrate concentrations were within the permissible value. A slight increase was found during the spring, with a maximum value of 5.36±4.29 mg/L recorded in the open station. Phosphate concentration ranged between 0.05±0.05mg/L to 1.33±0.30mg/L, with 0.05mg/l being the permissible value the open surface water recorded highest during the autumn. A low MPN index was observed during the spring and the summer, while MPN values exceeded the permissible range during the monsoon, with the Deposit and the inlet station showing the highest values. Significant variations between sampling stations and across seasons were observed through Kruskal Wallis statistics.

Table 6: Effect of lake water on somite embryonic developmental stage of the D. rerio

Somite developmental stages and heart rates in D. rerio embryos showed the following results. The embryos reached the 14^th somite stage after 16 hours in the open and the deposit station, similar to the control, while embryos reached only the 10^th somite stage in the inlet station. This delay in growth is due to pollutants. The heart rate recorded was 125 bpm in the control and 96-102 bpm in the open station. A gradual decrease in the number of beats (90-97 bpm) was recorded in the deposit station, while the inlet station recorded a drastically meager heart rate (64 bpm).

Figure 5: Effect of lake water on Heartbeat count in D. rerio Note: bpm stands for Beats per MinuteClick here to view Figure

Discussion

The study on Lingadheeranahalli Lake revealed significant seasonal dynamics insights into its physicochemical parameters and the developmental responses of D. rerio. Similar studies on other urban lakes have shown comparable trends. Seasons and anthropogenic activities have affected water chemistry. The pH of the lake water showed significant seasonal variations overall. The pH across all sampling stations remained slightly acidic throughout all seasons. Reduced water content and over vegetation were noticed in the study area. Previous studies indicate that drought or reduced water content results in the acidification of lake water ³¹, and inundated terrestrial vegetation can result in acidic pH ³². Previous studies on Sankey Tank Mallathahalli Lake in Bangalore have similar findings. A usual seasonal trend in temperature was observed across all stations. Season trends are forecasted for freshwater wetlands^{33, 34}.

Humidity is attributed to water quality imbalance ³⁵. The findings suggest higher humidity during autumn and summer; previous research suggests that the higher the temperature, the higher the moisture ³⁶. Water turbidity consistently remained high, peaking during the winter. This is attributed to colloidal dispersions, common in lake ecosystems ¹³ and could be the reason for the study sites. Water conductivity was the lowest during the winter and the highest in the inlet during the spring. The peak in conductivity is due to waste disposal and sewage inflow ^{37, 13}. Previous studies on Kumaun Himalayan Lake indicated that seasons and human influence significantly affect pH, conductivity, and nutrient concentrations¹.

DO of the lake was low; comparative research on Bellandur and Varthur Lakes reported similar findings due to high organic pollution from untreated sewage ^{9, 10}. DO saturation percentage suggests significant variations in the inlet station, emphasizing the need for monitoring. Organic pollution suggests the waste accumulation capacity of the wetland ³⁸. Studies on Varthur Lake reported high levels of BOD, underscoring stress on aquatic life ³⁹. Previous studies suggest that the lesser the DO, the higher the BOD ²⁴. COD is reported to be high after the rainy season, reflecting a similar trend in Ulsoor Lake and other urban Lakes in Bangalore ⁴⁰. Urban waste and anthropogenic activity lead to high values of COD ⁴¹.

Rainfall increases alkalinity ⁴², as indicated in the present study; alkalinity tends to increase during summers, and enhanced carbon sources due to bicarbonates facilitate algae growth ⁴³. High values of bicarbonates reported in the study might be due to contact with carbonate rocks and atmospheric gases present in water ⁴⁴. Past studies show increased hardness during the dry seasons ⁴⁵. The present study indicates increased hardness during the monsoon, calcite, and dolomite dissolution due to rainfall might be the reason for the increase in hardness during the monsoon ²⁰. TDS is mainly due to anions and cations ¹³ and depends on seasons ⁴⁶. Calcium in fresh surface water could be due to gypsum, limestone, and calcium-containing rocks ⁴⁷. Inflow retention of pollutants also leads to high calcium content ⁴⁸. Leaching of dolomite and magnesite during the monsoon can cause high magnesium levels ⁴⁹. High values observed during the winter at the inlet station are hypothesized to result from mineral leaching, drainage, and oxidation of sulfides ⁵⁰. The presence of phosphates generally leads to eutrophication during the dry seasons, as suggested by past studies, which is similar to the current research ⁵¹. Nitrate concentration in surface water is high, and spikes are only due to agricultural runoff and animal wastes ^{52, 53, 54}.  Previous studies on MPN indicate values go high after monsoon, similar to the current study ⁵⁴.

Statistical validation suggests significant environmental pollution between the inlet point and the open station, which aligns with previous studies showcasing spatial heterogeneity in water quality due to anthropogenic activities ⁵⁴.  Additionally, temperature, humidity, total hardness, calcium, magnesium, phosphates, and nitrates displayed seasonal differences with a significance level of p<0.001. Furthermore, DO, BOD, COD, alkalinity, TDS, potassium, and chlorides showed potent variations, with p<0.05 being the significance level. D. rerio data of the current study, in contrast with earlier studies conducted on Iblur and Mallathahalli Lakes in Bangalore, are similar ^{24, 55}. The limnological parameters and the physiological responses indicate deficient water quality and highlight a detrimental effect on aquatic life, emphasizing stringent water quality management.

Conclusion 

Comprehending various limnological variables of the wetland and physiological responses by D. rerio, the current investigation reports the influence of summer, monsoon and winter seasons on limnological parameters. Physiological responses of D. rerio embryos highlighted potent stressors present in the lake ecosystem, with delayed somite development and decreased heart rates. The water quality remains poor and continuous ecological stress was observed. The study emphasizes the importance of seasonal dynamics as an adaptive strategy in wetland monitoring to mitigate pollution and consciously spread awareness in society.

Acknowledgement

The authors would like to acknowledge JAIN (Deemed to be University), Bangalore, for the infrastructural support rendered throughout the study.

Conflict of Interest

The authors do not have any conflict of interest

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Data Availability Statement

This statement does not apply to this article.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval.

Author Contributions

Mathews P Raj: Conceptualization, Methodology, Writing – Original Draft, Supervision.

Reena Susan Philip: Data Curation, Formal Analysis, Writing – Review & Editing.

All authors have read and approved the final version of the manuscript.

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