3.     Water Quality Survey

3.1    Methodology

Collection of samples

Water samples from Varthur Lake were collected on three occasions: October,  November, and January 2002.  October samples were collected from the shoreline nearest to the following locations: Bellandur Canal, the south-southwest portion of the lake, and the northeast and southeast outlets. Water samples were collected from 10 to 30 cm below the surface of the water during the morning hours. These samples were collected and stored in white, 500 ml polyethylene containers, with the exception of those collected in borosilicate glass bottles for dissolved oxygen analysis. No preservatives were added as the samples were transported to the laboratory within six hours and either refrigerated or analysed immediately. 

Bore well water samples were collected in January from four locations closest to the southern shore of the lake. These samples were collected and stored in clean, white, 500 ml polyethylene containers that had not been used for lake sampling. No preservatives were added, as samples were taken to the lab and analysed immediately. 

Analysis of Samples

On-site analysis of lake water included air and water temperature, transparency and, in the case of October and November sampling, dissolved oxygen. Laboratory analysis included: acidity, alkalinity, biochemical oxygen demand (BOD), chemical oxygen demand (COD), chloride, chlorine residual, coliform bacteria, dissolve oxygen (DO), electrical conductivity (EC), fluoride, hardness, iron, nitrate, pH, phosphate, potassium, sodium, sulphate, solids (total, total dissolved, and total suspended) and turbidity. 

The majority of lake water analyses followed standard procedures published by the Indian National Environmental Engineering Research Institute (NEERI, 1998) and the American Public Health Association (APHA, 1985). Ammonia, coliform bacteria, fluoride, iron, pH (in the field), phosphorus, residual chloride, and turbidity for October and November samples were tested using a Jal-Tara Water Quality Testing Kit produced by Development Alternatives in New Delhi (Development Alternatives  2000). 

Bore well samples were tested for ammonia, chloride, coliform bacteria, EC, fluoride, nitrate, and pH. EC and pH were measured using an electrical conductivity meter and a pH meter, respectively. All other parameters were tested using a Jal-Tara Water Quality Testing Kit.           

3.2 Results

3.2.1 Lake Water Samples

A complete set of results from analysis of October, November and January water samples is provided in Appendix B. The following is a brief summary of these findings. 

General Parameters

Dissolved oxygen (DO) levels in Varthur Lake were extremely low. Water temperature ranged from 22 to 26°C prior to 9:00 AM on all sampling dates. The pH of the water was found to be slightly alkaline (approximately 7.5 to 8.0) for all water samples. November water samples exhibited a strong ability to neutralise acids in solution due to the presence of bicarbonate. The acidity of the samples was much less than their alkalinity.  Total hardness showed little variation during the sampling period, indicating that the overall concentration of calcium and magnesium salts is fairly constant; hardness due to calcium carbonate ranged from 59 to 68% of total hardness for November and January samples. 

In November, light was able to penetrate the upper 19 to 24 cm of the water column. Transparency was substantially reduced during January. Further examination of physical properties revealed high concentrations of suspended and dissolved solids. The concentration of total dissolved solids (TDS) showed substantial seasonal variability, increasing three-fold between November and winter sampling periods. This increase in TDS corresponds to a similar increase in electrical conductivity. Moderate to high concentrations of total suspended solids (TSS) were also present in January samples. Water from the middle of the lake exhibited the highest concentration of TSS by far. 

Nutrients

Nitrate concentrations present in October samples were low, averaging only 0.24 mg/l. The average concentration of nitrate increased to 1.00 mg/l and 1.27 mg/l in November and January, respectively. Ammonium was estimated to be in excess of 3.0 mg/l for three of the four October samples. Phosphorus concentrations from January samples were very high, averaging 15.1 mg/l. 

Organic Matter

The BOD of water samples was extremely high and nearly equivalent to COD.

Microbial Contaminants

            Bacterial culturing confirmed the presence of the bacteria E. coli in the lake.

Inorganic Constituents

The concentration of chloride ions in November samples averaged 102 mg/l. In January samples, these values increased 60 to 70 percent. October lake water samples contained less than 0.2 mg/l of residual chlorine, which is the minimum detection level of the Jal-Tara kit. Sulfate concentrations in the lake were consistently low, however, a substantial decrease in sulfate occurred between November and January sampling dates.  Sodium concentrations for November were only moderately high. Elevated levels of potassium were observed in November samples. January samples were well within standard range for unpolluted surface waters.

3.2.2 Groundwater Samples

Results from the groundwater survey are presented in Table 3.1. Two of the samples tested positive for minor concentrations of coliform bacteria. These well were located at opposite ends of the lake, approximately 250m and 750 m from the southeastern and southwestern shorelines, respectively. 

Table 3.1  Groundwater Survey Results     

3.3 Observations

3.3.1 Lake Water Samples

Results of the analysis for samples taken near the northeast outlet during October, November and January are presented in Table 3.2. This table also includes standard values for unpolluted water bodies as well as regulations and guidelines. 

Table 3.2   Comparison of Water Quality Data and Various Pollution Standards

* values subject to interference. See section 3.2

** total ammonia, depends on pH

^1,  UNESCO, WHO, UNEP  1996  Water Quality Assessments: A Guide to the Use of Biota, Sediments and Water in Environmental Monitoring. Second Edition. E & FN Spon,  Madras.  

The wide variation between TSS concentrations for various sampling sites could be due to the presence of organic floatables observed during collection of the samples. The presence of these clumps of matter could significantly increase the TSS value for a sample in comparison to a similar sample without clumps. 

Turbidity from organic and inorganic suspended matter in Varthur has the potential to impact the ecology of the lake in several ways. Many toxic contaminants, such as heavy metals and some pesticides, could potentially find their way into Varthur by adhering to solids in solution. Eventually, much of the suspended matter will settle in the bottom of the lake where they smother benthic organisms and contribute to siltation. Turbidity is also the most important factor in prolonging the survival of faecal coliform in water bodies because the particulate matter shelters bacteria from harmful solar radiation (DWI, 1995). 

The bacterium Escherica coli is indigenous to the intestines of animals, including humans. Its presence in Varthur indicates that faecal matter contaminates the lake. Faecal contamination is often associated with other types of pathogenic bacteria and viruses found in untreated sewage. The turbidity of the lake water, along with its warm temperature, mildly alkaline pH, and low oxygen levels, could lead to prolonged survival of pathogenic bacteria for up to several days.

Varthur contains significant amounts of the macronutrients required by aquatic plants in large quantities in order to survive and grow, especially phosphate. Excess amounts of phosphorus could be the result of contamination from sewage and/or fertilisers. Both the population of Bangalore and the availability of fertilizers have increased in recent years. Eutrophication has resulted in large populations of algae to develop in Varthur, which imparts a green colour. This process has also assisted in the intrusion of Eichhornia crassipes (water hyacinth). Although the amount of lake surface occupied by this plant fluctuated dramatically between sampling dates, the western portion of the lake was consistently covered with mats of hyacinth, as were the two main outlets. Overall, coverage by water hyacinth increased during the winter months.    

The concentration of nitrate was slightly higher than standard values for unpolluted waters in October samples, but increased substantially in November and January. The relatively low nitrate concentrations observed in Varthur could be a result of several biological processes. Loss of nitrate in Varthur could be the result of ammonification, the conversion of organic nitrogen to ammonium during the decomposition of organic matter. High concentrations of ammonia observed in October samples support this explanation. Under anoxic conditions, nitrate may also be converted to nitrite; it is likely that such conditions exist near the bottom sediments of Varthur lake, given the extremely low oxygen levels of the surface layers, and that this process may be partly responsible for the lower concentrations of nitrate in the water. Loss of nitrate also occurs through uptake by macrophytes and algae; during periods of high plant growth, this process may significantly reduce nitrate concentrations in the lake. 

November ammonia concentrations in Varthur were high enough to be toxic to many forms of aquatic life.  Given the warm temperature, alkaline pH of the water, and organic pollution present in Varthur, these concentrations may have been substantially greater than 3.0 mg/l, which is the maximum detection of the Jal-Tara kit. When water samples from January were viewed under a microscope, the most dominant zooplankton by far was Daphnia, a species that is highly tolerant of ammonia.   

Potassium is also an essential element for plant growth. Elevated levels of potassium were observed in November samples, indicating potential contamination from industrial effluents or fertilizer. Potassium concentrations dropped substantially in January, possibly due to uptake by the increasing macrophyte population. A similar trend was observed for sulfate and could be caused by winter plant uptake as well. 

The high BOD of the water samples indicates that decomposition of organic matter is one of the main factors leading to the low DO concentrations observed in the lake. Much of the remaining oxygen is likely consumed through nighttime respiration by aquatic plants. Eutrophic lakes similar to Varthur often experience a daily cycle of hyper- and hypo-oxygenation due to the high concentration of photosynthetic algae that produce oxygen during daylight hours and consume oxygen at night. However, the data collected is insufficient to confirm these diurnal-nocturnal fluctuations in DO. 

The low DO content of Varthur limits diversity of animal life that can survive in the lake. Anoxic conditions also affect many other chemical processes within the lake that can be detrimental to organisms, such as the conversion of organic nitrate to toxic ammonia. 

The high BOD values imply that virtually all of the organic matter contained in the samples was biologically degradable, and that the combined concentrations of sulphates,  nitrates, ferrous iron, and other organic components that cannot be oxidized by bacteria are comparatively low. Based on these findings, only a small proportion of the organic pollution in Varthur could have its origin in industrial effluents. The majority of organic pollution likely comes from animal and plant sources, such as sewage and plant death within the lake. In addition to sewage, several aquaculture ponds are seasonally drained into the lake also have the potential to contribute substantial amounts of nutrient-rich organic debris. 

Elevated chloride values could be due to many factors, including sewage, industrial effluents, and agricultural runoff. The seasonal variation may due to the fact that January concentrations were not diluted by monsoon rainwater. 

The water sample taken from the Bellandur Canal in November was very similar in composition to those taken from Varthur Lake, and it is likely that many of the contaminants that enter Bellandur Lake from its own substantial catchment area eventually make their way to Varthur.

3.3.2 Groundwater samples

The following groundwater parameters were found to be within the limits set by the 1983 Indian Standards Specification for Drinking Water: ammonia, chloride, electrical conductivity, fluoride, nitrate, and pH. There is a possibility that coliform bacteria present in two if the sample could have originated from sewage effluent in the lake, however, these bacteria could also have been present on the pump itself due to human contact.

3.4 Conclusions

The water quality survey for Varthur Lake indicates that it is a eutrophic lake containing high concentrations of organic wastes and phosphorus. Nutrient enrichment has allowed substantial populations of water hyacinth and algae to develop in the lake. The decay of organic matter present in the lake, much of which comes from plant life growing in the lake itself, has resulted in extremely low concentrations of dissolved oxygen and elevated ammonia content. 

The pollution entering Varthur Lake comes mainly from non-point sources that are, by nature, difficult to identify with certainty. The tank is part of a large network of interconnected canals and reservoirs, the largest of which is Bellandur Lake, which receives all of the overflow sewage and wastewater from central, eastern, and southeastern Bangalore city. A variety of industries, sewage outlets, urban wastewater, and agricultural runoff contribute to the current condition of these water bodies and it is, therefore, very difficult to determine the most significant sources of pollution. Any restoration efforts for Varthur Lake must address the interconnected nature of these sources contaminating the lake. 

Pesticides have become readily available through government-sponsored programs in Bangalore area, increasing the potential for contamination of local water bodies.