Spatial variations in nutrients, pH and alkalinity of ground water in the coastal city, Visakhapatnam
Groundwater, the water beneath earth surface, stored in aquifers is one the most valuable natural resources of our country. It plays a crucial role as a source of drinking water for millions of people in India. It is also an important source for agricultural farms and industries. Although it is less susceptible to contamination than surface water bodies, many land and water based activities like improper disposal of industrial wastes, fertilizers and pesticides used in agricultural farms, hydraulic fracturing, landfill leachate etc is contaminating this precious source. Common pollutants of groundwater include arsenic, fluorine, nitrate, phosphate etc. Excessive concentration of these constituents in groundwater is very harmful for any consumer. pH and alkalinity are also very good indicator of groundwater quality. In this project I have done a case study on spatial variability of groundwater quality in several locations of Visakhapatnam based on five parameters- pH, total alkalinity, nitrate, phosphate, silicate.
Groundwater plays a crucial role as a source of drinking water in many rural and urban areas of India. It is also intensively used for irrigation, household works and industrial purposes. Groundwater is generally less susceptible to contamination and pollution than surface water bodies as it is stored underground in aquifers. But in India, where it is excessively used, a variety of land and water based anthropogenic activities are polluting this valuable source. When certain chemical constituents, like arsenic, fluoride, nitrate, phosphate, trace metals, are above the permissible levels in groundwater then the water is considered to be polluted. Excessive concentrations of these constituents in groundwater can cause severe damage to both consumer and environment. For example, a 2007 study found that over 137 million people in more than 70 countries are probably affected by arsenic poisoning in drinking water. The acceptable level as defined by WHO for maximum concentrations of arsenic in safe drinking water is 0.01 mg/L. Arsenic contaminated drinking water can transmit diseases like diarrhoea, dysentery, typhoid, cholera etc. Like arsenic high concentrations of fluoride in groundwater used for drinking can cause dental and skeletal fluorosis. Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause blue baby syndrome. Nitrate, phosphate and silicate are major nutrients in groundwater. We know that nutrients are essential for plant growth but the overabundance of nutrients in water can have many harmful health and environmental effects. When groundwater overloaded with nutrients mixes with sea water (Submarine Groundwater Discharge), it supplies excessive nutrients to the sea water and affects the coastal phytoplankton dynamics and may also trigger Harmful algal blooms (HABs) which eventually affects the marine ecosystem.
Alkalinity is a measure of the capacity of the water to resist a change in pH that would tend to make the water more acidic. The common ions that contribute to alkalinity are bicarbonate, carbonate, hydroxide and among them bicarbonate is dominant. In some waters, other species such as ammonia, phosphate, borates and silicates may contribute to alkalinity which is termed as total alkalinity (a measure of all contributing ions). The measurement of total alkalinity and pH is needed to determine the corrosivity of the water. In this project I have examined the quality of ground water in the urban city, Visakhapatnam. Several samples were collected from different location in the Visakhapatnam city for measurement of nutrients, pH and total alkalinity.
To evaluate the spatial variability of nutrient pollution in groundwater in the coastal city- Visakhapatnam.
Groundwater samples were taken from 10 locations in Visakhapatnam. Name of the locations are -
|Locations||Location Name||Latitude (in degrees)||Longitude (in degrees)|
|1||Chinnawaltair Netaji Street||17.724||83.331|
|2||Chinnawaltair Bazar Street||17.725||83.334|
|3||Babujinagar (near drain)||17.726||83.339|
|4||Gandhinagar Street, Peddawaltair||17.732||83.336|
|5||Jalarinda Yindda Pealem||17.739||83.342|
|6||MVP Sector 9||17.744||83.343|
|7||Adarsh nagar (near temple)||17.735||83.333|
|8||Adarsh nagar, Peddawaltair||17.737||83.332|
|10||Palikiwar Street (near fish market)||17.734||83.336|
MATERIAL AND METHODS
In this project, 10 groundwater samples were taken each for nutrient analysis (Nitrate, phosphate and silicate) and measurement of pH and total alkalinity from 10 different stations as stated above.
- Samples for nutrient analysis were taken in 200ml plastic bottles
- Samples for measuring pH and total alkalinity were taken in 60ml glass bottles.
- pH and total alkalinity were measured using pH electrode and Gran titration technique respectively with Titrando autotitrator.
- Nutrients (nitrate, phosphate and silicate) were measured using colorimetric technique using EcoLAB Insitu Nutrient Auto analyser.
- Silicate and phosphate concentrations were measured using SYSTEA µMAC-1000 autoanalyzers.
RESULTS AND DISCUSSION
pH of the Groundwater Samples
Spatial variations in pH of groundwater in 10 locations of Visakhapatnam is shown in Figure 2. The value of pH ranges from 5.934 (Dalaivari Street) to 6.84 (Jalarinda Yindda Pealem). Most of the groundwater samples are either neutral or slightly acidic. Although there are no health based drinking water standards for pH, water with pH value away from the neutral can lead to high concentrations of metals for which the water can become unsuitable for drinking. Groundwater sample with the lowest pH value (5.934) is acidic and therefore can have high concentrations of metals. The value of pH in groundwater depends on soil and rock in contact, for example reactions between groundwater and sandstones result in pH values about 6.5 to 7.5, whereas groundwater reacting with limestone can have pH values as high as 8.5 . Low pH values also induce high silica dissolution. Predicting the nature of aquifer rock from only pH data would be premature so I will discuss this after discussing the silicate data of the samples.
|1||Chinnawaltair Netaji Street||6.061|
|2||Chinnawaltair Bazar Street||6.349|
|3||Babujinagar (near drain)||6.283|
|4||Gandhinagar Street, Peddawaltair||6.108|
|5||Jalarinda Yindda Pealem||6.84|
|6||MVP Sector 9||6.508|
|7||Adarshnagar (near temple)||6.5|
|10||Palikiwar Street (near fish market)||6.334|
Total Alkalinity of the Groundwater Samples
Spatial variations in total alkalinity of groundwater in 10 locations of the study area is shown in Figure 3. Total alkalinity (TA) ranges from 2616 μM (Adarshnagar, Pedda waltair) to 30171 μM (Dalaivari Street). TA values of all the locations are very high (above the permissible level), so all the samples can be considered as Hard water. High alkalinity also indicates higher amount of carbonate and bicarbonate dissolution.
|stations||Station Name||Total alkalinity|
|1||Chinnawaltair Netaji Street||3970.59|
|2||Chinnawaltair Bazar Street||5621.60|
|3||Babujinagar (near drain)||7964.39|
|4||Gandhinagar Street, Peddawaltair||4179.61|
|5||Jalarinda Yindda Pealem||10374.82|
|6||MVP Sector 9||8771.33|
|7||Adarshnagar (near temple)||5644.80|
|10||Palikiwar Street (near fish market)||8702.26|
Nitrate (NO3) Concentration in the Groundwater Samples
Spatial variation in NO3 concentration (µM) of the groundwater samples in 10 locations are shown in Figure 4. NO3 conc in the samples range from 65.81 µM (Adarshna) to 2108 µM (Jalarinda Yindda Pealem). NO3 conc(µM) of all the samples are above the permissible level except the sample from Adarshnagar, Peddawaltair. The permissible level of NO3 in drinking water is 10mg/l (620 µM). So it is advisable not to drink these water without proper purification. Excessive high concentration of NO3 in drinking water may cause ‘Blue baby Syndrome’ (in which the ability of blood to transport oxygen is impaired). Nitrogen pollution in groundwater has some indirect impact also. When groundwater with high NO3 conc mixes with sea water (Submarine Groundwater Discharge) it supplies excessive nitrogen to sea water and eventually affects coastal plankton dynamics. The source of this excessive NO3 in groundwater can be diverse. Improper disposal of industrial waste, sewage sludge disposal and excessive use of nitrogen containing fertilizers in agriculture. High amount of bacterial activity in groundwater also enhances the amount of NO3 (because bacteria can transform NH4 to NO3).
|stations||Station Name||NO3 conc(µM)|
|1||Chinnawaltair Netaji Street||1070.0|
|2||Chinnawaltair Bazar Street||1089.0|
|3||Babujinagar (near drain)||2036.1|
|4||Gandhinagar Street, Peddawaltair||730.5|
|5||Jalarinda Yindda Pealem||2108.5|
|6||MVP Sector 9||1610.7|
|7||Adarshnagar (near temple)||1303.8|
|10||Palikiwar Street (near fish market)||724.0|
Phosphate Concentration (µM) in the Groundwater Samples
Spatial variations in PO4 conc (µM) of the groundwater samples in the study area is represented in Figure 5. PO4 concentration in the groundwater samples range from 0.73µM (Babujinagar) to 5.39µM (Jalarinda Yindda Pealem). PO4 conc in most of the samples is within the permissible limit except the sample from Jalarinda Yindda Pealem. High PO4 concentration in groundwater usually indicate contamination from fertilizer or sewage systems. High PO4 can also promote excessive algae growth depending on N:P ratio.
|stations||Station Name||PO4 conc(µM)|
|1||Chinawaltair Netaji Street||0.83|
|2||Chinawaltair Bazar Street||1.12|
|3||Babujinagar (near drain)||0.72|
|4||Gandhinagar Street, Peddawaltair||1.11|
|5||Jalarinda Yindda Pealem||5.38|
|6||MVP Sector 9||1.72|
|7||Adarshnagar (near temple)||1.45|
|10||Palikiwar Street (near fish market)||2.53|
Silicate Concentration(µM) in the Groundwater Samples
Silicate is a non-pollutant chemical constituent in groundwater and it comes from breakdown of silicate minerals. So silicate concentration in groundwater increases with increasing interaction with silicate rocks. There is also a direct correlation between silicate content in groundwater and age and depth of the aquifer. Spatial variation in Silicate concentration of groundwater in the study area is shown in Figure 5. Silicate concentration ranges from 51.0 (Dalaivari Street) to 567.4 (Palikiwar Street). This varying silicate values indicate varying lithology of the area. Places with high silicate concentration might have more siliceous rocks and places with low silicate concentration and high alkalinity (high carbonate dissolution) may have more carbonaceous rock. Also low pH promotes high silica dissolution. Also groundwater samples with high silicate conc may be coming from a older and deeper aquifer (Palikiwar Street-567.4) and groundwater samples with low silicate conc are may be ascending from a shallower level and relatively younger aquifer (Dalaivari Street-51.0)
|stations||Station Name||Silicate conc(µM)|
|1||Chinawaltair Netaji Street|
|2||Chinawaltair Bazar Street||79.4|
|3||Babujinagar (near drain)|
|4||Gandhinagar Street, Peddawaltair||55.0|
|5||Jalarinda Yindda Pealem||134.5|
|6||MVP Sector 9||237.4|
|7||Adarshnagar (near temple)||277.1|
|10||Palikiwar Street (near fish market)||567.3|
After studying the spatial variations in pH, Total alkalinity and nutrients (Nitrate, Phosphate and Silicate) of groundwater in 10 locations of the coastal city Visakhapatnam, following conclusions can be made
- Overall the groundwater of the locations are neutral to slightly acidic.
- Groundwater in most of the locations are corrosive (hard water) because of high alkalinity.
- Most of the samples are showing excessively high concentration of NO3 which implies the groundwater is highly polluted (Nitrogen pollution) and it is recommended not to intake that water directly. This Nitrogen polluted groundwater has some bad impact on marine ecosystem as well. If this groundwater (with high amount of nutrient) mixes with sea water it can supply excessive nutrients to the sea water and affect the coastal plankton dynamics.
- PO4 concentration is within permissible range in most of the locations.
- Silicate is a non-pollutant constituent and silicate content varied depending on geology of the area
- Todd Keith David, Mays.W Larry. Groundwater Hydrology
It is my great pleasure to acknowledge all the persons from whom I received considerable help in the successful completion of this project. The most important acknowledgement goes to Dr VVSS Sarma under whose supervision I have done this project. Moreover, I want to thank all the project assistants in NIO, Visakhapatnam for their constant support during my internship project. I would also like to thank Aditi Sharma (who has also worked under Dr VVSS Sarma) for her cooperation and constant help in this internship project.