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2.2 MATERIALS AND METHODS
2.2.3 Water samples
2.2.3.1 Physicochemical characterization
All physicochemical parameters were analysed according to standard operating procedures (APHA, ASTM, EPA). Samples were stored at 4°C for further analyses.
2.2.3.1.1 pH
pH for water samples was recorded at the time of sampling with a pH electrode from Wagtech Potkait, water analyser portable kit.
2.2.3.1.2 Electrical conductivity
EC for water samples was recorded at the time of sampling with an EC electrode from Wagtech Potkait, water analyzer portable kit. EC was measured in µScm-1.
2.2.3.1.3 Turbidity
Turbidity was checked at the time of sample collection with a turbidity meter (transparency tube) from Wagtech Potkait, water analyzer portable kit. Turbidity was measured in NTU (Nephelometric Turbidity Units).
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2.2.3.1.4 Nitrate
Nitrate (NO3-) was estimated by Phenol Disulfonic Method (APHA). Nitrate reacts with phenol disulfonic acid to form a nitro-derivative which in alkaline medium develops a yellow colour. Absorbance for the yellow colour was recorded at 410 nm in Cary 100 UV − Visible spectrophotometer. Nitrate was calculated from a standard curve of absorbance versus concentration of KNO3 solution ranging from 0 mg/L to 1 mg/L at an interval of 0.1 mg/L.
2.2.3.1.5 Ammonia
Ammonia was estimated by Micro Phenate Method (Clesceri, 1998; APHA) using sodium nitroprusside. Presence of ammonia was confirmed by development of an intensely blue compound known as indophenol, as a result of reaction between ammonia, hypochlorite, and phenol catalyzed by sodium nitroprusside. Absorbance for blue coloration was measured at 640 nm in Cary 100 UV − Visible spectrophotometer.
Ammonia was calculated from a standard curve of absorbance versus concentration of NH4Cl solution ranging from 0.1 mg/L to 1 mg/L at an interval of 0.2 mg/L.
2.2.3.1.6 Sulphate
Sulphate (SO42-) was estimated by Turibidimetric Method (APHA). SO42- is precipitated in the form of Ba2SO4 by adding BaCl2 in acidic medium (HCl).
Concentration of sulphate was determined from the absorbance of Ba2SO4 measured at 420 nm in Cary 100 UV − Visible spectrophotometer. SO42-
was calculated from a
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standard curve of absorbance versus concentration of Na2SO4 solution ranging from 0 mg/L to 40 mg/L of SO42-mg/L at an interval of 5 mg/L.
2.2.3.1.7 Phosphate
Phosphate (PO43-) was estimated by Ammonium Molybdate Method (APHA). All forms of phosphorus in water were dissolved into inorganic form by digestion with concentrated HClO4 – HNO3. The phosphate released was colorimetrically measured in presence of SnCl2 as an indicator, at 690 nm in Cary 100 UV − Visible spectrophotometer. The concentration of phosphorus was calculated from a standard curve of absorbance versus concentration of K2HPO4 solution ranging from 0.5 mg/L to 5 mg/L of PO43-
– P mg/L at an interval of 0.5 mg/L.
2.2.3.1.8 Fluoride
Fluoride (F-) was estimated by SPADNS Method (APHA). SPADNS [2−(parasulfophenylazo)−1,8−dihydroxy−3,6−naphthalene disulfonate] and zirconyl chloride octahydrate (ZrOCl2.8H2O) together form an acid zirconyl−SPADNS reagent known as zirconium-dye lake. F- reacts with the zirconium-dye lake, dissociating a portion of it into a colourless complex anion (ZrF62-
) and the dye. As the amount of F- increases, the colour (initially reddish orange colour) produced becomes progressively lighter. Colorimetric absorbance was measured at 570 nm in Cary 100 UV − Visible spectrophotometer. F– was calculated from a standard curve of absorbance versus concentration of NaF solution ranging from 0.1 mg/L at 1.0 F– mg/L at an interval of 0.1 mg/L.
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2.2.3.1.9 Chloride
Chloride (Cl-) was estimated by Argentometric Method (Mohr’s Method) (APHA). Cl- reacts with AgNO3 to form a slightly white precipitate of AgCl. In presence of chromate as an indicator, free Ag+ react with chromate to form reddish brown complex detected by titration against AgNO3. Cl- concentration was obtained in mg/kg.
2.2.3.1.10 Dissolved oxygen
Dissolved oxygen (DO) was estimated after water sampling with a DO electrode (Make: Systronics). DO concentration was obtained in mg/L.
2.2.3.1.11 Chemical oxygen demand
Chemical oxygen demand (COD) was estimated by Titrimetric Method (EPA). Organic and oxidizable inorganic substances in water samples were oxidized by potassium dichromate in 50% sulfuric acid solution at a reflux temperature of 150°C. Ag2SO4 was used as a catalyst and Hg2SO4 was added to remove chloride interference. The excess Cr2O72- was titrated with standard (NH4)2 Fe(SO4)2.·6H2O, using orthophenanthroline ferrous complex or ferroin as an indicator, color change visible as blue-green to a reddish hue at the end point.
2.2.3.1.12 Trace elements: Na, Ca, Mg and K
Trace elements (Na, K, Mg and Ca) for water samples were analysed in Flame Photometer (Make: Systronics), calibrated with standard reference material. The concentration of trace elements was obtained in mg/L.
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2.2.3.1.13 Sodium Adsorption Ratio
Sodium adsorption ratio (SAR) is the proportion of sodium to Ca and Mg that can affect their availability to agricultural crops. SAR is often used to express the relative activity of Na ions in exchange reactions with soil. Greater the SAR value, the less suitable is the water for irrigation. SAR evaluates sodium hazard in relation to Ca and Mg concentrations. SAR was calculated as:
SAR
The formula for SAR calculation was given by Richards (1954). He classified the water to be used for irrigation with SAR index less than 10 as excellent, between 10
− 18 as good, 18 − 26 as fair and greater than 26 as of poor quality (Table 2.1).
2.2.3.1.14 Soluble Sodium Percentage
Soluble Sodium Percentage (SSP) is referred to as Na percentage. Higher value of SSP indicates soft water whereas lower value of SSP indicates hard water. SSP was calculated as:
SSP=
The formula for SSP calculation was given by Todd (1980). In general, values of SSP <50 indicate good quality of water and higher values (>50) indicate that the water is unsafe for irrigation purpose (Table 2.1).
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2.2.3.1.15 Kelly’s Ratio
Kelly’s ratio (KR) is another important water quality indicator that check suitability of water for irrigation. Na is measured against Ca and Mg was considered by Kelly (1957) to calculate this parameter. Kelly’s Ratio was calculated as:
KR=
The formula for KR calculation was given by Kelly (1963). The Kelly’s ratio of unity or <1 is indicative of good quality of water for irrigation purpose, values >1 is suggestive of unsuitability of water for agricultural activities due to alkali hazards (Kumar et al., 2014) (Table 2.1).
Table 2.1 The critical limits of water suitability for irrigation purpose (Source:
Adapted from Kumar et al., 2014)
Parameters Range Water Class
Sodium Absorption ratio
10 Excellent
18 Good
18-26 Doubtful
26 Unsuitable
Soluble Sodium Percentage
<50 Good
>50 Unsuitable
Kelly’s Ratio
<1 Suitable
1-2 Marginal
suitable
>2 Unsuitable