Surveillance of the Water Quality Ascertainment of Vellayani Lake

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Surveillance of the Water Quality Ascertainment of Vellayani Lake

Sruthi S B1, Akhila S R1, Vidhya Varghese1, 1B. Tech student, Department of Civil Engineering, John Cox Memorial CSI Institute of Technology Trivandrum, Kerala- 695011, India

Professor N Vijayan2

2Head of the Department, Department of Civil Engineering,

John Cox Memorial CSI Institute of Technology Trivandrum, Kerala- 695011, India

Abstract- Water, the magical substance from which all life springs forth, is essential to the very existence of every life form on earth. The role of water in the living organism has not changed since lifes first creation in salt water billions of years ago. Pure water is elixir of life. Vellayani Lake is the second largest fresh water lake in Kerala. It is parallel to coast. The lake is facing degradation due to anthropogenic activities such as diverting human waste, soil erosion due to distribution of vegetables and agricultural wastes pose a great threat to the usefulness of the water. This study ascertained the quality of water in Vellayani lake by using Swamee and Tyagi Water Quality Index method and Weighted Arithmetic Water Quality Index method. From the study, it is found that the water is polluted and treatment is required.

Keywords- Water, Water quality index, Swamee and Tyagi method, Weighted Arithmetic method.

  1. INTRODUCTION

    Water as we know it very-very important and vital for our survival on this blue planet. An adequate supply of water alone would not guarantee our well-being as the quality of water would be a serious measure. Nowadays lakes, streams, rivers, oceans, and other water bodies are seriously polluting due to the addition of large amounts of materials to the water such as sewage, agricultural wastes, industrial wastes, domestic wastes etc.

    Water quality is a term used to describe the chemical, physical and biological characteristics of water, usually in respect to its suitability for a particular purpose. Although scientific measurements are used to define water quality, its not a simple thing to say that this water is good, or this water is bad." After all, water that is perfectly good to wash a car with may not be good enough to serve as drinking water. When the average person asks about water quality, they probably want to know if the water is good enough to use at home, to play in, to serve in a restaurant, etc., or if the quality of our natural waters is suitable for aquatic plants and animals.

  2. MATERIALS AND METHODS

    1. Study Area

      Vellayani lake, the largest freshwater lake in Thiruvananthapuram, Kerala, is located between latitude 8°2490 – 8°2630 North and longitude 76°5908 – 76°5947 East [5]. The major sources of water in the lake are seasonal rains (southwest monsoon) and underground sprouts. It is linear in form, and nearly 4 km in areal extent. The area of the lake which was 750 Hectares in 1926, had been reduced to 397.5 Hectares by 2017. The area of wetlands around the lake has also changed as a result of development of agricultural land and construction. At present, the lake basin no longer discharges water via surface water courses. The canal at the north end of the lake, formerly its natural outlet, is at present discharging irrigation reflux into the lake. The climate of the Vellayani lake area is classified as hot tropical. The lake catchment includes several small towns, grassland, woodland and agricultural land used for row crops, paddies fig. 1.

      Eight sampling stations were chosen along the Vellayani Lake: fig. 2. Station 1, Vandithadam is subjected to boating activities, oil pollution and dumping of solid waste; Station 2, Agricultural college is the station subjected to pollution due to synthetic fertilizer management, and the use of pesticides; Station 3, Kakkamoola right is disturbed due to anthropogenic activities such as disposal of wastes, recreational activities, dredging; Station 4, Venganoor is subjected to human disturbance due to the presence of local people; Station 5, Kakkamoola left is disturbed due to disposal of personal care products and household chemicals; Station 6, Koliyoor is subjected to heavy infestation with water hyacinth, pollution and siltation; Station 7, Vavvamoola right is disturbed due to plastic materials and waste in contact with water; Station 8, Vavvamoola left is disturbed due to illegal discharges of waste.

    2. Sampling and method of analysis

    Water samples were collected directly in polyethylene bottles for a period of four months during January 2018 to April 2018 for analysis . The standard methods for examination of water was strictly followed [1]. The samples were analysed for selected nineteen parameters. Water temperature was measured using a high quality standard mercury- filled Celcius thermometer (±0.1

    ºC accuracy). pH were measured in the laboratory using a pH meter. Electrical conductivity of water was measured using conductivity meter. Parameters such as free Carbon dioxide, Total hardness, Total Dissolved Solids, Nitrate,

    Sulphate, Colour, Turbidity, Acidity, Alkalinity, Calcium, Magnesium, Chloride, Iron, Fluoride, E-coli and Coliform were estimated by standard laboratory procedures [7].

    Fig 1: Location of Vellayani Lake

    Fig 2: Location of eight sampling stations

    (Source: Google Map)

  3. WATER QUALITY INDEX (WQI)

    Water quality index (WQI) is valuable and unique rating to depict the overall water quality status in a single term that is helpful for the selection of appropriate treatment technique to meet the concerned issues. Water quality of any specific area or specific source can be assessed using physical, chemical, and biological parameters. The values of these parameters are harmful for human health if they occurred more than defined limits. Therefore, the suitability of water sources for human consumption has been described in terms of Water quality index (WQI), which is one of the

    ( Source: Brown et al., 1970)

    b)WEIGHTED ARITHMETIC WATER QUALITY INDEX

    Weighted arithmetic water quality index method classified the water quality according to the degree of purity by using the most commonly measured water quality variables. The method has been widely used and the calculation of WQI was made by using the following equation:

    most effective ways to describe the quality of water. Various WQI determination methods have been described here in.

    a) SWAMEE AND TYAGI WATER QUALITY INDEX

    WQI = qn×Wn

    where,

    (2)

    Swamee and Tyagi (2000) suggested a mathematical form that is free from eclipsing and ambiguity [4].

    qn = Quality rating of nth water quality parameter.

    Wn= Unit weight of nth water quality parameter

    =1

    I = (1-N+ where,

    -1/k)-k (1)

    The quality rating (qn) is calculated using the

    k = 0.4, a positive constant

    S = sub index value for ith water quality variable.

    The highest water quality index of water can receive is 1. Once overall WQI known, it can be compared against descriptor given in table 1

    Table 1: Water Quality Index ranges of Swamee & Tyagi WQI

    expression given in equation:

    qn = [(Vn Vid) / (Sn – Vid)] x 100

    where,

    Vn = Estimated value of nth water quality parameter at a given sample location.

    Vid = Ideal value for nth parameter in pure water. (Vid for pH = 7 and 0 for all other

    parameters)

    Sn = Standard permissible value of nth water quality parameter

    Very Bad

    Descriptor Word

    Numerical range

    0 – 0.25

    Bad

    0.26 0.50

    Medium

    0.51 0.70

    Good

    0.71 0.90

    Excellent

    0.91 1.00

    The unit weight (Wn) is calculated using the expression given in equation:

    Wn = k / Sn

    where,

    Sn = Standard permissible value of nth water quality parameter.

    k = Constant of proportionality and it is calculated by using the expression k = [1 /(1/ Sn = 1, 2. . . n)]

    Table 2: Water Quality Index ranges of Weighted Arithmetic WQI

    Sl. No

    WQI

    Status

    Possible usages

    1

    0 25

    Excellent

    Drinking, Irrigation and Industrial

    2

    25 50

    Good

    Domestic, Irrigation and Industrial

    3

    51 -75

    Fair

    Irrigation and Industrial

    4

    76 100

    Poor

    Irrigation

    5

    101 -150

    Very Poor

    Restricted use for Irrigation

    6

    Above 150

    Unfit for Drinking

    Proper treatment required before use

  4. RESULT AND DISCUSSION

    A detailed study is attempted from the results obtained after the laboratory analysis of water collected from the Vellayani Lake. These results are also compared with drinking water standards as per IS 10500-2012 [3].

    Table 3: Various water quality parameters of the lake water during January 2018

    Sl No

    Station point

    Unit

    P1

    P2

    P3

    P4

    P5

    P6

    P7

    P8

    1

    Colour

    Hazen/Pt.Co.Uni t

    29

    29

    29

    29

    37

    34

    34

    38

    2

    Turbidity

    NTU

    5.98

    4.92

    5.33

    6.05

    10.7

    7.38

    8.25

    9.96

    3

    pH

    6.20

    6.7

    6.72

    6.53

    6.94

    7.38

    7.26

    7.56

    4

    Electrical Conductivity

    µs/cm

    122.7

    126.4

    122.4

    123.7

    123.4

    126.6

    125.3

    127.7

    5

    Temperature

    C

    24.3

    24.3

    24.3

    24.3

    24.3

    24.3

    24.3

    24.3

    6

    Acidity

    mg/L

    9

    11

    7

    7

    5.5

    5.5

    4.7

    4.7

    7

    Alkalinity

    mg/L

    35

    37

    37

    29

    29

    34

    34

    35

    8

    Sulphate(as SO4)

    mg/L

    3.4

    3.4

    4.8

    3.9

    5.3

    5.9

    5.9

    6.1

    9

    Total Dissolved Solids(TDS)

    mg/L

    60.7

    63.4

    61.7

    62.1

    62.1

    60.9

    60.8

    62.1

    10

    Total Hardness as

    (CaCO3)

    mg/L

    29

    29

    25

    25

    25

    32

    31

    27

    11

    Calcium(Ca)

    mg/L

    7

    7

    7

    7

    7

    7.3

    7

    7

    12

    Magnesium(Mg

    mg/L

    2.32

    2.37

    1.39

    1.33

    1.37

    1.49

    2.56

    3.15

    13

    Chloride as (Cl)

    mg/L

    29

    32

    33

    33

    32

    34

    32

    34

    14

    Fluoride as(F)

    mg/L

    0.22

    0.24

    0.24

    0.23

    0.26

    0.26

    0.25

    0.26

    15

    Iron as(Fe)

    mg/L

    0.361

    0.301

    0.362

    0.314

    0.417

    0.45

    0.353

    0.413

    16

    Nitrate as(NO3)

    mg/L

    0.58

    0.609

    0.583

    0.59

    0.63

    0.45

    0.431

    0..47

    17

    Residual Chlorine(RC)

    mg/L

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    18

    Coliform

    MPN/100mL

    150

    1050

    250

    25

    1100

    470

    510

    980

    19

    E.coli

    MPN/100mL

    150

    1050

    150

    8

    48

    450

    490

    980

    Table 4: Various water quality parameters of the lake water during February 2018

    7

    Station point

    Units

    P1

    P2

    P3

    P4

    P5

    P6

    P7

    P8

    1

    Colour

    Hazen/Pt.Co.Units

    30

    30

    30

    30

    35

    40

    35

    40

    2

    Turbidity

    NTU

    6.39

    6.9

    6.97

    6.15

    7.56

    11.76

    8.69

    10.48

    3

    pH

    6.83

    6.87

    6.81

    6.94

    7.23

    6.96

    7.91

    7.89

    4

    Electrical Conductivity

    µs/cm

    123.1

    128.3

    124.9

    124.8

    127.8

    124.7

    126.4

    128.9

    5

    Temperature

    C

    25.5

    25.5

    25.5

    25.5

    25.5

    25.5

    25.5

    25.5

    6

    Acidity

    mg/L

    10

    12

    8

    8

    6

    6

    5

    5

    Alkalinity

    mg/L

    36

    38

    38

    30

    35

    30

    35

    36

    8

    Sulphate(as SO4)

    mg/L

    3.6

    3.6

    5

    4.2

    6.1

    5.6

    6.1

    6.3

    9

    Total Dissolved Solids(TDS)

    mg/L

    61.4

    64.2

    62.4

    62.5

    61.7

    62.2

    61.8

    63.4

    10

    Total Hardness as

    (CaCO3)

    mg/L

    30

    30

    26

    26

    33

    26

    32

    28

    11

    Calcium(Ca)

    mg/L

    8

    8

    8

    8

    7.4

    8

    8.2

    8.9

    12

    Magnesium(Mg)

    mg/L

    2.43

    2.43

    1.458

    1.458

    1.567

    1.458

    2.89

    3.45

    13

    Chloride as (Cl)

    mg/L

    30

    34

    34

    34

    36

    34

    33

    35

    14

    Fluoride as(F)

    mg/L

    0.24

    0.255

    0.25

    0.25

    0.28

    0.25

    0.27

    0.28

    15

    Iron as(Fe)

    mg/L

    0.377

    0.316

    0.387

    0.322

    0.498

    0.421

    0372

    0.491

    16

    Nitrate as(NO3)

    mg/L

    0.591

    0.615

    0.594

    0.608

    0.467

    0.644

    0.456

    0.498

    17

    Residual Chlorine(RC)

    mg/L

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    18

    Coliform

    MPN/100mL

    150

    1100

    150

    28

    580

    1100

    530

    1100

    19

    E.coli

    MPN/100mL

    150

    1100

    150

    11

    560

    53

    365

    1100

    Table 5: Various water quality parameters of the lake water during March 2018

    Sl No

    Station point

    Units

    P1

    P2

    P3

    P4

    P5

    P6

    P7

    P8

    1

    Colour

    Hazen/Pt.Counits

    30

    40

    30

    30

    40

    35

    35

    40

    2

    Turbidity

    NTU

    6.2

    6.53

    5.61

    5.08

    10.5

    7.56

    8.69

    7.98

    3

    pH

    6.93

    6.29

    6.89

    6.93

    6.97

    7.1

    6.92

    6.9

    4

    Electrical Conductivity

    µs/cm

    120.3

    131.4

    125.8

    125.8

    125.4

    126.7

    125.9

    129.4

    5

    Temperature

    C

    25.9

    25.9

    25.9

    25.9

    25.9

    25.9

    25.9

    25.9

    6

    Acidity

    mg/L

    4

    4

    6

    6

    6

    6

    7

    7

    7

    Alkalinity

    mg/L

    30

    30

    30

    30

    30

    33

    34

    36

    8

    Sulphate(as SO4)

    mg/L

    7

    6.4

    3.2

    4.4

    3.2

    4.3

    3.2

    3.9

    9

    Total Dissolved Solids(TDS)

    mg/L

    60.2

    65.6

    63

    62.8

    62.8

    62.3

    62.8

    64.7

    10

    Total Hardness as

    (CaCO3)

    mg/L

    34

    34

    24

    30

    44

    38

    37

    41

    11

    Calcium(Ca)

    mg/L

    9.6

    9.6

    8

    8

    8.8

    7.7

    8.9

    9.8

    12

    Magnesium(Mg)

    mg/L

    2.43

    2.43

    0.97

    2.43

    5.346

    1.89

    2.42

    3.78

    13

    Chloride as (Cl)

    mg/L

    36

    36

    32

    34

    36

    35

    33

    34

    14

    Fluoride as(F)

    mg/L

    0.26

    0.27

    0.26

    0.26

    0.265

    0.26

    0.28

    0.29

    15

    Iron as(Fe)

    mg/L

    0.36

    0.478

    0.35

    0.27

    0.396

    0.567

    0.46

    0.518

    16

    Nitrate as(NO3)

    mg/L

    0.48

    0.494

    0.48

    0.46

    0.47

    0.567

    0.46

    0.518

    17

    Residual Chlorine(RC)

    mg/L

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    18

    Coliform

    MPN/100mL

    460

    1100

    290

    11

    1100

    550

    477

    1100

    19

    E.coli

    MPN/100mL

    460

    1100

    42

    3

    1100

    540

    245

    1100

    Table 6: Various water quality parameters of the lake water during April 2018

    Sl no

    Station point

    Units

    P1

    P2

    P3

    P4

    P5

    P6

    P7

    P8

    1

    Colour

    Haze/Pt.Co.Unit s

    32

    33

    42

    35

    32

    32

    40

    42

    2

    Turbidity

    NTU

    6.4

    6.64

    5.85

    5.09

    10.98

    8.95

    9.54

    5.34

    3

    pH

    7.14

    6.58

    6.98

    7.94

    7.54

    6.86

    7.29

    7.93

    4

    Electrical Conductivity

    µs/cm

    122.6

    141.9

    128.5

    124.6

    128.4

    124.6

    127.5

    131.2

    5

    Temperature

    C

    25.8

    25.98

    25.7

    25.9

    25.9

    25.9

    25.9

    25.9

    6

    Acidity

    mg/L

    5

    8

    7

    6

    6

    5

    7

    10

    7

    Alkalinity

    mg/L

    32

    35

    36

    38

    39

    34

    36

    38

    8

    Sulphate(as SO4)

    mg/L

    7

    6.9

    6.8

    7.4

    6.5

    4.8

    5.68

    6.54

    9

    Total Dissolved Solids(TDS)

    mg/L

    62.5

    65.8

    63.5

    62.8

    62.8

    61.8

    62.4

    62.1

    10

    Total Hardness as (CaCO3)

    mg/L

    32

    32

    25

    28

    34

    28

    27

    32

    11

    Calcium(Ca)

    mg/L

    9

    9

    9

    98

    8

    7.9

    7.9

    8.9

    12

    Magnesium(Mg)

    mg/L

    2.54

    2.68

    1.984

    2.64

    2.54

    2.54

    2.51

    1.95

    13

    Chloride as (Cl)

    mg/L

    32

    34

    35

    34

    38

    35

    38

    37

    14

    Fluoride as(F)

    mg/L

    0.26

    0.294

    0.272

    0.294

    0.264

    0.28

    0.271

    0.247

    15

    Iron as(Fe)

    mg/L

    0.34

    0.367

    0.358

    0.384

    0.349

    0.42

    0.429

    0.381

    16

    Nitrate as(NO3)

    mg/L

    0.6

    0.652

    0.67

    0.674

    0.639

    0.55

    0.475

    0.48

    17

    Residual Chlorine(RC)

    mg/L

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    NIL

    18

    Coliform

    MPN/100mL

    160

    1100

    160

    30

    1100

    600

    570

    1100

    19

    E.coli

    MPN/100mL

    160

    1100

    160

    10

    56

    600

    465

    1100

    Swamee and Tyagi WQI method was used for calculating WQI. Eight parameters are used for calculating WQI by this method. The significant parameters considered are pH,

    Temperature, Total Dissolved Solids, Nitrate, Fluride, Coliform, Turbidity and Iron.

    Table 7: WQI using Swamee & Tyagi method

    STATION

    WQI of January 2018

    WQI of February 2018

    WQI of March 2018

    WQI of April 2018

    P1

    0.46

    0.44

    0.47

    0.45

    P2

    0.48

    0.47

    0.48

    0.49

    P3

    0.48

    0.45

    0.47

    0.48

    P4

    0.45

    0.44

    0.46

    0.44

    P5

    0.46

    0.46

    0.47

    0.46

    P6

    0.45

    0.45

    0.48

    0.46

    P7

    0.47

    0.45

    0.46

    0.46

    P8

    0.46

    0.45

    0.47

    0.48

    Monthly variations of WQI

    0.5

    0.49

    0.48

    0.47

    0.46

    0.45

    0.44

    0.43

    0.42

    0.41

    January

    February

    March April

    P1 P2 P3 P4 P5 P6 P7 P8

    Sampling Points

    WQI

    Fig 3: Monthly variation of WQI according to Swamee & Tyagi WQI

    Weighed Arithmetic WQI method is used for calculating WQI with the significant parameters. In this method, eight parameter is used for calculating WQI. The

    parameters used are Total Dissolved Solids, Iron, pH, Nitrate, Total Hardness, Chloride, Sulphate and Alkalinity.

    Table 4: WQI using Weighted Arithmetic method

    STATION WQI of January 2018 WQI of February 2018 WQI of March 2018 WQI of April 2018 P1 91.39 92.32 93.99 91.67

    P2 93.34 93.96 92.96 94.59

    P3 91.89 93.25 92.82 92.56

    P4 92.56 91.12 91.08 92.21

    P5 93.01 91.78 92.89 92.04

    P6 92.69 93.64 91.93 92.31

    P7 92.86 92.64 91.56 93.48

    WQI

    P8 92.05 91.74 92.58 93.21

    Monthly variation of WQI

    95

    94

    93

    92

    91

    90

    January

    February March

    April

    89

    P1

    P2

    P3

    P4

    P5

    P6

    P7

    P8

    Sampling Points

    Fig 4: Monthly variation of WQI according to Weighted Arithmetic method

    The monthly variations of various water quality parameters of the lake water during January 2018 to April 2018 are shown in Table 3, Table 4, Table 5 and Table 6. Colour varies from 29 Hazen unit to 38 Hazen unit in January 2018, 30 Hazen unit to 40 Hazen unit in February 2018, 30 Hazen unit to 40 Hazen unit in March 2018 and 32 Hazen unit to 42 Hazen unit in April 2018 which shows that intensity of colour exceeds the permissible limits which is 5 Hazen unit, due to the excessive growth of algae. The turbidity varies from 4.92 NTU to 9.96 NTU, 6.15 NTU to 11.76 NTU, 5.08

    NTU to 10.51 NTU and 5.09 NTU to 10.98 NTU in January 2018, February 2018, March 2018 and April 2018 respectively which indicates turbidity were above the desirable limit (1 NTU) for all the above said months due to the presence of dissolved salts in it. The pH varies from 6.2 to 8.45 in January 2018, 6.83 to 7.91 in February 2018, 6.93

    to 8.23 in March 2018 and 6.58 to 7.94 in April 2018 indicating that the water samples were almost neutral range of 6.5 to 8.5. pH is one of the most important sigle factor which influences aquatic life since most of the aquatic organisms are adapted to an average pH and do not withstand abrupt changes. The electrical conductivity varies from 122.4µs/cm to 127.7 µs/cm in January 2018, 123.1µs/cm to 128.9µs/cm in February 2018,120.3 µs/cm to 131.4µs/cm in March 2018 and 122.6µs/cm to 141.9µs/cm in April 2018. This seasonal variation in the values of conductivity is mostly due to increased concentration of salts because of evaporation, dilution resulted from precipitation brings down its values. Temperature for January 2018, February 2018 , March 2018 and April 2018 are 24C, 25.5C, 25.9C and 25.8C respectively which indicates that it is equal to the atmospheric temperature. The acidity varies from 4.7mg/L to 11mg/L in January 2018, 5mg/L to 12mg/L in February 2018, 4mg/L to 7mg/L in March 2018 and 5mg/L to 10mg/L in April 2018 indicating that the acidity is more higher in the month February 2018 as a result of seasonal rainfall. The low value of acidity in other months may be due to higher water temperature. The alkalinity is a measure of buffering capacity of water and is important for aquatic life in a fresh water system because it equilibrate the pH range that occur as a result of photosynthetic activity of plants in water. In the present study, the alkalinity varies from 29mg/L to 37mg/L, 30 mg/L to 38mg/L, 30mg/L to 36mg/L and 32mg/L to 39 mg/L in January 2018, February 2018 March 2018 and April 2018 respectively indicating that alkalinity of the lake water is within the desirable limit of 200mg/L. Total dissolved solids varies from 60.7mg/L to 62.1mg/L in January 2018, 61.4mg/L to 64.2mg/L in February 2018, 62.8mg/L to 65.6mg/L in March 2018 and 61.8mg/L to 65.8mg/L in April 2018 which shows that total dissolved solids concentration increases from January 2018 to April 2018 but the variations are within the permissible limit (500mg/L) for all the months. The Sulphate varies from 3.4 mg/L to 6.1mg/L in January 2018, 3.6mg/L to 6.1mg/L in February 2018, 3.2 mg/L to 6.4mg/L in March 2018 and 4.8mg/L to 7.4mg/L in April 2018. During the study period, the concentration of Sulphate does not showed marked difference, although low values were observed. The total hardness of the lake varies from maximum of 44mg/L to

    minimum of 25mg/L which shows that the water samples is within the permissible limit of 200mg/L. High values of hardness may be probably due to regular addition of sewage and detergents to the lake from nearby residential areas. The Calcium varies from 7mg/L to 7.3mg/L in January 2018, 7.4mg/L to 8.9mg/L in February 2018, 7.7mg/L to 9.6mg/L in March 2018 and 7.9mg/L to 9.8mg/L in April 2018 indicating that the water samples is within the desirable limit of 75mg/L. The maximum amount of Calcium was observed in pre-monsoon months and it may be due to shrinkage of water volume in those months. The Iron varies from 0.301mg/L to 0.417mg/L in January 2018, 0.316mg/L to 0.498mg/L in February 2018, 0.271mg/L to 0.567mg/L in March 2018 and 0.348mg/L to 0.429mg/L in April 2018 indicating that the water samples were slightly exceeds the permissible limit 0.3mg/L because of the chemicals and fertilizers discharged from the agricultural college nearby the lake. The fluoride varied from 0.22mg/L to 0.26mg/L in January 2018, 0.24mg/L to 0.28mg/L in February 2018, 0.26mg/L to 0.29mg/L in March 2018 and 0.26mg/L to 0.294mg/L in April 2018 shows that the fluoride concentration in the lake water is within the permissible limit 1mg/L.

    The Magnesium varies from 1.33mg/L to 3.15mg/L in January 2018, 1.458mg/L to 3.45mg/L in February 2018, 0.972mg/L to 5.346mg/L in March 2018 and 1.95mg/L to 2.68mg/L in April 2018 indicating that the magnesium concentration is higher in the month March 2018 and also concentration of Magnesium in the lake water is within the permissible limit 30mg/L. The decreased amount of Magnesium may occur when there is an abundance of diatoms. The Chloride varies from 29mg/L to 34mg/L in January 2018, 30 mg/L to 36mg/L in February 2018, 32mg/L to 36mg/L in March 2018 and 32mg/L to 38mg/L in April 2018 shows that concentration of Cloride increases from January 2018 to April 2018. The permissible limit of Chloride in water is 250mg/L. Nitrate varies from 0.431mg/L to 0.63mg/L in January 2018, 0.456mg/L to 0.644 mg/L in February 2018, 0.467mg/L to 0.567 mg/L in March 2018 and 0.48 mg/L to 0.674 mg/ Lin April 2018 which exceeds the permissible limit 45mg/L, that shows presence of organic matter. E.coli varies from 8 to 1050 in January 2018, 11 to 1100 in February 2018, 3 to 1100 in

    March 2018 and 10 to 1100 in April 2018 indicating that Vellayani Lake was infected heavily in all months. This is because of native peoples attach their domestic animals in the banks of the lake and thereby causing fecal contamination from domestic animals. Coliforms varies from 25 to 1100 in January 2018, 28 to 1100 in February

    2018, 11 to 1100 in March 2018 and 30 to 1100 in April 2018 indicating that Vellayani lake was polluted heavily in all months because of fecal contamination from animals and humans.

    From the results obtained from the above said methods for the months January 2018 to April 2018, it is clear that the most polluted location is P2 (Agricultural College) and the least polluted is P4 (Venganoor). P2 is heavily polluted and it is be due to the waste disposal from nearby Agricultural College.

  5. CONCLUSION

According to Swamee and Tyagi WQI method, the water quality index was found to be varying from 0.44 to 0.49. Based on the values the water is bad and treatment is required. As per Weighted Arithmetic method, water quality index is between 91.08 and 94.59 so the water is of poor quality. Hence water from these station points should be avoided for drinking purpose and can used for other purposes like irrigation.

ACKNOWLEDGMENT

The authors would like to express their gratitude to one and all who helped in doing this work.

REFERENCES

  1. APHA (2012) Standard methods for the examination of water and waste water. American Public Health Association Washington D.C.

  2. Brown, R.M., McClelland, N.I., Deininger, R.A. and Tozer, R.G., Water quality index-do we dare?, Water Sewage Works, 117(10). 339-343. 1970.

  3. Bureau of Indian Standards, Specification for drinking water. IS: 10500, New Delhi, India 2012.

  4. P K Swamee and A.Tyagi. Describing water quality with aggregate index. Journal of Environmental Engineering 2000.

  5. P.S.Harikumar. Water quality status of Thiruvananthapuram District, Kerala. Background paper, Research unit local self- government (RULSG), Centre for development studies, Thiruvananthapuram, February 2017.

  6. S.K Garg, A text book of Environmental Engineering. Water Supply Engineering: Environmental Engineering – Vol. I Published on: 2017.

  7. U. G. Abhijna. Monitoring and assessment of a eutrophicated coastal lake using multivate approaches. Global J. Environ. Sci. Manage, 2(3): 275-288, Summer 2016.

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