physico-chemical characteristics of idukki reservoirshodhganga.inflibnet.ac.in › bitstream ›...

Chapter - 3

PHYSICO-CHEMICAL CHARACTERISTICS OF IDUKKI RESERVOIR

3.1 Introduction

3.2 Materials and Methods

3.3 Results

3.4 Discussion

3.1 Introduction

Water resources are of critical importance to both natural ecosystem and human development. It is a vital factor of life and is considered as a precious compound of the biosphere. About 71% of earth’s surface is covered by water; but approximately 97% of it makes up the oceans. Only 2.7% of the total water is freshwater of which 1% is ice free water scattered in the rivers, tributaries, rivulets, streams, reservoirs, lakes, canals, tanks and ponds (Trivedy, 1988). The water bodies in India are found in different geographical and geological position. Usually the physico-chemical characteristics of water change from region to region, in a broad sense, sometimes within the region also. Therefore, qualities of water from these water bodies are not same and not always consumable or useful. So there is a need of serious characterization of water quality both physico-chemically and microbiologically before use. Water bodies are, in general, vulnerable to contamination due to their easy accessibility for disposal of various types of wastes. Water bodies play a major

Chapter 3

40 Studies on Physico-chemical charact eristics, Plankton diversity and I chthyofauna of Idukki reservoir, Kerala, India

role in assimilation of the municipal and many other waste waters constituting the constant polluting source and run-off from agricultural land, a seasonal phenomenon, largely affected by climate in the basin (Gundu, 2011).

A large number of streams and rivers in India have been impounded to store water for multipurpose beneficial uses like irrigation, fisheries, power generation and drinking water supply. Now-a-days, the ecology of many reservoirs is under stressed condition due to fast pace of development, deforestation, cultural practices and agriculture. These activities trigger the rate of sedimentation of the reservoir bed characterised by silt and organic suspended material which initiates the process of eutrophication at a very early stage and show a deterioration of habitat quality (Agarwal and Rajwar, 2010). Water quality can be defined as an ensemble of physical, chemical and biological (including bacteriological) characteristics of the given water (Straskraba and Tundisi, 1999). Water quality investigations are carried out to provide information on the health of water bodies and for developing strategies that help in better management of catchment and water resources.

The maintenance of a healthy aquatic ecosystem depends on the physico-chemical properties of water and the biological diversity. The main purpose of analysing physical, chemical and microbiological characteristics of water is to determine its nutrient status. Since, the water contains dissolved and suspended materials in various proportions, its physical and chemical characteristics differ along with its biological characteristics. The water quality is also affected by pollutants which act on elements existing in water such as dissolved oxygen or produce substances such as ammonia, nitrates, etc. It is not possible to understand biological phenomena fully without the knowledge of water chemistry as the limnobiological and limnochemical components of the ecosystem (Tiwari, 1992). The physico-chemical means are useful in detecting the effects of pollution on the water quality but changes in the trophic conditions of water are reflected in the biotic community structure

Physico-Chemic al Characteristic s of Idukki Reservoir

Studies on Physico- chemi cal charact eristics, Plankton diversity and I chthyofauna of Idukki reservoir, Kerala, India 41

including species pattern, distribution and diversity (Kaushik and Saxena, 1995). The freshwater sources in India are mainly contributing for augmenting the crop productivity in agriculture. Therefore, it has become obligatory to analyze at least the important water parameters when ecological studies on aquatic ecosystems are carried out. It is necessary to know the physico-chemical properties of water to study the rearing practices of the fish in water bodies (Jhingran, 1991). Water quality plays a big role in plankton productivity as well as the biology of the cultured organisms and final yields (Dhawan and Karu, 2002).

In India large number of studies on limnology of lentic water bodies have been carried out in past 30 years (Kant and Anand, 1978; Ahmed and Krishnamurthy (1990); Kulkarni et al., 1995; Kumar and Sharma, 2001; Shanthi et al., 2002; Nandan and Aher, 2005; Negi et al., 2006; Zuber, 2007; Narayana et al., 2008; Jawale and Patil, 2009; Haroon et al., 2010; Joseph and Yamakanamardi, 2011). As Kerala is blessed with 30 reservoirs, the investigations undertaken to assess the water quality of reservoirs were only few ones (Harikrishnan and Aziz, 1989; Thomas, 2002; Thomas et al., 2002; Radhika et al., 2004; Ray et al., 2004; Krishnan, 2008). In Idukki reservoir, Desa et al. (2009) detected only DO, chlorophyll, turbidity and temperature in May 2006 and May 2007. However, detailed water quality studies were not reported from Idukki reservoir after Khatri (1985). Therefore, the present work is an attempt to study some important physico-chemical parameters of Idukki reservoir to evolve the present status of the reservoir.

3.2 Materials and Methods

The details of collection of samples and analysis are illustrated in chapter 2.

Chapter 3


3.3 Results

In the three years of study, surface water showed a uniform pattern in the distribution of physico-chemical parameters studied. Significant seasonal and spatial variations were observed in the case of atmospheric temperature, water temperature, turbidity, electric conductivity, transparency, pH, chloride, calcium, magnesium, nitrate and sulphate where as the parameters such as dissolved oxygen, free CO2, total hardness, total alkalinity, total dissolved solids, COD, BOD, sodium, potassium, phosphate and iron were not showed much spatial variations in the reservoir. COD and BOD were not showed seasonal variation also. The mercury, cadmium, zinc and copper were found below traceable level. H2S was also not recorded in the reservoir during the period of study. The correlation analysis was carried out to check the possible relationship between relevant parameters.

3.3.1 Rainfall Monthly rainfall data of Idukki reservoir area collected from the Kerala

State Electricity Board (KSEB) at Cheruthoni (Idukki), during the study period is

presented in Fig. 3.1. Seasonwise analysis showed that the average rainfall in the

watershed of Idukki reservoir was found higher in the monsoon season

(652.87 mm) followed by postmonsoon (125.43 mm) and it was very low in

premonsoon period (83.21mm) (Table 3.1). In the first year of study (2007

February to 2008 January), the total annual precipitation was 3967.70 mm, which

decreased to 3000 mm in the second year (2008 February to 2009 January) and

slightly increased to 3370.30 mm in the third year (2009 February to 2010

January) (Table 3.2). Highest rain fall was recorded in the month of July 2007

(1155.60 mm) while the months of February 2007, January 2008, December 2008

and February 2009 recorded almost zero rainfall.



Fig.3.1 Monthly variations in the rainfall (mean) recorded at Idukki res ervoir

The fluctuations in the total rainfall during monsoon season was

recorded as 3155.50 mm in the first year of study, 2269.10 mm in the second

year, and 2409.80 mm in the third year (Table 3.2). The month of highest

rainfall recorded during monsoon was July 2007 (1155.60 mm) and the month

of lowest rainfall was September 2008 (404.60 mm). The fluctuations

recorded in postmonsoon were 539.80 mm, 334.80 mm and 630.50 mm

respectively in the first, second and third year of study. During the

postmonsoon period, October 2007 was the month of highest rainfall (419.30

mm) and January 2009 remained the month of lowest fall (9.20 mm). The total

rainfall recorded in the premonsoon of investigation period was 272.40 mm in

the first year, 396.1mm in the second year and 330 mm in the third year. In

premonsoon period, March 2008 was the month of the highest rain fall (230.50

mm) while May 2008 recorded the lowest rain fall (13.30 mm).

0

200

400

600

800

1000

1200

1400

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Tota

l rain

fall (

mm)

Feb '07-Jan '08 Feb '08-Jan '09 Feb '09-Jan '10

Chapter 3


Table 3.1 Physico-chemical characteristics (mean) of I dukki reservoir

Sl. No Parameters Premonsoon Monsoon Postmonsoon 1 Rainfall (mm) 83.21 652.87 125.43 2 Atmospheric temperature (oC) 31.69 25.80 28.56 3 Water temperature (oC) 29.19 24.14 26.90 4 Transparency (cm) 384.13 74.50 209.09 5 Turbidity (NTU) 0.01 1.46 0.99 6 Electrical conductivity (µS/cm) 55.56 29.74 44.38 7 TDS (ppm) 33.79 18.94 27.89 8 pH 7.87 7.03 7.48 9 D.O (mg/l) 7.09 8.44 7.65 10 Free CO2 (mg/l) 2.18 1.95 2.09 11 Total alkalinity (mg/l) 31.52 18.60 22.19 12 Chloride (mg/l) 9.61 7.13 7.83 13 Total hardness (mg/l) 10.76 6.79 8.24 14 Calcium (mg/l) 8.11 5.59 6.38 15 Magnesium (mg/l) 2.68 1.20 1.87 16 COD (mg/l) 3.17 3.08 3.10 17 BOD (mg/l) 0.56 0.47 0.49 18 Sodium (mg/l) 1.21 0.53 0.84 19 Potassium (mg/l) 0.75 0.64 0.61 20 Nitrate mg/l 0.02 0.11 0.07 21 Phosphate (mg/l) 0.01 0.00 0.02 22 Sulphate (mg/l) 0.013 0.000 0.003 23 Iron (mg/l) 0.013 0.000 0.006

Table 3.2 Details of the rainfall obt ained in Idukki reservoir during F eb.2007 to Jan.2010.

Season Month Feb '07-Jan '08 Feb '08-Jan '09 Feb '09-Jan '10 Premonsoon February 0 46.9 0 March 18.8 230.5 109.8 April 126.6 105.4 65.8 May 127 13.3 154.4 Total 272.4 396.1 330 Monsoon June 711.7 547.3 411.5 July 1155.6 656.2 1010.2 August 575.5 661 472.7 September 712.7 404.6 515.4 Total 3155.5 2269.1 2409.8 Postmonsoon October 419.3 287.8 306.6 November 71.5 37.8 246.5 December 49 0 59 January 0 9.2 18.4 Total 539.8 334.8 630.5 Grand Total 3967.70 3000.00 3370.30



3.3.2 Atmos pheric Temperature

The atmospheric temperature brings about interesting spatial and

temporal thermal changes in natural waters which manifest in setting up of

convection currents and thermal stratification. The seasonal variations in

atmospheric temperature of the 16 stations under study are presented in the

Fig. 3.2. ANOVA of atmospheric temperature showed significant difference

among stations (P < 0.05) and seasons (P < 0.05) (Appendix I, Table 1).

During the present investigation, the average of seasonal variations in

atmospheric temperature was 31.690C, 25.800C and 28.560C during

premonsoon, monsoon and postmonsoon respectively. High temperature was

recorded during premonsoon season whereas the low temperature was noted in

monsoon season in the reservoir (Table 3.1).

The average of 3 years study revealed that, the atmospheric temperature

in premonsoon season varied from 310C to 33.330C at all stations (Fig. 3.2).

The lowest temperature was recorded at stations 8 and 14 and high

temperature was at station 1. During the monsoon season, the average of

atmospheric temperature at all stations ranged from 250C to 270C. The mean

value of 250C was registered from station 13 and 270C was recorded from

stations 1 and 16. The atmospheric temperature recorded in postmonsoon

season was varied 27.50C to 29.830C with the lowest mean at station 13 and

highest value at station 1.

Chapter 3


Fig.3.2 Stationwise seasonal variations in the atmospheric t emperature (mean) recorded

from Idukki reservoir

3.3.3 Water Temperature

It is a well known fact that the water temperature directly as well as

indirectly influences many abiotic and biotic components of the aquatic

ecosystem. Many hydro-biological features, parameters such as density,

surface tension, viscosity, diffusion, solubility of gases, conductivity,

speciation of nutrient, salt, etc undergo changes with the change in

temperature. The seasonal variations in the water temperature of the surface

water of the 16 stations under study are presented in the Fig. 3.3. ANOVA of

water temperature showed significant difference among stations (P < 0.05) and

seasons (P < 0.05) (Appendix I, Table 2).

The seasonwise analysis showed that the mean temperature of the

surface water in the reservoir was highest during premonsoon period

(29.190C). The rise in the temperature during the premonsoon season declined

33.33

32.33

32.17

31.5

31.5

31.83

31.17

31 31.5

31.5

31.33

31.17 31.5

31 31.5 32

.67

27 26 26 25.5

25.5 26

.25

25.5

25.5

25.5

25.8

3

25.5

25.5

25 25.5

25.7

5

27

29.8

3

29 28.8

3

29 28.8

3

29.1

7

28.6

7

28.5

28.3

3

28 28 28 27.5

27.7

5

28.2

5

29.2

5

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Atm

osph

eric

tem

pera

ture

( 0 C

)

StationsPremonsoon Monsoon Postmonsoon



with the advent of the monsoon (24.140C). It was moderate during

postmonsoon season with the average of 26.900C (Table 3.1).

The seasonal mean temperature of water recorded at all stations of the

Idukki reservoir was ranged from 280C (station 14) to 30.50C (station 1)

during premonsoon season (Fig. 3.3). The mean value of surface water

temperature during the monsoon season was varied from 23.50C to 25.670C

with the lowest average at stations 11, 12 and 15 and the highest at station 1.

The average of water temperature in postmonsoon season was ranged from

25.830C at station 13 to 27.830C at station 1.

Fig.3.3 Stationwise seasonal variations in the wat er temperature (mean) recorded from Idukki reservoir

Analysis of coefficient of correlation of the pooled annual data of the

various stations under study indicated that there was a positive correlation

between water temperature and atmospheric temperature (r = 0.996) (Table 3.3).

30.5

29.8

3

29.5

29.1

7

28.8

3

29.7

5

29.7

5

29 29 28.4

2

28.7

5

28.7

5

29.2

5

28 28.5 30

25.6

7

24.7

5

24.2

5

24 23.7

5

24.2

5

23.7

5

24 24 24 23.5

23.5 24 24 23.5 25

.2527

.83

27 26.6

7

27 27 27.6

7

27.6

7

27 26.8

3

27 26.3

3

26.3

3

25.8

3

26.1

7

26.5 27

.5

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Wat

er te

mpe

erat

ure

(0 C)


Chapter 3


Tabl

e 3

.3 C

orre

latio

n an

alysis

of p

hysic

o-ch

emica

l par

amet

ers r

ecor

ded f

rom

Iduk

ki re

serv

oir

AT=

Atm

osph

eric

te

mpe

ratu

re

(o C),

WT=

Wat

er

tem

pera

ture

(o C

), TR

=Tra

nspa

renc

y (c

m),

TB=T

urbi

dity

(N

TU),

EC=E

lect

rical

co

nduc

tivity

(µS

/cm

),TD

S (p

pm),

pH,

D.O

(m

g/l),

CO

2= Fre

e C

O2

(mg/

l), T

A=

Tota

l al

kalin

ity (

mg/

l), C

l= C

hlor

ide

(mg/

l),TH

=Tot

al

hard

ness

(m

g/l),

Ca=

Cal

cium

(m

g/l),

Mg=

Mag

nesi

um (

mg/

l), C

OD

(m

g/l),

BO

D (

mg/

l), N

a=So

dium

(m

g/l),

K=P

otas

sium

(m

g/l),

N

O3=N

itrat

e (m

g/l),

PO

4=Pho

spha

te (

mg/

l), S

O 4=Sul

phat

e (m

g/l),

Iron

(mg/

l) .



3.3.4 Transparency

The seasonal variations in transparency at the various stations studied

are recorded in Fig. 3.4. ANOVA of transparency is depicted in Table 3

(Appendix I), which revealed significant difference among stations (P < 0.05)

and seasons (P < 0.05).

The mean seasonal variation of transparency showed the highest

transparency values during premonsoon season and lowest during rainy season

(monsoon). The mean value of water transparency in summer (premonsoon)

was 384.13 cm and that in the monsoon was 74.50 cm. The mean transparency

was measured as 209.09 cm during postmonsoon season (Table 3.1).

Fig.3.4 Station wise seasonal variations in t he transparency (mean) recorded from Idukki reservoir

The transparency recorded in the 3 years of study at all stations varied

from 355.5 cm to 400 cm in premonsoon period with the lowest average at station

1 and the highest at stations 11, 12 and 13 (Fig. 3.4). The average transparency

in monsoon season was ranged from 60 cm (station 1) to 85 cm (station 10).

355.

5 380 39

0

365

370.

5 390

382.

5

370 39

0 395 400

400

400

385

392.

5

380

60

75 80 72.5

65

80 70 65

80 85 72.5 80 80 82 75 70

170.

5 200 205 210 22

0

205

200

185.

5

200 22

5

216

220 225

230 235

198.

5

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Tran

spar

ency

(cm

)


Chapter 3


During postmonsoon season, station 15 recorded the highest average transparency

(235 cm) and station 1 marked the least seasonal mean (170.5 cm).

3.3.5 Turbidity

Turbidity in natural waters is caused by suspended matter like clay, silt,

organic matter, phytoplankton and other microscopic organisms. It is actually

the expression of optical property in which the light is scattered by the

suspended particles present in water. The temporal and spatial variations in

turbidity recorded at the 16 different stations during the study are given in the

Fig. 3.5. ANOVA of the turbidity is given in Table 4 (Appendix I) which

showed significant difference among stations (P < 0.05) and among seasons (P

< 0.05). Monsoon season registered significantly higher turbidity values (1.46

NTU), compared to postmonsoon (0.99 NTU) and premonsoon season (0.01

NTU) in the current study (Table 3.1).

Fig. 3.5 shows the average turbidity recorded at all stations during

premonsoon season. It varied from 0 NTU (stations 1, 2, 4, 9, 10, 12, 13, and

14) to 0.03 NTU (station 16). During monsoon season, the turbidity was found

comparatively high and the highest average of 1.97 NTU was observed at

station 1 and the lowest of 0.97 NTU registered at station 10. The values

ranged from 0.27 NTU to 1.30 NTU in postmonsoon season with the lower

value at station 10 and higher at station 1.

Turbidity showed a negative correlation with transparency (r = - 0.992)

(Table 3.3).



Fig.3.5 Stationwise seasonal variations in the turbidity (mean) recorded from Idukki reservoir

3.3.6 Electrical Conductivity (EC)

Electrical conductivity is a numerical expression of ability of an aqueous

solution to carry electric current. The seasonal mean of the conductivity values

recorded during the entire period of observation in the reservoir waters are

illustrated in Fig.3.6. Significant difference was recorded in ANOVA among

stations (P < 0.05) and seasons (P < 0.05, Appendix I, Table 5).

A comparison of the average electrical conductivity observed at

different seasons is given in Table 3.1. The highest average seasonal value of

conductivity recorded in the study area was during premonsoon season (55.56

µS/cm) and the minimum conductivity was recorded during the monsoon

season (29.74 µS/cm), while the moderate value (44.38 µS/cm) recorded in

postmonsoon season.

Among stations, premonsoon mean values were varied from 49.23 to

62.20 µS/cm with higher value at station 13 and lower value at station 4 (Fig.

3.6). The variation of EC during monsoon was ranged from 19.87 µS/cm

0 0 0.01

0 0.02

0.01

0.01 0.02

0 0 0.02

0 0 0 0.02

0.03

1.97

1.73

1.33 1.37 1.

47

1.47 1.

6

1.9

1.2

0.97

1.3

1.17

1.37 1.

47

1.33

1.77

1.3

1.12

1.1

1.1

0.97

1.17 1.2 1.23

0.37

0.27

0.73

0.67

1.2 1.

27

0.97

1.2

00.25

0.50.75

1

1.251.5

1.75

22.25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Turb

idity

(NTU

)

Stations Premonsoon Monsoon Postmonsoon

Chapter 3


(station 1) to 40.13 µS/cm (station 9) and the post monsoon averages were

ranged between 39.63 µS/cm at station 11 and 50.93 µS/cm at station 6.

The coefficient of correlation of the annual pooled data of the physico-

chemical parameters illustrated positive correlation between electrical

conductivity and atmospheric temperature (r = 0.993) and water temperature (r

= 1.00). Electrical conductivity was negatively correlated with turbidity (r = -

0.962) (Table 3.3).

Fig.3.6 Stationwise seasonal variations in t he electrical conductivity (mean) recorded

from Idukki reservoir

3.3.7 Total Dissolved Solids (TDS)

Total dissolved solids are simply the sum of cation and anion

concentrations expressed in mg/l. The seasonal mean variations in the total

dissolved solids (TDS) of water of the 16 stations studied are shown in Fig.

3.7. Table 6 (Appendix I) shows the ANOVA of total dissolved solids where

significant difference was noticed among seasons (P < 0.05) but insignificant

difference was observed among stations (P > 0.05).

58 56.1

7

51.6

7

49.2

3

59.0

7 61.9

3

53.8

3

51.5

61.3

7

55.2

3

52.1

7

59.4

3 62.2

52.8

7

51.0

3

53.2

7

19.8

7 26 26.6

7 30.8

29.0

7

26.7

7

24.8 27

.03

40.1

3

34.5

3

29.2

3

29.7

3

38.9

3

29.6

27.1

3

35.5

342.1

3 46.5

3

44.6

3

40.0

3 45.3

50.9

3

45.1 46

.33

47.9

43.7

3

39.6

3

41.6

7 46.6

39.7

46.5

3

43.4

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Elec

trica

l con

duct

ivity

(µ

S/cm

)




The average of 3 years study of TDS revealed that the total hardness in

the reservoir was found to be high in premonsoon season than postmonsoon

and monsoon. The average values of TDS were recorded as 33.79 ppm, 27.89

ppm and 18.94 ppm during premonsoon, postmonsoon and monsoon season

respectively (Table 3.1).

Among stations, mean TDS value varied from 25.75 ppm at station 4 to

39.18 ppm at station 6 in premonsoon season (Fig.3.7). During monsoon

season the mean value of TDS varied from 11.62 ppm (station 2) to 26.08 ppm

(station 9), whereas in postmonsoon season it was ranged between 22.90 ppm

at station 14 and 31.58 ppm at station 6.

TDS displayed positive correlation with electrical conductivity (0.999)

and negative correlation with turbidity (r = -0.950) (Table 3.3).

Fig.3.7 Stationwise seasonal variations in the TDS (mean) recorded from Idukki reservoir

38.9

6

38.5

3

32.6

3

25.7

5

37.4

2

39.1

8

32.7

3

31.7

37.2

2

32.3

8

30.0

2

34.6

3

35.7

2

31.2

2

31.6

1

30.9

6

13.7

1

11.6

2

17.1

3 20.4

8

17.4

15.0

2

15.4

8 18.1

8

26.0

8

22.1

8

19.3

8

19.5

25.3

5

18.1

2 20.9 22

.43

29.2

2 31.2

8

29.8

7

24.9

28.8 31

.58

29.0

1

29.9

9

30.7

4

26.2

1

24.7

8

26.1

2

27.1

6

22.9

27.1

8

26.4

4

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

TDS

(ppm

)


Chapter 3


3.3.8 pH

pH is the measure of the intensity of acidity or alkalinity and measures

the concentration of hydrogen ions in water. The seasonal variations in pH at

the various stations studied are showed in Fig. 3.8. ANOVA of pH is depicted

in Table 7 (Appendix I) in which significant difference was noticed among

stations (P < 0.05) and seasons (P < 0.05).

The average of pH during the three years study at different seasons

showed the maximum pH during the premonsoon period (7.87), minimum

during the monsoon (7.03) and moderate during the postmonsoon (7.48). The

mean pH was above neutral at all the sampling stations during the study period

(Table 3.1).

The mean seasonal variation of pH at all stations varied from 7.50 to

8.15 in premonsoon with the highest average at station 11 and the lowest value

at station 1 (Fig. 3.8).

Fig.3.8 Stationwise seasonal variations in the pH (mean) recorded from Idukki res ervoir

7.5

7.7 7.

75

8.04

8.01

8 7.95

8.1

7.85 7.

9

8.15

8

7.9

7.8

7.78

7.55

7 7.05

7.05 7.

1

7 7 7.05 7.

1

7.02

7 7 7

7.1

7 7.05

7

7.15

7.5

7.5 7.

6

7.5 7.

6

7.55

7.7

7.5 7.

56

7.4 7.

45

7.38

7.3

7.48 7.

58

6.4

6.6

6.8

7

7.2

7.4

7.6

7.8

8

8.2

8.4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

pH

Stations

Premonsoon Monsoon Postmonsoon



The average of pH in monsoon season was ranged from 7.0 (stations 1,

5, 6, 10, 11, 12, 14 and 16) to 7.10 (stations 4, 8 and 13). During postmonsoon

season, station 1 recorded the lowest average pH (7.15) while station 8 showed

the highest seasonal mean (7.70).

3.3.9 Dissolved Oxygen (DO)

Oxygen dissolved in water, often referred to as DO, is a very important

parameter of water quality and is an index of physical and biological processes

going on in water. The seasonal variations in DO of the surface water of the 16

stations under study are presented in the Fig. 3.9. ANOVA showed significant

difference among seasons (P < 0.05) but it was insignificant among stations (P

> 0.05) (Appendix I, Table 8).

The present study revealed that seasonal average of DO was maximum

(8.44 mg/l) during monsoon season and minimum (7.09 mg/l) during premonsoon

season. In postmonsoon, the average of DO was 7.65 mg/l (Table 3.1).

During premonsoon season, the average DO at all stations was found to

be varied from 6.56 mg/l (station 12) to 7.68 mg/l (station 2) (Fig. 3.9)

whereas during monsoon the mean value recorded varied from 8.17 mg/l at

station 5 to 8.81 mg/l at station 4. During postmonsoon season, the mean value

ranged 7.25 mg/l to 8.01 mg/l with highest value at station 8 and lowest value

at station 12.

In the present study, the positive correlation between DO and turbidity

(r = 0.956) were observed but it was negatively correlated with atmospheric

temperature (r = -0.991), water temperature (r = -0.999) and transparency (r = -

0.985) (Table 3.3).

Chapter 3


Fig.3.9 Stationwise seasonal variations in the dissolved oxygen (mean) recorded from Idukki

reservoir

3.3.10 Free Carbon Dioxide (Free CO2)

Respiratory activity of aquatic organisms and the process of

decomposition are important sources of CO2 in water bodies. The seasonal

variations in free CO2 at the various stations studied are recorded in Fig. 3.10.

ANOVA of free CO2 is depicted in Table 9 (Appendix I) which showed

significant variations among seasons (P < 0.05) but insignificantly varied

among stations (P > 0.05).

The mean seasonal variation of free CO2 showed the highest value of

2.18 mg/l in premonsoon season and lowest value of 1.95 mg/l in monsoon

season. The mean value of free CO2 in postmonsoon period was 2.09 mg/l

(Table 3.1).

The free CO2 recorded in the study at all stations varied from 2.10 mg/l

to 2.27 mg/l in premonsoon period with the highest average at station 10 and

the lowest at stations 2, 12 and 14 (Fig. 3.10). The average free CO2 in

7.35 7.

68

6.96 7.

15

7.16

6.92 7.

28 7.62

6.95

6.82 7.

19

6.56 6.

86 7.22

6.91

6.86

8.33

8.18 8.

6 8.81

8.17 8.

63

8.6

8.33 8.46

8.23 8.

57

8.25 8.35 8.

6

8.57

8.33

7.4

7.97

7.7

7.27 7.

68

7.64 8 8.

01

7.83

7.47 7.

72

7.25 7.

66

7.6 7.

75

7.46

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Diss

olve

d ox

ygen

(mg/

l)




monsoon season was ranged from 1.47 mg/l at station 4 to 2.13 mg/l at

stations 1 and 16. During postmonsoon season, station 16 showed the highest

average of free CO2 (2.18 mg/l) and station 11 marked the least seasonal mean

1.97 mg/l.

Positive correlation between free CO2 and transparency (r = 0.979) and

pH (r = 0.996) were noticed. Free CO2 with turbidity (r = -0.945) and DO (r = -

0.999) were inversely related (Table 3.3).

Fig.3.10 Stationwis e seas onal variations in the free carbon dioxide (mean) recorded from Idukki

reservoir

3.3.11 Total Alkalinity

The alkalinity values observed at the 16 stations during the present

study are represented in the Fig. 3.11. ANOVA of the alkalinity showed

significant difference among seasons (P < 0.05), but insignificantly varied

among stations (P > 0.05) (Appendix I, Table 10).

2.17

2.1 2.

17 2.2

2.17 2.

2

2.17

2.13 2.17 2.

27

2.23

2.1 2.

2

2.1 2.

23

2.2

2.13

1.93 2.

07

1.47

2

1.73

2

1.8

2.03 2.

1

1.93 2 2

1.8

2

2.13

2.1

2.1 2.13

2.03 2.

13

2.13

2.1

2.07

2.07 2.1

1.97 2.

07

2.04

2

2.17 2.18

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Free

CO 2

(mg/

l)


Chapter 3


The average seasonal alkalinity recorded during the present study was

highest in premonsoon season with a highest value of 31.52 mg/l and the

minimum seasonal average was noted during monsoon (18.60 mg/l). The average

of alkalinity observed in postmonsoon season was 22.19 mg/l (Table 3.1).

During premonsoon season, the lowest average value of alkalinity

(28.33 mg/l) was registered at station 3 and the highest average of 34.33 mg/l

was observed at station 10 (Fig. 3.11). The average alkalinity value at all

stations during monsoon season varied from 15.67 mg/l at station 11 to 20.67

mg/l at station 1, while in postmonsoon period it was ranged from 20.67 mg/l

(stations 2 and 13) to 24.33 mg/l at station 6.

Total alkalinity exhibited a direct relationship with pH (r = 0.957) and

free CO2 (r = 0.927) whereas it was negatively correlated with turbidity (r = -

0.999) and DO (r = -0.939) (Table 3.3).

Fig.3.11 Stationwise s easonal variations in t he total alkalinit y (mean) recorded from

Idukki res ervoir

30 30.6

7

28.3

3 31.3

3

29.3

3 33

31.3

3

32.6

7

34 34.3

3

30.6

7

29.3

3 31.3

3

32.6

7

33.3

3

32

20.6

7

17.3

3

18 18.3

3 20

18.6

7

18.6

7

19.3

3

20 20

15.6

7 18 18.3

3

19

17.6

7

18

22

20.6

7

21.3

3 23.3

3

22.6

7 24.3

3

23

21.3

3

21.3

3 23 22.6

7

22.6

7

20.6

7

22 21.3

3

22.6

7

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Tota

l alk

alin

ity (

mg/

l)

Stations




3.3.12 Chloride

The salts of sodium, potassium and calcium contribute chlorides in

waters. The seasonal variations in the chlorides of the surface water of the 16

stations under study are presented in the Fig. 3.12. ANOVA of chloride

showed significant difference among stations (P < 0.05) and among seasons (P

< 0.05) (Appendix I, Table 11).

The analysis of 3 years study showed that the average chloride

concentration of the surface water in the reservoir was maximum (9.61 mg/l)

during premonsoon and minimum (7.13 mg/l) during monsoon. The moderate

value (7.83 mg/l) was observed in postmonsoon season (Table 3.1).

The seasonal mean value of chloride recorded at all stations of the

Idukki reservoir was ranged from 7.91 mg/l (station 16) to 10.39 mg/l (station

14) during premonsoon season (Fig. 3.12). During monsoon season, the

chloride concentration varied between 6.71 mg/l and 7.99 mg/l. The lowest

average in monsoon was registered at station 11 and the highest was at station

1. The mean value of chloride in postmonsoon period recorded varied from

7.08 mg/l at station 16 to 9.25 mg/l at station 1.

The coefficient of correlation of the annual pooled data of the physico-

chemical parameters showed positive correlation between chloride and

atmospheric temperature (r = 0.978), water temperature (r = 0.955) and

transparency (r = 0.985) (Table 3.3).

Chapter 3


Fig.3.12 Stationwise s easonal variations in t he chloride (mean) recorded from Idukki reservoir

3.3.13 Total Hardness

Hardness is the property of water which prevents the lather formation

with soap and increases the boiling point of waters. The seasonal mean

variations in the hardness of water of the 16 stations studied are shown in Fig.

3.13. ANOVA showed (Appendix I, Table 12) significant difference among

seasons (P < 0.05) but insignificant variations among stations (P > 0.05).

The 3 years study revealed that the mean of total hardness in the

reservoir was found to be high during premonsoon season than postmonsoon

and monsoon season. The average values of total hardness were recorded as

10.76 mg/l, 8.24 mg/l and 6.79 mg/l in premonsoon, postmonsoon and

monsoon season respectively (Table 3.1).

The seasonal mean hardness during premonsoon varied from 10.08

mg/l at station 14 to 12 mg/l at station 13 (Fig. 3.13). During monsoon season

the mean value of hardness at all stations varied from 6.0 mg/l (station 11) to

10.1

6

9.43

9.03

10.1

7

8.86

9.84

9.25

10.0

1

9.17

10.0

5

9.26

10.2

9

9.74 10

.39

10.1

8

7.917.99

7.43

6.93 7.03 7.

28

6.92 7.

13

7.03 7.2

6.85

6.71 7.

08 7.17 7.23 7.32

6.77

9.25

8.16

7.18

8.3

7.49 7.54 7.

92

7.29

8.19

8.01 8.12

8.15

7.28

7.23

8.07

7.08

0

2

4

6

8

10

12

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Chlo

ride

(mg/

l)




7.50 mg/l (station 16), whereas in postmonsoon season it was ranged between

7.67 mg/l at station 13 and 8.83 mg/l at stations 1 and 16.

Total hardness displayed positive correlation with free CO2 (r = 0.959)

and chloride (r = 0.996) but was negatively correlated with turbidity (r = -

0.999) and DO (r = - 0.968) (Table 3.3).

Fig.3.13 Stationwise s easonal variations in t he total hardness (mean) recorded from Idukki reservoir

3.3.14 Calcium

The temporal and spatial variations in calcium at the 16 different

stations during the period of study are given in the Fig. 3.14. ANOVA showed

significant difference among stations (P < 0.05) and seasons (P < 0.05,

Appendix I, Table 13).

The average values showed that premonsoon season registered higher

calcium concentration (8.11 mg/l), compared to the postmonsoon (6.38 mg/l)

and monsoon seasons (5.59 mg/l) in the current study (Table 3.1).

10.3

3

10.5 10.6

7

11.1

7

10.5 10.6

7

10.1

7 11.5

10.8

3

10.6

7

11.1

7

10.5

12

10.0

8

10.5 10

.83

7 7 6.83 7

6.5 7

6.5 6.58 7.

17

6.5

6

6.67

6.67 7 6.75 7.

5

8.83

8.5

8.33 8.

58

8

8.5

8.33

8 7.83

7.83 8.

33

8.33

7.67 7.83 8.

17 8.83

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Tota

l har

dnes

s (m

g/l)


Chapter 3


The values showing 3 years average of calcium at all stations during

premonsoon season was given in Fig. 3.14. It varied from 7.17 mg/l (station

12) to 9.17 mg/l (station 13). During monsoon season, the calcium was

comparatively low and the average ranged from 5.0 mg/l at stations 13 and 15

to 6.67 mg/l at station 16. The values ranged from 5.50 mg/l to 7.17 mg/l in

postmonsoon season with the lower value recorded at station 13 and the higher

at stations 6 and 7.

Positive correlation was revealed between calcium and atmospheric

temperature (r = 0.984), water temperature (r = 0.964), transparency (r =

0.990), free CO2 (r = 0.940), chloride (r = 1.00) and hardness (r = 0.998).

However, calcium showed negative correlation with turbidity (r = -1) and DO

(r = -0.951) (Table 3.3).

Fig.3.14 Stationwise s easonal variations in t he calcium (mean) recorded from Idukki reservoir

3.3.15 Magnesium

The seasonal variations in magnesium at the various stations studied

are recorded in Fig. 3.15. The ANOVA of magnesium is depicted in Table 14

7.99

8 8.17 8.

5

8

8.33

8.17 8.

33

8.17

7.5

8.67

7.17

9.17

7.75

7.67 8.

17

5.33 5.

83 6 5.83

5.5 6

5.67 6

5.5

5.17 5.

33

5.33

5

5.33

5

6.67

6.5

6.5 6.67

6.5

6.33

7.17

7.17

6.5

5.67 5.83

6.5

6.17

5.5 5.

83 6.17

7

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Calci

um (m

g/l)




(Appendix I) in which significant difference among stations (P < 0.05) and

seasons (P < 0.05) were recorded.

The mean of magnesium obtained in the study during different seasons

showed the highest values in premonsoon season (2.68 mg/l), lowest in

monsoon period (1.20 mg/l) and moderate during the postmonsoon (1.87 mg/l)

(Table 3.1).

The mean seasonal variation of magnesium at all stations varied 2.0

mg/l to 3.36 mg/l in premonsoon with the highest average at station 1 and the

lowest at station 7 (Fig. 3.15). The average of magnesium in monsoon season

was ranged from 0.58 mg/l (station 8) to 1.75 mg/l (station 15) and during

postmonsoon season, station 1 registered the highest average of magnesium

(2.33 mg/l) and station 7 marked the least seasonal mean (1.17 mg/l).

Fig.3.15 Stationwise s easonal variations in t he magnesium (mean) recorded from Idukki res ervoir

Magnesium showed positive correlation with atmospheric temperature

(r = 1.00), water temperature (r = 0.994), transparency (r = 1.00), pH (r =

3.36

2.5

2.5 2.

67

2.5

2.33

2

2.67

2.67

3.17

2.5

3.33

2.83

2.33

2.83

2.67

1.67

1.17

0.83

1.17

1 1

0.83

0.58

1.67

1.33

0.67

1.33

1.67

1.67 1.

75

0.83

2.33

2

1.67

2.08

1.67

1.33

1.17

1.5

2.17

2

1.83

2.17

2.17

2 2

1.83

0

0.5

1

1.5

2

2.5

3

3.5

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Mag

nesiu

m (m

g/l)


Chapter 3


0.995), free CO2 (r = 0.983), chloride (r = 0.981), hardness (r = 0.995) and

calcium (r = 0.987) were noticed. Magnesium with turbidity (r = -0.989) and

DO (r = -0.989) were inversely related (Table 3.3).

3.3.16 Chemical Oxygen Demand (COD)

Chemical oxygen demand (COD) is the measure of oxygen consumed

during the oxidation of oxidizable organic matter by a strong oxidizing agent.

The COD values observed at the 16 stations during the present study are

depicted in Fig. 3.16. ANOVA showed an insignificant difference among

stations (P > 0.05) and among seasons (P > 0.05), (Appendix I, Table 15).

Seasonal analysis of chemical oxygen demand (COD) in the reservoir

revealed that the highest value (3.17 mg/l) was noted in premonsoon season

and lowest (3.08 mg/l) in monsoon season. The average COD in postmonsoon

season was recorded as 3.10 mg/l (Table 3.1).

COD values recorded at all stations during premonsoon season varied

from 2.20 mg/l at station 14 to 4.10 mg/l at station 7 (Fig. 3.16). In monsoon

period it was ranged from 2.03 mg/l (station 2) to 3.67 mg/l at station 4.

During postmonsoon season, the lowest average value of COD (2.30 mg/l)

was registered at station 15 and the highest average of 3.83 mg/l was observed

at station 5.

COD exhibited a negative correlation with turbidity (r = -0.993) and

DO (r = -0.914) (Table 3.3).



Fig.3.16 Stationwise s easonal variations in t he COD (mean) recorded from Idukki reservoir

3.3.17 Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand (BOD) is the amount of oxygen utilized

by microorganisms to stabilize the organic matter and it is used as an index of

organic pollution in water. Figure 3.17 illustrates the BOD recorded at various

stations during the period of observation. Table 16 (Appendix I) gives the

ANOVA of the BOD in which insignificant difference were noticed among

stations (P > 0.05) and seasons (P > 0.05).

Seasonal analysis revealed that BOD values in the reservoir were more

during premonsoon season than postmonsoon and monsoon. The average

value of BOD levels were 0.56 mg/l, 0.49 mg/l and 0.47 mg/l during

premonsoon, postmonsoon and monsoon respectively (Table 3.1).

The 3 year average of BOD observed during premonsoon varied from

0.40 mg/l at stations 10 and 14 to 0.90 mg/l at station 4 (Fig. 3.17). In

monsoon season, it was ranged from 0.30 mg/l (station 5) to 0.70 mg/l (station

3.07

2.93 3.

1

2.6

3.77

3.17

4.1

3.53

3.13

3.5

2.9

2.77

3.57

2.2

3.23

3.17

2.33

2.03

3.23

3.67

3.07 3.

17

3

2.8

3.1 3.

37

3.33

3.17

3.57

3.23

3.1 3.17

2.47

2.87

3.2

3.17

3.83

2.8

2.53

3.6

3.33 3.

57

3.4

3.17

2.67

3.63

2.3

3.1

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

COD

(mg/

l)


Chapter 3


2). Seasonal mean BOD values ranged from 0.30 mg/l at stations 6 and 16 to

0.90 mg/l at station 1 during postmonsoon.

Positive correlation was recorded between BOD and COD (r = 0.997)

but a negative correlation observed with turbidity (r = -0.999) and DO (r = -

0.942) (Table 3.3).

Fig.3.17 Stationwise s easonal variations in t he BOD (mean) recorded from Idukki reservoir

3.3.18 Sodium

The seasonal variations in the sodium concentrations recorded from the

surface water of the 16 stations under study are presented in the Fig. 3.18. The

ANOVA of sodium showed significant difference among seasons (P < 0.05)

but insignificant difference among stations (P > 0.05) (Appendix I, Table 17).

The seasonal variations in the mean value of sodium showed that it was

higher during premonsoon period with the average of 1.21 mg/l. The lowest

sodium concentration was observed (0.53 mg/l) during monsoon season

whereas the moderate was during postmonsoon season (0.84 mg/l) (Table 3.1).

0.7

0.7

0.5

0.9

0.5

0.5

0.8

0.5

0.5

0.4

0.5

0.5

0.5

0.4

0.5

0.5

0.4

0.7

0.4

0.5

0.3

0.5

0.4

0.6

0.4

0.5

0.5

0.4

0.5

0.5

0.5

0.4

0.9

0.6

0.4

0.5

0.6

0.3

0.6

0.4

0.4

0.4

0.4

0.5

0.6

0.4

0.6

0.3

0

0.10.20.30.40.5

0.60.70.80.9

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

BOD

(mg/

l)




The seasonal mean value of sodium recorded at all stations of the Idukki

reservoir was ranged from 0.97 mg/l (station 5) to 1.43 mg/l (stations 3 and 13)

during premonsoon season (Fig. 3.18). The mean of sodium concentration during

the monsoon season was varied from 0.47 mg/l to 0.60 mg/l. The lowest average

in monsoon was registered at stations 6 and 13 and the highest was at stations 2

and 14. The average amount of sodium in postmonsoon season was ranged from

0.70 mg/l at station 4 to 0.97 mg/l at station 3.

Positive correlation was observed between sodium and atmospheric

temperature (r = 1.000), water temperature (r = 0.996), pH (r = 0.996), free

CO2 (r = 0.985), chloride (r = 0.979), calcium (r = 0.985) magnesium (r =

1.00), electrical conductivity (r = 0.993), TDS (r = 0.987) But an inverse

relationship was exhibited between sodium and turbidity (r = -0.987) and DO

(r = -0.990) (Table 3.3).

Fig.3.18 Stationwise s easonal variations in t he sodium (mean) recorded from Idukki reservoir

1.03

1.3

1.43

1.07

0.97 1.

07 1.13 1.

2

1.33

1.33

1.07

1.03

1.43

1.2 1.

3 1.4

0.57 0.

6

0.57

0.5

0.5

0.47 0.

5 0.57

0.53

0.53

0.53

0.5

0.47

0.6

0.5

0.5

0.9

0.77

0.97

0.7

0.87

0.83

0.8 0.83

0.77 0.

83

0.8 0.

9

0.87

0.87 0.

9

0.87

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Sodi

um (m

g/l)

Stations


Chapter 3


3.3.19 Potassium

The temporal and spatial variations in potassium at the 16 different

stations during the period of study are given in the Fig. 3.19. ANOVA of the

potassium showed significant difference among seasons (P < 0.05) but

insignificant difference among stations (P > 0.05) (Appendix I, Table 18).

Comparing the mean values, premonsoon season registered

significantly higher potassium values (0.75 mg/l), than the monsoon (0.64

mg/l) and postmonsoon seasons (0.61 mg/l) in the current study (Table 3.1).

The 3 years average values of potassium at all stations during

premonsoon season was given in Fig. 3.19. It varied from 0.37 mg/l (station

11) to 0.98 mg/l (station 1). During monsoon season, the highest average of

potassium concentration (0.80 mg/l) was observed at stations 1 and 2 and the

lowest of 0.53 mg/l at stations 10 and 14. The values ranged from 0.47 mg/l to

0.80 mg/l in postmonsoon season with the lower value at station 8 and higher

at stations 1 and 2.

Positive correlation was revealed between potassium and atmospheric

temperature (r = 0.778), water temperature (r = 0.718), transparency (r =

0.802), pH (r = 0.726), chloride (r = 0.892), calcium (r = 0.877), magnesium (r

= 0.789), electrical conductivity (r = 0.702), TDS (r = 0.672), COD (r =

0.922), BOD (r = 0.890) and sodium (r = 0.781). A negative correlation was

observed between potassium and turbidity (r = -0.870) and DO (r = -0.687)

(Table 3.3).



Fig.3.19 Stationwise s easonal variations in t he potassium (mean) recorded from Idukki reservoir

3.3.20 Nitrate

Nitrate is the oxidized form of nitrogen and the end product of aerobic

decomposition of organic nitrogenous matter. The different nitrate values

observed at all stations during the present study are depicted in the Fig. 3.20.

ANOVA showed significant difference among stations (P < 0.05) and among

seasons (P < 0.05) (Appendix I, Table 19).

In the present investigation, the average values of nitrate were recorded as

0.11 mg/l, 0.07 mg/l and 0.02 mg/l during monsoon, postmonsoon and premonsoon

seasons respectively. The highest concentration of nitrate was recorded during

monsoon season and lowest during premonsoon season (Table 3.1).

The average of the 3 years study revealed that the nitrate at all stations

varied from 0.01 mg/l (stations 3, 4, 6, 7, 9, 10, 11, 12, 13, 14 and 15) to 0.04

mg/l at station 8 during premonsoon season (Fig. 3.20). In monsoon period, it

was ranged from 0.08 mg/l at station 16 to 0.16 mg/l at station 8. During

0.98

0.6

0.93

0.77 0.

8 0.83 0.

9

0.9

0.77

0.87

0.37

0.7

0.63 0.

67

0.53

0.7

0.8

0.8

0.67

0.67 0.

73

0.6

0.6

0.6

0.57

0.53

0.63

0.57

0.67

0.53 0.

6

0.6

0.8

0.8

0.53

0.53 0.

6

0.53 0.

6

0.47

0.57 0.

6

0.6 0.

63

0.73

0.7

0.5 0.

53

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Pota

ssiu

m (m

g/l)

Stations


Chapter 3


postmonsoon season the mean nitrate varied from 0.04 mg/l to 0.11 mg/l with

high value recorded at station 8 and low at stations 4, 11 and 14.

Fig.3.20 Stationwise s easonal variations in t he nitrate (mean) recorded from Idukki reservoir

3.3.21 Phosphate

Phosphorus bound in rocks is generally insoluble in water, so in natural

waters its content is mere minimum. Domestic and industrial effluents and

agricultural runoff are the major sources of phosphorus in water. The seasonal

values of phosphate are given in the Fig. 3.21. ANOVA of the phosphate is

presented in Table 20 (Appendix I) where significant difference among seasons (P

< 0.05) was noticed but insignificant difference among stations (P > 0.05).

During the present investigation, phosphate content was below

detective level in monsoon season. Postmonsoon period showed a maximum

average value of 0.02 mg/l, whereas the mean value of 0.01 mg/l was noted

during premonsoon season (Table 3.1).

0.03

0.02

0.01

0.01 0.

02

0.01

0.01

0.04

0.01

0.01

0.01

0.01

0.01

0.01

0.01 0.

02

0.14

0.12

0.12

0.1

0.09

0.11 0.

12

0.16

0.1

0.09 0.

1

0.13

0.12

0.1

0.09

0.08

0.1

0.09

0.08

0.04

0.08

0.08 0.

09

0.11

0.1

0.07

0.04 0.

05

0.05

0.04 0.

05

0.07

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Nitr

ate

(mg/

l)




During premonsoon season, the average of phosphate at all stations

varied from 0.01 mg/l (in all stations except 3,5 and 16) to 0.02 mg/l (stations

16) and it was not recorded from stations 3 and 5 (Fig. 3.21). The value was

0.01 mg/l to 0.02 mg/l in postmonsoon also with the highest value (0.02 mg/l)

at stations 1, 2, 5, 7, 8, 12, 15 and 16 while the lowest was recorded in all

other stations ( 3, 4, 6, 9, 10, 11, 13 and 14).

Phosphate showed positive correlation with calcium (r = 0.437),

electrical conductivity (r = 0.677) and TDS (r = 0.707) (Table 3.3).

Fig.3.21 Stationwise s easonal variations in t he phos phate (mean) recorded from Idukki res ervoir

3.3.22 Sulphate

The seasonal variations in sulphate in the surface water recorded during

the study are presented in the Fig. 3.22. ANOVA of the sulphate showed

significant difference (Appendix I, Table 21) among stations (P < 0.05) and

seasons (P < 0.05).

Sulphate concentration was found mere minimum in almost all stations

studied and in many stations the values were recorded near zero. The seasonal

0.01

0.01

0

0.01

0

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.02

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0.02

0.02

0.01

0.01

0.02

0.01

0.02

0.02

0.01

0.01

0.01

0.02

0.01

0.01

0.02

0.02

0

0.005

0.01

0.015

0.02

0.025

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Phos

phat

e (m

g/l)

Stations


Chapter 3


average of sulphate was highest (0.013 mg/l) during premonsoon season and

lowest (0.003 mg/l) during postmonsoon season. Sulphate content was not

recorded in monsoon season during the entire period of study (Table 3.1).

During premonsoon season, the average sulphate concentration was

found to be varied 0.01mg/l (except stations 1, 5, 8 and 16) to 0.03 mg/l at

station 8 (Fig. 3.22). During postmonsoon season, it ranged between 0.01 mg/l

(stations 1,5,12 14 and 16) and 0.02 mg/l at station 8. The value was recorded

below traceable level in all other stations (2, 3, 4, 6, 7, 9, 10, 11, 13 and 15).

Fig.3.22 Stationwise s easonal variations in t he sulphate (mean) recorded from Idukki reservoir

The coefficient of correlation of the physico-chemical parameters

showed positive correlation between sulphate and atmospheric temperature (r

= 0.970), water temperature (r = 0.944), transparency (r = 0.978), pH (r =

0.947), free CO2 (r = 0.915), calcium (r = 0.997), magnesium (r = 0.974),

electrical conductivity (r = 0.936), TDS (r = 0.921), COD (r = 0.999), sodium

(r = 0.971) and potassium (r = 0.908). Sulphate was inversely related to

turbidity (r = -0.997), DO (r = -0.928) and nitrate (r = -0.983) (Table 3.3).

0.02

0.01

0.01

0.01

0.02

0.01

0.01

0.03

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.02

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0.01

0 0 0

0.01

0 0

0.02

0 0 0 0.00

1

0 0.00

1

0

0.01

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Sulp

hate

(mg/

l)




3.3.23 Iron

The seasonal variations in the iron content at the surface water of the 16

stations under study are presented in the Fig. 3.23. ANOVA of iron showed

significant difference among seasons (P < 0.05) but insignificant difference

among stations (P > 0.05) (Appendix I, Table 22).

Seasonal analysis of iron content in the reservoir revealed that the

highest value of 0.013 mg/l was noted in premonsoon where as the lowest

value of 0.006 mg/l in postmonsoon season. But the amount of iron was below

traceable level during monsoon period at all stations (Table 3.1).

The seasonal mean iron concentration of surface water recorded at all

stations was ranged from 0.01 mg/l (stations 3, 4, 6, 7, 9, 10, 11, 12, 13, 14 and 15)

to 0.02 (stations 1, 2, 5, 8 and 16) during premonsoon season (Fig. 3.23). In

postmonsoon season, it was recorded as 0.01 mg/l at stations 1, 2, 7, 8, 9, 10, 13, 15

and 16. The iron content was found below traceable level at all other stations.

Fig.3.23 Stationwise s easonal variations in t he iron (mean) recorded from Idukki reservoir

0.02

0.02

0.01

0.01

0.02

0.01

0.01

0.02

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.02

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0.01

0.01

0 0 0 0

0.01

0.01

0.01

0.01

0 0

0.01

0

0.01

0.01

0

0.005

0.01

0.015

0.02

0.025

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Iron

(mg/

l)

Stations


Chapter 3


Iron exhibited positive correlation with pH (r = 0.992) (Table 3.3).

3.4 Discussion

Water is a prime natural resource, a basic human need and a precious

natural asset. It is indeed required in all aspect of life and health for producing

food, agricultural activity, energy generation and maintenance of environment

and a substance of life and development. Human activities that involve

urbanization, agricultural development, over use of fertilizers, inadequate

management of land use and sewage disposal have directly or indirectly

affected the quality of water and making it unfit for domestic purpose.

Therefore, now-a-days fresh water has become a scare commodity due to over

exploitation and pollution (Singh and Mathur, 2005). The quality of natural

water is generally governed by various physico-chemical and biological

parameters. Physico-chemical properties of water in any aquatic ecosystem are

largely governed by the existing meteorological conditions and are essential

for determining the structural and functional status of natural waters (Zuber,

2007).

3.4.1 Rainfall

Kerala state is endowed with liberal rainfall. Some of the last remnants

of the tropical rain forests of India are situated here and it is the privilege of

Kerala to usher in the southwest monsoon to the country. The tall, well-

wooded hills of Western Ghats precipitate a bountiful rainfall that flows down

to the Arabian sea through 41 small, west-flowing drainages. Kerala receives

copious rain (average 3000 mm a year) each year. Rugged mountains and

forests cover about 97 percent of the total area of Idukki district. The

comparison of rainfall between different seasons in the Idukki reservoir area

showed that rainfall was a major atmospheric factor and like temperature



which also contributed to seasonal variations in climate in the system. In the

present investigation difference in rainfall pattern was evident between the

seasons. However, monsoon remained the season of highest rainfall during the

3 year period of study and lowest rainfall was recorded during the premonsoon

period. This result was coincided with the finding of Krishnan (2008) in

Periyar lake, Kerala.

3.4.2 Atmos pheric Temperature

Since changes in air temperature show a close proportional influence to

that of the water (Kaul et al., 1980) simultaneous measurements of both are

important. Spatial fluctuations in atmospheric temperature experienced during

a particular season might be due to the timing of collection and the influence

of weather, which quite fluctuate diurnally and seasonally in Idukki reservoir.

Since the air temperature was recorded during the actual visit to a station, the

time of record was not uniform at all the stations and this is the reason for a

significant difference in air temperature across different stations in the

reservoir area. Krishnan (2008) recorded similar fluctuations in air temperature

in different stations in Periyar lake, Kerala. The highest average air

temperature in the Periyar lake was 300C during the premonsoon and the

lowest average air temperature was 240C during the postmonsoon. In the

present observation also high atmospheric temperature was observed in

premonsoon season (31.690C) whereas the low values were recorded in

monsoon season (25.800C). Murthuzasab et al. (2010) and Patil et al. (2011)

also noticed the maximum air temperature in summer season in Hirahalla

reservoir, Karnataka and Lotus lake, Maharashtra respectively. Khatri (1985)

recorded the air temperature within the range of 21.20C to 29.80C in Idukki

reservoir.

Chapter 3


3.4.3 Water Temperature

Temperature is an important factor affecting the aquatic chemistry and

biological processes of the organisms dwelling therein. A rise in temperature

of the water leads to an increase in the rate of chemical reaction in water

besides reducing the solubility of gases (Haroon et al., 2010). All metabolic

and physiological activity and life processes such as feeding, reproduction,

movements and distribution of aquatic organisms are greatly influenced by

water temperature (Senthilkumar and Sivakumar, 2008). According to

Sugunan (1995), reservoirs having water temperature more than 220C are

highly productive reservoirs. In the tropics, water temperature variations are

governed by climatic conditions. Rainfall and solar radiations are the major

climatic factors that influence the physico-chemical hydrology of water bodies

(Kadiri, 2000). Water temperature is dependent on duration and intensity or

daily iridescence received by the water body. The intensity of solar radiation

may be modified by variations in cloud cover, water flow, phytoplankton

species composition and diversity, surface area, depth, wind velocity, solid

matter suspension, altitude, etc. resulting in fluctuations in water temperature

(Atoma, 2004).

The water temperature in Idukki reservoir remained lesser than

atmospheric temperature during the entire period of study. Similar

observations were made by Ade and Vankhede (2001) and Murthuzasab et al.

(2010). According to Moundiotiya et al. (2004) and Shinde et al. (2011), water

temperature was consistently lower than atmospheric temperature. In Idukki

reservoir, the higher water temperature (29.190C) was observed during the

summer season and it may be due to the clear atmosphere, bright sunshine

(greater solar radiation), air temperature and low water level. Swarnalatha and

Rao (1998), Shastri and Pendse (2001) and Sakhare (2006) also made similar



observation in their study on Banjara lake, Dahikhura reservoir and Jawalgaon

reservoir (Maharashtra) respectively. According to Sharma and Jain (2000),

the fluctuations in water temperature have relationship with the air

temperature.

During monsoon season, water temperature was found to be lower

(24.140C) in the reservoir and it may be due to the frequent clouds, high

humidity, high current velocity and high water level. Jain et al. (1996) and

Surve et al. (2005) also observed diurnal variations in water temperature in

Halai reservoir and Kandhar dam (Maharashtra) respectively. Water

temperature varies with changing climatic conditions (Sharma et al., 2008).

Temperature fluctuations in water were influenced considerably by air

temperature, humidity and solar radiation (Shashikanth and Vijaykumar,

2009). The variation in the water temperature at the sampling stations in the

present investigation may be due to the difference in sampling time and the

effect of season. Jayaraman et al. (2003) and Tiwari et al. (2004) also support

these findings. The narrow range of fluctuation of surface water temperature in

Idukki reservoir was also on account of the high altitude location of the

reservoir as well as the presence of thick evergreen forests around. The present

observation of surface water temperature in Idukki reservoir agrees with the

observations of Krishnan (2008) in Periyar lake, Kerala.

Kamble et al. (2008) reported the temperature of Khadakwasala

reservoir, Maharashtra ranged between 20.080C and 26.220C. The average

water temperature of Ujani reservoir (Maharashtra) was recorded as 28.620C

and 29.770C (Kumbhar et al., 2009). The surface water temperature of Ilorin

reservoir, Nigeria was fluctuated from 240C to 310C (Achionye-Nzeh and

Isimaikaiye, 2010). In Jawalgaon reservoir, water temperature ranged between

190C and 310C (Sakhare, 2006). The water temperature of Neyyar reservoir in

Chapter 3


Kerala was found to be varied from 280C to 320C during different seasons

(Harikrishnan and Aziz, 1989). Surface water temperature of Parappar

reservoir in Kerala was ranged from 250C to 290C (Sahib, 2005). The lowest

seasonal surface-water temperature noticed in the Periyar lake, Kerala was

240C, in the postmonsoon period and the maximum noticed was 290 C during

the premonsoon (Krishnan, 2008). The observations made on the water

temperature in Idukki reservoir in the study is also fully corroborate with the

above findings. However, Khatri (1985) recorded the water temperature within

the range of 21.80C to 26.30C in Idukki reservoir.

3.4.4 Transparency

The light penetration depends on transparency of a standing water

column. Water transparency is dependent on turbidity which is directly

proportional to the amount of suspended matter. Jhingran (1975) stated that, as

the depth of the reservoir increases, the light intensity decreases. The light

penetration depends on the available intensity of the incident light which

varies with geographical location of the water body. According to Reid and

Wood (1976), the transparency of water depends on several factors such as

silting, plankton density, suspended organic matter, latitude, season and the

angle and intensity of the incident light.

The transparency of Idukki reservoir was high and it ranged from

74.50 to 384.13 cm with high value during premonsoon season and low value

during monsoon season. Pulle (2000), Rao and Shrivastava (2002), Jayabhaye

and Madlapur (2005), Sakhare (2006), Kadam et al. (2007), Pawar et al.

(2009), Kumbhar et al. (2009), Shinde et al. (2011) and Patil et al. (2011) also

observed highest transparency in premonsoon and lowest in monsoon period

in Gandhisagar reservoir (Madhya Pradesh), Isapur dam (Maharashtra), Parola

dam (Maharashtra), Jawalgaon reservoir (Maharashtra), Masoli reservoir



(Maharashtra), Panshewadi dam (Maharashtra), Ujani reservoir, Harsool-

Savangi dam (Maharashtra) and Lotus lake respectively.

In Idukki reservoir, the higher dry season secchi-disc transparency

value compared to that of the rainy season could be due to the absence of

floodwater, surface run-offs and settling effect of suspended materials that

followed the cessation of rainfall in dry seasons. The similar findings were

also reported by Ibrahim et al. (2009) in Kontagora reservoir, Nigeria.

Moreover, during summer season, when there was less water current in the

reservoir (due to low and moderate velocity of winds) and clear sky, the

transparency was high; higher the transparency values, deeper will be the

penetration of sunlight, consequently. The present finding is in accordance

with the findings of Krishnamurthy and Bharathi (1995) and Vijaykumar et al.

(2005).

The lower transparency recorded in the reservoir during monsoon

season was probably due to the heavy rains, turbulence due to winds of high

velocity and comparatively high turbidity (due to floodwater and surface run-

offs). This is in confirmation with the findings of Sakhare (2006) in Jawalgaon

reservoir, Ibrahim et al. (2009) in Kontagora reservoir and Patil et al. (2011)

in Lotus lake. According to Baijot et al. (1997), water transparency varies

directly with rainfall.

Dwivedi et al. (2000), Rao and Shrivastava (2002), Sakhare and Joshi

(2003), Devaraju et al. (2005), Sakhare (2006), Garg et al. (2006), Garg et al.

(2009), Shinde et al. (2011) and Sharma et al. (2011) have reported

transparency ranging from 36 to 55 cm in Naktara reservoir (Madhya

Pradesh), from 30 to 261 cm in Gandhisagar reservoir; from 73 to 117 cm in

Hilegaon reservoir (Maharashtra), from 131.86 to 339.66 cm in Muddur lake,

from 27 to 69 cm in Jawalgaon reservoir, from 48.75 to 114.25 cm in Harsi

Chapter 3


reservoir, from 66.59 to 116 cm in Ramsagar reservoir (Madhya Pradesh),

from 5.50 to 22.70 cm in Harsool-Savangi dam and from 87.4 to 149.60 cm in

Pichhola lake (Rajasthan) respectively. The result of the present study showed

that the transparency values recorded in Idukki reservoir (74.50 cm to 384.13

cm) were comparatively higher than that of above studies except in Muddur

lake, where the values showed similarity with idukki reservoir. Nevertheless,

Khatri (1985) in his study in Idukki reservoir recorded higher range of

transparency (55 to 540 cm) than observed in this present study.

3.4.5 Turbidity

Clay, silt, organic matter, plankton and other microscopic organisms

cause turbidity in natural waters (Kishor et al., 2005). In Idukki reservoir, only

less amount of turbidity was observed. Comparatively higher value of turbidity

(1.46 NTU) was recorded during monsoon and minimum (0.01 NTU) during

premonsoon. The increased turbidity during monsoon season may be

attributed to the heavy rain, surface runoffs and higher wind flow which

created water waves in rainy season, whereas low values in summer

(premonsoon) might be due to reduction in the water level of dam. During

summer season, settlement of silt and low wind flow resulting low turbidity.

Shinde et al. (2011) also supported these findings; they observed high

turbidity values during monsoon and minimum during summer in Harsool-

Savangi dam. According to them, high values of turbidity in monsoon might

be due to higher wind flow which created water waves in rainy season which

brought clay, silt and organic matter, where as low values were in summer

might be due to reduction in the water level. Garg et al. (2009) and Agarwal

and Rajwar (2010) observed maximum value of turbidity during monsoon

period and minimum during winter period in Ramsagar reservoir and Tehri

dam reservoir (Himalaya) respectively. Garg et al. (2009) opined that during



monsoon season silt, clay and other suspended particles contribute to the

turbidity values while during winter season settlement of silt and clay resulting

low turbidity. According to Agarwal and Rajwar (2010), the increased

turbidity in Tehri dam reservoir during rainy months was due to the soil

erosion from the catchment area and the massive contribution of suspended

solids. He emphasized that the suspended solids play an important role in

governing turbidity, which enter the reservoir through land erosion. Bhaumik

et al. (2003) and Garg et al. (2006) have also reported high turbidity during

rainy season.

3.4.6 Electrical Conductivity (EC)

Electrical conductivity measures the capacity of a substance or solution

to conduct electrical current. Conductivity of water depends upon the

concentration of ions and its nutrient status and the variation in dissolved solid

content. High value of EC designates pollution status of the lake (Kadam,

1990). Electrical conductivity increases with an increase in total dissolved

solids (Shinde et al., 2011). Addition of some pollutants (Trivedy and Goel,

1984), silt carried through runoff (Kamble et al., 2008) and the enrichment of

organic conducting species from soaps and detergents (Gopalsami et al., 2003;

Arasu et al., 2007) also cause a sudden rise in the conductivity of water.

According to Trivedy and Goel (1984), a sudden rise in conductivity in water

during monsoon and postmonsoon season indicates the addition of some

pollutants.

In the present investigation, the highest average seasonal electrical

conductivity observed was 55.56 µS/cm during the premonsoon and the lowest

electrical conductivity reported was 29.74 µS/cm during the monsoon. Higher

conductivity values obtained during dry season could be attributed to the

concentration effect as a result of reduced water volume. Kolo and Oladimeji

Chapter 3


(2004) and Ibrahim et al. (2009) observed a similar trend in Shiroro reservoir

(Nigeria) and Kontagora reservoir (Nigeria) respectively. Kamath et al.

(2006), Sharma et al. (2010) Jafari and Alavi (2010) and Sharma et al. (2011)

also reported high conductivity during summer in different water bodies. In

Periyar lake, Kerala, the highest average of EC observed was 80 µS/cm during

premonsoon and the lowest EC was 15.20 µS/cm during the postmonsoon

(Krishnan, 2008).

The lowest conductivity observed in the reservoir during the monsoon

season was due to the dilution of water. Moundiotiya et al. (2004) and Verma

and Singh (2010) also observed lowest electrical conductance during rainy

season in Jamwa Ramgarh wetland (Rajasthan) and Laddia dam (Rajasthan)

respectively and according to them, dilution of water during the rains causes a

decrease in electrical conductance.

Olsen (1950) classified water bodies having conductivity values

between 200-500 µS/cm as mesotrophic and greater than 500 µS/cm as

eutrophic. On the basis of this classification, Idukki reservoir comes well

under oligotrophic category with average value 29.12 - 55.56 µS/cm. This very

low electrical conductivity of reservoir water implies the presence of reduced

level of ionic species. According to Blakar et al. (1990), low ionic content in

natural waters is generally attributed to slow chemical weathering in the

catchments.

3.4.7 Total Dissolved Solids (TDS)

In natural waters, dissolved solids are composed mainly of carbonates,

bicarbonates, chlorides, sulphates, phosphates, nitrates, calcium, magnesium,

sodium, potassium, iron, manganese etc. (Esmaeili and Johal, 2005; Garg et

al., 2006). Klein (1972) reported that the excess amount of TDS in waters



disturbed the ecological balance and caused suffocation of aquatic fauna. High

concentration of TDS enriches the nutrient status of water body (Singh and

Mathur, 2005).

In Idukki reservoir, highest TDS levels (33.79 ppm) recorded during

premonsoon season when water temperature was elevated and water levels

decline leading to dissolution of more salts in water as well as accumulation

due to evaporation. Lowest values of TDS (18.94 ppm) were evident in the

high water level during monsoon period, due to the excessive dilution,

stagnation and low rate of evaporation. These findings resembled the findings

of Patil et al. (2011) in Lotus lake and Tiwari (2005) in Khanpura lake,

Rajasthan. Hulyal and Kaliwal (2008a) and Sharma et al. (2011) also recorded

high TDS in summer season in Almatti reservoir (Karnataka) and Pichhola

lake respectively.

3.4.8 pH

pH is the intensity of the acidic or basic character of a solution at a

given temperature. pH values from 0 to 7 are diminishingly acidic, whereas

values of 7 to 14 are increasingly alkaline (Shinde et al., 2011). pH of a water

body is a diurnally variable property according to temperature variation in the

system (Ojha and Mandoli, 2004). The pH balance in an ecosystem is

maintained when it is within the range of 5.5 to 8.5 (Chandrasekhar et al.,

2003).

The surface water study of Idukki reservoir showed the reservoir water

was alkaline (7.03-7.87) throughout the study period. The higher concentration

of pH during summer season, in Idukki reservoir could be attributed to

decreased water level, high temperature, enhanced rate of evaporation and

increased photosynthesis. This is in accordance with Anitha (2002), Kadam et

Chapter 3


al. (2007), Narayana et al. (2008) and Shinde et al. (2011) who observed the

higher concentration of pH during summer season due to low water levels in

Mir-Alam lake of Andhra Pradesh, Masoli reservoir, Anjanapura reservoir of

Karnataka and Harsool-savangi dam respectively. Shashikanth and

Vijaykumar (2009) observed the higher pH during summer in Karanja

reservoir (Karnataka) due to high rate of evaporation and photosynthetic

activity. According to Wani and Subla (1990), high pH values in natural

waters were produced by photosynthetic rate that demands more CO2 than

quantities furnished by respiration and decomposition. According to Verma

and Singh (2010) the fluctuation in pH may be due to rise in temperature and

decrease in water level, rain fall and soil properties. Sakhare (2006) reported

maximum values of pH during summer in Jawalgaon reservoir and it was

probably due to increased photosynthesis in the algal blooms resulting into the

precipitation of carbonates of calcium and magnesium from bicarbonates.

Borse and Bhave (2000) also observed factors like photosynthesis, respiratory

activity and temperature bring out changes in pH values.

The low pH in Idukki reservoir during monsoon (rainy) season may be

due to dilution caused by heavy freshwater inflow into the water body. This

observation agrees with the trends noted on studies conducted in other

freshwater bodies particularly in reservoirs and lakes by Tiwari (2005), Tiwari

and Chauhan (2006), Sakhare (2006), Kamble et al. (2008), Narayana et al.

(2008), Verma and Singh (2010) and Shinde et al. (2011). Sakhare (2006),

Sharma et al. (2008), Kumbhar et al. (2009) and Agarwal and Rajwar (2010)

were also recorded high pH during summer and low during monsoon in

Jawalgaon reservoir, lakes of Udaipur (Rajasthan), Ujani reservoir and Tehri

dam respectively. Desmukh and Kanchan (2004), Shashikanth and

Vijaykumar (2009), Karekal et al. (2009) and Rajashekhar et al. (2010)



recorded highest values of pH during summer season in ‘Pani Ki

Dharamshala’ reservoir (Himachal Pradesh), Karanja reservoir, Bhutnal

reservoir (Karnataka) and Khaji Kotnoor reservoir (Karnataka) respectively.

Ugale and Hiware (2005), Tiwari (2005) and Tiwari and Chauhan (2006)

observed low pH during monsoon in Jagatungasamudra reservoir of

Maharashtra, Khanpura lake of Rajasthan and Kitham lake of Delhi

respectively.

pH value of majority of lakes and reservoirs in India has been found

between 6 and 9 (Senthilkumar and Sivakumar, 2008). Khatri (1985) recorded

the pH within the range of 6 to 9 in Idukki reservoir. The pH range recorded

in Jawalgaon reservoir was 7.4 to 8.5 (Sakhare, 2006) and that recorded in

Ujani reservoir was varied from 7.46 to 8.67 (Kumbhar et al., 2009). The pH

range recorded in Vellayani lake (Kerala) was 6.62 to 7.50 and that recorded

in Sasthamkotta lake (Kerala) was 7.20 to 7.30 (Krishnakumar et al., 2005). In

Parappar reservoir of Kerala, pH varied from 6.31 to 7.81 (Sahib, 2005).

Pawar et al. (2009) recorded the pH range between 7.2 and 7.8 in Panshewadi

dam of Maharashtra. Joshi (2006) observed pH range of 7.2 to 8.4 in Ekruk

reservoir of Maharashtra. Karekal et al. (2009) recorded the pH range and 6.8

to 8.7 in Bhutnal reservoir. Verma and Singh (2010) reported the pH range

from 6.7 to 8.2 in Laddia dam. The pH of the water samples from Idukki

reservoir was within permissible limit (6.5-8.5) of ISI (1983) and WHO (1984)

which indicated the suitability of water for all purposes. According to Jhingran

and Sugunan (1990), the pH range between 6 and 8.5 was medium productive

reservoirs, more than 8.5 were highly productive and less than 6 were less

productive reservoirs. Based on these criteria, Idukki reservoir is a medium

productive type.

Chapter 3


3.4.9 Dissolved Oxygen (DO)

Dissolved Oxygen (DO) is an important water quality parameter in

assessing water pollution. Biologically available DO is much less concentrated

in water than in air (Moyle and Cech, 2004). Oxygen enters the water column

through diffusion from the atmosphere (this is potentially facilitated via

turbulence and mixing) and by photosynthetic production (Kalff, 2000 and

Stickney, 2000). Many studies revealed that the distribution of DO in the

reservoir water is governed by a balance between input from the atmosphere,

rainfall, photosynthesis and losses by the chemical and biotic oxidations

(Ficke et al., 2007; Sivakumar and Karuppasamy, 2008; Senthilkumar and

Sivakumar, 2008). Fluctuation in DO is also due to the fluctuation in water

temperature and addition of sewage waste demanding oxygen as reported by

Kozhy and Nayar (2000). Higher DO means the rate of O2 replenishment in

water is greater than O2 consumption and this is healthy for almost all aquatic

systems (Adak et al., 2002). A low DO content is a sign of pollution (Bhatt et

al., 1999).

Throughout the investigation period, comparatively higher average

value of DO (8.44 mg/l) was recorded in monsoon season and low value (7.09

mg/l) was recorded in pre monsoon season in Idukki reservoir. The lower

values of DO in the reservoir during premonsoon season may be due to an

increased temperature of water and higher rate of decomposition of organic

matter as reported by Rani et al. (2004). The low O2 values coincided with

high temperature during the summer season as reported earlier by Sultana and

Sharief (2004) and Deshmukh and Ambore (2006). Tiwari (2005) also noticed

the low DO during summer months due to higher rate of decomposition of

organic matter and limited flow of water in low O2 holding environment due to

high temperature. Present observations are in agreement with similar ones



made by Shastri and Pendse (2001), Shanthi et al. (2002), Awasthi and Tiwari

(2004), Naz and Turkmen (2005), Garg et al. (2009), Vijaykumar et al. (2005)

and Sharma et al. (2010) who studied the Dahikhura reservoir, Siganallur lake,

Govindgarh lake (Madhya Pradesh), Golbasi lake (Turkey), Ramsagar

reservoir, Bennithora dam (Karnataka) and Gundolav lake (Rajasthan)

respectively.

High DO in monsoon season in Idukki reservoir can be attributed to

low temperature which helps the water to hold high O2 in the dissolved state.

Similar findings were also reported by Wetzel (1983), Deshmukh and Pingle

(2007), Kumbhar et al. (2009), Laskar and Gupta (2009) Ayoade et al. (2009)

and Agarwal and Rajwar (2010). Moreover, there is a chance of re-

oxygenation of water during the monsoon due to wind action, circulation and

mixing by inflow after the monsoon rains as reported by Hannan (1979).

The DO varies greatly from one water body to the other (Naz and

Turkmen, 2005; Garg et al., 2009). The DO ranged from 3.41 to 6.21 mg/l in

Seetadwar lake of Uttar Pradesh (Tewari and Mishra, 2005), from 5.30 to 9

mg/l in Deoria tal of Uttarakhand (Rawat and Sharma, 2005), from 3 to 6mg/l

in Kandhar dam (Surve et al., 2005), from 2 to 14 mg/l in Jawalgaon reservoir

(Sakhare, 2006), from 3.61 to 9.18 mg/l in Wilson dam of Maharashtra

(Deshmukh and Pingle, 2007), from 4.6 to 8.3 mg/l in Periyar lake (Krishnan,

2008), from 6.78 to 11.59 mg/l in Ramsagar reservoir (Garg et al., 2009) and

from 2.8 to 9.7 mg/l in Panshewadi dam (Pawar et al., 2009) respectively. Do

concentrations of 5 mg/l or more are acceptable for most aquatic organisms

(Stickney, 2000). It favours good growth of flora and fauna (Das, 2000). The

concentrations below 2-3 mg/l are considered hypoxic (Kalff, 2000).

Chapter 3


3.4.10 Free CO2

Free carbon dioxide liberated during respiration and decay of organic

matter is highly soluble in natural waters. The carbon dioxide content of water

depends upon the water temperature, depth, rate of respiration, decomposition

of organic matter, chemical nature of the bottom and geographical features of

the terrain surrounding the water body (Sakhare and Joshi, 2002). Although

CO2 is a minor component of air, it is abundant in water because of its

solubility which is 30 times more than that of oxygen and the amount of CO2

in water usually shows an inverse relationship with oxygen (Radhika et al.,

2004). High summer temperature and bright sunshine accelerate the process of

decay of organic matter resulting into the liberation of large quantities of CO2

and nutrients (Agarwal and Rajwar, 2010).

Free CO2 is essential for photosynthesis and its concentration affects

the phytoplankton and its productivity. Garg et al. (2010) stated that free CO2

content was generally higher in polluted waters and its higher value is

attributed to the higher decomposition of organic matter. The limit of free CO2

as per acceptable standards is 10 mg/l of surface water. Increase in CO2

indicates increase in pollution load (Koshy and Nayar, 1999). Surface water

contains less than 10 mg free CO2 per litre while as the ground water may

easily exceed the concentration of 30 to 50mg/l (Haroon et al., 2010).

In Idukki reservoir the free CO2 was ranged from 1.95 mg/l to 2.18mg/l

with highest value recorded in premonsoon and the lowest in monsoon. The

low CO2 concentration in the reservoir may be due to the alkaline nature of

water and absence of pollution. In Ramsagar reservoir, highest free CO2 was

recorded as 6.32 mg/l, however, its absence or low content was recorded in

most of the times due to alkaline nature of reservoir water (Garg et al., 2009).

The CO2 content of surface water of Periyar lake in Kerala was varied from



1.6 mg/l to 3.4 mg/l (Krishnan, 2008). Dwivedi and Sonar (2004) observed an

average of 2 mg/l of free CO2 in reservoirs of Arunachal Pradesh. CO2 in

Oyun reservoir, Nigeria ranged between mean of 1.6 mg//l and 3.0 mg/l

(Mustapha, 2009a). Radhika et al. (2004) reported an annual variation of 2.42

to 10.47 mg/l of CO2 in Vellayani lake, the maximum being in the

postmonsoon, minimum during the monsoon. Pandey and Soni (1993)

observed high values of free CO2 in highly polluted Naukuchiyatal lake of

Uttarakhand.

3.4.11 Total Alkalinity

Alkalinity is a measure of the quantity of compounds that shift the pH

to the alkaline side of neutrality (above 7) or it is a measure of the capacity of

water to neutralise acids. Raising the alkalinity always raises pH. If the

alkalinity of water is too high, the water can be turbid, which inhibits the

growth of underwater plants. Too high alkalinity in the water body raises the

pH level, which in turn harms or kills fish and other organisms (Kamble et al.,

2008). In Idukki reservoir, the highest alkalinity value (31.52 mg/l) was

observed during premonsoon and lowest value (18.60 mg/l) during monsoon

periods. High values of total alkalinity during premonsoon season may be due

to the high water temperature, low water level and increased rate of

decomposition. This is in accordance with the findings of Sharma and Kaushal

(2004). The low alkalinity during the monsoon period may be attributed to

dilution effect due to heavy rainfall. This view has also been supported by

Shastri and Pendese (2001), Moundiotiya et al. (2004), Srivastava et al. (2009)

and Ayoade et al. (2009).

Sharma et al. (2000), Moundiotiya et al. (2004), Desmukh and

Kanchan, (2004), Kumbhar et al. (2009) and Srivastava et al. (2009) also

recorded higher alkalinity values during summer and lower during monsoon in

Chapter 3


lakes of Udaipur, Ramgarh wetland, ‘Pani Ki Dharamsala’ reservoir, Ujani

reservoir and lakes of Rajasthan (Jalmahal, Amer, Nevta and Ramgarh)

respectively. Sharma and Kaushal (2004), Mustapha (2009) and Agarwal and

Rajwar (2010) were registered higher alkalinity values during summer months.

Sakhare (2006) observed lower total alkalinity values during monsoon season

in Jawalgaon reservoir. The observation of the present study also corroborate

with these findings.

The alkalinity value varied from 22.5 to 35 mg/l in Talwade reservoir

of Maharashtra (Shastri and Bhogaonkar, 2006), 27.82 to 49.07 mg/l in

Khadakwasala reservoir (Kamble et al., 2008), 12.50 to 25 mg/l in Vellayani

lake and 12.20 to 31.73 mg/l in Sasthamcotta lake (Krishnakumar et al., 2005).

Philipose (1960) suggested that a water body with alkalinity value >100 mg/l

is nutritionally rich. On this basis, water of the Idukki reservoir can be

declared as not rich in nutritive contents.

3.4.12 Chloride

The salts of sodium, potassium and calcium contribute chlorides in

water. Large contents of chloride in freshwater is an indicator of organic

pollution (Venkatasubramani and Meenambal, 2007), eutrophication (Hynes,

1963), pollution due to sewage (Chourasia and Adoni, 1985) and pollution due

to domestic and industrial pollutants (Goel et al., 1980; Sinha, 1998).

In the present study, the water of Idukki reservoir showed highest

average value (9.61 mg/l) of chloride in premonsoon season and lowest

average value (7.13 mg/l) in monsoon season. This is in agreement with the

work of Garg et al. (2009) in Ramsagar reservoir in which chloride

concentration varied from 13.13 to 22.36 mg/l with the concentrations higher

in summer season and lower in monsoon season. Deshmukh and Kanchan



(2004), Sharma et al. (2008) and Sharma et al. (2010) have also found

maximum chloride contents in summer and minimum in monsoon in various

reservoirs.

The concentration of higher chloride during the summer period in

Idukki reservoir could be due to the increased temperature and the evaporation

of water. This observation is in good agreement with the findings of

Moundiotiya et al. (2004) and Shashikanth and Vijaykumar (2009). According

to Verma and Singh (2010), the higher chloride content in Laddiya dam might

be due to the decrease in water level and addition of domestic wastes. In the

present study also higher chloride values obtained during summer when

decrease in water level is taking place. Laskar and Gupta (2009) also recorded

higher chloride concentration (61.6 mg/l) in premonsoon season.

The lower chloride values in the Idukki reservoir during monsoon

season could be attributed to the dilution effect as reported by Sakhare (2006).

In Ujani reservoir, the maximum chloride content was recorded during

summer and minimum during winter with the average value varied from 23.78

mg/l to 46.95 mg/l (Kumbhar et al., 2009). The chloride range in Sasthamcotta

lake was 3.55 mg/l to 17.73 mg/l and that in the Vellayani lake was 16.57 to

21.30 mg/l (Krishnakumar et al., 2005). The chloride range reported from

Manjara reservoir of Maharashtra was 17.55 to 33 mg/l (Chavan et al., 2006)

and the range in Khadakwasala reservoir was between 4.27 and 12.39 mg/l

(Kamble et al., 2008). Maximum concentration of chloride found in Wilson

dam water was 38.33 mg/l and minimum concentration was 2.44 mg/l

(Deshmukh and Pingle, 2007). Chloride content of Urmilasagar reservoir was

ranged between 8 and 9 mg/l (Sharma and Kaushal, 2004). According to ISI

(1983), the upper limit of chloride in drinking water is 250 mg/l. In the present

Chapter 3


study, the lower chloride concentration recorded can be taken as a tangible

proof that the reservoir is free from any pollution.

3.4.13 Total Hardness

Hardness is mainly due to the percentage of calcium or magnesium

salts of bicarbonates, carbonates, sulphates and chlorides. The maximum limit

of total hardness for drinking water is 300 mg/l (ISI, 1983; WHO, 1984; Arasu

et al., 2007). In Idukki reservoir the total hardness was found to be miniscule.

The water samples from Idukki reservoir showed the average of total hardness

from 6.97 mg/l to 10.76 mg/l indicating the suitability of water for drinking

purpose. Sawyer (1960) classified water on the basis of hardness into 3

categories ie, soft (0-75 mg/l), moderately hard (75-150 mg/l) and hard (151-

300 mg/l). Kannan (1991) has classified water on the basis of hardness values

in the following manner; Soft (0-60 mg/l), moderately hard (61-120 mg/l),

hard (121-160 mg/l) and very hard (>180 mg/l). According to these

classification, water in the Idukki reservoir falls in the category of soft water

body with hardness ranging from 6.97 to 10.76 mg/l.

In Idukki reservoir, the total hardness was high during premonsoon

season while it was low during monsoon season. This result was coincided

with that of Tiwari (2005), Sharma et al. (2008) and Pawar et al. (2009) who

observed highest total hardness in summer season and low in monsoon in

Khanpura lake, lakes of Udaipur and Panshewadi dam respectively.

Higher values of total hardness in the reservoir during premonsoon

season may be attributed to decrease in the water volume and increase in the

rate of evaporation at high temperature. This finding is consonance to the

findings of Moundiotiya et al. (2004), Kumbhar et al. (2009) and Agarwal and

Rajwar (2010). Minimum hardness in the reservoir during monsoon season



may be due to ultimately heavy rainfall and subsequent dilution. Similar

findings of seasonal variation was reported by Naik and Purohit (1996) and

Nair and Rajendran (2000).

Productive waters should have hardness value above 20 mg/l (Das,

1996). High hardness of an aquatic body implies the presence of high chloride

content (Raja et al., 2008), eutrophication (Pandey, 2008) and domestic

pollution (Unni, 1985). Higher values of hardness in a water body may be due

to the surface runoff and the sewage discharge (Chattopadhyay et al., 1984),

presence of high chloride content (Raja et al., 2008), addition of calcium and

magnesium salts from detergents and soaps (Arasu et al., 2007), washing of

clothes, bathing and cleaning of animals (Mohanta and Potra 2000; Sanap et

al., 2008; Verma and Singh 2010). According to Khan et al. (1986) the

hardness varied from reservoir to reservoir due to their geological setting also.

Shekhar et al. (2008) recorded the total value of hardness from the unpolluted

station of River Bhadra was varied from 20 to 44 mg/l. Sunkad (2005)

recorded the hardness of 2.2 to 9.4 mg/l in Rakasakoppa reservoir.

3.4.14 Calcium

In aquatic environment calcium serves as one of the micronutrients for

most of the organisms. It’s main source being leaching of rocks in the

catchment (Pawar et al., 2009), industrial waste and sewage (Gupta et al.,

2009). The general acceptable limit of calcium in water is usually 75 mg/l

whereas its maximum permissible limit is 200 mg/l (ICMR, 1975). Calcium in

natural waters differs according to difference in geographic regions or

anthropogenic impact (Krishnan, 2008).

During the present study, the average value of calcium was ranged

between 5.59 and 8.11 mg/l in Idukki reservoir. The calcium values were low

Chapter 3


in monsoon season, but were marked high in premonsoon season which fully

agrees with the observation of Osborne et al. (1987) and Krishnan (2008).

They found that Ca was inversely proportional to water level; increased during

low water levels (premonsoon) and decreased during high levels (monsoon) in

the study conducted respectively in Lake Murray of Papua New Guinea and

Periyar lake of Kerala. Lower calcium level in the reservoir during monsoon

may be attributed to dilution by rain water. Similar observation was made by

Gurumayum et al. (2000) and Ayoade et al. (2009). Ray et al. (2007) also

observed the seasonal average of Ca content in Periyar lake waters varied from

2 mg/l during monsoon to 3.5 mg/l during summer. In Hirahalla reservoir,

average calcium content ranged from minimum of 5.07 mg/l in monsoon to

15.85 mg/l in postmonsoon season (Murthuzasab et al., 2010). Sharma and

Kaushal (2004), Deshmukh and Pingle (2007), Ray et al. (2007), Hussain

(2008), Garg et al. (2009) and Ayoade et al. (2009) recorded the calcium level

of Urmilasagar reservoir, Wilson dam, Periyar lake, Omkareshwar reservoir

(Madhya Pradesh), Ramsagar reservoir and Tehri dam ranged between 20.6 to

24.6 mg/l, 18.9 to 80.4 mg/l, 2 to 3.6 mg/l, 13.75 to 34.93 mg/l, 11.21 to 33.81

mg/l and 7.86 to 20.04 mg/l respectively.

3.4.15 Magnesium

Magnesium is often associated with calcium in all kinds of waters, but

its concentration remains generally lower than the calcium (Venkatasubramani

and Meenambal, 2007). The main source of magnesium is leaching of rocks in

the catchment (Pawar et al., 2009), industrial waste and sewage (Gupta et al.,

2009). The general acceptable limit of Mg in water is usually 50 mg/l whereas

its maximum permissible limit is 100 mg/l (ICMR, 1975).

Magnesium content of Idukki reservoir varied from 1.36 to 2.68 mg/l

with the minimum during the monsoon season and the maximum during the



premonsoon season. According to Osborne et al. (1987), the concentration of

magnesium varied according to water level, increased during low water levels

and decreased during high levels. Lower concentration of magnesium in the

reservoir during monsoon may be the result of dilution by rain water, which

was corroborated with the observations of Gurumayum et al. (2000) and

Ayoade et al. (2009). The magnesium content of Wilson dam ranged from

3.82 to 16.61 mg/l (Deshmukh and Pingle, 2007). Dwivedi et al. (2000)

recorded magnesium content up to 3.27 mg/l in Naktara reservoir. Garg et al.

(2009) observed the magnesium content up to 5.60 mg/l in Ramsagar reservoir

with higher concentration during winter season and lower concentration in

monsoon season. Venkateswarlu et al. (2002), Chavan et al. (2004) and

Desmukh and Kanchan (2004) also observed lower concentration of

magnesium during monsoon season. The magnesium concentration in Kawar

lake varied from 8.86 to 29.58 mg/l (Kumar et al., 2002); in Urmilasagar

reservoir it varied from 14.8 to 16.8 mg/l (Sharma and Kaushal, 2004); in

Vellayani lake it ranged from 0.62 to 3.25 mg/l and in Sasthamkotta lake it

ranged between 1.22 and 4.86 mg/l (Krishnakumar et al., 2005); in

Khadakwasala reservoir it varied from 0.99 to 7.14 mg/l (Kamble et al., 2008);

in Omkareshwar reservoir it ranged from 16.43 to 35.38 mg/l (Hussain, 2008)

and in Periyar lake it varied from 3.1 to 6.6 mg/l (Krishnan, 2008).

3.4.16 Chemical Oxygen Demand (COD)

Chemical oxygen demand (COD) is a measure of the oxygen

equivalent of the organic matter content of water that is susceptible to

oxidation by a strong chemical oxidant. Thus, COD is a reliable parameter for

judging the extent of pollution in water (Amirkolaie, 2008). The COD of water

increases with increasing concentration of organic matter (Boyd, 1981). In

Chapter 3


other words, COD is a measure of pollution in aquatic ecosystems. It estimates

carbonaceous factor of organic matter (Agarwal and Rajwar, 2010).

In the present study, COD ranged from 3.08 to 3.17 mg/l with slightly

higher values during premonsoon season and lower values during monsoon

season. The increase in COD during hot period is mainly attributed to the

increase in the air and water temperatures, facilitating the decomposition and

oxidation of organic matter. These findings show similarities with those of

Abdo (2002) and Agarwal and Rajwar (2010) on the occurrence of highest

COD in summer. Such a seasonal variation was also observed by Fokmare and

Musaddiq (2002) in Loco reservoir of West Bengal, Chatterjee and Raziuddin

(2003) in Kapsi lake and Mustapha (2009) in Oyun reservoir. According to

Abdo (2005), the COD values increased during hot period and decreased

during cold period.

Chemical oxygen demand in Khadakwasala reservoir ranged between

1.56 mg/l and 18.42 mg/l (Kamble et al., 2008). The range of values of COD

in Tehri dam reservoir was 5.9 to 39.4 mg/l (Agarwal and Rajwar, 2010).

COD in Oyun reservoir varied from 1.2 mg/l to 2.6 mg/l (Mustapha, 2009).

3.4.17 Biochemical Oxygen Demand (BOD)

The rate of removal of Oxygen by microorganisms in aerobic

degradation of the dissolved or even particulate organic matter in water is

called BOD and it is used as an index of organic pollution in water. The more

the oxidisable organic matter present in water, the more the amount of O2

required to degrade it biologically that cause the higher BOD. BOD

determines the strength of sewage, effluents and other polluted waters and

provides data on the pollution load in all natural waters. BOD above 6 mg/l in

a water body is considered as polluted and high BOD values are attributed to



the stagnation of water body leading to the absence of self purification (Iqbal

and Katariya, 1995).

In Idukki reservoir, very low BOD values were observed,

comparatively higher values (0.56 mg/l) were observed during premonsoon

period and lower values (0.47 mg/l) during monsoon period. This may be

attributed to the photosynthetic activity and abundance of phytoplankton

during hot period. This is in confirmation with the findings of Abdo (2005) in

Abu-Za’baal lake, Egypt. Chatterjee (1992) recorded higher BOD values

during postmonsoon and attributed to the enhanced biological activity at

higher temperature. The decline of BOD in Idukki reservoir during monsoon

may be attributed to the decrease in phytoplankton and temperature. Bhatt et

al. (1999) observed highest BOD in summer and lowest in winter in Taudaha

lake of Nepal and the decrease of BOD in monsoon followed by winter was

attributed to the decrease in temperature which in turn retards microbial

activity. Devaraju et al. (2005) and Garg et al. (2009) recorded low BOD

values in monsoon and high in summer season in Muddur lake and Ramsagar

reservoir respectively. Sharma et al. (2010) noted high BOD content in

Gundolav lake during summer.

BOD values in Idukki reservoir were very low when compared to other

reservoirs. In Hirahalla reservoir, BOD values ranged between 0.26 and 3.23

mg/l (Murthuzasab, 2010). The BOD in Tehri dam reservoir was varied from

0.30 to 4.7 mg/l (Agarwal and Rajwar, 2010). BOD in Ramsagar reservoir was

recorded in the range of 0.93 mg/l to 4.68 mg/l (Garg et al., 2009). The

biochemical oxygen demand values in Khadakwasala reservoir ranged

between 0.16 mg/l and 3.23 mg/l (Kamble et al., 2008). According to Singh et

al. (2008), water bodies with low BOD have low nutrient levels, therefore,

much of the O2 remains in the water. They reported that unpolluted natural

Chapter 3


waters would have a BOD value of < 5 mg/l and it confirms that Idukki

reservoir is an unpolluted water body.

3.4.18 Sodium

In Idukki reservoir, a higher value of sodium (1.21 mg/l) was observed

in premonsoon season and lower value (0.53 mg/l) in monsoon season. Low

water level in the reservoir and evaporation of water were the significant

factors in increasing sodium level during summer season. Garg et al. (2009)

also recorded highest sodium content during summer season and lower content

during monsoon season in Ramsagar reservoir and they mentioned that

increase in the sodium concentration during summer season was due to the

evaporation of water. Osborne et al., (1987) also reported that the

concentration of Na varied (22 mg/l to 31 mg/l) according to the water level ie,

increased during low water levels and decreased during high levels in Lake

Murray.

The sodium concentration in Khadakwasala reservoir varied from 3.50

mg/l to 9.80 mg/l (Kamble et al., 2008). In Periyar lake, the seasonal average

of Na ions varied from 1.9 mg/l to 6.5 mg/l (Krishnan, 2008). Halverson

(2004) reported 0.29 to 0.39 mg/l of Na in Lake Antnsjoen, a Norwegian

mountain lake. The observations on sodium made in the present study revealed

that the value was comparatively very low from these findings.

3.4.19 Potassium

Like sodium, potassium is also a naturally occurring element, but the

concentrations in freshwater bodies remain quite lower than the sodium and

calcium. Under low potassium concentration, the growth rate and

photosynthesis of algae especially blue green algae becomes poor and

respiration was increased (Wetzel, 2001). In Idukki reservoir, potassium



content was very less and comparatively higher concentration of potassium

(0.75 mg/l) was recorded during premonsoon season and lower concentration

(0.61 mg/l) was recorded in monsoon season. The high value during summer

might be due to the low water level and evaporation and low value in monsoon

may be due to dilution. Garg et al. (2006) observed high value of potassium

during summer in Harsi reservoir. Garg et al. (2009) also recorded higher

potassium content in summer season and lower in monsoon season in

Ramsagar reservoir.

In Periyar lake, the amount of K ions in the surface water varied from

0.9 mg/l (monsoon) to 2 mg/l (postmonsoon) (Krishnan, 2008). In Ramsagar

reservoir potassium content varied from 1.97 to 4.86 mg/l (Garg et al., 2009).

The value of potassium ranged between 0.30 and 0.80 mg/l in Khadakwasala

reservoir (Kamble et al., 2008). Halversen (2004) reported 0.23 to 0.30 mg/l of

K in Antnsjoen lake. The observations in the present study are also supported

by these findings.

3.4.20 Nitrate

The presence of nitrate in fresh water bodies depends mostly upon the

activity of nitrifying bacteria, domestic and agricultural source (Chauhan and

Sharma, 2007; Murthuzasab, 2010). Domestic sewage contains very high

amount of nitrogenous compounds. Runoff from agricultural fields is also

contains nitrate. Atmospheric nitrogen fixed into nitrates by the nitrogen fixing

organism is also a significant contributor to nitrates in the water (Trivedi and

Goel, 1987). According to them, unpolluted natural water contains usually

only minute amount of nitrate.

In Idukki reservoir, nitrate values were very less and comparatively

higher values (0.11 mg/l) were observed during rainy season (monsoon) than

Chapter 3


the dry season (premonsoon). The higher nitrate concentration in this reservoir

during rainy season could be due to the surface runoff as well as the

decomposition of organic matter. Ufodike et al. (2001), Kennedy and Hains

(2002) and Ibrahim et al. (2009) made similar observations for Dokowa mine

lake (Nigeria), Verkhne Viiskii reservoir (Russia) and Kontagora reservoir

respectively.

The depletion of nitrate in Idukki reservoir during summer may be due

to the utilization by plankton (photosynthetic activity of the algae) as observed

by Kannan (1978) and Sivakumar and Karuppasamy (2008). The seasonal

distribution of the phytoplankton biomass is much influenced by the

availability of inorganic nitrate and phosphate (Wetzel, 1983). In the present

study, the phytoplankton density was high in premonsoon season, where

subsequently the nutrients in the water were decreased. According to Agarwal

and Rajwar (2010), decrease in nitrate content in Tehri dam reservoir during

winter months was probably due to its utilization as nutrient by the algal

community as evidenced by the luxuriant growth of algae particularly in the

winter months. According to Krishnan (2008), in deep lakes settling of

suspended matter can lead to low nutrients in the epilimnion during summer.

Sivakumar and Karuppasamy (2008), Mustapha (2010) and Shinde et al.

(2011) also observed highest nitrate values during monsoon and lowest during

summer in Veeranam reservoir, Harsool-Savangi dam and Oyun reservoir

respectively.

The nitrate content in natural waters is likely to vary (Sivakumar and

Karuppasamy, 2008). In Tehri dam reservoir, the values of nitrate ranged from

0.08 to 0.97 mg/l (Agarwal and Rajwar, 2010). The maximum value of nitrate

was recorded as 0.30 mg/l whereas minimum value was recorded as 0.013 mg/

l in Laddia dam (Verma and Singh, 2010). The nitrate value in Ramsagar



reservoir was varied 0.011 to 0.033 mg/l (Garg et al., 2009). In Hirahalla

reservoir nitrate content varied from 0.32 mg/l to 1.09 mg/l (Murthuzasab,

2010). The nitrate values in Khadakwasala reservoir ranged between 0.27 mg/l

and 1.55 mg/l. (Kamble et al., 2008).

3.4.21 Phosphate

In natural water, phosphate is present in small quantities. Generally

aquatic ecosystems receive excess of this nutrient through untreated domestic

sewage and agriculture runoff (Malathi, 1999). In Idukki reservoir, the

concentration of phosphate was very low and it confirms the unpolluted status

of the reservoir and less deposition of organic matter in it. The low content of

phosphate (0.01 mg/l) in Idukki reservoir during summer (premonsoon) season

may be due to the utilization of phosphate by the phytoplankton. Kaul et al.

(1980) and Murthuzasab (2010) have also observed similar findings in the

water bodies they studied. During plankton multiplication, automatically

phosphate concentration is decreased (Moss and Balls, 1989; Wani and Subla,

1990). Phosphate was not recorded in Idukki reservoir during monsoon season

and it may be due to the dilution factor. Comparatively high value of

phosphate in postmonsoon period (0.02 mg/l) might be due to surface runoff

as explained by Shinde et al. (2011).

Low values of phosphate recorded in Idukki reservoir was also

supported by many workers. In Hirahalla reservoir, phosphate ranged from a

minimum of 0 mg/l to a maximum of 0.47 mg/l (Murthuzasab, 2010).

Phosphate was found only in smaller amount in Tehri dam (Agarwal and

Rajwar, 2010). A range of 0.002 to 0.005 mg/l of phosphate was observed in

water bodies of Berach river system by Sharma et al. (2000). The phosphate

concentration of Ilorin reservoir was 0.06 mg/l to 0.85 mg/l (Achionye-Nzeh

and Isimaikaiye, 2010). In Periyar lake, phosphate at surface water was varied

Chapter 3


from 0.01 to 0.1 mg/l during all the seasons (Krishnan, 2008). Sharma et al.

(2010) reported high value of total phosphate in Gundolav lake, which was

ranged between 1.76 and 7.86 mg/l and it was due to the pollution and high

organic matter of the lake. However Khatri (1985) did not record phosphate

content in Idukki reservoir.

The phosphate values were recorded minimum during summer in

Harsool-Savangi dam also (Shinde et al., 2011). Romero et al. (2002)

considered Lake Pamvotis (Greece) with a phosphate content of 0.11 mg/l as

one of intermediate nutrient status. In Idukki reservoir the phosphate content

was less than 0.1 mg/l.

3.4.22 Sulphate

Increased concentration of sulphate in a water body is always regarded

as an indicator of eutrophication (Sharma et al., 2002). Sulphate was recorded

only during premonsoon season in Idukki reservoir and which may be due to

low water level, increase in the air and water temperatures followed by the

high evaporation rate. These results agree with the findings of Abdel-Satar

(2005), Abdo (2005), Garg et al. (2009) and Shinde et al. (2011). Sulphate

content was not recorded during monsoon and postmonsoon season in Idukki

reservoir, which may be due to the dilution factor. Sharma et al. (2008)

reported higher values of sulphate during summer season and lower value

during monsoon season in Udaipur lakes.

3.4.23 Iron

Iron is a chemical element and one of the most important metals in

water. The normal range of Iron in freshwater is 0.1 ppm to 0.5 ppm (Singh et

al., 2008). In Idukki reservoir, the iron content was observed in minor amount

during the entire investigation period and it ranged 0 to 0.01 mg/l. During



monsoon season, the iron content was not recorded and this may be due to the

dilution factor. The iron concentration during premonsoon and postmonsoon

was 0.01mg/l and it may be attributed to low water level and evaporation.

Kamble et al. (2008) recorded the iron concentration of 0.04 mg/l to

1.53 mg/l in Khadakwasala reservoir. They observed minimum iron

concentration during the beginning of monsoon whereas maximum value was

observed during winter.

3.4.24 Correlation coefficient between different physico-chemical

parameters

The determination of correlation coefficient analysis can be used as an

important method for the interpretation among the physico-chemical

parameters and pollution levels of the surface waters of the reservoir.

According to Tiwari and Patel (1990), the correlation studies were site specific

and correlation coefficient can vary considerably from location to location. In

the present study, the water and air temperature always showed a direct

relationship with each other, as the solar energy is the only source for water

temperature rise which is in agreement with Ahmed and Krishnamurthy

(1990) and Shayestehfar and Seyfoddin (2010). There is an inverse

relationship recorded between dissolved oxygen with atmospheric

temperature, water temperature and transparency in the reservoir. According to

Rani et al. (2004), at high temperature the O2 holding capacity of water

decreases. Solubility of oxygen in the water increases when water temperature

decreases as reported by Awasthi and Tiwari (2004) and Patil et al. (2011). In

the present study, turbidity showed a negative correlation with transparency.

Shinde et al. (2011) opined that high light penetration increases the value of

transparency. The turbidity, created by suspended inorganic and organic

matter reduces the transparency of water as reported by Saxsena (1987).

Chapter 3


Positive correlation between DO and turbidity was observed in the Idukki

reservoir. Ayoade et al. (2009) also supported this finding. Free CO2 values

revealed the positive affinity with transparency and pH in Idukki reservoir. A

strong positive correlation observed between pH and free CO2 in Ramsagar

reservoir by Garg et al. (2009). The values of chloride showed positive

correlation with atmospheric temperature, water temperature and transparency

in the present study. Sharma et al. (2011) stated that high temperature and

consequent evaporation during the summer caused the higher chloride

concentration. The major cations (sodium, potassium, calcium and

magnesium) and anions (iron and chloride) of surface water samples were

significantly correlated with pH in the reservoir during the period of study.

Similar results were obtained by Sen et al. (2011) and according to them, pH

of the surface water depends on the hydrolysis of ions. In the present study,

the values of total hardness, calcium, magnesium, total alkalinity, electrical

conductivity, TDS, sodium, potassium, sulphate, phosphate and iron were

showed the direct relationship with atmospheric temperature, water

temperature, transparency, pH, CO2 and chloride. Hardness showed direct

relationship with atmospheric temperature, water temperature and pH

(Rajagopal et al., 2010a). A direct relationship observed between magnesium

with hardness and calcium. It is suggested that total hardness of water samples

is mainly due to the presence of MgCl2 (Bhol et al., 2005). Sodium and

potassium were positively correlated with calcium in the present study. These

types of positive correlation between the metal ions indicate that the metal

ions are from the same source as reported by Rajmohan et al. (2003), they also

showed similar type of positive correlation among the major cations. The

excellent correlations between the anions were also observed by Rajmohan et

al. (2003) and Mruthunjaya and Hosmani (2004). The hardness of surface

water is positively correlated with chloride (Sen et al., 2011). At Lotus Lake,



CO2 is positively correlated with TDS (Patil et al., 2011). The direct

relationship between alkalinity and pH observed in the present study was

possibly due to the metabolic activity of biotic material interactions, which is

in agreement with Shayestehfar and Seyfoddin (2010). Rajagopal et al.

(2010a) also recorded positive correlation between BOD and atmospheric

temperature, water temperature, pH and electrical conductivity. Sen et al.

(2011) also noted a positive correlation between iron and temperature and they

stated that the increase of temperature dissolves more iron in water. Kataria

and Jain (1995) and Sharma et al. (2010) also found the positive correlation

between conductivity and temperature. Calcium values showed positive

correlation with hardness during the present observation. Total dissolved

solids revealed the significant affinity with EC in the present study. Prajapathy

and Mathur (2003) and Beena (2009) also observed positive correlation

between TDS and electrical conductivity. Potassium showed positive

correlation with hardness, calcium, magnesium, alkalinity, conductivity and

TDS. The values of sulphate showed positive correlation with hardness,

calcium, magnesium, electrical conductivity, TDS, sodium and potassium. A

direct relationship observed between phosphate with electrical conductivity

and TDS. Iron exhibited positive correlation with hardness, calcium,

magnesium, alkalinity, electrical conductivity and TDS, while negative

correlation noticed with nitrate.

The inverse relationship is recorded between the free CO2 and DO in

the present study as is also reported by Sivakumar and Karuppasamy (2008)

and Patil et al. (2011). The comparison of BOD with DO in the present study

indicated that there is an inverse relationship between both parameters. Similar

relationship was also reported by Das (2000) and Tiwari (2005). Hussain

Chapter 3


(2008) stated that the presence of high level of BOD and COD caused to

further deplete of the dissolved oxygen content in the water.

*******

physico-chemical characteristics of idukki reservoirshodhganga.inflibnet.ac.in › bitstream ›...

Documents