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Environ Monit Assess (2010) 169:553–568DOI 10.1007/s10661-009-1196-y

Study on the hydrogeochemical characteristicsin groundwater, post- and pre-tsunami scenario,from Portnova to Pumpuhar, southeast coast of India

S. Chidambaram · AL. Ramanathan · M. V. Prasanna ·U. Karmegam · V. Dheivanayagi · R. Ramesh · G. Johnsonbabu ·B. Premchander · S. Manikandan

Received: 4 April 2009 / Accepted: 9 October 2009 / Published online: 27 October 2009© Springer Science + Business Media B.V. 2009

Abstract Natural hazards cause great damage tohumankind and the surrounding ecosystem. Theycan cast certain indelible changes on the naturalsystem. One such tsunami event occurred on 26December 2004 and caused serious damage to theenvironment, including deterioration of ground-water quality. This study addresses the groundwa-ter quality variation before and after the tsunamifrom Pumpuhar to Portnova in Tamil Nadu coastusing geochemical methods. As a part of a sepa-rate Ph.D. study on the salinity of groundwaterfrom Pondicherry to Velankanni, water qualityof this region was studied with the collection ofsamples during November 2004, which indicatedthat shallow aquifers were not contaminated bysea water in certain locations. These locations

S. Chidambaram (B) · U. Karmegam ·V. Dheivanayagi · R. Ramesh · G. Johnsonbabu ·B. Premchander · S. ManikandanDepartment of Earth Sciences, Annamalai University,Annamalai Nagar, Tamil Nadu, Indiae-mail: [email protected]

AL. RamanathanSchool of Environmental Sciences,Jawaharlal Nehru University, New Delhi, India

M. V. PrasannaDepartment of Applied Geology,School of Engineering and Science,Curtin University of Technology, Sarawak Campus,CDT 250, 98009, Miri, Sarawak, Malaysia

were targeted for post-tsunami sample collectionduring the months of January, March and August2005 from shallow aquifers. Significant physicalmixing (confirmed with mixing models) within theaquifer occurred during January 2005, followedby precipitation of salts in March and completeleaching and dissolution of these salts in the post-monsoon season of August. As a result, maxi-mum impact of tsunami water was observed inAugust after the onset of monsoon. Tsunamiwater inundated inland water bodies and topo-graphic lows where it remained stagnant, es-pecially in the near-shore regions. Maximumtsunami inundation occurred along the fluvialdistributary channels, and it was accelerated bytopography to a certain extent where the southernpart of the study area has a gentler bathymetrythan the north.

Keywords Groundwater · Hydrogeochemistry ·Tsunami · Salt leachate · Mixing

Introduction

The historic event of the tsunami on December26th, 2004, caused havoc, disturbing the naturalenvironment and causing heavy losses in humanlives and property. Causalities of this event intsunami-affected Indian states show Tamilnaduas one among the worst affected in the south

554 Environ Monit Assess (2010) 169:553–568

eastern part of the Indian subcontinent (Pal 2005).It is appealing to study their remains and examinethe extent of damage, or changes incurred to thenatural system off the coast caused by the deepwater brought by the tsunami. There are few re-gions where tsunami run-up water have washedthe surface and returned back to the sea, but thereare many places where water has easily enteredinland through distributary channels of rivers andalong river mouths, where water got locked upand slowly infiltrated till shallow aquifers. Onesuch area is from Portnova to Pumpuhar, locatedin the southeast coast of India. The study areais geomorphologically a coastal plain chiefly ofrecent alluvium. The estuary of the Vellar andColeroon rivers forms a lagoonal environmenthosting the mangroves of Pichavaram. Consid-erable extraction of groundwater for agriculturepurposes and aquaculture ponds is also takingplace along this coastal tract. In this scenario, thisstudy was attempted to understand the impact ofthe tsunami on the costal groundwater quality, es-pecially on the shallow aquifers in the district weremillions of people were using this groundwater fortheir domestic and drinking water supply beforethe tsunami.

Palanivelu et al. (2006) has studied the groundwater quality assessment in the tsunami-affectedcoastal areas of Chennai, located 250 km northof the study area. They have studied the TDSvalues and observed that at few locations awayfrom the sea showed an increase of TDS from Mayto September 2005. Villholth et al. (2005) reportedthe tsunami impacts on shallow groundwater andassociated water supply on the east coast of SriLanka. They have inferred that the salinity lev-els in flooded wells decreased significantly fromthe estimated levels at the time of the tsunami(29,400 μS/cm) till the start of their monitoring(3,200 μS/cm). Seven months after the tsunami,flooded wells had higher average salinity levelthan background, non-flooded wells, indicatingthat the groundwater still had not recovered fullyfrom the tsunami, and that at least one more rainyseason was required to flush the system and re-store the aquifers to pre-tsunami conditions. TheWorld Health Organization (2005) report afterthe tsunami observed that destruction brought bythe tsunami (mainly in India) on piped-in water

supplies and groundwater pumps, the saline waterintrusion of shallow wells and surface sources, ren-dered much of the pre-tsunami supplies through-out the affected area completely unusable.

Muralideran et al. (2005) has studied theimprint of the 26 December 2004 Sumatra earth-quake in aquifers of Hyderabad granite plu-ton. They explained that the earthquake hadinduced hydrological changes caused by changesin hydrostatic pressure due to earthquake-inducedchanges in crustal volumetric strain. The studyindicates that a rise in water level during theearthquake period was observed by them and bythe nearby observatory wells along the coast inAndhra Pradesh, India.

Kanakasabai and Rajendran (2005) reportedthe trend of micrometeorological parameters dur-ing the tsunami in the east coast of India. Theymeasured the micrometeorological parameterscontinuously at Portonova on the east coast ofIndia. The parameters like wind speed, wind di-rection, temperature and solar radiation wererecorded during the time of the tsunami.

Geophysical techniques were used to find outthe impact post-tsunami in the shallow groundwa-ters and the contamination in the perched aquifer(Chidambaram et al. 2008). The impact of thetsunamigenic sediment on the Pichavaram man-grove region was studied in detail before andafter the event, by collecting core samples. It wasnoted that high concentrations of Cd, Cu, Cr, Pband Ni were observed in tsunamigenic sediments.There were little variations with respect of Fe,Zn and Mn concentrations (Ranjan et al. 2008).Similar studies were carried out by Szczucinskiet al. (2005) and Scheffers and Kelletat (2003).Observations of tsunami in the Kerala coast ofIndia were made by Narayana et al. (2005).

All these studies focused on the importance ofground water quality and its role in drinking watersupply to tsunami-affected regions in Asia. Ourstudy is also aimed in this direction to get insightinto the ground water quality deterioration andthe processes responsible for the hydro chemicalchanges immediately after the tsunami. The studyalso focuses on its evolution over a period of timewhich will reflect the present situation of groundwater quality in these affected regions and help inguiding various utility purposes.

Environ Monit Assess (2010) 169:553–568 555

Study area

The study area extends from Parangipettai (Port-nova) to the Pumpuhar area between 79◦ 46′E and79◦ 51′ E longitudes and 11◦07′ N and 11◦ 30′ Nlatitudes (Fig. 1). It occurs within the survey ofIndia toposheets no. 58 M/15 & 16. The Vellarand Coleroon are the major rivers flowing into thestudy area; they form an estuary with a marshymangrove environment at Pichavaram.

Geological successionEra Age formations LithologyQuaternary Recent Soils, alluvium

Sub-recent Laterite andcoastal sands,clays, kankarand laterite

The maximum temperature ranges between27.9◦C and 36.9◦C, with mean ranging from 20.8◦C

to 27.1◦C. The long-term analysis of the rainfalldata from January to May indicates that averagerainfall is in the order of 1,162.35 mm/year witha maximum contribution from the NE monsoon(53.01% of the total rainfall). The groundwaterof this region is found in both unconfined andconfined aquifers (Fig. 2). In the major part ofthe study area, depth to water table ranges from5 to 20 m below ground level (mbgl) during pre-monsoon, whereas during post-monsoon it rangesbetween 2 and 10 mbgl. In the south-eastern partof the study area along Coleroon alluvial belt, theshallow water table less than 2 mbgl is observed.The Vellar alluvium and coastal alluvial forma-tions in the east signify the extent of water loggingconditions during the postmonsoon period. Thewater level observations for certain locations inthe study area during the tsunami indicate consid-erable increase of water level in certain locationsaccompanied by falls in a few regions. Aquiferparameters, like specific capacity, transmissivity

Fig. 1 Study area withthe groundwater samplinglocations

Coleroon river

Vellar river

Uppanar river

Cauvery river

11 51’

11 12’

79 70’

79 86’


Marcasite

Medium Sand

Coarse Sand

Lime Stone

Lignite

Shatiathope B.Muttalur

Clay

Fine Sand

Legend

Laterite

valaiamadeviPudukuriapetPuvanur

K-11.72S-772x10-2

-260

-240

-200

-160

-120

-600

-500

-400

0+40+60

-40

-60

K-16.47

S-3.1x10-4

Coast

K-Field Permeability

S-Storativity

T-Transmissivity

Fig. 2 Hydrogeological cross section from inland to coast derived from lithologs

and hydraulic conductivity of the region, wereanalysed. The transmissivity ranges from 295 to838 m2/day (CGWB 1997). Hydraulic conductivityestimated by storativity (S) is 1.77*10–3 m2/dayapproximately. The movement of water from oneregion to another is governed by (K), whichranges from 13.6 to 23.6 m/day.

Methodology

In total, 11 samples were collected (Fig. 1) in themonths of November 2004, January 2005, March2005 and August 2005. The samples were col-lected from shallow aquifers through tube wellsof depth 20 mbgl. Samples collected in the monthof November 2004 (suffix ‘pr’ collected for Ph.D.work on sources of salinity in coastal aquifers inAnnamalai University), January 2005 (J), March2005 (suffix ‘M’) and August 2005 (suffix ‘A’).Around 40 samples collected during November

2004 from Pondicherry to Velankanni showedthat 11 locations in shallow groundwater wereuncontaminated by seawater intrusion along thecoast and, hence, are identified/selected for post-tsunami impact studies (these 11 sampling loca-tions were selected for targeting the changes aftertsunami). The samples were collected mainly fromshallow aquifers (40–100-ft depth). The inundatedregion ranges from 0.5 to 1 km from the coast(Table 1). These wells were selected in such away that they are in the tsunami-inundated regionranging at least from about 0.2 to a maximumof 3 km from the coast and also were not ear-lier affected by salt water intrusion. The chem-ical parameters analysed for all these samplesare electrical conductivity (EC), pH, TDS, Na,K, Ca, Mg, HCO3, Cl and SO4. These parame-ters are used for the hydrogeochemical interpre-tations. The samples collected are analysed formajor cations like Ca and Mg by titrimetry and


Table 1 Run up andinundation duringtsunami in the study area

S.No Location Dissidence from Inundation Runcoast in KM distance (km) up (m)

1 Thirumulaivasal 0.32 102 272 Melmokkarai 0.52 0.75 223 Poombukar 0.2 0.32 34 Vazhuthalakudi 2.80 3.24 295 Palayar 0.64 0.78 266 T.kulam 1.66 2.97 1.167 Kulayar 1.96 2.67 1988 T.S Pettai 1.97 3.1 219 Portnova 1.12 168 2010 Kottayamedu 0.32 0.72 311 Nayakarpalayam 0.8 156 27

Na and K by flame photometer (CL 378). Theyare also analysed for anions like Cl and HCO3

by tirimetry and SO4 by spectrophotometer (SL171 minispec). EC and pH were determined inthe field using electrodes. The analyses were doneby adopting standard procedures (APHA 1998).The results of the analysis were checked by thecation anion balance, which was within ±8%. Acomputer programme WATCLAST in C++ wasused for calculation and graphical representations(Chidambaram et al. 2003). An experiment con-ducted with sea water evaporation and seawaterinfiltrate (Xue et al. 2000) was used for delineatingthe sea water impact on fresh groundwater. Thesaline soils formed by the evaporation of stagnantsea water by forming white crust were observedin an area north of the study area, due to poordrainage and high evaporation. Hence, lechatefrom those soils with these salt precipitates wasalso studied as lechate. The 100 g of sediment withsalt deposits on the surface were taken and addedto 250 ml of distilled water, and it was stirred(mechanically) for 24 h. Later, this was filteredand the filtrate was taken and analysed as lechate.These results were compared to the standard andmeasured seawater chemistry from Palayar regionin the study area.

Results and discussion

Groundwater is generally alkaline in nature withpH ranging from 7 to 8.8, with an average of7.58, pre-tsunami and from 7.1 to 8.1, with anaverage of 7.44, post-tsunami. EC ranges from 261

to 2,897 μS/cm, with an average of 1,284 μS/cm,pre-tsunami and from 294.83 to 6,743 μS/cm, withan average of 2,127 μS/cm, post-tsunami (Table 2).

Anions

Chloride concentration in samples varies between26.7 and 744 mg/l, with an average of 242 mg/l,pre-tsunami and from 177.25 to 3,217 mg/l, withan average of 1,146 mg/l, post-tsunami, indicatingthe long residence time of the tsunami water inthe shallow aquifers. Bicarbonate concentrationin analysed samples varies between 44.18 and549 mg/l, with average of 237 mg/l, pre-tsunamiand from 24.39 to 1,043 mg/l, with an average of378 mg/l, post-tsunami. Sulphate ranges from 16.9to 110.24 mg/l, with an average of 51.66 mg/l, pre-tsunami and from 38.13 to 507.5 mg/l, with anaverage of 164 mg/l, post tsunami.

Cations

With Na being the dominant cation, it ranges from11.34 to 280.19 mg/l, with an average of 83.78 mg/l,pre-tsunami, and it ranges from 69.7 to 1,837 mg/l,with an average of 495 mg/l, post-tsunami; thisshows there was an increase in Na concentra-tion after the tsunami. The coastal groundwaterof this region shows higher concentrations of Nafollowed by Ca (Chidambaram et al. 2005). Caranges from 28.99 to 340 mg/l, with an averageof 104.81 mg/l, pre-tsunami and from 40.75 to311.99 mg/l, with an average of 134.39 mg/l, post-tsunami. Magnesium concentration ranged from7.98 to 72.16 mg/l, with an average of 29.41 mg/l,


Tab

le2

Che

mic

alco

mpo

siti

onof

grou

ndw

ater

inth

est

udy

area

for

diff

eren

tper

iods

S.N

oL

ocat

ion

pHE

CC

aM

gN

aK

Cl

Hco

3So

4T

DS

pr1

Nov

embe

r,20

04K

otta

iyam

edu

7.4

1,61

034

0.68

30.5

472

.43

72.1

374

4.42

134.

264

1,12

7pr

2T

.kul

am7.

272

318

0.36

23.2

843

.45

11.2

177.

2442

7.09

27.8

650

6.1

pr3

Poo

mbu

kar

7.4

1,89

069

.36

37.2

917

1.35

9.78

177.

2449

4.1

57.8

91,

323

pr4

Thi

rum

ulla

ivas

al8.

895

356

.39

72.1

683

.14

36.6

631

9.05

195.

244

.89

667.

1pr

5V

alut

hala

ikud

i7.

81,

920

140.

2829

44.1

834

.435

4.48

122.

0372

.45

1,34

4pr

6P

aran

gipe

ttai

7.6

1,66

061

30.5

495

.45

42.1

313

6.83

305.

0664

1,16

2pr

7M

elm

okka

rai

7.8

261

28.9

99.

4520

.78

1.61

31.7

112

2.03

16.9

182.

7pr

8P

alay

ar7

1,49

082

.62

7.98

62.6

142

.92

177.

2444

.18

110.

241,

043

pr9

Kul

ayar

7.2

340

29.8

311

.86

11.3

46.

7326

.747

.89

63.9

823

8pr

10T

.S.p

etta

i7.

538

042

.02

9.01

36.7

4.23

59.5

917

6.94

19.1

226

6pr

11N

ayak

arpa

laya

m7.

72,

897

121.

462

.36

280.

1948

.56

438

549.

1226

.94

2,02

7.9

j1Ja

nuar

y,20

05K

otta

iyam

edu

7.02

1,08

016

519

3511

367.

2512

9.35

1273

9.12

j2T

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291,

100

227.

6614

85.9

3138

2.64

359.

941

1,12

2.09

j3P

oom

buka

r7.

762,

130

3819

210

1526

0.9

231.

894

868.

7j4

Thi

rum

ulla

ivas

al7.

62,

430

8093

110

4113

6.83

693.

1164

12,2

10j5

Val

utha

laik

udi

7.79

1,89

063

4278

4418

1.5

311.

198

815.

6j6

Par

angi

pett

ai7.

891,

750

5744

192

5118

6.2

438.

2410

21,

088.

44j7

Mel

mok

kara

i7.

5120

447

.29

1.7

21.7

92.

0430

.13

143.

997.

8225

4.73

j8P

alay

ar7.

161,

854

104.

7210

.61

142.

654

.418

9.54

268

125.

889

5.87

j9K

ulay

ar8.

0619

4.27

348.

9810

.26.

830

.13

51.8

578

.222

0.16

j10

T.S

.pet

tai

6.95

393.

4367

.33

11.4

244

.26.

833

.92

278.

2221

.76

463.

65j1

1N

ayak

arpa

laya

m7.

753,

060

2.72

76.5

377.

454

.453

8.9

424.

6515

.64

1,49

0.21


m1

Mar

ch,2

005

Kot

taiy

amed

u7.

6292

4.77

98.8

590

.81

261.

1512

7.28

933.

1782

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110.

1520

0.06

m2

T.k

ulam

7.18

740.

9458

.82

52.9

426

1.15

77.5

453

8.37

319.

175

.417

4.79

m3

Poo

mbu

kar

7.45

1,87

1.87

107.

5611

6.45

390.

822

5.03

1,06

3.45

427.

0911

6.48

430.

2m

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hiru

mul

laiv

asal

7.21

942.

8810

0.49

144.

2139

0.8

234.

751,

063.

4561

0.13

87.9

522

6.53

m5

Val

utha

laik

udi

7.6

2,01

018

4.34

163.

127

5.86

426.

231,

240.

6942

7.09

296.

181,

407

m6

Par

angi

pett

ai7.

111,

567.

2479

.93

72.6

420

6.9

95.8

453

1.73

305.

0687

.21

430.

2m

7M

elm

okka

rai

7.32

548.

8740

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34.6

925

2.87

56.5

443

1.31

294.

3838

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134.

06m

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alay

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252,

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9513

3.56

123.

543

6.78

174.

261,

238.

6436

6.08

179.

2161

0.72

m9

Kul

ayar

7.18

294.

8390

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189.

8539

0.8

178.

661,

417.

9418

3.04

103.

282

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m10

T.S

.pet

tai

7.2

1,30

3.72

53.3

552

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396.

7894

.789

0.39

143.

9959

.931

2.24

m11

Nay

akar

pala

yam

7.45

3,71

8.63

135.

0414

6.42

574.

7135

8.28

1,77

2.42

75.0

520

6.46

790.

45A

1A

ugus

t,20

05K

otta

iyam

edu

7.1

3,21

5.53

311.

9916

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8.3

103.

61,

102.

7921

3.5

170

2,25

0.87

A2

T.k

ulam

7.1

2,18

2.5

8867

.236

4.2

459

3.79

298.

914

7.5

1,52

7.75

A3

Poo

mbu

kar

7.6

1,76

6.57

190

4535

3.6

2257

6.2

542.

910

0.5

1,23

6.6

A4

Thi

rum

ulla

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al7.

52,

133.

1222

021

61,

837

363,

217.

0998

8.2

507.

51,

493.

19A

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alut

hala

ikud

i7.

96,

743.

8423

1.99

144

1,24

613

4.3

2,38

4.01

536.

827

04,

720.

69A

6P

aran

gipe

ttai

7.1

3,38

3.57

140

76.8

518.

729

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195.

2519

312

7.5

2,36

8.5

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Mel

mok

kara

i7.

71,

532.

1260

3669

.729

177.

2530

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2.5

1,07

2.49

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Pal

ayar

7.7

4,57

6.16

8093

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2.3

797.

6324

.428

7.5

3,20

3.31

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Kul

ayar

7.5

555.

9318

015

680

0.9

119.

91,

347.

189

0.6

125

389.

15A

10T

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9,5

99.0

414

084

898.

259

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8833

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220

1,11

9.33

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Nay

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8.1

3,18

2.71

231.

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4.8

250

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115

02,

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sea

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515

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1.2

5,76

519

1.8

10,2

30.5

195.

221

510

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r2Sa

ltle

acha

te7.

421

,571

.43

7287

87,

720

141.

813

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152.

518

515

,100

r3St

anda

rdse

aw

ater

8.2

50,2

07.1

441

11,

290

10,8

0039

219

,400

142

2,71

035

,145

All

valu

esin

mg/

lexc

epte

lect

rica

lcon

duct

ivit

y(E

C)

inμ

S/cm

and

pH


pre-tsunami and from 16.8 to 304.8 mg/l, with anaverage of 110.33 mg/l, post-tsunami. The is anotable increase in the average of Mg rather thanCa, during the post-tsunami period. Potassiumranges from 1.61 to 48.56 mg/l, with an average of25.49 mg/l, pre-tsunami and from 4 to 426 mg/l,with an average of 136 mg/l, post-tsunami.

Discussion

The pH in these groundwaters has slightly de-creased after the tsunami, whereas EC shootsup considerably, reflecting the impact of tsunamiwaters which exist even 3–8 months after thetsunami. Cl average value is 1,146 mg/l post-tsunami, which has increased several folds later,indicating the long residence time of the tsunamiwater in the shallow aquifers. Bicarbonate withan average of 378 mg/l in post-tsunami reflectsthe leaching of sea water. Sulphate is generallyderived from oxidative weathering of sulphide-bearing minerals (Prasanna et al. 2007) like Marc-asite (which is abundant in these regions), but thesudden shoot of these ions to above 500 mg/l is

a clear indication of the role played by tsunamiwaters. Dominance of anions in the study area isas follows: Cl > HCO3 > SO4 both pre-tsunamiand post-tsunami. Though the order of dominanceis maintained, the value of Cl shows a higher valuepost-tsunami. The order of abundance of cations isas follows: Ca > Na > Mg > K pre-tsunami and Na> K > Ca > Mg post-tsunami. Na dominates thecations during the post-tsunami period. Amongthe major ions, the many-fold increase of Na andCl is indicative of the long residence time spent bytsunami waters in these aquifers.

The Piper (1944) trilinear diagram shows(Fig. 3) that there are two groupings; one isnear the weathering zone and another is in theevaporation-dominant zone. Later in the subse-quent periods, there has been an increase in Cland Na in the system, which has eventually helpedin the migration of these groups towards thesea water composition. It is also observed thatthere is a subsequent decrease of relative HCO3

concentration in the system. The arrows in thediagram indicate the migration of samples fromthe pre-tsunami period to the sea water composi-tion in August 2005. These observations indicatethe long-term impact of tsunami waters on theaquifers’ water quality.

Fig. 3 Piper plot showingthe migration of chemicalcomposition of samplestowards sea watercomposition (sampled fora period from November2004 to August 2005)


Ternary diagram

The ternary diagram with Ca, Cl and HCO3 atthe vertex of the triangle with equivalent part permillion (epm) values indicates that the samplesof the pre-tsunami period and of January fall inthe central part zone II, with HCO3 dominance,whereas in March and August, samples fall in zoneI, which indicates dominance of Cl (Fig. 4). This issimilar to the Spensers triangle of three compo-nents to represent the pathway or the evolutionof water composition (Jones and Bodine 1987;Spencer et al. 1990). The migration of this com-position is also witnessed in the Pipers plot. Theternary diagram with epm values of Ca, Mg andHCO3 indicates that they fall in zone II with dom-inance of HCO3 during the pre-tsunami period,but during March and August, there is an increaseof Mg content relative to Ca and HCO3, but theystill have higher concentrations of HCO3 (Mulleret al. 1972) observed in August than in March.This indicates the predominance of evaporationduring March when compared to August, whereasdilution is significant after monsoon. This is alsosupported by the other observations as discussedbelow.

The total ionic strength (IS) of the samples isless during pre-tsunami and January. Later, they

have increased in March and subsequently in Au-gust (Fig. 5). The EC of the samples also variesfrom low to very high values. In general, the ISof the samples is below 0.06. Higher IS is notedin March and in August. The higher ranges ofEC were noted in January and in August, butAugust sample show higher EC and IS as well.The increase of IS is mainly due to the longerresidence time of the saline water in the aquifer(Chidambaram et al. 2005) or recharge of theevaporated saline water.

Saturation index

The saturation index (SI) of carbonate miner-als (McMahon and Chapelle 1991) in the sam-ples for different periods indicates that they aresaturated to near-saturated with calcite (C) andaragonite (A) (Fig. 6). They are under-saturatedto near-saturated with magnesite (M). Dolomite(D) shows under-saturation in the pre-tsunamisamples, but it shows super saturation duringAugust. This may be due to the increase of Mgconcentration in the subsequent periods. It canbe related that Ca is weakly correlated with otherions in January, which may be due to the removalof Ca from the system by precipitation of calciumcarbonate salts. The SID is still higher in August

Fig. 4 Spencer diagram for Ca–Cl–HCO3 and Ca–Mg–HCO3, indicating the clustering of samples collected in differentperiods


Fig. 5 The relationship ofionic strength withelectrical conductivity insamples collected indifferent periods

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 1000 2000 3000 4000 5000 6000 7000 8000

Electrical Conductivity in µS/ cm

Ion

ic s

tren

gth

November , 2004

January, 2005

March, 2005

August, 2005

than in March because of the dissolution of thesalts that precipitates after March, thereby addingmagnesium into the system.

Since the study covers periods like monsoon,post-monsoon and summer, there are variationsin temperatures. This study will throw more lighton the relation of the SI with temperature andvarious other mechanisms operating in the un-derground environment that control the SI ofcarbonate minerals. It is generally known that

there is a significant change in SI of mineralswith temperature (Garrels and Christ 1965). Thevariation of SI of the Palayar region sea water atdifferent temperatures was discussed. Carbonateminerals show positive SI in the following order:SID > SIC > SIA (SID, dolomite; SIC, calcite andSIA, aragonite), though with increase of temper-ature the trend becomes positive, there is a par-allelism between SIC and SIA. Hence, it can beinferred that the temperature variation effects on

Fig. 6 Variation ofsaturation indices fordifferent carbonateminerals in groundwatersamples collected fromNovember 2004 toAugust 2005

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25 30 35 40 45 50

Samples of different periods

Sat

ura

tio

n in

dex

(S

I)

Magnesite Dolomite (d) Calcite Aragonite

August March January Pretsunami


SIC and SIA are similar but the trend with SID

varies (Fig. 7), and the increase of temperaturethus increases the SI. It is further noticed thatthe higher temperatures noted in March lessenthe SI of carbonate minerals. This may be dueto the impact of infiltered rain water or due tothe removal of ions by precipitation of salts. Sinceno showers of rainfall were recorded during themonths of February or March, along with higherEC and IS than the pre-tsunami waters, it rules outthe possibility of dilution by rain water. Lechatecomposition chiefly reflects the evaporate concen-tration of the sea water entrapped in the land.The SI of lechates matches with the groundwatersaturations in August. Thus, it indicates that thechanges in groundwater chemistry during Augusthave not attained similar compositions with in-crease in temperatures but due to precipitationand dissolution.

Statistics

The correlation between the chief cation and an-ion was carried out. They indicate, during the pre-

tsunami condition, that good correlation existsbetween Na and HCO3: Ca and Cl. Mg has alsohad good correlation with all ions. Ca and SO4

do not have correlation with any other ions. InJanuary, Na develops positive correlation withCl, Mg and K. Good positive correlation existsbetween Mg and HCO3. Ca and SO4 did notcorrelate with other ions present in the system.During March, good correlation exists betweenmajor cations Ca and Mg. Cl shows good corre-lation with Na; SO4 with K, Ca, Mg and Cl. Thesamples in August reveal that HCO3 has goodcorrelation with Na, Mg, Ca and Cl: good corre-lation also exists between Na, SO4 and Cl. All theions are represented well in the correlation matrix(Fig. 8). The matrix records show that there is norelationship between Na and Cl during the pre-tsunami period, but it developed a poor positivecorrelation during January. After that, they showexcellent correlation between Cl and Na in Marchand August. It is further noted that the associationof HCO3 with Na decreased from November 2004to August 2005. The enrichment of HCO3 in Au-gust compared to March indicates that dissolution

Fig. 7 Variation ofsaturation index (SI) ofcarbonates in Palayar seawater at differenttemperature (OC)

3731 33 35 39 41 43 45

Temperature

Calcite Dolomite Aragonite

25

0.4

0.2

027 29

Sa

tura

tion

Ind

ex(

SI)

1.4

1.6

1.2

1

0.8

0.6


Na

SO4

Cl

HCO3

MgCa

January 2005

0.75-1

Cl

NaMg

HCO3K

March 2005 August 2005

K

0.5-0.75

Ca

Na

Mg

Cl

K

November 2004

Mg

HCO3Na

ClCa

K

SO4

Correlation

coefficient

Fig. 8 Correlation of different ions in groundwater sam-ples collected in different study periods

of the precipitated salts was prominent only dur-ing August, i.e. after the onset of monsoon. Therains during June and July have increased themigration of ions either by weathering or leachingof salts precipitated in summer (Srinivasamoorthyet al. 2007). In total, it is believed that K–Mg–Na–Cl represents the dominant ionic group during theperiod of study.

PCA was done by using Varimax rotation(Table 3). Factor analysis indicate that threeprominent factors were extracted for pre-tsunamiand January (post-tsunami) and two for Augustand March. The first component of factor loadingin pre-tsunami was represented by HCO3, Mgand Na, indicating the process of weathering. Thefirst component of January was represented by Cl,HCO3, K, Mg and Na, indicating the mixing effectof sea water and fresh water. But during March,the first factor representation was slightly changedto Cl, Ca, K, Mg, and Na, indicating the existenceof the evaporation mechanism. The second fac-tor was represented by Cl and Na with negativerepresentation of Ca, HCO3, Mg and SO4, whichindicates that there is a removal of these ionsfrom the system by the precipitation of salts in

Table 3 Factor analysis of major cations and anions duringPre and Post tsunami conditions

Factor 1 Factor 2 Factor 3

November, 2004Ca −0.2 0.98 0.03Cl 0.32 0.90 0.23HCO3 0.83 0.02 −0.38K 0.45 0.43 0.72Mg 0.84 0.21 0.09Na 0.94 0.09 0.06SO4 −0.23 0.04 0.91

January, 2005Ca −0.10 −0.07 0.99Cl 0.67 −0.53 0.30HCO3 0.81 0.21 0.05K 0.87 0.37 0.09Mg 0.85 0.00 −0.22Na 0.82 −0.09 −0.31SO4 0.16 0.89 −0.03

March, 2005Ca 0.96 −0.07Cl 0.80 0.59HCO3 0.27 −0.78K 0.96 0.04Mg 0.86 0.18Na 0.47 0.72SO4 0.91 −0.02

August, 2005Ca 0.28 0.58Cl 0.93 0.30HCO3 0.39 0.78K −0.25 0.79Mg 0.29 0.86Na 0.97 0.16SO4 0.86 0.07

pore spaces from the surface due to precipitation(Chidambaram et al. 2008). Hence, there is anenrichment of Cl and Na. In August, the firstfactor is represented by Cl, Na and SO4, wherethe impact of saline water is noted along with theassociation of Ca, HCO3, Mg and K as a secondfactor. This is due to the leaching and dissolutionof salt precipitated during March. Later, the rainsduring June and July have considerably increasedleaching and added the ions into the system.

Comparison

The comparison is calculated by the similaritycoefficient between the samples (including pre-and post-tsunami) with the sea water of the study


area. This is done by means of a linear regressionlogarithm. Similar samples that have correlationcoefficients close to the correlation coefficient ta-ble ratios were taken into account rather than theabsolute values. Therefore, samples being dilutedby precipitation may still have a correlation co-efficient with respect to its original compositioneven though the quality of dissolved minerals isvery different. The difference in absolute concen-tration is expressed by the Euclidean distance.

Dij =∑

n k − 1(Xik − Xjk

)

n,

where Xik denotes the Kth variable measured onsamples i and Xjk is the Kth variable measured onsample j, in all ‘n’ variables are measured on eachsample and Dij is the distance between sample iand sample j.

This is obtained by comparison of seven para-meters, Ca, Mg, Na, K, Cl, HCO3 and SO4 wheresamples with correlation coefficient values greaterthe 0.75 are displayed (Fig. 9). The comparisonis done with all the samples, first with that of

seawater then with the salt-leached water. Highercorrelation was found in the samples of Marchand August (A10, A5, A7, M10, A4 and A8). Thesamples show better correlation to salt leacheatesthan that of the seawater. Hence, it is clear thatsamples from August have better comparison tothe leachate and seawater than with other periods.Thus, it is evident that the mechanism that has al-tered the groundwater is not the direct infiltrationbut due to precipitation and dissolution of the saltsentrapped from sea water.

Percent of mixing

The chemical compositions of different samples ofthe study area for different seasons are comparedwith the chemical composition of the sea water inthe study area and the leached waters from thesalt precipitate (Xue et al. 2000). The samples ofAugust identified by earlier comparison and theircorresponding pre-tsunami compositions were se-lected to identify the mixing proportion. This wasdone by using the following formula:

Fig. 9 Diagram showingthe relationship ofcorrelation coefficientsfor groundwater samplesto seawater of the studyarea and the salt leachate

A1

A2

A4

A5 A6

A8

A9

A10

M1

M2

M3

M4

M5 M6

M7

M8M9

M10

M11

A1

A2

A4

A5

A8

A9

M1

M2

M3

M4

M6

M7

M8

M10

M11

A6A10

M5

M9

0.75

0.8

0.85

0.9

0.95

1

0 2 4 6 8 10 12 14 16 18 20

Samples of different period with correlation coeffeicient >0.75

Co

rrel

atio

n c

oef

feic

ein

t

Series1

Series2Salt leachate

Sea water

Mixing percentage

= (Cl + Na + SO4) concentration in post-tsunami − (Cl + Na + SO4) pre-tsunami concentration ∗ 100

(Cl + Na + SO4) concentration in sea water of the study area


Table 4 Percent of sea water mixing identified in theAugust samples

S.No Location Percentage of mixing

1 Kottaiyamedu 42 T. Kulam 44 Thirumulaivasal 345 Valuthalakudi 226 Parangipetai 118 Palayar 710 T S Pettai 18

The results were also confirmed usingAquachem software. So, the pre-tsunami waterchemistry of the region is taken for the respectiveAugust location and the amount of mixing iscalculated.

The percentage of sea water mixed with thegroundwater after the tsunami event is obtainedby the above said equation. The results of the mix-ing percentage of the sea water with groundwaterin the sample (Table 4) shows the following order:A4 > A5 > A10 > A6 > A8 > A1 = A2. Thehigher rate of mixing is noted in the regions withmore distribution channels of rivers where thewater has entered and stagnated, precipitated andleached into the system. It is also noted that the

bathymetry is gentle in the southern part of thearea, where the tsunami water might have entereda long distance inland, where the inundation isfavoured by the distributary’s channels and rivermouth. From this study, we have inferred thatthese processes (Fig. 10) might have been con-trolling the hydro-geochemical changes of groundwater after the tsunami. After the tsunami, sea-water entered the water table through the openwells or tube wells (M1), and the entrapped water(M2) got infiltered into the water table of thecoastal alluvium during January 2005. Later hightemperature in the summer months might resultin the formation of salt precipitates (M3) (dueto evaporation of infiltered/stagnated water byimpermeable clay layers) near the surface or inpore spaces and subsequent dilution in the end ofMarch 2005 by sparse rain. After precipitation anddissolution, salt leached out from surface to theshallow groundwater zones (M4), enhancing theEC and TDS of the groundwater of August 2005.Thus, the impact of direct infiltration or directmixing of tsunami waters (M1) has a relativelylower effect than the subsequent precipitation anddissolution of salts formed by the entrapped seawater, which happened after the tsunami event.

Fig. 10 A schematicrepresentation of thepossible factors for thehydrogeochemicalchange, after the tsunami


Conclusion

It is inferred that the sea water has also enteredinland along the river mouth and drainage canalduring the event. Most of the water has drainedback to the sea, and the rest was stagnated inland.This study suggests that, after the tsunami, salinewater had entered the subsurface groundwater,forming a mixture of fresh and saline water duringthe month of January. Later, during March, therehad been depletion in the water table along withthe increase in temperature, resulting in evapora-tion and precipitation of salts in the pore spaceand on the surface. The changes in the composi-tion during these months are well established bythe variation in the IS and by the Spencers plot.A clear shift in hydrogeochemical facies of thegroundwater is also noted with respect to differentperiods of observation. The subsequent rains dur-ing June/July have leached the precipitated saltsolution from the surface and the pore spaces,which has increased the complexity of the chem-ical relationship in August. The rise in the waterlevel has dissolved the precipitated salt in the porespace. The statistical analysis of the data and theSI of the carbonate minerals in the groundwateralso confirm the above observations. Higher per-centage of seawater is noted in the groundwatersof the southern part of the study area in samplesA4 and A5. Both shallow unconfined aquifers andperched aquifers got altered due to inundation,stagnation, precipitation and subsequent leaching,which resulted in water quality deterioration.

Acknowledgement The author wishes to thank the De-partment of Science and Technology, India, for their fi-nancial support. The authour is also thankful to Mr. B.Premchander for permitting us to avail of a part of hisPh.D. data for this study.

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