fluvial geochemistry of subarnarekha river basin, india

J. Earth Syst. Sci. (2018) 127:119 c© Indian Academy of Scienceshttps://doi.org/10.1007/s12040-018-1020-6

Fluvial geochemistry of Subarnarekha River basin, India

Abhay Kumar Singh*, Soma Giri and Aaditya Chaturvedi

Natural Resource and Environmental Management Division, CSIR – Central Institute of Miningand Fuel Research, Barwa Road, Dhanbad 826 015, India.*Corresponding author. e-mail: [email protected]

MS received 25 July 2017; revised 30 January 2018; accepted 12 March 2018; published online 26 October 2018

The fluvial geochemistry of the Subarnarekha River and its major tributaries has been studied ona seasonal basis in order to assess the geochemical processes that explain the water compositionand estimate solute fluxes. The analytical results show the mildly acidic to alkaline nature of theSubarnarekha River water and the dominance of Ca2+ and Na+ in cationic and HCO−

3 and Cl− inanionic composition. Minimum ionic concentration during the monsoon and maximum concentrationin the pre-monsoon seasons reflect concentrating effects due to decrease in the river discharge andincrease in the base flow contribution during the pre-monsoon and dilution effects of atmosphericprecipitation in the monsoon season. The solute acquisition processes are mainly controlled by weatheringof rocks, with minor contribution from marine and anthropogenic sources. Higher contribution ofalkaline earth (Ca2++ Mg2+) to the total cations (TZ+) and high (Na++K+)/Cl−, (Na++K+)/TZ+,HCO−

3 /(SO2−4 +Cl−) and low (Ca2++Mg2+)/(Na++K+) equivalent ratios suggest that the Subarnarekha

River water is under the combined influence of carbonate and silicate weathering. The river water isundersaturated with respect to dolomite and calcite during the post-monsoon and monsoon seasonsand oversaturated in the pre-monsoon season. The pH–log H4SiO4 stability diagram demonstrates thatthe water chemistry is in equilibrium with the kaolinite. The Subarnarekha River annually delivered1.477 × 106 ton of dissolved loads to the Bay of Bengal, with an estimated chemical denudation rateof 77 ton km−2 yr−1. Sodium adsorption ratio, residual sodium carbonate and per cent sodium valuesplaced the studied river water in the ‘excellent to good quality’ category and it can be safely used forirrigation.

Keywords. Subarnarekha River basin; weathering; solute acquisition; dissolved flux; saturation index;water quality.

1. Introduction

Water is the most essential natural resource forsustaining all forms of life, food production, eco-nomic development and general well-being. Wateris also one of the most manageable naturalresources as it can be diverted, transported, storedand recycled. India accounts for 2.4% of the global

land and 4% of the world water resources, but it hasto support 16% of the world’s human and 20% oflivestock populations (Kumar et al. 2005). Riversare the major source of fresh water for agricul-tural and industrial usage. River processes forma major link in the geochemical cycle and thehydro-chemical study of river basins reveals thenature of weathering at a basin scale and helps

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119 of 22 J. Earth Syst. Sci. (2018) 127:119

in understanding the exogenic cycling of elementsin the continent–river–ocean system. Nearly 90%of the natural weathered as well as man-madematerials that are transported in both dissolvedand particulate phases are delivered to the oceansby rivers (Meybeck 1987, 2003). The quantifica-tion of the major-ion composition of river waterhas broad implications in assessing the hydrogeo-logical characteristics; weathering processes, waterquality type and rainfall chemistry (Drever 1988;Gaillardet et al. 1999; Brennan and Lowenstein2002). In addition, information on river waterchemistry is essential to assess the water qual-ity for domestic, agricultural and industrial usesand useful in environmental impact assessment andpollution control. India is gifted with a river sys-tem comprising more than 20 major rivers withseveral smaller river basins and its tributaries.Many of these rivers are perennial and some ofthem are seasonal (Rao 1975). The rivers of Indiadrain a total area of about 3.1×106 km2 andannually discharge 1650 km3 of water, accountingfor 4.5% of the global river discharge (Krish-naswami and Singh 2005). The hydrological cyclein most of the Indian river basins is being mod-ified quantitatively and qualitatively as a resultof developmental activities such as constructionof dams and reservoirs; land use change; indis-criminate disposal of anthropogenic, industrial andmining wastes; unplanned application of agro-chemicals and discharges of improperly treatedsewage/industrial effluents (Chakrapani and Sub-ramanian 1990; Ramanathan et al. 1994; Singh andHasnain 1999; Subramanian 2000).

Previous studies have revealed the major-ionchemistry of some of the world’s large- andmedium-sized river systems including the Amazon(Gibbs 1972; Stallard and Edmond 1983, 1987;Gaillardet et al. 1997), Orinoco (Nemeth et al.1982), Mackenzie (Reeder et al. 1972), Missis-sippi (Presley et al. 1980), Mekong (Carbonneland Meybeck 1975), Changjiang and Huanghe(Hu et al. 1982; Zhang et al. 1990, 1995; Chenet al. 2002), Ganges–Brahmaputra (Abbas andSubramanian 1984; Sarin et al. 1989; Galy andFrance-Lanord 1999), Godavari (Biksham and Sub-ramanian 1988; Jha et al. 2009), Krishna (Rameshand Subramanian 1988; Das et al. 2005), Cau-very (Ramanathan et al. 1994; Pattanaik et al.2013), Mahanadi (Chakrapani and Subramanian1990); Damodar (Singh and Hasnain 1999) andMahi (Sharma et al. 2012). These extensive stud-ies not only reported the signatures of river systems

responding to natural processes, such asatmospheric precipitation and chemical weather-ing, but also detected the significant signaturesresponding to human activities. The chemical com-position of river water is determined by sev-eral factors such as relief and altitude of thecatchment, tectono-climatic setup, rainfall quan-tity and quality, bedrock geology, soil and vegeta-tion cover, biological and anthropogenic activitiesin the drainage basin (Berner and Berner 1987;Stallard and Edmond 1987; Rajamani et al. 2009).In comparison to large rivers, the smaller riversinvariably flow in less diverse geological terrains,having limited tectono-climatic variations and theeffect of human interventions could be better con-strained in a smaller river basin. The presentstudy deals with the fluvial geochemistry of theSubarnarekha River basin – a moderate size rain-fed river of eastern India flowing through India’simportant mining and industrial belt. This studyaims to characterise the major-ion chemistry andevaluates weathering and solute acquisition pro-cesses and anthropogenic influences on the surfacewater quality of the Subarnarekha River. Thisstudy also envisages the seasonal and downstreamcompositional changes, dissolved fluxes and suit-ability of surface water resources for irrigationuses.

2. Subarnarekha River basin

The Subarnarekha is a moderate sized river basin,extending over 19,296 km2 and covering 0.6% ofthe geographical area of India. The total annualyield of water flowing within the basins is inthe order of 7940 million m2 (CBPCWP 1986).It is a rain-fed river that rises from a seriesof contact springs located near the Nagri village(23◦18′N, 85◦11′E) at an elevation of 740m onthe Ranchi Plateau in Chhota Nagpur highland(figure 1). The Subarnarekha empties its enor-mous volume of water and sediment load intothe Bay of Bengal after its 395 km long jour-ney from its source at Nagri village to its mouthnear Kirtania port (21◦33′18′′N, 87◦23′31′′E). Outof its total length of 395 km, 269 km are in Jhark-hand, 64 km in West Bengal and 62 km in Odissastates. The Subarnarekha is a very important riverto satisfy the irrigation, industrial and munici-pal water demands of these three states. Raru,Kanchi, Karkari, Kharkai and Dulung are themajor tributaries of the Subarnarekha River.

J. Earth Syst. Sci. (2018) 127:119 of 22 119

Figure 1. Location map of Subarnarekha River basin showing sampling locations, major mines, minerals and industrialzones.

The major part of the Subarnarekha basin lieson the Indian Shield, where the ancient Precam-brian igneous and metamorphic rocks are exposed.In the lower reaches of the basin, the youngergeological formation such as Tertiary Gravels,Pleistocene Alluvium and Recent Alluvium areexposed. Pelitic schist, calc-magnesium metased-iments, ortho-amphibolites, tonalite-trondhjemite,banded iron formation, mafic lavas, phyllites,shales, metapellites, quartzites, soda-granites,granitic-gneiss, dolerite dyke swarms and gravelsare the major litho units associated with the geo-logical formations of the basin. The Subarnarekhabasin is rich in mineral resources mainly compris-ing ores of metals such as copper, iron, uranium,chromium, gold, and vanadium and non-metalssuch as kyanite, asbestos, barytes, apatite, chinaclay, talc, limestone, dolomite and building stones(figure 1). The basin is studded with a largenumber of mineral-based industries and mines

both working and abandoned with the attendantproblems of environmental hazard. Heavy Engi-neering Corporation (HEC), Usha Martin Indus-tries, Steel Authority of India (SAIL), HindalcoIndustries Ltd., Tata Steel and Iron Company,Hindustan Copper Ltd. (HCL) and Uranium Cor-poration of India (UCIL) are the major industrialunits in the basin.

The Subarnarekha basin is dominated by humidtropical climate with hot summers and mild win-ters. The mean monthly temperature varies from40.5◦C in May to 9.0◦C in December. The meanannual rainfall in the basin is ∼1400 mm. Therainfall distribution is not uniform and 85–95%of the annual precipitation and about 82% ofthe total annual flow actually occurs over onlyfour wet months (June–September), while in theremaining part of the year, the Subarnarekha Riverand its tributaries run almost dry. Agriculturalland accounts for 62% of the total basin area


Table

1.Chem

icalcompositionofsurface

waterofSubarn

arekhaRiver

anditsmajortributaries.

Sit

eco

de

Sit

enam

e/tr

ibuta

rypH

EC

(µS

cm−1)

TD

S(m

gl−

1)

F−

(µM

)C

l−(µ

M)

HC

O− 3

(µM

)SO

2−

4(µ

M)

NO

− 3(µ

M)

Silic

a(µ

M)

Subarn

are

khamain

channel

1a

Nagri

6.2

6116

87

12

274

533

22

154

187

b6.3

3138

99

16

305

590

25

189

232

c6.2

090

71

997

464

11

124

210

2a

Nam

kum

7.2

0570

427

18

1260

3623

149

186

392

b7.5

71000

645

27

3179

5229

256

4198

c7.0

8408

305

23

1175

1934

154

420

292

3a

Tati

silw

ai

6.7

2499

404

13

1817

2547

142

529

362

b7.3

81220

847

23

5802

5016

196

963

387

c6.9

5431

309

22

1533

1770

155

404

298

4a

Hundru

7.9

1183

157

19

229

1443

68

17

280

b8.0

0265

212

22

865

1557

95

9312

c7.8

5167

136

17

327

1213

61

9210

5a

Muri

7.7

2216

176

16

284

1600

96

28

284

b7.9

3762

599

65

1424

5000

629

38

323

c8.1

5190

129

22

555

902

97

36

135

6a

Chandil

8.2

5165

135

18

133

1229

56

10

320

b7.6

9177

154

31

177

1439

52

12

280

c8.0

9119

95

23

97

820

52

17

228

7a

Bara

bin

da

7.9

8162

140

21

131

1311

55

34

293

b8.1

9190

162

28

170

1500

48

30

315

c7.6

2125

100

22

92

852

57

27

230

8a

Kander

ber

a7.9

7154

134

55

141

1229

62

10

252

b8.5

4185

154

28

167

1500

44

2243

c8.0

8143

118

21

101

1066

70

22

228

9a

Jam

shed

pur

(Sonari

)7.7

2290

254

17

281

2459

131

28

343

b7.3

1221

187

22

272

1744

86

11

288

c7.7

9190

162

19

168

1475

91

28

256

10

aJam

shed

pur

(Mango)

7.6

2249

206

18

258

1956

93

23

355

b7.5

3216

190

20

279

1744

67

37

315

c7.8

2209

156

20

211

1311

113

59

256

11

aG

alu

dih

7.8

0395

340

37

581

2295

729

17

332

b7.5

1259

208

46

486

1672

151

37

278

c7.9

4163

138

24

150

1229

79

46

213

12

aM

oosa

baniU

/S

8.1

7293

246

26

316

2131

273

25

258

b8.7

3305

244

48

587

1744

347

1302

c7.8

4261

193

23

236

1311

423

52

218


aM

oosa

baniD

/S

8.1

4313

262

21

312

2377

265

26

248

b7.5

1297

227

48

574

1639

279

1315

c7.7

8186

150

23

223

1279

90

81

224

14

aShyam

sunder

pur

8.3

9249

210

39

301

1885

184

25

257

b7.7

9293

249

45

535

2016

240

34

280

c7.7

2174

143

23

164

1246

92

50

229

15

aB

ahara

gora

8.0

2238

209

19

275

1836

182

17

293

b7.6

5285

223

52

558

1621

247

19

315

c8.1

1165

137

22

188

1180

85

46

229

16

aG

opib

allav

pur

7.9

2227

201

33

253

1803

152

14

303

b8.3

8279

236

49

552

1852

229

18

290

c8.0

0168

137

22

131

1229

82

24

233

17

aM

ahapal

7.6

0304

275

17

259

2852

92

4280

b8.0

2283

227

44

531

1805

206

14

287

c7.7

8176

139

24

161

1262

64

22

235

18

aSonaka

niy

a7.9

1219

189

18

218

1718

121

7340

b8.9

3249

198

45

480

1500

190

7303

c8.0

3158

131

25

128

1213

70

16

221

19

aR

ajg

hat

7.8

3229

197

16

236

1803

126

23

321

b8.6

6246

221

44

406

1885

184

34

307

c8.2

0156

139

23

127

1279

74

16

249

Tributa

ries

20

aK

anch

i7.7

4165

140

15

122

1311

40

11

327

b7.8

9207

177

23

248

1623

57

14

305

c7.7

7148

118

20

346

869

58

18

270

21

aK

hark

ari

7.8

3198

174

14

384

1475

82

18

307

b8.0

2294

256

15

550

2361

70

20

342

c7.6

5186

163

16

344

1410

55

35

263

22

aK

hark

hai

7.8

7319

280

23

307

2705

146

46

338

b8.6

5566

453

28

1408

3449

376

197

375

c7.7

3231

197

18

234

1770

128

36

263

23

aG

arr

a7.6

0504

410

43

700

2623

943

23

326

b7.7

0803

585

57

2202

1621

2172

37

372

c7.8

7291

229

24

283

1836

336

19

254

24

aSankh

7.8

0253

219

34

118

2192

86

2377

b8.7

7315

247

48

518

1787

325

18

318

c7.9

7175

141

19

85

1295

73

13

305


Table

1.(C

ontinued.)

Sit

eco

de

Sit

enam

e/tr

ibuta

ryC

a2+(µ

M)

Mg2+(µ

M)

Na+(µ

M)

K+(µ

M)

SA

R(m

eq)

%N

aR

SC

(meq

)T

Z−

(meq

)T

Z+(m

eq)

NIC

B(%

)

Subarn

are

khamain

channel

1a

Nagri

188

102

406

54

0.7

644.3

−0.0

51.0

21.0

41.1

b203

118

441

58

0.7

843.7

−0.0

51.1

51.1

4−

0.4

c178

91

244

53

0.4

735.6

−0.0

70.7

20.7

95.0

2a

Nam

kum

1347

342

1687

278

1.3

036.8

0.2

45.3

85.3

4−

0.4

b1746

541

3230

492

2.1

444.9

0.6

58.9

58.2

9−

3.8

c1025

293

1208

268

1.0

535.9

−0.7

03.8

64.1

13.2

3a

Tati

silw

ai

1537

330

1601

239

1.1

733.0

−1.1

95.1

95.5

73.6

b3229

576

3209

419

1.6

532.3

−2.5

912.2

011.2

4−

4.1

c1111

284

1233

209

1.0

434.1

−1.0

24.0

44.2

32.3

4a

Hundru

440

214

449

66

0.5

628.2

0.1

31.8

41.8

2−

0.6

b672

232

910

114

0.9

636.1

−0.2

52.6

42.8

33.4

c384

170

371

69

0.5

028.4

0.1

01.6

91.5

5−

4.3

5a

Muri

475

204

578

76

0.7

032.5

0.2

42.1

22.0

1−

2.6

b420

301

5713

127

6.7

380.2

3.5

57.7

87.2

8−

3.3

c297

171

615

107

0.9

043.6

−0.0

41.7

11.6

6−

1.5

6a

Chandil

381

172

365

45

0.4

927.0

0.1

21.5

01.5

20.5

b482

200

472

42

0.5

727.4

0.0

71.7

61.8

83.2

c272

129

273

31

0.4

327.5

0.0

21.0

61.1

12.1

7a

Bara

bin

da

378

174

391

46

0.5

328.4

0.2

01.6

11.5

4−

2.1

b520

213

448

46

0.5

225.2

0.0

31.8

21.9

63.6

c319

137

259

37

0.3

824.5

−0.0

61.1

11.2

14.5

8a

Kander

ber

a395

189

393

45

0.5

127.3

0.0

61.5

61.6

11.5

b509

205

418

44

0.4

924.4

0.0

71.7

81.8

92.8

c384

185

262

31

0.3

520.5

−0.0

81.3

51.4

32.9

9a

Jam

shed

pur

(Sonari

)758

403

725

58

0.6

725.2

0.1

33.0

53.1

10.9

b591

247

548

61

0.6

026.7

0.0

62.2

22.2

81.4

c472

300

495

48

0.5

626.0

−0.0

71.8

72.0

95.4

10

aJam

shed

pur

(Mango)

557

268

623

62

0.6

929.3

0.3

02.4

42.3

4−

2.2

b599

246

595

55

0.6

527.8

0.0

52.2

12.3

42.7

c462

282

467

61

0.5

426.2

−0.1

81.8

32.0

14.8

11

aG

alu

dih

1050

626

1176

79

0.9

127.2

−1.0

74.3

94.6

12.4

b652

248

782

117

0.8

233.3

−0.1

32.5

42.7

02.9

c501

182

327

58

0.4

022.0

−0.1

41.6

11.7

54.3

12

aM

oosa

baniU

/S

816

406

679

76

0.6

123.6

−0.3

23.0

43.2

02.5

b769

300

947

127

0.9

233.4

−0.4

03.0

73.2

12.2

c661

301

470

80

0.4

822.2

−0.6

22.4

72.4

70.1


aM

oosa

baniD

/S

885

423

635

90

0.5

621.7

−0.2

53.2

73.3

41.1

b750

289

805

123

0.7

930.9

−0.4

42.8

23.0

13.2

c546

192

359

47

0.4

221.6

−0.2

01.7

91.8

82.7

14

aShyam

sunder

pur

631

255

631

77

0.6

728.5

0.1

12.6

22.4

8−

2.7

b777

310

879

137

0.8

431.8

−0.1

63.1

13.1

91.3

c519

177

342

52

0.4

122.0

−0.1

51.6

71.7

93.4

15

aB

ahara

gora

616

391

585

71

0.5

824.6

−0.1

82.5

12.6

73.0

b654

293

886

145

0.9

135.3

−0.2

82.7

42.9

23.1

c489

202

324

22

0.3

920.0

−0.2

11.6

11.7

33.7

16

aG

opib

allav

pur

594

376

551

59

0.5

623.9

−0.1

42.4

12.5

52.9

b714

295

923

139

0.9

234.5

−0.1

72.9

33.0

82.5

c504

182

323

29

0.3

920.4

−0.1

51.5

71.7

24.6

17

aM

ahapal

836

552

735

49

0.6

222.0

0.0

73.3

23.5

63.5

b670

308

896

127

0.9

134.4

−0.1

62.8

12.9

83.0

c490

212

331

44

0.3

921.1

−0.1

41.6

01.7

85.3

18

aSonaka

niy

a559

342

481

51

0.5

122.8

−0.0

92.2

02.3

32.9

b593

277

752

107

0.8

133.1

−0.2

52.4

12.6

03.8

c439

190

330

40

0.4

222.7

−0.0

51.5

21.6

33.4

19

aR

ajg

hat

536

362

537

65

0.5

725.1

0.0

02.3

32.4

01.4

b614

284

779

90

0.8

232.6

0.0

92.7

42.6

6−

1.4

c484

201

327

42

0.4

021.2

−0.0

91.5

91.7

44.4

Tributa

ries

20

aK

anch

i377

191

478

10

0.6

330.0

0.1

71.5

41.6

22.7

b482

210

750

51

0.9

036.7

0.2

42.0

22.1

93.9

c337

166

452

44

0.6

433.0

−0.1

41.3

71.5

04.7

21

aK

hark

ari

454

370

584

54

0.6

427.9

−0.1

82.0

52.2

95.3

b761

428

851

77

0.7

828.1

−0.0

23.0

93.3

13.4

c504

314

513

46

0.5

725.5

−0.2

31.9

12.2

06.8

22

aK

hark

hai

908

529

644

59

0.5

419.6

−0.1

83.3

73.5

82.9

b1394

540

1889

219

1.3

635.3

−0.4

35.8

35.9

81.2

c748

282

484

42

0.4

820.3

−0.2

92.3

12.5

95.5

23

aG

arr

a1567

711

1279

79

0.8

523.0

−1.9

45.2

85.9

15.7

b2306

478

2665

220

1.6

034.1

−3.9

58.2

68.4

51.2

c816

374

624

46

0.5

722.0

−0.5

52.8

33.0

53.6

24

aSankh

696

490

369

36

0.3

414.6

−0.1

92.5

22.7

84.9

b816

359

942

99

0.8

730.7

−0.5

73.0

23.3

95.8

c470

258

271

29

0.3

217.1

−0.1

71.5

61.7

66.0

Unit

s:C

once

ntr

ati

ons

are

inµM

l−1,ex

cept

pH

,E

C(µ

Scm

−1),

TD

S(m

gl−

1)

TZ+

(meq

l−1),

TZ−

(meq

l−1)

and

NIC

B(%

).

EC

,el

ectr

icalco

nduct

ivity;T

DS,to

taldis

solv

edso

lids;

TZ+,to

talca

tions;

TZ−

,to

talanio

ns;

NIC

B,norm

alise

din

org

anic

charg

ebala

nce

;a,post

-monso

on

(Sep

tem

ber

2011);

b,pre

-monso

on

(May

2012);

c,m

onso

on

(July

2012).


and nearly 31% of the area is devoted to forests.A number of dams/reservoirs (Getasuld, Hatia,Chandil, Galudih) have been constructed on theSubarnarekha and its tributaries mainly for thepurpose of electricity generation, flood control andirrigation.

3. Methodology

Seventy-two water samples were collected from 24sites along the Subarnarekha River and its majortributaries during the post-monsoon (September2011), pre-monsoon (May 2012) and monsoon(July 2012) seasons (figure 1). The sampling sea-sons were selected according to the hydrologicalregime in the basin. The samples were mostlycollected from the middle of the river, eitherfrom the bridge or with the help of a boat toavoid local heterogeneity and possible human influ-ence near the river banks. Water samples werecollected in the pre-washed narrow mouth 1-lhigh-density polyethylene bottles. Electrical con-ductivity (EC) and pH values were measured inthe field using a portable conductivity and pHmeter after recalibration with the standard buffersolutions. The water samples were filtered through0.45µm Millipore membrane filter to separate thesuspended particulates. The concentration of bicar-bonate (HCO−

3 ) and dissolved silica (SiO2) weredetermined by acid titration and molybdosilicatemethods, respectively (APHA 1998). The concen-tration of major F−, Cl−, SO2−

4 and NO−3 were

analysed by Dionex ion chromatograph (DX-120)using anions AS12A/AG12 columns. The majorcations (Ca2+, Mg2+, Na+, K+) were determinedby atomic absorption spectrophotometer (Varian680 FS) in flame mode. Three replicates were runfor each sample and the instrument was recali-brated after every 15 samples analysis. An overallprecision, expressed as per cent relative standarddeviation, was obtained below 5% for the entiresamples. Total cations (TZ+) and anions (TZ−)are coupled by the relation TZ+ = 0.947 × TZ− ±0.237 with a correlation coefficient of 0.989 andthe normalised inorganic charge balance (NICB)is within ±10% (table 1). USGS hydrogeochemicalsoftware (PHREEQC) is used for the estimationof saturation index values of carbonate mineralphases (Parkhurst and Appelo 1999). Aquachemand Grapher software of Waterloo Hydrologic havebeen used for Piper diagram and other graphicalpresentation.

Water quality parameters such as sodiumadsorption ratio (SAR), per cent sodium (%Na)and residual sodium carbonate (RSC) were com-puted to assess the suitability of the SubarnarekhaRiver basin water for irrigation by the followingequations:

SAR = Na+/√(

Ca2+ + Mg2+)/2, (1)

%Na = Na + K/ (Ca + Mg + Na + K) × 100, (2)

RSC =(CO2−

3 + HCO−3

) − (Ca2+ + Mg2+

). (3)

(All ionic concentrations used for the calculationare expressed in meq l−1.)

4. Results and discussion

4.1 Fluvial geochemistry

The analytical results of surface water samplesof the Subarnarekha River and its major tribu-taries during the post-monsoon, pre-monsoon andmonsoon seasons are given in table 1. Table 2shows the range and average concentration of themeasured parameters and ionic ratios in the Sub-arnarekha River water during the post-monsoon,pre-monsoon and monsoon seasons.

The pH of the Subarnarekha River water var-ied from 6.20 (mildly acidic) to 8.93 (alkaline),with most samples falling within a range of 7.0–8.0. The pH was slightly higher during the leanflow pre-monsoon (avg. 7.95) period as comparedto the high flow regimes of monsoon (7.74) andpost-monsoon (7.75). The water was slightly acidicin nature at the Nagri site, which might be dueto comparatively more organic loading near theorigin site of the Subarnarekha River. EC var-ied from 116 to 570µS cm−1 in post-monsoon,138 to 1220 µS cm−1 in pre-monsoon and 90 to431µS cm−1 during the monsoon season. On anaverage, the lowest EC is observed during themonsoon (196µS cm−1) and the highest in the pre-monsoon (377µS cm−1), while the post-monsoonseason is characterised by an intermediate value(271µS cm−1). Total dissolved solids (TDS) inthe Subarnarekha basin water ranged from 71 to847 mg l−1 with an average concentration valueof 225 mg l−1. The low TDS value is observednear the river origin site at Nagri village andit increases randomly at the downstream sites.Like EC, TDS concentration was relatively higher


Table

2.Range

andaverage

concentrationofmeasuredparametersandmajor-ionratiosin

Subarn

arekhaRiver

basinwaterforpost-m

onsoon,pre-m

onsoonandmonsoon

seasons.

Aver

age

(n=

72)

Post

-monso

on

(n=

24)

Pre

-monso

on

(n=

24)

Monso

on

(n=

24)

Para

met

ers

Range

Aver

age

±Std

.dev

.R

ange

Aver

age

±Std

.dev

.R

ange

Aver

age

±Std

.dev

.R

ange

Aver

age

±Std

.dev

.

pH

6.2

0–8.9

37.8

1±

0.5

16.2

6–8.3

97.7

5±

0.4

66.3

3–8.9

37.9

5±

0.6

6.2

0–8.2

27.7

4±

0.4

4

EC

(µS

cm−1)

90–1220

282

±195

116–570

271

±117

138–1220

377

±282

90–431

196

±81

TD

S(m

gl−

1)

71–847

225

±136

87–427

228

±91

99–847

292

±190

71–309

156

±57

F−

(µM

)9–65

27

±13

12–55

23

±11

15–65

36

±14

9–25

21

±3

Cl−

(µM

)85–5802

536

±822

118–1817

383

±389

167–5802

928

±1254

85–1533

298

±347

HC

O− 3

(µM

)464–5229

1792

±904

533–3623

1956

±667

590–5229

2162

±1222

464–1934

1259

±343

SO

2−

4(µ

M)

11–2172

187

±285

22–943

179

±214

25–2172

274

±428

11–423

107

±91

NO

− 3(µ

M)

0.8

1–963

65

±143

2.4

0–529

53

±110

0.8

1–963

73

±196

8.5

–420

67

±109

SiO

2(µ

M)

135–392

283

±52

187–392

307

±47

198–387

303

±43

135–305

239

±35

Ca2+

(µM

)178–3229

699

±476

188–1567

708

±363

203–3229

872

±673

178–1111

517

±221

Mg2+

(µM

)91–711

294

±130

102–711

351

±154

118–576

312

±118

91–374

220

±70

Na+

(µM

)200–5713

808

±831

365–1687

691

±368

418–5713

1280

±1246

200–1233

453

±261

K+

(µM

)10–492

92

±84

10–278

76

±59

42–492

135

±110

22–268

64

±57

TZ−

(meq

)0.7

2–12.2

02.7

9±

1.9

41.0

2–5.3

82.7

7±

1.2

21.1

5–12.2

03.7

5±

2.7

70.7

2–4.0

41.8

6±

0.7

7

TZ+

(meq

)0.7

9–11.2

42.8

8±

1.8

51.0

4–5.9

12.8

8±

1.3

31.1

4–11.2

43.7

8±

2.5

30.7

8–4.2

31.9

9±

0.8

2

NIC

B(%

)−4

.3-6

.83

2.2

0±

2.5

8−2

.71−5

.69

1.6

0±

2.4

1−4

.09–5.7

71.7

3±

2.5

7−4

.30–6.8

33.2

7±

2.5

7

Ionic

ratios

Na+

+K

+/C

l−0.6

3–4.1

02.2

6±

0.7

21.0

1–4.0

2.4

6±

0.6

60.6

3–4.1

02.0

2±

0.7

50.9

4–3.5

52.3

1±

0.7

1

*C

a2+/N

a+

0.0

7–1.8

81.0

3±

0.3

30.4

6–1.8

81.0

4±

0.2

70.0

7–1.2

20.8

2±

0.2

40.4

8–1.7

31.2

3±

0.3

3

*M

g2+/N

a+

0.0

5–1.3

30.4

7±

0.2

00.2

0–1.3

30.5

5±

0.2

30.0

5–0.5

60.3

3±

0.1

10.2

3–0.9

50.5

4±

0.1

6

*H

CO

− 3/N

a+

0.6

1–5.9

42.7

8±

0.9

61.3

1–5.9

43.0

8±

0.9

40.6

1–4.5

92.1

3±

0.7

31.4

4–4.7

83.1

2±

0.8

7

(Ca2+

+M

g2+)/

HC

O− 3

0.2

9–3.4

31.1

2±

0.3

90.8

4–1.7

41.0

6±

0.2

20.2

9–3.4

31.1

5±

0.5

30.9

1–1.5

71.1

5±

0.8

0

(Ca2+

+M

g2+)/

TZ+

0.2

0–0.8

50.7

1±

0.0

90.5

6–0.8

50.7

3±

0.0

60.2

0–0.7

60.6

5±

0.1

10.5

6–0.8

30.7

5±

0.0

6

(Ca2+

+M

g2+)/

Na+

+K

+0.2

5–5.8

52.6

9±

0.9

11.2

6–5.8

52.8

9±

0.9

00.2

5–3.0

92.0

5±

0.6

01.3

0–4.8

63.1

3±

0.8

6

(Na+

+K

+)/

TZ+

0.1

5–0.8

00.2

9±

0.0

90.1

5–0.4

40.2

7±

0.0

60.2

4–0.8

00.3

5±

0.1

10.1

7–0.4

40.2

5±

0.0

6

*H

CO

− 3/SiO

22.2

1–26.4

66.2

9±

3.1

72.8

5–10.1

96.3

2±

1.8

92.5

5–26.4

67.2

7±

4.9

02.2

1–7.2

25.2

6±

1.1

8

Ca2+/SO

2−

40.6

7–16.9

05.9

4±

3.1

31.4

4–10.8

55.8

0±

2.5

10.6

7–16.5

05.8

8±

4.0

11.5

6–16.9

06.1

4±

2.8

0

Ionic

rati

oin

equiv

ale

nt

unit

,ex

cept

*m

ola

rra

tio.


in the pre-monsoon (292 mg l−1) as comparedto the post-monsoon (228 mg l−1) and monsoon(156 mg l−1) seasons. Seasonal variation of EC andTDS values indicates an increase in ionic concen-trations during the pre-monsoon season, probablydue to excessive evaporation and/or contributionfrom the groundwater in the summer months anddilution effects of atmospheric precipitation in themonsoon season. The elevated temperature in thehot summer months increases water evaporationand causes a reduction in river flow, resultingin an enhancement in solute concentration. Spa-tial variations in ionic concentration show a sharpincrease at the Namkum–Tatisilwai–Muri indus-trial zone (sites 2, 3 and 5) and for the Garratributary (T-4). Namkum, Tatisilwai and Muriare under the influence of industrial activities.Huge quantities of industrial and urban effluentsare discharged into the Kharkai and the mainSubarnarekha River at these locations. TributaryGarra receives highly polluted water and effluentswith high sulphate contents and has high con-centration of total suspended and dissolved solidsmainly in the Jaduguda–Ghatsila mining complexareas.

HCO−3 , Ca2+, Na+ and dissolved silica account

for >75% of the total dissolved loads and domi-nate the major-ion chemistry of the SubarnarekhaRiver water. The HCO−

3 was the most domi-nant anion in the surface water of the Sub-arnarekha River followed by Cl−, SO2−

4 , NO−3

and F−. The major anions constitute 65% ofthe TDS. The plot of the analytical data onanion diagram relating HCO−

3 , Cl− and SO2−4

shows the clustering of plotted points near theHCO−

3 apex with a secondary trend towards Cl−

and SO−24 (figure 2a). Bicarbonate concentration

ranged from 464 to 5229µM with an averagevalue of 1792µM and it contributed 69% (20–87%) to the total anionic (TZ−) charge balancein equivalent unit. Bicarbonate in river water ismainly contributed from the dissolution of atmo-spheric CO2 and weathering of carbonates and/orsilicate minerals by the carbonic acid. The CO2

in the subsurface environment is mainly origi-nated from the decomposition of organic matter,which in turn combines with rainwater to formbicarbonates.

Chloride (Cl−) concentration in the analysedwater samples of the Subarnarekha River rangedfrom 85 to 5802µM (avg. 536µM) and it accountsfor 16% of the total anionic charge (TZ−). Excepthalite, most of the rock types contain very low

Figure 2. (a) Ternary anion diagram relating HCO3, SO4

and Cl and (b) ternary cation diagram relating Ca, Mg and(Na + K).

concentration of chloride and it is believed that themajor portion of Cl− in water is primarily derivedfrom either the atmospheric source or the sea water(Berner and Berner 1987). Leaching of salt andsaline residues in the soil, municipal, industrial,animal wastes and usage of fertiliser also plays avital role as the source of chloride (Appelo andPostma 1996; Singh et al. 2008). Large spatialvariations and increased chloride concentrations atsites W-2, W-3 and W-23 may be attributed toanthropogenic sources. The concentration of SO2−

4

and NO−3 in the surface water of the Subarnarekha

River basin was found in the range of 11–2172and 0.81–963 µM and it accounted for 12% and2.3% of the total anionic charge (TZ−) balance,respectively. Relatively the higher concentration ofnitrate at Namkum (W-2) and Tatisilwai (W-3)sites indicates the anthropogenic contribution from


1

10

100

1000

10000

Con

cent

ratio

n in

µM

, exc

ept E

C (µ

S/cm

) and

pH

pH EC TDS F- Cl- HCO3- SO4

2- NO3- SiO2 Ca2+ Mg2+ Na+ K+

Post-monsoonPre-monsoonMonsoon

Measured Parameters

Figure 3. Average concentration of measured parameters in Subarnarekha basin water.

the leaching of fertiliser from agricultural fields.The concentration of F− varied from 9 to 65µM(avg. 27µM) and on an average it contributed 1.2%to the total anions (TZ−).

Ca2+, Mg2+, Na+ and K+ together constitute25% of the TDS. Calcium was the most dom-inant cation in the water of the SubarnarekhaRiver, contributing 49% of the total cations (TZ+)followed by Na+ (26%), Mg2+ (22%) and K+ (3%).The calcium concentration ranged from 178 to3229µM, while the concentration of Na+ var-ied from 200 to 5713µM. The concentration ofMg2+ and K+ ranged from 91 to 711 and 10 to492µM, respectively, with an average value of 294and 92µM. Ca2+ and Mg2+ together account forabout 71% of the total cationic charge balance inthe equivalent unit. The cation concentration inthe Subarnarekha basin water generally followedthe decreasing order of Ca2+ >Na+>Mg2+ >K+

with some minor exceptional samples, where Na+

concentration was found to be higher than theCa2+ or Mg2+ exceeding the Na+ concentration.The plot of the analytical data on cation dia-gram relating Ca2+, Mg2+ and (Na+ + K+) showsthat the plotted points of the water samplesfall either in the ‘calcium’ or in ‘no dominant’zone (figure 2b). Dissolved silica (SiO2) concen-tration in the Subarnarekha River water variedfrom 187 to 392µM during the post-monsoon,198 to 387 µM in the pre-monsoon and 135 to305µM in the monsoon (table 2). On average,

the dissolved silica accounted for 9% (2–19%)of the TDS and it exceeds the chloride andsulphate concentrations at many sites. The aver-age concentration of dissolved silica (283µM) inthe studied river water is higher than the aver-age global (200µM) and Indian (117µM) rivers(Ramanathan et al. 1994). The higher concentra-tion of dissolved silica in the Subarnarekha Riverreflects the important contribution from the weath-ering of silicate rocks. The average HCO3/SiO2

molar ratio for the Subarnarekha and its tribu-taries vary between 2 and 26 (avg. 6.3); however,in a majority of samples it ranges between 5 and10, indicating the combined influence of carbonateand silicate weathering (Hounslow 1995). The highHCO3/SiO2 ratio (>10) in some water samplescan result from the supply of alkalinity from car-bonates, salt affected soils and/or anthropogenicsources. No specific trend has been observed in thedownstream variation of dissolved ionic concentra-tions. In general, the temporal variation of averageconcentration of major ions on the river basin scalefollows a decreasing order of pre-monsoon>post-monsoon>monsoon (figure 3).

The trilinear Piper plot (Piper 1944) for theSubarnarekha River water reveals the dominanceof alkaline earth (Ca2+ + Mg2+) metals overalkalis (Na+ + K+) and weak acid (HCO−

3 ) overstrong acids (SO2−

4 + Cl−). The plotted points ofmajority of samples fall in the field 5, signify-ing the carbonate hardness (secondary salinity)


1

2 3

45

6

7

8

9

9

Fields Characteristics/Nature of water

1 Alkaline earths (Ca+Mg) exceeds alkalies (Na+K)2 Alkalies exceeds alkaline earths3 Weak acids (CO3+HCO3) exceeds strong acids (SO4+Cl)4 Strong acids exceed weak acid5 Carbonate hardness (secondary alkalinity) exceeds 50%6 Non-carbonate hardness (secondary salinity) exceeds 50%7 Non carbonate alkali (primary salinity) exceeds 50%8 Carbonate alkali (primary alkalinity) exceeds 50%9 None of the cation or anion pairs exceed 50%


Figure 4. Piper trilinear diagram showing the hydrogeochemical character of river water and hydrochemical facies (afterPiper 1953).

that exceeds 50% (figure 4). Only five watersamples fall in the field 9, indicating water of anintermediate (mixed) chemical character having noone cation–anion pair exceeding 50%. Ca−HCO3

and Ca−Mg−HCO3−Cl are identified as the domi-nant hydrogeochemical facies in the surface waterof the Subarnarekha River basin.

The average chemical composition of theSubarnarekha River basin water along with someother Indian Rivers and the world and Indianaverages is summarised in table 3. The TDS con-tent of the Subarnarekha basin water is higherthan that of the Indus, Brahmaputra, Godavari,Damodar and the Indian and world average rivers,but it is lower as compared to the Krishna, Cau-very, Narmada, Tapti, Mahi and Gomti rivers andcomparable to Mahanadi, Son and Ganges aver-ages. Like other Indian rivers, the Subarnarekhahas high alkalinity, indicating the extent of mixingwith HCO3-rich groundwater and atmosphericallyregulated PCO2–water reactions, which mayfurther enhance the carbonate alkalinity. Potas-sium concentrations do not show much variation in

the Subarnarekha water as in the other river basins,suggesting conservative behaviour of this element.Berner and Berner (1987) reported that only 15%of the river transport of potassium is in the dis-solved form. The low concentration of dissolvedK in water may be attributed to the resistanceof potassium bearing minerals (orthoclase, micro-cline) against weathering. Potassium is commonlyfixed in specific clay minerals, after being releasedduring the primary weathering reactions and there-fore does not behave in the same way as the otherweathering derived ions (Stott and Burt 1997). Thehigher contributions of dissolved silica, Na+ andSO2−

4 to the TDS in comparison to the other riverbasins may be attributed to silicate weatheringand inputs from the sulphide weathering andanthropogenic sources in the drainage basin.

4.2 Weathering and solute acquisition processes

Chemical load in the river basin is consideredto be a reflection of its watershed and flood-plains and processes occurring in the tributaries

J. Earth Syst. Sci. (2018) 127:119 of 22 119Table

3.Average

compositionofSubarn

arekhabasinwaterin

comparisonto

other

majorIndianRiver

basins.

Riv

ers

Dra

inage

are

aD

isch

arg

eM

CM

HC

O3

Cl

SO

4H

4SiO

4C

aM

gN

aK

TD

SR

efer

ence

s

Subarn

are

kha

19,2

96

7940

109

19

18

17

28

719

3.6

225

Pre

sent

study

Dam

odar

25,8

20

12,2

10

94

11

21

22

15

916

4.0

191

Sin

gh

and

Hasn

ain

(1999)

Kri

shna

258,9

48

62,8

00

178

38

49

24

29

830

2.4

360

Ram

esh

and

Subra

mania

n(1

988)

Cauver

y87,9

00

20,9

50

135

20

13

23

21

943

4.0

272

Ram

anath

anet

al.

(1994)

Godav

ari

312,8

12

118,0

00

105

17

810

22

512

3.0

181

Bik

sham

and

Subra

mania

n(1

988)

Mahanadi

141,5

89

66,6

40

122

23

317

24

13

14

8.3

224

Chakra

paniand

Subra

mania

n(1

990)

Indus

321,2

89

79,5

00

64

915

527

11

2.1

122

Subra

mania

n(1

983)

Narm

ada

98,7

95

54,6

00

225

20

59

14

20

27

2.0

322

Subra

mania

n(1

983)

Tapti

65,1

45

17,9

82

150

65

116

19

22

48

3.0

322

Subra

mania

n(1

983)

Mahi

34,8

41

11,8

00

246

38

19

21

31

17

55

2.7

436

Sharm

aet

al.

(2012)

Gom

ti30,4

37

7390

262

915

14

29

18

27

4.8

380

Gupta

and

Subra

mania

n(1

994)

Son

71,2

50

22,4

20

125

18

10

18

29

814

3227

Mahara

naet

al.

(2015)

Ganges

861,4

04

468,7

00

128

10

11

18

25

811

3.0

214

Subra

mania

n(1

983)

Bra

hm

aputr

a258,0

08

627,0

00

38

15

10

729

7.4

12

2.5

148

Subra

mania

n(1

983)

India

nav

g.

3,2

87,7

82

1,8

58,1

00

74

15

13

730

712

3.0

159

Subra

mania

n(1

983)

Worl

dav

g.

––

62

49

12

16

44.4

1.5

115

Sari

net

al.

(1989)

Unit

s:m

gl−

1.T

DS:to

taldis

solv

edso

lids;

MC

M:m

illion

m3.

(Richey et al. 1990). Berner and Berner (1996)identified three possible sources of dissolved saltinto the inland waters as (i) sea salt carried in theatmosphere and deposited on the land; (ii) weath-ering reaction taking place in the drainage basinand (iii) anthropogenic input. The proportions ofcontribution from these sources vary in space andtime, resulting in seasonal and downstream varia-tions in the chemical composition within the riverbasin. The atmospheric contribution to the dis-solved salt in the inland water has been discussedby various authors (Stallard and Edmond 1983;Sarin et al. 1989; Berner and Berner 1996). Theinput of chloride concentration through precipita-tion is generally used as a parameter for evaluatingthe atmospheric contribution. This is because ofthe fact that Cl− is regarded as a conservativeelement as it reacts very little with other ions,does not form complexes and also does not par-ticipate in the biogeochemical cycling, except insmall basins where biota plays a dominant role(Viers et al. 2001). The atmospheric contributionto the dissolved salts in the aquatic water canbe assessed by comparing the chemical compo-sition with the local rainwater chemistry or bytaking the ratios of elements to Cl− (Sarin et al.1989; Pandey et al. 1994; Singh et al. 2005). Theaverage Na+/Cl−(2.03) and K+/Cl−(0.23) ratiosin the surface water of the Subarnarekha Riverwere found to be higher as compared to marineaerosols (Na+/Cl− = 0.85 and K+/Cl− = 0.0176).This indicates a limited contribution from theatmospheric precipitation and suggests that highproportions of dissolved ions in this water arederived from the weathering of rock-formingminerals and anthropogenic sources. The plot ofgeochemical data on Gibbs’s diagram (Gibbs 1970)that represents the ratio of (Na+ + K+)/(Na++K+ + Ca2+) and Cl−/(Cl− + HCO−

3 ) as a functionof TDS also indicates the dominance of weatheringof rocks as a major controlling factor to determinethe surface water chemistry of the Subarnarekhabasin (figure 5).

Weathering of different parent rocks (e.g.,carbonates, silicates and evaporites) yields differentcombinations of dissolved cations and anions in thewater (Drever 1988; Berner and Berner 1996). Forinstance, calcium and magnesium in the river waterare mainly derived from the weathering of carbon-ate and silicate minerals and evaporite dissolution.Silicate weathering along with evaporite dissolu-tion and atmospheric precipitation are the majorsources of sodium and potassium in the river water.


Weathering Dominance

Evaporation Dominance

Precipitation Dominance

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Na+K/(Na+K+Ca)

1

10

100

1000

10000

100000

Tota

l Dis

solv

ed S

olid

s (m

g L-

1 )

Weathering Dominance

Evaporation Dominance

Precipitation Dominance

0.6 0.80.0 0.2 0.4 1.0 1.2

Cl/(Cl+HCO3)

1

10

100

1000

10000

100000

Tota

l Dis

solv

ed S

olid

s (m

g L-

1 )

(a) (b)



Figure 5. Gibbs’s diagram representing the ratio of (a) Na+K/(Na+K+Ca) and (b) Cl/(Cl + HCO3) as a function of TDS(after Gibbs 1970).

Dissolved silica is exclusively derived from theweathering of silicates. The plot of (Ca2+ + Mg2+)vs. (HCO−

3 + SO2−4 ) will be close to 1:1 line if the

dissolution of calcite, dolomite and gypsum is thedominant reaction in a system. Figure 6(a) showsthat plotted points of the majority of the Sub-arnarekha water samples fall below the theoretical1:1 trend line in the variation diagram relat-ing (Ca2++Mg2+) to (HCO−

3 +SO2−4 ). The excess

of (HCO−3 +SO2−

4 ) over (Ca2++Mg2+) suggestscontribution from the non-carbonate source anddemanding that the required portion of(HCO−

3 +SO2−4 ) to be balanced by the alkalis

(Na++K+). (Ca2++Mg2+)/HCO−3 ratio demar-

cates the maximum portion of bicarbonate that canbe derived from the carbonate weathering (Stallardand Edmond 1983). The variation diagram between(Ca2++Mg2+) and HCO−

3 for the Subarnarekhabasin water shows that in the majority of samples(Ca2++Mg2+) the contents are in excess of alkalin-ity and the magnitude of excess being larger for thetributaries (figure 6b). The excess of (Ca2++Mg2+)over bicarbonate in these waters indicates someextra source of Ca2+ and Mg2+ and excess partof the positive charges is balanced by other anionssuch as SO2−

4 and/or Cl−. The data plot along theequiline on (Ca2++Mg2+) vs. TZ+ at lower concen-tration range suggests a significant contribution ofCa2+ and Mg2+ to the total cations. Deviations ofplotted points from 1:1 equiline at higher concen-tration especially during the pre-monsoon indicate

the increasing contribution of alkalis (Na++K+)to the total cations with increasing ionic concen-trations (figure 6c).

The concentrations of (Na++K+) in theanalysed water samples are significantly in excessover chloride and high (Na++K+)/Cl− ratio i.e.,2.26 suggests non-atmospheric source of alkaliswhich might be derived from silicates weathering(figure 6d). (Na++K+)/TZ+ and (Ca2++Mg2+)/(Na++K+) ratios can be used as an index to assessthe contribution of cations through silicate weath-ering (Stallard and Edmond 1983; Sarin et al.1989). The plot of (Na++K+) vs. TZ+ showsthe deviation of plotted points from the 1:1 equi-line and the (Na++K+)/TZ+ ratio varies between0.15 and 0.80 (figure 6e). The (Ca2++Mg2+)/(Na++K+) molar abundance ratio in the silicatesof upper crust is generally 1.0 (Taylor and McLen-nan 1985). The average (Ca2++Mg2+)/(Na++K+)ratio in the Subarnarekha River water is 2.7,comparable to the world (2.2) and Indian (2.5)river water averages (figure 6f). The observedlow (Ca2++Mg2+)/(Na++K+) ratio, i.e., 2.7 andhigher (Na++K+)/TZ+, i.e., 0.29 ratio in theanalysed waters suggest that the chemical com-position of the Subarnarekha River is under thecombined influence of carbonate and silicateweathering (Sarin et al. 1989; Singh et al. 2005).

Small rivers draining only carbonates arecharacterised by higher calcium and magnesiumconcentrations and have high Ca2+/Na+, i.e., 50;


100 1000 10000

TZ+ (µeq/l)

100

1000

10000

Na

+ K

(µeq

/l)

1000 10000

HCO3 + SO4 (µeq/l)

1000

10000

Ca

+ M

g (µ

eq/l)


100 1000 10000

Cl (µeq/l)

100

1000

10000

Na

+ K

(µeq

/l)

100 1000 10000Na + K (µeq/l)

100

1000

10000

Ca

+ M

g (µ

eq/l)

(e)

(c)

(b)

(d)

(f)

1000 10000

HCO3 (µeq/l)

1000

10000

Ca

+ M

g (µ

eq/l)

(a)

1000 10000

TZ+ (µeq/l)

1000

10000

Ca

+ M

g (µ

eq/l)

Figure 6. Scatter plot between (a) Ca+Mg vs. HCO3+SO4, (b) Ca+Mg vs. HCO3, (c) Ca+Mg vs. total cations, (d) Na+Kvs. Cl, (e) Na+K vs. total cations and (f) Ca+Mg vs. Na + K.

Mg2+/Na+, i.e., 10; and HCO−3 /Na+, i.e., 120

ratios (Gaillardet et al. 1999). The dissolved loadsof water draining silicate terrains is expected tohave a low Ca2+/Na+ molar ratio because of highersolubility of Na+ relative to Ca2+. The molarratios of Ca2+/Na+ = 0.35 ± 0.15, Mg2+/Na+ =0.24 ± 0.12, HCO−

3 /Na+ = 2 ± 1 are assignedfor the silicate end member. The observed molarratios of Ca2+/Na+ (1.04), Mg2+/Na+ (0.48) and

HCO−3 /Na+ (2.78) in the Subarnarekha River

waters are much lower than those of the watersdraining carbonate lithology and higher than thatdrain silicate rocks, indicating that the solutechemistry of the Subarnarekha River is essen-tially controlled by two-component mixing fromthe dissolution of silicates and carbonates. Theplots of HCO−

3 /Na+ vs. Ca2+/Na+ and Ca2+/Na+

vs. Mg2+/Na+ relating carbonate and silicate end


Silicates

Evaporites

Carbonates

100

Ca2+/Na+ (mM/mM)

0.01

0.1

1

10

Mg2+

/Na+ (

mM

/mM

)

Pre-monsoonMonsoonPost-monsoon

Silicates

Evaporites

Carbonates

0.01 0.1 1 10

0.01 0.1 1 10 100

Ca2+/Na+ (mM/mM)

0.1

1

10

100

HC

O3- /N

a+ (m

M/m

M)

(a)

(b)

Figure 7. Mixing diagrams using sodium normalised ratioof (a) Mg2+/Na+ vs. Ca2+/Na+ and (b) HCO−

3 /Na+ vs.Ca2+/Na+ relating carbonate and silicate end members(after Gaillardet et al. 1999).

members show the dominance of silicateweathering over the carbonate dissolution in soluteacquisition processes in the Subarnarekha Riverbasin (figure 7).

4.3 Saturation index and water mineralequilibrium

The saturation index (SI) of the studied waterwith respect to calcite (SIc) and dolomite (SId)was estimated using the USGS hydrogeochemical

software PHREEQC (Parkhurst and Appelo 1999)in order to investigate the level to which thenatural water has equilibrated with the carbon-ate mineral phases. PHREEQC is a widely usedmodelling code that employs various approachesand thermodynamic databases for solving solution–solid–gas equilibria (Lecomte et al. 2005; Binetet al. 2009; Tiwari and Singh 2014). The satura-tion index of a particular mineral phase can bedefined as SI = log10(IAP/Ksp), where IAP is theion activity product of the solution and Ksp is thesolubility product at a given temperature (Garrelsand Mackenzie 1967). A positive saturation indexspecifies that the water is being supersaturatedwith respect to a particular mineral phase andtherefore incapable of dissolving more of themineral and the mineral phase in equilibrium pre-cipitate under suitable physico-chemical condition.Undersaturation condition is denoted by a nega-tive index and suggests the dissolution of mineralphase, while neutral SI denotes the equilibriumstate with the mineral phase. The plot of sat-uration index of calcite (SIc) vs. dolomite (SId)demonstrates that most of the post-monsoon andmonsoon water samples are undersaturated withrespect to dolomite and calcite, while water issupersaturated with respect to both during the pre-monsoon (figure 8). The supersaturation conditionin pre-monsoon may be attributed to evaporationeffects during the lean water level period of sum-mer season which causes the preferential extractionof Ca by precipitation (Hardie and Eugster 1970).The undersaturation condition represents waterthat has come from an environment where rockmatrices contain insufficient calcite and dolomite orwhere Ca and Mg exist in other forms. Undersatu-rated waters are capable to dissolve calcite and/ordolomite when it comes in contact with sourcerocks.

The clay mineral assemblages, which wouldbe consistent with the natural water chemistry,can be established through thermodynamic data(Garrels and Christ 1965). The thermodynamicstability relationships of the Subarnarekha Riverwater are plotted in the silicate systems: (a)Na2O−Al2−SiO2−H2O, (b) K2O−Al2−SiO2−H2O, (c) CaO−Al2−SiO2−H2O and (d) MgO−Al2−SiO2−H2O at 25◦C to predict the possibleclay mineral assemblages which would be in equi-librium with the river water chemistry (figure 9).The pH–log H4SiO4 stability diagram demon-strates that the majority of data points fall inthe range of kaolinite stability field except some


DolomiteDolomite

SaturationUndersaturation

Und

er s

atur

atio

nS

atur

atio

nC

alci

teC

alci

te

Dol

omite

sat

urat

ion

inde

x (S

I d)

Calcite saturation index (SIc)

-3 -2 -1 0 1 2 3

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6Post-monsoonPre-monsoonMonsoon

Figure 8. Relationship between saturation indices of calcite (SIc) and dolomite (SId).

pre-monsoon samples which fall in the chlorite andCa-feldspar zones in MgO−Al2−SiO2−H2O andin CaO−Al2−SiO2−H2O system. The enrichmentof Mg and Ca in the water during pre-monsoonmay explain it (Das and Dhiman 2003). Water–mineral equilibria imply that the SubarnarekhaRiver water chemistry is in equilibrium with thekaolinite. Stability in the kaolinite field suggeststhat the CO2-enriched water reacts with silicateminerals contained in the host rock, particularly inplagioclase feldspar and converted into allophone–hallosite–kaolinite. The reactive water leached outCa, Mg, Na and HCO3 from the host silicates andresults in a more silica-rich clay minerals by thereaction:

(Na,K,Ca,Mg) silicates + H2O + CO2

= H4SiO4 + HCO3 + Na + K

+ Ca + Mg + Al2Si2O5 (OH)4 Clay mineral.

4.4 Dissolved fluxes and chemical denudation rate

The Subarnarekha River shows enormous spatialand temporal variations in the water discharge.Figure 10 shows the variation in water discharge

for the monsoon and non-monsoon seasons atfive locations. About 69–98% of the annual waterdischarge from the river occurs during the mon-soon (June–September) and 2–31% in the leanflow period of non-monsoon (October–May). Theannual dissolved fluxes and chemical denudationrates of the Subarnarekha River at various loca-tions and its major tributaries were calculated byusing the average TDS, catchment area and annualwater discharge (table 4). The Subarnarekha Riverannually transported 0.179 × 106 ton of dissolvedchemical loads to the Muri site and the esti-mated chemical denudation rate of the catchmentat this site was 135 ton km−2 yr−1. The dissolvedload and water discharge increase unsystemati-cally at downstream sites and the annual solutefluxes at Ghatsila and Rajghat sites were esti-mated to be in the range of 1.585 × 106−1.477 ×106 ton, respectively. Kharkai, the largest Sub-arnarekha tributary, annually delivered 1.023×106

ton of dissolved loads to the Subarnarekha Riverat Adityapur. The annual solute fluxes of the othertributaries such as Sankh (0.016 × 106 ton), Garra(0.082 × 106 ton), Kanchi (0.109 × 103 ton) andKarkari (0.188 × 103 ton) were low as comparedto the Kharkai (1.023 × 106 ton). The chemical


Gib

bsite

Kaolinite

Na-Montimorilinite

K-Mica

Gib

bsite

Kaolinite

Amor

phou

s Si

lica

Qua

rtz s

atur

atio

n

Am

orph

ous

silic

a

-5 -4 -3Log H4SiO4

1

3

5

7

9

Log

(Na+ )

/(H+ )


-5 -4 -3Log H4SiO4

3

5

7

9

Log

(K+ /H

+ )

Qua

rtz s

atur

atio

n

Ca-Feldspar

Kaolinite

Gib

bsite

Gib

bsite

Kaolinite

Chlorite

Am

orph

ous

Sili

ca

-5 -4 -3Log H4SiO4

6

8

10

12

14

16

Log

(Ca++

)/(H

+ )

-5 -4 -3Log H4SiO4

6

8

10

12

14

16

Log

(Mg++

)/(H

+ )

(a)

(b)

(c)

(d)

Amor

phou

s Si

lica

Albite

K- Feldspar

Figure 9. Mineral stability diagrams for the silicate system: (a) Na2O−Al2−SiO2−H2O; (b) K2O−Al2−SiO2−H2O;(c) CaO−Al2−SiO2−H2O; (d) MgO−Al2−SiO2−H2O (after Garrels and Christ 1965).

denudation rates of the Kharkai, Garra, Karkariand Kanchi catchments were estimated to be inthe range of 176, 169, 119 and 105 ton km−2 yr−1,respectively.

4.5 Water quality assessment for irrigation uses

EC and Na are the most important parametersfor determining the suitability of water for irri-gation uses. High salt concentrations in theirrigation water affect the soil structure, per-meability and aeration, which indirectly affectthe plant growth. Irrigation water can be clas-sified into low (EC =< 250µS cm−1), medium(250−750µS cm−1),high (750−2250µS cm−1)and

0

1000

2000

3000

4000

5000

6000

7000

Muri Jamshedpur Ghatsila Baharagora Adityapur

Wat

er d

isch

arge

(m

illio

n m

3 )

Site Name

MonsoonNon-monsoonAnnual

Figure 10. Seasonal variations in water discharge of the Sub-arnarekha and Kharkai rivers at different sites.


Table 4. Average annual solute fluxes and chemical denudation rate of the Subarnarekha and its tributaries.

River/tributarySite/tributaries

name

Area

(km2)

Discharge

(million m3)

TDS

(mg l−1)

Solute flux

(×106)(ton yr−1)

Chemical

denudation rate

(ton km−2 yr−1)

Subarnarekha Muri 1330 596 301 0.179 135

Adityapur 6309 2831 310 0.878 139

Jamshedpur 12,649 6593 201 1.325 105

Ghatsila 14,176 6950 228 1.585 112

Baharagora − 4974 190 0.945 −Rajghat 19,296 7940 186 1.477 77

Tributaries Kanchi 1036 750 145 0.109 105

Karkari 1575 950 198 0.188 119

Kharkai 5825 3300 310 1.023 176

Garra 483 200 408 0.082 169

Sankh 196 80 202 0.016 82

very high (2250−5000µS cm−1) salinity classesbased on the total concentration of soluble saltsin water (USSL 1954). The excess sodium in waterproduces undesirable effects on soil properties andreduces its permeability. High salt concentrationin water results in the formation of saline soil,whereas a high sodium concentration leads to thedevelopment of alkaline soil. The alkali hazardin the use of water for irrigation is expressedin terms of sodium absorption ratio (SAR) anddetermined by the absolute and relative concen-tration of cations. On the basis of SAR value,water can be classified as low (SAR<6), medium(6–12), high (12–18) and very high (>18) alkaliwater.

The calculated value of SAR in the surface waterof the Subarnarekha River basin ranges from 0.32to 6.73 (avg. 0.79). The plotted data of the major-ity of water samples on the US salinity diagramfall in the category of C1S1 and C2S1, i.e., low-to-medium salinity and low alkali water (figure 11).Such water can be used for irrigation in most of thesoil and crops with little danger of development ofexchangeable sodium and salinity. Four water sam-ples of the pre-monsoon season fall in the zonesof C3S1 and C3S2 indicating high salinity andlow-to-medium alkali hazard. High saline watersare not suitable to irrigate the agricultural fieldswith restricted drainage and it requires specialmanagement for salinity control. For utilisation ofsuch water, soil must be permeable, drainage mustbe adequate and irrigation water must be appliedin excess to provide considerable leaching.

%Na in water is a parameter computed toevaluate the suitability of water for irrigation use.%Na denotes the relative proportions of alkali

Sod

ium

Ads

orpt

ion

Rat

io (S

AR

)

100 250 750 2250

S1

S2

S3

S4

Low

Med

ium

Hig

hV

. Hig

hS

OD

IUM

(ALK

ALI

) HA

ZAR

D

SALINITY HAZARD

C1 C2 C3 C4Low Medium High V.High

Electrical Conductivity (µS/cm)

Post-monsoonPre-monsoon

0

4

8

12

16

20

24

28

32

0

10

20

30Monsoon

Figure 11. US salinity diagram for classification of irrigationwaters (USSL 1954).

to the total cations. The role of sodium in theclassification of irrigation water was emphasisedbecause of the fact that sodium reacts with soiland affects its physical condition and soil structureincluding the formation of crusts and reduction insoil aeration, infiltration rate and soil permeabil-ity. Maximum %Na of 60% is recommended forirrigation water. %Na in the analysed river waterranges between 15 and 44% in the post-monsoon,24 and 80% in the pre-monsoon and 17 and 44%in the monsoon seasons. The plot of analyticaldata on Wilcox (1955) diagram relating EC and%Na placed the Subarnarekha River water under


Exc

elle

ntto

good

Goo

dto

perm

issi

ble

Dou

btfu

lto

unsu

itabl

e

Permissible to doubtful

Unsuitable

Uns

uita

ble

Post-monsoonPre-monsoon

0 500 1000 1500 2000 2500 3000 3500Electrical Conductivity (EC) µS/cm

0

20

40

60

80

100

Per

cent

Sod

ium

0 5 10 15 20 25 30 35Total Concentration (meq/l)

Monsoon

Doubtful to unsuitable

Figure 12. Plot of %Na vs. EC (after Wilcox 1955).

excellent to good and good to permissiblecategories for irrigation uses (figure 12).

The relative abundance of alkaline earths (Ca2+

+Mg2+) with respect to bicarbonate and carbonatealso influences the suitability of water for irriga-tion uses. The excess of carbonates (CO2−

3 +HCO−3 )

over alkaline earths (Ca2++Mg2+) in irrigationwater may cause the complete precipitation ofCa and Mg as carbonates (Karanth 1989). Thewater with high RSC has high pH and land irri-gated with such water becomes infertile owing tothe deposition of sodium carbonate (Eaton 1950).Irrigation waters having RSC values >5 meq l−1

have been considered harmful to the growth ofplants, while waters with RSC values above2.5 meq l−1 are unsuitable for irrigation. A RSCvalue between 1.25 and 2.5 meq l−1 is consideredas the marginal quality and value <1.25 meq l−1

as the safe limit for irrigation. The calculated RSCvalues in most of the analysed water samples are<2.5 meq l−1, suggesting marginal to safe qualityof the Subarnarekha River water for irrigation use(table 1).

5. Conclusion

The hydro-geochemical study of the SubarnarekhaRiver basin has been carried out to evaluate the

major-ion chemistry, solute acquisition processes,dissolved fluxes and suitability of river water forirrigation uses. The analytical result shows that theSubarnarekha water is alkaline in nature like othermajor Indian rivers. Ca2+ and Na+ were the domi-nant cations, while HCO−

3 and Cl− dominate in theanion chemistry of the Subarnarekha River water.Seasonality in the ionic concentration is related tothe rainfall dilution and river flow regime. Increasein TDS and ionic concentrations during the pre-monsoon season may be attributed to enhance-ment in groundwater contribution during the lowflow regime of summer months. The SubarnarekhaRiver water chemistry is largely controlled byweathering of rocks with minor contribution fromthe atmospheric and anthropogenic sources. Thehigh concentration of HCO−

3 and (Ca2++Mg2+)and observed Ca2+/Na+, Mg2+/Na+, HCO−

3 /Na+

and HCO−3 /SiO2 ratios suggest that the major-

ion chemistry of the Subarnarekha River isessentially controlled by two-component mixingfrom the dissolution of silicates and carbonates.The high concentration of dissolved silica,low ratio of (Ca2++Mg2+)/(Na++K+) and high(Na++K+)/TZ+ ratio suggest significant contribu-tion of dissolved ions from the silicate weathering.The water chemistry is largely undersaturated withrespect to calcite and dolomite; however, most ofthe pre-monsoon water samples are supersaturatedwith respect to both. The supersaturation condi-tion in pre-monsoon may be attributed to evapo-ration effects during the lean water level periodwhich causes preferential extraction of Ca by pre-cipitation. The chemical behaviour of the riverwater in the silicate systems demonstrates kaoli-nite as the possible mineral that is in equilibriumwith the water. The Subarnarekha River annuallydelivered 1.477 × 106 ton of dissolved loads to theBay of Bengal and the estimated chemical denuda-tion rate of the catchment is 77 ton km−2 yr−1.The annual solute fluxes of the tributaries variedfrom a minimum of 0.016×106 ton (Sankh) to amaximum of 1.023×106 ton (Kharkai). The calcu-lated parameters of SAR, %Na and RSC show thatthe Subarnarekha River water is of the ‘excellentto good’ category for irrigation and can be usedto irrigate all soils for tolerant, semi-tolerant andsensitive crops.

Acknowledgements

Dr. Soma Giri is grateful to the Department ofScience and Technology, Government of India for


funding under Fast Track Young Scientist Scheme(Grant No. SR/FTP/ES-185/2010(G)). Authorsare thankful to Dr. P K Singh, Director, CSIR-CIMFR for providing the laboratory and otherinfrastructural facilities and lab colleagues for theirhelp during the study.

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Corresponding editor: Partha Pratim Chakraborty

fluvial geochemistry of subarnarekha river basin, india

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