aspects of weathering and solute acquisition processes controlling chemistry of sub-alpine...

HYDROLOGICAL PROCESSESHydrol. Process. 16, 835–849 (2002)DOI: 10.1002/hyp.367

Aspects of weathering and solute acquisition processescontrolling chemistry of sub-Alpine proglacial streams of

Garhwal Himalaya, India

Abhay Kumar Singh* and S. I. HasnainSchool of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India

Abstract:

An analytical study of major cations and anions of the proglacial streams of Garhwal Himalaya has been carried outto assess the weathering and geochemical processes in high altitude river basins. Calcium and magnesium are themajor cations, and bicarbonate and sulphate are the most dominant anions in these waters. A high correlation amongHCO3, Ca and Mg, a relatively high contribution of (Ca C Mg) to the total cations (TZC) and high (Ca C Mg/Na C K)ratio indicate carbonate weathering could be the primary source of the dissolved ions. Carbonic acid weathering isthe major proton-producing reaction in the Alaknanda River, while in the Bhagirathi River it is the coupled reactionwhich controls the solute acquisition processes. To know the geochemical factors controlling the chemical nature ofwater, R-mode factor analysis on major ion data from Ganga headwater streams has been performed. Factor 1 in theAlaknanda River is explicitly a bicarbonate factor showing strong loading of EC, Ca, Mg, HCO3 and TDS. In theBhagirathi River Factor 1 explains the sulphide dissolution and silicate weathering and Factor 2 explains carbonateweathering. Wide downstream variations are observed in the total dissolved solids (TDS) and total suspended matter(TSM) in the headwater streams of the Ganga. Quartz and feldspar are the common detrital minerals, and kaoliniteand illite the common clay minerals in the suspended sediment. Copyright 2002 John Wiley & Sons, Ltd.

KEY WORDS proglacial stream; Himalaya; suspended sediments; dissolved loads; weathering

INTRODUCTION

The glaciers of high Asia comprise by area 50% of all glaciers outside the polar regions, and containapproximately 33 times the areal coverage of the glaciers in the European Alps (Wissmann, 1959). TheHimalayas, with an average elevation of 6000 m, are the repositories of some of the highest and largestglaciers of the world. It has been estimated that about 38 221 km2 of the Himalayan ranges are glaciated(Bahadur, 1988). There are more than 5222 glaciers in the Himalaya, scattered in three river systems, i.e.Indus, Ganga and Brahmaputra (Puri, 1994). There are 20 principal glacial fed river systems in the Indiansubcontinent, which vary in glacier coverage. These glaciers contribute about 60–70% of the fresh water tothese main river systems of the Indian subcontinent. Thus glacier meltwaters form an important source ofwater and maintain water supply in north Indian rivers throughout hot and dry summer months (Bahadur,1988). The water reserves contained in the Himalayan glaciers, estimated to be about 1012 m3, are comparableto the groundwater reserves of India (Puri, 1994). A considerable amount of water has been harvested in thisregion for the generation of hydroelectric power due to the available hydrogeological conditions. Glaciers notonly meet the need for water supply, but are also an important source of information on climatic changes inthe past and present.

* Correspondence to: Dr Abhay Kumar Singh, Central Mining Research Institute, Barwa Road, Dhanbad, Jharkhand 826001, India.E-mail: [email protected]

Received 18 November 1999Copyright 2002 John Wiley & Sons, Ltd. Accepted 17 July 2000

836 A. K. SINGH AND S. I. HASNAIN

The Himalayan drainage system is characterized by high physical and chemical denudation rates. TheHimalayan rivers, Ganga and Brahmaputra, together account for 3% of the total global flux of thedissolved load to the world’s ocean (Sarin et al., 1989). The present estimates of the sediment yield ofthe Ganga–Brahmaputra Rivers together is about a billion tons per year, nearly 7% of the global annualsediment flux from the continents to the oceans (Milliman and Meade, 1983; Subramanian, 1993). It has beenestimated that the non-Himalayan (peninsular Indian) rivers of India carry less than 5% of the total masstransport compared to the Himalayan rivers (Subramanian, 1979). In this paper the assessment of weatheringand geochemical processes controlling the water chemistry and sediment transfer in the high altitude riversof the Garhwal Himalayan catchment of the Ganga River will be discussed.

GARHWAL HIMALAYA

The Ganga River basin, lying between 29°450 –31°300N and 78°20 –80°70E and having an area of 30 000 km2, iscalled Garhawal Himalaya (Figure 1). The Garhwal Himalaya contains more than 1020 large and small glaciers(Vohra, 1981). The basin has extreme variability in relief, precipitation and energy input. This is reflected inthe diurnal and seasonal variation in climate, and hence the variation in hydrology and dissolved and sedimentloads (Chauhan and Hasnain, 1993; Singh and Hasnain, 1998; Singh et al., 1999). The Himalayan proglacialstreams carry about 70–80% of their annual flow during the summer monsoon months (June–September),when both rainfall and rate of snowmelt are at a maximum (Bruijnzeel and Bremmer, 1989). The averagerainfall in the Garhwal Himalaya is between 1000 and 2500 mm, of which 50–80% falls during the monsoonperiod between June and September.

The Alaknanda and Bhagirathi are the two major proglacial streams of Garhwal Himalaya, forming themountainous catchment of the river Ganga. The Alaknanda emerges from twin glaciers, Satopanth andBhagirath Kharak, at the portal altitude of 3800 m, 13 km north of the temple town of Badrinath. Theriver Bhagirathi originates at an elevation of 3812 m from the Gangotri glacier at Gomukh on the westernslope of Chaukhamba in Uttarkashi district. These two streams flow approximately 225–240 km across theHimalaya before their confluence at Devprayag, forming the river Ganga. Dhauliganga, Nandakini, Pindarand Mandakini are the major tributaries of the Alaknanda River, and Bhilangna is the major tributaryof the Bhagirathi River. The Ganga, after a total run of 280 km, cuts through the Himalaya at Sukhinear Rishikesh, turns southwest for another 30 km and descends onto the vast Indo-Gangetic plains atHaridwar.

The higher reaches of the catchment are characterized by active glaciation. Cirque basins, glacial lakes,U-shaped valleys, moraines and avalanche slopes are common landforms in this region. The river in its upperreaches flows through narrow and deep gorges. The upper part of the catchment, lying between Gomukh(3812 m) and Harsil (2620 m) in the Bhagirathi and between Badrinath (3400 m) and Pondukeshwar (1200 m)in the Alaknanda, has a very steep gradient. This zone is located in a narrow glaciated valley and is dominatedby rapid waterfalls and cascades. However, the lower part of the basin (both in the Alaknanda and Bhagirathi)has a more moderate gradient.

The upper catchment of the Garhwal Himalaya (near the source of the Alaknanda and Bhagirathi) ismainly covered by Precambrian Central Crystalline rocks. These rocks are primarily medium to high-grademetamorphic rocks. Along the Bhagirathi River the major rocks include biotite gneiss, quartzite, quartz-schistand amphibolite. Crystalline limestone, quartzite and carbonaceous phyllites are also exposed near the Tehriarea in Bhagirathi valley (Gnesser, 1964; Valdiya, 1980). The Main Central Thrust (MCT) separates the CentralCrystallines from the lower Uttarkashi and Chandpur Formations. The Uttarkashi Formation primarily consistsof limestone and dolomitic rocks and is exposed in the middle part of the Alaknanda and Bhagirathi Riverbasin. The outcrop of the Chandpur Formation is mainly composed of phyllites and micaceous graywackesand is exposed in the lower part of the basin.

Copyright 2002 John Wiley & Sons, Ltd. Hydrol. Process. 16, 835–849 (2002)

WEATHERING AND SOLUTE ACQUISITION PROCESSES 837

CH

AN

NE

LE

RO

SIO

N

MA

SS

MO

VE

ME

NT

Teh

ri

Dev

pray

ag

Gan

ga R

iver

Kar

npra

yag

Nan

dpra

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adrin

ath

Josh

imat

h

KH

AT

LIN

GG

LAC

IER

Har

sil

Gom

ukh

GA

NG

OT

RI

GLA

CIE

R

SA

TO

PA

NT

HG

LAC

IER

PIN

DA

RI

GLA

CIE

R

INA

CT

IVE

SE

DIM

EN

TS

OU

RC

E

Ked

arna

th

Utta

rkas

hiP

ondu

kesh

war Dhauliganga

Indi

a

Uttar P

rade

sh

Sca

le

4040

km

GLA

CIE

R0

N

MANDAKIN

I

BHILGANGA

ANDARIVER

ALA

KN

NA

ND

AK

INIR

IVE

R

PIN

DA

RR

.

BHA G

IRATHI

Figu

re1.

Dra

inag

em

apof

the

Gar

hwal

Him

alay

aca

tchm

ent

show

ing

sam

plin

gsi

tes



METHODOLOGY

Water samples were collected from different glaciers and proglacial streams of the Garhwal Himalayan regionin the premonsoon season (June 1992). Prior to sampling, polyethylene bottles of 500 ml capacity werewashed in the laboratory with dilute hydrochloric acid and then rinsed twice with double distilled water. Atthe sampling sites, before collecting the samples, bottles were rinsed with the stream water. Water sampleswere collected following the methods of Ostrem (1975). The bottle was lowered into the stream and held at anangle of 45° upstream until filled almost to the neck. EC, pH and alkalinity were measured in the field. In thelaboratory, the water samples were filtered through 0Ð45-µm Millipore membrane filters to separate suspendedmatter and the filtered solution was analysed for major cations (Ca, Mg, Na, K), major anions (HCO3, SO4,Cl) and dissolved silica (H4SiO4). Major cations were determined by atomic absorption spectrophotometry.Ca and Mg were analysed in the absorbance mode and Na and K in the emission mode. The analyticalprecision for the measurements of major ions is about š5%. The molybdosilicate method and turbidimetricmethod were used to measure the concentration of dissolved silica and sulphate respectively (APHA, 1985).The mercury thiocyanate method was used for the determination of chloride (Florence and Farrar, 1971) andbicarbonate was determined by acid titration (APHA, 1985).

RESULTS AND DISCUSSION

Solute chemistry

The water chemistry at various sites is summarized in Table I. Bicarbonate and calcium are the twomajor constituents of stream water, constituting approximately 69% and 63% of the total anions and cationsrespectively. The next most abundant dissolved species are sulphate (28%) and magnesium (20%). Bicarbonateconstitutes 72–91% of the total anions and (Ca C Mg) constitutes 67–93% of the total cations on an equivalentbasis in the Alaknanda. In the Bhagirathi, sulphate is more significant and constitutes about 8–81% of thetotal anions. The downstream variation of various cations and anions is shown in Figure 2. There is a markedincrease in concentration of Ca, Mg and HCO3 between 50–90 km in the Alaknanda and between 15–40 kmin the Bhagirathi River. These increases in the concentration of Ca, Mg and HCO3 are related to the changesin lithology from schist, gneiss and granitic gneiss-bearing rocks of the Central Crystalline to the carbonate-bearing Uttarkashi Formation. In general, Alaknanda shows the increasing trend of ionic concentration ina downstream direction, but a similar trend is not observed for the Bhagirathi. In the Bhagirathi, HCO3,Ca and Mg show an increasing trend, however K, dissolved silica and SO4 are positively correlated withelevation, showing maximum concentration near the source region and progressively decreasing in thedownstream direction. The increasing trend of ionic concentration with decreasing elevation is related tosoil thickness, lithology and temperature. The mineral surface exposed to weathering in thicker soil at lowerelevations is much greater than in the thin or no soil zone at high elevation. The residence time of waterin contact with weatherable minerals will be greater in thicker soil zones (Drever and Zobrist, 1992). Athigher elevation, the river flows through the rocks of less reactive phases like schist, gneisses, granites andgranodiorites of the Central Crystallines; these would provide little contribution to the solute load. However,in the middle and lower reaches, the water flows through more reactive phases such as marble, calcite anddolomite of the Uttarkashi Formation, which would result in greater ionic concentrations. The occurrence ofpyritous–carbonaceous slates and phyllites in the geological units of the Higher Himalayas suggests that theoxidation of pyrites would be the primary source of sulphates near the source region of the Bhagirathi River.

Chemical weathering

High altitude proglacial streams are very active agents of weathering and erosion. The chemical compositionof glacier meltwater has demonstrated high rates of chemical weathering in subglacial environments (Collins,1979; Raiswell, 1984; Sharp et al., 1995). The weathering of rock-forming minerals, with a minor contributionfrom atmospheric and anthropogenic sources, is the major source of dissolved ions in aquatic systems



Tabl

eI.

Che

mic

alch

arac

teri

stic

san

dse

dim

ent

load

ofG

arhw

alH

imal

ayan

stre

ams

(Jun

e19

92)

Dis

tanc

e(k

m)

Stre

ams

Site

EC

pHC

aM

gN

aK

HC

O3

SO4

Cl

H4Si

O4

TD

ST

SM

0A

lakn

anda

Gla

cier

snou

t39

7Ð317

743

4242

221

408

3326

2163

15A

lakn

anda

Bad

rina

th34

7Ð12

198

2748

2819

057

1728

2464

255

Ala

knan

daJo

shim

ath

437Ð4

327

447

6348

284

6118

2633

511

90A

lakn

anda

Bir

ehi

142

7Ð57

1322

327

153

5718

8516

423

2916

354

015

0A

lakn

anda

Kar

anpr

ayag

148

7Ð898

732

666

6411

0794

1831

103

293

210

Ala

knan

daSr

inag

ar15

17Ð7

210

8031

574

6411

6415

436

4011

351

424

0A

lakn

anda

Dev

pray

ag15

08Ð2

1092

328

101

8111

5015

935

3811

458

50

Bha

gira

thi

Gla

cier

snou

t99

7Ð539

815

410

819

214

668

111

8870

1368

018

Bha

gira

thi

Gan

gotr

i85

7Ð437

114

782

132

142

633

1565

6248

6042

Bha

gira

thi

Har

sil

978Ð0

470

313

6772

467

371

1637

6899

011

0B

hagi

rath

iU

ttar

kash

i90

8Ð149

023

874

6650

723

127

3663

1004

164

Bha

gira

thi

Bha

ldia

na94

8Ð151

324

477

8455

516

733

3764

1054

175

Bha

gira

thi

Tehr

i93

8Ð152

823

175

105

536

248

4632

6812

8022

5B

hagi

rath

iD

evpr

ayag

103

8Ð258

125

379

128

546

307

4938

7418

9723

0G

anga

Dev

pray

ag13

58Ð4

1001

272

6499

1131

177

3631

109

1134

Tri

buta

ries

Dha

ulig

anga

Josh

imat

h11

27Ð6

751

196

5548

582

290

2727

6734

6N

anda

kini

Nan

dpra

yag

997Ð7

882

631

385

6297

743

821

3410

960

Pind

ari

Gla

cier

snou

t15

57Ð9

1051

319

3325

700

722

1812

106

1207

Pind

ari

Kar

npra

yag

134

7Ð42

895

319

6270

1035

113

1823

9721

0M

anda

kini

Rud

rapr

ayag

527Ð1

237

466

7840

361

7629

3942

56

Uni

ts:

�eq

uiv.

L�1

.,ex

cept

EC

(�S

cm�1

),H

4Si

O4

(�m

oll�1

),T

DS

and

TSM

(mg

l�1).



0

350

700

1050

1400Io

nic

Con

cent

ratio

n (µ

eq/l)

Ioni

c C

once

ntra

tion

(µeq

/l)Ca

Mg

Na

K

____ Alaknanda

------- Bhagirathi

0 30 60 90 120 150 180 210 240

Distance downstream (km)

0

350

700

1050

1400

1750HCO3

SO4

Cl

Figure 2. Downstream variation of dissolved ions showing sharp increase of Ca, Mg and HCO3 in the middle reaches of Alaknanda anddownstream decreasing trend of SO4 concentration in Bhagirathi River



Tabl

eII

.R

elat

ive

abun

danc

e(%

)an

dio

nic

rati

oof

the

diff

eren

tdi

ssol

ved

ions

Dis

tanc

eSt

ream

sSi

teC

aM

gN

aK

HC

O3

SO4

Cl

CaC

CaC

NaC

CaC

Na/

Cl

HC

O3/

SO4/C

lK

/Cl

C-r

atio

(km

)M

g/M

g/K

/M

g/H

4Si

O4

Na

CK

TZ

CT

ZC

HC

O3

0A

lakn

anda

Gla

cier

snou

t58

1414

1482

153

30Ð7

20Ð2

70Ð9

5Ð26Ð6

95

5Ð20Ð8

515

Ala

knan

daB

adri

nath

669

169

7222

63

0Ð75

0Ð25

1Ð22Ð8

6Ð78

3Ð31Ð6

0Ð77

55A

lakn

anda

Josh

imat

h63

1915

1178

175

30Ð7

40Ð2

51Ð1

3Ð510

Ð93Ð3

2Ð60Ð8

290

Ala

knan

daB

ireh

i71

188

390

81

70Ð8

80Ð1

10Ð8

6Ð665

7Ð12Ð4

0Ð915

0A

lakn

anda

Kar

anpr

ayag

6823

54

918

110

0Ð91

0Ð09

1Ð23Ð6

35Ð7

5Ð23Ð5

0Ð921

0A

lakn

anda

Srin

agar

7021

54

8611

210

0Ð91

0Ð09

1Ð22Ð0

29Ð1

4Ð21Ð7

0Ð824

0A

lakn

anda

Dev

pray

ag68

206

586

122

80Ð8

80Ð1

11Ð2

2Ð830

Ð24Ð5

2Ð30Ð8

70

Bha

gira

thi

Gla

cier

snou

t46

1813

2317

811

20Ð6

50Ð3

53Ð8

9Ð81Ð6

561

Ð017

Ð40Ð1

718

Bha

gira

thi

Gan

gotr

i50

2011

1817

802

20Ð7

10Ð2

93Ð6

5Ð42Ð1

42Ð2

8Ð80Ð1

42B

hagi

rath

iH

arsi

l51

347

855

432

60Ð8

50Ð1

51Ð6

4Ð112

Ð623

Ð14Ð5

0Ð511

0B

hagi

rath

iU

ttar

kash

i56

279

866

304

50Ð8

40Ð1

61Ð4

2Ð714

Ð08Ð5

2Ð40Ð6

816

4B

hagi

rath

iB

hald

iana

5527

89

7422

45

0Ð82

0Ð17

1Ð42Ð3

155Ð0

2Ð50Ð7

617

5B

hagi

rath

iTe

hri

5625

811

6530

64

0Ð81

0Ð19

1Ð41Ð6

16Ð7

5Ð32Ð2

0Ð622

5B

hagi

rath

iD

evpr

ayag

5624

812

6134

64

0Ð80

0Ð19

1Ð51Ð6

14Ð3

6Ð22Ð6

0Ð64

230

Gan

gaD

evpr

ayag

7019

47

8413

38

0Ð89

0Ð11

1Ð11Ð7

36Ð4

4Ð92Ð7

0Ð86

Tri

buta

ries

Dha

ulig

anga

Josh

imat

h72

148

765

323

60Ð8

50Ð1

51Ð0

2Ð021

Ð510

Ð71Ð7

0Ð66

Nan

daki

niN

andp

raya

g64

247

568

311

80Ð8

80Ð1

11Ð1

4Ð028

Ð720

Ð82Ð9

0Ð69

Pind

ari

Gla

cier

snou

t74

222

249

501

240Ð9

50Ð0

411Ð9

1Ð858

Ð340

Ð11Ð3

0Ð49

Pind

ari

Kar

npra

yag

6624

55

8910

29

0Ð90

0Ð098

1Ð23Ð4

456Ð2

3Ð80Ð9

0M

anda

kini

Rud

rapr

ayag

6712

147

7716

64

0Ð79

0Ð21

1Ð22Ð6

9Ð22Ð6

1Ð30Ð8

2



(Stallard and Edmond, 1983; Tranter et al., 1993). Dissolution of atmospheric CO2 in water and oxidation ofsulphides are the two main contributors of protons used for weathering of carbonates and silicates (Garrelsand Mackenzie, 1971).

The nature of weathering and source of dissolved ions in water can be evaluated by applying the massbalance approach and considering the relative abundance of ions, the correlations among solutes and thegeology of the drainage basin. In the case of weathering of minerals by carbonic acid, the equivalent ratioof Ca : HCO3 in the waters resulting from calcite weathering is 1 : 2, whereas for dolomite it is 1 : 4. Forsulphuric acid reactions the Ca : SO4 ratio would be 1 : 1 for calcite and 1 : 2 for dolomite (Sarin et al., 1989).The relative abundance and ratios of different cations and anions are given in Table II. The low concentrationof chloride and high ratio of SO4/Cl (13) and Na/Cl (4) rule out the possibilities of evaporite dissolutionor atmospheric inputs as the major contributor of dissolved ions. It has been estimated that atmosphericdeposition may contribute up to 20% of the Na and K and up to 5% of the Ca, Mg and SO4 to the major ionchemistry in the mountainous catchment of the Ganga River (Sarin et al., 1992). The high concentration ofbicarbonate and its positive correlation with Ca (r2 D 0Ð93) and Mg (r2 D 0Ð74) indicate carbonate dissolutionas a possible source of bicarbonate, calcium and magnesium. The high contribution of calcium and magnesium(82%) to the total cationic balance (Ca C Mg/TZC D 0Ð8) and low ratio of (Na C K/TZC� D 0Ð17 also suggestthat carbonate weathering is the major source of the dissolved ions, with minor contributions from silicateweathering (Sarin et al., 1989; Pandey et al., 1999; Singh and Hasnain, 1999). Furthermore, the low contentof dissolved silica and high HCO3/H4SiO4 molar ratio present in the system are clear evidence that the solutecontribution via silicate weathering plays a relatively minor role compared with the supply by the carbonatephase. Na, K and H4SiO4 in the drainage basin are mainly derived from the weathering of alumino-silicateminerals, with clay minerals as byproducts. Sodium and potassium in the Ganga headwater are mainly derivedfrom igneous and metamorphic rocks of the Central Crystalline rocks. Common parent minerals for sodiumand potassium released into the Ganga headwater include albite, orthoclase (KAlSi3O8) and micas, which mayreact with water and carbonic acid and accumulate various clay minerals in the sediments. Mineral stabilityis an important way in which the approach to equilibrium between clay minerals and natural water can beverified through thermodynamic data (Garrels and Christ, 1965). The plots of Na and K silicate systemsfor the Alaknanda and Bhagirathi Rivers demonstrate that the water of the Ganga headwater is in the rangeof the stability field of kaolinite, which implies that the chemistry of the water favours kaolinite formation(Figure 3). This is also supported by X-ray mineralogical studies on suspended sediments. The observed lowconcentration of dissolved silica in the Ganga headwater may be attributed to the high resistance of sialicminerals to weathering, and also consumption of H4SiO4 in the formation of secondary minerals (kaolinite).

The relative importance of two major proton-producing reactions—carbonation and sulphide oxidation—can be signified on the basis of the (HCO3/HCO3 C SO4) equivalent ratio, called the C-ratio (Brown et al.,1996). A C-ratio of 1Ð0 would signify carbonic acid weathering involving pure dissolution and acid hydrolysis,consuming protons from atmospheric CO2. Conversely, a ratio of 0Ð5 suggests coupled reactions involvingthe weathering of carbonates by protons derived from sulphide oxidation. Figure 4 shows the downstreamvariation of the C-ratio in the Alaknanda and Bhagirathi Rivers. For Alaknanda, the C-ratio is always higherthan 0Ð5, signifying that carbonic acid weathering is the major proton producer. In the Bhagiarthi River theC-ratio increases downstream, signifying the importance of carbonate dissolution in the middle and lower partof the basin. However, the low C-ratio near the source regions of the Bhagirathi (0Ð2–0Ð5) and Pinadri (0Ð49)suggests that either sulphide oxidation and/or coupled reactions (involving both carbonic acid weatheringand sulphide oxidation) control the solute acquisition in the Bhagirathi and Pindari Rivers. The downstreamvariation in the (Ca C Mg/Na C K) ratio shows a sharp increase in middle and lower reaches, indicating anincreased contribution of carbonate weathering in the downstream direction (Figure 4).

Total suspended matter

Suspended sediment is a very important component of proglacial streams. The physical weathering processesare very active in glaciated catchments, and the evacuation of sediments from glaciers depends very much on



2

4

6

8

Log

(Na+

)/H

+

−5 −4 −3 −2

−5 −4 −3 −2

Log H4SiO4

Log H4SiO4

2

4

6

8

Log(

K+)

/H+

Gibbsite Kaolinite

K-FeldsparK-Mica

Na-Montmorillonite

KaoliniteGibbsite

Am

orph

ous

Sili

ca

Qua

rtz

Sat

.

Alaknanda

Bhagirathi

Alaknanda

Bhagirathi

Am

orph

ous

Sili

ca

Qua

rtz

Sat

.

Figure 3. Equilibrium conditions of Na and K silicate system of Alaknanda and Bhagirathi river water



0.00

0.20

0.40

0.60

0.80

1.00

C -

Rat

io (H

CO

3/H

CO

3+S

O4)

0 30 60 90 120 150 180 210 240


0

2

4

6

8

10

12

(Ca+

Mg)

/(N

a+K

)

Alaknanda

Bhagirathi

Figure 4. Increasing trend of C-ratio and (Ca C Mg)/(Na C K) ratio in downstream signifies the importance of carbonate dissolution inmiddle and lower part of the basin

the amount of water draining through the glacier. The TSM concentration in the Garhwal catchment variesbetween 56 and 13 680 mg l�1. The TSM values are much higher for the Bhagirathi River in comparisonto the Alaknanda River. All the tributaries are characterized by low sediment concentrations. There is adecreasing trend of suspended sediment and an increasing trend of TDS concentration downstream for boththe Alaknanda and Bhagirathi Rivers (Figure 5). The suspended sediment concentration is very high near theglacier snout (the source region), indicating the importance of glacial activities in sediment production. Thedecrease in suspended sediment is more pronounced in the upper catchment. In Bhagirathi the suspendedconcentration decreased from 13 680 to 990 mg l�1 between Gomukh and Harsil and in the Alaknanda from2163 to 642 mg l�1 between the Sathopanth snout and Badrinath. This indicates that about 60–70% of thesuspended load goes into temporary storage in the watershed in only a 20–30 km stretch.



0 30 60 90 120 150 180 210 240


0

2000

4000

6000

8000

10000

12000

14000T

SM

Con

cent

ratio

n (m

g/l)

0

40

80

120

160

200

TD

S C

once

ntra

tion

(mg/

l)

TSM

TDS

___ Alaknanda

------ Bhagirathi

Figure 5. Downstream variation in TDS and TSM concentration. TSM concentration is very high near glacial portal region, indicatingdominance of physical weathering near the source region

The mineral compositions of suspended sediments of a few samples are given in Table III. The bulk of thesediments is composed of quartz and feldspar, constituting nearly 70–80% of the mineral abundance. Illiteand kaolinite are the common clay minerals. The abundance of feldspar and illite near the source regionsindicates the supply of fresh minerals from glacier erosion and weathering processes.

Factor analysis

Factor analysis is a useful explanatory tool in multivariate statistical analysis, and it can be applied todiscover and interpret relationships among variables to test hypotheses. The general purpose of factor analysis

Table III. Mineral composition of suspended sediments (wt%)

River Sites Quartz Feldspar Illite Kaolinite

Alaknanda Glacier snout 69 16 10 5Badrinath 51 12 26 11Joshimath 59 9 30 2Karnprayag 68 10 16 6Srinagar 64 10 17 9

Bhagirath Glacier snout 47 26 24 3Gnagotri 59 20 17 4Uttarkashi 73 16 8 3Tehri 71 14 11 4Devprayag 69 13 12 6



is to condense the information contained in a number of original variables into a smaller set of new compositedimensions with a minimum loss of information. Depending on the objective of the problem, one can performR-mode factor analysis or Q-mode factor analysis. Factor analysis is termed R-mode when the concern is theinterrelationships between variables and Q-mode when attention is devoted exclusively to interrelationshipsbetween samples. In the present study, R-mode analysis has been chosen as it has several positive features ininterpreting hydrogeochemical data (Lawrence and Upchurch, 1992).

Prior to the analysis, the data have been standarized to have a mean of 0 and a standard deviation of 1. Thisis necessary since the first step in factor analysis is computation of a correlation coefficient matrix, whichrequires normal distribution of all variables. The correlation matrix gives the intercorrelations among the setof variables. Principal factor analysis (or principal components) is nothing more than the eigenvectors of acorrelation or a variance–covariance matrix. Variance may be regarded as the average squared deviation ofall possible observations from the population mean. Total variance in a data set is a sum of the individualvariances. The percentages of eigenvalues are computed since the eigenvalues quantify the contribution of afactor to the total variation (the sum of the eigenvalues). The contribution of a factor is said to be significantwhen the corresponding eigenvalue is greater than unity (Briz-Kishore and Murali, 1992).

A step has been taken to rotate the factors (varimax rotated) in such a way that all their components arecloser to C1, 0 or �1, representing the importance of each variance (Briz-Kishore and Murali, 1992). Thus,where the factor loadings are high, it can be assumed that the variable contributes to that factor (Lawrenceand Upchurch, 1992). If the factor loading has a negative sign and is large, it indicates a negative correlationwith the factor. The final step in factor analysis is to project the data on the rotated significant factors. Thescores obtained by this projection are called factor scores. Dalton and Upchurch (1978) showed that factorscores are related to the intensity of the chemical process described by each factor, and that extreme negativenumbers (< �1) reflect areas unaffected by the process while extreme positive numbers > C1 indicate areasmost affected and near zero numbers those affected to an average degree (Lawrence and Upchurch, 1992).Communality provides an index to the efficiency of the reduced set of factors. By examining the factorloadings, communalities and eigenvalues, those variables belonging to a specific chemical process can beidentified and the importance of the major elements can be evaluated in terms of the total data set and interms of each factor. In the present study, in order to establish the weathering and geochemical processes andthe source of the ions, R-mode factor analysis with rotation was applied to normalized major ion chemistryof the Ganga headwater. The correlation coefficients of the variables (12) for 20 samples at 95% significancelevel are given in Table IV. It is observed from the correlation matrix that the EC, Ca, Mg, HCO3 and TDShave strong correlations with each other. The bicarbonate ions, which make up 70% of the total anions,and the corresponding cations (Ca, Mg), which make up 82% of the total cations, are to a large extentresponsible for the conductivity of the Ganga headwater. The positive correlation of TSM with K, H4SiO4

Table IV. Correlation matrix for the dissolved ions

EC pH Ca Mg Na K HCO3 SO4 Cl H4SiO4 TDS

pH 0Ð54 —Ca 0Ð91 0Ð42 —Mg 0Ð86 0Ð64 0Ð83 —Na 0Ð26 0Ð07 0Ð37 0Ð31 —K 0Ð11 0Ð26 �0Ð09 0Ð11 0Ð42 —HCO3 0Ð76 0Ð33 0Ð93 0Ð74 0Ð49 �0Ð2 —SO4 0Ð23 0Ð13 0Ð03 0Ð19 0Ð06 0Ð48 �0Ð22 —Cl 0Ð27 0Ð63 0Ð26 0Ð29 0Ð16 0Ð17 0Ð27 �0Ð20 —H4SiO4 �0Ð13 �0Ð13 �0Ð3 �0Ð17 0Ð43 0Ð83 �0Ð37 0Ð45 �0Ð16 —TDS 0Ð89 0Ð41 0Ð96 0Ð84 0Ð55 0Ð06 0Ð92 0Ð16 0Ð22 �0Ð14 —TSM −0Ð88 �0Ð15 �0Ð27 �0Ð2 0Ð27 0Ð79 �0Ð41 0Ð60 �0Ð31 0Ð87 −0Ð14



Tabl

eV

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inci

pal

and

vari

mox

rota

ted

R-m

ode

fact

orlo

adin

gm

atri

x

Var

iabl

esPr

inci

pal

fact

orm

atri

xV

arim

axro

tate

dfa

ctor

mat

rix

Ala

knan

daR

iver

Bha

gira

thi

Riv

erA

lakn

anda

Riv

erB

hagi

rath

iR

iver

Fact

or1

Fact

or2

Com

mun

alit

ies

Fact

or1

Fact

or2

Com

mun

alit

ies

Fact

or1

Fact

or2

Fact

or1

Fact

or2

EC

0Ð912

�0Ð28

30Ð9

120Ð5

960Ð7

890Ð9

790Ð9

470Ð1

19�0

Ð068

0Ð987

pH0Ð7

650.

�285

0Ð666

0Ð958

0Ð323

0Ð920

0Ð815

0Ð057

�0Ð78

50Ð5

51C

a0Ð9

67�0

Ð173

0Ð966

0Ð791

0Ð597

0Ð982

0Ð952

0Ð242

�0Ð33

50Ð9

33M

g0Ð9

310Ð2

230Ð9

170Ð8

35-0

Ð190

0Ð734

0Ð940

0Ð182

�0Ð80

40Ð2

96N

a0Ð6

400Ð4

840Ð6

44�0

Ð876

0Ð277

0Ð845

0Ð382

0Ð705

0Ð885

�0Ð24

7K

0Ð700

0Ð468

0Ð710

0Ð729

0Ð589

0Ð879

0Ð443

0Ð716

0Ð933

0Ð094

HC

O3

0Ð932

0Ð078

0Ð875

0Ð928

0Ð353

0Ð986

0Ð816

0Ð458

�0Ð58

50Ð8

02SO

40Ð3

11�0

Ð789

0Ð736

�0Ð92

30Ð2

030Ð8

890Ð6

14�0

Ð598

0Ð882

�0Ð33

2C

l0Ð5

610Ð4

500Ð5

780Ð6

73�0

Ð028

0Ð454

0Ð324

0Ð642

�0Ð57

80Ð3

45H

4Si

O4

0Ð109

0Ð862

0Ð756

�0Ð93

40Ð3

420Ð9

89�0

Ð257

0Ð830

0Ð969

�0Ð22

3T

DS

0Ð963

�0Ð12

80Ð9

45�0

Ð584

0Ð794

0Ð972

0Ð930

0Ð282

�0Ð55

30Ð9

84T

SM�0

Ð391

�0Ð42

30Ð3

32�0

Ð845

0Ð484

0Ð947

�0Ð18

1�0

Ð547

0Ð972

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7

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2Ð48

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Ð174

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and SO4 suggests the possibility of quick dissolution of freshly derived suspended sediments. Table V givesthe variables, principal factor matrix and rotated factor loading for the major ions for the Alaknanda andBhagirathi Rivers. Two factors with an eigenvalue >1 have been extracted. These two factors explain 75%and 88% of the total variance in the data matrix for these two rivers respectively. Factor 1 in the AlaknandaRiver contributes 54% of the total variance and shows strong loading of EC, Ca, Mg, TDS, HCO3 and pH.Factor 1 in the Alaknanda is explicitly a bicarbonate factor, which explains the dissolution of limestone anddolomite in the drainage basin. The second rotated factor in the Alaknanda River accounts for 21% of thevariance and shows high loading of Na, K and H4SiO4 and medium loading of HCO3 and Cl. This is a typicalsilicate weathering factor, indicating the weathering of silicate minerals like Na–K-feldspar. In the BhagirathiRiver, Factor 1 accounts for 66Ð6% of the total variance and shows strong loading of H4SiO4, TSM, K, Na andSO4. This factor explains the weathering of silicate minerals and sulphide oxidation. The high loading of TSMalong with the variables Na, K, SO4 and H4SiO4 substantiates the conclusion of quick dissolution of freshlyderived suspended sediments and oxidation of disseminated sulphide particles associated with suspendedsediments. Factor 2 in the Bhagirathi River is interpreted as a bicarbonate factor. It accounts for 22% of thevariance in the data matrix and shows high loading of EC, Ca, HCO3 and TDS and negative loading of TSMand SO4. Thus factor analysis also supports the conclusion that the Alakananda water chemistry is primarilycontrolled by carbonic acid weathering, while in the Bhagirathi River both carbonation and sulphide oxidationare controlling the solute acquisition processes in the Ganga headwater.

CONCLUSION

A detailed geochemical study of the water of the Garhwal Himalaya catchments has been carried out with theobjective of evaluating the weathering and geochemical processes controlling solute chemistry and sedimenttransfer in the Ganga headwater. The important conclusions are as follows.

1. The dominance of bicarbonate, calcium and magnesium, the high ratio of (Ca C Mg/Na C K) and lowvalues of (Na C K/TZC) suggest carbonate dissolution as the major source of the dissolved ions.

2. Carbonic acid weathering is the major proton-producing mechanism in the Alaknanda catchment, while inthe Bhagirathi both carbonation and sulphide oxidation, i.e. a coupled reaction, control the ionic composition.

3. The factor analysis of the major ion chemistry data extracts two factors operating in the headwater streamsof the Ganga River. Factor 1 in the Alaknanda River is explicitly a bicarbonate factor showing strongloading of EC, Ca, Mg, HCO3 and TDS. In the Bhagirathi River, Factor 1 explains the sulphide dissolutionand silicate weathering and Factor 2 explains carbonate weathering. The high loading of TSM along withthe variables Na, K, SO4 and H4SiO4 suggests quick dissolution of freshly derived suspended sedimentsand oxidation of disseminated sulphide particles associated with suspended sediments.

4. High TSM values near the glacial portal regions indicate that glacial weathering and erosion play animportant role in sediment production and transfer.

ACKNOWLEDGEMENTS

AKS is thankful to the JNU–UGC for providing a fellowship to conduct the research work. Financial supportprovided by CSIR (Government of India) and IAHS to attend the IUGG-1999, Birmingham, is also gratefullyacknowledged by the authors.

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