HYDROLOGICAL PROCESSES
Hydrol. Process. 16, 835–849 (2002)
DOI: 10.1002/hyp.367
Aspects of weathering and solute acquisition processes
controlling chemistry of sub-Alpine proglacial streams of
Garhwal Himalaya, India
Abhay Kumar Singh* and S. I. Hasnain
School 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 out
to assess the weathering and geochemical processes in high altitude river basins. Calcium and magnesium are the
major cations, and bicarbonate and sulphate are the most dominant anions in these waters. A high correlation among
HCO3 , 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 is
the major proton-producing reaction in the Alaknanda River, while in the Bhagirathi River it is the coupled reaction
which controls the solute acquisition processes. To know the geochemical factors controlling the chemical nature of
water, R-mode factor analysis on major ion data from Ganga headwater streams has been performed. Factor 1 in the
Alaknanda River is explicitly a bicarbonate factor showing strong loading of EC, Ca, Mg, HCO3 and TDS. In the
Bhagirathi River Factor 1 explains the sulphide dissolution and silicate weathering and Factor 2 explains carbonate
weathering. 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 kaolinite
and 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 contain
approximately 33 times the areal coverage of the glaciers in the European Alps (Wissmann, 1959). The
Himalayas, with an average elevation of 6000 m, are the repositories of some of the highest and largest
glaciers 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 Indian
subcontinent, which vary in glacier coverage. These glaciers contribute about 60–70% of the fresh water to
these main river systems of the Indian subcontinent. Thus glacier meltwaters form an important source of
water 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 comparable
to the groundwater reserves of India (Puri, 1994). A considerable amount of water has been harvested in this
region for the generation of hydroelectric power due to the available hydrogeological conditions. Glaciers not
only meet the need for water supply, but are also an important source of information on climatic changes in
the past and present.
* Correspondence to: Dr Abhay Kumar Singh, Central Mining Research Institute, Barwa Road, Dhanbad, Jharkhand 826001, India.
E-mail: [email protected]
Copyright  2002 John Wiley & Sons, Ltd.
Received 18 November 1999
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. The
Himalayan rivers, Ganga and Brahmaputra, together account for 3% of the total global flux of the
dissolved load to the world’s ocean (Sarin et al., 1989). The present estimates of the sediment yield of
the Ganga–Brahmaputra Rivers together is about a billion tons per year, nearly 7% of the global annual
sediment flux from the continents to the oceans (Milliman and Meade, 1983; Subramanian, 1993). It has been
estimated that the non-Himalayan (peninsular Indian) rivers of India carry less than 5% of the total mass
transport compared to the Himalayan rivers (Subramanian, 1979). In this paper the assessment of weathering
and geochemical processes controlling the water chemistry and sediment transfer in the high altitude rivers
of the Garhwal Himalayan catchment of the Ganga River will be discussed.
GARHWAL HIMALAYA
The Ganga River basin, lying between 29° 450 –31° 300 N and 78° 20 –80° 70 E and having an area of 30 000 km2 , is
called 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 in
the diurnal and seasonal variation in climate, and hence the variation in hydrology and dissolved and sediment
loads (Chauhan and Hasnain, 1993; Singh and Hasnain, 1998; Singh et al., 1999). The Himalayan proglacial
streams 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 average
rainfall in the Garhwal Himalaya is between 1000 and 2500 mm, of which 50–80% falls during the monsoon
period between June and September.
The Alaknanda and Bhagirathi are the two major proglacial streams of Garhwal Himalaya, forming the
mountainous catchment of the river Ganga. The Alaknanda emerges from twin glaciers, Satopanth and
Bhagirath Kharak, at the portal altitude of 3800 m, 13 km north of the temple town of Badrinath. The
river Bhagirathi originates at an elevation of 3812 m from the Gangotri glacier at Gomukh on the western
slope of Chaukhamba in Uttarkashi district. These two streams flow approximately 225–240 km across the
Himalaya before their confluence at Devprayag, forming the river Ganga. Dhauliganga, Nandakini, Pindar
and Mandakini are the major tributaries of the Alaknanda River, and Bhilangna is the major tributary
of the Bhagirathi River. The Ganga, after a total run of 280 km, cuts through the Himalaya at Sukhi
near Rishikesh, turns southwest for another 30 km and descends onto the vast Indo-Gangetic plains at
Haridwar.
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 upper
reaches 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 dominated
by 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) is
mainly covered by Precambrian Central Crystalline rocks. These rocks are primarily medium to high-grade
metamorphic rocks. Along the Bhagirathi River the major rocks include biotite gneiss, quartzite, quartz-schist
and amphibolite. Crystalline limestone, quartzite and carbonaceous phyllites are also exposed near the Tehri
area in Bhagirathi valley (Gnesser, 1964; Valdiya, 1980). The Main Central Thrust (MCT) separates the Central
Crystallines from the lower Uttarkashi and Chandpur Formations. The Uttarkashi Formation primarily consists
of limestone and dolomitic rocks and is exposed in the middle part of the Alaknanda and Bhagirathi River
basin. The outcrop of the Chandpur Formation is mainly composed of phyllites and micaceous graywackes
and is exposed in the lower part of the basin.
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
B
GI
RA
MASS
MOVEMENT
r
ve
i
aR
ng
Ga
Tehri
Uttarkashi
A
LG
BHI
GANGOTRI
GLACIER
I
IN
AK
D
40
Karnprayag
AL
AK
N
SATOPANTH
GLACIER
Kedarnath
Gomukh
A
R R.
Scale
0
PIND
A
Nandprayag
NI RIVE R
N A N D AKI
40 km
Joshimath
Pondukeshwar
Badrinath
GLACIER
N
INACTIVE SEDIMENT
SOURCE
PINDARI
GLACIER
a
MAN
Figure 1. Drainage map of the Garhwal Himalaya catchment showing sampling sites
Devprayag
NG
A
KHATLING
GLACIER
Harsil
D A RI
VER
CHANNEL
EROSION
Dh
ng
ga
au
li
Copyright  2002 John Wiley & Sons, Ltd.
HA
I
TH
N
India
h
es
ra
d
rP
Ut
ta
WEATHERING AND SOLUTE ACQUISITION PROCESSES
837
Hydrol. Process. 16, 835– 849 (2002)
838
A. K. SINGH AND S. I. HASNAIN
METHODOLOGY
Water samples were collected from different glaciers and proglacial streams of the Garhwal Himalayan region
in the premonsoon season (June 1992). Prior to sampling, polyethylene bottles of 500 ml capacity were
washed in the laboratory with dilute hydrochloric acid and then rinsed twice with double distilled water. At
the sampling sites, before collecting the samples, bottles were rinsed with the stream water. Water samples
were collected following the methods of Ostrem (1975). The bottle was lowered into the stream and held at an
angle of 45° upstream until filled almost to the neck. EC, pH and alkalinity were measured in the field. In the
laboratory, the water samples were filtered through 0Ð45-µm Millipore membrane filters to separate suspended
matter and the filtered solution was analysed for major cations (Ca, Mg, Na, K), major anions (HCO3 , SO4 ,
Cl) and dissolved silica (H4 SiO4 ). 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 analytical
precision for the measurements of major ions is about š5%. The molybdosilicate method and turbidimetric
method 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) and
bicarbonate 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 two
major constituents of stream water, constituting approximately 69% and 63% of the total anions and cations
respectively. The next most abundant dissolved species are sulphate (28%) and magnesium (20%). Bicarbonate
constitutes 72–91% of the total anions and (Ca C Mg) constitutes 67–93% of the total cations on an equivalent
basis in the Alaknanda. In the Bhagirathi, sulphate is more significant and constitutes about 8–81% of the
total anions. The downstream variation of various cations and anions is shown in Figure 2. There is a marked
increase in concentration of Ca, Mg and HCO3 between 50–90 km in the Alaknanda and between 15–40 km
in the Bhagirathi River. These increases in the concentration of Ca, Mg and HCO3 are related to the changes
in lithology from schist, gneiss and granitic gneiss-bearing rocks of the Central Crystalline to the carbonatebearing Uttarkashi Formation. In general, Alaknanda shows the increasing trend of ionic concentration in
a 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 with
elevation, showing maximum concentration near the source region and progressively decreasing in the
downstream direction. The increasing trend of ionic concentration with decreasing elevation is related to
soil thickness, lithology and temperature. The mineral surface exposed to weathering in thicker soil at lower
elevations is much greater than in the thin or no soil zone at high elevation. The residence time of water
in contact with weatherable minerals will be greater in thicker soil zones (Drever and Zobrist, 1992). At
higher elevation, the river flows through the rocks of less reactive phases like schist, gneisses, granites and
granodiorites 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 and
dolomite of the Uttarkashi Formation, which would result in greater ionic concentrations. The occurrence of
pyritous–carbonaceous slates and phyllites in the geological units of the Higher Himalayas suggests that the
oxidation 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 composition
of 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 contribution
from atmospheric and anthropogenic sources, is the major source of dissolved ions in aquatic systems
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
Copyright  2002 John Wiley & Sons, Ltd.
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Ganga
Tributaries
Dhauliganga
Nandakini
Pindari
Pindari
Mandakini
0
15
55
90
150
210
240
0
18
42
110
164
175
225
230
39
34
43
142
148
151
150
99
85
97
90
94
93
103
135
112
99
155
134
52
Joshimath
Nandprayag
Glacier snout
Karnprayag
Rudraprayag
EC
Glacier snout
Badrinath
Joshimath
Birehi
Karanprayag
Srinagar
Devprayag
Glacier snout
Gangotri
Harsil
Uttarkashi
Bhaldiana
Tehri
Devprayag
Devprayag
Site
7Ð67
7Ð78
7Ð9
7Ð42
7Ð12
7Ð3
7Ð12
7Ð43
7Ð57
7Ð8
7Ð72
8Ð2
7Ð5
7Ð4
8Ð0
8Ð1
8Ð1
8Ð1
8Ð2
8Ð4
pH
511
826
1051
895
374
177
198
274
1322
987
1080
1092
398
371
470
490
513
528
581
1001
Ca
96
313
319
319
66
43
27
47
327
326
315
328
154
147
313
238
244
231
253
272
Mg
Units: equiv. L1 ., except EC (S cm1 ), H4 SiO4 (mol l1 ), TDS and TSM (mg l1 ).
Streams
Distance (km)
55
85
33
62
78
42
48
63
153
66
74
101
108
82
67
74
77
75
79
64
Na
48
62
25
70
40
42
28
48
57
64
64
81
192
132
72
66
84
105
128
99
K
582
977
700
1035
361
221
190
284
1885
1107
1164
1150
146
142
467
507
555
536
546
1131
HCO3
290
438
722
113
76
40
57
61
164
94
154
159
681
633
371
231
167
248
307
177
SO4
27
21
18
18
29
8
17
18
23
18
36
35
11
15
16
27
33
46
49
36
Cl
Table I. Chemical characteristics and sediment load of Garhwal Himalayan streams (June 1992)
27
34
12
23
39
33
28
26
29
31
40
38
88
65
37
36
37
32
38
31
H4 SiO4
67
109
106
97
42
26
24
33
163
103
113
114
70
62
68
63
64
68
74
109
TDS
346
60
1207
210
56
2163
642
511
540
293
514
585
13 680
4860
990
1004
1054
1280
1897
1134
TSM
WEATHERING AND SOLUTE ACQUISITION PROCESSES
839
Hydrol. Process. 16, 835– 849 (2002)
840
A. K. SINGH AND S. I. HASNAIN
Ca
1400
____ Alaknanda
Mg
------- Bhagirathi
Ionic Concentration (µeq/l)
Na
K
1050
700
350
0
HCO3
Ionic Concentration (µeq/l)
1750
SO4
Cl
1400
1050
700
350
0
0
30
60
90
120
150
180
210
240
Distance downstream (km)
Figure 2. Downstream variation of dissolved ions showing sharp increase of Ca, Mg and HCO3 in the middle reaches of Alaknanda and
downstream decreasing trend of SO4 concentration in Bhagirathi River
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
Streams
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Alaknanda
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Bhagirathi
Ganga
Tributaries
Dhauliganga
Nandakini
Pindari
Pindari
Mandakini
Distance
(km)
0
15
55
90
150
210
240
0
18
42
110
164
175
225
230
Copyright  2002 John Wiley & Sons, Ltd.
58
66
63
71
68
70
68
46
50
51
56
55
56
56
70
72
64
74
66
67
Joshimath
Nandprayag
Glacier snout
Karnprayag
Rudraprayag
14
24
22
24
12
14
9
19
18
23
21
20
18
20
34
27
27
25
24
19
8
7
2
5
14
14
16
15
8
5
5
6
13
11
7
9
8
8
8
4
Ca Mg Na
Glacier snout
Badrinath
Joshimath
Birehi
Karanprayag
Srinagar
Devprayag
Glacier snout
Gangotri
Harsil
Uttarkashi
Bhaldiana
Tehri
Devprayag
Devprayag
Site
7
5
2
5
7
14
9
11
3
4
4
5
23
18
8
8
9
11
12
7
K
65
68
49
89
77
82
72
78
90
91
86
86
17
17
55
66
74
65
61
84
HCO3
32
31
50
10
16
15
22
17
8
8
11
12
81
80
43
30
22
30
34
13
SO4
3
1
1
2
6
3
6
5
1
1
2
2
1
2
2
4
4
6
6
3
Cl
6
8
24
9
4
3
3
3
7
10
10
8
2
2
6
5
5
4
4
8
0Ð85
0Ð88
0Ð95
0Ð90
0Ð79
0Ð72
0Ð75
0Ð74
0Ð88
0Ð91
0Ð91
0Ð88
0Ð65
0Ð71
0Ð85
0Ð84
0Ð82
0Ð81
0Ð80
0Ð89
CaC
CaC
Mg/
Mg/
Na C K TZC
0Ð15
0Ð11
0Ð041
0Ð098
0Ð21
0Ð27
0Ð25
0Ð25
0Ð11
0Ð09
0Ð09
0Ð11
0Ð35
0Ð29
0Ð15
0Ð16
0Ð17
0Ð19
0Ð19
0Ð11
NaC
K/
TZC
1Ð0
1Ð1
1Ð9
1Ð2
1Ð2
0Ð9
1Ð2
1Ð1
0Ð8
1Ð2
1Ð2
1Ð2
3Ð8
3Ð6
1Ð6
1Ð4
1Ð4
1Ð4
1Ð5
1Ð1
CaC
Mg/
HCO3
2Ð0
4Ð0
1Ð8
3Ð4
2Ð6
5Ð2
2Ð8
3Ð5
6Ð6
3Ð6
2Ð0
2Ð8
9Ð8
5Ð4
4Ð1
2Ð7
2Ð3
1Ð6
1Ð6
1Ð7
Na/Cl
Table II. Relative abundance (%) and ionic ratio of the different dissolved ions
21Ð5
28Ð7
58Ð3
45
9Ð2
6Ð69
6Ð78
10Ð9
65
35Ð7
29Ð1
30Ð2
1Ð65
2Ð1
12Ð6
14Ð0
15
16Ð7
14Ð3
36Ð4
HCO3 /
H4 SiO4
10Ð7
20Ð8
40Ð1
6Ð2
2Ð6
5
3Ð3
3Ð3
7Ð1
5Ð2
4Ð2
4Ð5
61Ð0
42Ð2
23Ð1
8Ð5
5Ð0
5Ð3
6Ð2
4Ð9
1Ð7
2Ð9
1Ð3
3Ð8
1Ð3
5Ð2
1Ð6
2Ð6
2Ð4
3Ð5
1Ð7
2Ð3
17Ð4
8Ð8
4Ð5
2Ð4
2Ð5
2Ð2
2Ð6
2Ð7
0Ð66
0Ð69
0Ð49
0Ð90
0Ð82
0Ð85
0Ð77
0Ð82
0Ð9
0Ð9
0Ð8
0Ð87
0Ð17
0Ð1
0Ð5
0Ð68
0Ð76
0Ð6
0Ð64
0Ð86
SO4 /Cl K/Cl C-ratio
WEATHERING AND SOLUTE ACQUISITION PROCESSES
841
Hydrol. Process. 16, 835– 849 (2002)
842
A. K. SINGH AND S. I. HASNAIN
(Stallard and Edmond, 1983; Tranter et al., 1993). Dissolution of atmospheric CO2 in water and oxidation of
sulphides are the two main contributors of protons used for weathering of carbonates and silicates (Garrels
and Mackenzie, 1971).
The nature of weathering and source of dissolved ions in water can be evaluated by applying the mass
balance approach and considering the relative abundance of ions, the correlations among solutes and the
geology of the drainage basin. In the case of weathering of minerals by carbonic acid, the equivalent ratio
of Ca : HCO3 in the waters resulting from calcite weathering is 1 : 2, whereas for dolomite it is 1 : 4. For
sulphuric 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 concentration
of chloride and high ratio of SO4 /Cl (13) and Na/Cl (4) rule out the possibilities of evaporite dissolution
or atmospheric inputs as the major contributor of dissolved ions. It has been estimated that atmospheric
deposition may contribute up to 20% of the Na and K and up to 5% of the Ca, Mg and SO4 to the major ion
chemistry in the mountainous catchment of the Ganga River (Sarin et al., 1992). The high concentration of
bicarbonate and its positive correlation with Ca (r 2 D 0Ð93) and Mg (r 2 D 0Ð74) indicate carbonate dissolution
as 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 suggest
that carbonate weathering is the major source of the dissolved ions, with minor contributions from silicate
weathering (Sarin et al., 1989; Pandey et al., 1999; Singh and Hasnain, 1999). Furthermore, the low content
of dissolved silica and high HCO3 /H4 SiO4 molar ratio present in the system are clear evidence that the solute
contribution via silicate weathering plays a relatively minor role compared with the supply by the carbonate
phase. Na, K and H4 SiO4 in the drainage basin are mainly derived from the weathering of alumino-silicate
minerals, with clay minerals as byproducts. Sodium and potassium in the Ganga headwater are mainly derived
from igneous and metamorphic rocks of the Central Crystalline rocks. Common parent minerals for sodium
and potassium released into the Ganga headwater include albite, orthoclase (KAlSi3 O8 ) and micas, which may
react with water and carbonic acid and accumulate various clay minerals in the sediments. Mineral stability
is an important way in which the approach to equilibrium between clay minerals and natural water can be
verified through thermodynamic data (Garrels and Christ, 1965). The plots of Na and K silicate systems
for the Alaknanda and Bhagirathi Rivers demonstrate that the water of the Ganga headwater is in the range
of 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 low
concentration of dissolved silica in the Ganga headwater may be attributed to the high resistance of sialic
minerals to weathering, and also consumption of H4 SiO4 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 involving
the weathering of carbonates by protons derived from sulphide oxidation. Figure 4 shows the downstream
variation of the C-ratio in the Alaknanda and Bhagirathi Rivers. For Alaknanda, the C-ratio is always higher
than 0Ð5, signifying that carbonic acid weathering is the major proton producer. In the Bhagiarthi River the
C-ratio increases downstream, signifying the importance of carbonate dissolution in the middle and lower part
of 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 weathering
and sulphide oxidation) control the solute acquisition in the Bhagirathi and Pindari Rivers. The downstream
variation in the (Ca C Mg/Na C K) ratio shows a sharp increase in middle and lower reaches, indicating an
increased 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 processes
are very active in glaciated catchments, and the evacuation of sediments from glaciers depends very much on
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
8
6
Log (Na+)/H+
843
Amorphous Silica
Quartz Sat.
WEATHERING AND SOLUTE ACQUISITION PROCESSES
Na-Montmorillonite
4
2
Alaknanda
Gibbsite Kaolinite
Bhagirathi
−5
−4
−3
−2
Quartz Sat.
Log H4SiO4
8
K-Feldspar
Amorphous Silica
K-Mica
Log(K+)/H+
6
4
2
Alaknanda
Gibbsite Kaolinite
Bhagirathi
−5
−4
−3
−2
Log H4SiO4
Figure 3. Equilibrium conditions of Na and K silicate system of Alaknanda and Bhagirathi river water
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
844
A. K. SINGH AND S. I. HASNAIN
C - Ratio (HCO3 /HCO3+SO4)
1.00
0.80
0.60
0.40
0.20
Alaknanda
Bhagirathi
0.00
12
(Ca+Mg)/(Na+K)
10
8
6
4
2
0
0
30
60
90 120 150 180 210 240
Distance downstream (km)
Figure 4. Increasing trend of C-ratio and (Ca C Mg)/(Na C K) ratio in downstream signifies the importance of carbonate dissolution in
middle and lower part of the basin
the amount of water draining through the glacier. The TSM concentration in the Garhwal catchment varies
between 56 and 13 680 mg l1 . The TSM values are much higher for the Bhagirathi River in comparison
to the Alaknanda River. All the tributaries are characterized by low sediment concentrations. There is a
decreasing trend of suspended sediment and an increasing trend of TDS concentration downstream for both
the Alaknanda and Bhagirathi Rivers (Figure 5). The suspended sediment concentration is very high near the
glacier snout (the source region), indicating the importance of glacial activities in sediment production. The
decrease in suspended sediment is more pronounced in the upper catchment. In Bhagirathi the suspended
concentration decreased from 13 680 to 990 mg l1 between Gomukh and Harsil and in the Alaknanda from
2163 to 642 mg l1 between the Sathopanth snout and Badrinath. This indicates that about 60–70% of the
suspended load goes into temporary storage in the watershed in only a 20–30 km stretch.
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
845
WEATHERING AND SOLUTE ACQUISITION PROCESSES
14000
TSM
___ Alaknanda
TDS
------ Bhagirathi
200
160
10000
120
8000
6000
80
4000
TDS Concentration (mg/l)
TSM Concentration (mg/l)
12000
40
2000
0
0
0
30
60
90 120 150 180
Distance downstream (km)
210
240
Figure 5. Downstream variation in TDS and TSM concentration. TSM concentration is very high near glacial portal region, indicating
dominance 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 the
sediments is composed of quartz and feldspar, constituting nearly 70–80% of the mineral abundance. Illite
and kaolinite are the common clay minerals. The abundance of feldspar and illite near the source regions
indicates 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 to
discover and interpret relationships among variables to test hypotheses. The general purpose of factor analysis
Table III. Mineral composition of suspended sediments (wt%)
River
Alaknanda
Bhagirath
Sites
Quartz
Feldspar
Illite
Kaolinite
Glacier snout
Badrinath
Joshimath
Karnprayag
Srinagar
Glacier snout
Gnagotri
Uttarkashi
Tehri
Devprayag
69
51
59
68
64
47
59
73
71
69
16
12
9
10
10
26
20
16
14
13
10
26
30
16
17
24
17
8
11
12
5
11
2
6
9
3
4
3
4
6
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
846
A. K. SINGH AND S. I. HASNAIN
is to condense the information contained in a number of original variables into a smaller set of new composite
dimensions with a minimum loss of information. Depending on the objective of the problem, one can perform
R-mode factor analysis or Q-mode factor analysis. Factor analysis is termed R-mode when the concern is the
interrelationships between variables and Q-mode when attention is devoted exclusively to interrelationships
between samples. In the present study, R-mode analysis has been chosen as it has several positive features in
interpreting 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. This
is necessary since the first step in factor analysis is computation of a correlation coefficient matrix, which
requires normal distribution of all variables. The correlation matrix gives the intercorrelations among the set
of variables. Principal factor analysis (or principal components) is nothing more than the eigenvectors of a
correlation or a variance–covariance matrix. Variance may be regarded as the average squared deviation of
all possible observations from the population mean. Total variance in a data set is a sum of the individual
variances. The percentages of eigenvalues are computed since the eigenvalues quantify the contribution of a
factor to the total variation (the sum of the eigenvalues). The contribution of a factor is said to be significant
when 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 are
closer 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 (Lawrence
and Upchurch, 1992). If the factor loading has a negative sign and is large, it indicates a negative correlation
with the factor. The final step in factor analysis is to project the data on the rotated significant factors. The
scores obtained by this projection are called factor scores. Dalton and Upchurch (1978) showed that factor
scores are related to the intensity of the chemical process described by each factor, and that extreme negative
numbers (< 1) reflect areas unaffected by the process while extreme positive numbers > C1 indicate areas
most 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 factor
loadings, communalities and eigenvalues, those variables belonging to a specific chemical process can be
identified and the importance of the major elements can be evaluated in terms of the total data set and in
terms of each factor. In the present study, in order to establish the weathering and geochemical processes and
the source of the ions, R-mode factor analysis with rotation was applied to normalized major ion chemistry
of the Ganga headwater. The correlation coefficients of the variables (12) for 20 samples at 95% significance
level are given in Table IV. It is observed from the correlation matrix that the EC, Ca, Mg, HCO3 and TDS
have 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 extent
responsible for the conductivity of the Ganga headwater. The positive correlation of TSM with K, H4 SiO4
Table IV. Correlation matrix for the dissolved ions
pH
Ca
Mg
Na
K
HCO3
SO4
Cl
H4 SiO4
TDS
TSM
EC
pH
Ca
Mg
Na
K
HCO3
SO4
Cl
H4 SiO4
TDS
0Ð54
0Ð91
0Ð86
0Ð26
0Ð11
0Ð76
0Ð23
0Ð27
0Ð13
0Ð89
−0Ð88
—
0Ð42
0Ð64
0Ð07
0Ð26
0Ð33
0Ð13
0Ð63
0Ð13
0Ð41
0Ð15
—
0Ð83
0Ð37
0Ð09
0Ð93
0Ð03
0Ð26
0Ð3
0Ð96
0Ð27
—
0Ð31
0Ð11
0Ð74
0Ð19
0Ð29
0Ð17
0Ð84
0Ð2
—
0Ð42
0Ð49
0Ð06
0Ð16
0Ð43
0Ð55
0Ð27
—
0Ð2
0Ð48
0Ð17
0Ð83
0Ð06
0Ð79
—
0Ð22
0Ð27
0Ð37
0Ð92
0Ð41
—
0Ð20
0Ð45
0Ð16
0Ð60
—
0Ð16
0Ð22
0Ð31
—
0Ð14
0Ð87
—
−0Ð14
Copyright  2002 John Wiley & Sons, Ltd.
Hydrol. Process. 16, 835– 849 (2002)
Copyright  2002 John Wiley & Sons, Ltd.
EC
pH
Ca
Mg
Na
K
HCO3
SO4
Cl
H4 SiO4
TDS
TSM
Variables
0Ð912
0Ð765
0Ð967
0Ð931
0Ð640
0Ð700
0Ð932
0Ð311
0Ð561
0Ð109
0Ð963
0Ð391
Factor 1
0Ð283
0.285
0Ð173
0Ð223
0Ð484
0Ð468
0Ð078
0Ð789
0Ð450
0Ð862
0Ð128
0Ð423
Factor 2
0Ð912
0Ð666
0Ð966
0Ð917
0Ð644
0Ð710
0Ð875
0Ð736
0Ð578
0Ð756
0Ð945
0Ð332
0Ð596
0Ð958
0Ð791
0Ð835
0Ð876
0Ð729
0Ð928
0Ð923
0Ð673
0Ð934
0Ð584
0Ð845
Factor 1
Principal factor matrix
Communalities
Alaknanda River
Communalities
0Ð979
0Ð920
0Ð982
0Ð734
0Ð845
0Ð879
0Ð986
0Ð889
0Ð454
0Ð989
0Ð972
0Ð947
Eigenvalue
Variance(%)
Cumulative(%)
0Ð789
0Ð323
0Ð597
-0Ð190
0Ð277
0Ð589
0Ð353
0Ð203
0Ð028
0Ð342
0Ð794
0Ð484
Factor 2
Bhagirathi River
0Ð947
0Ð815
0Ð952
0Ð940
0Ð382
0Ð443
0Ð816
0Ð614
0Ð324
0Ð257
0Ð930
0Ð181
6Ð49
54Ð1
54Ð1
Factor 1
0Ð119
0Ð057
0Ð242
0Ð182
0Ð705
0Ð716
0Ð458
0Ð598
0Ð642
0Ð830
0Ð282
0Ð547
2Ð48
20Ð7
74Ð8
Factor 2
0Ð068
0Ð785
0Ð335
0Ð804
0Ð885
0Ð933
0Ð585
0Ð882
0Ð578
0Ð969
0Ð553
0Ð972
7Ð98
66Ð6
66Ð6
Factor 1
0Ð987
0Ð551
0Ð933
0Ð296
0Ð247
0Ð094
0Ð802
0Ð332
0Ð345
0Ð223
0Ð984
0Ð567
2Ð56
21Ð6
88Ð2
Factor 2
Varimax rotated factor matrix
Alaknanda River
Bhagirathi River
Table V. Principal and varimox rotated R-mode factor loading matrix
WEATHERING AND SOLUTE ACQUISITION PROCESSES
847
Hydrol. Process. 16, 835– 849 (2002)
848
A. K. SINGH AND S. I. HASNAIN
and SO4 suggests the possibility of quick dissolution of freshly derived suspended sediments. Table V gives
the variables, principal factor matrix and rotated factor loading for the major ions for the Alaknanda and
Bhagirathi 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 Alaknanda
River 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 and
dolomite in the drainage basin. The second rotated factor in the Alaknanda River accounts for 21% of the
variance and shows high loading of Na, K and H4 SiO4 and medium loading of HCO3 and Cl. This is a typical
silicate weathering factor, indicating the weathering of silicate minerals like Na–K-feldspar. In the Bhagirathi
River, Factor 1 accounts for 66Ð6% of the total variance and shows strong loading of H4 SiO4 , TSM, K, Na and
SO4 . This factor explains the weathering of silicate minerals and sulphide oxidation. The high loading of TSM
along with the variables Na, K, SO4 and H4 SiO4 substantiates the conclusion of quick dissolution of freshly
derived suspended sediments and oxidation of disseminated sulphide particles associated with suspended
sediments. Factor 2 in the Bhagirathi River is interpreted as a bicarbonate factor. It accounts for 22% of the
variance in the data matrix and shows high loading of EC, Ca, HCO3 and TDS and negative loading of TSM
and SO4 . Thus factor analysis also supports the conclusion that the Alakananda water chemistry is primarily
controlled by carbonic acid weathering, while in the Bhagirathi River both carbonation and sulphide oxidation
are 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 the
objective of evaluating the weathering and geochemical processes controlling solute chemistry and sediment
transfer 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 low
values 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 in
the 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 streams
of the Ganga River. Factor 1 in the Alaknanda River is explicitly a bicarbonate factor showing strong
loading of EC, Ca, Mg, HCO3 and TDS. In the Bhagirathi River, Factor 1 explains the sulphide dissolution
and silicate weathering and Factor 2 explains carbonate weathering. The high loading of TSM along with
the variables Na, K, SO4 and H4 SiO4 suggests quick dissolution of freshly derived suspended sediments
and 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 an
important role in sediment production and transfer.
ACKNOWLEDGEMENTS
AKS is thankful to the JNU–UGC for providing a fellowship to conduct the research work. Financial support
provided by CSIR (Government of India) and IAHS to attend the IUGG-1999, Birmingham, is also gratefully
acknowledged by the authors.
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