ORIGINAL ARTICLE

Arsenic mobility in fluvial environment of the Ganga Plain,northern India

Munendra Singh Æ Amit Kumar Singh Æ Swati ÆNupur Srivastava Æ Sandeep Singh Æ A. K. Chowdhary

Received: 8 October 2008 / Accepted: 16 March 2009 / Published online: 9 April 2009

� Springer-Verlag 2009

Abstract In the northern part of the Indian sub-continent,

the Gomati River (a tributary of the Ganga River) was

selected to study the dynamics of Arsenic (As) mobilization

in fluvial environment of the Ganga Plain. It is a 900-km-

long, groundwater-fed, low-gradient, alluvial river charac-

terized by monsoon-controlled peaked discharge. Thirty-six

water samples were collected from the river and its tribu-

taries at low discharge during winter and summer seasons

and were analysed by ICP-MS. Dissolved As and Fe con-

centrations were found in the range of 1.29–9.62 and 47.84–

431.92 lg/L, respectively. Arsenic concentration in the

Gomati River water has been detected higher than in its

tributaries water and characteristically increases in down-

stream, attributed to the downstream increasing of Fe2O3

content, sedimentary organic carbon and silt-clay content in

the river sediments. Significant correlation of determination

(r2 = 0.68) was also observed between As and Fe concen-

trations in the river water. Arsenic concentrations in the river

water are likely to follow the seasonal temperature variation

and reach the level of World Health Organization’s per-

missible limit (10 lg/L) for drinking water in summer

season. The Gomati River longitudinally develops reducing

conditions after the monsoon season that mobilize As into

the river water. First, dissolved As enters into pore-water of

the river bed sediments by the reductive dissolution of

Fe-oxides/hydroxides due to microbial degradation of sedi-

mentary organic matter. Thereafter, it moves upward as well

as down slope into the river water column. Anthropogeni-

cally induced biogeochemical processes and tropical

climatic condition have been considered the responsible

factors that favour the release of As in the fluvial environ-

ment of the Ganga Plain. The present study can be considered

as an environmental alarm for future as groundwater

resources of the Ganga–Brahmaputra Delta are seriously

affecting the human–environment relationship at present.

Keywords Arsenic � Gomati River � Alluvial rivers �Sub-tropical climate � Ganga Plain

Introduction

Tropical fluvial environment is unique for the strong

geochemical fractionation, elemental partitioning and

quantitative transportation resulting from its climatic

characteristics controlled by heavy seasonal rainfall with

long periods of drought and high ambient temperatures.

The hydro-geochemical study of this environment can be

easily linked with human health aspects that support the

development and progress of a newly emerging branch of

Earth System Science known as Medical Geology. A high-

quality database of a wide range of investigations from the

geosphere and biosphere is pertinent and should be,

therefore, considered as an essential component of envi-

ronmental knowledge (UNESCO 1995; Dissanayake and

Chandrajith 1999).

M. Singh (&) � A. K. Singh � Swati � N. Srivastava

Centre of Advanced Study in Geology, University

of Lucknow, Lucknow 226 007, India

e-mail: smunendra@gmail.com

S. Singh

Department of Earth Science,

Indian Institute of Technology,

Roorkee 247 667, India

A. K. Chowdhary

Institute Instrumentation Centre,

Indian Institute of Technology,

Roorkee 247 667, India

123

Environ Earth Sci (2010) 59:1703–1715

DOI 10.1007/s12665-009-0152-z

Arsenic is chemically classified as a metalloid and the

20th most abundant natural element of the earth’s crust. It

is an essential element at low concentration and behaves as

a classical poison at high level. The occurrences and dis-

tribution of As in natural waters vary by more than four

orders of magnitude ranging from\0.5 to[5,000 lg/L and

are mainly dependent on geology, hydrology, climate, as

well as various anthropogenic activities of the region.

Baseline concentrations of As in river waters are low (0.1–

0.8 lg/L but can reach up to 2 lg/L) and are controlled by

the composition of river water and sediments. For example,

Seyler and Martin (1991) reported As concentration as low

as 0.13 lg/L in river water draining the Krka region of

Yugoslavia. Waslenchuk (1979) found As concentration in

the range of 0.15–0.45 lg/L in the river water from south-

eastern USA. In river waters draining the basement rocks

of Norway, Lenvik et al. (1978) also found low average

concentrations of about 0.25 lg/L. On the other hand,

extremely high concentrations of naturally occurring As

were reported to affect around 150 million people at risk in

the Ganga–Brahmaputra Delta region of India and Ban-

gladesh. Average As in agricultural floodplain soil from

Faridpur (Bangladesh) was reported to be more than three

times higher than the world average limit (Ahsan et al.

2009). In this region, As concentrations in the groundwater

resources were reported in a very large range of\0.5 lg/L

to ca. 3,200 lg/L (Smedley and Kinniburgh 2002; Rahman

et al. 2001).

Arsenic-rich groundwater and its associated human

health problems has been well known in Argentina,

Chile, Mexico, China, India (West Bengal) and Bangla-

desh. In the past two decades, lot of research has been

carried out particularly on As-related issues in the

groundwater environment of the Ganga–Brahmaputra

Delta region. Recently, As contamination in the ground-

water of upper and middle parts of the Ganga Plain has

been reported by Chakraborti et al. (2003) and Ahamad

et al. (2006). The present As crisis is likely to affect

additional hundreds of million people housing in the

Ganga Plain region. However, our knowledge of As

mobilization in the fluvial environment of the Ganga

Plain region is limited. There is a need of integrated

study to understand sources, release, mechanism, mobi-

lization of As in rivers/streams of the Ganga Plain. Thus,

the major objectives of the present study are to find out

As concentrations in the water of the Gomati River

System and to understand dynamics of As mobilization in

alluvial rivers and streams draining the Ganga Plain

under sub-tropical climate. The proper understanding of

biogeochemical processes dealing with As mobilization in

fluvial environment would play a significant role in the

development and management of river water resources of

the Ganga Plain in the future.

Study area

Regional setting

In the northern part of the Indian sub-continent, the Ganga

Plain is located between the Himalaya in the north and the

peninsular India in the south and is an outstanding geo-

graphical feature characterized by its low elevation

(\300 m above mean sea level), low relief (20–35 m) and

high population density ([500 persons/km2). It is one of

the most densely populated regions of the world and serves

as the home to nearly 500 million people (Fig. 1a). The

plain exhibits variety of landforms, namely incised river

valleys, abandoned channels, palaeo-channels, alluvial

ridges, ponds, lakes, etc. The plain experiences a humid

sub-tropical climate characterized by three prominent

seasons; hot summer season (March–June) followed by the

monsoon season (July–October) of heavy precipitation and

then the cold winter season (November–February). Tem-

perature variation is extreme, ranging from maximum

(47�C) in summer and minimum (2�C) in winter, while

rainfall ranges from over 2,000 mm in the east to 300 mm

in the west. A large amount of water is lost into the

atmosphere through evapo-transpiration due to less rainy

days and large number of sunny days. Figure 1c displays

climographs showing annual variation in total rainfall and

maxi/min temperature variation at Allahabad meterological

centre located on southern margin of the Gomati River

Basin. The Ganga Plain, therefore, is characterized as a

hydrologically dry region where water loss through evap-

oration is much more than water received from total

rainfall in this region (Rao 1975).

During the 1960s–1980s, monsoonal rains were spread

out over 30–45 days. Low precipitation of longer durations

favour the recharging of ground water that maintains the

base level flow of number of alluvial rivers and streams

originating and draining the Ganga Plain after the monsoon

season. However, by the end of the twentieth century, the

monsoonal rains occurred with heavy downpour in a short

span of 20–25 days and therefore, drained out into the

alluvial rivers of the Ganga Plain that reduced the

groundwater recharge possibilities of the Ganga Plain

(Kothyari et al. 1997). All alluvial rivers of the Ganga Plain

experienced reduced water discharges during recent times

as compared to their recent past.

Lithologically, the Ganga Plain is made-up of interlay-

ered 1–2 m thick fine sand and silty mud deposits showing

extensive discontinuous calcrete horizons. Singh (1996)

identified two types of lithofacies association: muddy

interfluve deposits and sandy interfluve deposits. Muddy

interfluve deposits are made up of 0.2–1.0 m thick well

sorted silt with extensive calcrete development; 1.0–2.0 m

thick highly mottled fine sand deposits with 5–10 cm thick

1704 Environ Earth Sci (2010) 59:1703–1715

123

bedded calcrete and shell-bearing mud. Sandy interfluve

deposits are made up of 0.5–2.0 m thick lenticular sand

bodies representing meandering river deposits and 1.0–

2.0 m thick well sorted silty fine sand representing sheet

flood deposits with 10–50 cm thick discontinuous horizons

of calcrete.

The human population density of the Ganga Plain is

about 500 persons/km2. To maintain the needs of growing

population pressure, the cropping area of rice, wheat and

sugarcane was increased nearly four times (Dadhwal and

Chhabra 2002). Fertilizer consumption increased several

times leading to change in the chemical composition of the

river waters. Excessive withdrawal of groundwater from

this region shows a drop of groundwater level from 8 to

10 m. With this background, the Gomati River system is

selected for the present study of As mobility in fluvial

environment of the Ganga Plain. The integrated knowledge

on hydro-geochemical characteristics of the Gomati River

System is considered essential for the understanding of As

mobilization in the fluvial environment of the Ganga Plain.

Table 1 summarizes all the important characteristics of the

Gomati River along with its drainage basin, water char-

acteristics and sediment properties.

Gomati River system

The Gomati River originates from a swampy area in the

Piedmont Zone in Pilibhit district near Puranpur and ulti-

mately meets the Ganga River near Saidpur. It has a gently

sloping elongated drainage basin trending NW–SE direc-

tion (nearly parallel to the Himalayan front) and draining

more than an area of 30,437 km2 located in the interfluve

region of the Ganga and the Ghaghara Rivers (Fig. 1a).

The river system has dendrite to parallel network of

entrenched alluvial streams characterized by similar litho-

logical and climatological conditions. The Sai River is the

main tributary and drains nearly one-third part of the basin.

Other important tributaries of the Gomati River System are

the Jokhan River, the Bhainsi Nadi, the Chhiya Nala, the

Kathna River, the Sarayan River, the Behta Nala, the Reth

Nadi, the Loni Nala, the Rari Nadi, the Kalyani Nadi, the

Kundu Nala, the Pili Nadi, etc. Nala is local name of

Fig. 1 a Location map of the

study area showing the Ganga

River Basin, the Ganga Plain

and the Gomati River System.

The Ganga Plain is one of the

most densely populated and

highly farmed regions of the

Indian sub-continent, b the

Gomati River system showing

its sub-basin/microbasins

drained by several small alluvial

tributaries, c climographs

showing annual variation in

total rainfall and temperature

distribution at Allahabad

Meterological Centre located in

the southern margin of the

Gomati River Basin and

d schematic highly peaked

hydrograph of the Gomati River

Environ Earth Sci (2010) 59:1703–1715 1705

123

riverulets or ravines seasonally filled with groundwater and

flooded by monsoon rains in this region. All the tributaries

are essentially groundwater fed and flow nearly parallel to

the main channel with their drainage microbasin ranging in

areas of 100–2,000 km2. All significant microbasins of the

Gomati River are drained by third to fifth order alluvial

channels with drainage density and basin relief ranging

from 0.44 to 1.04 km/km2 and from 10 to 44 m, respec-

tively (Thakur 2008). Some important urban centres

located on the river banks are Lucknow, Sultanpur and

Jaunpur (Fig. 1b).

Gomati River water

Monsoonal rainwater interacts with the alluvium of the

Ganga Plain and enters into the groundwater system to

become a source of all tributaries of the Gomati River

System. The hydrology of the Gomati River is controlled

by the intensity of rainfall and the duration of monsoon

season. Throughout the year, the river flows in very slow

motion except during the rainy season. During monsoon

season, heavy rainfall causes *100-fold increase in

the river’s runoff. The river hydrograph is seasonally

controlled and highly peaked (Fig. 1d) with annual dis-

charge of the river to be about 7,390 9 106 m3 (Rao 1975).

River water chemistry plays an important role in quan-

tifying the water quality as well as in understanding of the

release of sediment-bound As in the Gomati River System.

Compared to global average river waters, the Gomati River

water is significantly enriched with Si, Ca, Mg, K and Na

ions. Ranges or mean values of the characteristic chemical

features of the Gomati River water are pH (8.0), total alka-

linity (210 mg/L), total dissolved solid (225–270 mg/L),

total suspended solid (40–50 mg/L), dissolved oxygen

(4–8 mg/L), biochemical oxygen demand (2–10 mg/L),

chemical dissolved oxygen (10–25 mg/L), chloride

(4–10 mg/L), sulfate (7–16 mg/L), phosphate (0.1–0.5 mg/L),

sodium (23–35 mg/L), potassium (4–7 mg/L), calcium

(40 mg/L), magnesium (15 mg/L) and total coliform

(1.6 9 104–2.4 9 109 MPN/100 ml) as reported in Singh

et al. (2004). There are seasonal as well as longitudinal

variations in all the above parameters. In the winter season,

the water temperature is 20�C, where as in the summer it

increases up to 30�C. Electrical conductivity in the winter

season is 425 lS/cm and increases to 470 lS/cm in the

summer season.

Figure 2a illustrates the main hydro-chemical features

of the Gomati River water by Piper diagram representing as

percentage of major cations and anions in meq/L. The river

water is classified as Ca??–Mg??-dominant HCO3- type

water. Additionally, Singh et al. (2006) investigated the

hydrogeochemistry of groundwater in the middle part of

the Gomati River Basin and found that univalent (Na–K)

cations and HCO3 anions show dominance over other

species. Groundwater of the river basin can be classified as

Na–K–HCO3 Type.

Gomati River sediments

In a fluvial system, the important characteristics of river

sediments related to the mobility of sediment-bound As are

mineralogy, sediment geochemistry, textural composition,

clay content and organic matter. Sediment characteristics

of the Gomati River are strongly controlled by the geology

of the Ganga Plain as the river derives its sediment-load

from the weathering of the Ganga Plain. Mean grain size

of the bed load is very fine sand, whereas suspended

load varies from coarse silt to very fine silt (Gupta and

Subramanian 1994). Kumar and Singh (1978) studied

mineralogy of channel sediments and compositionally

classified them as lithic greywacke. Average mineral

composition of the river sand includes quartz (55%), rock

fragments (19%), muscovite (15%), K-feldspar (8%), bio-

tite (2%) and plagioclase (1%). Relative abundance of clay

minerals in the river sediments shows illite (61%) along

Table 1 General characteristics of the Gomati River and its basin

(data: various sources)

Gomati River Basin

Drainage basin area 30,437 km2

Annual rainfall 81–125 cm

Maxi. and mini. elevation 186 m and 61 m

Maximum-Minimum Temperature 47–2 �C

Relief 25 m (maximum)

Sub and micro-basins Sai River sub-Basin

and 33 microbasins

Gomati River

Channel length 900 km

Valley width (mini.–max.) 0.25–10 km

Average flow (at Lucknow in Summer) 5.79 m3/s

Average flow (at Lucknow in Monsoon) 636.57 m3/s

Maximum Monsoon discharge 2,107 m3/s

Gomati River water

pH 8.1–8.4

Conductivity 320–350 lS/cm

Total suspended matter 18–26 mg/L

HCO3- 300 mg/L

Gomati River sediments

Grain size Vary fine sand

Mineral composition Quartz, muscovite,

biotite, rock fragments,

K-feldspar, plagioclase

Common clay minerals Illite and montmorillonite

1706 Environ Earth Sci (2010) 59:1703–1715

123

with smectite (26%), kaolinite (7%) and metastable chlo-

rite (6%).

In river sediments, As was found in association with

amorphous Fe oxides as it is probably adsorbed and or

co-precipitates with Fe oxides due to the relative con-

stancy of Fe/As ratio during dissolution (Aggett and

Roberts 1986). In the upper Isle River, France, three

As-bearing phases have been identified: (1) detrital pri-

mary sulphides with high in situ As percentage up to

43.7 wt.%; (2) secondary Fe–Mn oxyhydroxides occur as

precipitates with high in situ As percentage up to 59.8

wt.% and (3) fine-grained phase of Al–Si with in situ

As2O5 ranging from 430 to 5,020 mg/kg (Grosbois et al.

2007). Recent studies have suggested that biotite, musco-

vite and/or other phylosilicates are a possible primary

source of As in the fluvial environment (Chakraborty

et al. 2007; Seddique et al. 2008). Arsenic content in Fe

and Mn oxides is reported higher than in organic matter

(Anawar et al. 2003). Horneman et al. (2004) suggests

that the release of As is linked to the transformation of

predominantly Fe–oxyhydroxide coatings on sand gains

to Fe solid phases without necessarily resulting in the

release of Fe in the groundwater of Bangladesh. Iron

oxide content, therefore, is believed to be an important

indicator of As in natural waters. At the same time,

Fe fillings can be used for the removal of As from

groundwater highly contaminated with both organic and

inorganic As species (Cheng et al. 2005).

Natural organic matter is also a significant component of

river systems for modelling of the As behaviour in the

fluvial environment. The role of organic components in

geochemical processes in the aquatic system was empha-

sized by geochemists and other professionals in the 15th

International Symposia of Environmental Biogeochemistry

Biogeochemical Processes and cycling of elements in the

Environment held at Wroclaw, Poland, in 2001. In partic-

ular, sedimentary organic carbon acts as an active

scavenger of As in rivers. Iron oxides and organic matter

characteristics are, therefore, of special interest in fluvial

environment for deep understanding of As source and its

mobilization.

Iron oxides and sedimentary organic carbon contained in

the very fine sediments and suspended sediment fractions

in the Gomati River sediments are considered here in detail

as they may be geochemically important for transport,

capture and fate of As in the river water. Average Fe2O3

concentration in fine sand, very fine sand and silt-clay

fractions of the river sediments were 0.78, 1.98 and 2.35%,

respectively (Singh et al. 2005). Furthermore, Fe2O3 con-

centration increases up to 10.94% in heavy mineral

fractions. It exits in both in mineral phase (heavy minerals)

and as well as in the dispersed phase (e.g. as a coating) in

Fig. 2 a The Gomati River

Water: piper diagram

illustrating the main hydro-

chemical features of represented

as percentage of major cations

and anions (in meq/L). It is

classified as Ca??–Mg??-

dominant HCO3-type water

(left). Downstream depletion in

composition of d18O isotope of

the river water in the winter

season showing strong influence

of evaporation (right), b the

Gomati River sediments:

longitudinal variations of slit

and clay fraction (wt%) and

Fe2O3 concentration (%) in very

fine sand fraction (left) and in

sedimentary organic and

inorganic carbon (wt%) in

suspended sediments (right)

Environ Earth Sci (2010) 59:1703–1715 1707

123

the river sediments. The Gomati River sediments showed a

distinct longitudinal increase from 1 to 4% in Fe2O3 con-

tent in very fine sand fraction, mainly attributed by silt-clay

content in its channel sediments. Figure 2b also displays

the downstream increasing trend with distinct fluctuations

in Fe2O3 concentration and silt-clay content in the Gomati

River sediments.

Under the present environmental situation, a consider-

able amount of organic-matter rich, untreated liquid as well

as solid urban waste directly enters into the Gomati River.

As per estimate of the Central Pollution Control Board,

Lucknow, urban centre generates around 400 million litres

of sewage water per day, which directly drains into the

river by 22 open drains (CPCB 2002). During the summer

season, the untreated sewage discharge of Lucknow urban

centre (4.63 m3/s) is nearly same as the river’s average

flow (Table 1). This anthropogenic activity is common in

all urban centres located along the river banks and makes

the river bed rich in organic carbon. The amount and dis-

tribution of sedimentary organic matter may be used as a

parameter in order to understand elemental mobilization in

a river system. The Corg in the Gomati River ranges from

0.19 to 0.90% in the deposited suspended sediments (Singh

and Matschullat 2009). Figure 2b displays the downstream-

increasing trend in Corg and total sedimentary carbon in

the Gomati River. It is notable that downstream increase of

sedimentary carbon can be linked with the increase of silt-

clay content in the river sediments.

Methodology

Sampling

The Gomati River along with its 13 tributaries was

selected for the present study. Thirty-two unfiltered water

samples were collected from the middle of flowing

channel in a period of 8 days in the winter season (Jan-

uary–February 2006). Nineteen sampling sites (GO1–

GO19) belong to the Gomati River and 13 sampling sites

(GT1–GT13) to the Gomati River tributaries. Four sam-

ples were collected at GO3, GO4, GO8 and GO19

locations during the summer season (June 2005) for pre-

liminary analysis. Sampling sites along with their details

such as latitude, longitude and altitude are presented in

Table 2 and are also shown in Fig. 3. These water sam-

ples were collected in polyethylene bottles with watertight

caps and were acidified in the field with HNO3 (5 ml/L of

water), which will not affect the dissolved concentrations

of metals due to insignificant concentrations of particulate

matter in water samples collected during the winter sea-

son. In order to avoid any contamination, the samples

were transferred to polyethylene bags to avoid direct

contact and were stored at 4�C for preservation till further

chemical analysis.

Analytical procedure

All samples were filtered by using 0.45 lm cellulose filters.

Dissolved As and Fe concentrations were determined by

Induced Coupled Plasma Mass Spectrophotometer at the

Institute Instrumentation Centre, Indian Institute of Tech-

nology, Roorkee. Each sample was analysed in duplicate

and mean values were taken as the result. All chemicals of

analytical grade and MilliQ water were used. For quality

assurance, replicates and analytical blanks were also pre-

pared and analysed to check the reliability of the data.

Analytical precision for all samples were within ±5% in

As determination.

Results

Regional distribution

Results of As and Fe analysis of all collected water samples

from the Gomati River Basin are presented in Table 2.

Arsenic and Fe concentrations were found in the range of

1.29–7.16 and 47.84–120.23 lg/L, respectively. Mean As

concentrations for the Gomati River and its tributaries are

5.10 and 3.46 lg/L, respectively. Mean Fe concentrations

for the Gomati River and its tributaries are 100.57 and

77.2 lg/L, respectively. Figure 4a displays Box and

Whisker plots of the 10th, 25th, 50th, 75th, 90th percentiles

showing the distribution of dissolved As and Fe concen-

trations in waters of the Gomati River and its tributaries.

Dissolved As and Fe concentrations of the Gomati River

were recorded higher values than its tributaries.

In the Gomati River, dissolved As concentrations range

from 1.49 to 7.16 lg/L. At the source, the river has As

concentrations about 2.0 lg/L and increases downstream

up to 7.16 lg/L at Jaunpur (G016). Figure 4b displays the

longitudinal variations showing a distinct increasing trend

of As in the river water. In the middle segment of the river,

concentrations of As in the Gomati River water range in

between 3.0 and 5.0 lg/L and are same as its tributaries,

such as the Chhiya Nala, the Sarayan River, the Loni Nala

and the Kalyani Nadi, etc. It indicates that the qualitative

biogeochemical characteristics are playing a significant

role in the mobilization of As in the water of these tribu-

taries. In the lower segment, the concentrations of As in the

Gomati River water is lower than its tributaries such as the

Pili Nadi and the Sai River. Significant positive correlation

(n = 7, r2 = 0.57) was observed between the drainage

density of microbasins (the Kathna River, the Sarayan

River, the Behta Nala, the Reth Nadi, the Kalyani Nadi, the

1708 Environ Earth Sci (2010) 59:1703–1715

123

Table 2 Dissolved As and Fe concentrations in water collected during winter season from the Gomati River System of the Ganga Plain

S. no. Sample code Collection date

(dd/mm/yy)

River Location Elevation

(m a. s. l.)

Latitude Longitude As (lg/L) Fe (lg/L)

1. GO1 06/02/06 Gomati River Madho Tanda 185 28�380 80�080 2.24 84.70

2. GO2 06/02/06 Gomati River Khutar 160 28�090 80�120 1.49 87.54

3. GO3 06/02/06 Gomati River Maigalganj 148 27�440 80�160 3.35 90.03

4. GO3a 14/06/05 Gomati River Maigalganj 6.44 511.52

5. GO4 06/02/06 Gomati River Naimesarayan 128 27�210 80�240 3.53 98.33

6. GO4a 14/06/05 Gomati River Naimesarayan 4.97 817.49

7. GO5 06/02/06 Gomati River Itaunja 111 27�030 80�510 4.44 96.38

8. GO6 04/02/06 Gomati River Lucknow 106 26�540 80�530 4.25 96.12

9. GO7 04/02/06 Gomati River Gangaganj 101 26�430 81�130 3.62 92.13

10. GO8 31/01/06 Gomati River Haidergarh 100 26�390 81�240 4.74 109.43

11. GO8a 23/06/05 Gomati River Haidergarh 7.97 421.92

12. GO9 31/01/06 Gomati River Bazar Sukul 95 26�370 81�370 5.53 108.49

13. GO10 31/01/06 Gomati River Thauri 90 26�300 81�450 6.10 104.87

14. GO11 31/01/06 Gomati River Isauli 87 26�240 81�520 6.16 101.94

15. GO12 31/01/06 Gomati River Sultanpur 83 26�160 82�050 6.45 102.55

16. GO13 31/01/06 Gomati River Chanda 81 26�070 82�220 6.47 108.81

17. GO14 01/02/06 Gomati River Dhakwa 80 26�010 82�240 6.10 108.81

18. GO15 01/02/06 Gomati River Badlapur 79 25�580 82�330 6.15 110.62

19. GO16 01/02/06 Gomati River Jaunpur 77 25�450 82�440 7.16 102.86

20. GO17 01/02/06 Gomati River Kirakat 71 25�380 82�550 6.02 101.36

21. GO18 01/02/06 Gomati River Chandwak 70 25�350 83�000 6.43 102.77

22. GO19 01/02/06 Gomati River Kaithi 69 25�300 83�080 6.28 103.27

23. GO19a 24/06/05 Gomati River Kaithi 9.62 431.92

24. GT1 06/02/06 Jokhan River Puranpur 172 28�220 80�120 1.29 106.25

25. GT2 06/02/06 Bhainsi Nadi Pawayan 157 28�070 80�090 1.44 70.50

26. GT3 06/02/06 Chhiya Nala Pawayan 152 27�460 80�140 2.36 109.12

27. GT4 06/02/06 Kathna River Pisawan 141 27�390 80�280 3.57 106.85

28. GT5 06/02/06 Sarayan River Sindhauli 124 27�160 80�180 4.48 120.24

29. GT6 04/02/06 Behta Nala Kakori 120 26�540 80�470 3.39 57.35

30. GT7 31/01/06 Reth Nadi Barabanki 117 26�550 81�100 5.15 49.43

31. GT8 04/02/06 Loni Nala Gangaganj 114 26�440 81�110 3.82 49.66

32. GT9 31/01/06 Rari Nadi Haidergarh 109 26�430 81�270 5.29 85.80

33. GT10 31/01/06 Kalyani Nadi Ramsanehighat 107 26�470 81�330 2.64 51.18

34. GT11 31/01/06 Kundu Nala Musafirkhana 104 26�240 81�160 3.94 55.28

35. GT12 01/02/06 Pili Nadi Badlapur 82 25�550 82�290 3.13 47.81

36. GT13 01/02/06 Sai River Jalalpur 73 25�380 82�450 4.39 93.93

a Samples collected during the summer season

Fig. 3 Location map of water

sampling sites along the Gomati

River and its tributaries

Environ Earth Sci (2010) 59:1703–1715 1709

123

Kundu Nala, and Pili Nadi) and As concentration in the

tributaries water (Thakur 2008).

Inter elemental relationships

The present data show that a significant correlation

(n = 19; r2 = 0.68) exits between dissolved As and Fe

concentrations from the Gomati River water as shown in

Fig. 5a. This suggests that the release of As is linked to

biogeochemical processes that necessarily results in the

release of Fe to the river water. The correlation between

dissolved As and Fe and the additional significant corre-

lation of As with inorganic carbon supports the idea of

enrichment of As in water of the Gomati River is due to

the dissolution of more probable Fe–oxides/hydroxides.

The same correlation plot of the Gomati River including

its tributaries is poor (n = 32; r2 = 0.16) as shown in

Fig. 5b. Therefore, it is also necessary to understand why

concentrations of dissolved As in these tributaries are

uncorrelated with the concentrations of dissolved Fe. The

reason for this could be the differential use of more

probable phosphate fertilizers, pesticides and herbicides in

Fig. 4 a Box and whisker plotsof the 10th, 25th, 50th, 75th,

90th percentiles of the

distribution of dissolved As and

Fe concentrations in waters of

the Gomati River (n = 19) and

its tributaries (n = 13) in the

winter season. b Longitudinal

variations in dissolved As

concentration in water of the

Gomati River (line) and

contributions from its tributaries

(bar). Note the significant

downstream increase in As

concentrations that control the

dynamics of As mobilization in

the Gomati River

1710 Environ Earth Sci (2010) 59:1703–1715

123

intensively farmed microbasins of the Gomati River

tributaries. Based on the available data of sedimentary

organic and inorganic content at nine sites on the Gomati

River, Fig. 5c, d displays significant correlation of

dissolved As with sedimentary inorganic carbon and

insignificant correlations with organic carbon in deposited

suspended sediments of the Gomati River, respectively.

Seasonal control

In the Ganga Plain, high temperature (40–45�C) along

with high evaporation rates in the alluvial plain are the

important characteristics of the Gomati River Basin during

the summer season. This seasonal condition triggers the

development of strong reducing conditions at near neutral

pH values leading to the release of more As in the river

water than in the winter season (Smedley and Kinniburgh

2002). Figure 6a displays a bar diagram showing charac-

teristic increase of As concentrations in the Gomati River

water at Maigalganj, Naimesarayan, Haidergarh and Kaithi

locations. These locations show *30 to 55% increase in As

concentration in the river water during the summer season

as a result of increased microbial activity. These seasonal

high As concentrations also have significant negative

correlation (n = 4; r2 = 0.73) with Fe concentrations

as shown in Fig. 6b. In the same way, maximum As

concentrations were reported during the summer months in

the Waikato River System of New Zealand (McLaren and

Kim 1995).

Dynamics of As mobilization in fluvial

environment of the Ganga Plain

Arsenic mobilization in fluvial environment of the Ganga

Plain is a result of natural processes as well as anthropo-

genic activities. It is likely to derive from the dissolution of

mineral phase and is largely controlled by pH and redox

conditions of water bodies. Arsenic behaviour involves

complex linkages among bacterially driven chemical and

geological processes, occurring at local, regional and glo-

bal scales (Warren and Haack 2001). In the Gomati River,

hydrogeological and biological characteristics along with

anthropogenic activities govern As mobility in its water.

Figure 7 presents a schematic model for As mobilization in

the fluvial environment of the Ganga Plain that is charac-

terized by the biological, hydrological, geochemical

characteristics and processes operating at meso ([100 km),

field ([100 m) and micro ([100 lm) scales.

In the Ganga Plain, As is released from unconsolidated

sediments of the river bed or alluvium and can be governed

by biogeochemical processes operating at sediment-water

interface. Presence of organic matter along with sediments

Fig. 5 Bivariate plot showing the relationship between dissolved As

and Fe concentrations in water from (a) the Gomati River (n = 19)

and from (b) the Gomati River system (n = 32). The open circles are

for the Gomati River and closed circles for its tributaries. Note that

under reducing condition, As concentration increases with Fe

concentration in water of the Gomati River. At the same time, water

from some of the tributaries shows high As concentrations with low

Fe concentrations as compared to the Gomati River. Relationship

between As concentrations and c sedimentary inorganic carbon and

d sedimentary organic carbon present in deposited suspended sediments

of the Gomati River. Linear regression (grey line) and coefficient of

determination (r2) are given for each data set

Environ Earth Sci (2010) 59:1703–1715 1711

123

in the river plays an important role in As mobilization as it

facilitates microbial activity that plays an important role in

the generation of reducing conditions. The importance of

redox cycling of elements at the sediment-water interface

was significantly pointed out already by Gorham and

Swaine (1965). Reduction of Fe is derived by microbial

metabolism of organic matter present in the Gomati River

sediments. Burial of anthropogenically originated organic

matter and slow diffusion of O2 through these organic

sediments lead to reducing conditions in the sediment–

water interface at the river bed. Biodegradation of organic

matter consumes O2, produces CO2 that dissolves water

and lowers the pH. Arsenic along with Fe is dissolved in

river water as ions at low pH. Minerals of the Gomati River

Sediments, such as biotite contain Fe oxides as high as

*18 to 30% (Deer et al. 1966) and are chemically

weathered to release Fe as follows:

2KMgFe2AlSi3O10ðOHÞ2 þ 14CO2 þ 15H2O

! Al2Si2O5ðOHÞ4 þ 4Fe2þ þ 2Kþ þ 2Mg2þ

þ14HCO�3 þ 4H4SiO4:

Microbial reduction of such Fe containing minerals

occurs on a timescale of hours to days (Jones et al. 2000).

McArthur et al. (2004) has proposed that As mobilization is

controlled by the quantity and biodegradability of organic

matter. Increasing inputs of anthropogenic originated,

organic content-rich waste favour the release of As in river

water of the Ganga Plain. Widerlund and Ingri (1995)

reported As concentrations in the range of 1.3–166 lg/L in

the pore water of unconsolidated sediments of the Kalix

River estuary in Sweden, higher than in its overlying river

waters. Recent studies have shown that Fe-reducing bacteria

(Geobacter metallireduces and Shewanella alga) can use

organic matter and reduce amorphous as well as crystalline

Fe oxides present in the river sediments (Dong et al. 2000).

This biochemical reaction produces siderite in bicarbonate-

buffered solutions as expressed by the following reaction

where CH3COO- represents organic matter.

4Fe2O3þCH3COO� þ 7H2O! Iron reducing bacteria

! 8Fe2þ þ 2HCO�3 þ 15OH�

Fe2þ þHCO�3 þOH� ! FeCO3ðsideriteÞ þH2O:

The pH of the Gomati River Water ranges between 7.5

and 8.5 and favours the growth of siderite formation by Fe-

reducing bacteria. Carrillo and Drever (1998) also sug-

gested that oxyhydroxide adsorbs maximum As at pH

between 7 and 9.

High pore–water As concentrations reflect strong redox

gradients at the sediment–water interface in the river sed-

iments. Oxygen content at the sediment-water interface is

influenced by the metabolism of bacteria, algae and fungi

that migrate to and live within the interface. Oxygen is the

primary factor influencing the release of As from the sed-

iments. If the sediments receive light, even at very low

intensities, photosynthesis of algal communities growing

on the sediments can quickly produce highly supersatu-

rated concentrations of O2. This O2 can diffuse into

interstitial water of supporting sediment concentrations.

This hydrogeological characteristic of river water plays a

significant role in As mobilization at field scale. From

winter to summer season, average water temperature in the

Gomati River increases from 20 to 30�C that causes the

increase of As concentrations in the river water due to

development of more reducing conditions. Upward diffu-

sion and reworking of sediments at the river bed moves the

dissolved As from sediment pore water to water column

above the river bed.

The Ganga Plain is drained by several entranced alluvial

rivers/streams that have little and insignificant water dis-

charge flows during the winter and summer seasons after

monsoon season. At macro scale, seasonal changes,

Fig. 6 a Bar diagram showing As concentrations in the winter and

summer seasons at Maigalganj (GO3), Naimesarayan (GO4), Hai-

dergarh (GO8) and Kaithi (GO19) stations along the Gomati River.

Note significant increase in As concentration in the summer season at

all the stations. b Bivariate plot showing the negative significant

relationship between dissolved As and Fe concentrations in the

Gomati River water in the summer season

1712 Environ Earth Sci (2010) 59:1703–1715

123

drainage density, population pressure and monsoon precipi-

tation may dictate tributary flows and hence concentration of

dissolved As in the river water. Arsenic can be released in

solution when suspended particulate matter came from

oxidized ground water to moderately reduced conditions

(Roussel et al. 2000). All these groundwater-fed rivers/

streams have the concentration of suspended particulate

matter maximum due to significant input of weathering

products from overflows of the Ganga Plain surface during

the monsoon season and extremely low in winter and sum-

mer seasons. Arsenic contribution from natural suspended

particulate matter, therefore, will be insignificant in these

rivers. Microbasins with high drainage density in the plain

are prone to elevated As concentrations in their river/stream

water.

It is, therefore, important to note that groundwater along

with untreated urban effluents are the main contributor to

total discharge of these alluvial rivers. Under the present

situation, groundwater input decreases and inputs from

untreated urban/organic waste increases, as evident from

downstream increase in sedimentary carbon, were respon-

sible for generating reducing conditions in the river.

Mobilization of As from minerals phase to aqueous phase

takes place under these anthropogenically created reducing

condition of the river (Stuben et al. 2003). During the

summer season, water level is lowered due to the over-

exploitation of groundwater resources in the Ganga Plain.

It may have mobilized fertilisers used in agriculture along

with natural organic materials into shallow aquifers of the

plain that enhanced As mobilization activity at the micro

Fig. 7 Block diagram showing hydrological, geological and biological characteristics and processes involved in As mobilization in fluvial

environment of the Ganga Plain, northern India

Environ Earth Sci (2010) 59:1703–1715 1713

123

scale. The depleting trend of oxygen isotope (d18O) coin-

cides with the increasing trend of As concentration in the

Gomati River water as shown in Figs. 2a and 4b. It clearly

indicates the impact of evaporation that may cause the

upward and downstream mobilization of As in the Gomati

River.

Arsenic concentrations in river waters vary greatly

according to the natural processes as well as anthropogenic

causes. Table 3 represents the As concentration in the

waters of selected rivers around the world for the com-

parative study. In the future, exponentially increasing

population density will certainly generate down slope

increasing As concentrations in river water on a regional

scale. The key factors involved in the increasing trend of

dissolved As on a regional scale are the downstream

increase of sedimentary organic and inorganic carbon

along with the impact of population pressure that reduces

the availability of groundwater resources to maintain base

level flow in these alluvial rivers of the Ganga Plain.

Conclusions

The present study reveals that sources of As in the fluvial

environment of the Ganga Plain must lie within in the

alluvial plain sediments and river sediments. Dissolved As

concentration in river waters of the Ganga Plain shows a

downstream-increasing trend that might be anticipated by

downstream increase in organic sedimentary carbon, silt-

clay fraction and Fe2O3 concentration in the river sedi-

ments. The present data along with other recent studies

suggest the upslope migration of As crisis from the Bengal

Delta region through the lower and middle Ganga Plain to

the upper Ganga Plain. The mobilization of sediment-bond

As may have a significant influence on the environmental

quality of water resources that are heavily used by the

domestic and agricultural sectors of the region. The present

work is an attempt to explain As mobilization in the fluvial

environment of the Ganga Plain through the generalized

model and believes that it will provide a possible linkage of

anthropogenic activities with human-environment interac-

tion in sub-tropical climatic zone.

Acknowledgments This study is an outcome of constant

encouragement by Prof. Indra Bir Singh, University of Lucknow

and discussions with him at various stages are gratefully

acknowledged. Special thanks are also to Drs. Alok Thakur and

Anju Saxena for their assistance during sample collection. We

also thank the staff of the Institute Instrumentation Centre,

Indian Institute of technology, Roorkee, for analytical assistance.

Mr. Pramod Kumar Joshi helped in preparation of diagrams while

Mr. Jai Narayan safely drove us in the field. Initial draft manu-

script was benefited by comments and suggestions of Prof. Zsolt

Berner, Institute of Mineralogy and Geochemistry, Universitat

Karlsruhe (TH) and Dr. Ratan Kar, Birbal Sahni Institute of Pal-

aeobotany, Lucknow. This work was partly funded by Department

of Science and Technology (SR/FTP/ES-47/2000) to MS and

Council of Scientific and Industrial Research [9/107(303)/2005] to

AKS and University Grants Commission [16-767(SC)/2007] to

Swati. We thank to anonymous reviewer for providing comments

that substantially improved the paper and Dr. Jan Schwarzbauer for

his patience through the reviewing process.

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