chemical and isotopic characteristics of the euphrates river water, syria: factors controlling its...
TRANSCRIPT
ORIGINAL ARTICLE
Chemical and isotopic characteristics of the Euphrates Riverwater, Syria: factors controlling its geochemistry
Zuhair Kattan
Received: 12 January 2014 / Accepted: 2 October 2014
� Springer-Verlag Berlin Heidelberg 2014
Abstract Hydrochemical parameters and stable isotope
(18O and 2H) ratios were monitored at 10 stations along the
Euphrates River (ER) within the Syrian reach during
2004–2006. The average concentrations of major ions in
the ER were comparable to those of semi-arid and arid
zone rivers. Temporal variations of major ion concentra-
tions were small at the first two upper sites and more
pronounced at the lower downstream stations. Temporal
fluctuations of stable isotope ratios at the first two upper
sites were identical and have a distinct opposite evolution
trend to those of the remaining downstream stations, with
depleted values during summer–autumn and enriched val-
ues during February–May. Salinity and stable isotope val-
ues of the ER systemically increase with the distance
downstream, with sharp enrichments in stable isotope
values at Al-Assad Lake, primarily because of evaporation
from the lake. The chemical and isotopic properties of the
ER water suggest negligible role of precipitation and local
runoff compared with evaporation. Cluster analysis in
Q-mode resulted in classifying the major ions into: the
most predominant species (SO42-, HCO3
-, Cl-, Ca2? and
Na?), liberated as a result of rock–water interactions or
dissolution of soluble evaporate salts, and the less abundant
ions (Mg2?, K?, NO3- and SiO2), partially imported from
different sources (rainfall, silicate weathering and anthro-
pogenic pollution). Factor analysis suggests that the geo-
chemistry of the ER water is mainly controlled by four
factors: rock weathering or salt dissolution, dissolved CO2
partial pressure, water temperature (T) and evaporation.
These factors explain more than 80 % of the total variance
in the data matrix.
Keywords Hydrogeochemistry � Stable isotopes � Cluster
analysis � Factor analysis � Euphrates River � Syria
Introduction
Rivers are principally responsible for transport of dissolved
elements and suspended sediments to the oceans (Garrels
and Mackenzie 1971). Monitoring of the chemical com-
position of major large river waters in the world was started
in the last century by Clarke (1924). Since then a great
number of hydrological and geochemical studies were
continued and devoted to large rivers in the different
continents (Livingstone 1963; Gibbs 1970; Reeder et al.
1972; Meybeck 1979; Stallard and Edmond 1983; Kattan
1989; Probst et al. 1994; Gaillardet et al. 1999; Singh and
Hasnain 2002). Accordingly, it is well documented that
temporal and spatial variations of major ions in river waters
are generally function of several physical and chemical
processes that are mainly influenced by the geological
setting, climate and anthropogenic activities (Gibbs 1970;
Meybeck 1986, 1987; Hem 1992).
Stable isotopes (d18O and d2H) are equally ideal natural
tracers that have contributed remarkably for better under-
standing of the water cycle and related diverse water
modification processes (Gat 1996; Clark and Fritz 1997;
Criss 1999; Kendall and Coplen 2001; Winston and Criss
2003; IAEA 2005). Monitoring of such isotopes in riverine
systems has proven to be a useful tool for characterizing
the effect of snowmelt events, studying the mixing between
different water bodies, tracing the pathways of water in
small basins, estimating the mean residence time and
Z. Kattan (&)
Department of Geology, Atomic Energy Commission (AECS),
P. O. Box 6091, Damascus, Syrian Arab Republic
e-mail: [email protected]
123
Environ Earth Sci
DOI 10.1007/s12665-014-3762-z
storage properties of surface water, determining the salinity
sources, quantitative estimates of evaporation and irriga-
tion return flows and delineating the roles of dams, lakes
and input from tributaries on river flow (Payne et al. 1979;
Herrmann et al. 1990; Simpson and Herczeg 1991; Aly
et al. 1993; Vitvar and Balderer 1997; Frederickson and
Criss 1999; Gibson and Edwards 2002; Uhlenbrook et al.
2002).
Multivariate statistical analyses such as cluster and
factor analyses are also proved to be effective explanatory
tools in a number of hydrological and geochemical studies,
precisely for extracting comprehensive and meaningful
patterns of reliable groups and relationships among vari-
ables or water samples of certain characteristics (Reeder
et al. 1972; Davis 1986; Swanson et al. 2001).
Although the Euphrates River (ER) is one of the largest
rivers in the world this river is still among the less studied
systems in terms of dissolved, particulate and isotopic
compositions. However, few investigations were found for
this river in Turkey, mostly for the assessment of water
quality (Odemis and Evrendilek 2007; Iscen et al. 2009)
and sediment loads (Jansen and Painter 1974; Ozturk
1996). In Iraq, few studies were devoted to the evaluation
of upstream water chemistry (Zaidan et al. 2009; Al-Heety
et al. 2011) and sediment yields flowing within Shatt Al-
Arab into the Gulf (Milliman and Syvitski 1992). Studies
related to this river system in Syria are also few, and
mostly oriented towards the assessment of salinization
problems of soil and groundwater in the Euphrates down-
stream valley (GERSAR-SCET 1977; Kattan and Najjar
2005), estimation of irrigation return flows and determi-
nation of evaporation from Al-Assad Lake and the entire
ER reach in Syria (Kattan 2008).
Based on the importance of this large river as a major
resource of renewable surface water in Syria, and its sig-
nificant role in sustaining the national economy, a detailed
hydrochemical and isotopic study was conducted within an
international project that aims to better understand the
water balance and hydrological processes in some large
world rivers (IAEA 2012). The objectives of this paper are:
(1) to demonstrate the overall hydrochemical and isotopic
characteristics of the ER water in Syria, after a monitoring
period extended for 3 years (2004–2006); (2) to present the
temporal and spatial variations patterns of major ions and
stable isotope compositions; and (3) to delineate the prin-
cipal factors controlling inorganic water geochemistry of
the ER in Syrian territory.
General characteristics of the study area
The ER (entire length (L) &3,000 km and total
area &444,000 km2), constitutes with its twin, the Tigris
River, the main important rivers in western Asia (Fig. 1).
In the Syrian reach, the ER basin covers an area of about
75,480 km2 and has a length approximating 675 km. The
topography of the river basin is generally rough, with the
presence of a number of small hills near its banks, mainly
upstream Al-Assad Lake. The elevation of the ER course
varies between 350 m above sea level (m.a.s.l) at Jarablous
and 180 m at Albu-Kamal, with a stream slope
averages &0.25 m km-1.
Climate and precipitation
The climate of the ER basin in Syria ranges from semi-arid
to arid, with increasing aridity downstream. The winter
seasons are usually cool (5–10 �C) and rainy, while the
summers are warm (30–45 �C) and almost entirely devoid
of rainfall. The mean annual air temperature increases from
north to south, and varies between 18 �C in Jarablous and
20 �C in Albu-Kamal, where the aridity becomes more
accentuated. The mean annual value of the relative air
humidity varies between 56 % (Jarablous) and 47 % (Deir-
Ezzor), and declines to less than 44 % (Albu-Kamal), the
lowest registered value in the country. The highest values
of mean monthly relative humidity (60–70 %) are usually
observed during the cool period (Dec. to Jan.), while the
lowest (25–30 %) occur during the warmest months (Jul.
and Aug.). The potential evapotranspiration value highly
exceeds rainfall and generally ranges from 1,300 to
2,600 mm, with a mean annual value close to 2,100 mm.
Fig. 1 Location map of the Euphrates River (ER) basin showing
location of major dams
Environ Earth Sci
123
The mean annual precipitation decreases during the rainy
season (Oct. to May) from north to south, ranging between
350 mm (Jarablous) and less than 130 mm (Albu-Kamal),
with an intermediate value of 160 mm at Deir-Ezzor
(Fig. 2).
Geology and hydrogeology
From a geological point of view, the ER in Syria generally
flows within in a depression structure, tectonically due to
the so-called ‘‘Euphratian Fault System’’, and drains ter-
rains belong to the Paleogene, Neogene and Quaternary
(Ponikarov 1967). The Paleogene deposits (thickness
(H) &240 m), generally outcropping upstream, are mostly
composed of detritus argillaceous limestone sediments at
the bottom and massive Nummulitic limestone with inter-
beds of marl at the top. The Neogene deposits
(H & 220 m), vastly widespread between Al-Assad Lake
and the Iraqi border, are represented by the Middle Mio-
cene (gypsum, silty clays, sandstones and shelly beds),
Upper Miocene (sandstone, siltstones and clays), Lower
Pliocene (sands, siltstones marls, gypsum and pebbles), and
Upper Pliocene (sands, pebbles and sandstones). The
Quaternary deposits (H & 20 m) are represented by peb-
bles, gravels, loams and sandy loams deposits. Small sheets
of effusive volcanic (basaltic) rocks of Lower Quaternary
can also be seen near the river course in the vicinity of
Deir-Ezzor area. The river alluvial, primarily composed of
gravels and pebbles of bigger size at the bottom and finer
alluvial sediments (loams and sandy loams) at the top,
forms the most important aquifer in this basin (GERSAR-
SCET 1977).
Hydrology
Although the catchment area of the ER is shared by four
countries (Turkey 28 %, Syria 17 %, Iraq 40 % and Saudi
Arabia 15 %) most of its flow (88–98 %) is produced from
the highlands of southeastern Turkey, where rainfall
amount usually exceeds 1,000 mm year-1, and average
long-term annual river discharge (Q) is more than 1,000 m3
s-1 (Iscen et al. 2009).
The hydrographic network of the ER in Syria is mainly
represented by three tributaries (Fig. 2): the Sajour
(L & 48 km and Q & 3 m3 s-1), the Balikh (L & 105 km
and Q & 6 m3 s-1) and the Khabour (L & 400 km and
Q & 50 m3 s-1). As a result of over pumping and a resul-
tant decline in the groundwater table upstream, the Khabour
River has become completely dry (Kattan 2001), especially
during the drought period extended between 2000 and 2006.
Fig. 2 Map of Syria showing
the distribution of annual
rainfall and location of the
different sampling sites along
the ER course (adopted from
ICARDA 2006)
Environ Earth Sci
123
Historically, the hydrological regime of the ER was
characterized by sudden and violent flooding in spring
(April–May), mainly because of snows melting in the high-
lands. However, irregular flow regime related to irregular
rainfall events can also be observed (UNEP 2001). The ER
discharge at the Syrian–Turkish border ranges from 535 to
1,378 m3 s-1, with a mean annual flow ranging between
&974 m3 s-1 and &1,015 m3 s-1 (Iscen et al. 2009).
After construction of &20 dams across the ER in Tur-
key (GAP project), with a total storage value of
&90.9 billion m3, the ER regime has significantly modi-
fied, and thus the maximum river discharge has shifted
from spring to January and February (Trondalen 2009). In
Syria, three dams (Tishreen, Euphrates and Al-Baath) were
built across the river course, with the aim to generate
electricity and prevent from dangerous floods. The
Euphrates dam (ED), with its large lake (L & 75 km),
serves to regulate the river flow downstream. During the
last few decades, the ER flow has been controlled by
Turkey through a special protocol that fixes the minimum
annual flow for both Syria and Iraq at about 500 m3 s-1
(UNEP 2001). The average annual flow of the ER during
the study period was &686 and &568 m3 s-1 at Jarablous
and Albu-Kamal, respectively.
Sampling and analytical methods
Water samples were collected on a monthly basis from 10
sites distributed along the ER course in Syria during the
period from January 2004 to December 2006. Jarablous
station, situated close to the Syrian–Turkish border, is the
upstream sampling site, whereas Albu-Kamal, located
close to the Syrian–Iraqi border, is the furthest downstream
sampling station (Fig. 2). Unfortunately, few water sam-
ples were missed for each site during the sampling period.
Water samples were generally collected in two rinsed
plastic bottles, and immediately after returning back from
the field, all collected samples were preserved in a refrig-
erated room (T below 5 �C) until the time of analysis. A
500-mL bottle was filled for the determination of major
ions (Ca2?, Mg2?, Na?, K?, Cl-, SO42- and NO3
-) and
the related chemical analyses were carried out in the
Geology Department of the Syrian Atomic Energy Com-
mission (AECS), after filtration of water samples in the
Lab., through a 0.45-lm Millipore membrane, by HPLC
method, using a dual-column instrument (Dionex DX-100),
with the following analytical errors: Ca2? (±0.4 mg L-1),
Mg2? (±0.7 mg L-1), Na? (±0.1 mg L-1), K? (±0.1
mg L-1), Cl- (±0.1 mg L-1), SO42- (± 0.3 mg L-1) and
NO3- (±0.1 mg L-1).
A smaller number of separate river water samples was
also collected in order to determine the concentrations of
dissolved silica (SiO2), and the related analysis was also
carried out in the Geology Department of AECS by using a
portable (Lab.) spectrophotometer (Hach DR 2800) and
specific delivered kits for improved measurement accuracy
(±3 lg L-1).
A second small glass bottle (50 mL) was filled for the
determination of stable isotopes (d18O and d2H), and sub-
sequently analyzed at the Geology Department of AECS,
by equilibrating a 5-mL subsample with small amounts of
separate reference gases (CO2 and H2), and analyzing the
resulted gases using a Finnigan Mat DeltaPlus mass spec-
trometer. Measurement accuracy for d18O and d2H are
±0.1 and ±1.0 % versus VSMOW, respectively.
The water temperature (T), pH, electrical conductivity
(EC), dissolved oxygen (DO), together with the total
alkalinity (i.e., HCO3-) values of all water samples were
measured in the field during sampling. T measurements
were carried out using a WTW conductivity/temperature
meter (cond315i) with a precision of ±0.2 �C. The same
conductivity meter was also used for the measurement of
EC values corrected at 25 �C, with a precision of
±5 lS cm-1. Measurements of pH was determined using a
WTW pH meter (pH315i), after calibration with two
standard buffer solutions (pH = 4 and 7), with a precision
of ±0.01. Measurements of DO were carried out using a
WTW dissolved oxygen meter (oxi3310) with a precision
of ±0.5 % of value. Total alkalinity values were also
measured in the field on filtered 100 mL of water samples
through a 0.45 lm Millipore membrane, by a volumetric
titration method (Clark and Fritz 1997), using a WTW
pH315i-meter and 1.6 N sulfuric acid, with a precision of
±1.5 mg L-1.
Quality assurance procedures, according to the ISO/IEC
17025, are strictly adhered by all the AECS laboratories.
Both the chemical and isotopic analysis results are peri-
odically verified through the participation in the different
analysis comparison programs, managed by either the
IAEA or other local and international organizations.
Results and discussion
Water chemistry
Table 1 summarizes the average and standard deviation
values of measured and calculated hydrochemical and
isotopic parameters, together with the average discharge
values of the ER at five stations during the study period
2004–2006. The data show that the water quality of the ER
is generally fresh (240 \ TDS \ 540 mg L-1), with small
nitrate concentrations (NO3- \ 6 mg L-1). The compari-
son between the ER water with the average chemical
compositions of the world, semi-arid and arid zone rivers
reveals that the ER water is higher than that of average
Environ Earth Sci
123
Ta
ble
1A
ver
age
dis
char
ge
(Q)
val
ues
of
the
ER
atfi
ve
stat
ion
san
dav
erag
ep
hy
sico
-ch
emic
alan
dst
able
iso
top
e(d
18O
and
d2H
)co
mp
osi
tio
ns
of
wat
ersa
mp
les
coll
ecte
dfr
om
the
ER
at1
0
stat
ion
sal
on
git
sco
urs
ein
Sy
ria
du
rin
gth
ep
erio
d2
00
4–
20
06
Loca
tion
Jara
blo
us
Qar
aqousa
kE
uphra
tes
Dam
Al-
Man
soura
Al-
Baa
thD
amA
l-R
aqqa
Hal
abie
h-Z
alab
ieh
Dei
r-E
zzor
Al-
May
adin
eA
lbu-K
amal
Sit
eN
o.
12
34
56
78
91
0
DD
(km
)0
35
19
52
10
21
52
50
37
04
40
52
06
50
Alt
itu
de
(ma.
s.l)
34
53
37
30
32
55
24
52
36
22
71
97
18
41
73
Co
llec
tio
np
erio
d2
00
4–
20
06
20
04–
20
06
20
04–
20
06
20
04
–2
00
52
00
4–
20
05
20
04–
20
06
20
04
–2
00
62
00
4–
200
62
00
4–
20
06
20
04–
20
05
Q(m
3s-
1)
68
6±
13
46
83
±1
33
60
0±
18
2n
.a.
57
6±
18
2n
.a.
n.a
.n
.a.
n.a
.5
68
±1
92
T(�
C)
13
.6±
3.2
16
.5±
6.2
18
.4±
61
7.1
±5
.21
7.0
±5
.21
7.0
±5
.41
8.1
±5
.91
8.6
±6
.31
8.8
±6
.51
9.5
±6
.9
pH
8.3
0±
0.3
8.4
2±
0.3
8.4
9±
0.2
8.3
6±
0.2
8.3
7±
0.2
8.3
2±
0.2
8.5
0±
0.2
8.3
9±
0.2
8.2
9±
0.2
8.4
0±
0.3
EC
(lS
cm-
1)
36
0±
26
35
3±
27
40
3±
26
49
7±
10
24
28
±1
44
64
±4
76
35
±1
02
64
1±
12
37
27
±1
65
85
3±
21
3
SiO
2(m
gL
-1)
9.9
±1
.58
.3±
0.9
6.4
±2
.38
.2±
2.5
6.1
±2
.47
.3±
3.2
6.9
±2
.26
.8±
2.1
7.0
±1
.87
.7±
2.5
DO
(mg
L-
1)
6.6
±1
.66
.4±
1.4
5.9
±1
.45
.6±
1.5
5.6
±1
.35
.5±
1.3
5.9
±1
.46
.1±
1.3
5.8
±1
.25
.9±
1.4
DO
(%)
64
.7±
23
.86
2.0
±2
7.1
61
.1±
21
.95
8.8
±2
2.0
57
.5±
21
.15
6.1
±2
0.1
62
.2±
20
.56
3.2
±2
1.1
58
.0±
18
.16
2.3
±2
3.3
Na?
(mg
L-
1)
15
.5±
2.2
15
.7±
2.1
21
.2±
3.6
28
.0±
6.1
22
.1±
3.4
26
.6±
4.6
38
.2±
10
.03
9.8
±8
.55
0.2
±1
5.4
58
.2±
17
.3
K?
(mg
L-
1)
2.1
±0
.62
.0±
0.6
2.2
±0
.52
.3±
0.6
2.2
±0
.52
.3±
0.5
2.7
±1
.12
.5±
0.8
3.0
±1
.23
.4±
1.6
Mg
2?
(mg
L-
1)
13
.7±
1.5
13
.6±
1.3
15
.7±
1.8
19
.0±
3.6
16
.0±
1.9
17
.1±
1.7
21
.7±
4.2
21
.2±
3.7
25
.2±
6.9
28
.1±
6.8
Ca2
?(m
gL
-1)
34
.2±
4.5
33
.3±
4.4
33
.9±
3.9
42
.3±
10
.33
4.5
±4
.43
7.5
±4
.34
8.0
±9
.54
9.7
±7
.55
5.6
±1
2.4
57
.6±
14
.7
HC
O3
-(m
gL
-1)
12
5.2
±1
8.3
12
1.8
±1
9.2
11
8.8
±1
8.0
11
3.3
±1
7.4
11
1.7
±1
9.0
11
5.8
±1
9.3
11
5.7
±1
6.0
12
0.5
±1
7.1
12
4.1
±1
8.0
12
3.2
±2
0.9
CO
32
-(m
gL
-1)
1.9
±2
.82
.8±
3.1
3.2
±2
.92
.0±
2.9
1.8
±2
.61
.5±
2.0
3.1
±4
.22
.4±
2.7
2.0
±3
.33
.1±
3.1
Cl-
(mg
L-
1)
17
.4±
1.3
17
.9±
1.4
26
.5±
3.6
29
.5±
3.4
28
.0±
2.0
36
.2±
4.5
52
.8±
10
.95
2.9
±1
0.1
69
.8±
20
.58
6.7
±3
2.4
NO
3-
(mg
L-
1)
2.1
±0
.62
.0±
0.9
1.9
±0
.53
.7±
2.0
2.3
±0
.52
.3±
0.8
3.8
±0
.93
.4±
1.0
4.6
±1
.65
.3±
5.5
SO
42-
(mg
L-
1)
31
.9±
2.8
32
.1±
3.0
51
.1±
6.1
10
5.4
±5
9.7
56
.3±
6.0
64
.4±
12
.21
24
.5±
35
.81
23
.2±
33
.71
43
.3±
45
.71
77
.2±
65
.5
TD
S(m
gL
-1)
24
2±
20
23
8±
22
27
1±
22
34
3±
77
27
3±
25
30
2±
29
40
7±
74
41
3±
61
47
6±
97
54
0±
14
7
r(%
)4
.74
.72
.10
.42
.82
.31
.00
.50
.22
.1
log
pC
O2
(atm
.)-
3.3
04
±0
.3-
3.4
61
±0
.3-
3.5
50
±0
.2-
3.3
72
±0
.2-
3.3
89
±0
.2-
3.4
11
±0
.2-
3.4
99
±0
.2-
3.4
55
±0
.2-
3.3
49
±0
.2-
3.3
71
±0
.3
SI c
al
0.2
53
±0
.40
.405
±0
.40
.552
±0
.20
.44
1±
0.2
0.3
64
±0
.20
.373
±0
.20
.57
7±
0.3
0.5
35
±0
.30
.548
±0
.20
.590
±0
.4
SI d
ol
0.3
23
±0
.70
.740
±0
.71
.041
±0
.50
.76
8±
0.5
0.6
57
±0
.40
.650
±0
.51
.07
0±
0.5
0.9
97
±0
.51
.014
±0
.41
.137
±0
.7
SI g
yp
-2
.368
±0
.3-
2.4
01
±0
.2-
2.1
74
±0
.2-
1.7
25
±0
.3-
2.0
94
±0
.1-
2.0
37
±0
.3-
1.7
62
±0
.3-
1.7
83
±0
.3-
1.5
88
±0
.2-
1.5
34
±0
.4
SI q
ua
0.3
64
±0
.10
.218
±0
.10
.027
±0
.20
.16
8±
0.2
0.0
64
±0
.20
.108
±0
.30
.09
6±
0.2
0.0
86
±0
.20
.091
±0
.20
.106
±0
.2
d18O
(%,
VS
MO
W)
-8
.52
±0
.2-
8.3
9±
0.2
-7
.41
±0
.2-
7.3
1±
0.2
-7
.33
±0
.3-
7.4
1±
0.3
-7
.21
±0
.3-
7.2
4±
0.3
-7
.29
±0
.3-
7.0
1±
04
d2H
(%,
VS
MO
W)
-5
5.1
±2
.0-
54
.6±
1.7
-4
9.1
±1
.7-
48
.8±
1.2
-4
8.5
±1
.9-
48
.4±
1.8
-4
7.9
±1
.7-
48
.5±
1.7
-4
8.1
±1
.2-
46
.8±
2.3
d(%
,V
SM
OW
)1
3.0
±1
.01
2.5
±1
.11
0.2
±1
.19
.7±
1.6
10
.2±
1.3
10
.4±
1.4
9.8
±1
.29
.4±
1.1
9.6
±1
.59
.3±
1.3
DD
dis
tan
ced
ow
nst
ream
from
the
firs
tst
atio
nin
km
,m
a.s
.l.
hei
gh
tab
ov
ese
ale
vel
inm
eter
,n
.a.
no
tav
aila
ble
,r
chem
ical
anal
ysi
ser
ror,
±st
andar
dd
evia
tio
nv
alues
of
the
mea
sure
dd
ata,
pC
O2
par
tial
pre
ssu
reo
fd
isso
lved
CO
2,
SI
satu
rati
on
ind
exan
dth
elo
wer
case
indic
es:
cal,
do
l,g
ypan
dq
ua
refe
rto
the
min
eral
s:ca
lcit
e,dolo
mit
e,gypsu
man
dquar
tz,
resp
ecti
vel
y
Environ Earth Sci
123
world rivers (Meybeck 1979). However, the ER water at
Jarablous is somewhat comparable to that of semi-arid
zone rivers, mainly in terms of K?, Mg2? and HCO3
concentrations; whereas the river salinity levels at Albu-
Kamal are obviously higher than those of semi-arid and
arid zone rivers, with the exception that the Na?, Ca2? and
HCO3- concentrations are similar to those of arid zone
rivers.
Silica (SiO2) is an important chemical species, essen-
tially for studying chemical erosion, geochemical weath-
ering and biogeochemical cycles (Garrels and Mackenzie
1971; Wollast and Mackenzie 1983; Meybeck 1987; Ga-
illardet et al. 1999). This parameter, which was measured
during the period from August 2004 to August 2005, has an
average value of 9.9 ± 1.5 mg L-1 at Jarablous. This
value is very close to the value (10.4 mg L-1) provided by
Meybeck (1983) as an average for world rivers, but obvi-
ously lower than the value (13.1 mg L-1) reported by
Livingstone (1963) for this water category.
Temporal and spatial variations
Figure 3 shows the temporal evolutions of major ions and
total dissolved solid (TDS) concentrations, together with
EC values for the ER at Jarablous and Al-Mayadine sta-
tions during the study period (2004–2006). With the
exception of HCO3- and K? ions, which clearly differ in
their evolution patterns from those of other major ions, the
temporal evolution patterns of the remaining ions are
identical to those of TDS and EC, with rather small fluc-
tuations at Jarablous and more pronounced variations at
downstream stations. Although temporal variations in
HCO3- values are remarkably identical at Jarablous and
Al-Mayadine (Fig. 3b), the temporal evolution of this
species highly reflects the role of thermodynamic condi-
tions controlling the distribution of carbon species in nat-
ural water (Stumm and Morgan 1981).
The temporal variations in K? values are similar at both
sites, but with slightly higher values at Al-Mayadine. The
distinct K? increase at both sites during the autumn season
of 2005 (Fig. 3g) is most probably because of anthropo-
genic pollution or leaf decay within the river bed (Kattan
1989).
The increases in most remaining major ion concentra-
tions, and thus EC and TDS values, especially during
spring period, are mostly because of: (1) high irrigation
rates and flushing of accumulated alkaline salts developed
in soils; and (2) mobilization of resulted saline ground-
waters into the riverbed through the so-called ‘‘drainage
return flow’’ effect (Simpson and Herczeg 1991; Kattan
2008).
The average T value of the ER at Jarablous was the
lowest (13.6 ± 3.2 �C), compared with the other
downstream stations, which show a range from 16.5 ± 6.2
to 19.5 ± 6.9 �C. T value increases about 5 �C between
Jarablous and Al-Assad Lake, and slowly increases by
&1 �C downstream. In parallel, the average DO value
systematically decreases from 6.6 ± 1.6 mg L-1 (site No.
1) to 5.5 ± 1.3 mg L-1 (site No. 6) due to the solubility of
DO, which tends to decrease with increasing temperature
(Hem 1992). The average pH value slightly increases from
&8.3 ± 0.3 to &8.5 ± 0.2, with a remarkable increase in
Al-Assad Lake, most likely because of consumption of
dissolved CO2 gas by algae growth and the activity of
microorganisms and aquatic plants (Livingstone 1963;
Meybeck 1983, 1986). On the contrary, the decreases in
DO and pH observed at sites No. 6, 8 and 9 are mostly due
to urban contamination. Such decreases can be explained
by the oxidation of organic matter carried by river water,
which leads to further liberation of HCO3- and H? species
(Kempe 1984). Hence, strong correlations were found
between pH and dissolved CO2 partial pressure (pCO2)
values (R2 = 0.963), and to a lesser extent between pH and
HCO3- concentrations (R2 = 0.427). Therefore, the spatial
evolution of average pCO2 is marked by small fluctuations
around the atmospheric value (log pCO2 = -3.5), with a
minimum value (log pCO2 = -3.55) in Al-Assad Lake,
where the pH value was the highest (&8.5 ± 0.2).
As the ER flows from Jarablous towards Al-Assad and
Al-Baath Lakes, a progressive depletion of silica content
from &10 to &6 mg L-1 can be observed, most likely as a
result of silica consumption by diatoms growth (Meybeck
1986; Kattan 1989). The spatial evolution pattern of silica
content along the river path in the remaining downstream
sites is rather opposite to that of pH, also because of
thermodynamic dependents (Stumm and Morgan 1981).
The spatial variation pattern of average HCO3- con-
centrations along the ER path is completely different from
those of other dissolved ions. The concentration of HCO3-
slightly changes around 120 mg L-1, with a little decrease
between Jarablous and Al-Baath Dam, mostly because of
biological activity, consumption of dissolved CO2 gas and
precipitation of carbonate minerals (Hem 1992). Down-
stream of Al-Baath Dam, HCO3- concentration smoothly
increases in an opposite way to pH value, as the two
parameters are thermodynamically dependent (Stumm and
Morgan 1981).
The spatial evolutions of average major ion (Na?, K?,
Ca2?, Mg2?, Cl- and SO42-) concentrations show gener-
ally similar trends to those of TDS and EC evolutions, with
a relative increase at site No. 4, obviously because of
additional contributions of more saline waters from dif-
ferent ephemeral tributaries. The concentrations of K?,
Ca2?, Mg2? and NO3- increase within the section from the
ED to the Syrian–Iraqi border by factors of 1.6, 1.7, 2.1 and
2.5, respectively; whereas those of Na?, Cl- and SO42-
Environ Earth Sci
123
increase by factors of 3.8, 5 and 5.6, respectively. It is
noteworthy to be mentioned that a slight decrease in T
value, a distinct increase in SiO2 content, and a rather
higher pCO2 value than that of the atmosphere were
observed at site No. 4, where the river usually receives
additional contributions of colder and more mineralized
waters. Projection of all water samples collected from the
ER during the study period in the Piper diagram (Fig. 4)
0
25
50
75
100a
Jarablous Al-Mayadine
Ca2+
(mgL
-1)
50
100
150
200b
Jarablous Al-Mayadine
HC
O3- (m
gL-1)
0
10
20
30
40c
Jarablous Al-Mayadine
Mg2+
(mgL
-1)
0
50
100
150
200
250d Jarablous
Al-Mayadine
SO42-
(mgL
-1)
0
25
50
75
100e Jarablous
Al-Mayadine
Na+ (m
gL-1)
0
30
60
90
120f Jarablous
Al-MayadineC
l- (mgL
-1)
0
2
4
6
8g Jarablous
Al-Mayadine
K+ (m
gL-1)
0
2
4
6
8
10h Jarablous
Al-Mayadine
NO
3- (mgL
-1)
0
200
400
600
800i
JarablousAl-Mayadine
TD
S (m
gL-1)
Time (month)
1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2004 1/1/2005 1/1/2006 1/1/2007
0
200
400
600
800
1000
1200j
Jarablous Al-Mayadine
EC
(Sc
m-1)
Time (month)
1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2004 1/1/2005 1/1/2006 1/1/2007
1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2004 1/1/2005 1/1/2006 1/1/2007
1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2004 1/1/2005 1/1/2006 1/1/2007
1/1/2004 1/1/2005 1/1/2006 1/1/2007 1/1/2004 1/1/2005 1/1/2006 1/1/2007
Fig. 3 Temporal variations in Ca2? (a), HCO3- (b), Mg2? (c), SO4
2- (d), Na? (e), Cl- (f), K? (g), NO3- (h), TDS (i) and EC (j) values for the
ER at Jarablous and Al-Mayadine stations during the period 2004–2006
Environ Earth Sci
123
shows that the river water quality evolutes from usually
fresh waters of a Ca2?–Mg2? and HCO3- type, towards
more saline waters of Na?–Cl- type or Na?–SO42- type.
Thermodynamic equilibrium conditions
The average values of the saturation indexes with respect to
calcite, dolomite, gypsum and quartz, together with aver-
age values of the partial pressure of dissolved CO2 of all
water samples collected during the study period (Table 1)
were calculated using the software WATEQ4F (Plummer
et al. 1976). This software was also used for the calculation
of chemical activities of the appropriate thermodynamic
constraints (aH?, aCa?2, aMg2?, aNa?, aK? and aH4SiO4),
commonly used for examining geochemical weathering of
silicate minerals (Garrels and Christ 1965).
The saturation index (SI) of a water sample with respect
to any mineral susceptible to be precipitated was calculated
by Stumm and Morgan (1981):
SI ¼ logIAP
KSPðTÞð1Þ
where IAP is the ion activity product of the solution and
KSP(T) is the equilibrium constant of the reaction considered
at the temperature T (K).
Thermodynamically, the ER water at all monitored sites
was kinetically below the equilibrium state with respect to
gypsum, but oversaturated with respect to calcite, dolomite,
amorphous silica and quartz (Table 1). Similar spatial
evolution patterns can also be observed between the satu-
ration indexes with respect to quartz and amorphous silica
and pCO2, and opposite evolution patterns between the
saturation indexes with respect to calcite, quartz and
amorphous silica, especially for the upper six sites,
primarily because of the silica solubility that increases with
the increasing of pH values (Hem 1992).
The chemical activity diagrams related to silicate
weathering study (Fig. 5) were plotted to investigate the
controls on aqueous silica and major ion concentrations
with respect to certain silicate minerals susceptible to be
present in nature. Both plots representing the thermody-
namic constraints on Ca2? or Na?, H? and H4SiO4 activ-
ities for equilibrium reactions between calcium plagioclase
feldspars (anorthite) and gibbsite, kaolinite and Ca-mont-
morillonite (Fig. 5a) and sodium plagioclase feldspars
(albite) and gibbsite, kaolinite and Na-montmorillonite
(Fig. 5b) show that all of the ER water samples are obvi-
ously distributed in the kaolinite stability fields. This means
that after interaction with primary silicate minerals (mostly
basalts) the ER water evolves across the kaolinite stability
fields towards equilibrium with amorphous silica, quartz,
Ca-montmorillonite, Na-montmorillonite and Mg-mont-
morillonite (diagram is not shown here). However, the
equilibrium with respect to gibbsite cannot be achieved,
mostly because of the low feldspars weathering (Wollast
and Mackenzie 1983).
Stable isotope compositions
Table 1 reports the mean isotopic compositions (d18O and
d2H) of all water samples collected from the ER during
the study period, together with the values of mean deu-
terium excess (d), defined by Dansgaard (1964) as:
d ¼ d2H�8d18O.
The d2H–d18O relationship of the ER water samples,
together with projections of further two water samples
collected from the ER during 2000 (Fig. 6), demonstrates
that all water samples collected from all downstream sta-
tions were more enriched with respect to those of the ER
water at Jarablous, and that most enriched waters belong to
Al-Assad Lake or to stations located far downstream. The
ER water sample points nicely fit a least squares regression
line approximated by:
d2H ¼ ð5:48� 0:11Þd18O� ð8:51� 0:83Þ with
R2 ¼ 0:90 and N ¼ 276ð2Þ
The line slope (5.48) deviates significantly from the
value (8) given by Craig (1961) for the global meteoric
water line (GMWL), and also from the more recent value
(8.17) given by Rosanski et al. (1993) for the unweighted
GMWL of most world meteoric waters. This slope is also
lower than the value (7.52) of the local meteoric water line
estimated on a basis of some Syrian and Turkish stations
(Kattan 2001), meaning that the ER water is systematically
subjected to further fractionation by evaporation processes
after rainfall occurrences (Kattan 2008).
1
1
1
2
2
2
3 3
3
4 4
4
55
5
66
6
77
7
8
8
8
99
9
1010
10
1111
11
12
12
12
13
13
13
14
14
14
15
15
15
16 16
16
17 17
17
18
18
18
19 19
19
2020
20
21 21
21
2222
22
23 23
23
2424
24
25
25
25
26
26
26
27
27
27
2828
28
2929
29
3030
30
3131
31
3232
32
33 33
33
34
34
34
35 35
35
36 36
36
37
37
37
38
38
38
39
39
39
40
40
40
4141
41
42 42
42
43
43
43
4444
44
45
45
45
46
46
46
47
47
47
48
48
48
49
49
49
50
50
50
51
51
51
5252
52
5353
53
54
54
54
5555
55
5656
56
57 57
57
5858
58
5959
59
6060
60
6161
61
62
62
62
6363
63
6464
64
65 65
65
66
66
66
67 67
67
68 68
68
69
69
69
70
70
70
7171
71
72
72
72
73
73
73
74
74
74
75
75
75
76
76
76
77 77
77
78 78
78
7979
79
8080
80
8181
81
82 82
82
83
83
83
8484
84
85
85
85
86
86
86
87 87
87
8888
88
89 89
89
90
90
90
91 91
91
92 92
92
93
93
93
94
94
94
95
95
95
96
96
96
97
97
97
98
98
98
9999
99
100100
100
101 101
101
102 102
102
103103
103
104 104
104
105 105
105
106 106
106
107
107
107
108
108
108
109
109
109
110
110
110
111
111
111
112112
112
113113
113
114
114
114
115115
115
116116
116
117 117
117
118 118
118
119
119
119
120
120
120
121
121
121
122
122
122
123
123
123
124
124
124
125 125
125
126 126
126
127 127
127
128 128
128
129 129
129
130 130
130
131131
131
132132
132
133
133
133
134
134
134
135
135
135
136
136
136
137137
137
138 138
138
139 139
139
140140
140
141141
141
142142
142
143
143
143
144
144
144
145
145
145
146
146
146
147
147
147
148
148
148
149149
149
150150
150
151 151
151
152 152
152
153
153
153
154154
154
155
155
155
156
156
156
157
157
157
158
158
158
159
159
159
160
160
160
161161
161
162 162
162
163
163
163
164 164
164
165 165
165
166 166
166
167
167
167
168
168
168
169
169
169
170
170
170
171
171
171
172
172
172
173 173
173
174 174
174
175
175
175
176 176
176
177177
177
178178
178
179
179
179
180
180
180
181181
181
182
182
182
183
183
183
184
184
184
185
185
185
186 186
186
187
187
187
188
188
188
189189
189
190 190
190
191191
191
192192
192
193
193
193
194
194
194
195
195
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196
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197
198198
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200200
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201 201
201
202 202
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203 203
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209209
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210 210
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211 211
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212 212
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213 213
213
214 214
214
215 215
215
216216
216
217
217
217
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218
218
219
219
219
220
220
220
221221
221
222222
222
223223
223
224 224
224
225225
225
226226
226
227227
227
228228
228
229
229
229
230
230
230
231
231
231
232
232
232
233 233
233
234234
234
235235
235
236236
236
237237
237
238238
238
239
239
239
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240
240
241241
241
242
242
242
243243
243
244244
244
245
245
245
246
246
246
247247
247
248 248
248
249249
249
250
250
250
251
251
251
252
252
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253
254
254
254
255255
255
256
256
256
257
257
257
258
258
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259
259
259
260
260
260
261261
261
262262
262
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264264
264
265
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267267
267
268268
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271271
271
272272
272
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276
276
277 277
277
278
278
278
279
279
279
280
280
280
281
281
281
282
282
282
Sample No.5
Sea water
Mg2+
Ca2+ Na++K+ HCO3- Cl-
SO42-
Ca 2++Mg 2+SO
42- +C
l-
Fig. 4 Piper diagram of all water samples collected from the ER
during the period 2004–2006
Environ Earth Sci
123
Temporal and spatial variations
Figure 7 illustrates the temporal evolution patterns of d18O
and d2H concentrations of the ER water at four stations
(sites No. 1, 2, 6 and 9) during the period 2004–2006. The
data show that the waters of the first two upstream stations
have identical patterns of variation, with a small lag effect,
depleted d18O and d2H values during summer and autumn
and more enriched values from February to May, with
generally higher d-excess values (d [ 12 %). The waters
of the remaining downstream stations all have rather sim-
ilar evolution trends, distinctly opposite to that of the first
two upstream sites, with lower d-excess values (9 %\ d\12 %). The difference in the isotopic composition between
the above two water groups is clearly small during spring
and relatively higher during summer and autumn. Despite
there is a shift of about 3 % in the d-excess value between
the two groups, it is noteworthy to be observed that the
temporal evolution of d-excess parameter evolutes in a
similar way to those of d18O and d2H concentrations. The
magnitudes of temporal variations in stable isotope com-
positions of the ER during the study period were not too
considerable compared with those of other large world
rivers (Kendall and Coplen 2001; Winston and Criss 2003).
The spatial evolutions of d18O and d2H compositions
along the ER path were identical, with a significant
increase (&1.1 and &6 % for d18O and d2H, respectively)
between Jarablous and Al-Assad Lake. Patterns of this
evolution permit distinction between the less evaporated
river water (isotopically depleted) coming from Turkey and
more enriched water stored in Al-Assad Lake. Downstream
from the ED, the isotopic composition of the ER exhibits
slight enrichment (&0.4 % and 2.0 % for d18O and d2H,
respectively), meaning that the ER water is less fraction-
ated compared with the lake water. This behavior can also
be observed in the spatial evolution of d-excess values,
ranging from 12.5 to 13.0 % at upstream sites and fluc-
tuating within 9.3–10.4 % in the remaining downstream
sites, and completely opposite to those of d18O and d2H
values.
A comparison of the ER water with other large rivers in
the world, reveals generally that the range of stable isotope
variations in the ER is relatively small, compared for
example with that of the Murray River (Australia), where
d18O values vary from -8.3 % in the headwaters to
?0.37 % at its mouth (Simpson and Herczeg 1991).
Similarly, large isotopic ranges (-25.6 to ?10.4 % and
-198.3 to ?12.4 % for d18O and d2H, respectively) were
reported by Kendall and Coplen (2001) for a large number
of rivers in the USA. Those authors also showed that most
rivers with enriched values greater than 0 % are associated
with arid area rivers, such as those in Texas and Florida.
The reason that the isotopic composition of arid zone
rivers is considerably different from that of rivers in trop-
ical and moderate regions is primarily because seasonal
variations are not caused by changes in the isotopic com-
position of rainfall in the headlands, but by evaporation
from rivers in the lower parts, where rains become less
6
8
10
12
14
16
18
20
7374 75
767778 79
808182
8384
858687
8889
909192
939495
96979899 100101
102103
104105106107108
109110111 112113 114115116
117118119120
121 122123
124
125126 127128 129130
131132133134 135136
137 138139140 141142 143144145
146147
148
149 150 151
152153
154
155 156
157
158159160
161162 163
164165
166167 168
169170171172173174 175
176177
178
179180
181
182 183184
185186
187188189
190
191
192193
194
195196
197198199
200201
202
203
204
241242243
244245246
b
Ca-Montm
orillonite
Qua
rtz
Anorthite
KaoliniteGibbsite
log aH4SiO4
log
(aC
a2+/(a
H+ )2 )
-6 -5 -4 -3-6 -5 -4 -30
2
4
6
8
10
12
7374 75
767778
79808182
83848586
87
8889 909192939495
96979899 100101
102103104105106
107108
109110111 112113
114115116117
118
119120
121122 123124
125126 127128 129130131132
133 134135136137 138139140141142
143144
145 146147148
149 150 151152
153
154
155 156
157158159160
161162
163164165
166
167 168169170171172 173174 175176177
178
179180181
182183184
185 186187188189
190
191192
193
194
195196
197198 199200201
202
203204241 242
243244
245246
aNa-Montmorillonite
Qua
rtz
Albite
KaoliniteGibbsite
log aH4SiO4lo
g (a
Na+ /a
H+ )
Fig. 5 Projections of water
samples collected from the ER
during 2004–2006 in the
chemical activity diagrams
defining the stability fields for
calcium plagioclase feldspars
(anorthite), gibbsite, kaolinite
and Ca-montmorillonite (a) and
stability fields for sodium
plagioclase feldspars (albite),
gibbsite, kaolinite and Na-
montmorillonite (b) at 25 �C
-11 -10 -9 -8 -7 -6 -5-70
-60
-50
-40
-30
-20
111
111
11111
11
111
111
1111
11 1
22
22
22
222222
2 22
2
22
222
222
22
3
333
3
3
3
3
3 33 3
3
3
3
3 3
333
4
4
444
44 4
444444
44
4
444
555555 555
5555555555 5
5
555
55
66666666
6666
6
6
666 66 6
7
7777 777 7
7777
7
777777
8
88888 8
888
8
888
88 888 8
8
888 88
9
999
9 99 99
9 999
999 999 9 10101010101010
10
10101010
10
10
10101010101010
101010
10
10
1111
11111111111111
11111111 111111
111111 11
11
11
11 11 1111
1212121212
12
121212
121212
12
121212
12
121212
E
E
Evaporation LineLocal Meteo
ric Water
LineD=5.48
18 O -8.51
Al-Assad Dam Euphrates at Syrian-Turkish border
Site No.
D=7.5218 O+14.73
2 H (0 / 00
)
18O (0/00)δ
δ
Fig. 6 Relationship between d2H and d18O of ER water samples
collected from all stations during the period 2004–2006
Environ Earth Sci
123
abundant or completely disappear (Gat 1996; Martinelli
et al. 2004), which is exactly the case of the ER water.
Factors controlling water geochemistry
The software STATISTICA 6 (2007) was used to perform
the analysis of principal factors controlling the geochem-
istry of the ER water. The data matrix used for extracting
of such reliable factors consists of all the physico-chemical
variables reported in Table 1 (i.e., 23 variables and 241
observations). Noting, however, that the number of obser-
vations used in the case of SiO2 and SI-qua variables was
limited to 131 samples. Accordingly, four main factors
were extracted from the selected data matrix of the ER
water. These factors explain more than 80 % of the total
variance in the data matrix. Figure 8a, b shows projections
of Factor-1 versus Factor-2 and Factor-1 versus Factor-3,
respectively.
-10
-9
-8
-7
-6a
Site No. 1 Site No. 2 Site No. 6 Site No. 9
18O
(0 / 00)
Time (month)
-65
-60
-55
-50
-45
-40b
Site No. 1 Site No. 2Site No. 6 Site No. 9
2 H (0 / 00
)
Time (month)
1/1/2004 1/1/2005 1/1/2006 1/1/2007
4
8
12
16c
Site No. 1 Site No. 2Site No. 6 Site No. 9
d -ex
cess
(o / oo)
Time (month)
1/1/2004 1/1/2005 1/1/2006 1/1/2007
1/1/2004 1/1/2005 1/1/2006 1/1/2007
δδ
Fig. 7 Temporal variations in d18O (a) and d2H (b) concentrations
and deuterium excess (c) values at four stations (sites No. 1, 2, 6 and
9) along the ER course during 2004–2006
Fig. 8 Projections of Factor-1 versus Factor-2 (a) and Factor-1
versus Factor-3 (b) of principal components extracted from the
selected data matrix of ER water samples during 2004–2006
Environ Earth Sci
123
• Factor-1 is the highest one, and accounts for 47.61 % of
the total variance. This factor, which dominates over
the existing other factors, includes all of the major ions
except HCO3-. Although this factor also affects TDS,
EC and SI-gyp parameters, its importance is principally
due to the following ions: SO42-, Cl-, Ca2? and Na?.
This factor can therefore be interpreted as representing
the weathering products liberated as a result of natural
rock–water interactions (Reeder et al. 1972). Hence,
this factor obviously reflects the role of drained lands,
namely the dissolution of soluble evaporate rocks or
salts developed in the ER downstream valley. However,
as nitrate has no significant lithological source in the
study area, the liberation of NO3- may be associated
with the limited contributions from anthropogenic
sources and or atmospheric inputs (Singh et al. 2005).
• Factor-2 accounts for 16.93 % of the total variance, and
consists of the following variables: pCO2, pH, HCO3-
and CO32-. This factor, which includes to a lesser
extent the group of saturation indexes (SI-cal and SI-
dol) and strongly depends on pCO2 or pH values
(Stumm and Morgan 1981), can obviously be inter-
preted as representing the role of pCO2 on the
dissolution of carbonate rocks and distribution of
carbon species in an open system with the atmosphere.
• Factor-3 accounts for only 8.73 % and could be treated
as the temperature factor. This factor primarily affects
DO concentration and to a lesser extent the concentra-
tion of SiO2, and thus the SI-qua index that uniquely
depends on silica content. The reason that DO and
silica parameters are affected by the T factor may be
explained by the fact that the growth of microorganisms
(consumer of DO) and diatoms (consumer of silica) is
more active during certain periods, especially when the
T value of the ecosystem is usually cool (Meybeck
1986).
• Factor-4 is the less significant one and accounts for
only 7.47 % of the total variance. This factor affects
exclusively the variables of stable isotopes (d18O and
d2H) and d-excess parameter. This factor reflects
certainly the impact of evaporation process that
strongly affects all types of surface water in this
ecosystem.
The remaining factors are all of a low significant
importance, because all of their resulted explanations are
less than 5 % of the total variance.
Role of drained lands
The calculation results of average ionic ratios (Mg2?/Ca2?,
Na?/Cl-, Ca2?/SO42-, SO4
2-/HCO3-), expressed in
meq L-1, permit the distinction between the ER water of
the first two upstream stations and the river water of the
remaining sites.
The ER water of the first two upstream stations, which
was generally characterized by high ionic ratios (HCO3-/
Cl- [ 4 and Ca2?/SO42- [ 2.5), reflects in fact the influ-
ence of the upstream drained lands, largely of carbonate
character (Ponikarov 1967; Iscen et al. 2009).
Cluster analysis of the ER water was additionally
essayed, also by using the software STATISTICA 6 (2007)
and adopting the Ward’s linkage method with the Euclid-
ean distance as a measure of similarity of variables. The
data sets considered for such Q-mode cluster analysis
consist of 14 hydrochemical parameters and 20 water
samples collected from the ER at Jarablous and Albu-
Kamal stations during 2004–2006.
The output dendrogram of the Q-mode cluster analysis
for the ER water at Jarablous station (Fig. 9a) permits to
outline the importance of HCO3- ion as a key parameter
responsible for the major part of river water salinity (EC
and TDS) at this site. This ion, which can chemically be
balanced with Ca2? and Mg2?, and in the same time
Fig. 9 Dendrograms of Q-mode cluster analysis for 14 chemical
variables and 20 water samples collected from the ER at Jarablous
(a) and Albu-Kamal (b) stations during 2004–2006
Environ Earth Sci
123
affected by pCO2 variations, reflects the role of weathering
of carbonate rocks largely outcropping in the upstream
lands in Turkey.
Clustering of the ER data at Jarablous also allows to
delineate the following associations among studied
parameters:
– SO42- and Ca2? ions, usually liberated from the
dissolution of evaporate rocks (gypsum and anhydrite).
– NO3- and K? ions, most likely due to the influence of
anthropogenic pollution and/or atmospheric inputs.
– DO, SiO2 and pH parameters, eventually reflecting the
influence of pH changes on the solubility of dissolved
silica, and equally the role of diatoms as consumer of
silica and microorganisms as consumer of DO.
– Cl-, Mg2? and Na? ions, together with T parameter,
which were all strongly associated with SiO2, suggest-
ing hence that some parts of Mg2? and Na? were
liberated from silicate weathering, whereas the remain-
ing part of Na? was most likely imported by atmo-
spheric precipitation under the form of NaCl.
In a similar way, the output dendrogram of the Q-mode
cluster analysis for the ER water at Albu-Kamal station
allows to easily classify the chemical variables into two
main categories (Fig. 9b):
1. The most predominant ions, that can be regrouped
according to their weights in the total salinity as
follows: SO42- [ HCO3
- [ Cl- [ Ca2? [ Na?, obvi-
ously indicating that the major part of Ca2? and Na? is
strongly associated with SO42-, and thus the dissolution
of gypsum and anhydrite, together with certain soluble
salts rich in both calcium and sodium.
2. The other minor ions and parameters (pCO2, NO3-,
K?, DO, SiO2, pH, Mg2? and T), reflecting the
influence of several factors, such as the roles of pCO2,
T, anthropogenic pollution, silicate weathering and
atmospheric input.
In all the cases, the impact of ions related to the second
water group is of a minor importance because of their small
contributions to the total salinity value, compared with
SO42-, HCO3
-, Cl-, Ca2? and Na? ions enormously more
abundant in the first group.
In addition, the type of the ER water in the remaining
sites downstream from the ED, where the above-mentioned
ratios (Mg2?/Ca2?, Na?/Cl-, Ca2?/SO42-, SO4
2-/
HCO3-), together with Na?/Cl- and Ca2?/SO4
2- ratios,
become gradually lower with increasing river distance
(Fig. 10), reflects the influence of further progressive dis-
solution of gypsum and anhydrite, abundantly present in
the Lower Pliocene substratums, outcropping close to the
river course (GERSAR-SCET 1977).
Moreover, the relative enrichment in Na?, Cl- and
SO42- concentrations compared with those of other major
ions of the ER water in the farther downstream sites, pro-
vides another argument for the further salinity inputs,
librated as a consequence of flushing of saline soil hori-
zons, developed due to cyclic wetting and drying in some
parts of the river drainage area (Singh et al. 2005). The
predominance of SO42- over HCO3
- provides a strong
argument for the active dissolution of gypsum and anhy-
drite, that highly exceeds the dissolution of carbonate
formations (limestone and dolomite), characterizing the
upstream highland. The hypothesis that a small part of
Ca2? is linked with HCO3- (i.e., dissolution of carbonate
formations) and to a lesser extent a small part of Na? is
associated with Cl- (i.e., halite) could not be excluded.
In parallel, the relative enrichment in Na?, Cl- and
SO42- with respect to other ions present in the first water
group of clustering principally reflects the influence of dis-
solution of soluble evaporate salts, that could be formed as a
consequence of high evaporation rates of surface water
(including irrigation water), namely the salts of halite
(NaCl), thenardite (Na2SO4), mirabilite (Na2SO4 9
10(H2O) and bloedite [Na2Mg(SO4) 9 4(H2O)] minerals,
usually found in high quantities in the soil horizons within
the downstream Euphrates valleys (Kattan and Najjar 2005).
Accordingly, the dissolution of such soluble salts is the
primary cause for the further increase of groundwater
0.5
1.0
1.5
2.0a
Distance downstream (km)
Na/
Cl
0 100 200 300 400 500 600 700
0
1
2
3
4b
Distance downstream (km)C
a/SO
4
1 23
4
56 7
89 10
1 2
3
4
5 6
7 8 910
0 100 200 300 400 500 600 700
Fig. 10 Spatial variations in average Na/Cl (a) and Ca/SO4 (b) ratios
at the different sites along the ER during the period 2004–2006
Environ Earth Sci
123
salinity usually developed in the downstream ER valley, and
thus for the ultimate arrival of a portion of more evaporated
saline groundwater input, reaching the riverbed during
summer periods via drainage return flows (Kattan 2008).
The variation of molar equivalent Na? concentration as
function of molar equivalent Cl- and SO42- concentrations
generally suggests that &40 % of Na? content is associated
with Cl-, whereas the remaining &60 % is linked with
SO42- (Fig. 11). The distinct distribution pattern, which can
be observed for the ER water samples belonging to site No.
4, where the representative water samples fit a particular
Na?–SO42- relationship, with a slope close to a unity ratio,
proves also that most of the Na? content at this site is li-
brated from the dissolution of salts containing only SO42-
(i.e., thenardite, mirabilite and bloedite). The presence of
such soluble evaporate salts, which certainly enhances the
increase of soil and groundwater salinity, provides consis-
tently another argument for the active role of evaporation as
a secondary important geochemical process in such an arid
region.
Role of evaporation process
Evaporation, as a process by which liquid water is con-
verted into vapor and then transferred to the atmosphere, is
isotopically accompanied by fractionation, which leads
consequently to systematic isotopic depletion of the vapor
phase with respect to the liquid phase. Hence, the signifi-
cant enrichment in d18O and d2H values that was observed
in the ER water downstream from the ED, and accompa-
nied with lower d values, is primarily the result of isotopic
fractionation by evaporation from the ER and its tributar-
ies, especially from the related large reservoirs (Al-Assad
and Al-Baath Lakes).
Based on the systematic integral enrichment of stable
isotopes, that results from a combination of factors: such as
variations of stable isotope content in rains, downstream
contribution of runoff and evaporation (Winston and Criss
2003), the amount of evaporated water from the entire ER
system in Syria was estimated to be of the order of
&2–3 billion m3 (Kattan 2008). This huge amount of
water losses to the atmosphere represents approximately
25–30 % of the entire annual renewable surface water
resources in the country rounded to 10.5 billion m3. The
large volume of water in the lake (&11.9 billion m3), and
the relatively high mean residence time of the lake water
(&250 days), together with low d-excess values of the lake
water (d \ 10.2 %), support the potential evaporation
processes in such an arid environment.
Furthermore, the variations of ionic Na?/(Na??Ca2?)
and SO42-/(SO4
2-?HCO3-) ratios as a function of TDS,
plotted on modified Gibbs scheme diagrams (Gibbs 1970)
in order to determine the mechanism controlling the
chemistry of the ER water, show a hydrochemical evolu-
tion trend from a position close to rock dominance to
evaporation and crystallizations dominance (Fig. 12). This
evolution proves once more that the chemistry of ER water
is first controlled by dissolution of various rocks, and then
as water flows along the river path a second important
factor (evaporation) is controlling the river water chemis-
try. The plots also show that all water samples fall inside
the region that encompasses most of the earth’s surface
waters. The Gibbs assumption that at low-to-moderate
levels of TDS, Na? or SO42- values most of dissolved ions
are primarily supplied by precipitation is also valid, par-
ticularly for the upstream ER areas.
Conclusions
Monitoring of temporal and spatial variations of the
chemical and isotopic compositions of the ER water at 10
stations during the period 2004–2006 has so far led to the
following major conclusions:
• The average chemical composition of the ER water is
significantly higher than that for world river waters.
However, it is more comparable to that of semi-arid
zone rivers, in terms of K?, Mg2?, and HCO3- values,
and to that of arid zone rivers, in terms of Na?, Ca2?,
Cl- and SO42- concentrations. On the contrary, the
magnitudes of temporal and spatial variations of stable
isotope compositions are not too much considerable
compared with those of other large world rivers.
• As the river water flows towards its estuary, the river
salinity increases in two different rates: a low rate for
the upper stations, up to Al-Raqqa; and relatively a
higher rate for the remaining downstream stations. In
0 3 6 9 12 15 18
0
3
6
9
12
12
4334
4
799
10
12
65
4
34
78109
1243
4
447
8
910
1234
4
56
78
9
10
1234
4
5678
910
12
654
34
7
10
98
10987
65
4
342112
43
4
56
78910
910
87
654
34
21
9
10
8
7
5
4
346
21
9
10
87
5433
4
21
10
9
8
7
5443321
8
9
10
7
674
33
21
8
9
10
9
87
4
3321
910
109
87
4
3321
9
10
97
45
4
3321
91087
65
4
342
1
8
10
97
6544421
8
9107
65433
21
8
9
107
65433
21
89
6321
98
63
21
9
8
63
21213 6
98
89
6
321
89
6321
863
21
Na+ =0.4*Cl-
Na+ =0.6*SO4
2- SO42-
Cl-
Na+ =1*
X
Na+ (m
eqL-1
)
Cl- or SO42- (meqL -1)
Fig. 11 Relationships between molar equivalent Na? concentration
and molar equivalent Cl- and SO42- concentrations of water samples
collected from the ER during 2004–2006
Environ Earth Sci
123
parallel, the chemical composition changes from a
calcium–magnesium and bicarbonate type towards a
sodium–chloride type. Similarly, the concentrations of
stable isotopes gradually increase downstream, but with
a sharp enrichment at Al-Assad Lake.
• Whereas the high increasing rate of river water salinity
primarily depends on extensive dissolution of soluble
evaporate rocks and flushing of saline soils through
groundwater discharge via drainage return flows, the
isotopic enrichment is most likely because of multiple
factors: (1) high evaporation rates from the ER and its
tributaries; (2) long residence time of river water in Al-
Assad Lake (&250 days); and (3) the contribution of
evaporated irrigation water reaching the riverbed via
drainage return flows.
• Cluster analysis in Q-mode has resulted in separating
the most predominant ions (SO42-, HCO3
-, Cl-, Ca2?
and Na?), essentially liberated as a consequence of
dissolution of soluble evaporative rocks and salts, from
the less abundant ions (K?, Mg2?, NO3- and SiO2),
that could be imported from other different sources,
such as silicate weathering, atmospheric precipitation
input and anthropogenic pollution.
• Based on modified Gibbs scheme diagrams, it is
revealed that the primary factor controlling the geo-
chemistry of the ER water is rock weathering (i.e.,
dissolution of soluble salts), accompanied with evap-
oration–crystallization factor. However, factor analysis
results suggest the existence of four principal factors:
(1) rock weathering or dissolution of evaporative salts;
(2) dissolved CO2 partial pressure; (3) temperature; and
(4) evaporation. These factors explain more than 80 %
of the total variance in the data matrix.
• The role of precipitation as a diluting hydrological
process of river water seems to be negligible compared
with evaporation. Similarly, the role of tributaries as
contributors of local runoff is also limited, and consists
in providing additional amounts of colder, more
evaporated and more mineralized water.
• Although the presence of large dams across the ER has
many socio-economic benefits in reducing flood haz-
ards, providing reliable water supplies, and producing
hydroelectric power, their hydrological impacts on the
riverine ecosystem are negatives. The harmful effect is
not only demonstrated in enhancing the water lost by
evaporation, but also in deteriorating the river water
quality and equally the emergence of salinization
problems of soils and groundwater resources, mostly
at its estuary.
Acknowledgments The author is grateful to Prof. I. Othman,
Director General of AECS for his kind permission to publish this
paper. Prof. W. Rasoul-Agha is deeply acknowledged for his com-
ments and valuable remarks. The IAEA Organization, in particular,
Mrs P.K. Aggarwal and T. Vitvar are gratefully acknowledged for
financial assistance of the coordinated research project (contract-
12643). Helps rendered by the technical staff of the Geology
Department at AECS in analysis of water samples are also indebted.
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