J. Mt. Sci. (2
2016) 13(8): 14
453-1463
e-m
mail: jms@imd
de.ac.cn
http://jm
ms.imde.ac.cn
DOI: 10
0.1007/s11629
9-014-3076-3
Spatia
al varia
ation of stable isotope
i
es in diff
fferent w
waters
durin
ng melt season
s
in the Laohug
L
ou Glac
cial Catc
chmentt,
Shule
e River basin
b
WU Jin
n-kui1,2,3*
http://orcid.org/0000-00
003-0960-7813
3;
1
DING Yong-jian
Y
YANG Jun-hua2
e-mail: [email protected]
j
cn
http://orcid
d.org/0000-0002-7237-557
79; e-mail: [email protected]
http://orcid..org/0000-00
002-6175-3036
6; e-mail: hub
beixiantaoshi@
@126.com
hi-wei1
LIU Sh
htttp://orcid.org//0000-0002-7081-0223; e--mail: liushiw
[email protected]
CHEN Ji-zu2
htttp://orcid.org//0000-0002-3066-0726; e-mail: [email protected]
ZHOU Jia-xin1
QIN Xiiang2
h
http://orcid.o
rg/0000-000
02-5147-9280;; e-mail: [email protected]
http
p://orcid.org/0
0000-0002-19
998-595X; e-m
mail: qinxiang
[email protected]
* Correesponding autho
or.
1 Laborratory of Waterrshed Hydrolog
gy and Ecology, Cold and Arid Regions Enviro
onmental and E
Engineering Ressearch
Instittute, Chinese Accademy of Scien
nces, Lanzhou 730000,
7
China
2 Qilian
n Shan station of
o Glaciology an
nd Ecologic Env
vironment, Statte Key Laborato
ory of Cryospheeric Science, Colld and
Arid Regions Enviro
onmental and Engineering
E
Ressearch Institutee, Chinese Acadeemy of Sciencess, Lanzhou 7300
000,
China
3 Instittute for Landsca
ape Ecology and
d Resources Ma
anagement, Jusstus-Liebig-Univ
versity Giessen,, Giessen 35392
2,
Germ
many
Citatio
on: Wu JK, Din
ng YJ, Yang JH, et al. (2016) Spatial variation of
o stable isotopees in different waaters during meelt season in
the Lao
ohugou Glacial Catchment,
C
Shu
ule River basin. Journal
J
of Mountain Science 13
3(8). DOI: 10.10
007/s11629-014
4-3076-3
© Scieence Press and Institute
I
of Mou
untain Hazards and Environmeent, CAS and Sp
pringer-Verlag B
Berlin Heidelberrg 2016
Abstract: To evaluatee isotopic tracers at nattural
abundancess by providin
ng basic isottope data off the
hydrologica
al investigatio
ons and assesssing the imp
pacts
of differentt factors on the
t water cyccle, a total off 197
water samp
ples were co
ollected from
m the Laohu
ugou
Glacial ca
atchment in
n the Shulle River basin
b
northwesterrn China durring the 2013 ablation seassons
and analyzed their H- and O-isoto
ope composittion.
The results showed that the isotopicc compositio
on of
precipitatio
on in the Qilianshan Station in the
Laohugou Glacial ca
atchment was
w
remark
kable
variability. Correspondin
C
ngly, a higherr slope of δ18O-δD
O
diagram, wiith an averagee of 8.74, is obtained
o
based on
the precipiitation samples collected
d on the Gla
acier
No.12, main
nly attributed
d to the lowerr temperature on
of
Because
the
gllacier
su
urface.
Received: 18 March 2014
Revised: 26
6 August 2014
Accepted: 10 November 20
014
perccolation and elution, the isotopic com
mposition at
the bottom of the firn is n
nearly steadyy. The δ18O
/alttitude gradien
nts for preciipitation and
d melt water
werre -0.37‰/10
00 m and -0.3
34‰/100 m, respectively..
Exp
posed to the air
a and influeenced by stro
ong ablation
and
d evaporation
n, the isotopic values and
d the δ18O vs
δD diagram off the glaciall surface icce show no
altittudinal effectt, indicating that glacier ice has the
sim
milar origins with
w
the firn. The variation
n of isotopic
com
mposition in the
t melt water, varying frrom -10.7‰
to -16.9‰
(δ18O)
O and from --61.1‰ to -122.1‰ (δD)
indiicates the reccharging of ssnowmelt and glacial ice
mellt water prod
duced at diffferent altitud
des. With a
mea
an value of -13.3‰
for δ18O and -89..7‰ for δD,
the isotopic com
mposition of tthe stream wa
ater is much
closser to the meelt water, indiicating that stream water
is mainly
m
recharrged by the ab
blation water. Our results
of th
he stable isottopic compossitions in natu
ural water in
1453
J. Mt. Sci. (2016) 13(8): 1453-1463
the Laohugou Glacial catchment indicate the
fractionations and the smoothing fluctuations of the
stable isotopes during evaporation, infiltration and
mixture.
Keywords: Stable isotopes; Precipitation/snow/ice;
Altitude effect; Melt water; Laohugou Glacial
Catchment; Qilian Mountains
Introduction
Hydrological studies rely primarily on the
stable isotopes of oxygen and hydrogen (18O, 2H),
which are incorporated within the water molecule
(H218O, 1H2H16O), and exhibiting systematic
variations as a result of isotope fractionations
during water phase changes. Isotope fractionations
produce a natural labeling effect within the global
water cycle, therefore has been applied to study a
wide range of hydrological and climatic processes
at local, regional, and global scales (Jouzel et al.
2000). For more than four decades, the isotopic
composition of ice cores has been used to study
changes in the hydrological cycle on glacialinterglacial to seasonal/interannual timescales
(Yuan et al. 2004; Li et al. 2007; Zhang et al 2011).
The stable isotopic compositions in natural water
bodies respond sensitively to the environmental
variations and result in the fractionations of stable
isotopes during the processes of phase changes
and/or surface substances (Joussaume et al. 1984).
The magnitude of stable isotopic ratio in water
cycle is therefore an ideal index for distinguishing
different water sources (Zhang et al. 2003). Spatial
and temporal change of stable isotopic
compositions in precipitation is closely related to
the rainfall generation processes and the initial
conditions of vapor origins (Dansgaard 1964). With
the variation of precipitation, the isotopic changes
will correspondingly happen in the snowpack, melt
water, stream water and other water bodies.
Therefore, the stable isotopic compositions in
different water mediums can be used as physical
tracers to indicate the change of geographic
environment or mark the recharging of runoff
(Dansgaard 1964).
Glaciers are of crucial importance for the
livelihood of the arid regions, where people depend
on melt water for drinking and irrigation. The
Laohugou River Basin, located in the north edge of
1454
the Tibetan Plateau, is a typical glacierized basin.
Previous studies have mainly focused on the
variations (Du et al. 2008), ice movements (Liu et al.
2010) and surface energy budgets (Sun et al. 2012)
of the Laohugou Glacier No. 12. Based on a 20.12 m
shallow ice core drilled at the Laohugou Glacier No.
12 in 2006, Dong et al. (2013) investigated the
atmospheric environmental changes over the Qilian
Mountains and northwestern China based on ice
chemistry and its possible correlations with the
atmospheric circulation and the winter North
Atlantic Oscillation (NAO). The isotopic and
chemical characteristics in stream water (Hou et al.
2012) and the shallow ice core (Cui et al. 2011a, b)
were also investigated. However, little information
has been reported about the components and the
generation mechanisms of stream flow in the area.
The investigation of the glacial melt water
hydrochemical characteristics and dynamics is of
interest not only to enhance scientific understanding,
but also to promote effective water resource
utilization (Hodson et al. 2000; Feng et al. 2012).
This study focuses on the temporal and spatial
variations of the stable isotopes in different water
bodies in the Laohugou Glacial Catchment. We aim
to evaluate isotopic tracers at natural abundances,
by providing basic isotope data of the hydrological
investigations and assessing the impacts of
different factors on the water cycle. In addition, the
climatic conditions during the study period will be
correlated with the variation of stable isotopes
values to reveal the influences of climate on the
stable isotope compositions. Experimental field
studies, in which the spatial and temporal
variations of isotopic compositions from glacierriver water are investigated to provide additional
information on the catchment functions of
reducing epistemic uncertainty that related to the
inaccurate system conceptualization. This will help
to development of more reliable hydrological
models, by which the glacier contribution to the
local water resources will be better evaluated, and
ultimately it is helpful to more effective water
resources utilization.
1
Study Area
The Laohugou River Basin (96°10′~97°0′E,
39°10′~40°0′N) is located at the northern edge of
J. Mt. Sci. (2016) 13(8): 1453-1463
the Tibetan Plateau, Northwestern China (Figure 1).
There are 44 glaciers with a total area of 54.32 km2
in the basin. Glacier No.12 (39°26.4′N, 96°32.5′E,
World Glacier Monitoring Service ID 5Y448D12), a
valley glacier with 10.1 km in length and 21.9 km2
in area, is the largest glacier in this area. It consists
of two tributaries and the altitude ranges from
4260 to 5481 m a.s.l. (Liu et al. 2010). Glacier
geodetic measurement (Zhang et al. 2012)
indicates that the glacier surface elevation has
decreased by 18.6±5.4 m between 1957 and 2007.
Glacier melt water here feeds into the
Xiaochangma River, a tributary of the Shule River.
Our study area is located at the upper stretch of the
Qilianshan Station, a basin draining 30.2 km2 in
area (Figure 1) and hereafter named as the
Laohugou Glacial Catchment (LGC).
out a long-term monitoring of mountain glacier.
The LGC is characterized by the typical continental
climate influenced by the westerlies predominately
all around a year. According to the observation
data during 1959 to 1962 and 2009 to 2012, the
mean annual air temperature is -6.6°C at the
Qilianshan Station. The daily mean temperature in
summer is above 0°C. The annual total
precipitation varies between 160–450 mm/yr with
a mean value of 298.6 mm. Monthly precipitation
show remarkable seasonal variations, with more
than 70% of precipitation falling between May and
September.
2
Material and Methods
2.1 Field sampling
Figure 1 Sketch map showing the Laohugou Glacial
catchment and sampling sites.
The Qilianshan Station, located at 2-kilometer
lower from the terminus of Glacier No.12 (4180 m
a.s.1.) of Laohugou Valley, was set up in 2007 by
the Chinese Academy of Sciences in order to carry
An intensive investigation was carried out
between May and September in 2013 (the glacier
ablation season). Precipitation sampling was
carried out at the Qilianshan Station (Figure 1).
Precipitation samples were collected in plastic
basin sets immediately after each precipitation
event to minimize the alteration of heavy isotopes
by evaporation. Another additional seven plastic
basin sets were set at the Glacier No.12 to collect
precipitation samples (Figure 1), collected biweekly
or monthly. In this area the precipitation form is
usually as snow. Snow samples were collected into
a plastic bag and put in a warmer place to melt
naturally. When completely melted, water samples
were transferred into the sampling bottles.
A snow pit with 150 cm in depth was dug on
the glacier at an altitude of 4860 m on August 30
2013. Nine snow samples were collected at
different depths. Glacial ice samples were collected
biweekly at 4300, 4400, 4500, 4600 and 4700 m
a.s.1 (Figure 1). The surface 5 cm glacial ice was
gathered into a plastic bag and taken into a warmer
place to melt naturally and then transferred into
the sampling bottles.
Melt water was sampled at 4250 (the
terminus), 4300, 4400, 4500, 4600 and 4700 m
a.s.1, along a surface stream on the east branch of
Glacier No.12. The stream water was sampled
weekly at the Hydrological Gauging Station (Figure
1). Groundwater samples were taken biweekly from
the spring nearby the terminus of Glacier No. 12.
1455
J. Mt. Sci. (2016) 13(8): 1453-1463
2) the heavy isotope contents for the rainfall events
are influenced by varying sources of moisture (Wu
et al. 2010).
The isotopic composition of precipitation also
shows seasonal changes. Slight amount effect at
precipitation event scale was observed (Figure 2).
The δ18O of precipitation decreases with the
increasing amount of precipitation. Even though
the higher δ18O values appear at the warmer season
when precipitation was rich. The precipitation
weighted mean of δ18O and δD were -9.4‰ and
-51.5‰ during May to September. The δ18O and δD
of precipitation was depleted in colder months (the
precipitation weighted mean of δ18O and δD were
-11.7‰ and -77.0‰ in May, -13.0‰ and -77.0‰
in June, -9.7‰ and -52.8‰ in September) and
relatively enriched in warmer months (the
precipitation weighted mean of δ18O and δD were
-7.7‰ and -32.2‰, -7.3‰ and -36.7‰ in July and
August, respectively).
On the classical δ18O vs δD diagram (Figure 3),
samples align following the equation:
δD =7.80δ18O +16.87 (R2=0.95; n=36) (1)
Snapshot sampling (Grayson et al. 1997) was used
to collect grab water samples.
2.2 Meteorological data
collection
The meteorological parameters were measured
continuously by automatic weather stations (AWS)
installed at the Qilianshan Station, 4550 m and
5000 m on the Glacier No. 12. Geonor T-200B
gauges were used to measure the precipitation.
2.3 Sample analysis
Results
3.1 Isotopic composition in
precipitation
3.1.1 Qilianshan Station
The isotopic composition of
precipitation events during the
ablation seasons (May to October) at
the
Qilianshan
Station
show
remarkable variations from +3.0‰ to 19.1‰ in δ18O (Figure 2), and from
+24.3‰ to -139.1‰ in δD, respectively.
The differences of extreme δ18O and δD
values reached approximately 22‰
and 164‰. The possible explanations
are that: 1) a wide variations of
meteorological conditions (mainly for
temperature and precipitation) result
in different condensation mechanisms;
1456
δ18O
5.0
0.0
-5.0
-10.0
8.0
6.0
4.0
2.0
0.0
-15.0
-20.0
-25.0
5-7
5-23
6-6
6-18 6-20
7-1
7-9
date
7-14 7-26 7-30 8-31 9-17
Figure 2 The variation of precipitation and δ18O in events
precipitation in the Qilianshan Station.
80.0
40.0
0.0
δD/‰
3
precipitation
δ18 O/‰
precipitation/mm
All samples were kept in near-frozen condition
and transported for analysis at the State Key
Laboratory of Cryospheric Science, Cold and Arid
Regions Environmental and Engineering Research
Institute, Chinese Academy of Sciences for test.
The D and 18O composition of all water samples
were analyzed by Liquid-Water Isotope Analyzer
(DLT 100, Los Gatos, USA) based on the off-axis
integrated cavity output spectroscopy (OA-ICOS).
The isotopic ratios are expressed in per
20.0
mil (‰) units relative to Vienna
18.0
Standard Mean Ocean Water (V16.0
14.0
SMOW). Accuracies of δD and δ18O are
12.0
± 0.6‰ and ± 0.2‰ respectively.
10.0
-40.0
-80.0
δD = 7.80δ18 O + 16.87
R2 = 0.95
-120.0
-160.0
-25.0
-20.0
-15.0
-10.0
-5.0
0.0
5.0
δ O/‰
18
Figure 3 The relationship between δ18O and δD in events precipitation
samples in the Qilianshan Station.
J. Mt. Scci. (2016) 13(8
8): 1453-1463
The slope of the
ponds
regression line corresp
alue derived
d by
to the va
Rozanski et
e al. (1993
3) for
the global meteoric water
w
line (GMWL), indiccating
that
con
and
ndensation
precipitatio
on occur att full
equilibrium
m between vapor
v
and preciipitation ph
hases
(Dansgaard
d 1964). The
slope of th
he regression
n line
was also fa
airly close to the
multiple-yeear
observed
values in Northwest China
C
(7.88, Liu et
e al. 1997) and
a in
Heihe Riveer basin, an in
nland
river basin nearby our study
area (7.82, Wu et al. 2010).
2
In contrast to the GM
MWL,
the slope is slightly lower,
showing drrier and stro
onger
evaporation
n
condiitions
(IAEA 200
01). The inteercept
is higher, likely due to a
higher d-eexcess (Clark
k and
Fritz 1997
7; Kumar et
e al.
2010).
Table 1 Chara
T
acteristics of isotopic com
mposition in p
precipitation in
i Laohugou
G
Glacial
Catchm
ment
Sa
ampling site
ellevation
Sample
number
43
350 m
44
450 m
45
550 m
47
700 m
Total/mean
Sttation
13
13
14
12
52
13
Mean isotopic
compossition/‰
δ18O
δD
-6.1
-28.6
-6.6
-31.8
-7.0
-35.6
-7.8
-43.4
-6.9
-34.9
-5.9
-29.6
R
Relationship between
b
δ18O
and δD
S
Slope
Intercept
8
8.40
22.92
8
8.69
25.40
8
8.92
26..64
8
8.94
24..77
8
8.74
24..93
77.56
15.3
33
3.1.2 Surfface of
Glacie
er No.12
We had only few
samples ab
bove 4800 m in
Glacier No
o.12, due to
o the
precipitatio
on
colleection
system destroyed
d
b
by
a
strong wind
w
and the
consequentt alteration of
o the
fieldwork schedules. The
analyses are
a based on
n the
samples co
ollected at 43
350 m,
4450 m, 4550 m and 4700
m at Glacieer No.12. In order
comparison
n, some sam
mples
collected around
a
the same
periods att the Qilian
nshan
Station (4
4160 m) were
chosen. Th
he isotopic co
ompositions in precipita
ation
and the reelationships between δ18O and δD are
shown in Table
T
1 and Fiigure 4.
Figure 4 T
The relationsh
hip between
δ18O and δD of precip
pitation at
altitude 435
50 m, 4450 m,
m 4550 m
and 4700 m in the Glaccier No. 12
and paralleeled site the Qilianshan
Station, 416
60 m.
The isotop
pic compositiions of preccipitation in
the Glacier No
o.12 vary fro
om +0.8‰ to -16.9‰
(δ188O) and from
m +24.7‰ to -117.2‰ (δD
D), showing
lesss variability than
t
that colllected at thee Qilianshan
1457
J. Mt. Sci. (2016) 13(8): 1453-1463
-18.0
-16.0
-12.0
-10.0
0
20
d ep th o f firn / cm
Station. It is clearly that a high slopes and
intercepts of the regression lines exist. For the 4
sites, all slopes are larger than 8 whileas at the
Qilianshan Station is 7.56. Study of the isotopic
compositions in the firn pack at the July 1 Glacier
in Heihe River basin (Zhou et al. 2007) deduced
that the high slope of the line reflected the high
gradient of the precipitation.
δ18 O /‰
-14.0
40
60
80
100
120
3.2 Stable isotopic profiles of firn
140
3.3 Stable isotopes in glacial ice
The fluctuation of isotopic composition in the
glacial ice is small, ranging from -10.1‰ to -18.5‰
for δ18O and from -60.4‰ to -137.2‰ for δD
(Table 2). Alpine glaciers are complex water
storage compartments that to some degree behave
isotopically and chemically like a well mixed lake
(Moser and Stichle 1980). In addition, the isotopic
composition shows no depletion trend with the
increase of altitude. Since we collected samples the
surface 5 cm layer of the glacier ice, it can be
induced that the difference of isotopic values is
partly due to the different ablation conditions as air
temperature changes.
For the δ18O vs δD diagram (Figure 6),
samples align following the equation:
δD=7.77δ18O +15.70 (R2=0.83; n=32) (2)
The slope of the line (7.77) indicates that the
glacier ice has been undergone evaporation when
exposed to the air and sunlight.
1458
160
(a)
-60.0
-80.0
δ D /‰
The δ18O values along the whole vertical profile
at the firn vary from -10.9‰ to -16.7‰, with an
average of -12.8‰. The δ18O values in the first (05cm) and the second layer (6-20cm) are closer to
the latest two snowfalls, reflecting the isotopic
characteristic of the precipitation. Controlled by
the melting, refreezing and percolation, the
redistributed isotopic compositions results in
heavier isotopes enriched in the bottom of the
snow layers. After several percolation cycles, the
δ18O values keep nearly steady at the bottom layers
in the firn (Figure 5 (a)).
Compared with the precipitation on the glacier,
the slope of regression line in the firn is slightly
lower (Figure 5(b)). It indicates that evaporation
occurs during the firn formation processes.
-100.0
-120.0
-18.0
δD = 8.27δ18 O + 21.68
R2 = 0.99
-16.0
-14.0
-12.0
-10.0
δ18 O/‰
(b)
Figure 5 The variation of δ18O (a) and the δ18O vs δD
diagram (b) in a vertical firn profile.
3.4 Stable isotopes in melt water
The variation of isotopic composition in the
melt water, ranging from -10.7‰ to -16.9‰ (δ18O)
and from -61.1‰ to -122.1‰ (δD) (Table 3), is
generally smaller than that in glacier ice. The stable
isotopes in melt water indicates big amount of
recharging from snow/ice melt water produced at
different altitudes along glacier stream. The
mixture processes induced the stabilized isotopic
values in stream water.
The relationship between δ18O and δD in melt
water (Figure 7) is characterized by a high slope
and intercept, in consistent with that of the
precipitation at Glacier No.12. As we have
mentioned above, the melt water is a kind of
mixture. The current year’s snowmelt and summer
precipitation can be trapped within the glacier in
J. Mt. Sci. (2016) 13(8): 1453-1463
3.5 Stable isotopes in stream
water
The stream water at the LGC was
mainly originated from the recharging
from snowmelt in spring, glacier melt in
summer, precipitation and groundwater
during the whole ablation seasons. Our
runoff
observation
system
was
destroyed by a flood in July, so the
discharge weighted mean isotopic values
were not obtained. The overall isotopic
composition of the stream waters ranges
from -11.7‰ to -15.5‰ for δ18O, and
from -79.7‰ to -108.1‰ for δD,
respectively (Figure 8), with a mean
value of -13.3‰ for δ18O and -89.7‰ for
δD, which are much similar with the
melt water. The δ18O peaks occurred in
July and September while the lowest
values in June. The δ18O vs δD diagram
is distinctly characterized by a high
slope of 9.26.
Table 2 Characteristics of isotopic composition in glacial ice in
Laohugou Glacial Catchment
Sampling
Sample
site elevation number
4300 m
4400 m
4500 m
4600 m
4700 m
Total
6
7
7
6
6
32
Isotopic composition/‰
Mean
Max.
Min.
δ18O δD
δ18O δD
δ18O δD
-13.5 -90.1 -12.0 -79.0 -14.7 -102.5
-13.0 -86.2 -10.1 -65.5 -15.0 -105.4
-13.5 -88.2 -11.8 -72.6 -15.1 -106.5
-12.5 -79.6 -10.1 -60.4 -15.8 -113.6
-15.1 -103.1 -13.6 -86.3 -18.5 -137.2
-13.5 -89.5 -10.1 -60.4 -18.5 -137.2
Table 3 Characteristics of isotopic composition in melt water in
Laohugou Glacial Catchment
Sampling
Sample
site elevation number
4250 m
4300 m
4400 m
4500m
4600 m
4700 m
Total
13
6
7
6
6
4
40
Isotopic composition/‰
Mean
Max.
Min.
δ18O
δD
δ18O
δD
δ18O
δD
-13.2 -89.1 -10.8 -66.7 -14.9 -104.8
-13.7 -89.8 -10.7 -61.1 -15.7 -106.0
-14.0 -92.9 -11.8 -72.7 -15.8 -107.6
-14.2 -95.8 -12.3 -75.1 -15.5 -108.3
-14.4 -100.3 -13.0 -87.6 -16.2 -111.7
-15.0 -104.3 -13.5 -93.0 -16.9 -122.1
-14.1 -95.4 -10.7 -61.1 -16.9 -122.1
-40.0
-80.0
δD/‰
fissures to be frozen during winter, the
melting of the glacier can release water
that has been added from recent inputs
together with the stored water from
decades to centuries (Cable et al. 2011).
However, if one assumes that the glacier
mass is an integrator, then melt water
from the glacier may be attenuated
isotopically relative to seasonal and
inter-annual variations in meteoric
waters.
-120.0
δD = 7.77δ18 O + 15.70
R2 = 0.83
-160.0
-19.0
-17.0
-15.0
-13.0
-11.0
-9.0
δ18 O/‰
Figure 6 The relationship between δ18O and δD in glacial ice.
-40.0
3.6 Stable isotopes in
groundwater
-80.0
δD/‰
As for the groundwater, the δ18O
and δD values in spring show less
variability, ranging from -11.7‰ to
-10.1‰ and -57.7‰ to -75.3‰, and
with average of -10.6 ‰ and -68.1 ‰,
respectively. The less seasonal variation
indicates that the isotopic compositions
of groundwater are insignificantly
correlated with the melt water and the
precipitation. It suggests that the
processes of the precipitation and melt
-60.0
-100.0
δD = 8.77δ18 O + 28.00
R2 = 0.95
-120.0
-140.0
-18.0
-16.0
-14.0
-12.0
-10.0
δ18 O/‰
Figure 7 The relationship between δ18O and δD in melt water.
1459
J. Mt. Sci. (2016) 13(8): 1453-1463
water infiltrating into the subsurface results in
smoothing effects on changes of the seasonal
isotopic compositions.
-5.0
(a)
-5.5
δ 1 8 O /‰
-6.0
-6.5
-7.0
-7.5
-8.0
4100
δ18 O = -0.0037ALT+ 9.9395
R2 = 0.94
4200
4300
4400 4500
Altitude/m
4600
4700
4800
-13.0
(b)
-13.5
δ 1 8 O /‰
-14.0
-14.5
-15.0
-15.5
4200
δ18 O = -0.0034ALT+ 1.0591
R2 = 0.95
4300
4400
4500
Altitude/m
4600
4700
4800
Figure 8 The δ18O/altitude gradients for precipitation
(a) and melt water (b).
and August, 2013) from 3 automatic weather
stations at 4160 m, 4550 m and 4990 m, a gradient
of air temperature vs. altitude of -0.64°C/100 m
existed. The isotopic results of the mean δ18O
values in precipitation at the Qilianshan Station,
4350 m, 4450 m, 4550 m and 4700 m at the
Glacier No. 12 show a clear-cut relationship with
the altitude, approaching a linear correlation with
the line slope of -0.37‰ /100 m (Figure7(a)).
Modern worldwide gradients of δ18O vs.
altitude range from − 0.10‰ to −1.14‰ per 100 m
(Poage and Chamberlain 2001). Our result is
consistent with other reports of Muztagata Glacier
(-0.37‰~-0.39‰ /100 m, Li et al. 2006), Nevado
de Copa Glacier (-0.35‰ /100m, Niewodniczanski
et al. 1981), Kōhi Langari Jam Glacier (-0.34‰
/100 m, Niewodniczanski et al. 1981) and the
Yarlung Zangbo River Basin (-0.34‰ /100 m, Liu
et al. 2007).
Generally, the mean stable isotopic ratios in
melt water increase with decreasing altitude on a
glacier due to temperature effect, especially for
large glaciers (He et al. 2000). Values of δ18O
plotted against altitudes yield a best-fit line with a
slope of −0.34‰ per 100 m for melt water samples
collected between 4250 m and 4700 m. The slope is
very close to the precipitation, indicating that melt
water is highly mixed by the precipitation.
4.2 The high slope of δ18O vs δD diagram
As we have mentioned above, the slopes of
vs δD diagram at the glacier sites for
precipitation and firn are high. Rayleigh models are
based on the preferential condensation and
removal from the system of isotopically heavy
molecules of atmospheric vapor. Adiabatic and
isobaric Rayleigh models have been invoked
repeatedly to explain the dependency on the
temperature of the isotopic variations of
precipitation (Dansgaard 1964; Gat 1996;
Gonfiantini et al. 2001). As temperatures below
zero, occurrence of the supercooled liquid water is
assumed. Ice formation, if occurring, is supposed
to be taken place by freezing the water droplets
without affecting the isotopic composition.
Based on the Rayleigh fractionation theory,
Wang et al. (2009) determined the slope equation
of the meteoric water line as follows
δ18O
4
Discussion
4.1 The δ 18O/altitude gradients
The altitudinal effect has been reported at
many major mountain belts around the world
(Ambach et al. 1968; Niewodniczanski et al. 1981;
Gonfiantini et al. 2001; Poage and Chamberlain
2001; Li et al. 2006). This is due to the progressive
condensation of atmospheric vapor and rainout of
the condensed phase, which will occur when air
masses climb up along the slopes of high
mountains and cool off as a consequence of
adiabatic expansion (Gonfiantini et al. 2001). This
finding is still a result of the temperature effect (Li
et al. 2006).
According to the observations (between May
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J. Mt. Sci. (2016) 13(8): 1453-1463
s»
aD -1
a O -1
(3)
18
where αD and a 18 O are the fractionation factors of
D and 18O, respectively. We can see that the slope is
primarily determined by the fractionation factors
of D and 18O, which are generally associated with
the change of air temperature and humidity.
To calculate the fractionation factor α, we
convert it into an enrichment factor ε. The
relationship between the enrichment and the
fractionation factors expresses as
(4)
e = (a - 1)103
The enrichment factor is mainly composed of
two parts, i.e., the equilibrium fractionation factor
ε* and kinetic fractionation factor εk: e = e * + e k
The calculation of ε* for D and 18O (Braud et al.
2005) lists as
103
103
e *D = 24.844( )2 - 76.248 + 52.612 (5)
T
T
3
10
(6)
e *18O = 1.137( )2
T
where T is the air temperature (K).
εk is given by Gonfiantini et al. (1986):
(7)
e k = ck (1 - h)10 -3
Based on above formulas, slopes of meteoric
water line under low temperature conditions are
calculated. The results show that the kinetic
fractionation factor has slight influence on the
slopes. Assuming h=0.9, the relationships between
the temperature and slope are listed in Table 4.
Table 4 The relationship between the temperature
and slope of meteoric water line under low
temperature conditions
Temperature/°C
0
-5
-10
-15
-20
-25
-30
-35
-40
Slope
6.99
7.2
7.41
7.62
7.84
8.06
8.28
8.51
8.73
The air temperature on the glacier surface is
very low. According to the observation at 4550 m
and 4990 m, the mean air temperatures are -0.6°C
and -2.6°C during May to August, the warmest
season in the whole year. The minimum daily air
temperature reaches -30°C even during this period.
Low temperature results in the high slope of the
δ18O vs δD diagram in the precipitation and firn.
On the other hand, the isotopic fractionation in
the subsequent vapor condensation on the ice
surface, deviates from the equilibrium value because
the light molecules 1H216O may be privileged for
their higher diffusivity in air (Jouzel and Merlivat
1984). This effect tends to offset the thermodynamic
equilibrium by which the isotopically heavy
molecules are preferentially fixed in condensed
phases, and may determine a significant increase of
the deuterium excess, because of the relatively small
difference in diffusivity coefficients between HD16O
and H218O. The high deuterium excess leads to high
slope and intercept.
5
Conclusions
Variations of the stable oxygen and hydrogen
isotope in different water archives in Laohugou
Glacial Catchment, Shulehe River Basin are
analyzed to provide the basic isotope data for the
application of environmental isotopes in
hydrological investigations and assess the impact
of different factors on water cycle.
The isotopic composition of precipitation in
the Qilianshan Station show remarkable variability,
indicating that the precipitation formation
processes in this region are complicated. The mean
δ18O values of the precipitation at the Qilianshan
Station, 4350 m, 4450 m, 4550 m and 4700 m at
the Glacier No. 12 show a clear-cut relationship
with altitude which closely approaches a linear
correlation with the slope of -0.37‰ /100 m. Our
result contributes to the development of more
reliable hydrological models in this area. Because
of the percolation and mixture, the variability of
isotopic composition in firn, glacial ice, melt water,
stream water and groundwater show more and
more less significant. The isotopic composition at
the bottom of the firn is nearly steady. The isotopic
composition of stream water is much similar with
the melt water, indicating that the stream water is
mainly recharged by the melt water.
The δ18O and δD correlation is observed as
δD=7.80δ18O+16.87 in precipitation at the
Qilianshan Station. Correspondingly, the slope of
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J. Mt. Sci. (2016) 13(8): 1453-1463
δ18O vs δD diagram, with an average of 8.74, is
obtained from the precipitation on the Glacier
No.12. The high slope is attributed to the low
temperature and the isotopic fractionation on the
glacier surface.
Acknowledgements
This research was conducted within the
projects of National Major Scientific Research
Project (2013CBA01806), National Natural Science
Foundation of China (Grant Nos. 41271085,
41130641) and open fund project of State Key
Laboratory of Cryospheric Science (SKLCS-OP2013-05). We are very grateful to the staff of the
Qilian Shan station of Glaciology and Ecologic
Environment,
Cold
and
Arid
Regions
Environmental and Engineering Research Institute,
Chinese Academy of Sciences, for the samplings
and supplying meteorological data. We thank Xu
Rui for the measurements of isotopic composition
in the State Key Laboratory of Cryospheric Science,
Cold and Arid Regions Environmental and
Engineering Research Institute, Chinese Academy
of Sciences.
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