Environmental Engineering Reference
In-Depth Information
Results and Discussion
The isotopic data in Tehran station shows a wide variability with ʴ
18
O, ranging
from −15.34 ‰ to 9.3 ‰, while the ʴD values vary from −114.2 ‰ to 55.8 ‰,
respectively. In New Delhi station, the ʴ
18
O values vary from −15.3 ‰ to 8.2 ‰,
and ʴD values range from −120 ‰ to 55.8 ‰. These changes are controlled by
hydrological parameters. In general, values of isotope ratios are affected by
different factors including temperature, precipitation, altitude, latitude and sea-
sonal effect (Vodila 2011; Leibundgut et al.
2009
; Kumar et al.
2010a
). A sea-
sonal oscillation of stable isotope ratios is often observed as a result of
temperature (Leibundgut et al.
2009
). In this paper, the effects of temperature on
precipitation isotope data in the stations of Tehran and New Delhi have been
investigated and compared.
Local Meteoric Water Line
In order to study the overall stable isotopic characteristic, the isotope concentration
values for all seasons are plotted. In general, there is a linear relationship between
ʴ
18
O and ʴD, which in global precipitation, deines the global meteoric water line
(GMWL) (Craig
1961
). The GMWL was originally deined as ʴD = 8 × ʴ
18
O + 10. In
each area, the LMWL may be defined similar to GMWL. Figure
1
shows the ʴD and
ʴ
18
O values of the monthly precipitation samples collected in the stations of Tehran
and New Delhi. The variation in the slope and intercept of LMWL line strongly
depends on the weather condition in each area (Craig
1961
).
By fitting a straight line on isotopic data collected in Tehran and New Delhi sta-
tions, LMWL equations are obtained from the present study as follows.
δ
18
O(%
0
)
0
5
10
-15
-10
-5
50
GMWL:δD = 8 δ
18
O+10
New Delhi
δD= 6.483 δ
18
O+3.060
Tehran R
2
= 0.948
Tehran
0
δD= 7.022 δ
18
O+3.057
New Delhi :R
2
= 0.947
-50
-100
Fig. 1
The LMWL derived from the stable isotope composition in precipitation in the cities of
Tehran and New Delhi
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