Comparison of Relationship Between the Concentrations of Water Isotopes in Precipitation in the Cities of Tehran (Iran) and New Delhi (India)

Abstract

The term ‘Tracerhydrology’ is used as a short expression for the use of tracers in hydrology. It is understood as an advanced method that allows for an integrative investigation of the hydrologic system (Leibundgut et al. 2009). Environmental and artificial tracer can be used for investigating the movement of water in the hydrological cycle. Artificial tracers are described as those elements deliberately injected into the hydrologic system (Luhua et al. 2010). By studying the motion of the injected particles, one may measure some physical processes of hydrologic system such as the escape of water from a reservoir (Evans 1983). There are more than 1,000 isotopes known for about 92 chemical elements. Most of these isotopes are called as environmental isotopes which are either stable or unstable (Leibundgut et al. 2009). The stable isotopes of hydrogen and oxygen are recognized as important traces in hydrological cycle. The heavy stable isotopic components of water, HD¹⁶O and H₂O¹⁸, occur in natural waters in concentration of about 320 and 2,000 ppm, respectively (Evans 1983). The variation of isotopic concentration is due to fractionation caused by phase changes, evaporation, condensation, precipitation, and snow and ice formation (Chidambaram et al. 2009). Isotopic fraction is affected by meteorological factors such as temperature and altitude change (Leibundgut et al. 2009). The small variations of isotopic concentrations are usually measured by mass spectrometry. In general, the isotopic abundance ratios are expressed as parts per mil of their deviations as given by (Vienna Standard Mean Ocean Water, VSMOW)

$$ \delta =\frac{R_{\mathrm{sample}}-{R}_{\mathrm{SMOW}}}{R_{\mathrm{SMOW}}}\times 100{\mbox{\fontencoding{U}\fontfamily{wasy}\selectfont\char104}} $$

where R refers to the isotopic ratio (D/H) or (¹⁸O/¹⁶O) (Machavaram and Krishnamurthy 1995). In 1954, the International Atomic Energy Agency (IAEA), in co-operation with the World Meteorological Organization (WMO), conducted a worldwide survey of oxygen and hydrogen isotope content in precipitation. Since 1961, more than 780 meteorological stations in 101 countries have been monthly collecting precipitation samples. These samples are analyzed at the isotope hydrology laboratory (IAEA 2006).