Abstract
The LMWL was re-plotted from the isotopic analysis data (δ2H and δ18O) for rainwater samples collected from three stations in Baghdad city in the current study and data from previous studies. Four samples of shallow groundwater and five samples from the Tigris River were isotopically analyzed for 2H and 18O using a Liquid-Water Stable Isotope Analyzer (LWSIA). The samples were collected from the Al-Jaderia area within the University of Baghdad. The analysis was done against Vienna Standard Main Oceanic Water (VSMOW). The isotopic composition of groundwater ranges between -43.91‰ and -37.57 ‰ for 2H with an average of -40.06±2.7 ‰, while it ranges between -6.28‰ and -6.01‰ for 18O with an average of -6.14±0.1‰. These values are slightly more depleted compared to the isotopic composition of the Tigris River water (-38.79 ‰ to -37.87 ‰) for 2H with an average of -38.05±0.9‰ and between -6.23‰ to -5.11 ‰ for 18O with an average of -5.74±0.4 ‰. This is a logical result since the river is usually fed with fresh new rainwater, which isotopically is relatively more enriched. The current study confirms that the Local Meteoric Water Line (LMWL) has a formula of δ 2H‰ = 7.5 δ 18O‰ + 13. The LMWL is located above the Global MWL by +13.9‰ toward the Eastern Mediterranean (EMMWL δ2H‰ = 8 δ 18O‰ + 22), indicating the origin rainwater from the Mediterranean Sea and the Atlantic Ocean. The groundwater and surface water isotopic compositions were below the LMWL due to the evaporation of shallow groundwater. There is interconnection between river water and groundwater, directly or by recharge from irrigation water. Iraq may have two different MWLs, one for the northeastern region and the other for the middle, western and southern Iraq. The MWL for the northern eastern region of Iraq is close to that of the EMMWL, indicating Mediterranean climate and vapor source, while the rest of the areas of Iraq have MWL with various isotopic compositions affected by more hot climate in these regions and by the continental tropical air masses.
Published Version
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