Preparing Environmental Isotopes Databases for Determining Groundwater and Surface Water Relationships in Iraq

Abstract

This study is prepared to constitute an isotopic database of Deuterium (δ2H) and Oxygen 18 (δ18O) for groundwater and its relationship with the isotopic footprint for surface water The 311 samples of groundwater were collected between 2013 and 2021 and analyzed using a Liquid-Water Isotope Analyzer (LWIA). The study covered different regions of Iraq, including the Western region (Al-Anbar), Northern region (Kirkuk), Central Region (Samarra, Shirqat, Khanaqin, Baghdad, Karbala, Najaf, Diyala), and Southern region (Samawah، Nasiriya, Diwaniyah, Basra). In addition, the 208 surface water samples were collected from different sources including (the Tigris, Euphrates, Diyala, and Shatt Al-Arab) rivers during the same period. The isotopic measurements showed a linear relationship between the two stable isotopes (δ18O, δ2H) with a slope of 7.38 and an excessive deuterium reach to (-9.4597) compared with the excessive value of the domestic rain line of (14.15). It is defined according to the local meteoric water line equation (LMWL δ2H = 7.7035 * δ18O + 14.158), which characterized a fingerprint of groundwater and showed the impact of the climate on it. The study showed a significant interaction between groundwater and surface water of the Tigris and Euphrates Rivers in the Southern region of Iraq, due to the aquifers in these areas being close to the surface, with depth ranges between (6 – 40 m), and high porosity that simulative of the sedimentary plain characterization. The samples of these areas calculated the highest and the lowest value for δ2H of (12.04‰) and (-36.14‰) respectively. A similar result was found in the western regain. This region recorded the highest value of δ2H (-4.42‰) and the lowest value (-42.2‰), the depth of the wells ranged between (2 – 22 m), which explains the relationship between the groundwater and the Euphrates River. However, the study indicated that the wells in Diyala Governorate, have depth ranges between (10 – 70 m) and were not affected by rainwater or Diyala River, with the highest and lowest value for δ2H of (4.66‰), (-38.54‰), respectively. On the other hand, the highest and lowest values of δ2H were recorded in the Khanaqin area with a value of (-13.48‰) and (-32.67‰) respectively.