Application of Isotopic Techniques for Tracing High Salinity Levels in Shatt Al-Arab River, Southern Iraq

Shatt Al-Arab River, which originates from the confluence of Tigris and Euphrates rivers and emptied into the Arabian Gulf, provides lifeline benefits shared by millions of people living in its basin. The water quality of the river has deteriorated significantly due to increasing salinity levels over the last few decades. A lot of research dealing with seawater intrusion from the Arabian Gulf into Shatt al-Arab has been conducted, but conclusions as to the exact extent of such intrusion and its contribution to the river salinity have been controversial. Therefore, the main goal of this study was to apply isotopic techniques to understand and identify the contribution and extent of seawater intrusion to the river salinity in this coastal area. Oxygen isotope δO¹⁸ and salinity measurements were made on water samples collected during dry season (July and August, 2014 and 2015) as well as wet season (January and February, 2014 and 2015) at 16 stations along the river. Results revealed that enriched δO¹⁸ and high salinity during the dry season is consistent with decreased river discharge and high seawater intrusion, whereas depleted δO¹⁸ and low salinity during the wet season can be attributed to increased river discharge as well as high rainfall. Analyses displayed that seawater intrusion was 22% in July, 24% in August, 11% in January, and 9% in February. Analyses also revealed that during the dry season, when river discharge was low and sea level was high, a salt wedge was estimated to extend 110 km upstream from the river mouth; on the other hand, during the wet season when the river discharge was high and sea level was low, a salt wedge extension was restricted to less than 50 km upstream from the river mouth.