Oxygen and hydrogen stable isotopes as recharge indicators, Central Nile Delta Quaternary aquifer, Egypt

This work aims to utilize oxygen and hydrogen stable isotopes as tracers for determining the groundwater sources of recharge in the central Nile delta. The analyzed water samples were collected from canals and drains as surface water, soil water and shallow, intermediate and deep zones of the groundwater. The isotopic data indicated that surface water samples have higher isotopic content than recent Nile river water (8 18O = 2.39 parts per thousand and 82H = 22 parts per thousand) which reflect the influence of an evaporation process that takes place in surface water bodies during its flow. Soil water samples were affected by evaporation process during water infiltration via soil. It was estimated that soil water samples have higher enrichment isotopic contents than groundwater and less than surface and recent Nile water. Studied groundwater is composed of mixed source from groundwater recharged before and that recharged after High Dam construction. Few groundwater samples have depleted isotopic content which suggested a mixing source between the rainwater and the Nile River water before High Dam construction. The evaporation is indicated in the shallow groundwater by the deviation away from the global meteoric line. In the deep groundwater, more deviation from global meteoric line was noticed which reflects the effect of mixing between freshwater and seawater. The intermediate groundwater samples average line showed an intermediate deviation indicating the effect of both evaporation and seawater intrusion. (c) 2022 The Author(s). Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study utilizes oxygen and hydrogen stable isotopes as tracers to determine the sources of groundwater recharge in the central Nile delta. The isotopic data indicate that surface water is heavily influenced by evaporation, while soil water and groundwater have lower isotopic contents. The studied groundwater is found to have mixed sources, with a combination of pre- and post- High Dam construction recharge. The influence of both freshwater and seawater mixing is observed in the deep groundwater, while the shallow groundwater shows signs of evaporation.