Isotopic composition of groundwater resources in arid environments

Abstract

The availability and quality of limited groundwater resources in Egypt are negatively affected by both natural and anthropogenic forces. It is crucial to understand the recharge sources and mechanisms of country-scale aquifers in order to develop sustainable management scenarios for Egypt's groundwater resources. In this study, we compiled all historical hydrogen (δ2H) and oxygen (δ18O) stable isotopic compositions of 1618 ground- and surface-water samples collected for seven major aquifer and reservoir systems in Egypt. These data were then hosted in a public-domain web map application (https://bit.ly/3n9MtrM) that enables users to access, navigate, display, and analyze the isotopic composition of any water sample in Egypt. The developed application and customized web tools were then used to provide improved understanding of the country-wide water resources’ isotopic composition and to investigate the recharge sources and mechanisms of, and provide sustainable management scenarios for, the seven major Egyptian aquifer systems. Results indicate that (1) the alluvial and coastal aquifers are recharged from modern rainfall, floodwaters, and upward leakage from deep aquifers; (2) the Nile Valley and Delta, Moghra, and carbonate aquifers are receiving recharge from the Nile River, modern rainfall, irrigation canals and drains, and upward leakage from deep aquifers; (3) the Nubian aquifer receives modern recharge in areas of higher rainfall or close to surface water reservoirs; and (4) the fractured basement aquifers are recharged from modern rainfall and floodwaters. The developed cost-effective web application will guide locations and techniques for future field data collection; reduce time, efforts, and resources required for field activities; enable improved understanding the country-wide stable isotopic compositions of water resources; enhance understanding of nationwide recharge mechanisms; and enable the scientific community to address country-scale science questions in a unique way.