Electrical properties of the lithosphere in the western desert, Egypt, using magnetotelluric sounding

<p>We present electrical resistivity models of the crust and upper mantle estimated from 2D inversions of broadband magnetotellurics (MT) data acquired from two profiles in the western desert of Egypt, which can contribute to the understanding of the structural setup of this region. The first profile data are collected from 14 stations along a 250 km profile, in EW direction profile runs along latitude ~25.5°N from Kharga oasis to Dakhla oasis. The second profile comprises 19 stations measured along a 130 km profile in NS direction centered at longitude 28°E and crossing the Farafra. The acquisition for both profiles continued for 1 to 3 days at each station, which allowed for the calculation of impedances for periods from 0.01 sec up to  4096 sec at some sites. The wide frequency band corresponds to a maximal skin depths of up to 150 km that can provide penetration to the top of the asthenosphere. The inversion models display high-conductivity sediments cover at the near surface (<1-2 km), which can be associated with the Nubian aquifer. Along the EW-profile from Kaharge to Dhakla, the crustal basement is overly highly resistive and homogeneous und underlain by a more conductive lithospheric mantle below depths of 30-40 km. Along the N-S profile across Farafra, only the southern portion exhibits a highly resistive crust, whereas beneath Farafra northwards, moderate crustal conductivities are encountered. A comparison has been made between the resultant resistivity models with the 1° tessellated updated crust and lithospheric model of the Earth (LITHO1.0) which was developed by <em>Pasyanos, 2014</em> on the basis of seismic velocity data. The obtained results show a remarkable consistency between the resistivity models and the calculated crustal boundaries. Especially at the Kharga-Dakhla profile a clear matching can be noticed at the upper and lower boundaries of a characteristic anomaly with the Moho and LAB boundaries respectively.</p>

Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa

The Nubian Sandstone Aquifer System in Northeast Africa and the Middle East is a huge water resource of inestimable value to the population. However, natural radioactivity impairs groundwater quality throughout the aquifer posing a radiological health risk to millions of people. Here we present measurements of radium isotopes in Nubian Aquifer groundwater from population centers in the Western Desert of Egypt. Groundwater has 226Ra and 228Ra activities ranging from 0.01 to 2.11 and 0.03 to 2.31 Bq/L, respectively. Most activities (combined 226Ra + 228Ra) exceed U.S. EPA drinking water standards. The estimated annual radiation doses associated with ingestion of water having the highest measured Ra activities are up to 138 and 14 times the WHO-recommended maxima for infants and adults, respectively. Dissolved Ra activities are positively correlated with barium and negatively correlated with sulfate, while barite is approximately saturated. In contrast, Ra is uncorrelated with salinity. These observations indicate the dominant geochemical mechanisms controlling dissolved Ra activity may be barite precipitation and sulfate reduction, along with input from alpha-recoil and dissolution of aquifer minerals and loss by radioactive decay. Radium mitigation measures should be adopted for water quality management where Nubian Aquifer groundwater is produced for agricultural and domestic consumption.

Sustainable Agriculture Development in the Western Desert of Egypt: A Case Study on Crop Production, Profit, and Uncertainty in the Siwa Region

The Egyptian government initiated a development project in 2015 to reclaim 1.5 million acres with the primary goal of increasing agricultural production. Siwa is one of these areas in the Western Desert of Egypt, with 30,000 acres using groundwater from the Nubian Sandstone Aquifer System (NSAS). This study investigates if government goals are achievable in the next 20 years to secure the food and water needs of the Siwa region. Results show that total required crop areas are 7154 and 6629 acres in winter and summer, respectively. These areas are less than 17,010 acres of available area for cultivation (Av). The estimated total water use is 40.6 million cubic meters (MCM), which is less than the 88 MCM that is considered available groundwater in the Nubian Aquifer System (NAS). Due to available capacity in Siwa, an optimization model is used to maximize crop production considering government policies. The Autoregressive Integrated Moving Average (ARIMA) model was applied to predict production costs and sell prices of cultivated crops. Analysis included different scenarios beyond government-recommended approaches to identify ways to further expand agriculture production under sustainable conditions. Results provide valuable insights to the ability to achieve government goals from the project and changes that may be required to enhance production.

Hydrochemical and isotopic characteristics of thermal groundwater at Farafra Oasis, Western Desert, Egypt

Groundwater from the Nubian sandstone aquifer at Farafra Oasis in the Western Desert of Egypt has been investigated using chemical tracers and environmental isotopes to clarify the hydrochemical features of this aquifer. The majority of the collected samples are characterized by Ca-Cl water type, which may be attributed to dissolution of the carbonate-rich sediments. Calculated saturation indices show that the main hydrogeochemical processes were the dissolution of carbonates and evaporites and the precipitation of Fe-rich minerals. Temperatures calculated using the K-Mg geothermometer show that the reservoir temperature ranges from 58°C to 121°C. The groundwater samples have δD and δ18O values similar to the isotopic content of the Nubian aquifer palaeowater in the Western Desert. Additionally, the isotopic composition suggests that there is no active potential current recharge from the local precipitation. Gamma spectrometry of 226Ra, 232Th and 40K activities indicates that the groundwater of the Nubian aquifer is safe with respect to radioactivity. Groundwater in Farafra Oasis is the main source of irrigation and drinking water for local residents. All the samples are excellent for irrigation uses for all types of crops. It is suggested that the water samples may require some treatment regarding the high iron content before usage as drinking water.Supplementary material: Locations of the collected groundwater samples and their Na-K-Mg ternary cation plot is available at https://doi.org/10.6084/m9.figshare.c.4938252