Early Pleistocene stratigraphy, sedimentary environments, and formation contexts at Dmanisi in the Georgian Caucasus.

The Early Pleistocene site of Dmanisi is now well known for its large number of fossils of early Homo erectus as well as associated artifacts and faunal remains, recovered mainly in pipe-related geologic features. Testing in the M5 unit 100 m to the west of the main excavations revealed a thick stratigraphy with no evidence of pipes or gullies, indicating that the geologic record at Dmanisi included spatially distinct sedimentary environments that needed further investigation. Here we report the results of a geoarchaeological program to collect data bearing on contexts and formation processes over a large area of the promontory. That work has defined over 40,000 m2 of in situ deposits with artifacts and faunas. Stratum A ashes bury the uppermost Mashavera Basalt, which we have dated to 1.8 Ma in the M5 block. The Stratum A deposits contain stratified occupations that accumulated quickly and offer good potential for recovery of in situ materials. Stratum B1 deposits above the A/B unconformity include all of the pipe and gully facies at Dmanisi, reflecting a brief but very intense phase of geomorphic change. Those deposits contain the majority of faunas and all of the hominin fossils. B1 slope facies offer excellent formation contexts away from the piped area, and all B1 deposits are sealed by Stratum B2 over the whole promontory. Strata B2 to B5 register a return to slope facies, with no further evidence of pipes or gullies. Those deposits also present excellent contexts for recovery of in situ occupations. Overall, Dmanisi's geologic history preserves an exceptional record of the activities and environmental context of occupations during the first colonization of Eurasia.

Integrated Hydrogeological, Hydrochemical, and Isotopic Assessment of Seawater Intrusion into Coastal Aquifers in Al-Qatif Area, Eastern Saudi Arabia.

Seawater intrusion (SWI) is the main threat to fresh groundwater (GW) resources in coastal regions worldwide. Early identification and delineation of such threats can help decision-makers plan for suitable management measures to protect water resources for coastal communities. This study assesses seawater intrusion (SWI) and GW salinization of the shallow and deep coastal aquifers in the Al-Qatif area, in the eastern region of Saudi Arabia. Field hydrogeological and hydrochemical investigations coupled with laboratory-based hydrochemical and isotopic analyses (18O and 2H) were used in this integrated study. Hydrochemical facies diagrams, ionic ratio diagrams, and spatial distribution maps of GW physical and chemical parameters (EC, TDS, Cl-, Br-), and seawater fraction (fsw) were generated to depict the lateral extent of SWI. Hydrochemical facies diagrams were mainly used for GW salinization source identification. The results show that the shallow GW is of brackish and saline types with EC, TDS, Cl-, Br- concentration, and an increasing fsw trend seaward, indicating more influence of SWI on shallow GW wells located close to the shoreline. On the contrary, deep GW shows low fsw and EC, TDS, Cl-, and Br-, indicating less influence of SWI on GW chemistry. Moreover, the shallow GW is enriched in 18O and 2H isotopes compared with the deep GW, which reveals mixing with recent water. In conclusion, the reduction in GW abstraction in the central part of the study area raised the average GW level by three meters. Therefore, to protect the deep GW from SWI and salinity pollution, it is recommended to implement such management practices in the entire region. In addition, continuous monitoring of deep GW is recommended to provide decision-makers with sufficient data to plan for the protection of coastal freshwater resources.

Evaluating Diatomaceous Earth for Long-Term Use in Hydrogen Storage.

Efficient hydrogen storage is essential for its use as a sustainable energy carrier. Diatomaceous earth, a high-surface-area siliceous geomaterial, shows potential as a physisorption material for hydrogen storage. This study analyzes diatomaceous earth's long-term characteristics when subjected to high-pressure hydrogen injection. The diatomaceous earth was subjected to a hydrogen pressure of 1200 psi for a period of 80 days at room temperature. Neither notable morphological or mineralogical changes were observed. Nevertheless, there was a slight reduction in fine particles and a slight increase in larger particles. The Brunauer-Emmett-Teller (BET) surface area decreased slightly with a significant decrease in pore width. However, the hydrogen adsorption at 77 K temperature was increased significantly (45.5%) after the hydrogen storage test. Moreover, there was a delayed release of molecular water as the temperature increased. These changes suggest that a condensation reaction has occurred involving some of the opal-A silanol groups (Si-O-H), producing molecular water. Bonding through siloxane bridges (Si-O-Si) results in a significant decrease in pore width and increased hydrophobicity (i.e., the interaction between diatomaceous surface and H2 was increased), thereby enhancing hydrogen adsorption capacity. These findings indicate that diatomaceous earth holds promise as a material for hydrogen storage, with the potential for its hydrogen adsorption capacity to improve over time.

Hydrochemical Characterization, Geothermometry, and Origin of Ain Al-Harrah Hot Spring and Its Relationship to Al-Lith Geothermal System, Saudi Arabia.

The Al-Lith geothermal field in western Saudi Arabia is a characteristic medium-high enthalpy geothermal system, exhibiting features associated with tectonic activities linked to the Red Sea rifting. Ain Al-Harrah hot spring is located in the Al-Lith field, with discharge temperatures varying from 56 to 81 °C. The determination of water temperature and composition in a geothermal reservoir is critical to the design of utilization strategies, surface production facilities, and choice of materials. This research presents a comprehensive hydrochemical characterization of the Ain Al-Harrah hot spring and its relationship with the underlying geothermal system. This study was conducted in two main phases; first, the fieldwork involved the collection of water samples from the hot spring, measuring the temperature, pH, and electrical conductivity (EC) of the water. The second phase involved laboratory analyses of the collected samples, including major and trace element analyses, isotopic analysis, and geothermometry. The dominant hydrogeochemical processes in the region were determined by analyzing the hydrochemistry of the water samples. Thermal waters analyzed exhibited high concentrations of Na+ (410-463 mg/L), HCO3 - (64.48-90 mg/L), and Cl- (472.76-581.95 mg/L), intermediate levels of K+ (50.2-93.0 mg/L), and low levels of Mg2+ (1.27-2.04 mg/L). The total dissolved solids (TDS) concentration ranges between 1830 and 2055 mg/L. The hot spring is categorized as Na-HCO3 type facies that are moderately alkaline, with pH values ranging between 7.9 and 8.2. Analysis of trace element concentrations revealed that the hydrochemical processes were primarily governed by the abundance and solubility of trace elements in the rocks surrounding the hot spring, the pH, and the temperature of the hot spring water. The stable isotope data for δD (-12.36 to 15.21%) and δ18O (-2.84 to -3.38%) provided evidence that the thermal spring is of meteoric origin. Based on Na-K-Ca, K2/Mg, and quartz geothermometers, the temperature range of the reservoir was determined to be between 150 and 205 °C. The temperature range suggests a medium-to-high enthalpy geothermal system.

Suitability of treated wastewater for irrigation and its impact on groundwater resources in arid coastal regions: Insights for water resources sustainability.

Water scarcity threatens agriculture and food security in arid regions like Saudi Arabia. The nation produces significant quantities of municipal wastewater, which, with adequate treatment, could serve as an alternative water source for irrigation, thereby reducing reliance on fossil and non-renewable groundwater. This study assessed the appropriateness of using treated wastewater (TWW) for irrigation in a dry coastal agricultural region in Eastern Saudi Arabia and its impact on groundwater resources. Field investigations were conducted in Qatif to collect water samples and field measurements. A multi-criteria approach was applied to evaluate the TWW's suitability for irrigation, including complying with Saudi Standards, the Irrigation Water Quality Index (IWQI), the National Sanitation Foundation water quality index (NSFWQI), and the individual irrigation indices. In addition, the impact of TWW on groundwater was assessed through hydrogeological and isotope approaches. The results indicate that the use of TWW in the study area complied with the Saudi reuse guidelines except for nitrate, aluminum, and molybdenum. However, irrigation water quality indices classify TWW as having limitations that necessitate the use for salt-tolerant crops on permeable and well-drained soils. Stable isotopic analysis (δ2H, δ18O) revealed that long-term irrigation with TWW affected the shallow aquifer, while deep aquifers were minimally impacted due to the presence of aquitard layer. The application of TWW irrigation has successfully maintained groundwater sustainability in the study area, as evidenced by increased groundwater levels up to 2.3 m. Although TWW contributes to crop productivity, long term agricultural sustainability could be enhanced by improving effluent quality, regulating irrigation practices, implementing buffer zones, and monitoring shallow groundwater. An integrated approach that combines advanced wastewater treatment methods, community involvement, regulatory oversight, and targeted monitoring is recommended to be implemented.