Mohamed Hamdy Eid a,b*,  Attila Kovácsa and Péter Szűcs aaInstitute of Environmental Management, Faculty of Earth Science, University of Miskolc, 3515, Hungary; [email protected]; [email protected]; [email protected]. bGeology Department, Faculty of Science, Beni-Suef University, Beni-Suef, 65211, Egypt* Corresponding author: Mohamed Hamdy Eid a,b*; [email protected] ORCID: 0000-0002-3383-1826Final Paper Number: H31U-1778  Presentation Type: Poster Session Number and Title: H31U: Frontiers in Water Quality I Poster Session Date and Time: Wednesday, December 13th; 8:30 AM - 12:50 PM PST Location: MC, Poster Hall A-C – South Abstract The current study evaluates the different factors threatening the sustainability of Siwa Oasis including soil salinization, water quality deterioration, water logging, depletion of non-rechargeable water resources and providing water management plan. GIS and remote sensing supported with machine learning were used for change detection in the land cover from 1990 to 2020. The hydrodynamic condition in the deep Nubian sandstone aquifer (NSSA) was investigated using pressure-depth pro le. The groundwater salinity was monitored from 1998 to 2022. Geochemical model using PHREEQC was conducted to detect the types of minerals that have the ability to precipitate in the soil from irrigation water and decrease its permeability. The change detection in the land cover showed rapid increase in the surface area of the salt lakes from 22.6 km2 in 1990 to 60.6 km2 in 2020. The soil salinization increased in the central Siwa Oasis due to evaporation of water logged in the soil. Monitoring the water salinity from 1998 to 2022 showed rapid deterioration in groundwater quality of the Tertiary carbonate aquifer (TCA). The pressure-depth pro le showed that the water in NSSA is over hydrostatic pressure in the eastern and western part of the study area and the central part is under hydrostatic pressure indicating pressure decrease. Chadha diagram and piper diagram showed that the water type changed upward from Ca-Mg-HCO3 in the rst stage in NSSA to Na-Cl type in the last stage in TCA and surface water. The saturation index revealed that the majority of water samples were supersaturated with respect to calcite, dolomite, talc, Ca-montmorillonite, chlorite, gibbsite, illite, K-mica, hematite, chrysotile and kaolinite, while the samples were undersaturated with halite, anhydrite, gypsum, and CO2. The irrigation water quality indices showed that NSSA is suitable for irrigation purposes while TCA is not suitable for irrigation regarding magnesium hazards (MH) and potential salinity (PS). The water quality regarding sodium adsorption ratio (SAR) and sodium percent (Na%) range from good to poor and good according to residual sodium carbonate (RSC). Application of subsurface drip irrigation, and mixing water of TCA and NSSA could be the best management of the water resources in Siwa Oasis. 

aInstitute of Environmental Management, Faculty of Earth Science, University of Miskolc, 3515 Miskolc- Egyetemváros, Hungary; [email protected]; [email protected]; [email protected]. bGeology Department, Faculty of Science, Beni-Suef University, Beni-Suef, 65211, Egypt;  [email protected] * Corresponding author: Mohamed Hamdy Eid a,b*; [email protected] ORCID: 0000-0002-3383-1826Final Paper Number: H31U-1778  Presentation Type: Poster Session Number and Title: H31U: Frontiers in Water Quality I Poster Session Date and Time: Wednesday, December 13th; 8:30 AM - 12:50 PM PST Location: MC, Poster Hall A-C – SouthAbstract The current study evaluates the different factors threatening the sustainability of Siwa Oasis including soil salinization, water quality deterioration, water logging, depletion of non-rechargeable water resources and providing water management plan. GIS and remote sensing supported with machine learning were used for change detection in the land cover from 1990 to 2020. The hydrodynamic condition in the deep Nubian sandstone aquifer (NSSA) was investigated using pressure-depth pro le. The groundwater salinity was monitored from 1998 to 2022. Geochemical model using PHREEQC was conducted to detect the types of minerals that have the ability to precipitate in the soil from irrigation water and decrease its permeability. The change detection in the land cover showed rapid increase in the surface area of the salt lakes from 22.6 km2 in 1990 to 60.6 km2 in 2020. The soil salinization increased in the central Siwa Oasis due to evaporation of water logged in the soil. Monitoring the water salinity from 1998 to 2022 showed rapid deterioration in groundwater quality of the Tertiary carbonate aquifer (TCA). The pressure-depth pro le showed that the water in NSSA is over hydrostatic pressure in the eastern and western part of the study area and the central part is under hydrostatic pressure indicating pressure decrease. Chadha diagram and piper diagram showed that the water type changed upward from Ca-Mg-HCO3 in the rst stage in NSSA to Na-Cl type in the last stage in TCA and surface water. The saturation index revealed that the majority of water samples were supersaturated with respect to calcite, dolomite, talc, Ca-montmorillonite, chlorite, gibbsite, illite, K-mica, hematite, chrysotile and kaolinite, while the samples were undersaturated with halite, anhydrite, gypsum, and CO2. The irrigation water quality indices showed that NSSA is suitable for irrigation purposes while TCA is not suitable for irrigation regarding magnesium hazards (MH) and potential salinity (PS). The water quality regarding sodium adsorption ratio (SAR) and sodium percent (Na%) range from good to poor and good according to residual sodium carbonate (RSC). Application of subsurface drip irrigation, and mixing water of TCA and NSSA could be the best management of the water resources in Siwa Oasis.