الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Siwa Oasis located across 29° 05´ and 29° 24´ latitudes and longitudes 25° 14´ and 26° 06´. It is located about 560 km west of Cairo and 300 km south of the Mediterranean Sea. Siwa depression total area of about 1000 km2 with 82 km long, 21 km wide with. It lies at about 18 m below the sea level being surrounded by the Desert. It is marked by the dominance of hyperarid climatic conditions with very low rainfall rates. The climate is somewhat warmer and more humid in the summer than most other Desert areas of similar latitudes and is slightly colder in the winter.
Siwa Depression has an irregular elongated shape, about 75 km in the E-W direction. The lowest parts of the depression floor reach 18 m below sea level. Several major regions are distinguished in the depression, the most important of them from west to east are Bahe El Den, Al Maraky, Siwa, Aghurme, Abo Sharof, and Timeira- El Maasir regions. Recent and sub-recent alluvial and aeolian deposits are the main sediments characterizing the depression as they occur as thin deposits lying on the depression floor and as dune sand that bordering the depression on the south. Generally, the soils occupied the depression do not exceed 3 m in thickness in some localities, but they are very shallow in many places due to the high-water table level and/or rocky exposures. The most important landforms in Siwa Oasis are the saline lakes (Birket) e.g., Zeitun, Maraqi, Siwa, and Aghurmi. Around the saline lakes spread marshes, salinas, and sabkhas. The exposed sedimentary succession in Siwa Oasis belongs to the Miocene. This succession is overlain by Quaternary surficial deposits.
The groundwater in Siwa Oasis is available at different depths and lithology. Based on the lithology and water characteristics, two main regional aquifer systems are distinguished; they are the Tertiary Carbonate Aquifer System (TCAS) (Miocene and Eocene limestone and dolomite) and the Nubian Sandstone Aquifer System (NSAS) (Upper Cretaceous shale and marl layers).
A total of 49 water samples were collected representing the different water resources in the Siwa Oasis groundwater of TCAS (22 samples), groundwater of NSAS (10 samples), springs (12 samples), and bottled mineral water of different brands which extracted from the NSAS and purchased in local supermarkets (5 samples). A total of fifty-eight topsoil samples (0-20 cm depth) were collected from the study area. Forty samples were collected from the cultivated land representing the main suburbs in the Siwa Oasis; eighteen samples were collected from the barren areas representing the uncultivated soils. The collected samples are subjected to different analyses to give a geoenvironmental assessment of Siwa Oasis. This assessment focused on the most recent picture of the pollution in the Siwa Oasis groundwater and its soil sediments, with special attention to toxic metals contamination, regarding irrigation and drinking water quality and soil contamination and their impact on human health.
This study revealed that the studied groundwater samples of Siwa Oasis is slightly alkaline. Most of the studied groundwater has a moderate corrosive effect and marked electrical conductivity EC values.
Na+ is the most dominant cation in the studied water samples. Other cations (Ca2+, Mg2+, and K+; arranged in the order of decreasing concentration) are relatively less abundant than Na+. Also, the concentration of these cations is much higher in TCAS and springs water samples than in NSAS and bottled water samples. HCO3- is the most dominant anion in the studied NSAS and bottled water samples. Other anions (Cl-, SO42-, F- and NO3-; arranged in the order of decreasing concentration) are less abundant than HCO3-. On the other hand, Cl- is the most dominant anion in the studied TCAS and springs water samples Other anions (SO42-, HCO3-, NO3- and F-; arranged in the order of decreasing concentration) are less abundant than Cl-. Also, the concentration of these anions is much higher in TCAS and springs water samples than in NSAS and bottled water samples.
The investigated metals can order depending on their average concentrations as Fe > Al > Ba > Mn > Ni > Cu > Cd in NSAS and TCAS water samples and as Ba > Fe > Mn > Cu > Al > Ni > Cd in springs water samples and as Ba > Fe > Mn > Al > Cu > Ni > Cd in bottled water samples. Although, some samples have elevated concentrations of some metals when compared with the rest of the samples, these concentrations are considerably low. The elevated concentrations of (Ba), (Fe), and (Mn) in NSAS water samples reflect the lithology of the aquifer, which is composed of ferruginous sandstones, with local ironstone and manganese-rich bands, intercalated with shales and claystone.
Assessment of groundwater of Siwa Oasis for irrigation indicated that there is a big problem of EC and TDS concentrations in the TCAS and springs water samples and this water is unsuitable for irrigation. Combined SSP and SAR calculated values of Siwa Oasis groundwater indicate that there is a sodium problem in all TCAS and 32% of springs samples, respectively for irrigation. This groundwater has no RSC, MAR, or Cl- toxicity problem for irrigation. There is no problem with toxic metals concentration for using this groundwater for irrigation except for some samples which contain high concentrations of Cd, Fe, and Mn.
Assessment of groundwater of Siwa Oasis for the domestic purpose indicated that NSAS water can be used for different purposes. TCAS and springs water are hard water and have unacceptable TDS concentrations and a corrosive effect on the pipe system.
Regarding the use of NSAS and bottled groundwater of Siwa Oasis for drinking, all studied samples were clean from nitrate pollution. NSAS groundwater samples contain high concentrations of Al, Cd, and Fe that exceed the recommended limits in drinking water. These metals exceed these limits in 13.13 %, 23.66 %, and 40 % of the studied samples; respectively. On the other hand, Ba, Cu, Mn, and Ni don’t exceed all the recommended limits in all studied samples. However, these water samples have a low contamination level. The computed WQI values for NSAS and bottled water from Siwa Oasis indicate that this water can be classified as 86.66 % excellent and 13.33 % good. Generally, these results indicate that the NSAS and bottled groundwater of Siwa Oasis is safe for human consumption. Moreover, it should be consumed with care by filtration with suitable membranes for toxic metals.
The development of the Siwa Oasis soils under hot dry climatic conditions resulted in their mild alkalinity and considerable salinity. Differences in the chemistry of Siwa soils are expressed by differences in the relative abundances of the major cations (Ca2+, Mg2+, Na+, and K+) and anions (Cl-, HCO3- and SO42-). These differences are attributed primarily to differences in mineral composition. These cations and anions constitute the major parts of clay minerals, calcite, dolomite, halite, and gypsum which exist in different proportions in the different soil types.
Ca2+ and Mg2+ are the most dominant major cations in the cultivated soils of the Siwa Oasis. They are followed by Na+ and K+. The uncultivated soils, on the other hand, are characterized by the marked dominance of Na+ followed by Ca2+, Mg2+, and K+. The depletion of the cultivated soils in Na+ may be due to the dissolution of halite by irrigation water and/or cation exchange with Ca2+ and Mg2+. Arranged in the order of decreasing abundance, the major anions in the cultivated and the uncultivated Siwa soils are Cl-, SO42-, and HCO3-.
The recorded high concentrations of Ca2+ and Mg2+ may be inherited from exposed rocks which are mainly composed of limestone and shale. The relatively high salinity expressed by high concentrations of Na+, Cl- and SO42- recorded in these soils is related to local conditions. It reflects a significant role played by the saline near-surface groundwater in these area and/or inadequate drainage rather than their proximity to playa lakes.
The cultivated Siwa Oasis soils are invariably more enriched with heavy metals than the uncultivated (desert) lands. The associations that exist between chemical components in the Siwa Oasis soils are inherited from parent rocks and parent materials and are also affected by the weathering processes and the agricultural and industrial activities which enhance the accumulation of heavy metals.
A closer look at the soil quality has led to the conclusion that pH has elevated values in some locality, but it can lower by adding gypsum or elemental sulfur to the soil. Some locations suffer from high EC values (10.34 % very slightly saline fair soil). The consequence of using TCAS and springs groundwater of Siwa Oasis in irrigation is to increase the soil salinity. Siwa Oasis soils contain low concentrations of toxic metals which do not exceed the recommended limit in agricultural soil. Siwa Oasis soil is not contaminated with toxic metals except for (Cd) which higher than the world soil average and crustal average in some sites but still does not exceed the recommended limit in agricultural soil.
Data presented in this study are environmentally important whereas they can be considered as baseline data for any further development in Siwa Oasis. Lastly, researches on the presence of biochemical and microbiological contaminations are required to complete the picture and status of the safety of groundwater of Siwa Oasis.
1. Artificial recharge to TCAS of harvested rainwater to be encouraged.
2. Megaprojects must be conducted to mixing TCAS and springs water with NSAS water to reduce their salinity to take advantage of this huge stock of groundwater
3. Farmers to be educated against excessive use of pesticides and chemical fertilizers.
4. Periodic appraisal of treatment technologies used by bottled water companies.
5. We recommend performing periodical inspection for the agricultural and industrial activities and their wastes in the study area and monitoring the level of toxic metals in the studied soil as well as the cultivated crops.
6. Common effluent treatment plant and common hazardous waste treatment facilities to be established in industrial area on priority.
7. In order to evaluate the health risk due to toxic metals transferred from fertilizers to food crops, determination of the transfer factor soil-to-plant the daily intake of ingestion food crops was highly recommended.
8. Using modern irrigation methods (drip and pivot irrigation) to rationalize the use of NSAS water in the study area.
9. Cultivation of non-traditional crops and establish its complementary industries to maximize the economic returns of agriculture in the study area.