Mapping Soil Salinity and Evaluation of Water Quality in Siwa Oasis Using GIS

Abstract

Siwa Oasis represents a promising area for agricultural expansion projects in the western desert of Egypt due to the availability of water resources. However, these areas are suffering from land degradation problems, especially soil salinity. Accordingly, the main objectives of this work were to evaluate and map soil salinity as well as groundwater quality in Siwa Oasis. Therefore, twenty representative soil profiles were randomly distributed throughout the studied area. These profiles were sampled based on the development of soil horizons. A total of 46 soil-samples were collected and these samples were analyzed for their physical and chemical properties. Groundwater samples were collected from irrigation-wells and they were analyzed for their chemical parameters. Landsat images were also acquired at three different periods to monitor the changes in vegetation cover, soil salinity and water logging. The obtained results indicated a wide variability within soil physical and chemical properties in the Oasis. Most of the suited soils were very saline, non-sodic based on the EC and ESP values (EC= 77 dSm-1 and ESP= 14.62 in average). Agricultural areas were increased from 22 km2 in 1992 to 81 km2 in 2015. On the other hand, saline soils were increased from 35 km2 to 64 km2 and water logged areas were also increased from 19 to 51 km2 from 1992 to 2015, respectively. These results could be due to the expansion in reclamation-projects, increase in crop irrigation and poor drainage. The salinity of groundwater varied from 2.28 to 5.45 dSm-1 (3.76 in average), which indicates a degradation in its quality. In summary, soils in Siwa Oasis are salt-affected and they need a proper land reclamation program and development of effective irrigation and drainage systems.