Anthropogenic Impacts on Soils of Wadi Al-Molak, Suez Canal West, Egypt

Abstract

The past three decades saw rapid and massive agriculture in Wadi Al-Molak at west of Suez Canal, Egypt. Land cover and pedon changes were studied in 850 km of the Wadi Al-Molak catena using time series and paired-site approach, respectively. The aim was to better understand the anthropogenic impacts responsible for the change of land cover and soil characteristics vertically within pedons and horizontally across landscapes under different ages of cultivation. Five landscapes were recognized: mountains and piedmont slope at upland; alluvial plain at midland; bajada plain and Nile old deltaic plain at lowland. The available Landsat images were analyzed from December 1986 to December 2016 of the Wadi to track the agrarian expansions in epochs (till 1986, 1987-1996, 1997-2006, and 20072016). Forty-three pedons were randomly distributed throughout the five landscapes representing both of cultivated soils under all periods and native soils. Detailed soil morphological as well as selected physical and chemical characteristics were studied. Soil morphology and taxonomy from five landscapes were used to interpret the anthropogenic impacts. Landscapes and soils were altered by conversion to agriculture for direct human use. Among out key findings are that (1) the agricultural areas increased from 225 km in 1986 to 475 km in 2016 while the annual expansion rate decelerated from 11.8 kmyr in 1996 to 2.2 kmyr in 2016; (2) the majority of agrarian expansions during 1987-2016 mainly occurred on alluvial plain landscape; (3) availability of irrigation water, soil potentialities, and national policies were the major driving forces; (4) solum horizons and redoximorphic/ped surface features occurred in cultivated soils and absent in native soils; (5) soil moisture regime was changed to anthraquic under sustained paddy cultivation, suggesting a modification in USDA Soil Taxonomy; (6) soil solum thickness increased with increasing time of cultivation; (7) formation of salic and natric horizons with high soil bulk density in lowland indicated soil degradation process as a result of mismanagement; (8) pedons under cultivation contained greater concentrations of organic carbon, total nitrogen, and clay than pedons under natural vegetation; and (9) the cultivated soils were classified as Aridisols or Vertisols while the native soils were classified as Entisols. The results demonstrated that agricultural expansion had changed the land cover, soil morphological, physical, and chemical properties, even the soil types. These results are very valuable for better understanding soil genesis and evolution with agricultural utilization.