Topographic Controls on Soil Formation and Development in the Lake Habbaniyah Basin: A Morphometric and Pedological Investigation.

الملخص

This study assessed the effect of topographic control on soil formation and development in the Lake Habbaniyah Basin using an integrated morphometric and pedological approach, and examined the relationship between land-surface features and the pedogenic processes controlling horizon formation and soil development. Basin morphometry was analyzed and three pedons were selected from contrasting topographic positions (upper, middle and lower slope). Standard laboratory procedures were used for morphological description, physical and chemical analysis, diagnostic-horizon identification, and classification according to the USDA Soil Taxonomy. The basin showed marked diversity in elevation, slope and drainage, strongly influencing soil distribution and development. Horizon thickness, differentiation and structural development varied clearly among the pedons with topographic position. Physical analyses showed a gradual decrease in sand and increase in silt and clay toward the lower positions due to transport and deposition, while chemical analyses showed neutral-to-slightly-alkaline reaction with a progressive increase in electrical conductivity, calcium carbonate, gypsum and salinity indices toward the lower positions. Calcification, gypsification and salinization, together with erosion and deposition, were the primary pedogenic processes, and their severity was strongly linked to the topographic gradient. The lower-basin pedon showed the greatest pedogenic development, the middle-slope pedon was intermediate, and the upper-slope pedon was least developed. All soils were classified as Aridisols, with the upper pedon in the Calcids suborder and the middle and lower pedons in the Gypsids suborder. The study concludes that topography is the main factor controlling soil formation and development in the Lake Habbaniyah Basin, through its effect on water movement, sediment redistribution, salt accumulation, the intensity of pedogenic processes, and the formation of diagnostic horizons, and hence on the degree of soil development and classification. These supports combining morphometric analysis with pedological study for assessing soil resources and planning sustainable land management.