Due to almost lack of rainfall in Central East Sahara, salts in the soil cannot be washed out. Soluble salts are usually enriched at a small depth in soil. In addition to Solonchaks,Solonchaks most of the Vertisols as well as the Leptosols and all Histosols (Alaily in Geopotential and ecology—analysis of a desert region, vol 26, pp 100–123, 1993b) derived from tamariskTamarisk remains are rich in soluble salts. In well-drained sandy soils, soils in depressions, and with decreasing aridity, the salts are washed out or enriched at greater depth. Compared with the dynamic of soluble salts and gypsum which depend on their ion reaction in the solution, carbonates dynamic depends mainly on CO2 partial pressure. The CO2 content of soil air depends on biological activity; most soils in the area studied—outside the oases and Birs—are almost free of living organisms. Salt solubility value and the direction of water movement determine the accumulation sequence of salts in the soils. Thus, the soluble salt horizon is found above the gypsum enrichment horizon, and this above the carbonateCarbonate enrichment horizon in soils that are mainly influenced by ascending water (e.g., groundwater, stagnant water). The reverse order can be found in soils in which descending water (e.g., precipitation water, irrigation water) is predominant. Enrichment of soluble salts at the soil surface from terrestrial locations does not take place, as the capillary rise of water is slower than the water loss due to evaporation, and therefore the water can only move as vapor in the dry topsoil. Lateral salt differentiation occurs in depressions that are influenced by groundwater. The highest water losses caused by evaporation are usually found in the lowest part of the depression. According to the salt concentrations and their solubility, soils at the edge of the depression are enriched mainly with carbonates and gypsum, in the center of the depression with soluble salts. This can be observed in Bir Safsaf and its surrounding area. Gypsum occurs in various forms in arid areas, but in the extreme deserts, it is usually enriched in the soil as white powder. In groundwater soils, carbonate often accumulates in concretions and soluble salts as crusts on the soil surface. Sources of salts in soils are groundwater (Phreatic salts), atmospheric dust (Atmogenic salts), and the soil parent material (Lithogenic salts). In addition, soils of inhabited oases are enriched with various salts by human activities (irrigation water and mineral fertilizers = Anthropogenic salts).

Soluble Salts, Gypsum and Carbonates

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发表日期：

2025年

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Fayez Alaily

摘要

Due to almost lack of rainfall in Central East Sahara, salts in the soil cannot be washed out. Soluble salts are usually enriched at a small depth in soil. In addition to Solonchaks,Solonchaks most of the Vertisols as well as the Leptosols and all Histosols (Alaily in Geopotential and ecology—analysis of a desert region, vol 26, pp 100–123, 1993b) derived from tamariskTamarisk remains are rich in soluble salts. In well-drained sandy soils, soils in depressions, and with decreasing aridity, the salts are washed out or enriched at greater depth. Compared with the dynamic of soluble salts and gypsum which depend on their ion reaction in the solution, carbonates dynamic depends mainly on CO2 partial pressure. The CO2 content of soil air depends on biological activity; most soils in the area studied—outside the oases and Birs—are almost free of living organisms. Salt solubility value and the direction of water movement determine the accumulation sequence of salts in the soils. Thus, the soluble salt horizon is found above the gypsum enrichment horizon, and this above the carbonateCarbonate enrichment horizon in soils that are mainly influenced by ascending water (e.g., groundwater, stagnant water). The reverse order can be found in soils in which descending water (e.g., precipitation water, irrigation water) is predominant. Enrichment of soluble salts at the soil surface from terrestrial locations does not take place, as the capillary rise of water is slower than the water loss due to evaporation, and therefore the water can only move as vapor in the dry topsoil. Lateral salt differentiation occurs in depressions that are influenced by groundwater. The highest water losses caused by evaporation are usually found in the lowest part of the depression. According to the salt concentrations and their solubility, soils at the edge of the depression are enriched mainly with carbonates and gypsum, in the center of the depression with soluble salts. This can be observed in Bir Safsaf and its surrounding area. Gypsum occurs in various forms in arid areas, but in the extreme deserts, it is usually enriched in the soil as white powder. In groundwater soils, carbonate often accumulates in concretions and soluble salts as crusts on the soil surface. Sources of salts in soils are groundwater (Phreatic salts), atmospheric dust (Atmogenic salts), and the soil parent material (Lithogenic salts). In addition, soils of inhabited oases are enriched with various salts by human activities (irrigation water and mineral fertilizers = Anthropogenic salts).