Soil salinisation as a land degradation process in the dried bed of the North-eastern Aral Sea, Kazakhstan

Soil salinisation is among the most well-known land degradation processes determining the ecological state of the land surface. Anthropogenic soil salinisation, wind erosion and soil alkalinisation prevail among the soil degradation processes in the dried Aral Sea bed. In addition to soil, the vegetation cover has also degraded. In this region, the dominant plant communities (perennial saltwort plants, black and mixed saxauls, etc.) include halophytes and psammophytes; the majority of which have been degraded to strong (7%) and significant (21.2%) degrees. The former Aral Sea bed is now a saline anthropogenic desert, Aralkum, covered by saline soils mostly comprising solonchaks (typical and seaside (coastal) solonchaks), takyrs and takyr-like soils, meadow and meadow-boggy soils, brown desert soils and solonetzic desert sands. Saline soils are widely distributed in the dried bed of the Aral Sea. These soils contain high concentrations of soluble salts such as chlorides, sulphates, sodium and hydrocarbonates. According to the soil salinity chemistry results, at a 1-m depth, sulphate-chlorides prevail: sulphate-chloride (57%), chloride-sulphate (28%) and soda-sulphate (14%) are the greatest contributors. The cation and anion contents in the studied soil can be ranked as follows: Cl˃ SO 4 ˃ HCO 3 ˃ Ca ˃ Na + K ˃ Mg. According to the soil salinity degree, highly (strongly) saline soils and solonchaks prevail in the soil cover on the dried Aral Sea bed. Highly saline soils prevail in all soil layers. Salt horizons predominate in the middle and lower layers, and the studied soils can be classified as saline in the middle and deep soil layers.