Marina Lvovna Sizemskaya

The features of soil and hydrological conditions of the solonetzic complex of the semi-desert of the Northern Caspian region, a long-standing object at 70-year monitoring of their natural and anthropogenic transformations, were studied at the Dzhanybek Research Station of the Institute of Forest Science of the Russian Academy of Sciences. The classical works of Professor A.A. Rode  and the research led by Professor T.A. Sokolova  became the standard for comparison when conducting it at the present stage. The soils of virgin areas and meadow-chestnut soils of micro- and mesorelief depressions under separated forest stand and massive forest plantation, mainly of pedunculate oak and squat elm, were studied. The data of weather and climatic conditions were analyzed, the coefficient of humidification of the territory was calculated, the dynamics of groundwater levels, their chemical composition and mineralization were traced, the composition of water extract from soils was determined and supplies of easily soluble salts and chlorine ion by half-meter layers were calculated. Three significantly different periods of changes in soil and hydrological conditions caused by fluctuations of the groundwater table and changes in moisture content in the region have been identified. The modern stage, which began in the early 2000s, turned out to be the driest with a moisture coefficient of 0.24±0.07. Against this background, the rise of the groundwater level characteristic of the early 80s of the XXth century was replaced by its lowering. Under meadow-chestnut soils of virgin depressions at a groundwater level of 5.6±0.2 m and their average mineralization of 3.41±0.27 gl-1, at the present stage, the previously appeared tendency of their salinization has been preserved due to the accumulation of Cl-, Ca2+, Na+ ions in them. In the depressions of the micro- and mesorelief under the separated and massive forest stands, there is an increase in groundwater mineralization caused by high evapotranspiration of the trees, but due to the additional accumulation of snow by forest strips and the periodically flushing type of water regime with limited desuction, a root-accessible desalinated zone with a thickness of 350 and 250 cm, respectively, persists there now. The revealed patterns, covering a 70-year period of observations, allow a more reasonable approach to the creation of demanded landscaping in such unfavorable climatic conditions.