Monitoring of micromorphological changes in a virgin Solonetz under regional changes in hydrology and climate (Northern Caspian Lowland, Russia)

Over the past 40 years, a clear trend towards an increasing humidity and a rising groundwater table has been observed in the south-eastern semidesert part of European Russia. According to the published data, two clear periods of climate are distinguished: 1950s-1970s and 1970s-2000s. The thin sections of a Solonetz sampled in different periods of time (1950s, 1960s, 1970s, 1982, 2002 and 2013) at the Dzhanybek research station were studied micromorphologically to observe how these natural changes influenced soil pedofeatures. A comparison of thin sections showed no significant changes in soil properties between 1950s and 1982, when the hydrological (ground water table) and climatic parameters remained relatively stable. However, between 1982 and 2013, due to a significant increase in climatic moisture and rising groundwater, the following changes in soil microfeatures took place: the activation of humus accumulation and biogenic structuring, the eluviation of the silty clay-humus matter, the development of solodic features, gleyization of the soil mass, and the accumulation of opaque black organic grains about 2-3 µm formed in the topsoil due to the long stagnation during the springtime after snow melting. The water table rise leads to the consequent rise of the upper boundary of the accumulation of gypsum and carbonates.