Geoecological Consequences of Aral Sea Regression at the Mesoscale Level

Abstract

The article shows that the most important result of the Aral crisis consists in the formation of the Aralkum desert on the territory of the dried seabed, which determines the development of a complex of geoecological problems. The key ones include the formation of constant center of dust storms in the Central Asian region and the source of silt aerosols for long-distance transfer. Therefore, the problem of atmospheric and ecological influence of Aralkum is assigned to priority ones. The transport of tiny particles is the least studied, making their monitoring difficult. It is known that aeolian dust, consisting of pelitic particles less than 0.01 mm in size, can travel significant distances in a suspended state due to the ability to migrate by air. These tiny particles, which are formed on the dried-up bottom of the Aral Sea, are a potential source of pollutants, entering the natural environment of other regions. In this regard, in order to identify the main soil-lithological patterns, we studied the results of research of the transformation of solonchaks and sands of the Aralkum. The granulometric analysis of surface sediments sampled in the western part of the Aralkum desert (Uzbekistan) was performed. Based on the results of the granulometric analysis of the samples taken, it has been established that the concentration of pelite in dried bottom sediments consistently decreases with the distance from modern areas to those that previously entered the continental phase of development. Surface deposits that existed for about 35 years as continental ones contain less than 30% of pelite, whereas in areas that have been in the subaerial regime for a shorter period of time, its concentration is maximal (≈45–65%).The decrease in the concentration of pelitic particles in surface sediments with time may be considered as one of the most important features of the desertification process of this territory. Using the NOAA HYSPLIT model for 2024, direct trajectories of air masses from the surface of the Aralkum Desert were simulated, which enabled us to identify areas of their potential effect related to their ability to transport pelitic material, to determine the area of expected dust transport to Russia in particular. The area that became drained after 1989 was identified as the main source of pelitic particles in the Aralkum desert, the center of long-distance transport. To identify the supposed source of the removal of the smallest particles from the drained surface, space imagery data from two systems (Terra MODIS and Landsat-5) and index images created on their basis were used. The area of this source of long-range transport in 2024 is almost 35 000 km² (or about 60% of the surface of the dried bottom of the Aral Sea, including the eastern part of the Big Sea). To reduce the atmospheric and ecological impact of the Aralkum desert, it is necessary to more widely implement phytomeliorative measures on the drained surface and increase their effectiveness. Further study of the influence of long-distance transport on ecosystems requires research of the elemental and material composition of the substance accumulated in natural archives (mosses, lichens, snow cover) in the undisturbed territories of Siberia.