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Ramazonov Baxtiyor Ramazonovich, Senior researcher applicant, Research institute of Soil science and Agrochemistry E-mail: [email protected] Kuziev Ramazon, DSc., (Doctor of science in Biology), professor, Research institute of Soil science and Agrochemistry E-mail: [email protected]
EVOLUTION OF SOILS OF THE ARAL SEA AREA UNDER THE INFLUENCE OF ANTHROPOGENIC DESERTIFICATION
Abstract: The article summarizes information on changes in natural and anthropogenic processes of desertification and patterns of their manifestation in the Aral Sea area. In connection with the intensification of desertification, arid-zonal factor - the rapid transition of hydromorphic soils to automorphic desert regions - began to play a decisive role in soil-forming processes. It was revealed that because of sharp change of climate and intensification of desertification in the main part of the Aral Sea region, hydromorphic conditions disappeared and landscapes acquired a desert nature, the soil cover reached a typically deserted stage of development, its biogeocenoses disappeared, and tugai vegetation also dried out.
Keywords: Aral Sea, zonal factors, desertification, aridization, hydromorphic soils, automorphic soils, soil formation, climate.
At the end of the 1950s and 1960s, the water flow of which lasts 25-30 years, refer to residual-meadow and
the Amudarya and the Syrdarya declined sharply, which led to significant changes in the natural and ecological situation in the Aral Sea area. With the draining of the Aral Sea - the process of desertification, changes in soil formation conditions began here. A decisive role in soil-forming processes began to play the arid-zonal factor, which led to a sharp transition of hydromorphic soils to automorphic desert soils. Such a rapid transition, when for a few years the groundwater level has significantly decreased and soil has dried up, predetermined the peculiarities of their evolution in the first stage of aridization. As a result of the development of evolutionary processes, the evolutionary soils have fallen out of evolutionary chain, and the transition from meadow soils to marshy soils, characteristic for the ancient lowland plains of the lower reaches, has been erased. The genesis of soils at this stage, with the exception of solonchaks, is almost completely determined by the features inherited from the preceding, initial soil-forming processes. Therefore, the soils of the first stage - the drying stage,
residual-meadow tugai. And together with these soils, solonchaks are formed, also having residual signs of the original floodplain-alluvial soils [9].
According to the data of N. V. Kimberg, M. I. Ko-chubey and S. Sh. Shuvalov, in the "living" delta areas, on the site of the dried up lakes there were about 40% of the total area, semihydromorphic solonchaks and residual peaty-bog or silty-bog soils are developing. In the group of residual soils, drying desiccating soils are distinguished (Borovskii, Pogrebinsky, 1958, Kievskaya, 1983). The criterion for separation is the degree of desiccation of the soil profile, determined by the composition ofthe changed vegetation, as well as the signs of desertification and soil degradation. At the end of the last stage, the soil acquires the characteristics of one of the zonal desert soils [1].
The evolutionary orientation of the development of soils in the delta is not uniform, it is determined by geomorphological and hydrogeological conditions, and together with this lithological composition of soils and grounds [8].
The soil map of the lower part of the delta of the Amudarya (Popov, Sektimenko, Tursunov, 1992) reflects the current state of its soil cover. The location of soils within geomorphological regions in a certain genetic sequence - from hydromorphic soils to desert automorphic ones - allows us to see the paths of their evolutionary development under conditions of sharply arid and widely spread aridization [8].
Hydromorphic conditions on the prevailing part of the territory disappeared long ago and landscapes acquired a deserted character, the soil cover reached a typically deserted stage of development. Takyr, desert sandy soils and residual solonchaks are widespread in these territories, and the residual-hydromorphic soils have clear signs of takirazation. Deep cracking of soils during drying, formation of large karst-suffosive valleys and huge basins of blowing, formation of sandy hillocks and drifts is very widespread here. Funnels of shrinkage-erosion origin are formed where there are clayey and heavily loamy soils with a large volume shrinkage coefficient. When dried, they form pronounced cracks of desiccation (Felitsiant, 1953; Zemsky, 1954; Shelayev, Weilert, 1956) [9].
The distribution of sandbi in these parts of the delta is to a certain extent connected with the location of ancient channels, in which almost sand deposits are deposited, sometimes covered with a thin clayey crust. As a result of the intensification of the aridity of the climate, deflation processes become more active. In the paleochan-nels, huge funnels are formed, blowing up to 2-3 m in depth, up to 10 m in diameter. Also in the paleochan-nels as a result of accumulation of deflated material, so-called chokalaks are formed and a kind of chokalak relief is formed. The height of the sandy hillocks reaches 5 m, the diameter is 10-15 m. Often their dimensions are smaller, respectively 2 and 3-5 m. All of the above negative phenomena leading to soil degradation are the indispensable companions of desert soil formation on drying delta plains.
As a result of extensive aridization of the region, some elevated areas passed through a stage of alluvial meadow and semi-hydromorphic drying soils and entered the phase of desert automorphic soil formation, which, depending on the nature of the deposits, flows in two directions, takyr soils are formed on loams and clays, with residual marshy features, and on sand and sandy
loams - desert sandy soils. Together with the aforementioned solonchaks with increasing aridization, they pass a semi-automorphous stage of solonchak soils and subsequently desalinate surface of them and become takyr. In the evolutionary development, in some cases, can reach the stage of the residual marsh soils [13].
To date, the delta is dominated by various genetic variants of residual semihydromorphic soils, including solonchaks. They have more than half the territory. The initial stage of the evolution of soils under the influence of anthropogenic aridization is completed and places in semi-automorphic conditions of the soil enter the next stage of desertification, which this stage will also be transitional. In the future, under the influence of high desert hydrothermal factors, the residual signs of meadow and bog soils in their morpho-genetic characteristics will have subordinate significance and begin to prevail signs of takyr and desert soils. Similarly, the processes of desertification will affect solonchaks (Popov et al., 1982, 1985a, Tursunov, 1987) [11].
V. V. Egorov (1959), considering the question of the evolution of the soils of the delta of the Amu Darya, comes to the conclusion that "... the transition from the marshy to the meadow stage does not always occur gradually. A sharp decrease in the water regime towards drainage may be accompanied by a weakening ofbiologi-cal activity and a relative decrease in the effective fertility of soils. Only with great convention can you name such soils, as is done, marsh-meadow. In them only the residual properties of bog soils predominate, while the properties of meadow soils have not yet developed. The systematic position of these soils also needs to be clarified, taking into account the fact that their immediate passage into desert soils in the corresponding zone ..." The correctness of these conclusions is confirmed even now, and they can be extended not only to hydromorphic soils, but also to the rest of the variety of transitional soils common in the lower reaches. Following the disappearance of the Aral Sea and the appearance of the base of the Aral Sea (Aralkum), the decrease in the basis of erosion and the sharp drop in the level of the delta's groundwater, meadow and marshy soils, as well as solonchaks, quickly transform into semi-hydromorphic humidification conditions and undergo a drying. Within 25-30 years they retain the basic morphogenetic features of hydromorphic soils, although by the end of this stage groundwater
in them can descend deeper than 5 m. In them, as it were, the high reserves of organic matter inherent in marsh and meadow soils are preserved. Here, residual signs of oxide and especially ferrous iron forms of gley horizons are clearly preserved. That is why at the first stage of the general process of regional anthropogenic aridization of the Aral Sea, during the drying out stage, the transitional soils were decided to be called residual-marsh and residual-meadow soils. They are also isolated as an independent genetic subdivision and soils drying tugai - residual-meadow tugai soils [8].
With the desiccation of the Aral Sea and desertification of the delta, its biogeocenoses sharply declined and its tugai vegetation dried up. Reed is modified into molding forms and perishes. Most of the territory of the Aral Sea is used as pastures, often unproductive. In the future, with the broad development of the processes of desertification and degradation, the quality of pastures will further decrease. Proceeding from this, it is necessary to resort to periodic flooding of pasture and hayfields, which simultaneously with increasing their productivity somewhat suspend the desertification of individual territories. It should also be noted for a good experience of creating the juniper reeds in Muynak.
At the stage of desertification, the soil will acquire the characteristics of one of the zonal soils-takyr, desert sandy or residual solonchaks. Differences in soil processes in the prognostic stage are smoothed out, but facies differences that predetermine salinity, deflation, the degree of profile differentiation to genetic horizons, and fertility indicators of soils acquire great importance. In extra arid conditions, there is a further convergence of soils, and the main indicators on which their division was-the content of humus, the level of provision of gross and mobile forms of nutrients is leveled. The level of facies and lithologic properties or differences in the mechanical composition come to the fore [9].
According to V. Y. Sektimenko and other scientists, based on the study of soil cover, the main variety of soils in the lower part of the Amudarya delta can be represented by the following list:
I-hydromorphic: 1-meadow-residual-bog, 2-solon-chaks typical, 3-solonchaks bog, 4-solonchak-meadow;
II-transitional: 1-residual-bog, (a-drying, b-dried, in-desiccated), 2-residual-meadow (a-drying, b-dried, in-desiccated), 3-residual-meadow tugai (a-drying, b-
dried, in-desiccated), 4-meadow-takyr, 5- solonchaks-residual-bog, 6-solonchaks-residual-meadow.
III-automorphic: 1-takyr, 2-desert sandy (a - on alluvial deposits, b - on tertiary sandstones), 3-solonchaks residual.
IV-irrigated: 1-meadow, 2-meadow-takyr [9].
The systematic list reflects both the classification-taxonomic levels of genetic groups of soils in accordance with the "Classification and diagnostics of soils" (1977), and the same indicators according to the classification of B. V. Gorbunova and N. V. Kimberg (1962, 1974).
In addition, the list includes classification-taxonomic levels for residual-bog, residual-meadow, residual-meadow tugai soils, as well as solonchaks-residual meadow and residual-marshy (V. E. Sektimenko, A. A. Tursunov, 1988) which are revealed in the delta for the first time [10].
The aforementioned soils represent one of the stages of drying of bog soils formed in these territories during the past alluvial-flood regime ofhumidification, which is also reflected in the residual signs of the marsh process along their profile. Therefore, these meadow soils are referred to meadow residual-bog soils, which, with further drying of the delta, can go to meadow-takyr or residual-meadow through a stage of intensive salinization [9].
Meadow residual-bog soils occupy the youngest surfaces in the lower part of the Amu Darya delta and are mainly confined to territories that, as a result of local support of river and waste waters, maintain a close ground-water level, most often within three meters. The profile of soil data is characterized by the presence of gley horizons in both the upper and lower layers. In the absence of flooding, there is an effusion and dissociative-effluent water regimes that, with mineralized groundwater, contribute to the formation of a salt profile in the type of solonchaks. With meadow soil formation, a special composition ofvegetation develops. In meadow residual-bog soils, first of all, reeds grow, which, with increasing drying, turns into a creeping shape, in the form of separate plants up to 10-15 cm in height. Meadow communities from tamarisk, reed, and chingil come to replace marsh vegetation. From leguminous plants there is licorice, and also a camel thorn. With increasing of soil salinity, meadow vegetation dies off, giving way to halophytes -Kareliania, parselystnik, Kermek, some solyanka. Meadow residual-bog soils are formed mainly on sediments of the lake facies of sedimentation [5].
In the desert zone, bog solonchaks are widespread, it is a subtype of solonchaks combining salt accumulation with swamping. These solonchaks are called in various places by blinders, salty mud. An indispensable condition for their development are constantly close, highly mineralized, drainless groundwater, which together with capillary removal of salts to the surface of the soil creates conditions for anaerobiosis in it. This affects the strong gleying of the entire profile. Solonchaks of the described subtype are developed on the coasts of saline lakes, as well as in closed depressions of modern alluvial plains. The profile of the bog solonchaks of the desert zone is given in the example of the sample cut No. 27.
Sample cut 27, 2017 August 23. B. R. Ramazonov, A.J. Ismanov. Muynak district, from the road 350 meters to the north-west. The surface is devoid ofvegetation and covered with a rough dark crust with white spots.
0-1 cm. Earth-salt, durable moist crust.
1-6 cm. Rick, moist, saturated with salts.
6-40 cm. Light-brownish, gray and rusty patches, weakly dense, wet loam.
40-92 cm. Clay of the same color, but with 75-78 cm intensely blue with bright rusty spots, reed residues and a mass of large particles of gypsum.
92-150 cm. The whitish gray, moist, medium sand with large rusty and bluish spots, there are small sea-shells - Cardium edula.
From 150 cm begins salty groundwater.
Bog solonchaks are allocated in a large amount of salt accumulation, usually by the chloride character of salinity and increased carbonate content. Residual saline solonchaks of the desert zone - in which the solonchak process has stopped, salt accumulations are relict in character and with them signs of a transition to some sort of, depending on lithology, automorphic soil: takyr or desert sand. Residual solonchaks are always found on high river terraces, in ancient deltas or dried parts of modern deltas. All these surfaces in the recent past experienced hydromorphic conditions, as evidenced by rusty stains of iron oxide. Morphological varieties of residual solonchaks are the same as typical: plump, cortical, cortical-plump. In addition, there are solonchaks with a takyr surface, which are called takyr solonchaks [6]. The impact of mankind and its economic activities on the environment is one of the most important issues of our time. Nature itself undergoes changes under the influence of various factors. Especially dynamic are the water systems, and their evolution even in one developed natural history area proceeds in different ways depending on the set of environmental conditions.
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