In the periods of intensive development of the countries adjacent to the Aral Sea, the increase in irrigated areas resulted in withdrawal of most of water for this purpose, and the sea level had immediately dropped. Unfavorable periods wars, revolutions, etc.
Kes and a number of the prominent geographers in the s, showed that the Amu Darya and Syr Darya rivers changing regularly their flow direction and migrating throughout Central Asian in the historic period have not often reached the Aral Sea, and as a result the sea has dried up and a desert zone has formed on its territory. At the same time, as the sea was drying up, water salinity was considerably increasing and promoting precipitation of salts, which were found by the geologists at the bottom of the Aral Sea.
Thick layers of mirabilite precipitations are especially impressive. The migration of both the Amu Darya and Syr Darya deltas has established a very peculiar downstream area, where the depressions filled with boggy deposits alternating with deserted, fine-silty, and sandy deposits that formed the delta and the most part of the Amu Darya River bed itself and its branches. On the other hand, the field studies carried out by zoologists, in particular, by Polishchuk and Aladin from the Zoological Institute under the Academy of Sciences of USSR in have shown that the Aral Sea itself is characterized by very poor original fauna and the absence of many species that are in the Caspian Sea which is similar according to its origin.
At the same time, endemic species were found in the Aral Sea indicating that salinization of the Aral Sea, which took place from time to time affected these large-scale transformations. The analysis carried out by zoologists has shown that a small number of marine and oceanic species remained in the Aral Sea; however communities of brackish water species including the Caspian-estuary fauna have been destroyed here.
All the rivers emptying into the Aral Sea have not retained marine fish species or, at least, remains of this fauna. It means that water of the Amu Darya and other rivers, in one way or another, has penetrated both into the Aral Sea depression and through the Uzboy valley into the Caspian Sea. At the same time, it is necessary to note very developed deltas of the Syr Darya and Amu Darya rivers, which occupy sufficiently large areas. According to data of N.
The delta of the Syr Darya was also significantly developed. At the same time, a highly intensive vegetative background was widely spread in the delta. The periodically flooded delta was characterized by large areas of fructiferous reeds, tugai, hayfields and pastures. In particular, till only in the Amu Darya delta the area of reed thickets amounted to , ha, tugai — 1, Appropriate areas in the Syr Darya delta were also occupied by deltaic and other vegetation.
Kes has her somewhat different opinion. In the late Stone Age, the Amu Darya River, having filled up the Khorezm depression with alluvium, has burst into the Sarykamysh depression and formed the big Audan Lake here and in the Assaka depression; about 20 percent of water of this lake it was restricted by hydraulic parameters of the Uzboy channel have released through the Uzboy channel into the Caspian Sea.
This inflow continued during the 4th and 3rd millennium B. Yanshin tried to prove the presence of transgression in this period, the subsequent studies by L. Kiryukhin, Kravchuk and P. Fedorova as well as the most recent studies carried out by I. The Heads of these states approved the Concept, in which the proposal to establish a new sustainable anthropogenic-natural complex in the South Prearalie in order to rehabilitate the productivity of this territory as much as possible was formulated.
However, due to economic decline after disintegration of the USSR, implementation of this program faces difficulties. The existing ecological situation is of great concern for all peoples living both inside and outside the Aral Sea basin. As a result, there have appeared many plans and proposals in order to solve, to a greater or lesser extent, the following issues: protecting the population from adverse impacts of desertification; restoring fauna and flora diversity to a maximally possible extent; creating workplaces for the local population by means of rehabilitation of fishery, muskrat breeding, cattle breeding, processing sectors, etc.
Formerly, these issues had been addressed in two interrelated sustainable ecological zones the Aral Sea and Prearalie based on a certain hydrological regime of the Amu Darya and Syr Darya rivers. Croplands had to be flushed with larger and larger volumes of river water. The loss of the moderating influence of such a large body of water made winters colder and summers hotter and drier. In a last-ditch effort to save some of the lake, Kazakhstan built a dam between the northern and southern parts of the Aral Sea.
The Kok-Aral dike and dam, finished in , separates the two water bodies and prevents flow out of the North Aral into the lower-elevation South Aral. The dam has led fisheries in the North Aral to rebound, even as it has limited flow into the South Aral. Between and , water levels in the North Aral rebounded significantly and very small increases are visible throughout the rest of the time period.
Most of the changes in climate and landscape in the Aral Sea basin that we are about to explore are at the least indirect products of Human induced changes. Thus, the difficulty lies as much in understanding the way climate and other natural systems function as in being capable of weighing the potential consequences of our actions before we undertake them. Risk assessment combined with scientific understanding should undercut our actions more efficiently; adding an ethical dimension to the equation remains more than welcome in addition to those more accessible and quantifiable factors, but is too fragile to be the centerpiece on which our decisions rely before we commit to large scale actions which can often, as we are about to see, engender even larger responses from our environment.
The Aral Sea Crisis. Copyright Thompson, All Rights Reserved.
0コメント