CHANGES OF THE ARAL SEA ECOSYSTEM PhD., Docent Guzlira Kdirbaeva ARAL SEA Aral Sea, Kazakh Aral Tengizi, Uzbek Orol Dengizi, a oncelarge saltwater lake of Central Asia. It straddles the boundary between Kazakhstan to the north and Uzbekistan to the south. The shallow Aral Sea was once the world’s fourth largest body of inland water. The remnants of it nestle in the climatically inhospitable heart of Central Asia, to the east of the Caspian Sea. The Aral Sea and its demise are of great interest and increasing concern to scientists because of the remarkable shrinkage of its area and volume that began in the second half of the 20th century—when the region was part of the Soviet Union—and continued into the 21st. That change resulted primarily because of the diversion (for purposes of irrigation) of the riverine waters of the Syr Darya (ancient Jaxartes River) in the north and the Amu Darya (ancient Oxus River) in the south, which discharged into the Aral Sea and were its main sources of inflowing water. GEOLOGY The Aral Sea depression was formed toward the end of the Neogene Period (which lasted from about 23 to 2.6 million years ago). Sometime during that process the hollow was partially filled with water—a portion of which came from the Syr Darya. In the early and middle parts of the Pleistocene Epoch (about 2,600,000 to 11,700 years ago), the region appears to have dried up, only to be inundated again sometime between the end of the Pleistocene and the early Holocene Epoch (i.e., after about 11,700 years ago)—the latter instance being the first time by the Amu Darya, which had temporarily changed its course from the Caspian to the Aral Sea. After that, except for some relatively brief dry spells between the 3rd and 1st centuries BCE, the two rivers’ combined flows generally maintained a high water level in the sea until the 1960s. CLIMATE AND HYDROLOGY The Aral Sea area is characterized by a desertcontinental climate that features wide-ranging diurnal air temperatures, cold winters, hot summers, and sparse rainfall. The rate of precipitation—an annual average of 4 inches (100 mm) in all, occurring mainly in the spring and autumn—is only a tiny fraction of the lake’s traditional rate of evaporation. Northwesterly winds prevail in autumn and winter, and westerly and southwesterly winds are common in spring and summer. THE DIMINISHING SEA PHYSIOGRAPHIC CHANGES In 1960 the surface of the Aral Sea lay 175 feet (53 metres) above sea level and covered an area of some 26,300 square miles (68,000 square km). The Aral Sea’s greatest extent from north to south was almost 270 miles (435 km), while from east to west it was just over 180 miles (290 km). Although the average depth was a relatively shallow 53 feet (16 metres) or so, it descended to a maximum of 226 feet (69 metres) off the western shore. The sea’s northern shore—high in some places, low in others—was indented by several large bays. The low-lying and irregular eastern shores were interrupted in the north by the huge delta of the Syr Darya and were bordered in the south by a wide tract of shallow water. The equally vast Amu Darya delta lay on the lake’s southern shore, and along the lake’s western periphery extended the almost unbroken eastern edge of the 820-foot- (250-metre-) high Ustyurt Plateau. ENVIRONMENTAL CONSEQUENCES The rapid shrinkage of the Aral Sea led to numerous environmental problems in the region. By the late 1980s the lake had lost more than half the volume of its pre-1960 water. The salt and mineral content of the lake rose drastically because of that, making the water unfit for drinking purposes and killing off the once-abundant supplies of sturgeon, carp, barbel, roach, and other fishes in the lake. The fishing industry along the Aral Sea was thus virtually destroyed. The ports of Aral in the northeast and Mŭynoq in the south were now far from the lake’s shore. A partial depopulation of the areas along the lake’s former shoreline ensued. The contraction of the Aral Sea also made the local climate noticeably harsher, with more-extreme winter and summer temperatures.