Central Asia's inland seas curiously rise and fall
Over the past three decades, rivers feeding the Aral Sea in formerly Soviet central Asia have been increasingly diverted for irrigation, and as a result its water level has plummeted. So sudden has been the drop--some 15 meters in the past 20 years--that fishing boats, once grounded in shallows, were completely isolated from the retreating shoreline and have rusted amid the newly formed dunes.
This scene has become somewhat of an environmental symbol. In his 1992 book, "Earth in the Balance," Vice President Al Gore used the powerful image of camels walking past derelict "ships of the desert" to show the dangers of interfering with nature. The U.S. Agency for International Development has instituted programs to aid communities surrounding the shrinking sea, and the World Bank may fund a restoration project.
But the lessons to be drawn from central Asia are not so straightforward. For although the Aral Sea is indeed emptying, the nearby Caspian Sea--a much larger body of water--is rising.
Like the Aral, the Caspian long appeared to be obeying an elementary principle of hydrology: river modification upstream leads to less water downstream. For decades the Caspian's height moved in concert with efforts to harness inflowing rivers, such as the Volga. In the 1930s numerous hydroelectric dams were erected, and the Caspian fell; during World War II, such projects were suspended, and sea level stabilized. After the war, construction of dams and reservoirs intensified, and sea level dropped further.
In 1977 a strange turnabout occurred. Human use of the rivers continued to grow, but the Caspian began inexplicably to rise. Soviet hydrologists initially considered the shift to be a temporary aberration and completed a dam to isolate the shallow Kara-Bogaz Bay on the eastern shore. Cutting off evaporative loss from the bay was seen as a way to slow the overall decline in sea level.
But the Caspian kept on swelling. Because many settlements and industrial sites were finding themselves underwater, the government of Turkmenistan decided in 1992--after the sea had risen two meters--to breach the Kara-Bogaz Dam. "The approach they used in earlier years was that 'we can change nature,'" says Sergei N. Rodinov, formerly of the State Oceanographic Institute in Moscow. "Now the approach is the opposite." Although resigned to let nature take its course, scientists nonetheless would like to understand what is happening and why.
Most researchers attribute the rise to changing weather patterns over the Caspian drainage basin: more precipitation increases river influx. Several Russian scientists argue, however, that recent tectonic shifts in this geologically active region might also contribute by affecting the seafloor. Other Russians have suggested that water from the Aral--perched some 70 meters higher in elevation--may be flowing underground into the Caspian, deftly explaining the seesawing levels of both.
Philip P. Micklin of Western Michigan University, a leading American specialist on the Aral Sea, discounts that idea as "totally crazy." He points out that there is not enough water being lost from the Aral to account for the Caspian's rise and that increased discharge from the Volga clearly indicates where the excess water is coming from: "Why look for far-out explanations when it's clear what's happening?"
Micklin does recognize, however, that alternating phases in these neighboring inland seas take place. He notes that the Amu Darya River, which currently feeds the Aral from the south, has been known to flow through its left bank and empty into Lake Sarykamysh to the west. That body, in turn, spills into the Caspian. Such redirection probably happened repeatedly in the past, sometimes spurred on by invading armies. Because flow of the Amu Darya toward the Aral has depended on dikes and dams upriver, their destruction has at times raised Sarykamysh and lowered the Aral.
Past acts of strategic environmental manipulation may explain why Dimitriy O. Eliseyev of the Leningrad Pedagogical Institute found submerged tree stumps in the northern Aral in 1990. The ancient trees showed that the sea was once even lower. According to Micklin, U.S. and Russian researchers established that the trees grew for several decades, about 400 years ago. This period corresponds to the years that the Amu Darya last flowed west toward the Caspian, before shifting north in 1575 to feed the Aral.
Thus, the conviction that humans could bend nature to suit their will apparently held well before the Soviets arrived in central Asia. Yet Russian planners seemed to show an unmatched enthusiasm for such pursuits. They even worked out a strategy for feeding the Caspian and Aral seas by diverting river water that was flowing into the Arctic Ocean.
Had the political and meteorological winds sweeping the Soviet Union been delayed, planners might have been able to pursue their grand schemes for river diversion. Such efforts may well have proved their premise--"We can change nature"--correct, although catastrophic Caspian flooding might not have been the change they were expecting. As it is, the rise and fall of two seas remains hard to handle.--David Schneider
SCIENTIFIC AMERICAN July 1995 Volume 273 Number 1 Page 14
Scientific American (ISSN 0036-8733), published monthly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright 1995 by Scientific American, Inc. All rights reserved. Except for one-time personal use, no part of any issue may be reproduced by any mechanical, photographic or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. For information regarding back issues, reprints or permissions, E-mail SCAinquiry@aol.com.
