In 1960, the Aral Sea in central Asia was the world’s fourth largest lake. But massive irrigation programmes begun during the Soviet era diverted water from the rivers that feed it, reducing the lake’s volume to just 10 percent of what it had been and leaving large areas dry. In less than a century, humanity destroyed the Aral Sea. It is one of the emblematic environmental disasters. But now it seems the sea has collapsed at least twice before and recovered both times.
The ecosystem collapsed, the desiccated lake bed is now laced with pesticides spread by dust storms, and drinking water is polluted. Now geologists have discovered that the Aral Sea has previously recovered naturally from such severe declines. “History tells us don’t give up hope,” says Philip Micklin of Western Michigan University in Kalamazoo, who was not involved in the study. “The sea really has dried in the past and has come back.”
Sergey Krivonogov of the Institute of Geology and Mineralogy in Novosibirsk, Russia, and his colleagues have compiled data showing how the Aral Sea has changed over the past 2000 years. Researchers had carbon-dated the shelves etched into the shoreline by past waves, and drilled cores to reveal which layers were once exposed. It turns out that water levels in the Aral Sea have varied widely, says Krivonogov. Humans may have played a role, because we have been farming the area for 2500 years.
In 1960, the lake’s surface was 54 metres above sea level. Yet between AD 400 and 600, it was just 10 metres above sea level, and recovered. Then between AD 1000 and 1500 it fell to 29 metres above sea level. The lake grew again after 1600, until Soviet irrigation began. The modern collapse is no worse than the older ones. By 1989, the lake was 40 metres above sea level, and a small northern lake split from the rest. Since then the northern part has rebounded. In 2005, a dam separated it from the south, cutting water loss from the north.
The north Aral Sea is back up to 42 metres above sea level, and native fish have returned from river refuges, says Nikolay Aladin of the Russian Zoological Institute in Saint Petersburg. “The fish catch is a small fraction of what it was in the mid-1950s, but the rehabilitation of the northern part has been pretty amazing,” says Micklin. The southern part is still shrinking though. It has split into three salty lakes less than 29 metres above sea level. The eastern one is so salty that only brine shrimp live there. No work is under way to restore this southern region. It has always looked like a lost cause. So it will keep shrinking and getting saltier until only brine shrimp are left, says Aladin.
Using less water to irrigate crops could restore the entire Aral Sea, says Micklin. But it would devastate the farms, which have actually increased the irrigated area since the end of the Soviet era in 1991. Some have shifted from water-hungry rice and cotton to winter wheat, but many farmers need the cotton money.