【英語專四聽力周計(jì)劃】短文理解23

One of the foremost examples of modern human-induced environmental degradation is the drying-up of the Aral Sea in Central Asia. Its ecological demise dates from the 1950s when intensive irrigation began in the central Asian republics of the USSR. This produced a dramatic decline in the volume of water entering the sea from its two major tributaries. In 1960, the Aral Sea was the fourth largest lake in the world, but since that time it has lost two-thirds of its total volume, its surface area has halved and its water level has dropped by more than 216 meters. A knock-on effect of this ecological disaster has been the release of significant new sources of wind-blown material, as the water level has gone down. And the problems don't stop there. The salinity of the lake has increased so that it is now virtually the same as sea water. This means that the material that is blown from the dry bed of the Aral Sea is highly saline. Scientists believe it is adversely affecting crops around the sea because salts are toxic to palnts. This shows that dust storms have numerous consequences beyond their effects on climate, both for the workings of environmental systems and for people living in dry lands.