中亚干旱区的荒漠化与土地利用

笔者在实地考察、航片和卫星影像判读的基础上,参考国际上最新研究成果,以咸海盆地和古丝绸之路沿线地区为例,分析探讨了中亚干旱区荒漠化发生的过程、机制及其对自然和人文环境系统的影响和危害。由于大量从阿姆河和锡尔河引水扩大灌溉、浪费水源及单一农作物种植,使1960年时还为世界第四大湖的威海水面和蓄水大减,在干枯了的湖底和周围耕地上荒漠化快速发展,造成自然环境系统的严重退化和社会经济的巨大损失。虽然在我国丝绸之路沿线地区自古以来就有荒漠化现象,但荒漠化的规模在近40年来发生了根本性变化。塔里木河下游和克里雅河下游及玛纳斯河下游的湖泊干枯,植被退化甚至消失,不少野生动物灭绝。

DESERTIFICATION AND LAND USE IN THE ARID AREAS OF CENTRAL ASIA

To provide enough food for the rapidly growing population, all countries of Central Asia have been exploiting the virgin land for generations. Desertification has plagued this region for more than 1 000 years, but particularly during the last four decades. The aim of thes paper is to examine the process of desertification and its background, impactas well as the threat in the arid areas of Central Asia on the basis of case studies mainly done in the Aral Sea Basin and along the ancient Silk Road. Change to the Aral Sea Basin is regarded as one of the most extreme cases of environmental degradation of the twentieth century. The Aral Sea was the world's fourth largest lake in surface area in 1960. By 1992 its area had decreased by 54%,lake levels had fallen more than 16 meters, and volume droPPed by 75%. In 1989the sea had receded into two separate parts. This desiccation has been mainly caused by the large-scale expansion of irrigation in the sea's drainage basin initiated in the 1960s. Additionally, a large amount of water has been wasted because of mismanagement.Approximately six bines more water is used for irrigating a hectare cotton field in Uzbekistan than in lsrael. Owing to the desiccation of the sea, desertification has been rapidly spreading. 80% of the northern area of the former Aral Sea is now desertified.The progressive desertification has reduced the productivity of pasture land and destroyed the forests and meadows which are being replaced by psammophytic vegetation. Some of the former ports are being buried under mobile dunes. Salt and dust storms arise from the exposed bottom of the sea and adversely affect a large adjacent area. The ecosystem of the sea and delta were damaged; over 200 species of faUna and flora disappeared. The mean salinity in the sea has increased from 9% in 1957 to 36% in 1991.The groundwater level has sharply dropped along the coast. The priority to cotton growing has made the soil impoverished. In order to limit the drop in yield, the consumption of chemical fertilizer and pesticide has been increased continuously. In the area of Uzbekistan the use of pesticides reaches 54 kg/ ha on average. These fertilizer and pesticides pollute the surface and ground water badly.Because of the arid conditions the habitants have no other drinking water resources except for the two rivers of Amu-Darya and Syr-Darya. The contaminated warer has led to the highest morbidity and mortality rates recorded anywhere in the former Soviet Union. The infant mortality rate in the Aral Sea region is four bines higher that in the European territory of the former Soviet Union. Along the Silk Road numerous ancient oases, e.g. Subashi in Kuqa and Loulan near Lop Nur, are partially submerged beneath sand sheet and spare shrubs. These oases, mainly located in the southern and northern Tarim Basin, experienced their especially prosperous bine during the Han and Tang Dynasties. Owing to the long-term irrational irrigation, salinisation and alkalinisation of soils and waterlogging took place.The vegetation disappeared and the aeolian movement of the sand in the alluvial plains was. initiated. Also the change of river courses has caused the environmental deterioration. The evaluation of historical literatUre shows that the Kenya River crossed the Tarim Basin and flowed into the Tarim about 2 000 aB.P., 400 a B.P.and 200 a B.P. Since then, as it does today, the Kenya River disappears in the middle of the Takelamagan desert. Additionally, wars, which happened frequently in the history of Central Asia, have accelerated the process of desertification in some areas such as in the Turpan Basin. Gaochang was an ancient city located southeast to the present town Turfan. It was created in the Han Dynasty and had been settled until the 16th century.In the 12th century Gaochang was the Capital of the Xizhouhuihu, a kingdom at that bine in the region. Because of the war in the 17th century the irrigation system was destroyed, and consequently the city and the land around it became desert-like landscape.The author saw these kind