塔克拉玛干沙漠地区沙漠化过程及其发展趋势

塔克拉玛干沙漠处于内陆盆地,在极端干旱多风的气候条件下,丰富的冲积、冲积-湖积沙物质在风力作用形成面积广大、形态复杂的流动性沙漠,它是在中更新世至全新世时期逐渐形成。然而,以自然因素为主形成的沙漠,同样亦存在着沙漠化问题。塔克拉玛干沙漠地区的沙漠化土地约有28266平方公里,占总土地面积的9.2%,其中历史时期形成占65.1%,现代形成的占34.9%。该区历史时期沙漠化过程多发生在南部和东部沙漠中河流下游的绿洲地段,由于河流改道(自然的或人为的),潜水面下降,造成古耕地和居民点废弃,形成沙漠化土地,在北部,塔里木河两岸和天山南麓一些洪积、冲积扇前缘,则由于河道迂移或人为的垦区长期不合理灌溉,地下水位上升,土壤严重次生盐渍化,不能耕种而废弃。沙质干河床或废弃的垦区受到风力作用成为沙漠化土地。塔克拉玛干沙漠地区近百年来由于人为因素的干扰,对自然资源利用不当,破坏了脆弱的生态系统或对水资源利用不当而引起现代沙漠化过程的加剧。当然,也有局部地区是沙丘前移入侵的结果。根据沙漠化土地的形成可以划分三种类型:1.沙丘前移入侵型;2.沙丘活化型;3.戈壁风沙流型。

Desertification Processes and Developmental Tendency in Taklimakan Desert Region

The Tkalimakan Desert, situated in the inland basin where there are plenty of alluvial and lacustrine deposit, was gradually formed in Mid - Pleistocene and Holocene under the extreme dry and windy climate. It is a huge and moving sandy desert with complex landforms, However, there are also desertification problems for the deserts mainly formed by natural factors, The desertified land in the Taklimakan Desert Region covers an area of 28,266 km²,or 9.2% of the total area, of which 6.5% was formed in historical period and 34.9% in contemporary age. The desertification process of historical period in this region mainly occurred in the oases of lower reaches of rivers in the southern and eastern parts of the desert. Owing to the ancient rivers changed their courses (caused by natural or anthopogenic factors) and the reduction of phreatic surface, farmland and settlement were abandoned, thus forming the desertified land. In the northern part, both sides of the Trim River and frontal margin of diluvial and alluvial fans south of the Tianshan Mountain, dry sandy riverbed or abandoned farmlands turned into desertified land due to the river changed its course or long period of irrational irrigation caused the rise of water table and severe secondary salinization of soils. For nearly one hundred years, the desertification process in the Taklimakan Desert Region was aggravated thanks to the interferences of man-made factors and misuse of natural resource destroyed the fragile system, of course, local places resulted from sand dune encroachment. Based on the formation causes, the desertified lands can be divided into three types: l.Sand dune encroachment type 2.Sand dune activation type 3.Gobi sand drift type According to the developmental processes and present status of desertification in the Taklimakan Desert Region, the developmental tendency of desertification was predicted and its controlling measures were suggested. 1. "Green Corridor" area in lower reaches of the river at fringe of the Taklimakan Desert: In the past 25 years, desertification developed rapidly, belonging to severe desertification. It's necessary to work out an overall plan so as to rationally allot water resource in upper, middle and lower reaches: use land resource with establishing grassland as the main aspect; establishing wind breaks to protect farmland, settlement and roads. 2.Shrub sand mound area at fringe of newly reclaimed region: Shifting sand is rapidly explanding, measures must be taken to protect the existing vegetation, in addition to, it needs to establish artificial protective forest at fringe and within the reclaimed area by using trees and shrubs. 3. River banks situated deep in the desert: wind erosion is serious. It's not suitable for the farming here due to high water table and soil secondary salinization. However, there is vast area of natural populus diversifolia forest, therefore, it suits to establish natural preserve.