策勒绿洲—沙漠过渡带风沙流挟沙粒度的垂直分异

Vertical distribution of grain size in aeolian flow in Cele oasis-desert ecotone

在策勒绿洲一沙漠过渡带选取流动沙地、半流动沙地两个典型下垫面,采集下垫面地表0~1 cm沙样,利用梯度集沙仪收集风风沙流中垂直高度层中1~20 cm的沙通量,利用mastersizer2000分析所收集沙样的粒度。结果表明研究区风沙流挟沙粒度的垂直分布特征为:沙粒平均粒径随高度增加而减小,风沙流中沙粒的平均粒径小于床面沙粒平均粒径。其中粉沙含量随着高度的增加,其相对含量呈现幂函数增加,极细沙和细沙含量随高度的增加呈幂函数规律递减。风沙流中平均粒径(φ)值在3.58~3.81;分选系数集中在0.46~0.55,分选性较好;偏度值变化范围为-0.006~0.1,峰度变化值在0.94~0.96。半流动沙地风沙流中平均粒径小于流动沙地,分选性较好。平均粒径(φ)与分选系数、峰度和偏度均呈正相关,分选系数与偏度、峰态间呈现正相关,峰态与偏态之间呈现正相关。研究区沙粒主要以细沙、极细沙和粉沙为主,分选性较好,沙粒粒径分布符合正态。流动沙地较半流动沙地风蚀程度大,地表沙粒粒径粗。策勒地区地表风沙来源主要为风成沙,沙粒运动方式以跃移质为主,悬移质次之。

Selecting two different underlying surface including mobile sandland and semi-mobile sandland in Cele oasis-desert ectone, Xinjiang, China, via gathering sand grain in 0-1 cm depth on sand bed surface and collecting vertical sand transportation by gradient sand trap in the height of 0-20 cm when it has wind and dust activity, then measureing grain size by using of mastersizer2000, and all of sand granularity parameters were calculated by Folk ＆Ward＇ s equation as well as its judgement standard. The result indicates that the sand bed grain size is larger than the vertical＇ s in wind-sand flux, and the mean sand grain size decreased with the height. In vertical layer of mobile sandland, its mean silt content is about 28.67%, and its very fine sand and fine sand content accout for 62.31% and 8.94% respectively, and medium sand is the least, its content is only 0.08%. The same measuement was been con- ducted in semi-mobile sandland, the result displays that silt content of semi-mobile sandland is much more than mobile sandland, it is about 32.25%, and very fine sand content decreased to 58.26% correspondingly. Above sand bed surface, milt increase with the vertical height. Adversly, the very fine sand, fine sand and the medium sand de- crease with vertical height. Both the mobile sandland and semi-mobile sandland, its grain size distribution displays the same pattern in vertical layers. Sand grain size percentage grows in power function when its size is less than 0.08mm, and its percentage decreases when its size is larger than 0.08 mm. The mean grain size in aerolian sand trans- port displays negative correlation with its sorting efficient, skewness and kurtosis, and its sorting efficient displays positive correlation with its skewness and kurtosis. The underlying surface grain is mainly consisted by silt, very t^ne sand and fine sand,its sorting efficient is high. From mobile sandland to fixed sandland, the wind erosion degree eas- es, so the mean grain size decreases. The deposition of the study area is derived from wind-blown sand, and the sand grain transportation mainly by saltating and suspending. All in all, the grain size is tiny in Cele oasis-desert ecotone, where is easy to be the sand-storm source,so it＇s necessary toprevent and govern local sand movement.