敦煌莫高窟崖顶灌木林带防风固沙效应

The effects of blown sand on the shrub belt over the top of the Mogao Grottoes

敦煌莫高窟的风沙防治必须要建立一个完整的防护体系 ,灌木林带的建立是这一综合防护体系中不可缺少的重要组成部分。通过对已建立的两条灌木林带防护效应的观测分析 ,结果表明 :灌木林带使其周围的气流场重新分布 ,改变了近地表风沙流结构 ,0 .5、2 m高处的风速梯度发生显著变化。在林带高 2 0～ 30倍的有效防护范围内风速降低 6 8.1%～ 4 0 .7% ,两条林带后2 m处的输沙率分别是林带前缘 30 m对照处的 1/ 38和 1/ 138,3a时间灌木林带内积沙厚度达 0 .7m。沙地浅层 (0～ 2 0 cm )细沙(0 .2 5～ 0 .1m m)和微沙 (0 .1～ 0 .0 5 mm)含量分别增加了 2 0 .6 %、5 .5 % ,有机质含量在植物根系分布范围内成倍增加。灌木带对区域小气候的改善效应明显。流沙地 0 .5、1和 1.5 m高处日平均气温比灌木带内分别高出 0 .5、0 .9和 0 .2℃ ,而相对湿度灌木林带内比流沙地平均高 0 .4、0 .3和 0 .1%。浅层土壤 (0～ 2 0 cm)温度昼夜变程与地表温度变化基本呈正弦态分布 ,并以垂直方向向下传递 ,但变幅较地表为小。灌木林带内 0～ 2 0 cm土壤平均温度比流沙地高 0 .

A blown sand control system is needed to protect the top of the Mogao Grottoes. In particular, a shrub shelter belt is an essential component of such a control system. Observational results show that the airflow field nearby shrub shelter belt is redistributed, and the near-surface sand stream is dramatically changed. The effective prevention range is 20～30 times of the height of shrub shelter belt, while wind velocity decreases from 68.1 to 40.7%, and sand transport rates at 2m behind every shrub shelter belt are 1/38 and 1/138 as much as the sand transport rates at 30m in front of the shrub shelter belt. Furthermore, the depth of sand accumulation in the shrub shelter belt reaches 0.7m. The fine and very fine sand on surface (0～20cm) layer increases by 20.6 and 5.5% respectively, and the organic content increases greatly in the area of vegetation roots development. Moreover, the shrub shelter belt also has an effect on micro-climate. The daily average temperature in dunes at 0.5, 1.0 and 1.5m heights is 0.5, 0.9 and 0.2℃ higher than in the shrub shelter belt, respectively. The relative humidity of the shrub shelter belt also increases at these heights by 0.4,0.3 and 0.1% than in the shifted sand. The variation of daily and night temperature on the surface (0～20cm) layer is sinusoidal in distribution.