内蒙古高原小叶锦鸡儿(Caragana microphylla)灌丛沙丘:形态特征及表面气流

Caragana microphylla NEBKHAS IN INNER MONGOLIA PLATEAU: MORPHOLOGY AND SURFACE AIRFLOW

小叶锦鸡儿灌丛沙丘是内蒙古高原阴山北麓农牧交错带的主要风沙堆积类型。野外调查表明灌丛沙丘在该区主要分布在耕地、冲积扇下风侧和村落周围等人类活动频繁的地段。根据对耕地、冲积扇下风侧典型样地灌丛沙丘形态参数的详细测量和沙丘及丘间地气流的系统观测结果,发现灌丛沙丘覆盖度及风沙沉积量顺风向减小,近地面气流空气动力学粗糙度顺风向减小;在沙丘单体,风速廓线由迎风坡经丘顶至背风坡趋于复杂。在沙丘形态诸参数中,沙丘高度与水平尺度之间存在良好的幂函数相关,表明在目前风况和沙源环境中该区灌丛沙丘处在加积增高阶段,但其速率小于水平扩展。该区灌丛沙丘的规模主要受上风侧可供沙源有效性和灌丛生长状况的控制,灌丛沙丘的出现是该区土壤风蚀和土地退化的主要标志。

Caragarta microphylla nebkha is the main aeolian deposit in the agro-pastoral transitional zones of the northern foothills of YinShan Mountain range in Inner Mongolia, Plateau. Field investigations showed that the nebkhas mainly distributed at the downwind sites of cultivated land and alluvial fans, and around residential areas with frequent human disturbance. Detailed measurements and analysis of the morphological parameters and systematic observation of near surface airflow over the nebkhas were conducted in typical sample plots in downwind side of cultivated land and alluvial fans. The results indicate that both the thickness of aeolian sand deposition of the nebkhas and the near surface aerodynamics roughness of airflow decreased toward downwind direction. For a single dune, wind velocity profile became more complex from windward slope to leeward slope across the dune. Among all the parameters of nebkhas morphology,the relation between the height and horizontal scale of the dunes can be expressed by power function. In the conditions of present wind regime and sand source, the dunes are in the stage of vertically accretion, but the growing rate of height was less than horizontal expansion rate. The nebkhas size is mainly controlled by shrub growth and the upwind side sand availability, and accordingly,the formation and development of the nebkhas is the main indicator of soil wind erosion and land degradation in this region.