库布齐沙漠南缘沙丘固定初期的动态变化研究

The fringe area of desert is very sensitive to climatic changes, which is showed by morphological changes, active and stabilized of aeolian dunes. Our research focused on typical dunes with different vegetation coverage on the southern fringe of Hobq Desert, using remote sensing, topographic survey and spatial analysis techniques for tools to investigate the dynamic change and morphology of the dunes and their relationship with climatic factors. Through time series of remote sensing images and times topographic measurements morphological parameters, rates of dune migration and the dynamic change of vegetation on typical dunes during the incipient phase of stabilization will be evaluated. Wind velocities, sand transport and patterns of erosion and deposition will be measured in order to unveil interactions between flow dynamics and vegetation coverage over dune surfaces. Surface sediment will also be analyzed in order to show the relationship between grain size sorting and dune mobility. Understanding the dynamic changes of dunes during the incipient phase of stabilization may provide evidences for dune landscape management and the research of desert landscape response in the context of the changing climate.

沙漠对气候变化的响应在其边缘地带尤为明显，并体现在单体沙丘的活性、形态及移动等动态变化上。本项目拟在库布齐沙漠南缘，采用遥感监测、地面测量、采样分析和空间分析相结合的方法，研究沙丘固定初期动态变化及其与气候要素之间的关系。开展典型沙丘形态的重复测量，揭示沙丘形态、植被覆盖和移动等动态变化规律；开展沙丘表面风沙输移及蚀积格局的观测与测量，阐明不同植被覆盖程度或活性沙丘的形态动力学特征；开展沙丘表层沉积物的重复采样分析，探讨沙丘表面沉积物粒度分布及其对沙丘活性变化的响应。项目研究可为理解沙漠景观对气候变化响应提供基础数据以及为实施防沙治沙工程提供理论参考。

沙漠边缘的单体沙丘对气候变化响应敏感，本项目在库布齐沙漠南缘，监测单体沙丘的活性、形态及移动等动态变化，分析沙丘固定初期动态变化及其与气候要素之间的关系。近24a来，研究沙丘大致经历了沙斑-成形-半固定-固定的演化过程，自发育成形以来，沙丘植被覆盖面积不断增加，沙丘移动速率波动下降，2012年夏季，沙丘表面发育大量植被，沙丘逐渐固定。1998-2022年，研究沙丘平均移动了74.9 m，平均移动速率为0.5~8.9 m a-1，移动方向在82.5°~103.2°之间，在移动速率波动下降过程中经历了两次明显快速移动。相对而言，新月形沙丘移动速率较快，抛物线形沙丘移动速率较慢，抛物线形沙丘移动速率由大到小依次是中型、小型和大型。沙丘在移动过程中平面形态发生明显变化，抛物线形沙丘两翼拉长，新月形沙丘兽角变短而平面形态变为“贝壳”形。沙丘面积、长度、宽度和长宽比趋于增大，沙丘高度和体积趋于减小。沙丘迎、背风坡变长变缓，迎风坡趋于下凹，背风坡滑落面变小最后消失，沙丘表面侵蚀主要发生在两翼内侧坡面和迎风坡风蚀坑部位，堆积主要发生在灌丛沙堆和背风坡处。植被由两翼外侧向主体发展，在翼间平地顺风向呈带状扩展，沙丘植被发育因沙丘形态各不相同，规模越大越难被植被完全固定。沙丘固定过程中粒径变细，分选变好，固定前沙丘粒径自迎风坡向背风坡变细，而固定后出现相反分布状况。研究区气候呈暖湿化趋势，起沙风、输沙风能明显下降。沙丘的动态变化受气候要素和自身形态的共同影响，沙丘移动速率与区域降水量和风况变化相吻合，沙丘活性较强的新月形沙丘和低矮的中型抛物线形沙丘的移动速率对气候要素变化的响应更加敏感。