科尔沁沙地流动沙丘掘穴蚁（Formica cunicularia）筑丘活动及其对土壤的作用

 以科尔沁沙地典型流动沙丘作为研究对象,通过调查不同坡度地形上掘穴蚁的蚁丘直径、密度和盖度分布,讨论了不同坡度地形对掘穴蚁筑丘活动的影响,并分析了掘穴蚁筑丘对不同坡度地形土壤的作用。结果表明,迎风坡和背风坡的坡底、坡中及丘顶对蚁丘直径、密度和盖度分布影响明显,其中蚁丘直径迎风坡坡中显著小于其他坡度地形（P<0.05）;密度和盖度分布顺序均表现为:丘顶>坡中>坡底。掘穴蚁筑丘改变了土壤性状,导致土壤含水量升高,pH值变小而电导率变大,有机质和全氮含量增加;微地貌条件下,蚁丘含水量和全氮含量迎风坡坡底较高,而蚁丘有机质含量背风坡坡底较高,但蚁丘土壤pH值和电导率丘顶较小。整个流动沙丘土壤基质均比较疏松,流动沙丘微环境易受风力作用而改变,从而影响掘穴蚁的筑丘活动分布,但不同坡度地形间蚁丘分布差异基本上均没有达到显著水平（P>0.05）。     

风向对半固定沙垄表面风速影响——以古尔班通古特沙漠为例

利用DETI可移动测风系统对古尔班通古特沙漠半固定沙垄表面风速进行实地观测,获取了主要风季不同风向条件下沙垄表面7个典型部位距离地表20 cm、40 cm、60 cm、100 cm和200 cm 5个高度的风速系列数据,系统研究风向对半固定沙垄表面坡面风速及风速廓线的影响。结果表明,迎风坡的气流加速和背风坡的风速降低现象在实际观测中得到证实,但受风向的影响甚大。垄顶风速放大率随入射角的增大呈指数关系递增,而背风坡风速占垄顶风速的比率则随入射角的增大呈线性关系递减。大角度入射气流速度变化主要受控于沙垄形态,小角度入射气流速度变化主要受控于地表植被状况。无论气流以何种角度入射,距沙垄表面20 cm高度气流的加速均较其他高度缓和。沙垄底部和坡中下部的风速廓线变化趋势基本一致,且呈较好的对数拟合关系;两坡中上部和垄顶部的对数拟合方程相关系数偏小;受回旋涡流的影响,风速廓线在背风坡上部有明显偏折,初步断定涡流中心在距地表40 cm左右的高度。     

呼伦贝尔沙地沙丘砂来源的定量分析--逐步判别分析(SDA)在粒度分析方面的应用

Quantltatively determining the sources of dune sand uis one of the problems necessarily and urgently to be solved in aeolian landforms and desertification research. Based on the granulometric data of sand materials from the Hulun Buir Sandy Land, the paper employs the stepwise discriminant analysis technique (SDA) for two groups to select the principal factors determining the differences between surface loose sediments. The extent of similarity between two statistical populations can be described quantitatively by three factors such as the number of principal variables, Mahalanobis distance D^2 and confidence level α for F-test. Results reveal that: 1) Aeolian dune sand in the region mainly derives from Hailar Formation (Q3), while fluvial sand and palaeosol also supply partially source sand for dunes; and 2) in the vicinity of Cuogang Town and west of the broad valley of the lower reaches of Hailar River, fluvial sand can naturally become principal supplier for dune sand.     

横向沙丘背风侧气流重附风洞模拟

二次流在沙丘形成和形态维持过程中扮演着重要角色。沙丘迎风坡气流加速和背风侧气流分离是最常见的二次流形式。沙丘背风侧的二次流,尤其是气流分离形成的分离涡和气流重附对沙丘背风坡的塑造、沙丘间距和排列模式都具有重要的控制作用。因此,设计了一系列具有不同迎风坡坡度的横向沙丘模型,采用粒子图像测速技术,通过风洞实验模拟了沙丘背风侧的气流分离和重新附着。实验结果表明,当来流风速垂直于沙丘脊线时,沙丘背风侧的气流重附距离介于4\^8 H~10\^8 H之间(H为沙丘高度),最大重附距离出现在迎风坡坡度为15°的沙丘背风侧;沙丘迎风坡坡度是控制背风侧气流重附距离的主要因素,而自由风速对气流重附距离的控制作用较小。根据实验结果,还讨论了气流分离与重附对沙粒运移和沙丘形态维持的沉积学意义。     

科尔沁沙地沙漠化正逆过程的地面判别方法

在实地调查和多年定位研究的基础上, 根据目前沙漠化过程研究的需要,介绍了沙地、沙丘、沙漠化土地等相关概念及其主要区别,阐述了沙地、沙丘、沙漠化土地类型的划分标准以及类型互换使用中应该注意的问题;通过分析影响沙漠化发展方向和过程的关键因素,建立了沙漠化正\,逆发展过程的地面判别指标体系,并讨论了不同类型沙丘的主要来源、发展方向及转换过程的判别方法。所建立的沙漠化正\,逆过程的地面判别方法,具有较强的实用性、可操作性和准确性, 可用于科尔沁沙地以及类似环境条件同类型沙地的野外调查和定位研究。     

Aeolian system sediment state: theory and Mojave Desert Kelso dune field example

The sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply, sediment availability and the transport capacity of the wind. The sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system. Numerous factors impact the susceptibility of grains on a surface to transport, but these are cumulatively manifested by the actual transport rate, which serves as a proxy for sediment availability. Transport capacity is the potential sediment transport rate of the wind. Because the three aspects of sediment state can be given as a volumetric rate, they are directly comparable. Plotted simultaneously against time, the generated curves define nine possible classes of sediment state. Sediment supply that is stored occurs because it is transport or availability limited, or generated at a rate greater than the potential or actual transport rates respectively. Contemporaneous or lagged influx to an aeolian system may be limited by sediment availability, but cannot exceed the transport capacity of the wind. For the Kelso dune field in the Mojave Desert of California, a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system. The sediment supply was generated during the latest Pleistocene and earliest Holocene during humid periods of enhanced discharge by the Mojave River to form the Lake Mojave fan delta or terminal fan, and has been calculated over time from the sedimentation rate and the frequency of floods. Estimation of transport capacity over time was based upon modern wind data, with an allowance for greater winds during the Pleistocene based upon climatic models. Sediment availability was approximated by calculation of a modern dune mobility index, with variation over time based upon climatic inferences. While quantifying the Kelso or any natural system is subject to numerous uncertainties, the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at Kelso, as well as illuminating questions for future research.     

沙粒级配和沙丘分布的分形分析

研究了沙粒级配和沙丘分布的分形特征,并对其分形维数作了定量计算。结果表明:沙粒级配的粒径分布的分形维数在2.43~2.69之间,沙丘分布的盒分形维数为1.28,这对用数学模型进行风沙动力学的定量研究有重要的参考价值。     

卵砾石沙波临界水流条件的水槽试验

以往对沙波的研究多针对河流中下游、河口海岸段的细沙(粒径D<1 mm),而长江上游等卵砾石输移河段(D>2 mm)是否会出现沙波以及卵砾石沙波的临界条件,尚需开展进一步研究。通过长江上游九堆子、筲箕背等卵石滩的现场踏勘,观察到明显的天然沙波形态。采用中值粒径D₅₀=1.8 mm和5.3 mm的天然沙和D₅₀=4.8 mm的轻质沙进行水槽试验,成功模拟出砾石沙波。根据恒定均匀流条件下,产生沙波的比降、水位、流量等水流条件及试验沙的粒径、比重,提出卵砾石沙波的临界条件公式。结果表明,卵砾石沙波的临界条件可以用量纲起动功率w_* 、R／D及比降S表达,并据此提出判别系数G_Dcr。当研究河段的卵砾石输移带上的水流条件满足判别系数G_Dcr,则可以判断能够产生沙波现象。     

荒漠地区土壤初始状况对水平入渗的影响

通过对沙坡头荒漠地区人工植被固沙区生物土壤结皮与固沙区外天然沙丘沙以及天然植被红砂、珍珠分布区砂粘土在不同初始含水率（θ_i）条件下土壤水平入渗过程的对比试验研究,探讨土壤质地以及θ i对水平入渗系数（λ_f）、剖面平均含水率（θ_m）状况的影响。生物土壤结皮对降水入渗量的截持作用大于沙丘沙,因而将显著地改变降水入渗过程中土壤水分的再分配格局,减少降水对深层土壤（沙丘沙）的有效补给。通过对土壤剖面平均含水率θ_m与距离湿润锋前缘0～5 cm、5～10 cm处体积含水率θ_fA、θ_fB比较,生物土壤结皮的θ_m、θ_fA和θ_fB分别约为沙丘沙的1．5倍。