The effects of sorting by aeolian processes on the geochemical characteristics of surface materials： a wind tunnel experiment

The geochemical characteristics of aeolian and surface materials in potential source areas of dust are frequently employed in environmental reconstructions as proxies of past climate and as source tracers of aeolian sediments deposited in downwind areas. However, varia- tions in the geochemical characteristics of these aeolian deposits that result from near-surface winds are currently poorly understood. In this study, we collected surface samples from the Ala Shah Plateau （a major potential dust source area in Central Asia） to determine the influence of aeolian processes on the geochemical characteristics of aeolian transported materials. Correlation analyses show that compared with surface materials, the elements in transported materials （e.g., Cu, As, Pb, Mn, Zn, Al, Ca, Fe, Ga, K, Mg, P, Rb, Co, Cr, Na, Nb, Si, and Zr） were subjected to significant sorting by aeolian processes, and the sorting also varied among different particle size fractions and elements. Variations in wind velocity were significantly correlated with the contents of Cr, Ga, Sr, Ca, Y, Nd, Zr, Nb, Ba, and Al, and with the Zr/Al, Zr/Rb, K/Ca, Sr/Ca, Rb/Sr, and Ca/Al ratios. Given the great variation in the geochemical characteristics of materials transported under different aeolian processes relative to those of the source materials, these results indicate that considerable uncertainty may be introduced to analyses by using surface materials to trace the potential source areas of aeolian deposits that accumulate in downwind areas.

Simulating the effect of wind erosion on aeolian desertification process of Horqin sandy land and its significance on material cycle:a wind tunnel study

Samples from the Horqin sandy land were exposed to a series of wind velocities,and sink particles were collected at the end of the diffusion section of a wind tunnel.Grain sizes of collected samples show great variation because of the granularity difference of the surface samples.The original samples show lower average content of SiO_(2) and higher average content of Al _(2)O_(3),Fe_(2)O_(3),MgO,CaO,Na_(2)O,and K_(2)O than collected samples.Compared with other dust source areas in China,the Horqin sandy land had higher content of Zr,Ba,SiO_(2),Al_(2)O_(3) and K_(2)O.Compared with the average upper continental crust(UCC)composition,surface samples were rich in the content of Y,Zr,Nb,Ba,La,Nd.Geochemistry characteristics of fine grain components of the Horqin sandy land differ from those from other dust source regions,because fine-grained particles in the Horqin sandy land were mostly derived from various local deposits formed in its unique depositional environments influenced by several tectonic activities.

Geochemical-geomorphological Evidence for the Provenance of Aeolian Sands and Sedimentary Environments in the Hunshandake Sandy Land, Eastern Inner Mongolia, China

Identifying the provenance of aeolian sediments in the Hunshandake Sandy Land is of great importance for understanding the formation of the dune fields in the mid-latitudes and for deciphering information about desert＇s responses to global change. By determining the major and trace elements concentrations of aeolian sands in three grain size fractions from the central and western parts of the Hunshandake Sandy Land, we systematically study the provenance and the depositional history of aeolian sands in this desert environment. Our results show that aeolian sands from the Hunshandake Sandy Land are enriched in SiO2 and are depleted in many other elements compared to those of the Upper Continent Crust （UCC）. Variations of the immobile elements ratios like Zr/Hf, La/Yb, Th/Nb, La/Nb, LaN/YbN, GdN/YbN are relatively large in the coarse and medium fractions but minor in the fine fractions. Eu anomalies are quite different in the coarse fractions, but mostly positive in the medium fractions and all negative in the fine fractions. Decreasing tendency of Zr concentrations from the west to the east in the Hunshandake Sandy Land is evident in the coarse sands but rather weak in the fine grain size fractions. Our geochemical data indicate that the sources for the coarse and medium fractions of aeolian sands are diverse, influenced by local geology and geomorphology, while the fine sand fractions are more homogenous due to intensive mixture mainly by aeolian processes. Various ratios of immobile elements suggest that these sands should be sourced primarily from the surrounding mountains by fluvial/alluvial processes rather than from any remote territories. Aeolian sands with Ce negative anomalies are widely distributed in the Hunshandake Sandy Land, indicating that aquatic environments have occurred extensively prior to the occurrence of the dune field.

科尔沁沙地粗—细组分的碎屑锆石U-Pb年龄特征:对定量物源及区域构造-岩浆演化事件的指示

追踪干旱—半干旱地区大型沙地的物源和风-河流相互作用机制对于理解陆地景观格局演变、地表过程与地貌动态以及大气圈和岩石圈之间的联系至关重要。然而,目前科尔沁沙地的物源仍存在较大争议,且缺乏具有统计意义的锆石U-Pb年龄数据库。因此,本研究对科尔沁沙地地表风成沙进行多点取样,根据不同粒级(<63μm和>63μm)选取1500颗碎屑锆石进行U-Pb测年分析,并利用逆向蒙特卡罗模型对其物源进行定量约束。结果表明,从目视定性的角度看,科尔沁沙地的碎屑锆石U-Pb年龄谱特征非常相似。但定量重建结果显示沙地的物源整体上以中亚造山带的贡献为主(50.5%~61.3%),然而东南部体现出华北克拉通的绝对优势(~75.8%)。科尔沁沙地的物源存在空间异质性,沙地西部和北部的锆石年龄谱极为相似,与南部锆石年龄特征显著不同。科尔沁沙地的碎屑锆石U-Pb年龄特征基本不受粒度分异的影响,但沙地东南部除外。本文认为,风与河流的协同作用及其由此导致的沉积分异和再循环作用解释了科尔沁沙地碎屑锆石的U-Pb年龄特征。结合区域构造演化历史,科尔沁沙地在~2.5 Ga和~1.85 Ga的U-Pb年龄峰值分别是前寒武纪华北克拉通的生长、拼合与碰撞过程中的两期构造事件的产物。此外,~1.7 Ga的锆石年龄可能是对Columbia超大陆聚合与裂解的综合响应。古生代以来的锆石年龄峰值(500~400 Ma、300~250 Ma、130~110 Ma)记录了在古亚洲洋的俯冲闭合、蒙古-鄂霍次克海俯冲碰撞和古太平洋的俯冲、回退的区域构造背景下多期区域构造-岩浆事件。

Variations in aeolian landform patterns in the Gonghe Basin over the last 30 years

Wind erosion,or the transportation and deposition of sand into desert dunes and aeolian loess,is one of the most important aeolian activities.The progression of aeolian landforms expands arid and barren landscapes,leading to the degradation of adjacent areas.The Gonghe Basin,as a typical plateau with abundant sand sources,is highly sensitive to changes in the local climate conditions.In order to quantify the spatial-temporal variations in the aeolian landforms in the Gonghe Basin,we conducted field surveys and also analyzed twelve remote sensing(Landsat5 TM and Landsat8 OLI)images that sample the Gonghe Basin from 1989 to 2019.In the Gonghe Basin,we identified aeolian landforms such as climbing dunes on the windward slopes of the foothills,checkerboard dunes in the southeastern part of the basin,flat dunes,parabolic dunes and crescent dunes on the east and west sides of Longyangxia Reservoir,shrubby sandbanks on the valley slope in Shazhuyu,Tanggemu,and Indel,and sandy thickets at the bottom of the valley near the Dalian Sea,the Longyangxia Reservoir,and the tributaries of the Yellow River.From 1989 to 2005,the area of the aeolian regions expanded by 816.7 km2,with an annual conversion rate of 0.05%.From 2015 to 2019,the area of the aeolian regions shrunk by 2411.9 km2,with an annual conversion rate of−0.15%.The number and size of the fixed and semi-fixed dunes(e.g.the shrubby sandbanks on the valley slope and the sandy thickets at the bottom of the valley)were more stable than those of the mobile dunes(e.g.the checkerboard dunes,the flat dunes,the crescent dunes,the parabolic dunes,and the climbing dunes).The fixed and semi-fixed dunes were arranged in an irregular ring shape,and the location of the center of gravity of this ring did not change significantly from 1989 to 2019;in this time,the mobile dunes migrated to the northwest.

Spatial distribution and formation mechanism of aeolian sand in the middle reaches of the Yarlung Zangbo River

Aeolian sand landforms in the Yarlung Zangbo River(YZR) valley are a special type of aeolian landform that has attracted the attention of many scholars. However, the spatial distribution as well as the formation mechanism of aeolian sand has rarely been reported with integrated studies. In this paper, for remote sensing interpretation, scanning electron microscopy(SEM), X-ray diffraction(XRD) and particle size distribution(PSD) methods were used to analyze the spatial distribution and the deposition characteristics of aeolian sand. Combined with wind data and topography, the main driving factors and the formation mechanism of aeolian sand landforms were also examined. In the middle reaches of the YZR valley, there is a total of 2324.43 km^2 of aeolian sand, especially on the north bank of the wide valleys. In different wide valleys, the aeolian sand landforms exhibit a decreasing trend from the upstream to the downstream regions in both the area and expansion rate of aeolian sand. The cyclonic vortexes generated by the westerly winds and glacial winds are the main driving factors for transporting alluvial sand to the riverbank areas to form aeolian dunes. There are three main types of sand dunes in the river valley: climbing dunes, lee dunes and circumfluent dunes. Climbing dunes and lee dunes are mostly located west of the Jiacha Gorge, and the circumfluent dunes are mostly located east of the Jiacha Gorge.

碳化-盐冻作用下风积沙混凝土损伤劣化机理及寿命预测

为评估风积沙混凝土碳化-盐冻作用后的耐久性能,以质量损失率、相对动弹性模量、抗压强度为指标,分析碳化作用对风积沙混凝土抗冻性能的影响,通过扫描电镜(SEM)与核磁共振(NMR)技术分析碳化-盐冻后其内部结构和孔结构变化特征,采用Wiener随机过程概率分布预测碳化作用后风积沙混凝土盐冻循环寿命.结果表明:碳化作用提高了混凝土强度,且使得盐冻循环作用下质量损失率增加,相对动弹性模量下降;无害孔与有害孔的比值反应了混凝土内部结构损伤特征;相对动弹性模量对混凝土盐冻环境最敏感,碳化28 d混凝土经受372次盐冻循环后完全失效.

风积沙堤坝填筑碾压工艺性能试验研究

采用风积沙作为堤坝填筑材料是一项新技术,它对沙漠区兴修水利工程具有重要意义。为研究风积沙碾压工艺性能并确定合理的施工工艺和参数,依托古浪县黄花滩调蓄水供水工程,通过对风积沙和粉土风积沙混合料进行颗粒分析试验、击实试验以及不同组合工况的现场碾压试验,开展了风积沙堤坝碾压工艺性能研究。试验结果表明:在现场施工条件下,干作业下最大干密度呈“双峰”特性的低含泥量天然风积沙呈不可碾压性,推荐采用湿作业;采用轻重振动组合碾压工况更加合理,天然风积沙湿作业时,单层摊铺厚度取400 mm,采用26 t压路机碾压5遍(静压1遍、轻振碾压1遍、重振碾压2遍、最后再静压1遍),压实度可以满足要求;掺入13%粉土后的风积沙混合料可碾压性更好,可有效提高坝面施工效率和工程质量;上层风积沙填筑碾压过程对下层风积沙的压实度有再次提升效果。

波浪—海滩—沙丘相互作用研究进展

基于Web of Science数据库搜索关键词“波浪—海滩—沙丘相互作用”,筛分出与主题紧密相关的文献近百篇并对其梳理与分析,将研究阶段与理论模式进行划分,厘清当前研究存在的问题与机遇。结果发现,波浪—海滩—沙丘相互作用研究自1980s以来经历了理论提出、区域拓展、深入研究3个发展阶段。理论模式从单一的概念模式发展为不同尺度概念下的相互作用理论模式,研究方法从单一的野外测绘和海图测深资料发展到野外实地观测、室内风洞试验、3S技术与数值模拟相结合的综合研究方法;研究区域,从澳大利亚东南部海岸扩展到欧洲、北美洲、南美洲和亚洲等地海岸。同时,波浪—海滩—沙丘相互作用研究中也存在一些尚未解决的问题:针对不同区域的海岸沙丘动力地貌系统难以总结出一个具有普适应的理论模式;微观尺度内,已有的理论内容难以完全的揭示波浪、潮汐水动力与碎波带/海滩和风动力与海滩—沙丘地貌之间的复杂相互作用机理;中观尺度内,整个碎波带、海滩与沙丘系统对风暴的响应与反馈机理还需要进一步观测与深入研究,且建立事件尺度内的动力与地貌响应过程和中期地貌形态变化之间的联系还需要更长时期的实地观测与模型改进;宏观尺度内,海平面抬升引起海岸变化的预测模型需要多时空的实地观测数据支持与验证。未来可结合历史资料、实地观测数据、高分辨率遥感影像数据,综合分析各环境要素与碎波带、海滩、沙丘地形地貌之间的动力过程与形态响应关系,采用数值模拟技术揭示不同时空尺度的波浪—海滩—沙丘相互作用关系机理,进一步完善波浪—海滩—沙丘相互作用理论内容。

^(137)Cs法在风沙过程研究中的应用前景

１３７Ｃｓ法在土壤侵蚀与泥沙沉积研究中已得到普遍的应用，但在风沙过程研究中尚未引起足够的重视。针对风沙过程研究中存在的有关问题，对１３７Ｃｓ法的应用前景作了展望，并提出了１３７Ｃｓ应用的若干建议。

Interactive effects of wind speed,vegetation coverage and soil moisture in controlling wind erosion in a temperate desert steppe,Inner Mongolia of China

The rapid desertification of grasslands in Inner Mongolia of China poses a significant ecological threaten to northern China. The combined effects of anthropogenic disturbances （e.g., overgrazing） and biophysical processes （e.g., soil erosion） have led to vegetation degradation and the consequent acceleration of regional desertification. Thus, mitigating the accelerated wind erosion, a cause and effect of grassland desertification, is critical for the sustainable management of grasslands. Here, a combination of mobile wind tunnel experiments and wind erosion model was used to explore the effects of different levels of vegetation coverage, soil moisture and wind speed on wind erosion at different positions of a slope inside an enclosed desert steppe in the Xilamuren grassland of Inner Mongolia. The results indicated a significant spatial difference in wind erosion intensities depending on the vegetation coverage, with a strong decreasing trend from the top to the base of the slope. Increasing vegetation coverage resulted in a rapid decrease in wind erosion as explained by a power function correlation. Vegetation coverage was found to be a dominant control on wind erosion by increasing the surface roughness and by lowering the threshold wind velocity for erosion. The critical vegetation coverage required for effectively controlling wind erosion was found to be higher than 60%. Further, the wind erosion rates were negatively correlated with surface soil moisture and the mass flux in aeolian sand transport increased with increasing wind speed. We developed a mathematical model of wind erosion based on the results of an orthogonal array design. The results from the model simulation indicated that the standardized regression coefficients of the main effects of the three factors （vegetation coverage, soil moisture and wind speed） on the mass flux in aeolian sand transport were in the following order： wind speed〉vegetation coverage〉soil moisture. These three factors had different levels of interactive effects on the mass flux in aeolian sand transport. Our results will improve the understanding of the interactive effects of wind speed, vegetation coverage and soil moisture in controlling wind erosion in desert steppes, and will be helpful for the design of desertification control programs in future.

风水两相作用和人类活动对无定河粗泥沙输沙量的影响

风沙活动、降雨和人类活动是干旱-湿润过渡区影响粗泥沙(d>0.05mm)入黄的几个重要因素。粗泥沙输沙量的变化取决于全沙输沙量和粗泥沙在全沙中所占的比例。基于悬移质输沙量和泥沙粒径构成、降雨量、沙尘暴日数和水土保持面积等数据,分析了粗泥沙输沙量与影响因素之间的关系,利用Arc-GIS和SPSS软件定量分析了影响无定河流域代表自然过程的风水两相作用和人类活动对粗泥沙输沙量的影响,并通过回归分析确定了不同影响因素对全沙输沙量和粗泥沙比例的贡献。结果表明,影响全沙输沙量的主要因素是降雨量和水土保持措施,而影响粗泥沙比例的是风沙活动和水土保持措施。利用二元回归分析确定了各因素的贡献比例,认为降雨量的减少和人类活动对全沙量减少的贡献相当,人类活动对粗泥沙比例降低的贡献高于风沙活动的作用。

风沙床面颗粒起动临界受力平衡模型的对比分析

风沙颗粒起动的受力平衡模型是风沙起动机制研究的重要内容。根据已有的研究成果,论述风沙颗粒起动的临界条件,介绍几种代表性模型。认为,影响自然状况下颗粒起动过程的因素是复杂的,尽管对主要影响因素的作用还未获得深入的认识,但是已提出的风沙颗粒起动的受力平衡模型对于认识风沙起动过程和机理具有重要的指导和启发作用,然而这些模型往往包含了较多的简化、假设以及有待于通过实验测定的系数,所以,不能够在实践中直接应用。而且,这些模型都是在特定的条件下得出来的,其应用范围具有局限性。有鉴于此,关于风沙颗粒起动的机制研究仍有较多的创新空间。

沙丘背风侧气流及其沉积类型与意义

在腾格里沙漠东南缘对现代沙丘表面气流、沉积过程的野外观测结果表明 ,由于区域气流、沙丘形态及其相互作用等的不同使沙丘背风坡气流发生变化 ,在此发现三种背风坡次生气流 :分离流、附体未偏向流和附体偏向流。前者以弱的反向流为特征多发生在横向气流条件下坡度较陡的背风坡 ;后二者具有相对高的风速 ,其中附体流多发生在坡度缓和的背风坡 ,其方向在横向气流条件下保持原来的方向 ,而在斜向气流作用下发生偏转且其强度为原始风入射角的余弦函数。根据背风坡气流方向及强度 ,作者阐述了不同区域气流环境中沙丘背风坡沉积过程、层理类型及特征 。

沙漠化过程中生物量损失的初步评估——以内蒙古科尔沁地区为例

内蒙古科尔沁地区近50a来沙漠化土地经历了发展—再发展—逆转的过程,到2000年,该地区的不同类型和程度的沙漠化土地总计达50200km2,态势依然严峻。研究表明,沙漠化过程中生物量的损失主要体现在生态系统的退化中,其基本特征是伴随着生态系统的结构功能逐渐受到破坏,植被沙生化和土壤沙质化,最终导致低级的沙漠(地)生态系统的形成,生物生产量的降低。2000年度科尔沁地区旱作农田由于沙漠化过程所造成的地上生物量损失约为68.6万t,放牧草地的地上生物量损失量约为1008.2万t,总的损失量为1076.8万t。而在可以进行计算和评估的41a间,该地区由于沙漠化过程所造成的地上生物量损失量约为44148.8万t。

青海共和盆地多石在沟河道沙丘现代风水交互过程

选择青海共和盆地多石在沟河道中6道新月形沙丘链作为研究对象,采用Trimble4700DGPS与常规测量手段,结合野外风沙观测与自动气象站数据,初步观测分析了2006年多石在沟河道沙丘在不同季节的形态变化过程,计算出2006年风季前比雨季后多石在沟河道沙丘体积减小了548.3m3,风积量为2351m3,流水的蚀平量为2899m3,2006年风水两相营力对河道沙丘的侵蚀贡献率约为45%∶55%,流水的搬运作用强于风力的堆积作用。但从较长的时间尺度来看,研究区的风力侵蚀作用强于流水侵蚀作用,河道沙丘不断增大。多石在沟河道沙丘是一个典型的风水交互作用系统,河道成为风力与流水交互作用的"中转站",在风水的交替作用下,沉积物由风积环境进入流水环境中。

不同高度阻沙栅栏蚀积过程及防沙效益研究

通过对不同高度阻沙栅栏蚀积过程的野外观测,结合同时期区域风况资料,分析了阻沙栅栏前后地表蚀积形态、蚀积量以及蚀积强度的时空变化特征。结果表明,在沙源充足条件下,不同高度阻沙栅栏上风向表现为风沙堆积,下风向风蚀与堆积共存,且程度与栅栏高度有关,栅栏总体蚀积量和蚀积强度的变化趋势与下风向变化趋势相近。其中,60和70cm高度阻沙栅栏风沙堆积量最大,防沙效果最佳,但二者积沙方向存在差别。70cm高度阻沙栅栏上风向积沙较多;60cm高度阻沙栅栏下风向积沙较多。在实际应用中,应依据防护对象合理配置阻沙栅栏并适时加高,避免阻沙栅栏过低或过高,进而影响防沙效果。此外,依据断面形态、蚀积量和蚀积强度的变化,将栅栏前后分为风沙堆积区、风蚀区和蚀积平衡区。

人工防护林作用下风沙土成土过程的研究进展

人工防护林是防风固沙、有效防治沙漠化的重要措施之一。在沙漠地区建立人工防护林,可以有效防止土壤侵蚀,促进土壤有机质及黏粒积累,促使地表结皮形成,不仅对流沙起到了固定作用,而且促进了风沙土的成土过程。本文结合植物-土壤相互作用理论,分别从植物地上部分对养分的阻滞、聚集和减少土壤表面蒸发,以及地下部分的固沙和物质的分解与营养补给等方面综述了生物防护林在风沙土成土过程中的作用。同时,从以往的研究发现,在风沙土成土过程中,土壤机械组成变细,比重和容重减小;土壤剖面结构分异显著,分层增加;土壤含水量和养分显著聚集;土壤微生物数量和种类增加,活性增强,酶活性也大幅度提高。总之,随着沙漠生物防护林的建造,林下风沙土性质发生了明显的改良作用,逐渐发展成固定风沙土。说明人工防护林和风沙土的成土过程是协同发展的,这不仅有利于沙漠防护林的可持续管护,也有利于沙漠化的防治和退化生态系统的恢复与重建。

风沙起动形式与起动假说

风沙颗粒起动是风沙物理学与沙尘释放研究的重要内容,但是,这一领域的研究很不成熟。本文根据国内外目前的主要研究成果,讨论了风沙起动的形式,将风沙起动理论归纳为风压起动说、升力起动说、冲击起动说、压差起动说、振动起动说、斜面飞升说、猝发起动说、湍流起动说、负压起动说和涡旋起动说等10种假说。进一步将风沙起动假说归纳为以接触力为主的起动学说和以非接触力(气力)为主的起动说两大类。最后认为,风沙起动的影响因素是复杂的,各种学说都有其合理的成分,反映了真理的某个侧面,但试图仅仅靠某一种学说或某一种力来解释风沙的起动是不够完善的。风沙起动过程同时受多种力的作用,只是这些力所起的作用各异,在分析时要分清主次。再者,同一种力在不同性质(如不同密度、粒径和形状等)沙粒的起动过程中所起的作用也可能是不同的,在研究中还需要具体问题具体分析。风沙起动机制尚需全面、深入和科学的研究。

神北矿区矿井水资源化研究

为了将神木煤田矿井废水资源重新利用,根据当地天然的地域条件和风积砂资源,研究了利用当地风积砂进行矿井废水处理的可行性,在研究中发现,同一砂层厚度不同停留时间和同一流量不同砂层厚度都对处理效果有影响.在上述试验的基础上,提出了利用砂滤处理矿井废水的工艺流程.