Knowledge Resource Center for Ecological Environment in Arid Area
| 河西走廊东段干河床粉尘释放的实验模拟与分析 | |
| 其他题名 | The Aeolian Process of the Dried-up Riverbed in the Eastern Part of Hexi Corridor |
| 张彩霞 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 干河床广泛分布于中国北方干旱、半干旱区，虽然这一地貌类型的地表性质与戈壁有相似之处，但由于河流沉积分异和侧向侵蚀作用，不同河段河床沉积物组成和动力学性质都有差异，导致了干涸河床粉尘释放的复杂性。本论文对干河床内部最常见的沙物质表面、沙石结合表面以及泥质表面三类地表覆盖的粉尘释放特征进行了研究。 风洞实验表明干河床累积粉尘释放量可以达到247.85g，是河西走廊地区粉尘释放的潜在源地之一。干河床粉尘释放与下垫面覆盖类型相关。干河床有砾石覆盖或者表面为淤泥质的区段，粉尘释放率较低；而河床表面为沉积沙的区段是干涸河床的高粉尘释放段。在风速达到16m/s时，一旦下垫面有足够的松散物质供应，粉尘释放量快速增加。 风蚀条件下干河床物质组成变化特征，从粒度上来看，风蚀过程引起区域地表物质粒度的“粗化” ，干河床沉积物普遍存在着分选性差的特征，经过风力的分选作用后，风成物粒级级配向粗化方向移动，平均粒径变粗，分选变好，变为了近对称的正态分布类型。大气降尘样品以小于63μm的粉沙和粗粉沙为主，而干河床风成物以大于125μm的细沙和中沙组成为主，恰好解释了风成物缺失的细粒物质以粉尘的形式从干河床向大气释放。 河西走廊东段干河床的地表沉积物组成以硅酸盐矿物为主，常量氧化物以SiO2含量最高，占到平均77.87%，其次Al2O3为9.74%，其他氧化物含量较少，总计不到10%。从元素的赋存来看，SiO2和 K2O多赋存于较粗的部分，Al2O3, Fe2O3, MgO，CaO和Na2O多赋存于较细的部分。这也将意味着Al2O3, Fe2O3, MgO、CaO和Na2O更容易随着较细的颗粒随风进行迁移，而SiO2和K2O则较容易富集在原地。风蚀过程引起干河床样品常量和微量元素发生不同程度的迁移。由于风沙活动的影响，一些元素的含量和元素常用的代用指标都表现出了明显的差异。组成河西走廊东段干河床主要矿物有：石英，钠长石，正长石，大隅石，白云母和黑云母。从矿物组成上来看，主要以氧化物类和硅酸盐类矿物为主。从粗细组分的矿物对比来看，石英和正长石在粗粒部分含量较高，大隅石在粗细组分中基本均匀分布，其他矿物组分更容易在细颗粒中富集。干河床样品在风蚀条件下其矿物组分发生了一定程度的变化，如大于63μm组分中，白云石，正长石的含量变化与风速变化呈显著正相关，而铁铝石榴子石的含量变化与风速显著负相关。在小于63μm组分中，有机质和斜长石的含量变化与风速呈非常显著负相关，铁白云石含量变化与风速显著负相关，高岭石和阳起石含量变化与风速显著正相关。从干河床粉尘释放机理来看，祁连山区是河西走廊东段地表碎屑物质的主要源区，在重力侵蚀和流水侵蚀的作用下，经过河流作用和风力作用被不断的搬运和沉积，并沿着高程分布形成了高山-绿洲-荒漠的级联系统。在其中发育了山麓坡地、冲洪积扇、戈壁、沙丘、绿洲和冲击平原等地貌类型。在河流的末端或者是支流的末端，往往形成了干河床。这些河床由于地势较两侧冲击平原或者绿洲区域较低，在风力作用下，成为了风力搬运碎屑物的廊道，同时，以条带状向区外进行粉尘的输出。其所释放的粉尘在空气对流和湍流扩散的作用下，被输送入大气中，和他源粉尘释放一起，其中一部分作为凝结核参与到大气循环中，而一部分通过干湿沉降作用再次成为地表物质。在此过程中，干河床不仅作为释放源向外界释放粉尘，而且还是粉尘搬运的重要通道，因而在干旱区粉尘释放的研究中有非常重要的意义。 |
| 英文摘要 | Dried-up riverbeds cover a wide area in arid and semi-arid regions of China, Altough there are lots of similarities in its surface charactoristics with the Gobi desert, there were much differences between the riverbed sediments and dynamics characteristics due to the sediments difference and lateral erosion function, which led the complex of the dust emission from the riverbed. At present, wind tunnel studies, which remain limited, are important tool to understand the aeolian processes of dried-up riverbeds. The particle size, chemical composition and the mineral contents of sediments arising from the dried river beds are poorly understood.The paper discuss the dust emission characteristics of three typical land surfaces including aeolian deposits, pavement surfaces, and Takyr crust.Our wind tunnel experiment indicated that the accumulated aeolian transport material from the dry riverbeds can reached to 247.85g, and thus dried-up riverbeds could be one of the main sources of dust emission in the Hexi Corridor. The dust emission rate were related to the land surfaces types, surfaces with pavement surfaces, and Takyr crust were the lower area for dust emission, while the surfaces with the sand had higher emission rates. The process of wind erosion was reconstructed using a 3D scanner, and we found that as soon as the wind velocity reached 16 m/s, and assuming there was a plentiful supply of source material, aeolian transport intensity increased rapidly.The main component of the dried-up riverbed and associated aeolian processes was fine to medium sand. The dust samples were coarser than the parent riverbed samples, the sediment from the dried-up river bed had the characteristics of bad gradding type, as the aeolian processes have a sorting effect on the source sediment eroded from the riverbed, the grain size getting coarser, and well-sorting, which belongs to the asymmetrical normal distribution type.The dried-up riverbed sediment and the associated aeolian transported material were composed mainly of fine and medium sand. However, the transported samples were coarser than the bed samples, because of the sorting effect of the aeolian processes on the sediment. The dust collected from the atmosphere were mainly composed of the fine sand and coarse fine sand, while the aeolian material were mainly composed of medium sand, which means the fine part was emitted by means of the dust. The elements composed the sediments of the dried riverbed were silici minerals, The content of SiO2 were the highest, accounting for an average of 77.87%, followed by Al2O3 with 9.74% and other oxides with less than 10%. The averaged results indicated that SiO2, K2O, and Na2O are usually more abundant in the fraction coarser than 63 μm, whereas Al2O3, Fe2O3, MgO, and CaO were usually concentrated in the fraction finer than 63 μm. This will also mean that Al2O3, Fe2O3, MgO, and CaO are easier to migrate with the smaller particles, while SiO2 and K2O are easier to accumulate in situ. Due to the influence of wind and sand activities, there are obvious differences between the content of some elements and the commonly used proxy indicators.The main minerals contened in the dried river bed of the east section of hexi corridor were Quartz, Albite, Orthoclase,Osumilite, Muscovite and Biotite. In terms of mineral composition, The main mainly minerals includes oxide and silicate minerals. Quartz and Orthoclase were relatively higher in coarser part, Osumilite were equally distribution both in coarser and finer part, other mineral components were more easily enriched in the fine particles. Correlation analysis between the wind velocities and the mineral contents indicated that there were significant positive correlations between wind velocity and the dolomite and orthoclase contents and significant negative correlation between wind velocity and the almandine contents in materials coarser than 63 μm, and concentrations of the actinolite and kaolinite were significantly and positively correlated, and ankerite was significantly and negatively correlated, and there were strongly significant negative correlations between wind velocity and organic and plagioclase contents in materials finer than 63 μm . The correlation results indicated that the aeolian process seems to be effective in changing the mineral composition of the sediment.From the aspect of dust emission mechanism, the Qilian mountain is the main source area of detrital material in the eastern section of hexi corridor. Under the effect of gravity erosion and water erosion, detrital material were continuously transported and deposited, and formed the desert-oasis cascade system along the height distribution, inside which the mountain slope, alluvial fan, gobi, dune, oasis and deposited plain are developed. At the end of a river or at the end of a branch, there are always developed dry riverbed. As the riverbed is lower than the landscapes besides, it was easily to become the dust transportation corridor, at the same time, it emitted the dust to the near air. Under the action of air convection and turbulent diffusion, those dust was taken into the atmosphere. Part of those dust was involved in the atmospheric circulation as the condensation nuclei, and part of those dust were falled out to the surface by the dry or wet dustfall. During this process, the dried riverbed was not only the dust sources, but also the important dust transportation channels, as a result, the dried riverbed had very important significance in the dust emission study in arid areas. |
| 中文关键词 | 风沙活动过程 ; 干河床 ; 风洞试验 ; 河西走廊 |
| 英文关键词 | aeolian process dried-up riverbeds wind tunnel Hexi Corridor |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288132 |
| 推荐引用方式 GB/T 7714 | 张彩霞. 河西走廊东段干河床粉尘释放的实验模拟与分析[D]. 中国科学院大学,2018. |
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