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| 河西走廊绿洲边缘下伏黏土层沙丘特征及其土壤水分运移研究 | |
| 其他题名 | Study on characteristic and soil moisture migration of sand dunes with underlying clay layer in an oasis edge of Hexi corridor |
| 孙程鹏 | |
| 出版年 | 2018 |
| 学位类型 | 硕士 |
| 导师 | 赵文智 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 下伏黏土层沙丘是指剖面内存在均匀亚黏土的沙丘，其特点是土壤层间质地差异显著，且发生层间基本无过渡。下伏黏土层的空间异质性较大，埋藏深度在5－500 cm左右，厚度在5－100 cm之间。下伏黏土层具黏性，水分不易通过，因此其分布特征易引起水分等植被可利用资源分布的不确定性。当降水事件发生时，下伏黏土层的存在使沙丘土壤容易在砂土层之下、黏土层之上形成滞水层，从而改善沙丘土壤的水分状况，这对人工固沙植被的生长和繁殖具有重要意义。目前下伏黏土层沙丘土壤水分运移特征及下伏黏土层对邻近土层影响的研究还很薄弱。因此，本研究以河西走廊绿洲边缘下伏黏土层沙丘为研究对象，基于野外观测试验、室内分析实验和数值模拟相结合的方法，研究了0－60 cm土壤剖面内下伏黏土层分布特征和黏土层埋藏深度、厚度及物理性质对沙丘土壤持水性、导水性以及水分运移特征的影响，得出以下初步结论：1. 下伏黏土层分布特征及其对邻近土层物理性质的影响在河西走廊绿洲边缘，下伏黏土层沙丘占调查沙丘的25 %左右，沙丘高约2－6 m。黏土层常见于0－60 cm深处，厚达10－50 cm，呈砖红色或灰白色，黏粉粒含量高（82.37 %），容重小（1.26 g/cm3）。按砂土层与黏土层在剖面中的排列方式，将下伏黏土层沙丘分为黏土覆盖砂土型沙丘、砂土覆盖黏土型沙丘、夹黏沙丘和多层下伏黏土层沙丘四种类型。与无下伏黏土层沙丘相比，下伏黏土层对邻近砂土层土壤含水量无显著影响；表层砂土容重随着下伏黏土层埋深增加先增加后趋于稳定（6 cm<10 cm<13 cm<17.5 cm≈26 cm≈30 cm）；下伏黏土层可以通过增大下伏砂土层土壤的黏粉粒含量，使其饱和含水量（0.338 cm3/cm3和0.387 cm3/cm3）和孔隙度（45.28 %和48.25 %）增大、容重减小（1.49 g/cm3和1.41 g/cm3），并使土壤水分特征曲线在低吸力段释水速率减缓。2. 下伏黏土层对沙丘土壤持水性能的影响下伏黏土层对表层砂土田间持水量、凋萎系数和有效含水量无显著影响（下伏黏土层埋深为6 cm的夹黏沙丘除外），仅影响黏土层以下砂土的持水性能。以无下伏黏土层沙丘为标准，下伏砂土层土壤的凋萎系数增加了166.67 %，有效含水量降低了27.49 %；在下伏黏土层影响下，表层厚度为6 cm的砂土层，其田间持水量和有效含水量分别减小30.43 %和40 %。3. 下伏黏土层对沙丘土壤导水性能的影响下伏黏土层的存在降低了沙丘土壤的导水性。下伏黏土层沙丘饱和导水率随下伏黏土层埋深减小先减小后趋于稳定（30 cm<26 cm<17.5 cm≈13 cm≈10 cm≈6 cm）；沙丘有效饱和导水率与沙丘层状结构数呈反比，两层土壤结构的有效饱和导水率高于三层土壤结构（0.00116 cm/s和0.0002 cm/s）；而下伏黏土层对砂土－黏土界面的水势阈值无显著影响（-102.5－-103 cmH2O）。4. 下伏黏土层对沙丘土壤水分运移的影响下伏黏土层沙丘中存在两种水流障碍机制，能够有效减少水流的垂向运移，并形成大量的横向运动。黏土覆盖砂土型沙丘中存在毛管屏障，砂土覆盖黏土型沙丘中存在水力屏障，夹黏沙丘和多层下伏黏土层沙丘中两种屏障机制并存。与无黏土层沙丘相比，黏土覆盖砂土型沙丘、砂土覆盖黏土型沙丘、夹黏沙丘和多层下伏黏土层沙丘的累积入渗量依次减少了89.85 %、69.47 %、46.51 %和35.12 %；水分再分布过程中失水主要来自于砂土层。下伏黏土层的存在可以提高邻近土层土壤的持水能力、降低其导水性，同时可以有效减缓土壤水分入渗和水分再分布速率，为水分短暂滞留于沙丘中提供了条件，这对改善沙丘土壤的水分状况具有重要意义。 |
| 英文摘要 | Sand dunes with underlying clay layer refer to which the soil profile of dunes consists of one or more clay layers beneath sandy soil layers, they are characterized by texture contrast between soil layers, and there are basically no transition between soil horizon. The spatial heterogeneity of underlying clay layer is relatively large. Deposits of the clay layer occur at depths of 5－500 cm and it ranges in thickness from 5 to 100 cm. Moisture is difficult to pass through clay layer, the distribution of this layer is likely to cause water and other vegetation available resources distributed in a discontinuous way. When the precipitation occurs, the presence of the underlying clay layer makes it easier for dunes to form a water-retaining layer beneath the sand layer and above the clay layer, thereby improving the soil moisture condition of dunes. It is of great significance to the growth and propagation of artificial sand-fixing vegetation. At present, the study of the effect of the underlying clay layer to soil water flow of sand dunes and the influence of the underlying clay layer on the adjacent layer are still weak. Therefore, we choose ten sand dunes with underlying clay layer within 0－60 cm in an oasis edge of Hexi corridor, to study the characteristics and mechanisms of the response of the underlying clay layer to water-holding capacity, water conductivity and soil moisture movement characteristics, based on field observation experiments, indoor analysis experiments, and numerical simulation methods. The results showed in the follow:1. Distribution characteristics of underlying clay layer and its effect on the physical properties of the adjacent layer In an oasis edge of Hexi corridor, sand dunes with underlying clay layer account for about 25 % of the researched sand dunes, the height of dunes is about 2 to 6 m. Deposits of the clay layer usually occurs at depths of 0－60 cm and it ranges in thickness from 10 to 50 cm, this layer is usually red or gray. According to the location of the sand layer and the underlying clay layer in the profile, there are four sand dune types: clay-covered sand dune, sand-covered sand dune, sandwich dune with clay interlayer, and multi-layered underlying clay layer sand dune. The content of silt and clay of underlying clay layer is higher than sand layer (82.37 %), and bulk density is less than sand layer (1.26 g/cm3). Compared with the sand dunes with no underlying clay layer, the underlying clay layer has no significant effect on the soil moisture of the adjacent sand layers; the bulk density of the surface sand soil first increases as the increase of the sand thickness and then tends to be stable (6 cm<10 cm<13 cm<17.5 cm ≈ 26 cm ≈ 30 cm). Underlying clay layer can increase saturated water content (0.338 cm3/cm3 and 0.387 cm3/cm3), porosity (45.28 % and 48.25 %) and reduce the bulk density (1.49g/cm3 and 1.41g/cm3) and the soil water characteristic curves are smoother in the low suction section by increasing the content of silt and clay particles.2. The effect of underlying clay layer on the water-holding capacity of sand dunesUnderlying clay layer had no significant effect on the water-holding capacity, wilting coefficient and effective water content in the surface sand soil (except sandwich dune with clay interlayer which the thickness of surface is 6 cm), and only affected the water-holding capacity of the sand layer below the clay layer. Compared with original sand dune, the wilting coefficient of the sand layer which below clay layer increased by 166.67 %, effective moisture content of that layer decreased by 27.49 %. Underlying clay layer has an impact on field capacity and effective water content of sand layer which is on the surface and the thickness is 6 cm. Field capacity and effective water content decreased by 30.43 % and 40 %, respectively.3. The effect of underlying clay layer on soil hydraulic conductivity of sand dunesUnderlying clay layer reduces the saturated hydraulic conductivity of surface of sand dunes, and has the same impact on effective saturated hydraulic conductivity and hydraulic conductivity of sand dunes. Saturated hydraulic conductivity of sand dunes with underlying clay layer first increases with the increase of the sand thickness and then tends to be stable Coating the clay dune decreases as the thickness of the overlying sand decreases and then tends to be stable after the first decreases (30 cm<26 cm <17.5 cm ≈ 13 cm ≈ 10 cm ≈ 6 cm). The larger number of soil layer, the lower effective saturated hydraulic conductivity of sand dunes, and the effective saturated hydraulic conductivity of the duplex soil is higher than that of the multi-layered soil (0.00116 cm/s and 0.0002 cm/s). Moreover, underlying clay layer has no significant on critical water potential of interface between sand layer and clay sand (-10 2.5 to -10 3 cmH2O).4. The effect of underlying clay layer on soil moisture migrationThere are two kinds of water flow barriers in sand dunes with underlying clay layer, as a result, vertical migration of soil moisture is inhibited and horizontal migration is promotes. There are capillary barriers in clay-covered sand dunes, hydraulic barriers in sand-covered sand dunes, and two barrier coexist in sand dunes with clay interlayer and multi-layered underlying clay sand dune. Compared with original sand dunes, the cumulative infiltration of clay-covered sand dunes, sand-covered sand dunes, sand dunes with clay interlayer and multi-layered underlying clay sand dune decreases by 89.85 %、69.47 %、46.51 %,35.12 %, respectively. Loss of water is mainly from the sand layer during soil water redistribution.The presence of the underlying clay layer can increase the water holding capacity of adjacent soil layers and reduce its hydraulic conductivity, at the same time, it can effectively slow down the rate of soil moisture migration. It provides conditions for the temporary retention of moisture in sand dunes, and plays an important role in the improvement of the water conditions of dunes. |
| 中文关键词 | 绿洲边缘 ; 下伏黏土层沙丘 ; 持水性 ; 导水性 ; 水分运移规律 |
| 英文关键词 | oasis edge sand dunes with underlying clay layer water retention water conductivity soil moisture migration regularity |
| 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/2XILL650/288130 |
| 推荐引用方式 GB/T 7714 | 孙程鹏. 河西走廊绿洲边缘下伏黏土层沙丘特征及其土壤水分运移研究[D]. 中国科学院大学,2018. |
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