KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 塔里木盆地南缘策勒绿洲及其外围地带的降尘作用研究 | |
| 徐立帅 | |
| Subtype | 博士 |
| Thesis Advisor | 穆桂金 |
| 2016 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 自然地理学 |
| Keyword | 大气沙尘 降尘 粒度 绿洲 塔里木盆地 |
| Abstract | 绿洲为荒漠区多种生物提供了适宜的生息繁衍的环境，但严重的沙尘危害影响到绿洲的稳定性和可持续发展。研究表明，绿洲内部比周围荒漠区有更多的降尘，引起广泛关注。围绕绿洲内部促进沙尘沉降因素以及降尘的时空分布等问题，本研究选择了塔里木盆地南缘的策勒绿洲为研究区，通过对沙尘浓度变化、绿洲内外沙尘尘降的时空分布、绿洲内部尘源的二次释放与沉降等观测采样及实验分析，阐释了绿洲林木机械阻挡、绿洲小气候效应以及人为扰动等因素影响下的降尘机制，探讨了不同因素影响下的降尘空间模式。研究对深入认识绿洲降尘的时空分布及绿洲沙尘环境治理有重要科学意义和实际价值。主要获得了以下结论： （1）绿洲存在三种大气降尘作用：①粗糙下垫面的机械阻挡降尘作用，绿洲植被，尤其高大的树木对风速的削弱促进了贴地层的沙尘沉降；②绿洲小气候的降尘效应，夏季和秋季浮尘天气绿洲小气候是导致绿洲内部降尘大于外部的主要因素；③绿洲内部沙尘的二次释放和沉降促进了局部地段的大气降尘，包括植物叶面滞尘的脱落和人类活动释放的沙尘在当地的再次沉降。 （2）绿洲树木机械阻挡的降尘作用是绿洲降尘的主要方式，在绿洲边缘作用最为明显，向下风区逐渐减弱。因此，绿洲迎风向边缘降尘量最大，突显边缘效应，向下风向依次降低，到下风向绿洲外部降尘量最低。在沙尘组分上，机械阻挡的降尘呈现绿洲内部的平均粒径明显小于外部。 （3）绿洲小气候的降尘作用主要发生在浮尘天气。绿洲的“湿岛”效应和“冷岛”效应都有利于沙尘的沉降，因此绿洲内部降尘大于边缘且大于外部。由于受盆地环流以及绿洲与荒漠对流等诸多不对称空气流动因素影响，绿洲小气候降尘的几何中心偏向于绿洲的下风向。在颗粒组成方面，绿洲小气候的降尘作用沉降的浮尘，沙尘颗粒平均粒径相对更细，呈显著的细偏态分布，分选更差。 （4）非沙尘天气，绿洲内部尘源主要来自叶面滞尘和人类活动释放的尘，具有近源性和局地性特点且数量有限，不具有远距离扩散动力。 （5）防护林带主要是通过疏透度变化影响机械阻挡降尘作用。随疏透度下降防护林的机械阻挡作用加强。当疏透度降到约0.5时，林后风速被显著削弱，降尘增加。同时，受林后气流下沉和林木扰动湍流影响，在10倍或12倍林高范围内出现高降尘区。 |
| Other Abstract | Favorable environmental condition for various organisms living in desert regions is provided by the oasis. However, serious dust hazards greatly threaten the stability and sustainability of the oasis. That there is more dustfall inside the oasis than that in the adjacent desert region which was found in some research has attracted wide attention. To characterize the factors on enhancing dust deposition and the spatial–temporal distribution of dustfall in oasis, the Cele Oasis in the southern margin of Tarim Basin was chosen as a case study. This research interprets the mechanical obstruction effect of oasis woods, oasis microclimate effect and artificial disturbance etc. and the dust deposition distribution patterns under different influences factors, via a serious of sampling, observing and analysis of the variability of dust concentrations, spatial and temporal distribution of dust deposition inside and outside the oasis, which is important and meaningful to deeply understand the spatial–temporal distribution of dustfall and control dust pollution in oasis. The results are shown as below: (1) There are three ways of enhancing dust deposition in oasis. First, the mechanical obstruction effect due to the oasis vegetation, especially the tall trees which helps promote dust deposition through reducing wind speed. Second, the oasis microclimate impact, which is the main factor resulting in more dustfall inside the oasis than that around adjacent desert region during floating dust days in summer and autumn. Last, the second release and settlement of the dust from the internal oasis, including the foliar dust and the dust from human activity. (2) The mechanical obstruction effect is the main way of enhancing dust deposition in oasis, most obviously at the margin of oasis and decreasing gradually toward the leeward area. Therefore, the highest deposition rates appear at the windward margin of the oasis, highlighting the marginal effect, and decrease gradually toward leeward area and then reach minimum at the leeward outside the oasis. The mean grain size of the dust is apparently smaller inside the oasis than that outside the oasis. (3) The oasis microclimate effect of enhancing dust deposition mainly appeares in floating dust days. The “cold and wet island”effect provide favorable condition for dust deposition, illustrating more dustfall in the center of oasis than that at the magin and outside the oasis. Due to the effect of the basin circulation, oasis-desert circulation and other asymmetry air flow, the geometric space of oasis microclimate settlement effect deviates toward the leeward of the oasis. The dust deposited affected by oasis microclimate effect has a finer mean grain size with positive skewness and poor sorting features comparted with that affected by mechanical obstruction effect. (4) During non-dust days, the internal dust mainly comes from foliar dust and anthropogenic dust, which is characterized with a limited number and a proximal and regional feature, that is, it doesn’t have strong power for long-distance transmission. (5) The shelterbelts alter mechanical obstruction effect through the variations of porosity. As the porosity decreases, the mechanical obstruction effect improves. When the porosity decreases to 0.5, the dust deposition at leeward region of shelterbelt significantly increases due to the reduction of wind speed. Meanwhile, affected by the downdraft and turbulent disturbance, a high dust deposition zone appeared within the 10 H or 12 H (H represents the height of shelterbelt) region of the shelterbelt leeward. |
| Subject Area | 自然地理学 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/14740 |
| Collection | 研究系统_荒漠环境研究室 |
| Affiliation | 中科院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 徐立帅. 塔里木盆地南缘策勒绿洲及其外围地带的降尘作用研究[D]. 北京. 中国科学院大学,2016. |
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