|其他摘要||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.|