|其他摘要||Lake in arid land, which plays an incredible role in maintaining of the regional ecosystem balance, is an important part of the arid ecosystem and is highly sensitive to climate change and environment evolution. In the context of climate change, intense human activity leaded lakes in arid land to shrink and even dry up, which caused to the unpredictable negative dynamics of lakes beyond safety thresholds, and resulted in serious environmental degradation effect. In present time, some ecological security issues became actual, including drying of rivers, declining of natural oases, disappearance of wetlands, shrinkage of lakes, followed by environmental degradation and serious desertification. As a result, frequent dust storms (floating dust, blowing sand and dust storm) occurred.
This study is aimed to understand the mechanism of eolian dust from the playa of Ebinur lake and its diffusion characteristics in the atmosphere boundary layer, three key questions are urgent to be answered, i.e., how do the key parameters that affect the eolian dust change? What is the spatial pattern of key processes that control the dust emission from the playa? In addition, what are the main features of dust spread in the atmosphere? Within the selected Ebinur lake playa, quantitative studies were implemented through statistical analysis, positioning observations and model simulations to gain the land surface parameters and aerodynamic parameters and their variation, to understand spatial differences of the process that control the dust generation near the surface, and to define the pathways and range of dust suspended in the atmospheric boundary layer. This study identified the main factors influencing the occurrence of eolian dust, revealed regional differences of eolian dust generation in complex underlying surface thoroughly, interpreted dust emission characteristics and its tranport characteristics scientifically, and increased the understanding and awareness of the important dust source in the evolution process of lakes in arid land. Meanwhile, results of this project could provide a reference for tail-end lake area to take effective measures to defense eolian dust, as well as provide a scientific basis for construction and management of ecosystems in the tail-end lake area. Main conclusions drawn are listed below：
(1) Dry aggregates, aerodynamic roughness length, threshold friction velocity and friction velocity of different land cover types exhibit notifying different characteristics within shoreline since the late Pleistocene. Tamarix hispida desert, Haloxylon persicum desert, Tamarix ramosissima desert, and bareland compose by very fine sand and medium sand populaions; others compose by very fine sand, medium sand and coarse sand populaions. Aerodynamic roughness length of Haloxylon Persicum desert and Reaumuria songarica desert in the northeast of playa of Ebinur Lake reach up to 5.15 cm and 5.45 cm, while the smallest is distributed in the areas dominored by farmland and bareland with aerodynamic roughness 0.003 cm and 0.001 cm, respectively. Therefore, bareland and farmland has the potential to release large amounts of dust in the absence of moisture and vegetation effects. Threshold friction velocity of Haloxylon gravel desert in northwest and Phragmites communis meadow in southeast are 127.53 cm/s and 167.47 cm/s, respectively. This is greater than that of other surface types. The largest friction velocity is found in Reaumuria songarica desert with a value of 71.4 cm/s.
(2) Dust production model (DPM) model was used to simulate the dust fluxes from different land covers within the dry lakebed of Ebinur Lake. Those results shown that Haloxylon gravel desert located in the northwest and Reaumuria songarica desert in the north with the coarse particle size composition and a larger threshold friction velocity makes it difficult to release dust. Dust fluxes of bareland in the northwest can reach 153g/(km2·s) in the absence of moisture and vegetation. Farmland gains a dust emission flux reaching 83.8 g/(km2·s), which indicates that farmland has become an important source of dust in this region.
(3) Potential transport of dust from the playa has significant seasonal differentiation. Potential transport get maximum distance in spring and summer, while distance in autumn and winter is less lower 1000 meter above ground level, and low-density air mass trajectory can be transport for wide range above 1000 meter. Potential transport of dust exhibits clear direction in different seasons. There are two main transport pathways for the dust from the playa, namely the southeast and north-northeast. The main transport direction is southeast in spring and summer, mainly affecting the source region; it could potentially affect most parts of China and parts of Russia. However, the main transport direction in autumn and winter in the lower layer is to the northeast, and steering to east direction above 500 m, mainly affects Central Asia and parts of Russia. The main affected area is near the source region, including Jinghe and Bole.
(4) This study takes comparative analysis on changes characteristics of aerosol optical depth derived from MODIS and MISR and transport characteristics of dust from the playa of Ebinur Lake, Aral Sea, and Chaiwopu Lake in the arid central Asia within the same latitude band. The results show the dry lakebed in arid Central Asia has the potential to release large amounts of dust and salt dust with a extremely high content of fine particle sulfate, chloride and heavy metal elements, which is more poisonous than dust and will cause air pollution and increase atmospheric aerosols for long-term suspension in the atmosphere. In addition, salt dust settling in the Tianshan Mountains, coupling with climate change will be significantly accelerates the melting of snow and ice. Under suitable weather conditions, a lot of dust from the dried lakebed of tail-end lakes in the arid Central Asia can be transported for long-distance, which is far beyond imagination. It is suggested that dry lakebed, as a typical land surface in the arid Central Asia, is an important source and important part of eolian dust and sediments. As one of the elements of eolian dust and sediments in arid central Asia, the study of the release of dust from dry lakebed will undoubtedly provide some references for the dust system in arid central Asia.|