Characteristics of soil particle size distribution and its effect on dust emission in Taklimakan Desert

Transport of dust sand caused by wind erosion is a serious problem in many arid regions in the world, and it plays animportantrolein global biogeochemical cycle. The dust induced by transport of aeolian sand can affect atmospheric radiation balance, climate, environment, air quality and human health. It has hence attracted increased attention in various areas ranging fromgeomorphology and climatology to meteorology andecological-environmental science. In addition to its natural origin, dust could also be instigated by anthropogenesis activities due to desertification.However, the relative contribution of the two origins is still an issue remaining elusive. In addition, being able to accuratelyestimate the potential of a dust source is crucial to evaluating the influence of desertification andclimate change on dust flux. The Taklimakan desert(TD) is the second largest shifting sand desert in the world, with about 85% made up by shifting sand dunes.It is animportant source of the dusts seen in China. Understanding particle size distribution of the sand and dust emission is helpful to evaluate quality of the atmospheric environment and the consequence for climate at regional scale. We collected 138 samples from soil surface based on spatial distribution and types of thesurfaces including farmland, dune and desert. Particle sizesof each sample was analyzed using the Mastersizer 2000 laser particle size analyzer, and the associated dust release flux was calculated using the DPM model.The particle size distribution of the microaggregates in each sample was obtained to elucidate its potential influence on dust release flux. The results showed that: 1) The content of silt and clay in the 138 samples was least, accounting for 10% to 18% of the total particles inthe mobile sand dunes, and 20% to 30% of the total particles in the sand ridges (e.g., sandy soil and sandy-sandy loams). Most samples taken from farmland (e. g., oasis and forest belt) are meadow soil, with silt and clay content being 50%-80%, differing from the silt and clay content in samples taken from the Gobi (desert area). 2) Fine sand and silty-fine sand are the smaller particles in the surface soil and can be divided into three groups, eachdescribed by a lognormal distribution: silt-fine sand group, fine sand group and coarse sand group, with median particle size being 90, 225 and 500 μm, and the standard deviation being 1.02, 1.53 and 1.08, respectively, accounting for 30%, 49% and 21% respectively.3) Emission of silt-fine sand and fine sand is most potential, followed by medium-coarse sand. The coarse sand is least to emit; the difference between the maximum and the minimum emission was in the order of 10-2 μg/(m2•s) in magnitude. The results reflect the difference in dust emission from different soil surfaces and they are greatlyimportant for quantitative assessment of dust emission in the studied region and beyond.