Abstract: Qingtu Lake is a typical dry salt lake located at the downstream Shiyang River, Minqin County, Gansu Province, China in extreme arid areas. Under the action of wind, salt dust pollutes air, harms the surface vegetation, threatens ecological security and people's life seriously. Based on the soil dust data monitored by dust observation system in Qingtu Lake 0-50 meters surface layer, this paper analyzed the saline dust movement rule, the change characteristics of wind speed, and their relationship in each vertical gradient. In order to reveal the distribution characteristics of salt dust flux level, this paper also provided a reference for effective governance and accurate prediction of sand and dust weather in the area. The observation system consists of a 50 m high climb type observation tower and installations including the wind flux tracking filter dust level instrument, wind speed and direction, temperature, humidity, air pressure sensor and data collection and transmission system. The characteristics of dust change were monitored dynamically at 10 vertical gradients(1 m, 2 m, 6 m, 10 m, 14 m, 18 m, 26 m, 34 m, 42 m and 50 m). The results show as follows:(1) The distribution of wind speed in the 0-50 m vertical gradient followed the classic characteristics that wind speed increased with the increase of height, and the profile equation followed a power function relationship. The average wind speed was the maximum in May, the minimum in November, and showed significant seasonal variation characteristics; average wind speed in spring and summer was greater than that in autumn and winter. Wind shear index was larger in 18-2 m surface layer, and it was relatively small in the spring and summer; wind shear index change was small in 34-28 m and 50-34 m, the changes among the four seasons were not obvious.(2) The spatial distribution of saline dust flux level increased with the increase of height, and follow the change rule of power function in the vertical height; affected by Chenopodiaceae forest underlying surface, the saline dust flux level had a more obvious increase in the 6 m height.(3) There was a positive correlation between dust level flux and wind speed, which followed power function relationship. At the bottom of Qingtu Lake, the bare surface is an important supply source of salt dust in the air. To reduce the dust hazard in surface layer in Qingtu Lake, human intervention to decreased the amount of saline dust in the surface layer air by increasing vegetation coverage is a fundamental management measure.

Key words: downstrearm Shiyang River, surface layer, wind-blown dust