关键词: 风沙流结构, 输沙率, 土壤风蚀, 粒度分析, 乌兰布和沙漠

Abstract: [Objective] Influences of typical vegetation communities in desert ecosystems on the aeolian activities in the near surface were studied to reveal soil wind erosion characteristics of desert ecosystem under different underlying surface conditions.[Method] Five typical underlying surfaces, including semi-fixed dunes (coverage 20%) of Artemisia ordosica, semi-fixed dunes (coverage 30%) of Nitraria tangutorum, fixed dunes (coverage 40%) of A. ordosica and fixed dunes (coverage 40%) of N.tangutorum, and mobile sand dunes (served as the control), were selected in the desert-oasis ecotone at the northeast margin of the Ulanbuh desert. By using the wind erosion brazing and sand flow acquisition system, five kinds of underlying surfaces wind erosion dynamic were real-time monitored to quantitatively analyze the differences of soil wind erosion, vertical distribution and grain size composition under the different underlying surface conditions.[Result] Soil wind erosion thickness on different underlying surface during the same period in Ulanbuh desert was mobile sand dunes > semi-fixed dunes of A. ordosica > semi-fixed dunes of N. tangutorum > fixed sand dunes of A. ordosica > fixed sand dunes of N. tangutorum. Sand peristalsis could be observed in mobile sand dunes when the wind speed reached to 4.1 m·s^-1, and the wind erosion material was able to be collected when the wind reached to 5.1 m·s^-1.In semi-fixed dunes of A. ordosica, semi-fixed dunes of N. tangutorum, fixed dunes of A. ordosica and fixed dunes of N. tangutorum, the wind erosion happened when wind speed reached to 6.3, 6.5, 6.8 and 7.9 m·s^-1, respectively. In the vertical section of 0-100 cm on the five bed surfaces, sediment runoff of 67.6%-90.0% distributed in 30 cm height, carrying airflow in the transport rate expressed as a power function declined with the increase of height, and increased with the increase of wind speed. The grain size composition of the wind erosion in each layer was in a unimodal distribution, with the peak between 250-100 μm; The peak value of the grain size composition in 0-20 cm height layers was obviously different from that of the other layers, and tended to be larger. From below to top, the proportions of very fine sand particles showed an increasing trend, but the proportions of medium sand grain size showed a decreasing trend.[Conclusion] With the increase of vegetation coverage, soil wind erosion decreased significantly, and the annual wind erosion depth of mobile sand dunes, semi-fixed dunes and fixed sand dunes decreased. With coverage of 40% A. ordosica and N. tangutorum community, the soil wind erosion depth was only about 1.73%-1.52% of the wind erosion depth of mobile sand dunes at the same time, and the sediment transport rate in the range of 0-100 cm height was only 6.6%-5.1% transport rate of mobile dune sand. Vegetation alleviated stream erosion to the surface mainly by covering the surface, increasing the roughness of the underlying surface and blocking the movement of sand. Therefore, in the process of implementing anti-desertification project, we should fully consider and use the ecological effects of vegetation in resisting wind erosion.

Key words: sand flow structure, sand transport rate, soil wind erosion, size analysis, Ulanbuh desert