Wind erosion, which occurs in arid, semiarid and sub-humid areas, is a critical process in land desertification and soil degradation and causes a global environmental problem. Sand-laden wind is particularly an ecological, environment problem faced in Beijing and surrounding regions. Previous studies report the processes and mechanisms of wind erosion, such as sand moving characteristics, sand-laden wind blowing and impacts of wind erosion; contributing factors of wind erosion; blowing mode and pattern of sand-laden wind; the profiles of blown field and blown sand flux, soil erodibility, variation in sand-transporting ratio, and the mechanism of sand-preventing engineering.Based on a previous study of evolution of fluvial aggradations sand, Yongding River sand land, we chose typical land-use types: field land, barren grasslands, drifting sand land, forest belt, pear orchard and patch forest, in which experiments were undertaken. Following close observations at selected sites and quantitative analysis, we studied the surface sand-laden wind movement and the possible measurements to control sand-laden wind by vegetation and plantation. The scenarios include: ① Observation of sand-laden wind blow at 020 cm of height; ② Observation of wind velocity gradients at different altitudes: 2.0 m, 1.5 m, 1.0 m, 0.5 m, and 0.2 m; ③ Observation of roughness at different ground covers; ④ Analysis of sand particle sizes at depths of 010 cm; ⑤ Evaluation of wind-breaking efficiency using different types of artificial vegetation; ⑥ Analysis of eefficiency of preventing sand movement using different types of artificial vegetation.
Results of sand-laden wind movement experiments on different land uses showed that wind velocity of near-surface layer increased with altitudes, with the near ground wind velocity and altitude following the logarithm distribution. There were significant differences in friction velocities and thresholds of the wind speed in different land use types. A negative exponential relation existed between the sediment discharge percent and the altitudes (ranging from 020 cm). There was a significant exponential relation between sediment transport concentration and wind velocity.Experiments of wind breaking and sand preventing using artificial vegetation indicated that: ① Patch forest was the most effective when it is about 110 H from windward side, with a protective ratio of 22.0%; pear orchard was the most effective in 17 H from windward side, with a protective ratio of 68.8%; and forest belt was the most effective in 120 H from leeward side, with a protective ratio of 32.0%. ② The order of the three types of artificial vegetation on sand prevention was forest belt < patch forest < pear orchard. ③ Differences in compositions of vegetation led to the varying effectiveness of wind control and sand prevention using artificial vegetation associated with spatial structures and disparate distribution patterns of accumulated sand geometry.
Further study will consider the possible mechanisms of wind erosion of heterogeneous landscapes and interactions with a range of contributing factors that have not been examined.