关于土壤水分对风蚀起动风速影响研究的现状与问题

A REVIEW ON EFFECT OF SOIL MOISTURE ON WIND EROSION THRESHOLD VELOCITY

在土壤风蚀研究中,Bagnold建立的适用于干沉积物的起动风速与沉积物粒径的关系已被广泛接受。然而,沉积物中的水分亦是影响沙粒起动风速的重要因素,因为在湿润状态下,水分子与沉积物颗粒之间的张力增大了颗粒间的粘聚力,从而增大了起动风速。准确地估算土壤风蚀量或地表沙尘释放量及其所造成的危害需要建立沉积物起动风速与其含水率之间的关系,但这方面的研究目前远不能满足实际需要。本文较为全面地综述了近50年来有关沉积物起动风速与含水量关系方面的研究成果,将已有的研究成果归纳为半定量描述、经验模型和理论模型等三大类,分别介绍了代表性成果。通过对比发现,各家研究结论分歧较多,除了定性意义上较为相似外,定量关系五花八门,差异很大。作者将造成差异的原因归结为:问题本身的复杂性导致理论研究使用了过多的假设与简化、对颗粒之间的粘聚力与水分的关系缺乏清晰的认识、颗粒起动的判别标准与确定方法不同、实验过程中土壤水分的加入与确定方法以及实验土壤的颗粒特征和其他物理化学性质等不同。因此,这一领域的研究尚有很大的探索空间。

In wind erosion research, Bagnold＇ s threshold equation, applicable to determination of relationship between threshold wind velocity and particle size of loose dry sediments, is widely accepted. However, soil moisture is also an active factor influencing the threshold wind velocity because the tension of water molecules will increase the inter-particle cohesion between sediment particles, and hence the threshold wind velocity. To accurately and quantitatively estimate wind erosion and dust emission, it is essential to establish relationship between threshold wind velocity and soil moisture content, but so far the research in this field lags far behind the need of the reality. The review sums up research findings on relationship between threshold wind velocity and soil moisture content in the last five decades, into three categories, i.e. semi-quantitative description, empirical model and theoretical model, and cites some representative examples for each category. Comparison analysis reveals that conclusions of these researchers are various and diversified, especially concerning quantitative relationship, except for the connotation of nature determination. The authors attribute the differences to the lack of a clear understanding of the relationship between inter-particle cohesion and moisture content, definition of threshold wind velocity and moisture content, and physical and chemical properties of tested soil samples. It is suggested that further work be done in this research field.