آزمایشات تونل بادی سبک به منظور مطالعه فرسایش خاک
Abstract
1- Introduction
2- Material and methods
3- Results and discussion
4- Conclusions
References
Abstract
Soil erosion controlled by the wind effect on the surface, has been largely studied by field in-situ measurements as well as laboratory or numerical simulations. Nevertheless, more in-situ measurements and observations are needed to document this phenomenon for various desert areas. In the present study, we focus on the documentation of different properties of a wide range of semi-arid and arid soils of the Fars province, and how they control the soil erosion by wind. By improving our knowledge on soil properties which lead to the limitation of soil erosion by wind, it will be possible to better prevent wind erosion in the Fars province. Extensive wind tunnel experiments were conducted in 20 different arid and semi-arid regions. For each region, three wind tunnel experiments were done to encounter local soil variability. We determined threshold wind speeds for which soil erosion was observed. Other experiments were conducted at the same high wind speed, and duration conditions, allowing discussing soil erosion rates by wind regarding soil properties. As already documented in the literature, our results pointed out a significant negative power relationship between wind erosion rate and different soil physical properties, including soil surface gravel cover, the mean weight diameter (MWD) of soil particles, and soil clay and moisture contents. Moreover, a nonlinear relationship as a power function was found between the increase of soil organic carbon and the decrease of soil losses by wind in the studied semi-arid and arid soils. We determined critical values of these soil properties for which wind erosion in Fars province is limited under high wind speed conditions. Additionally, the effects of the electrical conductivity (EC), sodium adsorption ratio (SAR), and calcium carbonate equivalent (CCE) on wind erodibility were discussed at low and high concentrations and for different soil textures.
Introduction
Soil erosion by wind is a serious environmental problem in many arid and semi-arid regions; it is considered as a soil-degrading process (Webb et al., 2017) that affects over 500 million ha of land worldwide (Grini et al., 2005). In fact, wind erosion degrades soil by removing and emitting in the atmosphere fine soil particles that contain most of the soil organic carbon and nutrients (Van Pelt and Zobeck, 2007). The appraisal of this process at the soil-atmosphere interface is central to estimate of soil loss for soil conservation planning (Black and Chanasyk, 1989). The emission of top soil particles from land surfaces into the atmosphere impacts the soil productivity, and should also be considered for air quality and health issues (Webb et al., 2017; Pi and Sharratt, 2017; Pi et al., 2017). Soil erosion by wind is a function of the soil erodibility and the wind erosivity (Chepil and Woodruff, 1963). It is a threshold phenomenon controlled by surface winds and soil properties. There is a minimum wind stress that corresponds to a threshold velocity needed to initiate wind erosion on semi-arid and arid surfaces (Chepil, 1951; Gillette et al., 1982). Non-erodible elements such as vegetation and gravels on an erodible surface not only increase the apparent threshold wind velocity but also reduce the mass erosion rate. Even if the erosive action of the wind depends on its speed, several factors like the size and stability of the soil aggregates, clay content, and near-surface soil moisture affect the threshold velocity (Ravi et al., 2006). The size and stability of soil aggregates are significant factors that affect the soil susceptibility to wind erosion (Colazo and Buschiazzo, 2010; Négyesi et al., 2016). In general, soil aggregates are formed through the combination of mineral particles with organic and inorganic substances (Bronick and Lal, 2005; Mahmoodabadi and Ahmadbeigi, 2013). The binding of soil particles into stable aggregates is essential for the production of optimum soil tilth (Harris et al., 1966). Inter particle cohesion is a combined effect of the van der Waals force, liquid and chemical force, and electrostatic force. These effects are sensitive to soil properties, such as the particle shape and texture, the soil mineralogy, the packing arrangement, and the presence or absence of bonding agents such as soil moisture and soluble salts (Shao and Lu, 2000).