دانلود رایگان مقاله انگلیسی آزمایشات تونل بادی سبک به منظور مطالعه فرسایش خاک و ارتباط آن با ساختار خاک - الزویر 2019

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.

Conclusions

Extensive in-situ measurements were done using a portable wind tunnel for 60 experimental locations of 20 different arid and semi-arid regions of the Fars province, Iran. Using this device, the threshold wind speeds at which soil erosion occurs were estimated for these desert areas. They varied from 5 to 12 m s−1 at 0.25 m height, i.e. 10-m wind speeds between 6.8 and 9.7 m s−1 , and 16.4 and 23.3 m s−1 , respectively; such high wind speeds being measured in natural conditions by meteorological stations of the Fars province. These threshold wind speeds point out the large difference of sensibility to wind erosion of the semi-arid and arid areas of the Fars province. Wind tunnel experiments were also conducted at the same high wind speed (15 m s−1 at the height of 0.25 m) and duration conditions to study soil erosion rates by wind regarding soil properties. As it was previously shown for other arid areas, high values of the soil surface gravel cover percentage, the soil MWD, the clay and soil moisture contents, and the soil organic carbon significantly reduced the erodibility of the studied soils by wind. In fact, the measurements conducted at a 15 m s−1 constant wind speed (at 0.25 m height) pointed out that the soil with high surface gravel coverage percentage and soil MWD present the lower soil erosion rates both following a power function (R2 = 0.61, P < 0.001 and R2 = 0.60, P < 0.001, respectively). Our measurements also allowed us to establish nonlinear relationships as power functions between the increase of the relative soil clay content as well as the soil moisture content, and the decrease of the soil erosion rate (R2 = 0.41, P < 0.001 and R2 = 0.58, P < 0.001, respectively). Moreover, we found a negative power relationship between soil organic carbon and soil losses by wind (R2 = 0.21 and P < 0.001). These results are in agreement with previous studies on the susceptibility of soils to wind erosion performed in semi-arid and arid areas worldwide. Critical values of these soil properties, for which soil erosion by wind is inhibited, were proposed for the regions of the Fars province: 5% for the soil surface gravel cover, 0.3 mm for the soil MWD, between 10 and 15% for the soil clay content, 2% for the gravimetric soil moisture content, and 0.4% for the soil organic carbon. These critical values being obtained for a high constant wind speed; more investigations are still needed to determine how these values may vary under different wind speed conditions. Furthermore, for soil salinity increase up to 1 dS m−1 , as well as for soil sodicity up to 1.6 (meq L−1 ) 0.5, soil erodibility can be reinforced.