Experimental study on the effect of freezing-thawing cycles on wind erosion of black soil in Northeast China

    Experimental study on the effect of freezing-thawing cycles on wind erosion of black soil in Northeast China Tiejun Liu, Xiangtian Xu, Jie Yang PII: DOI: Reference:

S0165-232X(17)30015-0 doi:10.1016/j.coldregions.2017.01.002 COLTEC 2350

To appear in:

Cold Regions Science and Technology

Received date: Revised date: Accepted date:

24 August 2015 11 August 2016 16 January 2017

Please cite this article as: Liu, Tiejun, Xu, Xiangtian, Yang, Jie, Experimental study on the effect of freezing-thawing cycles on wind erosion of black soil in Northeast China, Cold Regions Science and Technology (2017), doi:10.1016/j.coldregions.2017.01.002

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Experimental study on the effect of freezing-thawing cycles on wind

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erosion of black soil in Northeast China

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Tiejun Liu1, 2, Xiangtian Xu1, *, Jie Yang1

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1. Inner Mongolia University, Hohhot 010002, China;

2. Institute of Water Resources for Pastoral Areas, Ministry of Water Resources, Hohhot010020, China.

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Abstract: The black soil region in Northeast China suffers from the dual effects of

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freezing-thawing process and wind erosion in winter. We studied the influence of freezing-thawing cycles on wind erosion strength of black soil by simulating the conditions of the black soil region

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in Northeast China. An increase in the porosity on surface of soil specimens was correlated with

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the number of freezing-thawing cycles, such that soils with a surface moisture content of 5%, 7%

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and 8% increased porosity after 3, 6 and 9 freezing-thawing cycles. Freezing-thawing cycles induced increases in porosity lead to weakened cohesive forces within the topsoil. The net result

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was an increase in the sand transport rate of unit width within the height interval of 0 to 40 cm above the ground and an increase in the wind-sand flow structure height of 1-3 cm. In addition, after 6-9 freezing-thawing cycles, wind erosion strength increased by 1.2 and 2.0 times, when soil moisture contents were 5% and 7%, respectively. However, soil samples with a moisture content of 8% were not susceptible to freezing-thawing cycles enhanced wind erosion. The simulation experiment of freezing-thawing process induced wind erosion of black soil using a wind tunnel provided a theoretical basis for preventing freezing-thawing cycles induced wind erosion in black soil.

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* Corresponding author. Tel: +86 471 4996009 E-mail address: [email protected] (X. Xu) 1

ACCEPTED MANUSCRIPT Keywords: Black soil; Freezing-thawing cycles; Wind erosion; Sand transport rate of unit width

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1. Introduction

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Frozen ground accounts for 70% of the global land area, including 14% permafrost and 56%

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seasonally frozen soil (Maokuxitasaiyiyiqi, 1982). In China, permafrost covers approximately an area of 2.086×106 km2 and seasonally frozen soil covers approximately an area of 5.137×106

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km2; all together they account for 75% of the total land area of China (Xu, et al., 2001). In Northeast China, black soil is widely distributed. Black soil has a significant expansion coefficient

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and with enhanced coagulation and mineral matter forms a stable melanic complex; average

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organic matter is between 3%-10%. This area of China has significant grain production

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capabilities due to the high organic matter contents of the soils. This region is in the middle latitudes and is situated mostly within an area where the soils freeze seasonally and experience

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significant freezing and thawing cycles. Freezing-thawing cycles affect the soil structure, especially on the topsoil. This can lead to wind erosion, soil layer thinning, soil fertility decline,

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and reductions in grain yields.

Freezing-thawing cycles affect the structural, physical, and mechanical properties of the soil (Qi and Ma, 2010). Previous work has been conducted on the micro-structural changes of soil after freezing-thawing process. Tovey et al. (1992a; 1992b) used scanning electron microscopy to study soil microstructure; Graham and Au (1985) reported that the original structure of clay soils was damaged after freezing-thawing cycles and the pre-consolidation pressure of the soil sample was greatly reduced. Edwin and Anthony (1979) adopted an indoor freezing-thawing cycle test showing that freezing-thawing cycles significantly change the structure of fine grain soil. Most of the Chinese local studies on the freezing-thawing effects on soil microstructure focus on soil from 2

ACCEPTED MANUSCRIPT an engineering perspective. Ma et al. (1999) found that the shear strength of lime soil gradually declined with an increase in the number of freezing-thawing cycles. Wang et al. (2007) found that

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the elastic modulus and cohesive force of soil were reduced and the internal friction angle

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increased after freezing-thawing cycles. Yang et al. (2003) investigated the effects of freezing-thawing cycles on dry density, moisture content, and other physical properties of soil. Few studies have been performed on the micro-structural changes in agricultural soil following

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freezing-thawing cycles. Here, agricultural soil refers to the soil affected by activities such as

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cultivation, fertilization and irrigation.

Freezing-thawing process changes the structure of the topsoil thereby influencing the wind

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erosion strength. Most previous studies evaluate the influence of freezing-thawing cycles on wind

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erosion by using laboratory simulation. Qu et al. (2007) carried out a simulation experiment of

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freezing-thawing cycles induced wind erosion on buildings in northwest China and demonstrated that wind erosion was positively correlated with the increasing number of freezing-thawing cycles

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at a given moisture content. Zhang et al. (2007) classified and evaluated freezing-thawing cycles induced wind erosion in Tibet. Bullock et al. (2001) studied the variation of clay erodibility during winter in Alberta, Canada and found that snow-melting, freezing, and thawing changed the structure of the topsoil. Tatarko et al. (2001) studied the changes in stability of soil aggregates occurring in upland soil during the winter. Xie et al. (2012) carried out a wind tunnel simulation experiment with freezing-thawing cycles induced wind erosion in the Qinghai-Tibet Plateau of China, and showed that the wind erosion strength in the Qinghai-Tibet Plateau was positively correlated to the number of freezing-thawing cycles. With each of the first 6 freezing-thawing cycles the wind erosion strength increased substantially, but when the number of freezing-thawing

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ACCEPTED MANUSCRIPT cycles was greater than 6, the additional increases of wind erosion strength were relatively minor. In the present study, a quantitative simulation experiment was conducted using a wind tunnel to

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investigate the effects of freezing-thawing cycles on micro-structural changes of black soil from

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Northeast China. The results provide a theoretical basis for preventing freezing-thawing induced wind erosion of black soil and help to ensure the sustainable development of black soil areas in

2. Study area and experimental method

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2.1 Selection of study area

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China.

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To maximize the potential effects of freezing–thawing cycles on wind erosion of soils, we

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selected a relatively cold area within the region, an area that was also subject to significant wind

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and water erosion. Areas meeting the above conditions are extensive, including the wind erosion areas to the north of the Yinshan Mountains in central Inner Mongolia, on the south side of the

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Greater Xing'an Mountains, to the north of the Tianshan Mountains in Xinjiang, in the area surrounded by the Greater Xing'an Mountains-Xing'an Mountains-Changbai Mountains, and in areas in the Qinghai–Tibet Plateau. We studied the effect of freezing-thawing cycles on wind erosion in the black soil region of Northeast China. Areas meeting the above conditions include the black soil near the northeastern sandy land (Songnen Sandy Land, Horqin Sandy Land, Hulunbeier Sandy Land), which experience cold weather resulting in the freezing and thawing process of the black soil and also windy conditions leading to soil erosion. The black soil farmland of Tuquan County in Hinggan League of Inner Mongolia was selected as the study area. The location of the study area is shown in Fig. 1.

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ACCEPTED MANUSCRIPT Fig. 1 Location of the study area

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2.2 Overview of the study area

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The study area is located in the farmland of Tuquan County in Hinggan League of Inner

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Mongolia, at 45°21′18″N and 121°30′7″E, 320 m above sea level, in a semi-arid region. The mean annual air temperature of the study area is 5℃ and the annual average rainfall is 400 mm,

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occurring mainly from July to September. The study area is influenced by north to northwest winds in winter and spring and southeast winds in summer and autumn, with an annual average

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wind speed of 3.3 m/s; strong winds, blowing sand, and dust storms occur frequently, mainly from

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March to May. The soil type is chernozem, with a thin upper soil layer and the soil below 30-60

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cm being a calcic layer. The livelihood of people in the study area is mainly based on agriculture. Corn, sorghum, potato, sunflower, soybean and mung bean are planted and cultivated using plows

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and methods that greatly disturb the soil layer. The moisture content of the topsoil is generally low and wind erosion can be severe due to the continuous exposure to strong winds for seven months

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during winter and spring. As wind erosion has a significant impact on the topsoil, a field survey was conducted to a depth of 20 cm of farmland in the study area. The basic physical properties of the soil along the depth collected in-situ are listed in Table 1. Table 1 Basic physical properties of soil to the depth of 20 cm in the studied area

2.3 Experimental set

2.3.1 Sample collection and configuration In mid-November 2013, soil samples were collected to a depth of 12 cm from representative farmland within the study area, for a set of simulation experiments of wind erosion after

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ACCEPTED MANUSCRIPT freezing-thawing cycles. At the time of sample collection, farmland was plowed, planted with soybean or corn, and the topsoil was loose, dry and bare. Soil samples were collected from 3

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layers, each layer being 4 cm thick. The unit weight and moisture content of the undisturbed soil

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of each layer were determined before sample collection. The weight of the soil samples and moisture content of each layer were set according to the unit weight, moisture content and sample volume of the undisturbed soil. Corresponding soil samples were weighed and mixed evenly with

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water, and then placed in an insulation box for 24 h to ensure full integration of the soil particles

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with water. Sample configuration indicators are shown in Table 2. The outside of the insulation box (side and bottom) was covered by 10 cm thick insulation material and the inner wall was

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made of stainless steel, with length×width×height dimensions of 29.8 cm×19.8 cm×12 cm.

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The insulation box ensures a vertical freezing and thawing process from the soil surface to the

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bottom that is similar to outdoor conditions. Table 2 Sample configuration indicators

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2.3.2 Experimental design of wind erosion after freezing-thawing process After configuration in the insulation box, soil samples with different moisture contents in top layer were placed into the temperature controlled box to simulate the freezing and thawing process on the surface of black soil with one freezing-thawing cycle every 24 h; the freezing time was 14 h, thawing time was 10 h, and the freezing and thawing temperature difference was -12℃ to 15℃. The soil samples were exposed to 0, 3, 6 and 9 freezing-thawing cycles, and each experiment was repeated twice. The microstructure of soil samples before and after freezing-thawing cycles was observed using scanning electron microscopy. Water in soil after freezing-thawing cycles generally migrated upward due to the hydrothermal migration, which resulted in an increase of

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ACCEPTED MANUSCRIPT moisture content in the upper soil layer. However, the measure result shows the moisture content of soil samples within 0-2 cm soil layer remained unchanged. After freezing-thawing cycles, the

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insulation material was removed and the stainless steel box containing the soil samples was placed

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into the wind tunnel for simulation experiments.

Axis wind speeds (wind speed at the height of 30 cm in the experimental part of the tunnel) in the simulation experiments were maintained at 10 m/s, 15 m/s, 20 m/s and 25 m/s. The soil

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moisture contents and unit weights are shown in Table 2. Each experiment was repeated twice, and

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the experimental results were averaged for analysis. Wind exposure time of each soil sample was 4 min at different wind speeds. WITSEG, a multi-layer sand collector developed by Dong et al.

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(2003), was installed 30 cm from the sample plate to collect the eroded materials within the

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wind-sand flow section during each wind erosion test. Wind-sand flow section is the cross section

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that is perpendicular to the wind-blown sand. The eroded materials collected by the sand collector at each layer were weighed after each test. The weight of soil samples also has been weighed

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before and after wind erosion test. A diagrammatic sketch for the wind erosion test is shown in Fig. 2. The relevant parameters of the experimental design of freezing-thawing cycles induced wind erosion are shown in Table 3. Table 3 Simulation experimental design of wind erosion with freezing-thawing cycles Fig. 2 Diagrammatic sketch for wind tunnel test 2.3.3 Wind tunnel The simulation experiment of freezing-thawing cycles induced wind erosion was performed in the sandstorm-environment wind tunnel in the Key Laboratory of Desert and Desertification, at the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy

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ACCEPTED MANUSCRIPT of Sciences. The wind tunnel is of non-circulating blow-type with a total length of 37.78 m and composed of the following sections: power section, stabilization section, working section (16.23

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m long) and diffusion section. The apparatus is shown in Fig. 3. The maximum cross-sectional

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area of the extension segment was 2.4 m×1.2 m. The experimental segment had a cross-sectional area of 1.0 m×0.6 m. The wind speed was maintained between 2-30 m/s. The airflow stability coefficient was η<3.0%, the wind speed uniformity coefficient was δu=2.0%, the average

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turbulence was ε=0.6%, and the axial static pressure gradient was |dCp/dx|=0.01 m-1. The boundary

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layer thickness of the experimental segment was 12-15 cm.

Fig. 3 Wind tunnel apparatus

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3. Results and Analysis

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3.1 Influences of freezing-thawing cycles on the microstructure of black soil

After the freezing-thawing cycles experiment and prior to the wind erosion testing, sample

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surfaces were scanned using scanning electron microscopy (SEM). Five locations per sample, each with a diameter of 0.5 mm, were scanned and the scanned area was magnified 500 times. SEM photos representative of the soil samples with different moisture contents in top layer following 0, 3, 6 and 9 freezing-thawing cycles are shown in Fig. 4. During the scanning process, it was difficult to optically separate the particles (Sha and Chen, 2006). Soil particles and pores in the photos were therefore distinguished based on color. Pores in the photos were dark, while soil particles were relatively light, thus binary image processing of the photos was completed (Wang, et al., 2009). GIS software was used for data extraction of the pores between soil particles, and the reclassification function of ArcMap 9.3 provided binary processing of the photos according to a

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ACCEPTED MANUSCRIPT selected gray threshold. The classified photos were raster files, which were then transformed into polygon vector files. Based on a comparison between vector files and the original electron

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micrographs, polygons of soil particles and pores in the vector files were corrected, providing an

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accurate reflection of the true soil structure. This method measures pore distribution in the soil plane but not the pore volume. Therefore, the numbers or areas of the pores were reflected as percentages. In this paper, the changes of surface microstructure of black soil samples with

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different moisture contents on the top layer of soil samples after freezing and thawing were

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analyzed.

Fig. 4 Variation of porosity and structure of black soil with different moisture contents

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under freezing-thawing cycles (magnified 500 times)

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The surface pore characteristics of black soil samples were changed significantly by freezing

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and thawing. In addition, there were changes in soil skeleton features, causing internal displacement of the structural system of force transmission frame and resulting in structural

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changes from the surface to internal soil samples. The distribution of surface porosity in the samples with a surface moisture content of 5%, 7% and 8% is shown in Fig. 5 for a variable number of freezing-thawing cycles. The surface porosity of black soil specimens with surface moisture content of 5% was 21.63% before freezing-thawing process and 21.77% after 3 freezing-thawing cycles. Surface porosity increased with increasing numbers of freezing-thawing cycles, reaching 29.07% and 30.26% after 6 and 9 freezing-thawing cycles, respectively. The surface porosity of black soil specimens with surface moisture content of 7% was 21.21%, 22.53%, 30.68% and 31.18% after 0, 3, 6 and 9 freezing-thawing cycles, respectively. The surface porosity of black soil specimens with surface moisture content of 8% was 21.11%, 23.79%, 31.87% and

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ACCEPTED MANUSCRIPT 32.07% after 0, 3, 6 and 9 freezing-thawing cycles, respectively. It is clear that the surface porosity of black soil specimens increased significantly over the 9 freezing-thawing cycles. This

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might have resulted from the growth of ice crystals and the formation of cryogenic structure

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among the soil particles. Cryogenic structure describes the aggregates that form in the cementation process of the microscopic soil particles and ice crystals. The original spatial arrangement between soil particles could be disrupted by freezing and thawing. During the initial freezing and thawing

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stages, the growth of ice crystals and the formation of cryogenic structure increase the pore area,

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and particles are compressed to form a modified skeleton structure. Visually, the soil samples were clearly deformed and showed axial displacement. During the thawing process, internal ice

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crystals melted but the soil skeleton structure was not fully restored. This resulted in a weakening

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of cohesive forces between soil particles. With increasing numbers of freezing-thawing cycles, the

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internal structure of soil samples reached a new equilibrium arrangement. The black soil studied here reached this new equilibrium at 9 freezing-thawing cycles. As shown in Fig. 5, unsaturated

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soil samples with high moisture content were observed, and the surface porosity was greatly affected by the freezing-thawing process, which might be due to the increasing moisture content that provided more favorable conditions for the formation of ice crystals and cryogenic structure. The wind erosion strength in soil is negatively correlated to the cohesive force between soil particles on surface of samples, such that strong cohesive forces will greatly inhibit wind erosion. The cohesive force between soil particles on surface of samples is derived from the combined action of free molecular forces, structural cementation forces between particles (e.g., by soluble salts), and interlocking forces between structural particles. The molecular force primarily depends on soil mineral composition and density; an increase in pore number or size will decrease soil

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ACCEPTED MANUSCRIPT compactness and therefore decrease natural cohesive forces. In soil, the cementation force will be weakened due to freezing-thawing process damage to the soil structure that results in the

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separation of individual grains. Freezing and thawing of soil therefore leads to greater

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susceptibility of soil to wind erosion.

Fig. 5 Surface porosity of soil samples with different moisture contents under

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freezing-thawing cycles

3.2 Influences of freezing and thawing cycles on wind-sand flow structure of black soil

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Wind-sand flow structure describes the distribution and structural characteristics of sand

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transport rate of unit width in the stream as a function of height above the ground surface. The

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wind-sand flow structure is affected by wind speed, erodible particle content and underlying surface characteristics (Zhang, et al., 2002). Previous studies on the wind-sand flow structure of

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desert, gobi and farmland soils (Neuman and Nickling, 1994; Ha and Chen, 1996; Hasi, 2004; Chen, et al., 2010) demonstrate that the wind-sand flow structure of soil surfaces changes with

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freezing and thawing cycles.

Sand transport rate of unit width is a common parameter in erosion and is defined as the sand transport amount of unit time and unit width at a certain wind speed. The sand transport rate of unit width quantifies the wind erosion strength. After freezing and thawing process, the sand transport rate of unit width changes significantly. Fig. 6 shows that the sand transport rate of unit width at a given height was strongly affected by the number of freezing-thawing cycles, regardless of the initial moisture content of the topsoil. For example, when the moisture content of the topsoil 2

was 5% (Fig. 6a), the sand transport rate of unit width of soil samples were 0.66 g/cm ﹒min, 0.77 2

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g/cm ﹒min, 0.97 g/cm ﹒min and 1.04 g/cm ﹒min, for 0, 3, 6 and 9 freezing-thawing cycles, 11

ACCEPTED MANUSCRIPT respectively. This indicated that, compared to the sand transport rate of unit width without freezing-thawing process, the sand transport rate of unit width with 3, 6 and 9 freezing-thawing

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cycles increased by 0.17 times, 0.47 times and 0.58 times, respectively. In addition, the height of

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wind-sand flow for soil samples subject to freezing and thawing also increased. When the topsoil moisture content was 7% (Fig. 6b), the sand transport rate of unit width of soil samples was 0.18 2

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g/cm ﹒min without freezing-thawing process, 0.27 g/cm ﹒min with 3 cycles, 0.33 g/cm ﹒min 2

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with 6 cycles and 0.34 g/cm ﹒min with 9 cycles. These data show that, compared with the sand

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transport rate of unit width without freezing-thawing process, the sand transport rate of unit width with 3, 6 and 9 freezing-thawing cycles increased by 0.50 times, 0.83 times and 0.88 times,

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respectively. When moisture content of the topsoil was 8% (Fig. 6c), the sand transport rate of unit 2

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2

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width of soil samples with 0, 3, 6, and 9 freezing-thawing cycles were 0.13 g /cm ﹒min, 0.15 g 2

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/cm ﹒min, 0.16 g /cm ﹒min and 0.17 g /cm ﹒min, respectively, which indicates that the sand transport rate of unit width with 3, 6 and 9 freezing-thawing cycles increased by 0.15 times, 0.23

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times and 0.31 times, respectively, compared to that without freezing-thawing process. Freezing and thawing cycles can increase the sand transport rate of unit width. The sand transport rate of unit width near the ground (within the height of 40 cm from the ground) increased significantly, and the height of wind-sand flow was enhanced by 1-3 cm. The sand transport rate of unit width near the ground increased against an increase in number of freezing-thawing cycles from 0 to 6, but this trend was not insignificant until the number of freezing-thawing cycles reached 9. Moisture content on the surface of soil samples played a key role in the influences of freezing-thawing cycles on the structural variation of wind-sand flow. When moisture content in top layer of samples exceeded 7%, the influences of freezing-thawing cycles on the structural

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ACCEPTED MANUSCRIPT variation of wind-sand flow were weakened. The reason for this is that with water contents greater than 7%, water molecules increased the action of cohesive forces between soil particles to a level

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greater than the effect of freezing-thawing cycles on wind erosion.

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Fig. 6 Wind-sand flow structure of black soil with different moisture contents under freezing-thawing cycles

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3.3 Influences of freezing and thawing on wind erosion Strength

Freezing and thawing cycles weaken the cohesive forces between soil particles, increase sand

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transport rate of unit width within the wind-sand flow section, and affect the rate and strength of

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soil erosion. We used wind tunnel experiments to obtain wind erosion strength for black soil after

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freezing and thawing process, and reported the results in Table 4. The relationship between wind erosion strength and wind speed under different freezing-thawing cycles and moisture contents is

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reflected by Fig. 7. The wind erosion strength is generally adopted to describe the extent of wind erosion. The extent of wind erosion per unit time and unit area is a wind erosion parameter that

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measures and classifies the wind erosion strength. Freezing-thawing cycles in black soil affect the structure of soil, as well as the wind erosion strength. The test results indicated that the wind erosion strength is significantly related to freezing and thawing process of soil when moisture content is less than 8%. The wind erosion strength increased with an increasing number of freezing-thawing cycles. For instance, when the moisture content was 5%, after blastation for 16 minutes at the wind velocity of 10-25 m/s, the wind erosion strength with 3, 6 and 9 freezing-thawing cycles is 1.03 times, 1.20 times and 1.21 times, respectively, higher than that without freezing-thawing process. Similarly, when the moisture content was 7%, freezing thawing process with the three different numbers of cycles results in the increase in wind erosion strength 13

ACCEPTED MANUSCRIPT by 1.45 times, 1.96 times and 1.99 times, respectively. It can be seen that 3-6 freezing-thawing cycles significantly affected the wind erosion strength of black soil. After 6 freezing-thawing

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cycles, exposure to additional cycles did not strongly affect the wind erosion strength of soil.

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When the moisture content in top layer of sample was greater than 8%, the effect of freezing-thawing cycles on wind erosion strength was insignificant. This suggests that freezing and thawing process exerts a weaker influence on soil wind erosion strength under conditions of

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higher moisture content.

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Table 4 Wind erosion modulus of soil samples with different moisture contents under freezing-thawing cycles

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Fig. 7 Wind erosion strength of black soil with different moisture contents under

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4. Conclusions

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freezing-thawing cycles

The experimental findings in this study can be summarized in the following three aspects:

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(1) Freezing and thawing changes the structure of black soil. Surface porosity is increased by an increasing number of freezing-thawing cycles. After freezing and thawing process, the porosity of soil with initial moisture contents on the surface of soil samples of 5%-8% can increase by 1.4-1.5 times. After 6 freezing-thawing cycles, the internal structure of the soil samples reaches a new stable state. (2) Freezing and thawing cycles change the sand transport rate of unit width of soil during a wind erosion test. Sand transport rate of unit width gradually increases with the number of freezing-thawing cycles. The sand transport rate of unit width within 40 cm from the ground increases significantly up to 1.4 times. The height of wind-sand flow increases by 1-3 cm due to 14

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(3) Freezing and thawing cycles change the original structure of the black soil, and presumably

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weaken the cohesive forces between soil particles, thereby affecting the wind erosion strength. The wind erosion strength increases with the number of freezing-thawing cycles. After 6-9 freezing-thawing cycles, the wind erosion strength of soil samples with

moisture content of 5%

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and 7% increases by 1.2 times and 2.0 times, respectively. When the moisture content exceeds 8%,

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the influence of freezing-thawing cycles on wind erosion strength is not significant. In reality, the effect of freezing-thawing cycles on wind erosion strength of black soil under

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practical situations is affected by many additional factors, including pulsation of wind speed,

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changes of surface water, temperature fluctuations caused by solar radiation, and the influences of

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snow melting on soil moisture contents. Therefore, further research will be conducted through indoor simulation experiments together with practical conditions.

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Acknowledgements

This research was supported by the National Natural Science Foundation of China (51579157, 41301072, 41230630), the Natural Science Foundation of Inner Mongolia (2013MS0702, 2015MS0387), the Program of Higher-level talents of Inner Mongolia University (30105-125146), the Open Project Program of the State Key Laboratory of Frozen Soil Engineering (SKLFSE201208), the Chinese Ministry of Water Resources of public projects (1261330111117), the Free Inquiry Fund of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, and the China Institute of Water Resources and Hydropower Research (2016TS02).

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ACCEPTED MANUSCRIPT References Bullock, M.S., Larney, F.J., et al., 2001. Overwinter changes in wind erodibility of clay loam soils

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in southern Alberta. Soil Science Society of America Journal, 65(2): 423-430.

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Chen, Z., Ma, S.S., Zhao, Y.L., et al., 2010. Characteristics of drifting sand flux over conservation

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tillage field. Transactions of the CSAE, 26(1): 118-122. (In Chinese)

Dong, Z.B., Sun, H.Y., Zhao, A.G., 2003. WITSEG sampler: A segmented sand sampler for wind tunnel test. Journal of desert research, 23(6): 714-720.

of soils. Engineering Geology, (13): 73–92.

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Edwin, J.C., Anthony, J.G., 1979. Effect of freezing and thawing on the permeability and structure

MA

Graham, J., Au, V.C.S., 1985. Effects of freeze-thaw and softening on a natural clay at low stresses. Canadian Geotechnical Journal, 22(1): 69–78.

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Ha, S., Chen, W.N., 1996. Effect of tillage practices on soil wind erosion taking Bashang Area of

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Hebei Province as an example. Journal of Soil Erosion and Soil and Water Conservation, 2(1): 10-16.

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Hasi., 2004. A preliminary study on structural variation of surface wind-sand flow of dunes in southeastern Tengger Desert. Chinese Science Bulletin, 49(11): 1099-1104. (In Chinese) Ma, W., Xu, X.Z., Zhang, L.X., 1999. Influence of frost and thaw cycles on shear strength of lime

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silt. Chinese Journal of Geotechnical Engineering, 21(2): 158–160. (In Chinese) Maokuxitasaiyiyiqi., 1982. Physics of frozen soil. Tokyo Japan, The Publisher of Maolihaoku. Neuman, M.C., Nickling, W.G., 1994. Momentum extraction with saltation: Implications for experimental evaluation of wind profile parameters. Boundary-Layer Meteorology, 68(1/2): 35-50. Qi, J.L., Ma, W., 2010. State-of-art of research on mechanical properties of frozen soils. Rock and Soil Mechanics, 31(1): 133–143. Qu, J.J., Cheng, G.D., et al., 2007. An experimental study of the mechanisms of freeze/thaw and wind erosion of ancient adobe buildings in northwest China. Bulletin of Engineering Geology and the Environment, 66(2):153-159. Sha, A.M., Chen, K.S., 2006. Relationship between collapsibility and microstructure of compacted

16

ACCEPTED MANUSCRIPT loess. Journal of Chang’an University, 26(4): 1-4. (In Chinese) Tatarko, L.E., Wagner, C.A., Boyce., 2001. Effects of overwinter processes on stability of dry soil aggregates. Soil Erosion Research for the 21st Century, Proceedings, 459-462.

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Tovey N.K., Krinsley, D.H., Dent, D.L., et al., 1992a. Techniques to quantitatively study the

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microfabric of soils. Geoderma, 53(3-4): 217–235.

types of soil fabric. Geoderma, 53(3-4): 179–200.

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Tovey N.K., Smart P., Hounslow, M.W., et al., 1992b. Automatic orientation mapping of some

Wang, D.Y., Ma, W., Niu, H., et al., 2007. Effects of cyclic freezing and thawing on mechanical

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properties of Qinghai-Tibet clay. Cold Regions Science and Technology, 48(1): 34–43. Wang, J.D., Yuan, Z.X., Ren, Q., 2009. A study on loess microstructure pre and post liquefaction

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of high-speed railway foundation. Journal of Northwest University (Natural Science Edition), 39(3):480-483. (In Chinese)

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Xie, S.B., Qu, J.J., Han, Q.J., 2012. Mechanisms of Freezing-Thawing Induced Wind Erosion in

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Qinghai-Tibet Plateau. Bulletin of Soil and Water Conservation,32(2):64-68. Xu, X.Z., Wang, J.C., Zhang, L.X., 2001. Physics of frozen soil. Beijing, Science Press.

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Yang, C.S., He, P., Cheng, G.D., et al., 2003. Testing study on the influence of freezing and thawing on dry density and water content of soil. Chinese Journal of Rock Mechanics and Engineering, 22(S2): 2695–2699. (In Chinese )

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Zhang, H., Li, F.R., Zhang, T.H., et al., 2002. Wind-sand flow structure and its variation under different surface conditions in korqin sandy land. Journal of Soil Water Conservation, 16(2): 20-28. Zhang, J.G., Liu, S.Z., Yang, S.Q., 2007. The classification and assessment of freeze-thaw erosion in Tibet. Journal of Geographical Sciences,17(2): 165-174.

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ACCEPTED MANUSCRIPT List of figure captions Fig. 1 Location of the study area

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Fig. 2 Diagrammatic sketch for wind tunnel test

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Fig. 3 Wind tunnel apparatus

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Fig. 4 Variation of porosity and structure of black soil with different moisture contents under freezing-thawing cycles (magnified 500 times)

Fig. 5 Surface porosity of soil samples with different moisture contents under freezing-thawing

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cycles

Fig. 6 Wind-sand flow structure of black soil with different moisture contents under

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freezing-thawing cycles

Fig. 7 Wind erosion strength of black soil with different moisture contents under freezing-thawing

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cycles

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Fig. 1 Location of the study area

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Fig. 2 Diagrammatic sketch for wind tunnel test

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Fig. 3 Wind tunnel apparatus

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3 cycles

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9 cycles

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6 cycles

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(a) Surface moisture content 5%

3 cycles

6 cycles

9 cycles (b) Surface moisture content 7%

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CE P

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0 cycle

0 cycle

3 cycles

6 cycles

9 cycles (c) Surface moisture content 8%

Fig. 4 Variation of porosity and structure of black soil with different moisture contents under freezing-thawing cycles (magnified 500 times)

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Moisture content 5% Moisture content 7% Moisture content 8%

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Surface porosity/%

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20 2

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6

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Numbers of freezing-thawing cycles/n

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Fig. 5 Surface porosity of soil samples with different moisture contents under

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freezing-thawing cycles

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60 40 20 0 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035

100 80 60 40 20

0 0.000 0.002 0.004 0.006 0.008 0.010 0.012

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Sand transport rate of unit width/g/(cm min) 100 Moisture content 8%

0 cycle 3 cycles 6 cycles 9 cycles

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60 40 20 0 0.000

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Sand transport rate of unit width/g/(cm min)

0.002

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Height from the bed surface/mm

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0 cycle 3 cycles 6 cycles 9 cycles

Moisture content 7%

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Height from the bed surface/mm

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0 cycle 3 cycles 6 cycles 9 cycles

Moisture content 5%

0.004

0.006

0.008 2

Sand transport rate of unit width/g/(cm min)

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Fig. 6 Wind-sand flow structure of black soil with different moisture contents under

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freezing-thawing cycles

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Height from the bed surface/mm

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Moisture content 7%

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Wind erosion strength/g/(m min)

Moisture content 5%

0 cycle 3 cycles 6 cycles 9 cycles

0 10

15

20

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Wind speed level/m/s Moisture content 8%

25 20

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15 10 5 10

0

15

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0 cycle 3 cycles 3 cycles 3 cycles

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Wind speed level/m/s

15

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Wind erosion strength/g/(m min)

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20

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Wind erosion strength/g/(m min)

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0 cycle 3 cycles 6 cycles 9 cycles

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Wind speed level/m/s

Fig. 7 Wind erosion strength of black soil with different moisture contents under

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freezing-thawing cycles

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ACCEPTED MANUSCRIPT Tables Table 1 Table 1 Basic physical properties of soil to the depth of 20 cm in the studied area

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Table 2 Sample configuration indicators

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Table 3 Simulation experimental design of wind erosion with freezing-thawing cycles

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Table 4 Wind erosion modulus of soil samples with different moisture contents under

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freezing-thawing cycles

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ACCEPTED MANUSCRIPT Table 1 Table 1 Basic physical properties of soil to the depth of 20 cm in the studied area

(g/cm3)

0-5 5-10 10-15 15-20

1.29 1.35 1.47 1.49

4.8 9.2 12.3 12.8

d>200 (%) 4.85 4.20 3.95 3.47

particle diameter distribution (m) 200>d>100 100>d>40 40>d>20 (%) (%) (%) 10.94 33.21 25.48 10.28 35.47 26.78 10.77 34.12 26.92 11.10 33.55 25.37

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(cm)

Moisture content (%)

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Unit weight

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depth

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40>d (%) 25.52 23.27 24.24 26.51

ACCEPTED MANUSCRIPT Table 2 Sample configuration indicators Unit weight

Moisture content

3

(g/cm )

sample number

Layer 2 5-8cm

Layer 3 9-12cm

Layer 1 0-4cm

Layer 2 5-8cm

Layer 3 9-12cm

1.29 1.29 1.29

1.35 1.35 1.35

1.46 1.46 1.46

5 7 8

9.1 9.1 9.1

12.7 12.7 12.7

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Layer 1 0-4cm

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1, 2, 3, 4, 5, 6, 15, 16 7, 8, 9, 10, 17, 18 11, 12, 13, 14, 19, 20

Surface area of soil

(%)

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sample (m2) 0.059 0.059 0.059

ACCEPTED MANUSCRIPT Table 3 Simulation experimental design of wind erosion with freezing-thawing cycles

10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25 10, 15, 20, 25

each wind speed

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level (min) 4 4 4 4 4 4 4 4 4 4

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3 6 9 3 6 3 6 0 0 0

content (%) 5.0 5.0 5.0 7.0 7.0 8.0 8.0 5.0 7.0 8.0

Axis wind speed level (m/s)

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1, 2 3, 4 5, 6 7, 8 9, 10 11, 12 13, 14 15, 16 17, 18 19, 20

moisture

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sample number

Freeze-thaw cycle number

Blowing time at

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Topsoil

Surface area of soil sample (m2) 0.059 0.059 0.059 0.059 0.059 0.059 0.059 0.059 0.059 0.059

ACCEPTED MANUSCRIPT Table 4 Wind erosion modulus of soil samples with different moisture contents under freezing-thawing cycles Axis wind speed and blowing time

Surface moisture content

Wind erosion modulus/(g·m-2·min-1) 3 cycles

10m·s , 4min

10.59

11.44

13.56

13.56

10m·s-1-15m·s-1, 8min

32.84

33.68

46.40

48.94

64.26

71.61

72.03

-1

-1

-1

5%

10m·s -20m·s , 12min

63.41 69.70

10m·s-1, 4min -1

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10m·s -15m·s , 8min -1

7%

-1

10m·s -20m·s , 12min -1

10m·s , 4min -1

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10m·s -15m·s , 8min -1

-1

-1

-1

8%

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10m·s -20m·s , 12min

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10m·s -25m·s , 16min

71.50

83.10

84.28

17.37

18.22

18.64

19.00

33.47

35.38

36.44

20.82

43.50

53.95

55.22

29.38

42.48

57.52

58.47

9.02

9.32

10.59

11.02

22.06

23.09

23.52

25.00

26.19

26.41

26.83

27.26

27.05

27.43

27.86

28.18

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10m·s-1-25m·s-1, 16min

30

9 cycles

9.44

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10m·s -25m·s , 16min

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-1

6 cycles

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0 cycle

-1

ACCEPTED MANUSCRIPT Highlights: The freezing-thawing (F-T) cycle tests of agricultural soil are carried out The varieties of surface porosity of black soil are analyzed The effects of F-T action on wind erosion are evaluated

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Critical numbers of F-T cycles affecting porosity and wind erosion are determined

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  

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