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Journal of Arid Land  2023, Vol. 15 Issue (5): 491-507    DOI: 10.1007/s40333-023-0055-y
Research article     
Exploration of playa surface crusts in Qehan Lake, China through field investigation and wind tunnel experiments
LIU Dongwei1, HAN Lijing2,*(), KOU Zihan1, GAO Xinyu1, WANG Jingjing1
1School of Ecology and Environment, Inner Mongolia University, Hohhot 010021, China
2College of Geography and Remote Sensing Sciences, Xinjiang University, Urumqi 830017, China
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Globally, many lakes are drying up, leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere. Therefore, understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms. The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region, China to understand the salt dust release potential of different types of playa surface crusts. Various crust characteristics were investigated by field sampling in Qehan Lake, and playa surface crusts were further divided into five types: vegetated areas, salt crusts, clay flats, curly crusts, and margins. It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake. The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images, and the salt dust release potential of crusts was explored by the wind tunnel experiments. The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake, which were successively vegetated areas, clay flats, salt crusts, and margins. The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa, soil texture, and groundwater. There was a significant negative correlation between crust thickness and electrical conductivity. The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats (0.7-0.8 m/s) than in salt crusts (0.5-0.6 m/s). Moreover, the particle leap impact processes occurring under natural conditions may reduce this threshold value. Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts. This study provides a scientific reference for understanding how salt dust is released from a lakebed, which may be used for ecological restoration of dry salt lakes.

Key wordsplaya surface crust      curly crusts      salt crusts      salt dust release      wind tunnel experiments      Qehan Lake     
Received: 13 August 2022      Published: 31 May 2023
Corresponding Authors: *HAN Lijing (E-mail:
Cite this article:

LIU Dongwei, HAN Lijing, KOU Zihan, GAO Xinyu, WANG Jingjing. Exploration of playa surface crusts in Qehan Lake, China through field investigation and wind tunnel experiments. Journal of Arid Land, 2023, 15(5): 491-507.

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Fig. 1 Landsat image overview of Qehan Lake including East Qehan Lake and West Qehan Lake (a), and photo showing salt dust blowing over the playa (b). The Landsat-8 satellite false-color composite image (RGB bands 543) was captured on 14 July, 2019.
Fig. 2 Schematic diagram of the wind tunnel experiment
Fig. 3 Field images used for classifying playa surface crust types of the sampling sites. (a), vegetated areas located close to the center of the lake; (b), curly crusts occurred in a clay flat with a small area; (c), salt crusts located between the edge of the playa surface and clay flats; (d), margins appeared on the lakeshore; (e), clay flats occurred between vegetated areas and salt crusts.
Playa surface crust type Crust kind Crack kind Description
Vegetated areas Physical RCR, ICR, and RTH Large cracks with width higher than 1.00 cm and depth greater than 3.00 cm (trans-horizon). Crusts appear polygonal in shape, with large polygons accompanied by crust-related cracks inside. They are seasonal, formed by wetting and drying of the soil. The dominate plant species is Suaeda glauca.
Salt crusts Physical and chemical RCR Cracks with width less than 0.50 cm and depth of 0.50 cm. The surface soil is swell and saline.
Clay flats Physical RCR Shallow and transient (generally persist less than a few weeks) RCR at some locations. There are signs of salt dust release and wind erosion (Fig. 1b).
Curly crusts Physical RCR Brittle curly crusts. The area is very small and highly susceptible to wind erosion.
Margins Physical None There is coarse and fine gravel, sand, and lakeside vegetation (Achnatherum splendens, Nitraria tangutorum, and Stipa capillata).
Table 1 Description of playa surface crust types in Qehan Lake
Fig. 4 Box plot statistics of crust thickness (a), crust hardness (b), soil water content (c), and EC1:5 (electrical conductivity of the upper clear layer for a soil-to-water ratio of 1:5; d) of different crust types on the playa surface in Qehan Lake. The upper and lower limits of the box indicate the 75th and 25th percentile values, respectively; the horizontal line in each box represents the median of the distributions; and the upper and lower whiskers show the 95th and 5th percentile values, respectively.
Crust thickness Crust hardness Soil water content EC1:5
Crust thickness 1.000
Crust hardness 0.181 1.000
Soil water content 0.095 -0.275 1.000
EC1:5 -0.453** -0.266 0.059 1.000
Table 2 Pearson correlation results of crust thickness, crust hardness, soil water content (topsoil), and EC1:5
Fig. 5 Spatial distribution of playa surface crust types in Qehan Lake
Fig. 6 Box plots of crust thickness for each sampling site from the lake center to the lakeshore in belt transects A (a), B (b), and C (c). The upper and lower limits of the box indicate the 75th and 25th percentile values, respectively; the horizontal line in each box represents the median of the distributions; and the upper and lower whiskers show the 95th and 5th percentile values, respectively.
Fig. 7 Box plots of crust hardness for each sampling site from the lake center to the lakeshore in belt transects A (a), B (b), and C (c). The upper and lower limits of the box indicate the 75th and 25th percentile values, respectively; the horizontal line in each box represents the median of the distributions; and the upper and lower whiskers show the 95th and 5th percentile values, respectively.
Fig. 8 Scatter plot of crust thickness and hardness. Outlier sampling sites are marked in the figure. The red line indicates the fitted line after removing the outliers with the equation statistics in the lower right corner.
Fig. 9 Means and standard deviations of EC1:5 (a), crust thickness (b), and soil water content (c) for the five soil sample groups (I-V) from the wind tunnel experiments. The circles indicate the means and the bars indicate the standard deviations.
Group No. EC1:5 (mS/cm) Crust thickness (cm) Soil water content (%) Sand (%) Silt (%) Clay (%) Soil texture Playa surface crust type
I I1 13.83 0.29 7.30 41.13 58.04 0.83 Silty loam Salt crusts
I2 7.26 0.37 10.80 25.55 72.09 2.36 Silty loam
I3 11.46 0.20 4.30 33.92 59.75 6.33 Silty loam
II II1 7.07 0.29 9.30 76.11 22.77 1.12 Loamy sand Salt crusts
II2 9.22 0.24 11.10 67.94 32.06 0.00 Sandy loam
II3 5.35 0.30 9.20 70.76 28.86 0.38 Loamy sand
III III1 4.42 0.78 1.80 84.42 14.52 1.06 Loamy sand Clay flats
III2 3.70 0.51 2.40 89.68 9.73 0.59 Sand
III3 1.98 0.49 2.30 91.85 7.66 0.49 Sand
IV IV1 2.13 0.34 10.50 64.33 35.67 0.00 Sandy loam Clay flats
IV2 1.32 0.43 7.40 72.48 24.90 2.62 Sandy loam
IV3 3.44 0.20 7.70 63.54 35.68 0.78 Sandy loam
V V1 4.45 0.34 4.16 91.07 8.93 0.00 Sand Salt crusts
V2 12.00 0.23 3.55 76.94 23.06 0.00 Loamy sand
V3 9.66 0.25 4.56 83.44 16.56 0.00 Loamy sand
Table 3 Properties of soil samples used in the wind tunnel experiments and corresponding playa surface crust types
Fig. S1 Particle size distribution of soil samples belonging to clay flats that were not used in the wind tunnel experiments
Fig. 10 Relationship between horizontal dust flux and friction wind velocity (u*) for the five soil groups in the wind tunnel experiments. (a), group I; (b), group II; (c), group III; (d), group IV; (e), group V. The values 1, 2, and 3 after I-V represent the number of repeated samples in the wind tunnel experiments. The lines are the fitted lines of horizontal dust flux against u*.
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