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Sciences in Cold and Arid Regions ›› 2020, Vol. 12 ›› Issue (1): 12-21.doi: 10.3724/SP.J.1226.2020.00012.

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Aeolian processes on sandy desertification of an alpine meadow: A wind tunnel experiment

ZhiShan An1,2,3,4,KeCun Zhang1,2,3(),LiHai Tan1,2,3,BaiCheng Niu1,2,4,YanPing Yu1,2,4   

  1. 1. Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China
    2. Dunhuang Gobi and Desert Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China
    3. Key Laboratory of Desert and Desertification, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China
    4. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2019-07-05 Accepted:2019-09-12 Online:2020-02-29 Published:2020-03-17
  • Contact: KeCun Zhang E-mail:kecunzh@lzb.ac.cn

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Abstract:

In recent years, the desertification of alpine meadows has become a serious ecological problem and has gradually become a threat to regional economic activities in Maqu County. To reveal the mechanism for sandy desertification of alpine meadows, we conducted wind tunnel experiments on aeolian processes over sandy alpine meadows. Results show that the sand-flux profile of mix-sized sediment decays exponentially with increasing height. However, the profile pattern of a group of uniform-sized particles depends on the experimental wind speeds. The profile pattern of all the groups studied can be expressed by exponential decay functions when the wind speed is less than or equal to 16 m/s. while that for all the groups studied can be expressed by a Gaussian distribution function when the wind speed is above 16 m/s. The average saltation heights of mixed sands at wind speeds of 12 m/s, 16 m/s, 20 m/s, and 24 m/s were 2.74, 4.19, 5.28, and 6.12 cm, respectively. The mean grain size basically first decreases and then increases with increasing height under different wind speeds. The sorting improves with increasing wind speed, while the kurtosis and skewness show relationships with only the characteristics of the parent soil.

Key words: alpine meadow, sandy desertification, aeolian erosion, aeolian transport

Figure 1

Location map (data from Google Earth) for the study site in Maqu County"

Figure 2

Layout of the test apparatus"

Table 1

Composition and parameters of the study surface and their volume percentages"

Study surface (mm) Volume percentage Parameter
Very coarse 1-2 1.38% Mean diameter (0.172)
Coarse 0.5-1 6.43% Standard deviation (0.96)
Medium 0.25-0.5 23.40% Skewness (0.34)
Fine 0.125-0.25 35.85% Kurtosis (2.04)
Very fine 0.063-0.125 17.38% -
Silt 0.002-0.063 12.18% -
Clay<0.002 3.38% -

Figure 3

The sand-flux profiles under different experimental wind speeds"

Table 2

Values of regression coefficients in Equation (1) "

Wind velocity (m/s) A B R 2
12 0.13308 -0.02943 0.959
16 0.32445 -0.01613 0.994
20 0.68964 -0.01136 0.972
24 2.91430 -0.00981 0.977

Figure 4

Selected cumulative-percentage diagram illustrating characteristic heights"

Figure 5

The process of aeolian erosion and deposition over the alpine meadow"

Figure 6

Wind-erosion intensity versus sand flux. A strong linear relationship exists between sand flux and wind erosion"

Figure 7

Sand-flux profiles of different grain-size groups under wind speeds of 12 m/s(a), 16 m/s(b), 20 m/s(c), and 24 m/s(d)"

Table 3

The weight percentages of different grain sizes (in mm) under different wind speeds"

Wind speed

(m/s)

Coarse

0.5-1.0

Medium

0.25-0.5

Fine sand

0.125-0.25

 Very fine 0.063-0.125

Silt

0.002-0.063

Clay

<0.002
12 1.35% 13.50% 35.96% 28.65% 17.69% 3.59%
16 0.00% 13.22% 41.06% 28.59% 13.99% 3.14%
20 0.02% 15.51% 41.46% 26.31% 13.33% 3.37%
24 0.27% 18.10% 40.49% 25.01% 12.83% 3.30%

Figure 8

Mean grain size, sorting, skewness, and kurtosis changes with height at wind speeds of 12 m/s, 16 m/s, 20 m/s, and 24 m/s"

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