Sciences in Cold and Arid Regions ›› 2022, Vol. 14 ›› Issue (3): 196-211.doi: 10.3724/SP.J.1226.2022.2021-0013.

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Spatio-temporal variation of soil CO2 concentration in Loess Area of northwestern Shanxi Province, China

TianJie Shao1,4(),ZhiPing Xu1,LianKai Zhang2(),RuoJin Wang1,JunJie Niu3,MingYu Shao2   

  1. 1.College of Geography Science and Tourism, Shaanxi Normal University, Xi'an, Shaanxi 710062, China
    2.Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin, Guangxi 541000, China
    3.Research Center for Scientific Development in Fenhe River Basin, Taiyuan Normal University, Taiyuan, Shanxi 030001, China
    4.SNNU-JSU Joint Research Center for Nano-environment Science and Health, Shaanxi Normal University, Xi'an, Shaanxi 710062, China
  • Received:2021-02-25 Accepted:2021-10-18 Online:2022-06-30 Published:2022-07-04
  • Contact: TianJie Shao,LianKai Zhang;
  • Supported by:
    the National Natural Science Foundation(41671213);the Fundamental Research Funds for the Central Universities(GK201803055);Shaanxi province Postdoctoral Science Foundation(2016BSHEDZZ27)


CO2 released by soil serves as an important link between terrestrial ecosystems and atmospheric CO2, whose small changes may significantly affect the global carbon cycle. In order to reveal the spatio-temporal variations of CO2 concentrations in deep loess, this paper takes Qingliangsi Gully watershed in northwestern Shanxi Province, China as an example to systematically study soil CO2 concentration and its spatio-temporal variations and carbon sink significance under different watershed locations and different land use types. Results show that: (1) The release potential of the loess soil is larger in the depth range of 2 m, which is much more likely to be the CO2 release area. (2) Grassland and forest are more advantageous in terms of soil microbial activity and soil carbon reserve compared with farmland. In addition, the change of land use type from farmland to grassland can increase soil organic carbon reserve, which is of far-reaching significance to the global carbon cycle. This is especially true in an area like the Loess Plateau with densely covered hills, gullies, and serious soil erosion in an area of 64×104 km2. (3) In the study area, the diurnal concentration of soil CO2 at different depths shows a weak "high-low-high-low" trend from 08:00 to 07:00 next day; and in deep soil it has a lag time compared with the daily change of temperature, generally about 4-12 h, which may be caused largely by the more compact loess structure. It is worth pointing out that the Loess Plateau in China, with a thickness of the loess of tens to hundreds of meters, has the most abundant soil resources in the world, and also stores a large amount of terrestrial soil carbon, which carries the hope of promoting the research of global carbon cycle.

Key words: soil CO2 concentration, China Loess Plateau, carbon sink function, release potential

Figure 1

Watershed profile and location diagram of observation area"

Table 1

Soil characteristics (depth of 0-2 m) in Loess Area of northwestern Shanxi Province"



0-2 m Moisture contentTemperature (°C)Soil type
0.5 m1.0 m2.0 m
A1 (Spring)12.75%±0.89%12.37±0.789.36±1.257.66±0.78Ma Lan loess
A2 (Spring)12.95%±2.42%12.55±1.418.82±1.287.58±1.35Ma Lan loess
B (Spring)12.22%±0.89%13.30±0.719.95±0.748.43±0.64Ma Lan loess
C (Spring)10.18%±1.43%15.88±0.3912.50±0.4011.83±0.44Loess sediments deposited in river floodplains
A1 (Summer)7.38%±1.29%18.29±0.3918.79±0.4515.42±0.45Ma Lan loess
A2 (Summer)9.85%±2.93%20.05±0.3018.64±0.4016.84±0.41Ma Lan loess
B (Summer)6.80%±0.94%21.69±0.3320.31±0.436.80±0.94Ma Lan loess
C (Summer)7.52%±3.20%20.95±0.0919.54±0.3117.15±0.29Loess sediments deposited in river floodplains
A1 (Autumn)8.97%±2.45%5.97±0.248.76±0.3210.90±0.52Ma Lan loess
A2 (Autumn)10.87%±1.91%5.47±0.236.80±0.3310.03±0.29Ma Lan loess
B (Autumn)9.22%±2.20%5.58±0.507.10±0.3710.64±0.34Ma Lan loess
C (Autumn)7.83%±2.10%6.18±0.209.03±0.3710.81±0.74Loess sediments deposited in river floodplains

Figure 2

Soil CO2 concentration and its diurnal variation law in summer in the loess area of northwestern Shanxi Province. ((a), (b, (c) and (d) refer to farmland (A1) in A area, grassland (A2), farmland in B area and forest in C area, respectively; the abscissa 01∶02 refers to 02:00 next day, the same for the rest; -0.5 m, -1 m and -2 m separately refer to the depth of 0.5 m, 1 m and 2 m below the surface, the same below; the above remarks apply also to Tables 2-4, Figures 3, 4)"

Table 2

Statistical analysis results of soil CO2 concentration observed data in summer in the loess area of northwestern Shanxi Province"

LocationDepth (m)Average value (×10-4 m3/m3)Range (×10-4 m3/m3)Variation coefficient

Figure 3

Soil CO2 concentration and its diurnal variation law in spring in the loess area of northwestern Shanxi Province"

Table 3

Statistical analysis results of soil CO2 concentration observed data in spring in the loess area of northwestern Shanxi Province"

LocationDepth (m)Average value (×10-4 m3/m3)Range (×10-4 m3/m3)Variation coefficient

Figure 4

Soil CO2 concentration and its diurnal variation law in autumn in the loess area of northwestern Shanxi Province"

Table 4

Statistical analysis results of soil CO2 concentration observed data in autumn in the loess area of northwestern Shanxi Province"

LocationDepth (m)Average value (×10-4 m3/m3)Range (×10-4 m3/m3)Variation coefficient

Table 5

Diffusion coefficient of soil CO2 of different depths in the loess area of northwestern Shanxi Province (×10-5 m2/s)"

Position-QuarterDepth (m)Diffusion coefficientPosition-QuarterDepthDiffusion coefficient
Farmland (A1) -Spring0.51.49±0.02Farmland (B)-Summer0.5 m1.58±0.01
1.01.46±0.021.0 m1.56±0.01
2.01.45±0.012.0 m1.53±0.00
Grassland (A2) -Spring0.51.49±0.03Forest land (C)-Summer0.5 m1.57±0.00
1.01.46±0.031.0 m1.56±0.00
2.01.45±0.022.0 m1.53± 0.01
Farmland (B) -Spring0.51.50±0.01Farmland (A1)-Autumn0.5 m1.43±0.00
1.01.47±0.011.0 m1.46±0.00
2.01.45±0.012.0 m1.48±0.06
Forest land (C) -Spring0.51.52±0.01Grassland (A2)-Autumn0.5 m1.43±0.00
1.01.49±0.001.0 m1.44±0.01
2.01.49±0.012.0 m1.47±0.00
Farmland (A1) -Summer0.51.55±0.00Farmland (B)- Autumn0.5 m1.43±0.01
1.01.55±0.011.0 m1.44±0.00
2.01.52±0.012.0 m1.48±0.00
Grassland (A2) -Summer0.51.56±0.01Forest land (C)- Autumn0.5 m1.44±0.00
1.01.55±0.001.0 m1.47±0.01
2.01.53±0.012.0 m1.49±0.01

Figure 5

Distribution characteristics of soil CO2 concentration of different depths in the loess area of northwestern Shanxi Province. (Note: A1(-2) refers to the depth of 2 m of the farmland (A1) observation point, and the rest of the abscissa means in a similar way)"

Table 6

Soil water content and soil organic matter content of different depths in loess area of northwestern Shanxi Province"

Position (Quarter)Average moisture contentAverage organic matter content (g/kg)
0.0-0.5 m0.6-1.0 m1.1-2.0 m0.0-2.0 m0-2 m
A1 (Spring)13.87%±0.38%13.02%±0.44%12.06%±0.53%12.75%±0.89%6.42±2.61
A2 (Spring)10.47%±2.33%14.04%±1.20%13.63%±2.17%12.95%±2.42%7.54±4.78
B (Spring)11.45%±1.07%13.14%±0.47%12.14%±0.51%12.22%±0.89%5.25±3.02
C (Spring)10.59 %±0.90%9.96%±0.31%10.0%±2.00%10.18%±1.43%6.21±3.28
A1 (Summer)7.47%±1.57%6.53%±0.29%7.75%±1.36%7.38%±1.29%6.59±2.41
A2 (Summer)7.02%±2.47%9.30%±0.83%12.26%±2.17%9.85%±2.93%7.16±4.82
B (Summer)6.47%±1.28%6.57%±0.79%7.08%±0.84%6.80%±0.94%5.55±3.02
C (Summer)10.72%±4.87%5.34%±0.26%6.87%±0.38%7.52%±3.20%7.10±4.09
A1 (Autumn)12.39%±1.11%9.00%±0.02%7.24%±0.01%8.97%±2.45%6.26±2.36
A2 (Autumn)13.25%±1.23%10.36%±0.01%9.30%±0.01%10.87%±1.91%7.14±4.84
B (Autumn)11.62%±0.48%10.82%±0.01%7.22%±0.01%9.22%±2.20%6.15±4.86
C (Autumn)10.29%±1.81%6.86%±0.01%7.00%±0.02%7.83%±2.10%6.47±2.90

Figure 6

Linear fitting of air temperature and soil CO2 of spring farmland (A1 and B) in the loess area of northwestern Shanxi Province"

Figure 7

The distribution characteristics of soil particle size in the loess area of northwestern Shanxi Province"

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