Analysis of Ecological Approach for Stabilizing Shifting Sand in Shapotou District of Baotou-Lanzhou Railway

 

Xiao Honglang   Fan Hengwen   Zhao Yanhua

(Institute of Desert Research, Chinese Academy of Sciences and State Forestry Administration

260 Donggang West Road, Lanzhou 730000, P.R. China)

 

The Shapotou section of Baotou-Lanzhou Railway is located at the southeastern edge of Tengger Desert and west part of Zhongwei County. Duneforms are mainly the transverse dunes, and varies from 7 m to 20 m in height and the annual moving speed is estimated to up to 3 m southeasterly (Ling Yuquan et al., 1991). Climate is dry and much windy with 2.8 m/s of mean wind velocity. The annual mean rainfall is 186.2 mm and annual mean temperature is 9.6C. Ecological environment is fragile. Soils are mainly Cal-Orthic Aridisols and Sandic Entisols. The district is the transitional zone of the Loess Plateau and Alxa Upland and marginal area of desert steppe and semi-desert.

 

Sand-fixing system with xerophytes in Shapotou section was initiated since later 1950’s. Straw checkerboards were used to fixe shifting-sand initially. Then, sand-fixing plants were introduced and adapted one after another from 1950s to 1960s, from 1970s to 1980s without interval. The vegetative coverage was kept in a density of 20-40% in the succession from revegetation to natural growth for decades. Some xerophytes planted inside the straw checkerboards produced 43.6 g/m2 of withered branches and defoliation at the beginning stage (Shi Qinghui, 1993, 1995). With the formation of silt crust on the sand surface when the dunes were stabilized with species for 10 to 15 year, soil was improved and vegetative coverage was increased and the system became more and more perfect with the growth of microbes and lichen> This system is the most important part in the sand stabilization along the railway from Baotou to Lanzhou.

 

1 Dustfall Use

 

Arid desert is one of the sources of duststorms, which influence seriously our living environment. The Chinese scientists studied the issue and their research data show that there were plenty of loess silts sprays from the atmosphere (Zhang Deer, 1984). The observation and study on dustfall were carried out since 1980’s in Shapotou district (SSDRIDR, 1991). Annual dustfall, measured with collecting-dust installations at four spots, is different from 2,740 kg/ha to 6,760 kg/ha (Zhang Jixian, 1993). About 30-60% of particles suspended near the surface silt sediment in the revegetated section has been measured with FC1-instrument sampling dust. Average silt sediment of dustfall from October in 1984 to September in 1985 at Shapotou Station was 4,230 kg/hayr. Last study (Xiao Honglang, 1997) indicated that the particle size of dustfall is usually smaller than 0.25 mm in diameter, annual mean deposition rate was 4,358 kg/ha and the most dust storm and silt sediments were took place in May.

 

            During the first 5-10 years, dust and silt sediments were the dominant factor of evolution of soil ecosystem when the sands were stabilized. At the beginning of adaptation of mechanical measures, such as straw checkerboards, the sand surface roughness has been increased and the dust silt on surface was protected for fixing the mobile sands. Now shifting sand is no longer the only soil. The balance of soil was changed by the long-term silt sediment and the soil texture was improved greatly by the clay and fine sand from the dust silts. The average particle size of dust silt become smaller from former 0.2 mm in diameter to 0.08-0.14 mm and this fact brings about changes of ability of soil moisture retention (Table 1). Because available water source was increased about 5 time and the change of redistribution of soil moisture was took place, and no more water could not be infiltrated to the depth of 5 metres below and so that limited rainfall could be consumed by revegetation species in root layers, especially by the plants with shallow roots. Under such influence, the runoff could not infiltrate to deep layer and meanwhile evaporation could be strengthened.

 

Table 1. Parameters of surface soil physics

Soil type

Maximum hygroscopicity

(%)

Wilt

point

(%)

Capillary

adsorbed water

(%)

Porosity

(%)

Bulk

(g/cm3)

Proportion

(g/cm3)

Shifting aeolian sand soil

0.45

0.61

4.01

40.07

1.62

2.70

Fixed aeolian

sand soil

1.62

3.03

19.18

45.10

1.36

2.47

 

2 Development of Microbial Population

 

            Before vegetation grown up, microbe began to take part in soil genesis. Microbes have been formed on bare shifting sand and played a role of feeble accumulation of organic matter in Shapotou area. In the sandy soil, bacteria population covers highest percentage and occupies 67.01% of microbes in 16cm surface sandy soil, and actinomyces is the second highest one. In the same soil depth, bacteria accounts utterly for dominance 98.72% and actinomyces only 1.02% under plantation for fixing sand (Table 2), which revealed both ample algae existing vegetated area and microorganism evolvement from primary to high-level with shifting sands changes into fixing sand plantation. Influenced by surface unstability of drifting sand, microbe population is few in the 1 cm surface layer and centralize the sub-surface. However, in the fixing-sand plantation area microbe population covers 70.25% of total in 1cm surface layer.

 

Table 2. Microbial population under different soil types (106unit/kg soil)

Soil type

Soil depth (cm)

Bacteria

Fungi

Actinomyce

Total

Soil organic matter (g/kg)

Shifting aeolian sandy soil

0-1

6,196.10

10.18

20.10

6,226.38

11.73

1-6

2,537.48

5.43

22.79

2,565.70

4.77

6-16

63.11

1.54

6.70

71.35

1.13

Fixed aeolian

sandy soil

0-1.2

23.40

0.40

50.43

74.23

0.70

1.2-6

95.23

0.60

214.75

310.58

0.72

6-16

261.65

0.50

40.16

302.31

0.66

 

            Blue-green algae are given priority and diatom takes second place in Shapotou area. Variation of diatom, Navicula minima var atomoides, was checked on the surface of shifting sand. In the area of artificial plants dominant blue-green algae mainly includes 14 species of Lyngbya martensiana var calcerea, Oscillatoria pseudogeminata, Phormidium foveolarum and etc. diatom, besides one in shifting-sand, has four species, Pinularia microstaucon, Hantzschia amphioxys var capitata and etc.(Chen Zhuchun, 1991). That soil microbe takes part in mineral weathering and compound of organic matter behaves that there is a good quantity relationship between number of microorganism and content of soil organic matter (Table 3). Change of soil conditions and development of microbe belong to interaction.

 

Table 3. Quantity relationship between soil microbe and organic matter

Model

Correlated coefficient

Freedom degrees

F-statistic

H=0.7065+0.0031M-2×10-7M2

0.829

14

33.85

H=1.0529+0.0028B-10-7B2/10000

0.861

15

46.50

M=332,029-54.129H+47.4689H2

0.919

14

79.41

B=528.648-477.530H+149.079H2

0.932

14

63.60

              H: organic matter (g/kg), M: microbe population (106 unit/kg), B: number of bacteria (106 unit/kg)

 

            It is obvious that soil microbe goes through from nothing to existence and from simple to complex with soil development, and microbe has more multiplicity under the artificial vegetation than natural one. Special function for microbe to decompose organic matter and compose humus makes organic and abiogenesis processes become an integer to ensure energy transformation and material circulation and accumulation in the soil ecosystems.

 

3 Nutrient Dynamic of Soil-plant System

 

            In Shapotou area, the dynamic of soil nutrient can be summarized as the weathering of shifting-sand, the input of atmosphere processes, the losses of soil eluviation and bio-circulation of nutrient in the soil-plant systems. Development of soil-plant systems has ended the process of water infiltration in soil. Soil retention ability and bio-chemical processes are enhanced to speed up greatly the physical- chemical reaction and mineral decomposition. Meanwhile, fixed surface of drifting-sand keeps the nutrient preservable from atmosphere processes, such as dustfall and rainfall. Changes of soil formation conditions will create a new system of material circulation and energy transformation. Foundation of soil microbe population has developed dead aeolian sands (parent material) into living soil.

 

            From shifting-sand to fixing-sand lands, the accumulation of soil organic matter is well developed when plant growth was increased from mono-species to multi-fixing-plants species. The topsoil has been increased 10 times than that of shifting-sand at the leeward slope of dune. Influenced by surface features, the content of organic matter is the highest in the lowlying areas of inter-dunes. Accretion of N and P2O5 as well as K2O is similar to organic matters, but their contents and increase rates are lower than organic matter, especially K2O. Comparing with fixed aeolian sand soil under protection of natural vegetation, it is obvious that nutrient of surface soils in the plantation have exceeded natures in short term of decades, in subhorizon the nutrient of the plantation is not as good as natural one (Table 4).

 

Table 4. Change of soil nutrient in shifting-sand fixation

Fixing-term

(year)

Position

Depth

(cm)

O.M.

(g/kg)

Total (g/kg)

 

Available (mg/kg)

N

P2O5

K2O

 

N

P2O5

K2O

0(aeolian sand)

Mixing

0-5

0.86

0.06

0.29

18.67

 

7.05

7.05

115

14

Leeward slope

0-17

2.48

0.20

0.45

25.20

 

34.11

7.56

250

26

Winward slope

0-5

5.36

0.23

0.58

20.40

 

3.29

11.00

169

39

Winward slope

0-5

9.20

0.26

0.66

25.20

 

29.48

15.01

270

Wild vegetation

Winward slope

0-5

5.57

0.33

0.77

20.10

 

23.50

23.80

228

 

            Plant tissues are main storerooms of community nutrient. The contents of nitrogen and potassium are higher than phosphorus in branches and roots of Artemisia Ordosica, dominant specie of fixing-sand plantation, which indicates that plants must absorb large amount of nitrogen and potassium for normal growth. The contents of nitrogen and phosphorus and potassium are ampler in the new growths than perennial branches and roots. Nitrogen in the new growths is separately 2 times of perennial branches and 1.6 times of roots (Table 5). Because potassium is important element, which can increase water potential of desert vegetation and ability of water retention, potassium content is higher in branches than in roots. Annual grasses grow in season of good water condition and have not mechanism of anti-drought themselves. Though nitrogen and phosphorus are higher in grasses than in Artemisia Ordosica, potassium in Artemisia Ordosica is 1.5-2.5 times of grass.

 

Table 5. Content of nitrogen, phosphorus and potassium in fixing-sand plants

Nutrient

Artemisia Ordosica（g/kg）

Annual grass

（g/kg）

Perennial branches

New growth

Root

N

3.63

7.39

4.03

8.66

P2O5

0.64

1.74

1.07

1.51

K2O

15.00

25.00

10.00

10.00

           

            Soils are main nutrient storerooms of soil-plant systems. The nutrients of sand land have not been able to meet the needs of growth of fixing-sand vegetation with the plants absorbing. Available nutrients in 0-150cm-soil stratum trend to decrease with increase of fixing-sand age, such as available nitrogen and phosphorus in 1956 and 1965 separately occupy only 64.39% and 53.32% of ones in 1976. In various time fixing-s