Spatial variability of surface soil moisture content in a re-vegetated desert area in Shapotou, Northern China

doi:10.1016/j.jaridenv.2008.03.010

Journal of Arid Environments

Volume 72, Issue 9, September 2008, Pages 1675-1683

https://doi.org/10.1016/j.jaridenv.2008.03.010 Get rights and content

Abstract

Surface soil moisture content exhibits a high degree of spatial and temporal variability. The purpose of this study was (a) to characterize the spatial and temporal variations in soil moisture contents in the depths of 0–15 and 0–30 cm soil layer in an artificially re-vegetated desert area in Shapotou, China; and (b) to make inferences regarding the environmental factors that influence such variability. Over a period of 7-month experiment, soil moisture contents were measured with Time Domain Reflectometry (TDR) at an interval of every half a month at a grid space with 10 m intervals horizontally covering 4500 m² area, which include a topography from dune crest to dune hollow, and again to dune crest. Results indicated that the distribution of soil moisture at the grid scale was in a pattern of normal distribution with a significant temporal–spatial variability; the variability of soil moisture decreased with decreased mean soil moisture content, and it was higher in the depth of 0–15 cm than that in the depth of 0–30 cm. Relative elevation was a main influence factor of soil moisture variability especially after rainfall events and its influence was more tremendous in the depth of 0–30 cm than that in the depth of 0–15 cm. There was a consistent time-series pattern between the vegetation cover and the soil moisture content and the relative elevation, which increased under the rainstorm events. Soil texture (particle size distribution) had an opposite time-series pattern with relative elevation and vegetation cover, and the correlation was higher in the depth of 0–15 cm than that in the depth of 0–30 cm. We may conclude that local topography and vegetation cover were the main influencing factors of soil moisture variations immediately after the rainstorm events, whereas the soil texture was an important influencing factor as the soil dried up in the study area.

Introduction

Soil moisture stored near the land surface affects a wide variety of earth system interactions over a range of spatial and temporal scales. The moisture content of surface soils exerts a major control on the partitioning of net radiation into latent and sensible heat and rainfall into runoff and infiltration. Through the process of evapotranspiration, soil moisture provides a significant source of moisture for the formation of clouds and precipitation over land. Like the world oceans, soil moisture provides thermal inertia to the climate system (though to lesser degree) storing and later releasing heat, dampening out diurnal and seasonal variations in surface temperatures (Wei, 1995). Soil moisture is the key defining variable that integrates all components of the surface energy balance and as such is of major importance to climate models and their surface schemes (Rodriguez-Iturbe, 2000), though soil moisture has high degree of variability in both space and time, which are controlled by many factors, such as weather, soil texture, vegetation and topography, an understanding of soil moisture balance and its variability (spatial and temporal) is instrumental in quantifying the linkage between regional hydrology, ecology and physiography (geology) (Richard et al., 2004).

Under extremely dry conditions, water is the prime factor influencing environmental change. The soil water limits the number and size of perennial plant species in arid areas (Nash et al., 1991). The soil water dynamics is therefore of great importance for the vegetation system. In Shapotou desert ecosystems, the only source of water is natural precipitation, the groundwater table is located under 80 m depth and is not available for plants. Thus, the precipitation pattern and the soil water dynamics govern the soil water content and with that the natural vegetation and the possibility of reclaiming desertified lands, the interaction (spatial and temporal) between climate, topography, soil and vegetation is manifested through the soil moisture dynamics. To fully utilize the amount of available water for plant growth and understand the desert restoration process, it is of great importance to understand the mechanisms of the spatial variability of soil water in this area.

Therefore, the objectives of the present study were: (1) to find the spatial variability characteristics of the soil moisture in an artificially re-vegetated desert area in Shapotou, which had been stabilized for about 50 years; and (2) to identify the influence factors of soil moisture spatial variability in this area.

Section snippets

Study site description

The study was conducted at Shapotou in Ningxia Hui Autonomous Region at the southeast edge of the Tengger Desert at 37°32′N and 105°02′E with an average elevation of 1288 m, belonging to the steppe desert zone, an area that also can be described as an ecotone between desert and oasis (Li et al., 2002). The natural climatic conditions have been described in detail by Wang et al. (2004). The area has large and dense reticulate dune chains. The main dune crest migrates southeastward at a velocity

Rainfall characteristics

During the experimental periods in 2005, there were 26 rainfall events observed. The total precipitation was 64.7 mm and most fell between May and September. It is a typical extreme arid year according to the classification of McGinnies (McGinnies et al., 1968). The overall distribution of rainfall events and rain intensity during experimental periods is presented in Fig. 2. For 85% of the individual rainfall events, the precipitation were less than 5 mm, and about 92% had rainfall intensity (I₁₀

Conclusions

The soil moisture contents were normal distributed at grid-scale, with a significant variability in the depth of 0–15 cm than that in the depth of 0–30 cm owing to the instant influence of the environment factors such as precipitation and evaporation. The variability of soil moisture had a significant seasonal trend, the lowest mean soil moisture contents occurred in summer for both of the 0–15 and 0–30 cm soil depth. The heavier rainfalls and higher mean soil moisture contents were often

Acknowledgments

The research project on which this paper is based was funded by the Innovation Research Foundation of Chinese Academy of Sciences (KZCX2-YW-431). The authors are indebted to the reviewers for their helpful and constructive comments and suggestions for improving the manuscript.

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Spatial variability of surface soil moisture content in a re-vegetated desert area in Shapotou, Northern China

Abstract

Introduction

Section snippets

Study site description

Rainfall characteristics

Conclusions

Acknowledgments

Journal of Hydrology

Journal of Hydrology

Journal of Hydrology

Journal of Hydrology

Journal of Hydrology

Journal of Hydrology

Journal of Hydrology

Analysis of surface moisture variations within large field sites

Water Resources Research

Soil moisture variability within remote sensing pixels

Journal of Geophysical Research

Volume accuracy relationships in soil moisture sampling

Irrigation and Drainage Division, Proceedings of America Society of Civil Engineer

Surface soil moisture within a watershed: variation, factors influencing, and relationships to surface runoff

Soil Science Society of America Journal

Effects of microrelief on distribution of soil moisture and bulk density

Journal of Geophysical Research

Microbiotic soil crust and its effect on vegetation and habitat on artificially stabilized desert dunes in Tengger desert, North China

Biology and Fertility of Soils