Spatio-temporal variability of root zone soil moisture in artificially revegetated and natural ecosystems at an arid desert area, NW China

Abstract

Soil moisture is a major component of the hydrologic cycle, being highly variable and nonlinear in space and time. Knowledge of soil moisture regime, especially at the root zone, is critical to the management of water resources and restoration of vegetation. As such, techniques that allow identifying and reducing the number of samples for soil moisture analysis are required. In this study, a spatial variability and temporal stability analysis were used to analyze the volumetric soil moisture content of root zone collected by neutron probe at 36 days during three years in Shapotou, China. The specific concern was to investigate the temporal stability of soil moisture at different depths in the soil profile, determine the effects of soil and vegetation characteristics on temporal stability, and to conduct such a study in an area larger than 1km2. Additionally, we aimed to determine whether temporally stable sites are invariable at different depths, and compare with temporally stable shallow layer (0–6, 0–15, 0–30cm) sites that are previously identified by Wang et al. (2013b) in the same study area. Results showed that the mean soil profile moisture demonstrated a moderate spatial variability which decreased with increasing soil moisture content at 0–60cm depth; however, the variability of soil moisture and CV were both low and no significant correlations were found at 0–300cm depth. A high temporal stability existed at two deeper soil layers compared with the soil surface observed by Wang et al. (2013b). The sampling locations, representative of the dry conditions in the field, were always more temporally stable. Identified representative locations at two depths well-represented the mean soil moisture content in our study area larger than 1km2. Furthermore, strong correlations at two soil layers revealed that spatial patterns of sampling points were preserved for all depths and that time stability of shallow measurements was a good indicator of deep soil layer time stability. Soil texture was the primary influence factor on soil profile moisture temporal stability and the dependence of soil moisture temporal stability on soil texture was consistent among different soil depths. Knowledge of the underlying stable soil moisture distribution could provide a useful basis for precise water management in arid areas.