The deep soil water dynamics and its environmental controls after long-term revegetation

The increase in the extreme drought trend, reduction in soil erosion, and acceleration of deep soil desiccation are renewing interests in soil water dynamics and its environmental controls after long-term (>30 years) grass and shrub revegetation on the Chinese Loess Plateau (CLP). However, inconsistent findings have been reported on soil water dynamics in these typical land uses due to the multi-dependent environmental controls. The objectives of this study are to identify the spatial variability of soil water dynamics and its controls in a small watershed. For this purpose, spatiotemporal soil water storage in 1 m interval to a depth of 5 m was decomposed into a temporal mean (i.e., time-stable pattern) and temporal anomaly (A(tn)), which varies over time and is related to soil water dynamics. A(tn) was then decomposed into a space-invariant temporal anomaly (i.e., spatial mean of A(tn)) and a space-variant temporal anomaly (R-tn), which reflects the spatial variability of soil water dynamics. The R-tn was further decomposed using the empirical orthogonal function (EOF) to identify its major controls. Results showed that soil water dynamics (gain and loss) decreased from grassland to abandoned cropland followed by shrubland after long-term revegetation. The hot spots in deep soil water dynamics (2-5 m) were identified in layered soils with an overlying sand layer and underlying silt layer, and grassland with the coexistence of tree-shrub-grass and high deep soil organic carbon (SOC) content. 50-70% of the total variations of R-tn were explained by the first two spatial patterns (EOFs). Silt and SOC content controlled EOF1 of R-tn at 0-2 and 2-5 m, respectively. Plant canopy and soil profile properties (e.g., layered soils with an overlying sand layer and underlying silt layer) controlled EOF2 of Rtn at 0-1 and 2-5 m, respectively. The EOF analysis suggests that silt and SOC dominated soil water storage capacity, plant canopy regulated water flux, and variations of hydraulic properties in soil profiles may jointly drive spatial variability of soil water dynamics.