Depth Persistence of the Spatial Pattern of Soil Water Storage in a Hummocky Landscape

Information on surface soil water is readily available either from satellite images or from other surface measurements. Understanding the relationships between soil water at the surface and subsurface layers can help understand hydrological processes at depth. The objective of this study was to examine the similarities in the overall and scale specific spatial patterns of soil water storage at different depths. Soil water content was measured at the 20-cm depth increments, from the surface to a depth of 140 cm, using a neutron probe and time-domain reflectrometry along a transect traversed over several knolls and depressions at St. Denis National Wildlife Area (SDNWA), Saskatchewan, Canada. High soil water storage was observed in depressions and low water storage on knolls creating an inverse spatial pattern relative to elevation. High Spearman rank correlation coefficients between the surface and subsurface soil layers indicated strong similarity in the overall spatial pattern of soil water at different depths. Soil water contents in layers close in vertical distance had stronger similarity than that of layers far apart. Wavelet coherency analysis indicated strong similarity in the large-scale (>72 m) spatial patterns of soil water at the surface layer and deeper layers during recharge period. However, large-scale similarity was weaker during discharge period than during recharge period. The small-and medium-scale similarity changed with depths during both recharge and discharge periods. The scale specific similarity in the spatial pattern of soil water can be used to guide estimating subsurface soil water at different depths from the surface soil water.