Landscape characteristics influence the spatial pattern of soil water storage: Similarity over times and at depths

• Similarity in the spatial patterns was examined over time and at various depths.
• Similarity in the spatial patterns was scale and location dependent.
• Persistent spatial patterns indicated consistent underlying control.
• Macrotopography controlled consistent large-scale spatial patterns.
• Landform elements yielded variable spatial patterns over time and at various depths.

Similarity in the spatial patterns of soil water storage (SWS) over time and at depths at multiple scales and locations reflects the similarity in the underlying hydrological processes. The objective of this study was to examine the similarity in the spatial patterns of SWS and its characteristic landscape positions for variable soil depths and over time at a field scale. Soil water content (further converted to SWS by multiplying with depth) was measured for five years (2007–2011) along a transect of 128 points at a study site that has representative hummocky landscape of the North American Prairie Pothole region. Surface (0–20 cm) and subsurface (20–140 cm at 20 cm interval) soil water contents were measured using time domain reflectometry and a neutron probe, respectively. High rank correlation coefficient between the measurements over time and at any depth layers (surface = 0–20 cm, root zone = 0–60 cm and total active soil profile = 0–120 cm) indicated strong similarity of the spatial patterns of SWS and thus the underlying hydrological processes. The spatial patterns at large scales (> 72 m) were contributed by alternating knolls and depressions (dominant macro-topographical variations in this type of landscape) and were very similar between any measurement times and depth layers. Similarity over time was changed at medium scales (18–72 m) due to the changes in the landform elements. However, changes in the small-scale (< 18 m) spatial patterns were not associated with any landscape characteristics. Similarity was increased at different scales with increase in soil depth owing to strong buffering capacity. Information on the similarity of the spatial patterns at different scales and locations can be used to identify change in sampling domain as controlled by hydrological processes operating at different scales and locations and thus can deliver maximum information with minimum sampling efforts.