Identifying the Effects of Local and Nonlocal Controls of Soil Water Storage.

There are various factors governing the spatial and temporal variability of soil water storage including soil properties, topography, and vegetation. Some factors act locally, while others act non-locally, which means that a factor measured at one location has an effect on soil water storage at another location. The objective of this study was to examine the effects of local and nonlocal controls of soil water storage in a hummocky landscape. Soil water storage, soil properties, and terrain indices were measured along a 128-point transect of 576 m long from the semi-arid, hummocky, prairie pothole region of North America. There are large coefficients of determination (r²) between soil water storage and sand content (r² = 0.32 to 0.53), organic carbon content (r² = 0.22 to 0.56), depth to carbonate layer (r² = 0.13 to 0.63), wetness index (r² = 0.25 to 0.45), and other variables at the measurement scale at different times, indicating strong local effects from these variables. The correlation coefficients were also calculated by physically shifting the spatial series of soil water storage with respect to that of controlling factors. The shifting distance indicated the difference in the origin of a factor and its response in controlling soil water storage. For example, the correlation between soil water storage and relative elevation was very weak (r² = 0.02 to 0.08) at the measurement scale. However, the value of r² increased more than eight fold (r² = 0.47 to 0.61) after shifting the spatial series of soil water storage by 54 m, which was almost equal the average length of the existing slopes. This indicated the nonlocal effect from the relative elevation. Identification of nonlocal effects from factors improves the prediction of soil water storage.