Dynamics of Wavelet-Decomposed Soil Water Content Signals in Relation to Soil Pore Characteristics.

Climate and soil properties determine the dynamics of soil water content (SWC). In particular, responses of SWC to precipitation are driven by the geometry of soil pores. Wavelet analysis can be used to filter a signal into several wavelet components, each characterizing a given frequency. The purpose of this research was to investigate relationships between the geometry of soil pore systems and the responses of SWC to precipitation. The study site comprised five soil profiles along a 300-meter transect with about 8% slope in a tropical semi-deciduous forest located in Galia, state of São Paulo, Brazil. For each profile, three to four Water Content Reflectometer CS615 (Campbell Scientific, Inc.) probes were installed according to horizonation at depths varying between 0.1 m and 2.3 m. Bulk soil, three soil cores, and one undisturbed soil block were sampled from selected horizons for determining particle size distributions, water retention curves, and pore geometry, respectively. Pore shape and size were determined from binary images obtained from resin-impregnated blocks. SWC was recorded at a 20-minute interval and precipitation at a 15-minute interval over a 7-month period. The Mexican hat wavelet was used to decompose SWC measurements into wavelet components. The responses of wavelet components to wetting and drying cycles were correlated with the shape and size of soil pores and other horizon properties. The results will be discussed in the context of the location of the soil horizons within the toposequence.