Dominant Control of Macroporosity on Saturated Soil Hydraulic Conductivity at Multiple Scales and Locations Revealed by Wavelet Analyses

Knowledge on multi-scale and localized control of saturated soil hydraulic conductivity (Ksat) at the watershed scale is lacking. The objective of this study was to evaluate the multi-scale spatial relationships among Ksat and environmental factors (i.e., soil and topographic attributes and land-use systems) using wavelet coherency and multiple wavelet coherence methods. In the Fragata River Watershed (FRW) in southern Brazil, one hundred points were distributed at equal distances along a 15-km transect. In the 0–20 cm layer, clay and sand fractions, organic carbon content, bulk density, macroporosity, Ksat, and soil water retention curve were determined from soil sampled at each point. The digital elevation model was used for obtaining topographic attributes. A land-use map was developed by use of satellite images. All data sets were analyzed using descriptive statistics, and the relationship among Ksat and the other variables was evaluated through the Spearman correlation coefficient. Wavelet coherency and multiple wavelet coherence were used to examine the correlation among Ksat and each of the explanatory variables and to investigate the scale-specific and localized multivariate relationships among Ksat and predictor variables, respectively. According to the bivariate wavelet coherency and multiple wavelet coherence analyses, macroporosity showed the greatest mean wavelet coherence and percent area of significance coherence with Ksat. The variations of soil macroporosity itself were enough to explain the variations in Ksat in a multiple-scale and -location domain. Soil macroporosity could be used as a proxy for assessing runoff potential at different land-use systems with different scales in the FRW in southern Brazil.