Field-scale water and bromide transport during and after simulated rain

Natural heterogeneity of soil properties complicates the analysis of water and solute transport under field conditions. To overcome this limitation, a field experiment adopting a scale-dependent treatment distribution was conducted and frequency-domain analysis was used to characterize the spatial distribution of temporal water status change and Br^- concentration determined in soil solution samples at various times. The objective of this study was to evaluate the impact of soil surface roughness and rain characteristics on Br^- leaching and water infiltration during simulated rain and the following redistribution. On a 48- by 3-m transect, rain intensity and the time delay between Br- application and subsequent rain were arranged in a cyclic layout at distinct scales. Nests of tensiometers and suction probes were installed at 1-m intervals along the experimental transect to monitor temporal matric potential changes and Br^- concentrations at different depths, respectively. The results showed that Br- concentrations measured 1 h after simulated rain were generally greater than those measured 1 d later at all depths. The "dominant factors" influencing the horizontal distribution of Br^- measured at these two times differed for each depth except 100 cm. The spatial variation scale of temporal matric potential change varied with time and depth, corresponding with different boundary conditions. Matric potential change in some cases, reflected information other than the boundary conditions investigated, such as hydraulic conductivity, contributing to the scale-variant behavior of Br^- leaching. These findings have important implications not only for agricultural management but also for hydrological modeling at the field scale.