Field-Scale Bromide Leaching As Affected By Land Use and Rainfall Characteristics.

Natural heterogeneity in soil properties limits the understanding on water and solute transport at the field scale. A new experimental design with scale-dependent treatment distribution was adopted to assess the impact of land use and rainfall characteristics on Br^- leaching under field conditions in this study. On a transect with two land use systems, i.e., cropland and grassland, rainfall intensity and the time delay between solute application and subsequent rainfall were arranged in a repetitive pattern at different scales. Soil samples in 10 cm increments down to 1 m depth were collected along the transect for Br^- analysis after rainfall simulation. Owing to the more continuous macropores supporting the development of preferential flow, soil Br^- was more evenly distributed with soil depth and reached greater depth in grassland. And increasing rainfall intensity tended to enforce the deep leaching of Br^-. Frequency-domain analysis revealed that the dominant factor that controlled Br^- leaching varied with depth. At 0-10 cm, rainfall intensity was most strongly correlated with Br^- concentration; while in the soil layer right below, application time delay was the main driving force for the spatial distribution of Br^-. With the increase of soil depth, the spatial behavior of Br^- was mainly caused by soil properties such as soil texture and topography, rather than rainfall characteristics. Nevertheless, rainfall intensity was found to be positively correlated with Br^- concentration in deep soil, indicating a great risk of deep leaching and groundwater contamination under heavy rainfall. Results of the present study suggest that this novel experimental design is useful in studying hydrological processes at large scales.