Coarse and fine sediment sources in nested watersheds with eucalyptus forest

Abstract

AbstractKnowledge on sediment behavior in watersheds contributes to properly implement soil and water conservation practices and solve sediment‐related environmental problems. We examined the effects of suspended and bedload sediments and location of potential sediment sources. We used geochemical properties to calculate sediment contributions, with sediment fingerprinting approach, in a watershed (0.98 km2) and in a sub‐watershed (0.39 km2) cropped to commercial eucalyptus along with native forest. The sediment sources evaluated were eucalyptus stand, stream bank along the main channel, and unpaved roads in each watershed. Two size‐fractions of source and sediment samples including fine (<0.063 mm) and coarse (0.063–2 mm) particles were analyzed. Particle size and source location in the watershed are major factors affecting the contribution of sediment sources. The closer the sediment source, the higher the sediment source contribution, especially for coarse particles. Runoff connectivity probably explains large changes in sediment source contributions over very short distances between sampling sites. The stream bank had the greater relative contribution to sediment yield, suggesting that the focal point for erosion control practices should be the channel rather than on the slopes with eucalyptus or riparian vegetation. Future studies should consider uncertainties in grouping sediment sources with a much better signal‐to‐noise ratio.