Event-based hydrology and sedimentation in paired watersheds under commercial eucalyptus and grasslands in the brazilian pampa biome

Abstract Ecological and hydrological impacts are expected when watersheds are under commercial eucalyptus. In this study we evaluated event-based hydrology and sedimentation in paired watersheds under commercial eucalyptus and grasslands cover. Flow, suspended sediment concentration, and sediment production were measured and simulated with the Limburg Soil Erosion Model (LISEM) in paired hydrographic watersheds located in southern Brazil; one occupied with 7-years old Eucalyptus saligna plantation (forest watershed-FW; 0.83 km2) and another Pampa biome (Southern Grasslands) with native and exotic grasses used for beef cattle production (grassland watershed-GW; 1.10 km2). The effect of rainfall on hydrological and sedimentological variables was more evident in GW compared with FW. The shape of the hydrograph was steepest in GW, with rapid, marked increase and decrease in flow during rainfall. The parameters changed for model calibration in FW and GW were soil saturated hydraulic conductivity, initial soil moisture, and Manning roughness coefficient, whereby the statistical performance was classified as good (NSE> 0.75). Fourteen events different from those used in the calibration process were validated for FW and GW, with NSE index classified as “good” and “very good” for hydrology. Our study shows limitations of LISEM in calibrating and validating the sediment yield for individual events due to the spatial variability of factors controlling soil erosion. The validated modeling results of this study may be applied in simulating soil and crop scenarios in watersheds cultivated with commercial forest and grassland for grazing.