Riparian forests can provide an important service for aquatic ecosystems by sequestering hillslopederived sediments. However, the width of a riparian buffer zone required to filter sediments is not yet wellunderstood. Here are used two complementary tracers to measure sediment retention. The 137Cs technique and the soil carbon isotopic ratios (delta13C) are utilized to investigate sediment deposition and erosion rates on a slope transect cultivated with sugarcane followed by a secondary riparian forest zone in Iracemápolis, State of São Paulo, Brazil. The 137Cs technique and the delta13C analysis showed that the width of a riparian vegetation in accordance to a Brazilian Environmental Law (N masculine4.771/65) was not sufficient in trapping sediments coming from agricultural lands, but indicated the importance of these forests as a conservation measure at the watershed scale. The complementary delta13C analysis together with soil morphology aspects allowed a better interpretation of the sediment redistribution along the sugarcane and riparian forest transects.