Sediment Budgets 1 (Proceedings of symposium S1 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 291, 2005. 285 Sediment deposition in riparian ecosystems evaluated by different methods GERD SPAROVEK, OSNY OLIVEIRA SANTOS BACCHI, MIGUEL COOPER, JOSELINE FILIPPE, VLADIA CORRECHEL & CARLOS EDUARDO PINTO JUHASZ University of São Paulo, CP 9, CEP 13.400-970, Piracicaba, SP, Brazil gerd@esalq.usp.br Abstract Riparian forests play an important role in water conservation. These ecosystems filter and trap sediment produced by erosion and prevent this reaching the waterways. In Brazil, laws protect riparian forests. The established legal widths are determined empirically, based on the width of waterways, with no clear scientific basis. This paper combines three methodological approaches ( 137 Cs, WEPP and soil morphology) to study the effect of a riparian forest in trapping sediment mobilized from upslope sugarcane fields. The study area is located in the south of Brazil. The results will help support Brazilian legislation, by providing a better understanding of the functions of riparian forests in relation to water quality. A good correlation was found between the results provided by the three methodologies. All showed that most of the sediment deposition occurs in the first few metres of the riparian forest and decreases towards its interior. Estimates of soil loss provided by 137 Cs and WEPP were similar. The morphology of the sediment and the 137 Cs distribution in the profile suggests that deposition occurred during an extreme storm and probably a single erosion event. Key words caesium-137; erosion model; riparian forests; sedimentation; sediment trapping; soil morphology INTRODUCTION Riparian ecosystems are ecotones located between the aquatic and terrestrial systems and are important for recharging waterways and for improving water quality. The key mechanisms involved are the filtering and trapping of sediment that is mobilized by erosion in the watershed. Biologically, they are considered key areas for the stability of global biodiversity, they serve as protection niches for wildlife, and they act as ecological corridors between forest fragments (Rodrigues & Gandolfi, 1998, 2001). Riparian areas are protected by the Brazilian environmental legislation that prescribes a strip of land bordering the river system that must be preserved. The width of the strip is linked to the size of the river, but a clear scientific basis for ensuring benefits in terms of water quality or the biological status of the watershed is lacking (Lima & Zakia, 2001; Rodrigues & Gandolfi, 2001). Erosion and sediment deposition studies that integrate the agricultural systems (the main sediment sources) with riparian forests (the sediment traps of environmental law) are essential for understanding the functional aspects of complex landscapes containing both elements. This understanding may be useful for refining the related environmental legislation and for increasing the effectiveness of public intervention in