Samples of eroded sediments and storm runoff water were collected from 5 headwater ditches of forestry,agricultural, residential and mixed sub-catchment in a typical catchment of upper Yangtze River, located in hilly area of purple soil, Sichuan Basin. The Olsen P and degree of phosphorus saturation (DPS) of the eroded sediments and soluble reactive P (SRP) of runoff water were determined so as to evaluate potential of P release from eroded sediments. A significant split-line relationship of runoff water SRP between Olsen P and DPS of sediment was observed, and the changing points at 32mg/kg for Olsen P and 28％ for DPS, respectively, were detected as critical values for evaluation ofrelease risk of sediment P. If higher than the critical values, the risk of P release from the sediments would be greater. The P release risks of the eroded sediments originated from different land uses varied significantly. The sediment from residential area acted as a source ofrunoffwater SRP, whereas, the sediments from forestry land and paddy field served as a sink of water P. The sediments from dry cropland and mixed sub-catchment acted as a potential source of water P. The potential for P release from the sediment was dependent on sediment sources and their physicochemical properties.%采集紫色土丘陵区典型小流域不同土地利用方式(包括林地、水田、旱地、农村居民点等)下的侵蚀泥沙和降雨径流样,测定泥沙的生物有效磷(Olsen P)、磷吸持饱和度(DPS)和降雨径流的溶解性活性磷(SRP).结果表明,泥沙Olsen P和DPS与降雨径流SRP平均浓度呈显著的折线关系.通过折线模型计算出侵蚀泥沙磷释放的风险阈值为Olsen P 32mg/kg和DPS 28%.当泥沙Olsen P和DPS大于其阈值时,磷向水体释放的环境风险大大增加.不同土地利用方式下侵蚀泥沙中磷的释放环境风险差异显著.农村居民点沟渠泥沙的磷释放风险较大,足径流水体的磷源,林地和水田沟渠泥沙是径流水体的磷汇,旱地和综合沟渠泥沙属于潜在的磷释放源.泥沙磷的释放潜力取决于泥沙来源和泥沙理化性质.
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