三峡库区消落带农用坡地磷素径流流失特征

消落带是三峡库区重要的生态交错带，但自发农用和无序开发可能会造成更多的氮磷流失，进而加剧三峡库区水体富营养化。通过对库区连续3 a的定位监测（2011~2013年），研究了三峡库区消落带农用坡地的磷素流失特征。结果表明：次降雨事件中常规施肥处理的地表径流、壤中流总磷平均浓度分别为0.848±0.153、0.140±0.006 mg/L，其中地表径流中磷的形态以颗粒态为主，壤中流以溶解态的生物可利用磷为主。常规施肥下，地表径流、壤中流磷素年均流失通量分别为0.236±0.004、0.100±0.003 kg·hm 2，地表径流、壤中流磷素流失通量分别占总流失通量的70.2%、29.8%，地表径流是坡地磷素流失的主要途径，但壤中流也是不可忽视的重要途径。与常规施肥处理相比，减量施肥处理地表径流、壤中流磷素流失量分别降低了45.3%、40.0%。建议采取减量施肥的方式，以降低营养盐负荷，保护水环境。

Phosphorus Loss from Sloping Cropland in Water Fluctuation Zone of the Three Gorges Reservoir

Water fluctuation zone is an important riparian zone in the Three Gorges Reservoir area. Eutrophication could be exacerbated as the spontaneous and disorder reclamation of water fluctuation zone by local famers likely induce substantial soil phosphorus loss into receiving water bodies in the Three Gorges Reservoir. However, phosphorus loss characteristic via overland flow and interflow from sloping cropland in the water fluctuation zone of the Three Gorges Reservoir is unclear. In this study, plot experiments were conducted to study the characteristics of phosphorus loss via overland flow and interflow from sloping cropland in the water fluctuation zone of the Three Gorges Reservoir from 2011 to 2013. Results showed that the average concentration of total phosphorus in overland flow and interflow per runoff event were 0.848±0.153 mg/L and 0.140±0.006 mg/L in the conventional fertilization treatment, respectively. Particulate phosphorus was the main form in overland flow, while bioavailable phosphorus dominated in interflow. Annual phosphorus loss flux via overland flow for the conventional fertilization treatment was 0.236±0.004 kg/hm2, accounting for 70.2% of total hydrological phosphorus loss flux. By contrast, annual phosphorus loss flux via interflow for the conventional fertilization treatment was only 0.100±0.003 kg/hm2 that only accounted for 29.8% of total hydrological phosphorus loss flux. Our results indicated that overland flow was the main way of phosphorus loss from slope croplands in the water fluctuation zone of the Three Gorges Reservoir. However, phosphorus loss via interflow could not be ignored because its dominant form was bioavailable phosphorus. Moreover, compared with conventional fertilization, the optimized fertilization treatment reduced phosphorus losses of overland flow and interflow by 45.3% and 40.0%, respectively, which could represent an important practice of controlling phosphorus losses from sloping cropland in the water fluctuation zone of the Three Gorges Reservoir via reducing nitrogen fertilizer.