摘要
Critical source areas （CSAs）, characterized by severe soil erosion and high sediment yield, are considered to have a high priority for conservation. How to identify CSAs and assess the effectiveness of conservation practices is a key issue in site-specific watershed management. The Soil and Water Assessment Tool （SWAT） model is a useful tool for site-specific conservation practices design and several studies have attempted to identify CSAs based on watershed models. However, limited research has reported about the effectiveness of conservation practices targeting CSAs. The aim of this study was to assess the effectiveness of conservation pracrices targeted on CSAs using the SWAT model. CSA was firstly identified based on the 4-year average yearly erosion of each HRU. Appropriate soil conservation practices were then designed for the CSAs. A scenario with conservation practices for the whole watershed was also established as the contrasting counter parts scheme and then compared to the outcome of CSA-targeted conservation practices. The result shows that SWAT can accurately simulate sediment yield in the study area. CSAs were mainly located in slope farmland areas and steep gullies, coinciding with the distribution of land use and slope. The identified CSA covered 20% of the HRUs and contributed on average 44% of sediment yield. Conservation practices targeting CSAs had higher sediment reduction effectiveness （24 115 t km-2 y-1） than conservation practice covering the whole watershed （20 290 t km-2 y-1）. Thus conservation practices targeting CSAs are more effective than broad conservation practices. We conclude that soil conservation practices focusing on CSAs do increase sediment reduction effectiveness. Targeting the placement of soil conservation practices based on the CSAs concept will assist water quality control in watersheds.
土壤关键源区是指流域内对侵蚀产沙量起决定性作用的区域,控制了关键区域的土壤侵蚀就能有效降低流域的侵蚀量,因此,在关键源区识别的基础上评价基于关键源区的水土流失治理的有效性是流域管理的关键问题。SWAT模型是流域关键源区识别的重要工具,但现有的基于SWAT模型的关键源区识别研究,鲜有对于关键源区水土流失治理效益的评价。本文以黄土高原丘陵沟壑区典型小流域羊道沟流域为例,基于SWAT模型模拟流域内的土壤侵蚀过程,根据HRUs土壤侵蚀模数的排序,将产沙量排在前20%的HRU提取为关键源区。在所提取的关键源区上设置合理的水土保持措施,再基于模型模拟评价水保措施的减沙效果。研究结果表明,SWAT模型能较好地模拟流域的产流产沙过程,所提取的关键源区集中分布在坡度较陡的沟坡和坡耕地。覆盖流域内20%面积的关键源区,其产沙贡献量达到44%。覆盖关键源区的水土保持措施的单位面积减沙量(24115tkm-2y-1)要显著高于全流域治理的单位面积减沙量(20290tkm-2y-1),说明基于关键源区布设水土保持措施,能有效提高流域土壤侵蚀控制效率。因此,在关键源区识别的基础上合理布设水土保持措施,是一种有效的流域治理方法。
基金
the Knowledge Innovation Program,Chinese Academy of Sciences (KZCX2-YW-442)
National Basic Research Program of China (2007CB407207)
National Natural Science Foundation (40971236)
