Effectiveness Assessment of Soil Erosion Critical Source Areas for Soil and Water Conservation

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.

Nutrient Loss from Farmland:Research on and Application of Phosphorus Index Method

Phosphorus index method is an effective method to assess the risk of phosphorus loss,identify the critical source areas and reasonably control the agricultural non-point source pollution.The researches on phosphorus index assessment method have been started earlier in foreign countries.Currently,phosphorus index assessment method has been widely used in the United States and European countries through continuous development and improvement.However,the domestic research on non-point source phosphorus pollution assessment has just started,and the phosphorus index method that is suitable for the characteristics of agriculture in China has not yet been established.This paper summarizes and analyzes systematically the related research advances in phosphorus index method at home and abroad,and illustrates the issues presented in phosphorus index method.In addition,the researches on and application of phosphorus index method in China are discussed.