Identification And Evaluation Of Critical Areas Of Nitrogen And Phosphorus Runoff In Complex Land Use Systems

Economy development and population explosion are two major driving forces altering local land use and increasing non-point source pollution. To overcome the threat of the severe pollution and protect the limited water resource, developing an integrated evaluation approach to understand the risk of the nitrogen and phosphorous leached from soils associated with the complex land use systems is required.The objective of this study is to develop an integrated decision support assessment model to assess the critical area of nitrogen and phosphorous leaching in complex land use systems. Based on analysis of factors influencing P and N runoff from fields, assessment model was established:â…  50 fields and 15 water bodies were selected for collecting soil samples and 15 water samples. Soil and water samples were analyzed using routine methods. The relationships between land use types and soil N and P accumulation, and relationships between water quality in targeted water bodies and soil nutrients were statistically analyzed. The soil test results showed there were close connections between land use and soil nitrogen and phosphorus accumulation. But analysis results of water samples failed to tell the clear relationship between the water test nitrogen & phosphorus and the soil nitrogen & phosphorus accumulation The possible reason is that the quality of waters in the complex land use system was affected by both the point-source and non-point source pollutions. However, it could be concluded that the better plantation covering can help reduce the water pollution.â…¡ Several indicators were selected and the weight of different indicators were measured by Analytic Hierarchy Process. To simplify the complex land use, runoff curve number (CN) of Soil Conservation Service (SCS) was employ to show the different surface runoff resulted from the different land use, and the equivalent standard pollution index method was taken to make the various type of pollution sources comparable.â…¢ The assessment model was designed according to the principle of comprehensive index method. To evaluate its reliability, a case study of Huajiachi Campus, Zhejiang University was taken. And at the same time fuzzy set method was used as a reference. The model was modified according to the real situation, to ensure its good performance.The results indicated that the high pollution sources plus high pollutant transportation potential can result in high risk of nitrogen and phosphorous leaching. The residential area ,stock farm and heavy fertilized farm were the high risk area, while area with well vegetation covered has low risk. The assessment model established in the paper can be applied to evaluate runoff potentials of N and P leached from complex land systems.