Risk Assessment Of Soil Nitrogen And Phosphorus Losses And Identification Of Critical Source Areas Around Fenhe Reservoir

Fenhe Reservoir is the largest reservoir in Taiyuan city, Shanxi Province, and it is also one of the drinking water sources of Taiyuan city. It is found that the concentration of Nitrogen and Phosphorus of Fenhe Reservoir had grown based on the water quality monitoring data of Fenhe Reservoir for many years. So it is necessary to study the concentration and distribution of soil Nitrogen and Phosphorus and it is also important to assess the risk of soil Nitrogen and Phosphorus losses and identify the critical source areas around Fenhe Reservoir.We collected data of the natural environment and social economy, and set 115 sampling points. Through determined the concentration of Nitrogen and Phosphorus, we combined with the ArcGIS, then made the transfer factors and the source factors which affect the Nitrogen and Phosphorus losses into raster layers.According to the importance and distribution characteristics of factors, then it is found out the Nitrogen and Phosphorus evaluation index system and evaluation level from the domestic and foreign research methods. Put the quantized transfer factors and the source factors into Nitrogen and Phosphorus index assessment, then determined the critical source of Nitrogen and Phosphorus losses areas. Finally, I put forward the management and countermeasures. Conclusions are as follows:(1) Source factors include available Phosphorus, total Nitrogen factor, fertilization factor and population density factor. The distribution characteristics and land use patterns of available Phosphorus factor, total Nitrogen factor are interrelated; the high losses risk area of fertilization factor is small; spatial distribution characteristics of population density factor is obvious.(2) Transfer factors include soil erosion, surface runoff, and distance from soil Nitrogen and Phosphorus pollution source to the water. The risk rank of soil erosion is low, mild erosion accounted for more than half of the study area; research region is small scale, and annual runoff factor in medium risk losses areas; the distance factor risk rank is low.(3)Non-point source loss risk level of Nitrogen and Phosphorus are decided by transfer factors and source factors. Critical source area must have the conditions:a highly value of transfer factors, and highly value of source factors.(4)The evaluation that the Phosphorus index distribution in study area from low to very high levels respectively are:78.04%,2.72%,9.31%,9.93%, so we get that the critical source areas of Phosphorus losses are small. The Nitrogen index distribution from low to very high levels respectively were: 43.76%,12.22%,33.40%,10.59%, so we get that the critical source areas of Nitrogen losses are wider. Spatial distribution of Nitrogen index is similar to that of Phosphorus index.(5)According to the risk rank of non-point source losses of Nitrogen and Phosphorus, then put forward relevant management and countermeasures after recognized the critical source of Nitrogen and Phosphorus losses. The critical source areas of Nitrogen and Phosphorus losses mostly are populated regions. The types of land use are residential community and construction land in the study area. The study area is mainly composed of the scattered rural population. So we must strengthen the treatment of rural life pollution, and protect the ecological security of Fenhe Reservoir. To guarantee the harmonious development of social economy and ecological environment.