| Understanding the law of phosphorus loss is an important part of phosphorus prevention in a region and also an important component for non-point source pollution prevention.The construction of the Three Gorges Dam makes worse environmental problems. Studying the soil erosion features and non-point source pollutants in the loss of phosphorus characteristics of the Three Gorges Dam area,it can provide a theoretical basis of agricultural production and environmental protection and provide a reference parameter for the establishment of a regional non-point source pollution as well.The study bases on the small watershed in the Three Gorges reservoir area, we collect samples every 100m through grid, collected 118 soil profile samples of 0-20cm and 15 samples of 20-40cm at all. Analyzing the physical and chemical properties can provide reference of the soil characteristics in Fuling District; using interpolation for analyzing the spatial distribution of phosphorus to determine the high-risk areas of phosphorus loss; On this basis, take blocks of of mesa slope 4°,9°and 17°are experimental plots, statistic the data of rainfall and runoff during April 2009 to November 2009 period, analysis the differences among soil sediment erosion,runoff water and phosphorus loss amount, study the law of phosphorus loss. The main conclusions are as follows:1. Correlation analysis between nutrient content and phosphorus in soilMost part of the soil in Wangjiagou is acidic while alkaline soil only a small part. There is high content of organic matter, generally higher than 10g-Kg-1, and decreases with the soil depth increases. There is also high nitrogen content in the soil, total nitrogen is 1.20g-Kg-1 on average, most of the available nitrogen is higher than 100 mg-Kg-1, both of which show an increase with soil depth decreases; the content of total K is 6.8～22.7 g-kg-1 while available K is 9.69 mg-kg-1～173 mg-kg-1; the content of total phosphorus is rich,0.658 g-kg-1 on average, the content of available phosphorus in topsoil is higher than profile sample, the differences are large respectively, available phosphorus in topsoil is 1.61mg-kg-1～145mg-kg-1, while 1.44mg-kg-1～54mg-kg-1 in profile sample, the coefficients of variation are 99.67% and 110.53% respectively. Then analyze the physical and chemical properties, pH, total K and total phosphorus showed significant positive correlation; Total nitrogen, available nitrogen, total phosphorus show significant positive correlation on available phosphorus, pH, and available phosphorus show significant negative correlation, available K and available phosphorus show a significant positive correlation. It reflects that phosphorus is effected by pH, total K, total nitrogen, available nitrogen, available K and phosphorus also has certain correlation.2. Space diversity analysis of the phosphorus in soilThe second section is about the spatial distribution analysis of the phosphorus content in soil.The related distances of total phosphorus and available phosphorus in soil were 1550m and 102m.Both of them were greater than soil sampling distance (100m).It showed that the sampling distance can reflect the spatial relativity of soil and the maximal sampling distance was 102m.The determination coefficient of total phosphorus was 0.941 greater than the available phosphorus (0.257) in soil. It showed that the semi-variance model had the influence on the fitting degree of total phosphorus greater than available phosphorus in soil.The semi-variance model of the total phosphorus and the available phosphorus in soil were spherical model and Gaussian model respectively;the basement variances were 0.041 and 129.It showed that there were all kinds positive basement effects caused by sampling errors,short distance variations,random variations and natural variations.The nugge of the total phosphorus and the available phosphorus in soil were 50.6%和72.4% among 25%-75%,showed that they had medium spatial relativity, affecting by structural and random factors.The spatial distribution trend of soil total phosphorus was:the content of phosphorus was highest in northwest and northeast,the lowest in the middle and the content between two parts was in eastern and southern by Krieger interpolation.The content of total phosphorus can divide into 3 levels:0-0.58gkg-1; 0.58-0.84gkg-1; 0.84～1.73 gkg-1 and the available phosphorus also can divide into 3 levels:0～14.1mgkg-1; 14.1-32.7mgkg-1; 32.7～145mgkg-1.However,the content of available phosphorus was higher in northest and eastern,the lower in the middle and southern. The content was highest in eastern and southern, in the middle of the watershed and southwest was lowest, which may correlate with the total phosphorus content and soil structural characteristics and be affected by parent material and soil type.For this reason,we can see that the middle and the south of the small watershed is the high risk region where we need to control strictly, plant botanical zones,construct some intercepting drains and reservioirs and so on.3. Different slopes effects on the phosphorus loss in soil under arid hillside fieldWe count that the effect of different slopes on the quanlity of runoff and sediment and the change of phosphorus in runoff and sediment at the third section,by measuring the water sample and sediment sample from experimental Plot under different slopes at Wangjiagou small watershed from Apr.17 to Oct.9.The results show that the quanlity of runoff and sediment increased with the the slopes,and the order was 17°>9°>4°.The concentration and the loss amount of the total phosphorus and the water soluble phosphorus and the particulate phosphorus in surface runoff water also increased with the the slopes, the order was 17°>9°>4°.The loss amount of particulate phosphorus was greater than the soluble phosphorus,showing that the particulate phosphorus was easy to loss.During the same period,the concertration of the total phosphorus and the available phosphorus in the surface runoff sediment decreased with increasing slopes,the order 4°>9°>17°.The change of total phosphorus was more obvious.However,the loss amount of the total phosphorus and the available phosphorus in the surface runoff sediment increased with increasing slopes,the order17°>9°>4°.Under the same rainfall and same surface cover conditions,the loss amount of the total phosphorus and the available phosphorus firstly increased and then decreased,tended to be stabilized finally.4. Estimation of the total phosphorus loss under different slopes in arid hillside fieldThe fourth part is the statistics of phosphorus loss in experimental plots by April 17 to October 9. Combining arid hi(?)side field area of three slops in watershed,it can be calculated the largest volume of total phosphorus loss for mesa slope of 17°in the the region is 103.83kg;the volume of total phosphorus loss for mesa slope of 9°is 66.45kg; the volume of total phosphorus loss for mesa slope of 4°is 10.89kg.During this time, May 13 to July 2 is the peak of phosphorus loss and slope greater than 15°is the high-risk areas for phosphorus loss in need of special prevention and control; and the slope of 6°～15°is the middle-risk areas for phosphorus loss, but also require special processing to control phosphorus emissions. The phosphorus loss between the slpoe of 0～6°can be controled by a simple improvements in farming methods and an appropriate planting of hedgerow.5. The effects of different rainfall on the phosphorus lossThe fifth part is the relationship between different amount of rainfall and runoff and sediment, as well as phosphorus in runoff and sediment, so as to get the impact characteristics of rainfall on phosphorus loss. The results show that with the slope increases rainfall runoff and sediment increases, that is 17°>9°>4°. The greater of the correlation coefficient the greater the relevance of the rainfall and runoff slope is, that is 17°>9°>4°; but the the amount of rainfall and sediment loss is opposite, the smaller the slope, the stronger the correlation. As for the relationship between the concentration of total phosphorus and water soluble phosphorus in runoff, there is only a significant correlation in 4°slope, the two kinds of phosphorus concentration value of a single correlation coefficients were R2=0.2659,0.2789, while 9°and 17°of the plot do not reach correlation; for particulate phosphorus, the relationship between rainfall concentration and runoff of the slope of 4° and 9°achieve significant, the correlation coefficients are R2=0.2986,0.2674. The three kinds of phosphorus concentration in runoff water firstly decreases, then increases and stabilizes at last. It is extremely significant correlation between total phosphorus, water soluble and particulate phosphorus loss and runoff of slop 4°,9°and 17°experiment plot surface water. The correlation coefficients between runoff and total phosphorus, soluble phosphorus and particulate phosphorus are smallest when the slop is 9°, that are R2=0.6465,0.636 and 0.6429. Rainfall during this period is increased first and then decreased, then increased slightly, but it dose not reach its former high. But the total loss of the three kinds of phosphorus in runoff water is always decreases first, then increases and stabilizes at last, the change of phosphorus concentration and phosphorus loss in surface runoff sediment increases as the rainfall increases finally stabilized, but the concentration dose not increase with the rainfall increases at last. The loss amount of total phosphorus and available phosphorus of 4°,9°and 17°slop of the experimental plot sediment reaches significant correlation to rainoff, indicating a close relationship of the total loss between total phosphorus and available phosphorus, we can conclude that the amount of phosphorus loss is determined by rainfall. The correlation coefficients of total phosphorus loss to rainfall of slope 4°,9°and 17°of the experimental plot are R2=0.7591,0.6918 and 0.6981 respectively, ali of which reach significant correlation. It shows a close relationship between rainfall and total phosphorus loss, it can be said that the amount of phosphorus loss is determined by rainfall.6. Retention effects of engineering measures on the phosphorusIn part six, the key drains and reservoirs in Three Gorges Reservoir River in Fuling Wangjiagou are tracked and monitored during September 20,2008 to November 19,2009, figuring out the interception of phosphorus is 1.34kg/hm2 in terracing of sloping land slope to terrace regional engineering measures. Phosphorus loss can be effectively controlled by engineering measures.
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