Study On Soil And Water Erosion Of Small Watershed Scale In Three Gorges By Using ¹³⁷Cs Technique

Soil is one of basic factors which life beings in the earth rely on.Soil degradation increasingly restricts human development,and soil erosion is one of the reasons.China is one of the most serious soil erosion Country in the world,and the method that how to control and deal with it have been the focus of the world.Many scholars have studied the theories and mechanism of soil erosion from 1960's.with the development of computer technique,combined GIS with RS to study soil erosion has been the advanced filed in researching soil erosion quantificationally.Using nucleus tracer technique to quantificationally research soil erosion has unsubstituted advantage,such as exactness, speediness,precision,and so on.Now more and more researchers become to pay attention them.Based on the field survey advanced position and the surrounding area of Yang jiagou small watershed of Chen jiagou watershed in Wanzhou district,this study selected 20 typical soil sampling points.The conclusions of analysis are as follows.(1) There are a lot of factors that affect the ¹³⁷Cs content in small watershed,like slope position,slope,and land use status.As for lands that paddy field and slope soil,¹³⁷Cs content is forced to change because of humane activities.And within the spectrum of top of slope and woodland,the distributing rules of ¹³⁷Cs almost suit that of the physiognomy—the bigger the gradient is,the less the content is,and vice versa.(2) The soil erosion modulus is bigger than that is calculated through nuclide tracing method. And as the slope of paddy field equals zero,the grade scale of soil erosion intensity belongs to micro degree erosion theoretically.However,most of the paddy field locate on the bottom of this area, which is very close to the riverway;and the soil there is comparatively lossen.That is to say,when the rain season comes,as the water level raises,most soil would be washed out,thus produces more soil erosion.(3) The organic matter in small watershed is relatively imbalanced,which has less relativity with soil erosion modulus.But different Soil Utilty Status produce different effect to the distributed of organic matter.The rule of organic matter is:slope soil＜woodland＜economic fruit forest＜paddy field.The distribution rule is almost the same to the content of organic matter.(4) It is a very effective and efficient way to use nuclide tracing method work out the soil erosion quantity of the small watershed.Though this way,we can get that the total amount of Yangjiagou is 3402.12t.(5) The content of ¹³⁷Cs has certain pertinence with soil physical clay and soil physical silt.As the manifold of the clay and silt,the content of ¹³⁷Cs in the soil gets more,for the ¹³⁷Cs are mostly found in microaggregate such as clay and silt,and the more the physical sand in the soil becomes, the less the ¹³⁷Cs content gets.So we could prevent the water loss and soil erosion from increase soil aggregate by using this method.