| In this paper, Yangou watershed in the Loess Plateau was selected as a case study site. By using radionuclide tracer technique as a new method, the characters of erosion intensity evolvement in Yangou watershed were studied. It's analyzed that the characters of soil erosion intensity changed with time in the past several decades resulted from the influences of soil utilization type changes. The effects of soil conservation in different vegetation restoration manners were evaluated, and the evolvement trends of the erosion environment and erosion intensity in Yangou watershed were explored according to the analysis of erosion environment factors. Meanwhile, the feasibility and reliability of utilizing radionuclide tracer method to study the erosion intensity evolvement in a watershed scale were explored.1. The characters of 137Cs distribution in the soil and sediment were elucidated.The characters of l37Cs distributions in soil profiles in different land using patterns were studied to provide a foundation for using 137Cs tracer to estimate soil erosion. The relationship between the concentration of 137Cs and the grain size of soil was analyzed. 137Cs concentrations in clay layer and sand layer in a dam land were also compared. The results show the higher concentration of 137Cs the smaller the soil grain. The mechanical composition of the sediment at the outlet of the watershed has significant difference compared with that of soil in woodland and cropping slope fields, which indicates that there is soil particle selectivity occurred in the course of eroded soil transmitting. This means that the results need to be revised if 137Cs in sediment of the outlet is used to estimate erosion modulus of the watershed. Variation coefficients of 137Cs background value and the amounts of precipitation among different sampling sites of the watershed are 0.11 and 0.20 respectively. . It is obvious that the variability of precipitation would have important effect on the distribution of 137Cs.2. Develop a method to calculate average area concentrations of radionuclides and soil erosion intensity of a whole hillslope by using the average gradient of the hillslope and average area concentration of radionuclide on hillslope with the weighting method of slope length.These methods are proved to be feasible by other relative studies. They may offer new thoughts for studying erosion environment on a watershed-scale by using the radionuclides tracer technique.3. The characters of 137Cs distributions on hillslopes in Yangou watershed wereanalyzed.The result shows that 137Cs area concentrations on hillslopes are correlated with slope gradients more closely than that with slope lengths. It is evident that there exits great differences among l37Cs areal concentrations on hillslopes of different cultivation ages. There is a linear relationship among 137Cs areal concentrations, cultivation ages and slope gradients. The regressive equation is as follows: Cs=2356.79-22.77t-35.53S. Variation coefficient of 137Cs area concentration is 80.11% among hillslopes with different abandonment ages. The history of land utilization is considered to be the main cause that affects l37Cs area concentrations on hillslopes.4. It was studied about the relationships among soil erosion and terrain factors such as slope gradient, slope length and slope direction.The results show that erosion intensity is related closely to the shapes of hillslope. There exits a power function relationship or exponent function relationship between erosion modulus and gradients at sampling sites on hillslopes. Erosion modulus changes wavily along hillslope. The relativity between erosion modulus and average slope gradients on hillslopes is higher than that between erosion modulus and slope lengths, which indicates that hillslope with higher gradient suffers more serious soil erosion. The relationship among erosion modulus, slope gradient, and slope length can be expressed as: M = 104.18S1' 241Z.007924. Slope direction also plays a significant role...
|
PDF Full Text Request