| Soil erosion is one of the great environmental problems in the world, especially on Loess Plateau in China. It is important to reveal the law of soil erosion and develop soil erosion forecast model, which has a bearing on preventing the loess of water and soil. The spatial distribution of soil erosion within slope land on Loess Plateau was discussed by using Be tracer, 137Cs tracer and field survey in this paper. The main results of this work are as follows:1. The depth distribution of 7Be and 137Cs concentration has been studied at the study field and a nearby-undisturbed site.The results show that the majority of 7Be is retained in the top one centimeter of soils, and the concentration of 7Be decreases exponentially with soil depth. For the cultivated study field, the depth distribution of 7Be is very similar to the undisturbed site when it isn't subjected to erosion or deposition. For the undisturbed, there is abroad peak in the 137Cs profile close to the surface and the maximum concentration is found circa 2 cm below the surface. I37Cs Concentration decreases exponentially below the peak, and l37Cs is found circa 30 cm. For the cultivated study field, the 137Cs concentration is relatively uniform within the plough layer.2. The difference and sameness among the existing l37Cs models have been discussed, and their precision have been validated by comparing with the regressive model of soil erosion.Existing calibration models, proposed by Walling, Zhang, Yang and Zhou, have been compared and evaluated. The results show that there are differences among these establishment hypotheses and ways, especially considering the temporal pattern of the 137Cs deposition flux. However, the deviation among them can be neglected when they have been used to estimate rates of soil loss. Compared with Jiang's regressive model, the soil rates by 137Cs tracer is lower about 10% than that by Jiang's regressive mode when they has been used to estimate rates of soil loss on runoff plots.3. It is an attempt to simulate the temporal distribution of the 137Cs in the Northern Hemisphere by Weibull probability distribution model.The temporal pattern of the 137Cs deposition flux must be considered when developing calibration relationship between the loss or gain of and the rate of erosion or deposition. After studied the temporal pattern of the 137Cs deposition flux, it is fist to discover that the temporal distribution of the 137Cs fallout is very similar to Weibull probability distribution.The 137Cs fallout can be simulated by Weibull probability distribution, which can be employed to estimate the rate of soil erosion.4. The spatial distribution of the rainfall soil erosion rates has been investigated on the cultivated slope land.The results indicate that the spatial pattern of soil erosion is related to the slope land shape. It has clear vertical and horizontal distribution features. The soil erosion has become more and more intensive horizontally from the ridge to the center of the shallow gully. The soil erosion intensifies, and then weakens vertically from the divide to the edge of the gully. On the other hand, the contributions of interrill and rill erosion to the total erosion are 35% and 65% respectively, and their spatial distribution characters are different form each other.5. The spatial distribution of the medium-term soil erosion rates has been investigated on the cultivated slope land.The results show that the annual mean erosion rate (ca. 45 years) is 15850 t/km2-yr and its spatial distribution has clear difference. The soil erosion intensifies, and then weakens vertically from the divide to the edge of the gully, apart from the central section of the land because there is a ridge.6. The correlativity between short -term erosion and medium-term erosion has been discussed on cultivated slope land.The key advantage of the 137Cs and 7Be approaches is the provision of spatially distributed information on short-and medium-term rates of both erosion and... |
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