Quantitative Model for Estimating Soil Erosion Rates Using 137 Cs *1

A quantitative model was developed to relate the amount of 137 Cs loss from the soil profile to the rate of soil erosion. According to mass balance model, the depth distribution pattern of 137 Cs in the soil profile, the radioactive decay of 137 Cs, sampling year and the difference of 137 Cs fallout amount among years were taken into consideration. By introducing typical depth distribution functions of 137 Cs into the model, detailed equations for the model were got for different soils. The model shows that the rate of soil erosion is mainly controlled by the depth distribution pattern of 137 Cs, the year of sampling, and the percentage reduction in total 137 Cs. The relationship between the rate of soil loss and 137 Cs depletion is neither linear nor logarithmic. The depth distribution pattern of 137 Cs is a major factor for estimating the rate of soil loss. Soil erosion rate is directly related with the fraction of 137 Cs content near the soil surface. The influences of the radioactive decay of 137 Cs, sampling year and 137 Cs input fraction are not large compared with others.

Soil Erosion Spatial Distribution Character of Sloping Field in the Sichuan Hilly Basin:Taking a Cultivated Slope in Neijiang as Example

^137Cs nuclear tracing technique was used to estimate rates of soil redistribution on a sloping field with traditional erosion control measures located near Shangqiao Village, Neijiang City, in the Sichuan Hilly Basin of China. The downslope changes of ^137 Cs inventory and its corresponding soil erosion rates in the sloping field show a rolling trend and have two peak values in two inflexions of the sloping field, these result reflects that the changes of microphysiognomy play a key role on the spatial soil redistribution of the sloping field.

Using ^(137)Cs Tracing Methods to Estimate Soil Redistribution Rates and to Construct a Sediment Budget for a Small Agricultural Catchment in the Three Gorges Reservoir Region,China

Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam. To initiate management intervention to reduce sediment yields, there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region （TGRR）. The purpose of this study is to use 137Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR. Cores were taken from a pond and from paddy fields, for laTCs measurements. The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm-2 yr-1 and the corresponding amount of sediment deposited is 1,553 t. The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km-2 yr-1 and 2,600 t km-2 yr^1 respectively. Based on the estimated erosion and deposition rates, and the area of each unit, the post 197o sediment budget for the catchment has been constructed. A sediment delivery ratio of 0.5 has been estimated for the past 42 years. The data indicate that the sloping cultivated lands are the primary sediment source areas, and that the paddy fields are deposition zones. The typical land use pattern （with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields） plays an important role in reducing sediment yield from agricultural catchments in the TGRR. A 137Cs profile for the sediment deposited in a pond is shownto provide an effective means of estimating the land surface erosion rate in the upstream catchment.

Soil loss and sedimentation rates in a subcatchment of the Yellow river Basin in China

Soil loss by water erosion is one of the main threats to soil health and food production in intensively used agricultural areas.To assess its significance to overall sediment production,we applied the Water and Tillage Erosion Model/Sediment Delivery model(WaTEM/SEDEM)to the Luoyugou catchment,a sub-catchment of the Yellow River Basin within the Chinese Loess Plateau.WaTEM/SEDEM considers rill and interrill erosion and deposition rates to calculate the sediment yield rates leaving the catchment.Ter-races were established in the 1990s to reduce soil loss in this area,but no soil erosion modeling has been published regarding the effect of this mitigation measure.Therefore,we applied 1000 Monte Carlo simulations of the WaTEM/SEDEM,and the modeled average soil loss by rill and interrill erosion for 2020 was 12.2±0.5 t ha^(-1)yr^(-1),with a sediment yield at the outlet of 53,207.8±11,244.1 t yr^(-1).The results indicated that the terracing reduced gross soil loss rates(from 51.8t ha^(-1)yr^(-1)in 1986 to 12.2±0.5 t ha^(-1)yr^(-1)in 2020),while land cover changes,mainly the conversion of forests and grassland,partly coun-teracted the mitigation(combined effect:76%reduction).Modeled sediment loads by rill and interrill erosion accounted for 22.8%of the total long-term sediment production recorded by flow discharge measurements.Other processes not considered by the model,such as landslides,gully erosion,riverbank erosion,and sediment production by construction,seem to predominantly influence the overall sedi-ment yield.Considering years with baseline sediment production only,the measured and modeled sediment yields compared favorably,indicating that the latter processes primarily contribute during extreme events.

The assessment of soil loss by water erosion in China

Soil erosion is a major environmental problem in China.Planning for soil erosion control requires accurate soil erosion rate and spatial distribution information.The aim of this article is to present the methods and results of the national soil erosion survey of China completed in 2011.A multi-stage,unequal probability,systematic area sampling method was employed.A total of 32,948 sample units,which were either 0.2-3 km2 small catchments or 1 km2 grids,were investigated on site.Soil erosion rates were calculated with the Chinese Soil Loss Equation in 10 m by 10 m grids for each sample unit,along with the area of soil loss exceeding the soil loss tolerance and the proportion of area in excess of soil loss tolerance relative to the total land area of the sample units.Maps were created by using a spatial interpolation method at national,river basin,and provincial scales.Results showed that the calculated average soil erosion rate was 5 t ha-1 yr-1 in China,and was 18.2 t ha-1 yr-1 for sloped,cultivated cropland.Intensive soil erosion occurred on cropland,overgrazing grassland,and sparsely forested land.The proportions of soil loss tolerance exceedance areas of sample units were interpolated through the country in 250 m grids.The national average ratio was 13.5%,which represents the area of land in China that requires the implementation of soil conservation practices.These survey results and the maps provide the basic information for national conservation planning and policymaking.

Experimental study on the sampling efficiency of the whirl type separation sand sampler in a wind tunnel

A performance test was conducted in a wind tunnel by changing the principal configuration parameters of a sampler such as the diameter of the container, inlet width and cone height. The results show that the average sand collection rate is from 80% to 90% when any one of the configuration parameter levels is changed. However, the variation of a parameter level results in different ef-fects on the sand collection rate for each soil sample within a certain size range of sand grains. The results show that for various sand grain sized soil sample at each wind speed, the sand collection rate decreases when the diameter of the container changes from 50 mm to 40 mm, the sand collection rate increases by about 2%-3% when the inlet width changes from 10 mm to 8 mm, and the sand collection rate increases by about 3%-4% when cone height is altered from 100 mm to 125 mm. The average sand collection rate is enhanced by 2%-4% for the soil sample of different sized sand grains when the diameter of the container is 50 mm, the inlet width is 8 mm, and cone height is 125 mm.