运用¹³⁷Cs示踪技术,采用相关土壤侵蚀定量估算模型,探讨丹江口市小流域不同土地利用方式和土壤类型的土壤侵蚀状况。结果表明:研究区¹³⁷Cs本底值为2153.46Bq/m²;耕作土剖面中¹³⁷Cs呈均一分布,非耕作土剖面中¹³⁷Cs呈指数递减分布;不同土地利用方式下农用地土壤侵蚀速率从大到小依次为沟谷旱地>坡耕地>菜田>水田>草地;不同土壤类型结合不同地貌形态呈现不同的侵蚀速率,依次为低山丘陵区的石灰土>粘质的黄棕壤土>紫色土和砂质潮土;坡耕地的土壤侵蚀呈现垂直分异特征。

Danjiangkou Reservoir is the catchment area for the South-to-North Water Transfer (middle line) Project in China. Danjiangkou City is the main part of Danjiangkou Reservoir area, water surface area in this city accounts for 45% of the total Danjiangkou Reservoir water area. Cesium-137(¹³⁷Cs) with a half-life of 30.17 years is a man-made product resulting from thermonuclear weapon testing from the 1950s to 1970s.After reaching the soil surface, ¹³⁷Cs fallout can be adsorbed strongly and rapidly by soil organic matter and clay materials, and it is extremely difficult to substitute for this adsorption and most likely move with soil materials which has made ¹³⁷Cs a valuable erosion tracer. Based on ¹³⁷Cs tracer method and some soil erosion estimating models, the distribution of ¹³⁷Cs and the soil erosion rate on the agricultural lands of Danjiangkou City, Hubei Province were studied. Reference site with stable vegetation coverage and receiving little or no runoff since the onset of ¹³⁷Cs fallout was chosen according to the topographic map of the 1950s in this study, and the ¹³⁷Cs reference value was estimated to be 2153.46Bq/m². Most of ¹³⁷Cs in the uncultivated sites is distributed within the top 20 cm from surface, with retention of 80% of the ¹³⁷Cs in the upper 10 cm and sharp drop in ¹³⁷Cs activity below the depth, and exhibits exponential vertical distribution pattern. The vertical distribution of ¹³⁷Cs for the cultivated sites show a uniform distribution pattern due to cultivation practices, and the plough layer is the distribution depth of ¹³⁷Cs. Predicted soil erosion rates for different land uses and soil types varied from 599.07 t/(km² ·a) to 6055.5 t/(km² ·a), the highest erosion rate was observed in dry land on hilly areas, followed in sequence by cultivated slope soils, kale yard soils, paddy soils and grassland soils. The erosion rate for agricutural land is higher than that of uncultivated land. Erosion intensity belonged to moderate water erosion (quite obvious soil loss) and strong water erosion (relatively high soil loss) in cultivated soil, and slight water erosion (no soil loss or inconspicuous loss feature) and light water erosion (relatively obvious soil loss) in uncultivated soil. Different soil erosion rates occurred in different soil types and different parts of cultivated slope, the soil erosion rate for the foot hill location was higher than the crest location, which indicated a combination of effects due to a steep slope and long slope length compared with those of the top location. The result of ¹³⁷Cs tracer analysis correlate well with the result from the remote sensing method and these results have an important significance on soil erosion control and eco-environment improvement in the Danjiangkou Reservoir area.