坝地沉积旋回泥沙养分变化及其对小流域泥沙来源的解释

Variations of sediment nutrient in check dam and its implication for small catchment sediment resources

黄土高原广泛分布的坝地沉积泥沙中赋存了大量小流域侵蚀特征及侵蚀环境变化的信息,泥沙特性的变化则是这些信息的直接体现。该文通过对比分析淤地坝沉积旋回泥沙中和坝控小流域内不同泥沙源地土壤中有机质、全氮、全磷和全钾的含量,发现小流域内土壤养分含量变异性明显大于沉积旋回泥沙中的变异性,沉积旋回泥沙养分含量与沟壁土壤中的相接近,其中与沟壁中的全氮、全磷和全钾无显著差异(p>0.05),但显著小于荒草地和坡耕地中的有机质、全氮和全磷含量(p<0.05),表明淤地坝运行期间小流域泥沙主要来源于沟壁坍塌和沟道扩展,重力侵蚀和沟蚀是主要侵蚀类型;有机质和全氮在坝地沉积旋回中呈明显阶段性变化,分析认为其反映了农村土地联产承包责任制对小流域土地利用和土壤侵蚀的影响。

The sedimentological and nutritional characteristics of eroded soil particles from the Loess Plateau in China were investigated in this paper. The large number of check dams built in the Loess Plateau function, partly as the depositors of eroded soils, carries important information about the environemntal processes relating to soil erosion and deposition. In this study, the organic matter （OM） contents, total nitrogen （N） contents, total phosphorus （P） contents, and total potassium （K） contents in both deposits of the dams and in soil of different parts of the catchments were compared. The results showed that the variability of soil nutrients in the catchments was ,obviously larger than that in the dams; the variabilities of nutrients in the soils and in the gully walls were similar, where there was no significant difference between soil total N, total P, and total K in the gully walls and in sediments deposit profiles （p〉0.05）, but the soil nutrient contents were significantly lower than those on slope farmland and slope grassland （p〈0.05）. Those results implied that collapsing gully walls and expanding gullies were the main sources of sediments in check dams during the sediment trapping periods. The results also indicated that gravitational erosion and gully erosion were the two major erosion types in these small catchments. The variations of OM in the sediments and total N in the deposit profiles of the dams showed two different stages of development. It is concluded that sedimentological and nutritional differences result from the effects of the rural contract responsibility system on the land use and soil erosion.