降雨能量对东北典型黑土区土壤溅蚀的影响

Effects of raindrop kinetic energy on splash erosion in the typical black soil region of Northeast China

溅蚀特征研究可揭示溅蚀发生机理,而现有研究大多用溅蚀量来表征溅蚀特征,不能全面准确地反应溅蚀作用过程。为此,基于改进的试验土槽进行室内模拟降雨试验,研究降雨能量对坡面不同方向溅蚀量及溅蚀过程的影响。试验设计包括2种降雨强度(50 mm/h和100 mm/h)和10个降雨能量,其中10个降雨能量是通过2种降雨强度(50 mm/h和100 mm/h)和5个雨滴降落高度(3.5,5.5,7.5,9.5、11.5 m)来实现的。结果表明:在相同降雨强度下,坡面总溅蚀分量均随降雨能量的增加而增大。次降雨坡面溅蚀量均为向下坡最大,其次为侧坡溅蚀量,而向上坡溅蚀量最小。当降雨强度由50mm/h增加至100mm/h时,坡面向上坡溅蚀量增加2.3—5.0倍,向下坡溅蚀量增加1.7—5.1倍,侧坡溅蚀量增加1.9—4.3倍,总溅蚀量增加1.9—4.5倍,净溅蚀量增加1.2—6.4倍。对于不同降雨能量处理,坡面溅蚀率均表现为坡面产流前随降雨历时的增加而递增,产流后迅速达到峰值,之后逐渐减小并趋于稳定。定量分析了各溅蚀分量、总溅蚀量、净溅蚀量与降雨能量的关系,提出了溅蚀发生的降雨能量阈值,发现雨滴溅蚀发生的临界能量为3—6 J m^(-2)mm^(-1),且向上坡溅蚀量,向下坡溅蚀量,净溅蚀量和总溅蚀量皆与降雨能量呈幂函数关系,而侧坡溅蚀量与降雨能量呈二次多项式关系。

Splash erosion is an important form of soil erosion caused by the impact of raindrops. Raindrop kinetic energy is the principal factor that affects splash erosion, and studies on splash characteristics can reveal splash erosion mechanics. However, current studies only characterize the amount of splash erosion, which cannot accurately and comprehensively reflect the splash processes. Therefore, this study examines the effects of raindrop kinetic energy on splash erosion processes and on the amount of splash erosion from different directions on a hillslope. The experimental treatments included two rainfall intensities （50 and 100 mm/h） and 10 rainfall kinetic energies that were obtained with a combination of the two rainfall intensities and five raindrop falling heights （3.5 m, 5.5 m, 7.5 m, 9.5 m, 11.5 m） ; the slope gradient was set at 10°. In the experiment, all treatments were replicated twice. The soil used in this study was a Mollisol （USDA system ofSoil Taxonomy）, containing 3.3% sand, 76.4% silt, and 20.3% clay. The tested soil was collected from 0-20 cm depth in the Ap horizon of a maize field in Liujia Town （44°43＇N, 126°11＇E）, Yushu City, Jilin Province, located in the center of the Mollisol region in Northeast China. This study was completed in the rainfall simulation laboratory of the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Yangling City, China. A side-sprinkle rainfall simulator was used to apply rainfall and a soil pan was specially designed to measure both splash and sheet erosion. Results showed that directional splash erosion increased with the increase of raindrop kinetic energy for a given rainfall intensity. However, at each individual rainfall, the amount of splash erosion was in the order of downslope 〉 lateral slope 〉 upslope. When rainfall intensity increased from 50 to 100 mm/h, the total splash and net splash erosion increased 1.9-4.5 and 1.2-6.4 times, respectively; splash erosion on the upslope, downslope, and lateral slope were enhanced 2.3-5.0, 1.7- 5.1, and 1.9-4.3 times, respectively. For all rainfall kinetic energies, splash erosion rate gradually increased with rainfall duration; when runoff occurred, splash erosion rate reached the maximum value, and then gradually decreased until reaching a steady state. According to the relationships between directional, total, and net splash erosion and rainfall kinetic energy, the critical energy for splash erosion initiation was 3-6 Jm-2 mm-1. Splash erosion increased with an increase in raindrop kinetic energy above the critical value. Furthermore, the relationship between raindrop kinetic energy and upslope, downslope, total, and net splash erosion was expressed by power function, while raindrop kinetic energy had a quadratic polynomial relationship with lateral splash erosion.