Spatial variation of microtopography and its effect on temporal evolution of soil erosion during different erosive stages

摘要

Microtopography significantly influences soil erosion at hillslope scale. Currently, the influence of microtopography on temporal evolution of soil erosion is still unclear. A set of simulated rainfall experiments on three 2 m long, 1 m wide soil boxes under a rainfall intensity of 1.5 mm min(-1) on a 20 degrees slope were conducted in the Chinese purple soil region to quantify the spatial variation of microtopography and its effect on temporal variations of runoff and sediment yield during water erosion processes. Three local tillage practices: conventional tillage (CT), artificial digging (AD), and ridge tillage (RT) with different initial microrelief (smooth, rough, and very rough) were designed. The spatial heterogeneity of microtopography was characterized by directional derivatives, semivariogram, and fractal information dimension in terms of morphology and quantity. And we identified the temporal variability characteristics of runoff and sediment yield based on wavelet and resealed range (R/S) analyses. The results indicated that the spatial variability of different tillage practices had strong or medium autocorrelations during different water erosive stages. The spatial autocorrelation scales of CT, AD, and RT were 6.10, 5.32, and 4.01 m, respectively. The fractal information dimensions of tillage practices at various erosive stages were RT > AD > CT. There was a certain range of D-i critical values, which reflected the positive or negative effect on soil erosion. The Hurst indexes of the runoff time series were in the section between 0.632 and 0.718, and that of the sediment yield time series ranged between 0.741 and 0.846. The time series of runoff and sediment yield had long-range persistence and varied periodically every 12-16 min during water erosion processes. Overall, the dominant period and the persistence of runoff tended to decrease and increase respectively with the increase in microrelief, while the temporal variation in sediment yield was opposite to that of runoff. Characterization of the temporal variability characteristics of runoff and sediment yield response to microrelief changes would contribute to a better understanding of the hydro-geomorphological processes at hillslope scale.