Spatial heterogeneity of surface roughness during different erosive stages of tilled loess slopes under a rainfall intensity of 1.5 mm min−1

Abstract

The loess tilled slopes of the Chinese Loess Plateau are an area of serious soil erosion problems. Knowing the spatial heterogeneity of surface roughness (SR) will contribute to the understanding of the developmental process of slope erosion and reveal the coupled relationship between SR and slope erosion in this area. The objective of this study was to examine the spatial heterogeneity of SR of four typical tilled loess slopes during successive stages of soil erosion under a simulated rainfall: before rain (BR), splash erosion (SpE), sheet erosion (ShE) and rill erosion (RE). Soil surface elevation was measured and analyzed with both the semivariogram function and fractal dimension models. All four tilled slopes: artificial backhoe (AB), artificial digging (AD), contour tillage (CT) and linear slope (CK) had strong spatial autocorrelations and relatively stable spatial structure during the evolution of the erosion process. Rainfall in the SpE and ShE had a certain relief effect on SR. The fractal dimension of the SR at various erosion stages ranged from 1.54 to 1.86. All tillage methods showed a reduction in their SR variances at scales larger than 40cm, with CK showing the smallest reduction, followed by AB, AD, and then CT. Contrarily, these tillage methods displayed a similar trend of increasing SR variances at scales less than 40cm; increasingly weaker soil and water conservation effects were noted for these slopes. Since the SR of the 15° slope had a stronger spatial heterogeneity, it is expected to have a more potent inhibition of soil erosion at this slope than at other slope gradients. The overall autocorrelation scale of SR was 2.84m, although it differed under various tillage measures and slope gradients. The results of multifractal analysis reflected the spatial heterogeneity of SR at diverse scales or at different erosion processes better than a single fractal dimension. In this paper, we not only reveal the coupling relationship between SR of micro-topography and erosion, but also lay a theoretical foundation to guide future tillage practices on sloping areas of the Loess Plateau.