Spatial heterogeneity of loess contour tilled microtopographic slope in rainfall erosion

Abstract

Loess tilled surface is the geographical unit for the quantitative study of the soil erosion process. Contour tillage has been proved to be the most effictive measure for soil and water conservation in the Chinese Loess Plateau. Studies on the spatial heterogeneity of loess tilled surfaces will contribute to the understanding of the mechanism of erosion evolution. For this, a laboratory experiment was performed on contour tilled sloping surfaces where the hydrological-erosive processes were simulated. At different erosion stages, point cloud measurements were made using a terrestrial laser scanning system (TLS); then the heterogeneity depending on detrending and directionality were analysed by both the semivariogram method and the rescaled range analysis method. Results showed that: (1) the fractal dimensions D S and D R were equivalent when determined from either the semivariogram method or the rescaled range analysis method, although the semivariogram method appears to be more reliable in identifying the specific stage of the erosion evolution process; (2) the contour tilled microtopographies had an anisotropy behavior depending on direction; (3) the fractal dimension (either D S or D R ) in different erosion stages was less than 1.5, which indicates that the microtopography of the sloping surface exhibits characteristics of persistent fractional Brownian motion and positive spatial autocorrelation. Irrespective of tillage measure and slope percentage, the sloping surface can be regarded as having random roughness. The results reveals a quantitative relationship between microtopography and sloping erosion. Also, it may provide guidance for further studies regarding the spatial variability and heterogeneity of various tilled slopes on the microtopographic scale. ARTICLE HISTORY

Effect of Slope Gradient on Erosion Evolution Process at Microtopographic Tillage Soil Surfaces

“…A 3-D terrestrial laser scanning system (Leica, the vertical error less than 1 mm) was mounted to scan the surfaces before and after a rainfall event, and cloud data of point elevations for different erosion stages were obtained. The information from each scan was converted into a set of (x, y, z) coordinates which were imported into ESRI ArcGIS software (see: https://www.esri.com) to create the corresponding high resolution (6 mm × 6 mm) digital elevation models (DEMs) [14]. Subsequently, the 3-D representation of the soil surface microrelief was acquired, and then the 2-D projected area, 3-D surface area and 3-D surface volume for different erosion stages were calculated accordingly.…”

“…Some consensus has been arrived at that the slope is an important factor influencing runoff, has a correlation with erosion rate and runoff rate [2] [3] [4] [5], influences the duration of time for each stage of erosion [6], and governs soil erosion [7] [8] [9]; and runoff and erosion tend to increase when a rainfall event occurs on a steeper surface at a critical slope ranging between 5˚ and 25˚ [10] [11] [12] [13]. Besides, there is a general consensus that contour tillage (CT), as an agricultural farming practice widely used in the Chinese Loess Plateau, has favorable soil and water conserving effect [14] [15]. However, the optimal critical slope for appropriate tillage remains unidentified.…”

“…The soil erosion patterns show irregularities when they are observed on different scales. For example, DEMs are nowadays used to produce basic data for the soil erosion study, and fractal and anisotropic properties could be more prominent and distinct with a higher grid resolution used [14]. Therefore, the findings and conclusions made based on a macro scale don't apply to solve issues relevant here on a micro scale.…”

Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall

“…However, composite sediment samples are inadequate for capturing spatially distributed erosion and deposition information (Rengers and Tucker, 2015;Nouwakpo et al, 2016). Moreover, high spatial and temporal resolution measurements are essential for developing and calibrating physically based erosion and transport models (Huihui et al, 2016). In semiarid watersheds, vegetation is often patchy (Nearing et al, 2005), runoffgenerating precipitation events are characterized as of short duration (Goodrich et al, 2008) and soils are relatively heterogeneous (Osterkamp, 2008).…”

“…The discontinuous nature of runoff highlights the necessity of acquiring highly detailed measurements in order to quantify spatially distributed changes on eroded surfaces. Moreover, high spatial and temporal resolution measurements are essential for developing and calibrating physically based erosion and transport models (Huihui et al, 2016).…”