Impacts of topography on the morphological indices of ephemeral gullies in the Chinese mollisol region

Abstract

Ephemeral Gully (EG) erosion is a main erosion type on sloping croplands in the Chinese Mollisol region, causing severe land degradation and crop yield reduction, but how topographic factors, such as slope gradient, slope aspect, and upslope and lateral drainage areas, affect the morphological indices of EGs is still unclear. Thus, this study applied a high-resolution 5-cm Digital Elevation Model (DEM) obtained from Unmanned Aerial Vehicles (UAV) aerial surveys to quantify the impacts of topography on the morphological indices of EGs in a typical Mollisol region located in Keshan County, Heilongjiang Province. The results showed that the length of EGs decreased with an increase in slope gradient or increased with an increase in upslope and lateral drainage areas. The distribution density, dissected degree, and vertical gradient of EGs increased with an increase in slope gradient or a decrease in the upslope and lateral drainage areas. Moreover, 10 ha and 5 ha areas were critical values regarding the impacts of the upslope drainage area and lateral drainage area on the width, depth, and volume of EGs, respectively, and 0.11 m m⁻¹ and 0.03 m m⁻¹ were critical values regarding the impacts of slope gradients of the upslope drainage area and lateral drainage area on the width, depth, and volume of EGs, respectively. In addition, the number of EGs on sunny and semi-sunny slopes was 1.8 times higher than that on shady and semi-shady slopes. In particular, the topographic thresholds of EG occurrence, synthesizing upslope and lateral gradients, and upslope and lateral drainage areas, were determined, overcoming the current research deficiency of considering only the upslope drainage area and ignoring the lateral drainage area. The results provide an important basis for understanding EG erosion development and implementing precise soil conservation measures.