Quantification of red soil macropores affected by slope erosion and sediment using computed tomography

Abstract Soil structure is an important factor interacting with soil erosion and sediment processes. However, few studies have focused on the relationship between soil macroporosity and soil erosion across different terrains. The aim of this study was to quantify and compare soil properties and macroporosity characteristics in collapsing gully areas and to explore their impact on the formation and development of collapsing gullies. Soil cores were excavated at different positions of a typical collapsing gully and then scanned to analyze soil macropores. Soil properties and saturated hydraulic conductivity were also investigated. The results showed that the contents of sand, silt, and clay, the mean weight diameter of aggregates, and the infiltrate rates varied at different positions. The valley had the greatest macroporosity (1.09% ± 0.33%), the number (5919 ± 703), volume (1468 ± 194 mm 3 ), and surface area (10.4 ± 2.6 m 2 ) of macropores, as well as the mean volume (16.8 ± 7.4 mm 3 ) of macropores >1 mm 3 , whereas these indices were lowest at the slope (0.15% ± 0.14%, 1189 ± 747, 266 ± 188 mm 3 , 1.7 ± 1.4 m 2 , and 10.6 ± 2.9 mm 3 , respectively). The macroporosity and the number of macropore decreased with increasing depth but were also influenced by the erosion and sediment processes. The processes of sediment and the roots of vegetation also influenced the orientation of the macropores. Macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity and further affected the processes of water erosion and mass erosion.