Lichao Zhang

Quantitative measuring of gravity erosion contributes to a better understanding of soil-mass failure occurrence and prediction. However, the measurement of gravity erosion requires the continuous monitoring of the objective terrain, due to its occurrence, usually within seconds, and combination with hydraulic erosion. The photogrammetric technique can quickly obtain terrain data and provide a new method for measuring gravity erosion. Based on a continuous high-overlapping image-acquisition equipment, a Structure-from-Motion-Multi-View-Stereo (SfM-MVS)-integrated workflow, and volume calculation, a new working methodology was established for measuring gravity erosion on steep granitic slopes in the laboratory. The results showed a good match between the digital point clouds derived from SfM-MVS-integrated workflow and terrestrial laser scanning (TLS), achieving millimeter-scale accuracy. The mean distance between the point clouds derived from TLS and SfM-MVS was 1.13 mm, with a standard deviation of 0.93 mm. The relative errors among the volumes calculated by SfM-MVS and TLS or the conventional oven-drying method were all within 10%, with a maximum error of 9.3% and a minimum error of 0.2%. A total of 213 gravitational erosion events were measured in the laboratory by using the SfM-MVS method, further confirming its feasibility.

As one of the most serious soil erosion areas in China, red sandstone erosion areas in southern China have been seriously affected by abundant annual rainfall. To understand the effects of AM fungi and different grass strips on soil erosion characteristics in red sandstone erosion areas in southern China, we selected Cynodon dactylon, Lotus corniculatus, Zoysia japonica, and Astragalus sinicus. Two treatments were carried out for each grass: AM was the soil in its original state, and CK was the soil in which the original AM fungi were eliminated. Taking CK treatment as the control group, any changes of runoff and sediment yield and nutrient loss under different grass strip conditions were measured. The total yield of runoff and sediment in the four grass strips under CK treatment was greater than that of AM. The runoff ammonium nitrogen loss concentration in AM treatment was smaller than in CK treatment under continuous scouring. The ammonium nitrogen loss concentration of sediment during continuous scouring showed a decreasing trend. Under AM treatment, the loss concentration of sediment ammonium nitrogen showed a decreasing trend compared with the CK treatment. The percentage of sediment particles >2 mm in the four grass strips was significantly larger for CK treatment than AM treatment (p < 0.05), and except for Cynodon dactylon, the percentage of sediment particles in the size range of 1–2 mm for other grass strips was significantly larger for CK treatment than for AM treatment (p < 0.05); the percentage of sediment particles at 0.02–0.25 mm was significantly smaller for CK treatment than for AM treatment (p < 0.05). The mean weight diameter (MWD) of sediments produced by the four grass strips under simulated scouring showed an overall increasing trend with increased scouring time. The mean weight diameter (MWD) of sediments produced under CK treatment was larger than that of AM treatment. The fractal dimension (D) of sediments showed a decreasing trend with increased scouring time. These results showed that AM fungi can promote the growth of plant roots, strengthen soil anchoring, protect large particle aggregates in soil under rainfall scouring, and reduce soil erosion and nutrient loss in red sandstone erosion areas in southern China. Cynodon dactylon and Zoysia japonica were more prominent than Lotus corniculatus and Astragalus sinicus in inhibiting soil erosion in red sandstone erosion areas.