Purple soil can represent a predominant soil type extensively found in the Three Gorges Reservoir Area (TGRA). Severe soil erosion has also caused environmental problems in the soil properties and local topography. Particularly, the sustainable socio-economic development of the Yangtze River Economic Belt is closely related to the long-term ecological security and functional integrity of the reservoir. Fortunately, the Enzyme-Induced Carbonate Precipitation (EICP) can be expected to serve as a promising bio-cementation technique. The soil strength and erosion resistance can be significantly enhanced to catalytically generate the cementitious calcium carbonate crystals for the high interparticle bonding. While the EICP-treated soil has exhibited brittle failures. Although the fiber incorporation significantly improves the brittleness of the EICP-treated soil, it is often required for the fiber influence on the erosion resistance of the EICP-reinforced soil. This study aims to investigate the effect of the palm fiber on the anti-detachment capacity of the EICP-reinforced purple soil in the TGRA. The test material was taken from the purple soil from the TGRA. Experimental variables included the fiber content (0 and 0.1%), cementation solution concentration (0.5, 1.0, 1.5, and 2.0 mol/L), and curing duration (1, 7, 15, 30, 60, and 120 d). Untreated purple soil served as the control group (CK). Simulated scouring tests were conducted to clarify the influence mechanism of the palm fiber on the soil detachment capacity of the EICP-reinforced purple soil, particularly from the perspectives of the apparent cohesion and calcium carbonate content. The microscopic mechanism of the treatment was also analyzed after measurement. The results indicated that the soil detachment capacity of the EICP-treated soil was reduced by 58.63%, compared with the CK treatment, which further decreased by 25.81% after fiber incorporation. The apparent cohesion and calcium carbonate content of the EICP-treated group increased by 79.73% and 20.58 times, respectively, compared with the CK group, which were further enhanced by 16.50% and 16.01%, respectively, after fiber incorporation. The fiber incorporation promoted the calcium carbonate crystal formation and apparent cohesion in the EICP-treated soil. The curing duration and cementation solution concentration were attributed to the increasing apparent cohesion and calcium carbonate content in the EICP-treated soil. Under the same cementation solution concentration, the fiber incorporation increased the apparent cohesion for different incubation time. The apparent cohesion also increased for the cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, where the best performance was observed at 1.5 mol/L under the curing duration of 7 d. Similarly, the fiber incorporation increased the calcium carbonate content for the curing durations of 1, 7, 15, 30, 60, and 120 d, respectively. The fiber incorporation increased the calcium carbonate content for the cementation solution concentrations of 0.5, 1.0, 1.5, and 2.0 mol/L, with the best effect at 1.5 mol/L under the curing duration of 7 d. Both apparent cohesion and calcium carbonate content exhibited a highly significant exponential function with the soil detachment capacity of the purple soil (P < 0.01). The fiber incorporation further reduced the soil detachment capacity to increase the apparent cohesion and calcium carbonate content. Microscopic analysis indicated that the fiber provided the reaction site for the EICP, in order to promote the calcium carbonate crystals formation and the stability of the soil, thereby reducing the soil detachment capacity. This fiber incorporation further enhanced the erosion resistance of the EICP-treated purple soil in the region. The finding can also provide a theoretical basis for soil and water conservation in the TGRA.

Sloping farmland is one of the most main sources of soil and water loss in the Three Gorges Reservoir area. A large number of soil nutrients are lost with soil erosion, especially nitrogen and phosphorus in the soil. Water eutrophication and secondary river pollution have posed a serious threat to the ecological environment and sustainable reservoirs. The sloping farmland soil in the Three Gorges Reservoir is also characterized by the outstanding shallow and gravelly. However, it is still lacking the soil erosion and nutrient loss of gravel-containing soil on sloping farmland. Taking the gravel-containing soil on sloping farmland as the research object, this study aims to clarify the effects of gravel content on the soil nitrogen and phosphorus loss of sloping farmland. Artificial simulated rainfall experiments were conducted at three rainfall intensities (60, 90, and 120mm/h) and four gravel contents with different mass proportions (0, 10%, 20%, and 30%). The results indicated that the gravel promoted the runoff and sediment production by altering soil structure, thus increasing the nitrogen and phosphorus loss in soil. But there was also an outstanding effect on sediment yield. The runoff and sediment yield played an important intermediary role in the rainfall-induced soil nitrogen and phosphorus loss in the gravel-containing sloping farmland, although the primary pathway remained lost with the sediment. The gravel content was dominated by the low impact on the transform in the concentrations of nitrogen and phosphorus loss. The loss concentration under different gravel contents showed a trend of linear decline in a short period, and finally fluctuated within a small range. The higher coefficient of variation was found in the sediment yield under different gravel contents. There was also a more significant effect of gravel content on the nitrogen and phosphorus loss of sediment, compared with the runoff. Nitrogen and phosphorus were mainly lost with the sediment in the form of total phosphorus and nitrogen. The active components were accounted for a relatively small portion (less than 15%). Relatively speaking, the loss of the active ingredients with the runoff accounted for a higher proportion of the total. The amount of nitrogen loss in the runoff was about 10 times that of phosphorus. A large amount of nitric nitrogen accounted for about 70% of the available nitrogen loss. The cumulative sediment yield and the loss of nitrogen and phosphorus elements with the erosion reached the maximum at 20% gravel content, whereas, the loss was relatively small at 10% gravel content. Some suggestions were given to reduce the erosion sediment in the control of the nitrogen and phosphorus loss. Much more attention must be paid to water monitoring and fertilization control during heavy rainfall seasons. In addition, the gravel in the soil can be removed to keep the level less than 10%. There was a significant effect of the gravel on soil erosion and the nitrogen and phosphorus loss on the sloping farmland. The finding can provide the scientific reference to control the soil and water loss, as well as the nitrogen and phosphorus loss of gravel-containing soil on sloping farmland in the Three Gorges Reservoir.