Impact of soil surface properties on soil swelling of different soil layers in collapsing wall of Benggang.

Benggang is one of the most serious soil erosion problems in tropical and subtropical areas in southern China. Little work has been reported on the surface properties of soil colloidal particle and its influence on soil swelling of different soil layers in collapsing wall of Benggang. In this present work, the effects of sodium concentration on soil swelling, and the correlations between soil swelling rates and soil colloidal surface properties were comprehensively evaluated by carefully examining soil physicochemical properties and soil colloidal surface properties of red, sandy and detritus soil layers from a collapsing wall. Our results showed that the soil swelling rates of red, sandy and detritus soil layers all exponentially decreased with increasing initial water contents. The relationship between soil swelling rate and the thickness of shear plane showed an extremely significant negative correlation for red soil layer and no correlation for sandy and detritus soil layers. Moreover, the elevating sodium concentrations reduced the thickness of shear plane from 39.69 to 0.76 nm for red soil layer, followed from 22.56 to 0.79 nm for sandy soil layer and from 18.61 to 0.64 nm for detritus soil layer. These findings indicated that the soil particle interactions played a crucial role in the development and occurrence of Benggang. This work will be helpful in understanding the mechanisms of soil mass loss on the gully head and collapsing wall of Benggang.

Verification of the detachment-transport coupling relationship of rill erosion using colluvium material in steep nonerodible slopes.

The detachment-transport coupling equation by Foster and Meyer is a classical equation that describes the relationship between detachment and transport. The equation quantifies the relationship between sediment loads and soil detachment rates, deepens the understanding of soil erosion and provides a reliable basis for the establishment of an erosion model. However, the applicability of this equation to slopes with gradients greater than 47% is limited. In this work, the detachment-transport coupling relationship is investigated using the colluvium material of Benggang. A nonerodible rill flume 4 m long and 0.12 m wide was adopted. The slope gradient ranged from 27% to 70%, the unit flow discharge ranged from 0.56 × 10-3 to 3.33 × 10-3 m2 s-1, and the sediment transport capacity (Tc ) was measured under each slope and discharge combination. The sediment was inputted into the flume according to the predetermined sediment addition rate (from 0% to 100% of Tc ), and the detachment rate (Dr ) under each combination of the slope and discharge was measured. Dr linearly decreased with increasing sediment loads, which is consistent with the detachment-transport coupling equation by Foster and Meyer. The linear equations can predict the detachment capacity (Dc ) and Tc well (Nash-Sutcliffe efficiency coefficient (NSE) = 0.98 for Dc , and NSE = 0.99 for Tc ). The detachment-transport coupling equation can adequately predict the Dr (NSE = 0.89). However, its applicability to slopes of <47% (NSE: 0.92-0.96) was greater than that to slopes of ≥47% (NSE: 0.81-0.89), and the predicted Dr under Tc levels of 20% and 40% were higher than the measured values, while the predicted value under a Tc level of 80% was lower than the measured value. In summary, the detachment-transport coupling equation by Foster and Meyer can accurately reflect the negative feedback relationship between detachments and transports along steep-slope fixed beds and is suitable for colluvial deposit research. The results provide a basis for the construction of steep-slope colluvial deposit erosion models. In the future, the study of the hydrodynamic characteristics of sediment transport processes should be strengthened to clarify the detachment-transport effect of flows through hydrodynamics.

The Distribution Characteristics and Potential Risk Assessment of Lead in the Soil of Tieguanyin Tea Plantations in Anxi County, China.

Assessing the distribution and risks associated with the soil lead content in the Tieguanyin tea plantations of Anxi County is critical, given the county's significance as the primary Tieguanyin tea production area in Fujian Province. This study examined the distribution characteristics of soil lead in Anxi County's tea plantations according to the Kriging spatial interpolation of the parameters of the semivariance function of the exponential model. Moreover, the sources of lead content were analyzed, considering geological backgrounds and anthropogenic influences. Ecological risks and the issuance of early warnings were also assessed. The soil lead content in the rocks of the Tieguanyin tea plantations in Anxi County followed the order: andesite > dacite > rhyolite > granite. The soil lead content gradually decreased from the center toward the east and west, forming four distinct north-south parallel zones. High-lead-content areas were identified at the border of Jiandou, Bailai, and Hushang; in the central part of Lutian; and in the southern part of Huqiu. The high levels of soil lead in the tea plantations possibly originated from industrial and mining activities, automobile exhaust, and agricultural activities. The distribution of single-factor pollution indices and potential risk evaluation based on the Soil Environmental Quality Standard, Environmental Technical Conditions for Tea Production Area, and Environmental Technical Conditions for Organic Tea Production Area indicated that the soil in Tieguanyin tea plantations in Anxi County was clean and safe for tea cultivation.

Study on soil-water characteristic curves in the profiles of collapsing walls of typical granite Benggang in southeast China.

Benggang with steep collapsing walls is one of the worst soil erosion problems in South China. The collapse of walls is the most critical process in Benggang development. This is mainly due to the soil water properties. The soil water characteristic curve (SWCC) is a key indicator for analyzing soil moisture, but the SWCC and its mechanism of influence in collapsing walls remain obscure. A pressure plate meter was used for drying experiments to research the SWCCs of undisturbed soils of five layers (from top to bottom: red soil layer, transition layer I, sand soil layer, transition layer II and detrital layer) of two typical collapsing walls. The van Genuchten (VG) model can be fitted to the SWCCs for different layers (NSE ≥ 0.90). With increasing soil depth, the parameters a and θ s first decreased and then increased, the parameters n first increased and then decreased, θ r declined as the soil depth increased. These findings illustrate that soil water holding capacity decreases with increasing soil depth. The bottom of the soil is weak in water retention and water can easily reach saturation, resulting in a decline in soil stability, thus promoting soil collapse and finally inducing upper soil collapse. Furthermore, gravel content and particle morphology are factors that should not be neglected for SWCCs. The results of this study provide a theoretical basis for understanding the process of wall collapse in Benggang landforms in South China.

[Benggang (collapsing hill) erosion hazard zoning based on the minimum cumulative resistance model: A case study of a small watershed in Anxi County, Fujian, China]. / 基于最小累积阻力模型的崩岗侵蚀危险性分区­­ä»¥å®‰æºªåŽ¿å°æµåŸŸä¸ºä¾‹.

In order to understand the possibility and spatial pattern of Benggang (collapsing hill) erosion in risk assessment and distinguish the primary and secondary areas in Benggang prevention, we took a small watershed in Anxi County (Fujian, China) as the study area and Benggang as the source, and constructed the Benggang expansion resistance surface using the minimum cumulative resistance (MCR) model and divided the risk zoning. The results showed that the area around Benggang displayed a low resistance value, while the northwest and southeast areas displayed a high resistance value. The Benggang expansion resistance surface had an island type form. Based on resistance surface, the research region was divided into very high-risk, high-risk, medium risk, low-risk and very low-risk zones. We proposed corresponding Benggang management suggestions for those zones. A total of 21 strategic saddle points were extracted based on the resistance surface morphology. The strategic points in the lower safety zone were considered as the priority areas for Benggang prevention. We compared the hazard results based on the MCR model and the information quantity method. These results were consistent in spatial distribution, indicating the reliability of the results of hazard zoning by the MCR model.