Search

Preferential flow plays a vital role in infiltration processes in structured soil. However, knowledge of preferential flow in colluvial deposits of Benggang remains limited. In this study, three typical colluvial deposits with different formation times were selected. The formation times of colluvial deposits A, B and C increased in sequence. Water infiltration in colluvial soil was visualized through Brilliant Blue dye experiments (a total of 90 photos from the dyed soil profiles). The dye morphological characteristics of preferential flow were analysed, and the influencing factors were explored. The dye morphological parameters confirmed the occurrence of preferential flow in the colluvial deposits. The dye coverage of colluvial deposit A was the greatest (61.12%), followed by colluvial deposits B (50.41%) and C (46.81%). The matrix flow depth, preferential flow fraction and length index of colluvial deposits A and B were greater than those of colluvial deposit C. Preferential flow was more notable in colluvial deposits A and B than in colluvial deposit C. The migration process of dyed water varied spatially. There were more preferential flow paths at a 10 cm horizontal width. In addition to the bulk density and saturated hydraulic conductivity, the soil particle composition, especially the gravel content (r = 0.740), was closely related to the observed dye coverage. According to the principal component analysis results, the soil particle composition imposed the greatest influence on the formation of preferential flow in the colluvial deposits, with a contribution of 45.24%. The results provide a theoretical reference for explaining the mechanism of soil infiltration processes and a systematic basis for the treatment of colluvial deposits. [ABSTRACT FROM AUTHOR]

The rehabilitation of diverse and three‐dimensional forest vegetation patterns is crucial for preventing forest degradation and improving soil fertility. However, the relationship between soil microbial community and soil fertility was not clear. To accurately assess the capability of vegetation restoration measures on the real impact on degraded soil ecosystems. We selected three vegetation rehabilitation models of degraded Pinus massoniana forests in typical soil erosion areas in China as the research objects, with untreated bare land as the control. All three vegetation construction patterns increased the abundance and diversity of soil bacteria and fungi, thereby enhancing the stability of the soil ecosystem. Additionally, the vegetation rehabilitation models also altered the community structure of soil bacteria and fungi in the degraded P. massoniana forests. The pH and soil fertility index (IFI) were the main factors leading to variations in the community structure of the soil bacteria and fungi. Among them, the grass‐planting model showed a significantly greater improvement in the soil fertility of degraded P. massoniana forests than the shrub‐planting and arbor‐planting models. Furthermore, Ascomycota, Basidiomycota, and Glomeromycota exhibited the most significant response to IFI, indicating their potential as indicator microorganisms for soil fertility changes. The improvement in soil fertility in degraded P. massoniana forests was influenced primarily by the increase in urease activity (S‐UE) according to the vegetation rehabilitation models (84.20%, p = 0.000). In conclusion, the grass‐planting system effectively improved the soil ecosystem quality of degraded P. massoniana forests in southern erosion‐prone areas of China and was suitable for further application. [ABSTRACT FROM AUTHOR]

Soil bacterial communities play a crucial role in the evaluation of soil ecosystem stability. Vegetation restoration is a key determinant of soil bacterial communities in areas affected by soil erosion. However, it remains unclear how the structure and diversity of soil bacterial communities vary with soil depth. In this study, we collected soil samples from 0 to 10 cm, 10 to 20 cm, 20 to 30 cm, and 30 to 40 cm depths in vegetation restoration sites located in typical soil erosion areas in China. We compared and analyzed the differences in bacterial community characteristics among different soil depths, using untreated areas as controls. Compared to the untreated areas, the abundance of soil bacteria in the 0–10 cm, 10–20 cm, and 20–30 cm depths of the vegetation restoration sites increased by 1.63, 1.04, and 1.29 times, respectively. Furthermore, vegetation restoration enhanced soil bacterial diversity at the 0–10 cm, 10–20 cm, and 20–30 cm depths. Soil organic carbon (OC) was the main explanatory factor (53.50%, p = 0.000) for the decrease in soil bacterial diversity with soil depth. Additionally, after vegetation restoration in soil erosion areas, the dominant bacterial community composition shifted from Chloroflexi to Actinobacteria at the 0–10 cm, 10–20 cm, and 20–30 cm depths and to Proteobacteria at the 30–40 cm depth. The differences in soil bacterial communities among different soil depths were primarily driven by soil total nitrogen (TN) content, which explained up to 34.5% of the variation. In conclusion, in the subsequent management of vegetation restoration sites, increasing OC and TN content can enhance soil bacterial diversity, improve bacterial community composition, and ultimately enhance the stability of soil ecosystems. [ABSTRACT FROM AUTHOR]

'Benggang' is a local term for a widespread type of severgully erosion with steep collapsing walls in granitic, low, hilly areas of southern China, and its development and expansion are closely related to the shear strength of the collapsing wall. Plant roots play an important role in improving soil shear strength. However, the shear strength of root‐soil complexes in different layers of collapsing walls remains obscure. We selected Dicranopteris linearis fern roots and adopted the direct shear method to evaluate the effect of root weight density (RWD) (0–1.25 g 100 cm−3) on the shear properties of the lateritic, sandy and detritus layers. The results showed that roots could enhance soil shear strength, and the maximum increase in the lateritic layer was 11.53%, higher than that in the sandy (5.84%) and detritus layers (3.17%). As the root content increased, the cohesion of the sandy and detritus layers increased and then decreased, and their maximum increase in cohesion and the fitting optimal RWD were lower than those of the lateritic layer. The internal friction angle was not affected by roots. When the root content was constant, the shear strength and cohesion of the lateritic layer were significantly higher than those of the sandy and detritus layers, while their internal friction angle was significantly lower than that of the latter two layers. The average increment of soil cohesion calculated by the Wu‐Waldron model (WWM) was 10.52 kPa, which was 0.30, 3.75 and 19.38 times the measured average values of the lateritic, sandy and detritus layers, respectively. The correction coefficient k′ was 0.02–1.18, and the k'¯$$ \overline{k\hbox{'}} $$ in the lateritic layer was the highest (0.82), followed by that in the sandy and detritus layers. By combining the modified WWM with Coulomb's formula, new shear strength equations for root‐soil complexes of D. linearis were established. The predicted shear strength compared well with the measured shear strength (R2 > 0.90, NSE >0.90). Overall, the roots only had a significant reinforcement effect on the lateritic layer, and they could still not change the mechanical properties of the collapsing wall, which were more stable in the upper layers and weaker in the bottom. Therefore, other measures should be taken in the bottom layers to improve the stability of Benggangs. Highlights: Effect of D. linearis roots on the shear strength of collapsing walls in Benggang was studied.Roots could improve collapsing‐wall soil shear strength, mainly reflected in the cohesion.The roots enhancement effect in lateritic layer was better than that of sandy and detritus layers.New shear strength equations of root‐soil complexes were established based on the Wu‐Waldron model. [ABSTRACT FROM AUTHOR]

The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility, and critical shear stress on alluvial fans of benggang in south‐east China. A 4‐m‐long and 0.12‐m‐wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39 × 10−3 to 4.19 × 10−3 m2 s−1. The mean detachment capacities of P. mandiocanum and P. giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0‐ to 5‐cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE = 0.90). With the increase in soil depth, rill erodibility increased, whereas shear stress decreased. The mean rill erodibilities of P. mandiocanum and P. giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE = 0.88). The mean critical shear stress of P. mandiocanum and P. giganteum lands was 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE = 0.76). This study demonstrated that planting of the two grasses P. mandiocanum and P. giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of P. giganteum being more effective than the shallow roots of P. mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process. [ABSTRACT FROM AUTHOR]

Core IdeasMore salts were distributed in liquid water than saline ice during the saline water freeze‐thaw process.Leaching with saline ice melt‐water was better than leaching with saline water at reducing soil EC and SAR.Gypsum application could improve the soil Ks when leached by the saline ice melt‐water.The addition of gypsum could eliminate the soil alkalinity hazards post leaching. Saline‐alkali soils adversely affect both the construction of ecological landscapes and crop production in coastal areas. This study aimed to investigate the effects of freeze‐thaw process on purifying saline water, and evaluate the potential of combining saline ice melt‐water leaching and gypsum addition for remediating coastal saline‐alkali soil. Saline water with a salinity of 10 g L−1 was tested in this study, and the leaching experiment included four treatments: saline water direct leaching (S), saline water direct leaching combined with gypsum application (SG), saline ice melt‐water leaching (SI), and saline ice melt‐water leaching combined with gypsum application (SIG). The results showed that more salts were concentrated in the bottom ice layer than in the other ice layers after the saline water was completely frozen. The salinity of the melt‐water decreased during the melting process, and the mean salinity of melt‐water during the second half of the melting process was significantly lower than the salinity of source water samples. During the leaching phase, the cumulative leachate losses of Na+, Ca2+ and Mg2+ were significantly greater for the SI treatment than that for the S treatment. After leaching, the soil electrical conductivity (EC) significantly decreased, and the SI treatment exhibited better performance than the S treatment in terms of reducing the soil EC and sodium adsorption ratio (SAR). The application of gypsum improved the soil saturated hydraulic conductivity (Ks) and decreased both the soil pH and alkalinity when the coastal saline soil was leached by the saline ice melt‐water. [ABSTRACT FROM AUTHOR]

A precise estimation of sediment transport capacity (Tc) is key to establishing process‐based erosion models. However, few data are available for estimating transport capacity on steep slopes and test materials sorted at high coarse grain values of >2 mm. Colluvial deposits with loose, coarse material and steep slopes make up the packed materials underlying the collapsing walls in benggang, which collapse due to hydraulic pressure and gravity. The objectives of this study were to investigate how flow discharge and slope steepness affect Tc and to examine relationships between Tc and flow velocity, shear stress, stream power, and unit stream power for colluvial deposits found on steep slopes. A nonerodible rill flume of 4 m long and 0.12 m wide was used. Slope steepness values ranged from 18% to 84%, and unit flow discharge values ranged from 0.56 × 10−3 to 4.44 × 10−3 m2 s−1. Tc increased as a power function with flow discharge and slope steepness with a Nash–Sutcliffe model efficiency (NSE) value of 0.99, and the effects of flow discharge were stronger than those of slope steepness. Tc was overestimated for a colluvial deposit when the equations of the ANSWERS, Zhang et al. and Wu et al. models were considered and when Tc exceeded 5 kg m−1 s−1, as the slope steepness used in our study was much higher than those used (<47%) in the other models. Regression analyses show that Tc can be predicted from linear equations of flow velocity, stream power, and unit stream power, and Tc can be fit to shear stress with power function equation. Flow velocity optimizes to predict Tc with NSE = 0.97, and stream power and shear stress can also be successfully related to Tc (NSE = 0.91 and NSE = 0.81, respectively); however, unit stream power performs poorly (NSE = 0.67). These results provide a basis for establishing process‐based erosion models on steep colluvial slopes. [ABSTRACT FROM AUTHOR]