Soil Detachment Capacity Research Articles

Modelling the process of soil detachment by rill flow on steep loessial hillslopes

AbstractSoil detachment by rill flow is a key process of rill erosion, modelling this process can help in understanding rill erosion mechanisms. However, many soil detachment models are established on conceptual assumptions rather than experimental data. The objectives of this study were to establish a model of soil detachment by rill flow based on flume experimental data and to quantitatively verify the model. We simulated the process of soil detachment by rill flow in flume experiments with a soil‐feeding hopper using loessial soil on steep slopes. Seven flow discharges, six slopes and five sediment loads were combined. Soil detachment capacity, sediment transport capacity, and soil detachment rate by rill flow under different sediment loads were measured. The process of soil detachment by rill flow can be modelled by a dual power function based on soil detachment capacity and transport capacity deficit as variables. The established model exhibited high credibility (NSE=0.97; R2=0.97). The contributions of soil detachment capacity and transport capacity deficit to soil detachment rate by rill flow reached 60% and 36%, respectively. Soil detachment capacity exerted more influence on soil detachment rate than did transport capacity deficit. The performance of the WEPP rill erosion equation is also favourable (NSE=0.95; R2=0.97). The two power exponents in the model we established strengthen the role of soil detachment capacity in soil detachment rate and weaken that for transport capacity deficit. Soil detachment capacity and transport capacity deficit played important roles in the determination of soil detachment rate by rill flow. The results can be applied to implement the numerical modeling and prediction of rill erosion processes on steep loessial hillslopes. © 2019 John Wiley & Sons, Ltd.

Assessing and Modeling Soil Detachment Capacity by Overland Flow in Forest and Woodland of Northern Iran

Land use has significant effects on the erosion process, since it influences the soil detachment capacity by causing an overland flow (Dc). The effects of different land uses on the rill detachment capacity have not been explained in depth, and the hydraulic parameters providing accurate estimates of this soil property have not been completely identified. This study quantifies Dc at low flow rates in woodland and forestland, compared to two other land uses (cropland and grassland), in the Saravan watershed (Northern Iran), and develops prediction models of Dc and rill erodibility (Kr). Dc was measured on undisturbed soil samples, collected in the four land uses, and characterized in terms of the main physico-chemical properties in a flume experiment, simulating five slopes and five shallow water flows. The results showed that Dc was significantly lower in woodland and forestland compared to cropland and grassland, as the consequence of the changes in the main soil properties and the more developed vegetation cover and structure. Dc was positively correlated to clay and silt contents of soils, and negatively correlated to sand content, aggregate stability, root density, and organic matter. The stream power and unit stream power were found to be very accurate predictors of Dc in woodland and forestland, respectively. Kr values, which assumed the lowest values in woodland and forestland, were provided by interpolating Dc and the shear stress of water flow. Overall, this study has confirmed that vegetation cover and improved soil properties in forestland and woodland may help to reduce erosion in delicate environment ecosystems, such as the forests of Northern Iran.

Soil detachment capacity of shallow overland flow in Earth-Rocky Mountain Area of Southwest China

In process-based erosion models, soil detachment capacity (Dc) is a pivotal parameter that is typically estimated by hydraulic parameters. Purple soil in Earth-Rocky Mountain Area of Southwest China is a unique soil resource with characteristics including fast physical weathering, soft texture, and rich nutrient reserves. However, the prediction accuracy of Dc and its relationship with certain hydraulic parameters remains poorly understood for purple soil, which is defined as an Entisol in the US Soil Taxonomy system. The objective of this study was to investigate the relationship between Dc of shallow overland flow and hydraulic parameters to establish an accurate model for purple soil. A series of 825 flume experiments were conducted in a 12 m × 0.3 m hydraulic flume. Flow discharge was 8.33 × 10−3 to 41.67 × 10−3 m2 s−1, slope gradient was 8.7% to 39.1%, and rill length was 0.5 m to 10 m. Results showed that flow discharge and slope, stream power, and effective stream power were effective predictors of Dc. However, flow depth, flow velocity, shear stress and unit stream power were relatively poor predictors. Stream power was the optimal parameter for predicting the Dc of shallow overland flow. Flow discharge, slope and effective stream power were also useful parameters for predicting Dc. Linear equation between Dc and stream power was the optimal model for predicting Dc, which was recommended when flow depth and flow velocity data were available; however, power equation among Dc, flow discharge and slope also showed good performance in predicting Dc, which was recommended when only flow discharge and slope data were available. The results of this study provide theoretical guidance for predicting sediment yield in Earth-Rocky Mountain Area of Southwest China as well as a decision-making basis for controlling soil and water loss in Earth-Rocky Mountain Area of Southwest China.

Fine roots benefit soil physical properties key to mitigate soil detachment capacity following the restoration of eroded land

Trait-based approaches are increasingly used to improve ecological restoration in degraded ecosystems. The aim of this study was to evaluate how vegetation controls soil detachment capacity (Dc) by concentrated flow based on the linkages between root traits and soil physics. We selected 60 plots along a land degradation gradient caused by long-term water erosion in a small catchment, central China. These plots consisted of woodlands, scrublands, grasslands and bare lands. And soil physical properties, root traits and Dc were measured in each plot. Fine roots (0.2 mm < diameter < 2 mm) accounted for 51–93% of total root length in topsoil. Roots explained most of the soil variations in noncapillary porosity, aggregate stability and shear strength. Furthermore, our prediction model (R2 = 0.88, NSE = 0.85) showed that fine roots length density and soil shear strength were the primary factors reducing Dc. Vegetation restoration improves multiple soil physical properties key to mitigating Dc, and the root functional traits play a substantial role in this relationship. These findings could provide the basis for soil conservation, and for expanding the pool of species of interest, which can be used to provide erosion mitigation services in degraded ecosystems.

Effects of soil-incorporated plant litter morphological characteristics on the soil detachment process in grassland on the Loess Plateau of China

The Loess Plateau of China is one of the most eroded areas in the world. In the past 20 years, effective vegetation restoration measures have significantly changed the near-surface characteristics of soil. In natural conditions, plant litter is widespread in the topsoil. The effects of litter incorporated into soil on the process of soil detachment, which is closely related to plant litter morphology, are still not well known. This study aimed to detect the variation of litter morphological characteristics and quantify their effects on soil detachment capacity and rill erodibility when litter is incorporated into the soil. Four plant litters (Bothriochloa ischaemum (L.) Keng., Artemisia sacrorum Ledeb., Setaria viridis (L.) Beauv., and Artemisia capillaris Thunb.) with five length levels (<0.5, 0.5–2, 2–4, 4–6, and 6–8 cm) were incorporated into soil (idle for 50 days) at the same litter biomass rate (0.7 kg m−2). Then the soil was sampled and cores were subjected to overland flow under six flow shear stress levels (5.66, 8.31, 12.21, 15.55, 19.15 and, 22.11 Pa) using a hydraulic flume (4.0 m × 0.35 m). The results showed that the litter morphological characteristics of litter length density (LLD), litter surface area density (LSAD) and litter volume ratio (LVR) differed in plant species at the same litter biomass rate. Correspondingly, soil detachment capacity (ranging from 0.414 to 2.179 kg m−2 s−1) and rill erodibility (ranging from 0.037 to 0.177 s m−1) varied significantly and mean values from the Bothriochloa ischaemum (L.) Keng. treatments were the minimums, which were 28% to 37% and 23% to 35% less than that of the other treatments, respectively. The soil detachment capacity and rill erodibility were significantly correlated with the litter morphological characteristics of LLD, LSAD and LVR (p < 0.01). The contact area between litter and soil was the most critical factor affecting soil detachment. Incorporated plant litter residue litter effect on rill erodibility could be well estimated by LSAD.

A comparison of the effectiveness of the roots of two grass species in reducing soil erosion on alluvial fans in south‐east China

AbstractThe 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.

Soil detachment by overland flow on hillslopes with permanent gullies in the Granite area of southeast China

Permanent gullies are often initiated from rill erosion, followed by the formation of abrupt, deep and wide gullies when topsoil and subsoil are carried away by fast-flowing surface water. Few studies have been performed to evaluate soil detachment processes on hillslopes with permanent gullies, which may significantly affect the further development of gully erosion. Soil detachment was investigated by using natural undisturbed soil samples collected in different spatial locations (upper catchment, middle slope, lower slope, and scour channel) of hillslopes with permanent gullies. The relationships of soil detachment capacity with soil property, root system, and hydraulic parameters were quantified. Selected samples were tested in a hydraulic flume (3.8 m length × 0.2 m width) under five different shear stresses (3.67, 7.81, 10.50, 13.97 and 17.28 Pa). Soil detachment capacity was found to be significantly greater in the scour channel than in the other three hillslope positions. For the initial and stable gullies, the soil detachment capacity was notably reduced in the middle slope relative to the upper catchment and lower slope, while a different trend was observed in the active gully. The variability of soil detachment capacity at different spatial locations showed a negative correlation to bulk density, soil cohesion, clay, organic matter, and root density (P < 0.05), and a positive correlation to total porosity (P < 0.01). The rill erodibility (Kr) showed a power function decrease with soil bulk density, organic matter, and root density (P < 0.01). Critical shear stress (τc) had a significant and positive correlation with soil cohesion. Based on the WEPP model, detachment capacity of soil on hillslopes with permanent gullies could be achieved by using measurable parameters such of shear stress, bulk density, organic matter, root density, and soil cohesion.

Variation in soil erosion resistance of slips deposition zone with progressive vegetation succession on the Loess Plateau, China

Soil slips are widely distributed on the Loess Plateau. Most of them have experienced an ecological succession process, which has strong effects on the near-surface characteristics, and thereby influences soil detachment capacity by overland flow (Dc). This study quantified the effects of progressive succession of the deposition zone of soil slip on Dc and soil resistance to flowing water erosion reflected by rill erodibility (Kr) and critical shear stress (τc) on the Loess Plateau. Soil samples (diameter 10 cm, height 5 cm) were taken from seven deposition zones of soil slips covered by typical plant communities with different succession stages restored for 1 to 31 years. A 37-year grassland where no slip occurred covered by climax community was selected as the control. A hydraulic flume (4.0 m in length, 0.35 m in width) with a slope ranging from 0 to 60% was applied to determine Dc. Biological crusts thickness, soil texture, bulk density, cohesion (CH), water stability ability (WSA), organic matter content, root mass density (RD), and plant litter density (LD) were measured for each site. The measured Dc decreased rapidly when the soils were restored for 1 to 21 years, and then gradually leveled off. Dc could be well estimated by flow shear stress, CH, WSA, RD, and LD (NSE = 0.95). Kr decreased rapidly with succession till attained a stable stage after 21 years of succession. Kr could be well simulated by CH, WSA, RD, and LD (NSE = 0.92). τc increased generally with succession, although it fluctuated from 10 to 31 years. The temporal variation of τc was dominantly controlled by the biological crusts thickness and the content of WSA. Natural ecological succession is an effective approach to promote soil resistance to flowing water erosion for the deposition zone of soil slip. The near-surface characteristics, such as CH, WSA, RD, and LD, were the key factors to control soil erosion for the deposition zone of soil slip on the Loess Plateau.

Modelling soil detachment by overland flow for the soil in the Tibet Plateau of China

The overland flow erosion is common and became more serious because of the climate warming inducing more runoff in the Tibet Plateau. The purposes of this study were to evaluate the effects of flow rate, slope gradient, shear stress, stream power, unit stream power and unit energy of water-carrying section on the soil detachment capacity for the soil in the Tibet Plateau of China due to the information is limited. To achieve this aim, laboratory experiments were performed under six flow rates (5, 10, 15, 20, 25 and 30 L min−1) and six slope gradients (8.74%, 17.63%, 26.79%, 36.40%, 46.63 and 57.73%) by using a slope-adjustable steel hydraulic flume (4 m length, 0.4 m width, 0.2 m depth). The results indicated that soil detachment capacity ranged from 0.173 to 6.325 kg m−2 s−1 with 1.972 kg m−2 s−1 on average. The soil detachment capacity increased with power function as the flow rate and the slope gradient augmented (R2 = 0.965, NRMSE = 0.177 and NSE = 0.954). The soil detachment capacity was more influenced by flow rate than by slope gradient in this study. The relation between soil detachment capacity and shear stress, stream power, unit stream power and unit energy of water-carrying section can be described by using the linear function and power function, the power function relationship performed better than the linear function in generally. The stream power exhibits the best performance in describing the soil detachment capacity among shear stress, stream power, unit stream power and unit energy of water-carrying section in this study. The erodibility value in this study was larger than and the critical shear stress was less than those for soil in the eastern China. There has a huge potential for the soil in the Tibet Plateau eroded by the water erosion when enough runoff exiting. More attention should be payed to the water erosion process and mechanism in the Tibet Plateau area in the future.

Effect of Soil Water Content on Soil Detachment Capacity for Coarse‐ and Fine‐Grained Soils

Core Ideas Aging had a nonlinear effect on soil detachment capacity for fine‐grained soil. Detachment capacity of fine soil had a concave pattern as soil water increased. Detachment capacity of coarse soil had a convex pattern as soil water increased. A systematic set of flume tests was developed to explore the relation between soil water content and soil detachment capacity for a coarse‐grained soil and a fine‐grained soil. The experiments included aging treatments (three volumetric water contents of 4.0, 11.5, and 21.7% for the sandy loam soil and 5.0, 10.5, and 17.4% for the silt loam soil, and seven aging durations of 0, 12, 24, 36, 48, 60, and 72 h) and drying treatments (saturated soil samples oven‐dried for 0, 12, 24, 36, 48, 60, and 72 h). Results showed that soil detachment capacity for these two soils presented unique patterns as soil water content increased: the fine‐grained soil presented an increasing and then a decreasing trend under aging treatments, whereas the coarse‐grained soil showed a continuous increasing trend as soil water content increased. Both patterns could be fitted by quadratic equations. The effect of soil water content on soil detachment capacity was mainly reflected by water‐stable aggregate content. Higher soil water content results in weaker bonds for fine‐grained soil but in less slaking for coarse‐grained soil. Lower soil water content leads to less slaking for fine‐grained soil but more particle deposition and cementation for coarse‐grained soil. Future work will include additional soil textures and focus on soil erodibility and critical shear stress to expand our understanding of soil detachment influenced by soil water content.

Erosion vulnerability of sandy clay loam soil in Southwest China: Modeling soil detachment capacity by flume simulation

Soil detachment capacity (Dc) is a key parameter in many soil erosion models and is typically estimated using hydraulic parameters. However, the accuracy of predicting Dc and its relationship to hydraulic characteristics remains poorly understood for many soil types. This study investigates the predictability of Dc with hydraulics by simulated scour rill flow and quantifies erosion vulnerability to rill erosion as reflected by rill erodibility and critical hydraulic values for an Entisol from Southwestern China. Small samples (10 cm in diameter, 6 cm in depth) of sandy clay loam of Entisol were subjected to scouring by simulated rill flow under the combinations of flow discharges (18.8, 26.3, 46.6, 54.4, 64.6 l min−1) and slope gradients (3.5%, 8.7%, 17.6%, 26.8% and 36.4%). The results showed that Dc increased as a power function with flow discharge irrespective of slope gradients, and at low discharge gradients Dc increased as a power function with slope and with transitions to a linear function at higher discharge gradients. The association of flow discharges and slope gradients was a better predictor of Dc than flow depths and slope gradients. Shear stress and stream power were similar and better predictors of Dc than flow velocity, unit stream power and unit energy. Rill erodibility related to all hydraulic parameters were significantly different from zero under combination of flow discharges and slope gradients, and this was true for critical hydraulic values related to comprehensive data. Relatively higher rill erodibility and lower critical hydraulic values compared with other soils demonstrated that sandy clay loam of Entisol is susceptible to detachment. These results highlight the erosion vulnerability of Entisols and provide deeper insights on the reliability of hydraulic parameters which strongly affect soil detachment modeling.

Impacts of sediment load and size on rill detachment under low flow discharges

Rigorous validation of the first-order detachment-transport coupling concept using different sediment sizes is nonexistent in the literature. We hypothesized that particle sizes in a sediment-laden flow can affect soil detachment. The objectives of this study were to investigate the relationship between detachment rates by rill flows and hydraulic parameters under low flow discharges, and to quantify the responses of soil detachment rates to sediment loads and median sizes. A concentrated flow flume test was conducted under three low flow discharges (0.00033, 0.00067 and 0.00100 m2·s−1) and three sediment concentrations (50, 100 and 200 kg·m−3) with five median sizes (0.233, 0.204, 0.169, 0.115 and 0.078 mm). The results showed that the relationship between soil detachment capacity and shear stress fits the Water Erosion Prediction Project (WEPP) model well (R2 = 0.89). Stream power, compared with shear stress, is a better hydraulic parameter in simulating soil detachment rates under different sediment concentrations. The soil detachment rates by sediment-laden rill flows were negatively related to both sediment loads and sediment median sizes, validating the first-order sediment feedback relationships used in the WEPP model. The overall responses of soil detachment rates to sediment loads and sediment median sizes followed multivariate linear relationships, further demonstrating the negative feedbacks of sediment load and size on soil detachment by rill flow.

Soil resistance to flowing water erosion of seven typical plant communities on steep gully slopes on the Loess Plateau of China

Steep gully slopes are widespread and have been recognized as the main sediment source on the Loess Plateau. Different vegetation growth may lead to the differences in soil properties and plant roots, and thus likely affects soil resistance to flowing water erosion, reflected by rill erodibility and critical shear stress. However, few studies have been conducted to evaluate this effect on steep gully slopes on the Loess Plateau of China. This study was performed to investigate the effects of vegetation growth on soil resistance to flowing water erosion on steep gully slopes, and quantify the main potential influencing factors on the Loess Plateau. Three typical shrub communities and four typical grass communities that distributed on different gully slopes were selected. 240 undisturbed soil samples were collected from these seven gully slope lands and one slope farmland (control), and were subjected to detachment by overland flow under six different shear stresses (6.64 to 17.85 Pa). The results showed that the mean detachment capacity of slope farmland was 6.9 to 47.8 times greater than those of steep gully slopes covered with different plant communities. The rill erodibilities of steep gully slopes covered with different plant communities reduced greatly by 77.0% to 95.1% compared to the control slope. The critical shear stress of slope farmland (2.72 Pa) was only 57.2% and 39.6% of that of shrubland (4.76 Pa) and grassland (6.88 Pa). Both shrub and grass communities were effective in reducing soil detachment capacity and rill erodibility, and increasing critical shear stress on steep gully slopes. But the effects were more obvious for the grass communities. The differences in rill erodibility between slope farmland and gully slope lands were mainly explained by the changes in root mass density (82.4%). Plant roots had strong direct effects on increasing soil cohesion (0.78), organic matter content (0.56), and water stable aggregation (0.92). Rill erodibility was negatively related to root mass density as an exponential function (p < 0.05), and soil cohesion and water stable aggregation as power functions (p < 0.05). Critical shear stress was positively related to root mass density and soil water stable aggregation following a logarithmic function.

Modelling soil detachment capacity by rill flow with hydraulic variables on a simulated steep loessial hillslope

AbstractModelling soil detachment capacity by rill flow with hydraulic variables is essential to understanding the rill erosion process and developing physically based rill erosion models. A rill flume experiment with non-erodible flume bed and small soil samples was conducted. Seven flow discharges and six steep slope gradients were combined to produce various flow hydraulics. The soil detachment capacity increases with the increase in slope gradient and flow discharge. The critical slope gradients of 21.26 and 26.79% cause the detachment capacity to increase at a slow pace. The soil detachment capacity can be defined by a power function of flow discharges and slopes. The contribution rates of slope gradient and flow discharge to soil detachment capacity are 42 and 54%, respectively. The soil detachment capacity increases with shear stress, stream power and unit stream power; the increase rates of these parameters are greater under gentle slopes than steep slopes. Stream power is the superior hydrodynamic parameter describing soil detachment capacity. The linear model equation of stream power is stable and reliable, which can accurately predict soil detachment capacity by rill flow on steep loessial hillslopes. This study can help to sufficiently clarify the dynamic mechanism of soil detachment and accurately predict soil detachment capacity for steep loessial hillslopes.

Response of soil detachment capacity to plant root and soil properties in typical grasslands on the Loess Plateau

It is likely that grassland has a significant effect on the process of soil detachment by overland flow. This study tests how soil detachment capacity responds to variation in plant root and soil properties between ten typical grasslands found on the Loess Plateau. 300 soil samples were collected from five grasslands with tap root system and five grasslands with fibrous root systems representing the typical community compositions of different succession stages, then subjected to flow scouring in a hydraulic flume under six shear stresses (ranged from 4.98 to 16.37 Pa). The results showed that the mean soil detachment capacity of each grassland fell between 0.030 kg m−2 s−1 (Poa sphondylodes Trin.) and 3.297 kg m−2 s−1 (Astragalus melilotoides Pall.). The mean soil detachment capacity across all grasslands with tap root systems was 14.7 times greater than that of grasslands with fibrous root systems, indicating that fibrous root systems are significantly more effective at reducing soil erosion. Soil detachment capacity was effectively simulated by power functions of flow velocity, shear stress, or stream power (with mean R2 values ranging from 0.87 to 0.90) and less effectively simulated by a power function of unit stream power (mean R2 = 0.74). Soil detachment capacity decreased exponentially with soil bulk density, aggregate, and cohesion (with R2 values ranging from 0.87 to 0.99) as well as with root mass density (R2 = 0.31, n = 150 for tap root systems and R2 = 0.17, n = 150 for fibrous root systems). Soil detachment was significantly worse in grasslands with tap root systems where the root mass density was less than 4 kg m−3. A model was developed to estimate soil detachment capacity based on hydraulic parameters, plant root, and soil properties on the Loess Plateau, and its performance was satisfactory (R2 = 0.86; NSE = 0.73). Root mass density, soil aggregate, and soil cohesion were indicated as the primary features of grasslands which influencing the process of soil detachment.

The effects of varied soil properties induced by natural grassland succession on the process of soil detachment

The changes in soil properties caused by vegetation succession might have great effects on the process of soil detachment by overland flow. This study was carried out to quantify the effects of varied soil properties induced by natural grass succession on soil detachment capacity by overland flow and soil resistance to flowing water erosion on the Loess Plateau. 300 undisturbed soil samples (without roots) were collected from ten typical grasslands, and subjected to flow scouring under six shear stresses ranging from 4.98 to 16.37 pa. The results showed that the maximum soil detachment capacity (3.80 kg m−2 s−1) was found in Astragalus melilotoides Pall. grassland, where it was 49.0 times greater than that of the minimum found in Poa sphondylodes Trin. grassland. Soil properties induced by fibrous root herbage have strong effects on the process of soil detachment. In comparison to grasslands with tap root systems, grasslands with fibrous root herbage have lower soil detachment and rill erodibility by 84.6% and 84.3%, respectively, and critical shear stress which is higher by 15.2%. Stream power was a better parameter than velocity, shear stress or unit stream power for simulating soil detachment capacity. Soil cohesion, bulk density, organic matter and median soil grain size were the main factors affecting the process of soil detachment. Rill erodibility decreased with cohesion or clay content as an exponential or power function, and increased with the median soil grain size as an exponential function. A model was developed to estimate soil detachment capacity based on hydraulic parameters and soil properties on the Loess Plateau. The result was satisfactory and the performance of model was greatly improved in comparison to previous studies (R2 = 0.77; NSE = 0.61; p < 0.01).

An analysis of soil detachment capacity under freeze-thaw conditions using the Taguchi method

Soil detachment is one of the most important processes of soil erosion, as it is of great significance for the prevention and treatment of soil erosion in areas subject to seasonal freeze-thaw. However, little research on soil detachment capacity (SDC) during the thawing period has been carried out and this process remains unclear. In order to elucidate the effects of slope, flow discharge and freeze-thaw factors on SDC, the indoor artificial freezing-thawing method was applied in combination with scour to simulate the soil detachment process. Signal-to-noise (S/N) ratio analysis was also used to evaluate the experimental results by applying the Taguchi method. The results showed that SDC increased with the increased of slope and flow discharge. As the number of freeze-thaw cycles and moisture increased, SDC initially decreased and then increased. A maximum soil detachment value was achieved at 12° slope and when moisture was 12%, flow discharge was 1.2L/min, and there were ten freeze-thaw cycles. Statistical analysis with the help of Taguchi method showed that the percentage contribution of the different factors to SDC occurred in order, slope (76.02% at p=0.002)>flow discharge (13.39% at p=0.019)>soil moisture (6.92% at p=0.047)>the number of freeze-thaw cycles (3.67% at p=0.106), while factors related to hydrodynamic conditions exert a greater influence than those related to freeze-thaw. Finally, the Taguchi and orthogonal analysis methods showed the similar predictive results R2=0.98 and R2=0.97 respectively. However, the Taguchi method was more accurate than the orthogonal analysis methods due to less relative error 8.98% and 15.11% respectively. These results provided a scientific reference for the study of the mechanisms of soil erosion as well as for the applicability of the Taguchi method.

Quantifying the Binding and Bonding Effects of Plant Roots on Soil Detachment by Overland Flow in 10 Typical Grasslands on the Loess Plateau

Core Ideas Plant root reduced soil detachment by 54%, of which 41% was by root binding effect. Fibrous root was 1.6 times greater than tap root in reducing the soil detachment. Correction coefficients of 10 typical herbs were presented for the WEPP model. Plant roots penetrating the soil may enhance soil resistance and protect the topsoil against scouring by overland flow, but their mechanisms are not fully understood. This study was performed to quantify the binding and bonding effects of plant root systems on the process of soil detachment by overland flow. Ten typical dominant species of herbage representing two different root architectures on the Loess Plateau were selected, and 900 soil samples were collected from these grasslands for detachment capacity measurements under different flow shear stresses. The results showed that the existence of plant root systems greatly reduced the soil detachment capacity by 53.6%, of which 41.4 and 12.2% were attributed to the root binding and bonding effects, respectively. The contribution rate of the binding and bonding effects depended on plant root architecture (i.e., the tap and fibrous roots). For tap root, the average contribution of the plant root for protecting soil from detachment was 41.6%, of which 33.2 and 8.4% were induced by the root binding and bonding effects. For fibrous root, the mean contribution of plant root was 65.7%, of which 49.7 and 16.0% were attributed to the root binding and bonding effects, respectively. Series correction coefficients that took into consideration the root binding and bonding effects of 10 typical dominant plants for their rill erodibility in the Water Erosion Prediction Project model on the Loess Plateau; the result was satisfactory with Nash–Sutcliffe efficiency coefficients that ranged from 0.48 to 0.58.

Quantifying the surface covering, binding and bonding effects of biological soil crusts on soil detachment by overland flow

AbstractBiological soil crusts (BSCs) have impacts on soil detachment process through surface covering, and binding and bonding (B&amp;B) mechanisms, which might vary with successional stages of BSCs. This study was conducted to quantify the effects of surface covering, binding and bonding of BSCs on soil detachment capacity by overland flow in a 4 m long hydraulic flume with fixed bed. Two dominant BSC types, developed well in the Loess Plateau (the early successional cyanobacteria and the later successional moss), were tested using natural undisturbed soil samples collected from the abandoned farmlands. Two treatments of undisturbed crusts and one treatment of removing the above‐ground tissue of BSCs were designed for each BSC type. For comparison, bare loess soil was used as the baseline. The collected soil samples were subjected to flow scouring under six different shear stresses, ranging from 6.7 to 21.2 Pa. The results showed that soil detachment capacity (Dc) and rill erodibility (Kr) decrease with BSC succession, and the presence of BSCs obviously increased the critical shear stress, especially for the later successional moss crust. For the early successional cyanobacteria crust, Dc was reduced by 69.2% compared to the bare loess soil, where 37.7% and 31.5% are attributed to the surface covering and B&amp;B, respectively. For the later successional moss crust, Dc decreased by 89.8% compared to the bare loess soil, where 68.9% and 20.9% contributed to the surface covering and B&amp;B, respectively. These results are helpful in understanding the influencing mechanism of BSCs on soil erosion and in developing the process‐based erosion models for grassland and forestland. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Soil Erosion as Affected by Freeze‐Thaw Regime and Initial Soil Moisture Content

Core Ideas Freeze‐thaw generally increased detachment capacity by an average of 36.5%. The impact of freeze‐thaw on soil erosion was affected by initial moisture content. Detachment capacity and rill erodibility was increased at 30 and 45% moisture. Soil erosion was reduced at 20% moisture content after 5 or 10 freeze‐thaw cycles. The effect of freeze‐thaw exponentially increased with the freeze‐thaw cycles. To quantify the effects of freeze‐thaw (F‐T) on rill erosion, scouring test using a tilting flume (5 m length, 0.4 m width) was conducted. Typical black soil in Northeast China was tested. Five F‐T cycles (FTCs; 0, 1, 3, 5 and 10), four gravimetric moisture contents (θg; 10, 20, 30 and 45%), and seven flow shear stresses (τ; evenly spaced from 1.90 to 14.59 Pa) were examined. The soil samples subjected to 0 FTC were termed as the unfrozen control group. The results showed that the F‐T processes increased soil detachment capacity (Dc) by an average of 36.5% across all experimental conditions together. The effects of F‐T on Dc varied with initial θg. To eliminate the consolidation impact induced by water spraying, the Dc ratio (RDc) between each F‐T group and the corresponding unfrozen control group was calculated. This ratio was found to exponentially increase with FTCs, with an R2 of 0.94. The rill erodibility (Kr) increased with FTCs only at initial θg of 30 and 45%. Soil critical shear stress (τc) of the experimental group was significantly higher relative to the unfrozen control group and reached its maximum after 10 FTCs at the initial θg of 20%. These findings help to understand the effects of FTCs on soil erosion and thereby to improve soil erosion models, e.g. modifying rill erodibility parameters.