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Context 1
... depth is closely associated with the runoff coefficient and with soil detachability, which determines the degree of mixing under specific conditions ( Heilig et al., 2001). RIs, slope gradients, initial water contents, soil amendments with PAM, and soil types, however, exert different effects while regulating soil detachment and the runoff coefficient (Table 2). Fig. 2 presents the rain-induced soil detachment under the influence of various factors. ...
Context 2
... the energetic raindrops would destroy the structure of the topsoil, decrease soil permeability, and increase splash erosion (Schmidt, 2010). Second, raindrop impacts could induce some amount of soil sealing, which would prevent infiltration (AbuAwwad, 1997;McIntyre, 1958), induce a high capacity for transport of the runoff and cause overland flow, and scour solutes and soil from the loessial slope (Table 2). ...
Context 3
... bulk densities were 1.35, 1.32, and 1.3 g cm −3 for the silty clay, silty loam, and sandy loam soils, respectively. The runoff intensity, r(t), and the runoff time, t p , were measured directly ( Table 2). The soil sorption-partition coefficient, k, was obtained by the method of linear isothermal adsorption, at 3.34 ml g −1 . ...
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Core Ideas
Generation of overland flow from 6.5 (control) and 10° lagged 30 min behind rainfall peaks, whereas the other slope gradients investigated synchronized with rainfall peaks.
Interflow comprised between 83 and 91% of total runoff.
The relationship of sediment loss flux and discharge of overland flow can be simulated by the power function a...
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Citations
... Thus, the higher volume and frequency of rainfall altogether with the texture characteristics of the Nitisol explain to great extend its higher runoff volume, sediment yield, and P losses. The greater slope increases the displacement speed of the flowing water, reducing the stability of soil particles (Yang et al., 2015). In addition, greater slopes potentiate sediment losses due to the greater angle of impact of raindrops and, consequently, greater shear capacity of the soil (Liu et al., 2015). ...
... In addition, greater slopes potentiate sediment losses due to the greater angle of impact of raindrops and, consequently, greater shear capacity of the soil (Liu et al., 2015). Additionally, with the increase in slope, there is an increase in the effective depth of soil that interacts with the flow (Yang et al., 2015). Nutrients adsorbed to soil particles are also lost more significantly in steeper areas (Berger et al., 2010;Fang et al., 2015). ...
The objective of this study was to quantify the losses of water, sediments and phosphorus (P) fractions by surface runoff as a function of terrain slope and P rates applied in two soils with contrasting textures. Six field trials installed in 2015 were evaluated in 2018 and 2019, in a Nitisol and in a Cambisol, with 642 and 225 g kg − 1 of clay. Averages of 0, 55, 110 and 220 kg ha − 1 year − 1 of P were applied superficially, corresponding to 0, 32.5, 65, 130 m 3 ha − 1 year − 1 of pig slurry. Pig slurry was applied under three terrain slopes at each site: 10%, 20% and 30% in the Nitisol and 15%, 25% and 35% in the Cambisol. After natural rainfall events, the drained solution was collected and the flow volume, amount of sediments and fractions of dissolved reactive P (DRP), particulate P (PP) and total P (TP) lost by surface runoff were determined. At the beginning of 2019, soil samples were collected in the 0-10 and 10-20 cm layers and the Mehlich-1 extractable P was determined. Increase in terrain slope substantially increased the losses of water, sediments and P. Considering the highest slope of each site, the losses of water, sediments and TP in the Nitisol were 35.3, 13.5 and 21.8 times higher than in the Cambisol. Mehlich-1 extractable P in the Nitisol was 1.7 times higher than that observed in the Cambisol. DRP represented about 73% of the total P lost, but the participation of PP increased with the increase in slope. It was concluded that the Nitisol undergoes higher losses of water, sediments and P by surface runoff, compared to the Cambisol, much due to the higher rainfall volume, rate of transported material, lower water infiltration in the soil profile and accumulation of P in the surface layer of the soil.
... Thus, to improve the prediction capacity of P losses potential of agricultural areas to aquatic environments, models such as P-threshold proposed for southern Brazil, need to incorporate other variables related to P transport, among them, the slope is one of the most impactful ones in the P transport because it is positively related to soil and water losses (Borda et al., 2014;Bouraima et al., 2016;Khan et al., 2016;Mahmoodabadi and Sajjadi, 2016;Morbidelli et al., 2016;Sharpley, 1985;Yang et al., 2015), in addition to being easy to determine in the field. Coupled with that, the clay content can also affect the proportion of macropores and micropores, changing the dynamics of water infiltration into the soil. ...
... Lourenzi et al. (2015) assessing P losses by runoff in no-till areas under grain cropping and subjected to pig slurry application observed values ranging from 2.4 to 50.4 kg P ha −1 year −1 , which was attributed to the rate of pig slurry input, rainfall volume, and soil coverage. The increase in the land slope increases the effective depth of soil that interacts with the runoff (Sharpley, 1985;Yang et al., 2015) and, consequently, increases the volume of soil that contributes to the loss of P (Ahuja et al., 1982;Dong et al., 2013). This effect, associated with the higher volume of water and sediment losses with the increase in slope, resulted in the increase of P losses in all fractions evaluated, regardless of the soil. ...
Phosphorus (P) loss from agricultural areas to waterbodies is a worldwide concern. However, the effect of soil source and transport factors, as clay (C) content and slope (S) degree, under the magnitude of the P transport in Brazilian Subtropical soils still incipiently know. The objectives of this study were i) to quantify the loss of P fractions by runoff in areas receiving pig slurry application and with variations in S and C content; ii) propose an environmental critical limit model of P (P-threshold) for Brazilian Subtropical soils. Thus, two series of experiments were conducted from 2016 to 2018, one under a Nitisol with 642 g kg ⁻¹ of C and another under a Cambisol with 225 g kg ⁻¹ of C. The treatments were four P rates (0, 56, 112 and 224 kg ha ⁻¹ year ⁻¹) superficially applied as pig slurry, on Tifton (Cynodon sp) pasture, and three S (10, 20 and 30% in the Nitisol and 15, 25 and 35% in Cambisol). P losses increased in both soils as the S and P rates rase. The clayey soil showed P losses three times higher than the less clayey one. Soil S above 25% promotes P losses at a rate three times higher than in soil below this limit. Consequently the P-threshold is proposed in Brazilian Subtropical soils being “P-threshold = (42.287 + C) - (0.230 S + 0.0123 CS)” in soils with a S of up to 25% and " P-threshold = (42.287 + C) - (-0.437 S + 0.039 CS) ” in soils with a S of more than 25%, where both C and S are shown in percentage. The soil clay content and slope degree are aggravating factors to the P transfer process, thus must be considered in suitable models to predict the P losses risk.
... These models were adopted to simulate the nutrient transfer process with ponding under rainfall conditions and the ensemble Kalman filter model was used to eliminate errors in the experimental observation data. Therefore, models based on mixed layer theory have been widely used in predictions of nutrient transfer on slopes because of their clear physical meaning Tong & Yang, 2008;Yang et al., 2016c;Yang, Wang, Xu, & Lv, 2015). ...
... The exchange layer is the uppermost thin layer in the soil profile. Chemical transport in the exchange layer is mainly controlled by infiltration, hydrodynamic dispersion, and raindrop splash erosion (Dong et al., 2013;Gao et al., 2004;Yang et al., 2015). This is calculated as: ...
... Both d e and e r increased with an increase in rainfall intensities; they increased from 0.68 to 1.32 and from 0.006 to 0.023 respectively. This conclusion was consistent with the increase in soil erodibility as rainfall intensity increased (Yang et al., 2015). The R 2 values of nitrate-N and ammonia-N loss rates were distributed across 0.834 to 0.922 and 0.800 to 0.921 respectively. ...
Under natural rainfall, the surface runoff erosion of sloping farmland tends to remove large quantities of soil particles and constitutes nonpoint source pollution. The existing sediment and nutrient loss models focus on estimating the total amount of pollutants in the long term. The Existing mathematical models that describe the nutrient loss process on slopes have some shortcomings, which have not accounted for the effect of infiltration on nutrient concentrations in the exchange layer before runoff starts. Here, an approximate semianalytical model of sediment yield and nutrient loss was based on surface runoff processes. Simulated rainfall experiments were performed to calibrate the model's parameters and verify its reliability. The established model incorporated raindrop splashing, diffusion, and water infiltration effects on nutrient transfer in the exchange layer. Raindrop splashing played a leading role in nutrient translocation from the exchange layer to runoff. The simulated runoff, sediment, and nutrient matched their measured values reasonably well (R² > 0.8; Nash–Sutcliffe efficiency > 0.347). The model's sediment yield items were more sensitive to runoff erosion than splash erosion. The raindrop‐induced water transfer rate in the nutrient loss simulation dramatically affected the peak nutrient loss rates, whereas the depth of the exchange layer clearly affected the overall range of change in nutrient loss rate and boosted the total nutrient loss. Therefore, measures such as vegetation coverage or deep fertilization should be adopted to weaken raindrops’ kinetic energy and reduce nutrient concentrations in the exchange layer to prevent agricultural nonpoint source pollution in the Loess Plateau.
... For simple and practical applications, the depth of 10 mm was incorporated in many agriculture chemical transport models, such as CREAMS (Chemicals Runoff and Erosion from Agriculture Management, Knisel 1980), AGNPS (Agricultural Nonpoint Source, Young et al. 1987), SWAT (Soil And Water Assessment Tools, Arnold et al. 2012), ANSWERS (Areal Nonpoint Source Watershed Environment Response Simulation, Bouraou and Dillaha 1996), etc. The results showed that the depth of mixing layer increased with the increase of rainfall intensity, rainfall time and runoff energy, slope degree, surface coverage, soil moisture, and permeability of the soil surface layer (Ahuja 1986;Yang et al. 2015). According to the potassium loss experiments under simulated rainfall with clay loam soil in Yangling County, Yang et al. (2016) put forward that the effective mixing depth in complete mixing model, the effective mixing depth in incomplete mixing model, and the equivalent depth of transfer could be expressed with a regression equation related to rain intensity, slope gradient and initial soil content, respectively. ...
... Ahuja et al. (1981) put forward that although the amounts of 32 P coming off the 1.5-and 2.0-cm 32 P placements were relatively much smaller in comparison with that from soil surface and shallower placements, the actual mixing depth of soil interacting with rainfall and runoff might exceed 2.0 cm. Furthermore, the mixing layer depth was influenced with solute properties (Zhang et al. 2007;Yang et al. 2015). According to the artificial rainfall experiments with sandy loam soil in Ansai County, Wang (2006) used the equivalent mixing depth model to calculate EDI of soil nutrients, and obtained the EDI order of nitrate nitrogen > potassium > phosphorus. ...
... 3.1 Br − transport amount with surface runoff Under rainfall condition, the initial soil moisture of slope would affect runoff initiation time, surface runoff amount, and water infiltration with permeable bottoms (Heathman et al. 1985;Zhang et al. 1997b;Yang et al. 2015Yang et al. , 2016. The average runoff initiation time for 3.5% soil moisture experiments was 3.37 and 13.65 times that of the 10 and 20% ones, respectively (Table 1). ...
Purpose
The mixing zone depth is a critical parameter in many popular agricultural non-point source pollution (NPS) models. Its variation for some special soil conditions and easily erosive region was limitedly studied. This study dealt with the extent of Br⁻ releasing from soil to surface runoff, the actual mixing depth and the calculated one on the unsaturated loess slope, and the influences of soil initial moistures.
Materials and methods
Br⁻ was placed as a tracer at different soil depths in the loess slope with three soil initial moistures. Br⁻ concentration in surface runoff and soil profiles was monitored under simulated rainfall condition. The actual mixing layer depth was determined by whether Br⁻ in that layer could be detected in surface runoff during the whole rainfall process. The average effective depth of interaction (EDI) was calculated by the confirmation method reported before.
Results and discussion
The shallower the application depth, the higher the Br⁻ concentration and loss risk in surface runoff. The net loss rate had an exponential decreasing correlation with the solute-applied depth. The depth of Br⁻ peak content in soil profile after the rainfall ended increased with the application depth. Br⁻ concentration in the surface soil was more than that in the runoff at the end of rainfall, which indicated an incomplete mixing between runoff water and soil water in the mixing layer. Under this experimental condition, the actual mixing layer depth for 3.5% soil moisture slope was about 3 cm, that for 10% soil moisture was 6 cm or so, and that for 20% soil moisture was more than 7 cm. The average EDI calculated for 3.5, 10, and 20% soil moisture was 2.31, 3.76 and 4.95 cm, respectively, which were less than the actual mixing layer depth and more than some former studies.
Conclusions
The traditional 1.0-cm mixing depth in many agricultural NPS models might not be so exact for some special region.
... Experimental chemical transfer to runoff simulated by these models typically declined exponentially with time during the initial stage of overland flow initiation [2,24,25], and model performance showed a good agreement with the observed data [26]. Wang et al. [12] found that model performance of soluble phosphorus transfer under water scouring was better than NO 3 -N. ...
... The runoff time for various treatments, t p , were measured by stopwatch and listed in Table 2. Rainfall intensities, R, were 0.4, 1.0 and 1.8mm min -1 . The soil adsorption rates obtained by linear isothermal adsorption method [24], Author Copy • Author Copy • Author Copy • Author Copy • Author Copy • Author Copy • Author Copy • Author Copy • Author Copy were 2.34, 0.83 and 2.06 cm 3 g -1 for NH 4 -N, NO 3 -N and TN respectively. For the refined time-increasing h m , the basic mixing depth parameter, h n was determined using 1 cm as the simplicity of the effective mixing model and we achieved optimal fitted results at this value while the initial mixing depth parameter, h 0 , was obtained from curve fitting as well as time-averaged h m in the original model. ...
... Among the parameters of the nutrient transport model, soil detachability has been confirmed to be closely related to the sediment concentration, runoff coefficient, slope gradient, and initial soil water content, but the relationship with slope length is unknown (Dong et al., 2013;Yang et al., 2015). According to Table 4, with the increase in rainfall intensity and slope length, e r , a, and e showed an increasing trend. ...
... According to Table 4, with the increase in rainfall intensity and slope length, e r , a, and e showed an increasing trend. This result agreed well with the conclusion that the soil detachability increased with the increase in rainfall intensity (Yang et al., 2015). The results also indicated that the soil detachability increased with the increase in slope length. ...
Soil, water and nutrient losses are major causes of environmental pollution, with runoff accompanied by nutrient transport and sediment loss. The existing runoff and erosion models focus on estimating the total amount of pollutants in the long term. There are few studies on the process of nutrient transport during individual rainfall events, and there are still some shortcomings in the mathematical models that describe the nutrient transport process on slopes with consideration of both the dissolved and adsorbed solute in the runoff. In this study, a mathematical model was constructed for describing the nutrient transport process during individual rainfall events by combining a dissolved solute transport model and an adsorbed solute transport model. After adding the nutrient model to the runoff and erosion model KINEROS2, the runoff, sediment yield, and total nitrogen loss on slopes during individual rainfall events were simulated, and the simulation results were verified using a field experiment with different rainfall intensities and different slope lengths. The results showed that the behaviour of the total nitrogen loss was consistent with the runoff and the sediment yield. The values all first increased and then gradually stabilized, and the time to reach steady state was shortened with the increase in rainfall intensity. The runoff and sediment yield simulated by KINEROS2 were consistent with the measured data, indicating that KINEROS2 could successfully simulate the processes of runoff and erosion in runoff plots (NSE > 0.22; R² > 0.35). Likewise, the amount of total nitrogen loss at different time points was simulated well (NSE > 0.36; R² > 0.54). Therefore, KINEROS2 shows potential for simulating nutrients and has good applicability on the runoff plot scale in the arid and semi-arid regions of China.
... The results showed that the depth of the exchange layer, which was influenced by the rainfall intensity and slope gradient, was between 0.4 cm and 0.6 cm. The results of Yang, et al. [42] indicated that the depth of the interaction zone increased with an increase of rainfall intensity and slope gradient, which was similar to our results. The mixing depth ranged from 0.08-0.38 ...
The removal of nutrients by overland flow remains a major source of non-point pollution in agricultural land. In this study, a mathematical model of ammonium nitrogen transport from soil solution to overland flow was established. The model treated the mass transfer coefficient (km) as a time-dependent parameter, which was not a constant value as in previous studies, and it was evaluated with a four-slope gradient and three rainfall intensities. The kinematic-wave equation for overland flow was solved by an approximately semi-analytical solution based on Philip’s infiltration model, while the diffusion-based mass conversation equation for overland nutrient transport was solved numerically. The results showed that the simulated runoff processes and ammonium nitrogen concentration transport to the overland flow agreed well with the experimental data. Further correlation analyses were made to determine the relationships between the slope gradient, rainfall intensity and the hydraulic and nutrient transport parameters. It turned out that these parameters could be described as a product of exponential functions of slope gradient and rainfall intensity. Finally, a diffusion-based model with a time-dependent mass transfer coefficient was established to predict the ammonium nitrogen transport processes at the experimental site under different slope gradients and rainfall intensities.
... The ecological environment of the Loess Plateau is threatened by soil erosion, so the sample was representative. The samples were dried out (2.3% soil-water content), and visible organic material was discarded (Yang et al. 2015). A 5-mm mesh was used to separate out the soil. ...
... where C r is the solute concentration in runoff. Yang et al. (2015) found that the soil solute concentration in the course of slope rainfall decreased with a power function. So, the soil nutrient concentration at different times during rainfall is written as ...
Overland flow caused by rainfall is one of the critical factors influencing soil erosion and loss of soil nutrients. Therefore, the study on the mechanism and controlling measures of soil nutrient transport proposed is considered important. A simulation experiment was performed to investigate the effects of polyacrylamide application rates (0, 1, 2, 4, and 8 g/m²) and flow rates (400 ml/min, 600 ml/min, and 800 ml/min) on runoff, infiltration rate, soil losses, and the concentration of ammonium nitrogen (NH4⁺) in runoff at loess slope (0.8 m (width) × 1.5 m (length) and 5°). As the results suggest runoff, sediment loss, and soil nutrient loss increased by increasing flow rate. Applicable amount of polyacrylamide (PAM) can effectively increase infiltration and reduce soil erosion, but excess amount of dissolved PAM would plug porosity of soil which could decrease the infiltration. The ammonia nitrogen loss amount was decreased with the increase of the PAM application rate. The ammonia nitrogen loss amount respectively decreased by 40.0%, 57.0%, 59.1%, and 63.4% with the PAM application rate of 1, 2, 4, and 8 g/m². The best performance with the coefficient of determination (R²) showed that the ammonium transport with runoff can be well described by the proposed model in flow scour experiments of this study. Furthermore, the model parameter b has a significant positive exponential relation with the total amount of sediment.
... However, omission of soil inversion leads to gradual P stratification (i.e., accumulation of labile P in the uppermost soil layer) (Thompson and Whitney, 2000;Cook and Trlica, 2016;Baker et al., 2017). This layer is highly influential in determining dissolved reactive P (DRP) concentration in overland flow (Sharpley et al., 1978;Ahuja et al., 1982;Yang et al., 2015). Consequently, the P stratification in no-till soils results in elevated DRP concentrations in surface runoff and often higher DRP losses in overland flow than from plowed soil (Sharpley and Smith, 1994;Puustinen et al., 2005;Smith et al., 2015a). ...
No‐till as a water protection measure is highly efficient in controlling erosion and particulate P (PP) loss but tends to increase dissolved reactive P (DRP) concentrations in runoff water. In a 9‐yr field study on a clay soil in Southwest Finland, the effects of no‐till and autumn plowing on surface runoff and subsurface drainage water quality were compared. The site had a 2% slope and was under spring cereal cropping, with approximately replacement fertilizer P rates. Vertical stratification of soil‐test P that had developed during a preceding 6‐yr grass ley was undone by plowing but continued to develop under no‐till. During the 9‐yr study period, no‐till soil had 27% lower cumulative total P losses than plowed soil (10.0 vs. 13.7 kg total P ha ⁻¹ ). Concentrations and losses of PP were clearly lower under no‐till than under plowing (5.6 vs. 12.3 kg PP ha ⁻¹ ), but DRP loss showed the opposite trend (4.3 vs. 1.4 kg DRP ha ⁻¹ ). There was an increasing trend in subsurface drainflow DRP concentration under no‐till, possibly because of development of a conductive pore structure from soil surface to drain depth. The potential benefit of no‐till in water protection depends on how much of the PP transported to water is transformed into a bioavailable form and used by aquatic organisms. The beneficial effect of no‐till in controlling P‐induced eutrophication at the study site would only be realized if the bioavailable share of PP exceeds 43%. Otherwise, no‐till would not be an efficient eutrophication control measure at this site.
Core Ideas
No‐till decreased total P losses by 27% compared with autumn plowing.
No‐till produced 4.5‐fold higher DRP loss and 54% lower PP loss than plowing.
When changes in DRP and PP are opposite, TP changes should be interpreted with caution.
In this case, the effect on eutrophication largely depends on PP bioavailability.
At the study site, increased DRP load is compensated if PP bioavailability is >43%.
... Guo et al. (2010a, b) performed indoor and outdoor experiments on the transport of sediments and solutes in the runoff from stone-covered soil surfaces. Several physical-based models were refined and applied to describe the process of solute transport into runoff on loessial slope land Yang et al. 2015Yang et al. , 2016. In the indoor experiments, an interaction was observed between the effects of rainfall splash and water scouring on the transport of sediment and solutes in the runoff. ...
Overland flow and concomitant solute transport were a major source of pollutants in receiving surface water. The objective of this study was to better understand the mechanisms of soil erosion, solute transport from soil to runoff and lost via runoff, especially the effects of cumulative infiltration before the runoff generation. Laboratory experiments were conducted with three initial soil moisture contents, three rainfall intensities and three slope gradients to evaluate the effects of these variables and their interactions on soil erosion and solute losses to the runoff. The results indicated that if infiltration could be facilitated, the loss of solutes could be increased. Rainfall intensity increases the mass of sediment carried away by the runoff, decreases the time required for runoff formation and increases the solute content in the surface layer. Both the masses of solute and sediment in the runoff increase as the slope gets steeper. The rainfall splash and infiltration before runoff generation were found to play important roles in soil erosion and solute lost to the runoff, if ponding time could be prolonged, the loss of solutes could be reduced. The relationship between cumulative infiltration during ponding time and the average solute concentration in the runoff can be well described by the linear equations. The average solute concentration in the runoff was positive linear correlation with solute concentration in the soil surface layer at the time when runoff took place.
