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Natural hillslopes are mostly composed of complex slope shapes, which significantly affect soil erosion. However, existing studies have mainly focused on uniform slopes to simplify complex hillslopes, and the mechanisms responsible for the influence of slope shape on soil and nutrient losses are still not well understood, especially in the application of soil improvers to reduce soil loss. To investigate the effects of slope shape and polyacrylamide (PAM) application on runoff, soil erosion and nutrient loss, this study conducted artificial field rainfall experiments involving two PAM application rates and nine slope shapes. The results indicate that the average amount of soil loss from convex slopes was 1.5 and 1.3 times greater than that from concave and uniform slopes, respectively, and the average amount of ammonia nitrogen loss and phosphate loss increased by 24.0%–58.6%. Soil and nutrient losses increased as the convexity of the convex slopes increased. For runoff, there was little difference between concave and convex slopes, but the runoff amount for both slopes was greater than that for uniform slopes. After PAM application, the soil loss decreased by more than 90%, and the nutrient loss decreased by 28.2%–68.1%. The application of PAM was most effective in reducing soil erosion and nutrient loss from convex slopes, and it is recommended to appropriately increase the PAM application rate for convex slopes. A strong linear relationship between ammonia nitrogen and phosphate concentrations and sediment concentrations was found in the runoff on slopes with no PAM application. However, this linear relationship weakened for slopes with PAM application. The findings of this study may be valuable for optimizing nonpoint source pollution management in basins. [ABSTRACT FROM AUTHOR]

Raindrop splashing is one of the driving forces of soil erosion, and it also leads to the loss of soil nutrients. However, the effects of raindrop splashing on nitrogen loss and the mechanisms of detachment are still not well understood, especially under different types of rainfall and soil amendment applications, such as polyacrylamide, which has been widely used to reduce soil erosion. In this paper, indoor artificial rainfall experiments were performed to investigate the impact of the raindrop diameter and polyacrylamide (PAM) applications on runoff and soil and nitrogen losses. Three raindrop diameter treatments (1.52, 2.45 and 3.59 mm) and three PAM application treatments (0, 1.0 and 2.0 g/m2) were applied to Kastanozem soil. The results indicated that the infiltration rate, sediment rate and nitrogen concentration in the runoff decreased sharply with the rainfall duration for the first 10 min, but the runoff rate increased under simulated rainfall splashing. In general, the sediment rate for runoff and nitrogen loss increased with the raindrop diameter. The amounts of runoff, sediment, and ammonia and nitrate nitrogen loss were highly reduced with the addition of PAM. The soil and nitrate nitrogen loss decreased with the increasing PAM application rates, and a PAM application rate of 2 g/m2 was optimized for the soil of the test area. Moreover, the ammonia and nitrate nitrogen concentrations were linearly proportional to the sediment rate in the runoff, and the slopes of the linear regression equations increased with the increasing raindrop diameter but were reduced by PAM application. This study provides effective information on the runoff, soil erosion and nitrogen loss that occur during rainfall splash, and it can improve our understanding of splash erosion and nutrient transport. • The amount of raindrop splash and nitrogen loss was increased in the rainfall with the increase of raindrop diameter. • Polyacrylamide application improves soil conditions thus decreasing runoff, raindrop splash and nitrogen loss. • The ammonia and nitrate nitrogen concentration were linearly proportional to the sediment rate in runoff. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Unlabelled Image Highlights • Loss trend of total nitrogen is consistent with that of runoff and sediment yield. • Soil detachability was increased with the increase in slope length. • A new method was proposed to simulate the loss process of total nitrogen. • KINEROS2 model has good applicability on the runoff plot scale. [ABSTRACT FROM AUTHOR]

Slope length effects on the processes of soil erosion have been the focus of research on hillslope hydrology and sediment transport. A field experiment was conducted to investigate the effects of slope lengths (1, 5, 10, 15 and 20 m) and rainfall intensities (75, 50 and 25 mm h − 1 ) on runoff, soil and total nitrogen (TN) losses under simulated rainfall conditions. Kastanozem was selected in the experiment. Generally, runoff rates and runoff-associated TN loss rates decreased with slope length, whereas sediment and sediment-associated TN losses increased with slope length under three rainfall intensities. The relationship between runoff and time could be described by the Horton infiltration model, with a correlation coefficient R 2 > 0.85. The function parameters of final infiltration rate ( i f ) and coefficient ( c ) were closely related to slope length, suggesting that a model of runoff processes correlated to slope length was established. There was a significant positive power relationship between runoff and sediment yield rates ( p < 0.01). Runoff-associated TN losses were mainly controlled by runoff rates, whereas sediment-associated TN losses were mainly controlled by sediment yield rates, and positive linear correlations best represented their relationships. Because sediment-associated TN losses dominated the total TN losses, sediment yield rates were positively correlated with the total TN losses. Increasing rainfall intensity generally increased runoff, sediment yield and TN loss rates, but changes in rainfall intensity did not influence their relationships. This study demonstrated that a model could be established to simulate the processes of TN loss for different slope lengths. [ABSTRACT FROM AUTHOR]