Search

• A novel model integrating hillslope and in-stream sediment processes is developed. • We quantified the effects of soil-water conservation (SWC) on the Loess Plateau. • SWC contributes to 54.4% and 91.9% of the decline in discharge and sediment load. • Sediment reduction effect of hillslope SWC is more lasting compared to that of check dams. Soil erosion and sediment transport processes, which are intimately connected with hydrological processes, strongly affect land surface morphology and earth system dynamics. Over the past 60 years, intensive Soil-Water Conservation (SWC) measures implemented on the Loess Plateau have significantly reduced sediment load and concurrently exacerbated runoff declines, while the quantitative evaluation of the effects of SWC measures remains challenging. This study develops a sediment module which simulates the hillslope and in-stream sediment processes, and then incorporates the module into a Geomorphology-Based Ecohydrological Model (GBEHM). Besides, the model also couples with an explicit representation of different types of SWC measures, including both Hillslope SWC (HSWC) and River-network SWC (RSWC) measures. The newly developed hydro-sediment model is then applied to the Kuye River basin, a typical river basin on the Loess Plateau, and used for quantifying the effects of SWC measures on river discharge and sediment load during 1982–2019. Compared with Period 1 (1982–2000), the river discharge decreased by 48.7% in Period 2 (2001–2019), while the sediment load experienced a more substantial decrease of 95.3% between the two periods. Based on the numerical experiment results, HSWC and RSWC contributed to 25.4% (58 million m3/yr) and 28.9% (66 million m3/yr) of the annual runoff decline, as well as 58.1% (36 million t/yr) and 33.9% (21 million t/yr) of the annual sediment load reduction between the two periods, respectively. Besides, HSWC plays an increasingly important role in sediment reduction in recent years due to check dam silting. The model developed in this research is useful to evaluate the multi-faceted effects of existing SWC measures and to help with future SWC planning and policymaking. [ABSTRACT FROM AUTHOR]

Water erosion, a notorious major threat to food security and ecosystem sustainability, is strongly conditioned by spatial and temporal scale effects. This paper systematically reviews the scale issues in runoff and sediment delivery (SIRSD) as a research field by integrating the traditional review approach and bibliometric analysis. This review summarises SIRSD's roots and the scale effect on runoff and sediment delivery. Then, we provide quantitative insights into the SIRSD domain's development history, thematic structure, geographic distribution, international cooperation, and methodologies. Findings show that: i) SIRSD arises from the gap between the non-linearity of runoff and sediment delivery across scales and our ability to measure it. Point-based and short-term measurements cannot capture the non-linearities from the spatio-temporal heterogeneities and cross-scale interactions of factors or processes. ii) Previous literature provides evidence that the spatial scaling of specific runoff (r), soil erosion (SE), sediment yield (SSY), or sediment delivery ratio (SDR) with drainage area (A) or slope length (L) exhibits contrasting patterns due to distinct mechanisms. Infiltration-excess and saturation-excess processes account for inverse and positive r - A relations, respectively. Interrill-erosion and rill-erosion cause inverse and positive SE-L relations. Hillslope-erosion and channel/bank-erosion explain inverse and positive SSY-A relations. Downstream increasing deposition and additional sediment inputs drive inverse and positive SDR-A relations. These scaling relationships can be nonlinear or complex due to spatial heterogeneities in land use, vegetation, topography, climate, lithology, and soil characteristics. Hence, applying an empirical scaling equation developed from the region with distinct environmental contexts is not recommended. Furthermore, the existing scaling patterns or equations may require updating given global climate and land use change. iii) SIRSD is a complex and multidisciplinary issue investigated by scientists from 93 countries since 1928. International research has substantially facilitated the understanding of SIRSD; still, more collaboration should focus on less-developed countries with high soil and water loss risks and urgent conservation needs, such as those in Africa and South America under cropland expansion. iv) Scale mismatch and scale break have discredited large-scale erosion and sediment assessments. Incorporating gully and bank erosion into modelling, extending the scale range of the L factor, and expanding the sediment scaling scope from watershed to slope may make a difference. Therefore, more research with nested design incorporating multiple scales is necessary for cross-scale analysis and scalable modelling. Addressing global climate change requires improving real-time urban flood forecasting and integrating downscaled climate models with hydrology, erosion, and sediment transport models. • A bibliometric review of the global SIRSD research for the first time. • SIRSD is rooted in the gap between natural nonlinearity and our measuring ability. • Scaling of specific runoff, erosion, sediment yield, and SDR has diverse patterns. • Scale mismatch and scale break discredit large-scale modelling and assessments. [ABSTRACT FROM AUTHOR]

• The runoff, sediment load and runoff erosion power decreased significantly. • Compared with runoff, runoff erosion power-sediment relationship is better. • The power function of runoff erosion power and sediment is better than linear. • Erosion in particular geographic locations responds strongly to runoff erosion power. In recent years, the acceleration of urbanization in the Yangtze River Economic Belt (YREB) has brought about problems such as soil erosion, ecosystem degradation and decline in ecological service functions. Therefore, this paper selects the Fujiang River Basin (FRB) in Upper Yangtze River (UYR), and analyzes the relationship between runoff erosion power (REP) and sediment transport (ST) on the basis of analyzing the variation characteristics of hydrological elements. Based on SWAT model, a variety of scenarios are set up to quantitatively analyze the impact of different land use changes on runoff and ST and REP in the basin. The results indicated that: (1) The annual precipitation in FRB from 1960 to 2018 did not change significantly, while the annual runoff, annual ST and annual REP decreased significantly. Compared with runoff and runoff depth, the relationship between sediment transport modulus (STM) and REP is the best, especially the power function between them is better than the linear function. (2) The results of the evaluation indexes of the simulation results of the SWAT model based on the measured runoff and sediment data from 2008 to 2018 are pass and above, that is, the simulation results are considered reliable. (3) Under the five scenarios of conversion of sloping farmland to forest, conversion of dry land to paddy field and conversion of grassland to bushland and forest land, the runoff and ST in the basin decreased but the overall range was small. The simulation results of SWAT model show that the erosion of specific areas in the basin shows the greatest degree of weakening with the decrease of REP. [ABSTRACT FROM AUTHOR]

• Rainfall and runoff explained 70–85% of sediment yield variability in two karst watersheds. • Specific rainfall and runoff variables affecting sediment yield the most were identified. • The PLSR model provides a convenient way of solving variable collinearity. As one of the largest and most typical continuous karst distribution belts in the world, Southwest China is vulnerable to soil erosion and rocky desertification because of its unique geological conditions and heterogeneous landscapes. Understanding the rainfall-runoff-sediment transport relationships is critical to effectively controlling soil erosion in karst watersheds. This study aims to evaluate the sediment yield variability at different temporal scales (daily, monthly/seasonal, and annual) from 2014 to 2019 and to further identify the rainfall and runoff variables most associated with sediment yield in the selected Mahuangtian (2.26 km2) and Muzhaihe (0.09 km2) karst watersheds. Since rainfall and runoff variables were highly codependent, the partial least squares regression (PLSR) model was used to quantify the relative importance of rainfall and runoff variables to sediment yield. The variable importance of the projection (VIP) scores>1 was considered to be the most influential predictor of the PLSR model. Results showed that sediment yield was greatly influenced by rainfall and runoff, which can explain 70% and 85% of the variation of sediment yield in the Mahuangtian and Muzhaihe watersheds, respectively. For rainfall variables, three-day antecedent precipitation (VIP = 1.41) and five-day antecedent precipitation (VIP = 1.28) were the main first-order factors controlling sediment yield in the Mahuangtian watershed. In contrast, the rainfall amount (VIP = 1.35) was the dominant factor influencing sediment yield in the Muzhaihe watershed. For runoff variables, runoff amount, runoff coefficient, and maximum discharge were the primary variables controlling the sediment yield in these two karst watersheds. By partially eliminating the co-dependency of the variables, the PLSR approach can conveniently determine the dominant factors controlling sediment yield in heterogeneous karst watersheds. [ABSTRACT FROM AUTHOR]

Soil and water loss from farmland causes land degradation and water pollution, thus continued efforts are needed to establish mathematical model for quantitative analysis of relevant processes and mechanisms. In this study, an approximate analytical solution has been developed for overland flow model and sediment transport model, offering a simple and effective means to predict overland flow and erosion under natural rainfall conditions. In the overland flow model, the flow regime was considered to be transitional with the value of parameter β (in the kinematic wave model) approximately two. The change rate of unit discharge with distance was assumed to be constant and equal to the runoff rate at the outlet of the plane. The excess rainfall was considered to be constant under uniform rainfall conditions. The overland flow model developed can be further applied to natural rainfall conditions by treating excess rainfall intensity as constant over a small time interval. For the sediment model, the recommended values of the runoff erosion calibration constant ( c r ) and the splash erosion calibration constant ( c f ) have been given in this study so that it is easier to use the model. These recommended values are 0.15 and 0.12, respectively. Comparisons with observed results were carried out to validate the proposed analytical solution. The results showed that the approximate analytical solution developed in this paper closely matches the observed data, thus providing an alternative method of predicting runoff generation and sediment yield, and offering a more convenient method of analyzing the quantitative relationships between variables. Furthermore, the model developed in this study can be used as a theoretical basis for developing runoff and erosion control methods. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are being used in many products as they have unique antimicrobial-biocidal properties. After disposal of these products AgNPs can reach the soil environment possibly affecting soil organisms and disrupting plants. This work aimed to study the transport of AgNPs by water and sediment during overland flow and soil erosion. This was done in a laboratory setting, using a flume and rainfall simulator. A low concentration of AgNPs (50 μg·kg − 1 ) was applied to two soil-flumes with slope percentages of 20% and 10%. The rainfall was applied in four events of 15 min each with a total amount of rainfall of 15 mm during each event. After applying the rainfall, samples of the non-transported background soil (BS) and the transported sediment (Sf) were collected from the flume surface. Runoff sediment (RS) and water (RW) were collected from the outlet. AgNPs were detected in all samples collected. However, concentration varied according to sample type (soil or water), time of collection (for runoff water and sediment) and the slope of the soil flume. Higher concentrations of AgNPs in soil were detected in the BS than in the Sf likely due to the BS having more fine particles (silt and clay). The AgNPs concentration in the runoff sediments increased with subsequent applied rain events. In addition, increasing the slope of the flume from 10% to 20% increased the total AgNPs transported with the runoff sediment by a factor 1.5. The study confirms that AgNPs can be transported by both overland flow and sediment due to erosion. [ABSTRACT FROM AUTHOR]

Runoff and sediment yield in semi-arid catchments are highly influenced by infrequent but very heavy rains. These events occur over short temporal scales, so runoff and sediment transport can only be understood using an event-based analysis. We applied a hydrological and soil-erosion model, LISEM, to the Gule catchment (~ 12 km 2 ) in northern Ethiopia. The objectives of the study were: (a) to evaluate the performance of LISEM in describing event-based hydrological processes and sediment yield in a catchment under the influence of different water harvesting techniques (WHTs), and (b) to study the effect of the WHTs on catchment-scale event-based runoff and sediment yield. The model performed satisfactorily (NSE > 0.5) for most of the events when discharge was calibrated at the main outlet (Gule) and at a sub-outlet (Misbar). Runoff coefficients for the Gule catchment and Misbar sub-catchment were expectedly low due to the implementation of WHTs, which can store runoff from the rains and increase infiltration into the soil. Simulated and measured sediment yields were of similar orders of magnitude. LISEM generally overestimated sediment yield compared to the measurements. The poor performance of LISEM in predicting sediment yield could be attributed to the uncertainty of several factors controlling soil erosion and the inadequacy of LISEM in describing soil erosion on steep slopes. Catchment-scale model simulations indicated that runoff and sediment yield could be effectively reduced by implementing WHTs. The model estimated 41 and 61% reductions in runoff and sediment yield at the Gule outlet, respectively. Similarly, runoff and sediment yield at the Misbar sub-outlet were reduced by 45 and 48%, respectively. LISEM can thus be used to simulate the effects of different existing or new WHTs on catchment hydrology and sediment yield. The results of scenario predictions could be useful for land-use planners who intend to implement different measures of catchment management. [ABSTRACT FROM AUTHOR]

• Physically based 2D hydrodynamic and sediment transport model, CCHE2D. • High resolution mesh, topography photogrammetry, experimental landform evolution. • Watershed hydrology, raindrop soil detachment, displacement, erosion and transport. • Distributed solution, tilled watershed, cornfield tillage ridge and furrow morphology. • Simulated runoff, sediment transport, landform evolution; channel network analysis. Soil and gully erosion is a critical threat to sustainable agricultural land management and productivity. Soil erosion by rain splash, sheet runoff, and concentrated flow are complex problems conditioned by the combined interactions of soil physical properties, hydrology, human activity, landscape topography, and climate. Effective management of erosion processes driven by rainfall and surface runoff requires a combined effort of field observation, physical experimentation, and numerical simulation. A physically-based hydrodynamic numerical model, CCHE2D with updated raindrop erosion effects, is applied to simulate landscape evolution processes as a result of raindrop impact and overland flow. The numerical model simulates a thin layer of runoff and concentrated flow over complex terrains, and predicts sediment transport due to raindrop splash detachment, transport and soil surface erosions. Soil erosion and landform evolution simulations due to rainfall are presented for an experimental landscape and a tilled large scale agricultural field. Photogrammetric field data were collected using an unmanned aerial system (UAS) following planting and subsequent rainstorms. Numerical simulation results agreed well with the observed experimental soil surface topography, sediment yield, and drainage network developments. The simulated soil and gully erosion in the tilled field also agreed well with observations. This research successfully demonstrates how high resolution spatial and temporal topographic measurements in experimental and field landscapes can be simulated and interrogated by 2D physically-based hydrodynamic and morphodynamic models. The accurate predictions of tillage field and gully erosion process in agriculture watersheds with complex tillage conditions also indicated the usefulness of the model for studying soil and landscape degradation. [ABSTRACT FROM AUTHOR]

• Under the action of concentrated flow, the change of surface runoff of karst gently sloping farmland is mainly controlled by the magnitude of concentrated flow. • Under the action of concentrated flow, the underground runoff of karst gentle slope farmland is significantly negatively correlated with the slope. • Concentrated flow can lead to severe soil erosion in karst gently sloping farmland. Exposed bedrock in karst areas considerably alters runoff paths causing partial runoff to converge into a concentrated flow, which is a potential source of soil erosion risk. However, research is lacking on how concentrated flow affects regional soil erosion. In this study, the surface and underground dual structure in karst areas was simulated in a steel tank. Combined with runoff plot monitoring, the runoff conversion process and erosion characteristics of gently sloping farmland in karst areas under different water discharge rates were examined through indoor concentrated flow discharge scouring tests, and the influence of concentrated flow changes on the runoff spatial distribution and sediment yield in gently sloping farmland was clarified. The results demonstrated the following: (i) there existed a significant positive correlation between surface runoff and the water discharge rate (p < 0.01); the partial correlation coefficient value reached 0.87. The higher the water discharge rate, the more surface runoff formation was facilitated. (ii) When the slope remained the same, the underground runoff was relatively high at 3 L/min. Given the same discharge, a significant negative correlation between underground runoff and slope was found (p < 0.05); the partial correlation coefficient value reached −0.71. (iii) In response to a water discharge rate of 5 L/min, surface soil erosion was serious, and the maximum sediment transport modulus was 174.088 g/min∙m2. A significant cubic function relationship existed between the scouring time and surface sediment yield. Overall, a critical flow rate occurred between 3 and 5 L/min, which controlled changes in surface runoff, subsurface runoff and surface sediment yield. Under highly concentrated flow, drastic soil erosion could occur. These results can provide a scientific basis for the control and prevention of concentrated flow-induced erosion in karst areas. [ABSTRACT FROM AUTHOR]

Abstract: Different hydraulic parameters, including the hydraulic shear stress, unit length shear force, steam power, unit steam power, and effective stream power were used to quantify flow detachment. Most former studies were conducted for flow detachment under uniform slope surface conditions, while a few studies compared different slope surface conditions. The uniform bare loess was prepared in laboratory experiments. Natural fallowed soil loess with stone covers was prepared in field experiments. The objective of this study was to assess the differences in hydraulic parameters and sediment detachment under these different soil surface conditions. Our results show that the unit sediment load (Rs ) has a good linear relationship with the unit runoff rate (Rr ) for the flume and field experiments, and the relationship can be expressed as the function: Rs =0.262Rr −0.802 (R 2 =0.947). The rate of Manning roughness coefficient to mean flow depth (n/h) is a good hydraulic indicator like as the stream power and Reynolds number for predicting the sediment load. Hydraulic parameters n/h, Re, and ω are good indicators for the unit area sediment load for both the flume and field experiments, while Fr, f, and τ are good indicators for the unit area sediment load only when the flume experiments and field experiments are individually analyzed. Among the three good indicators (ω, Re , and n/h), n/h is better than the other two for predicting sediment load in rill erosion for both flume and field experiments, as well as for the unit solute transport rate (MBr ). The parameter of n/h probably is not only a good hydraulic parameter as an indicator for both sediment and solute transport, but also a good hydraulic parameter which link with runoff energies. The parameter n/h represents the flow wave of runoff and is an important factor to represent the energy for water and sediment transport, and the flow wave celerity (vw ) is related to n/h by: vw =1.585(n/h)−0.527 (R 2 =0.978). [Copyright &y& Elsevier]

Abstract: During runoff on soil surface, aggregates travel, abrade, and produce finer and more transportable particles, resulting in a significant effect on sediment transport, water infiltration and soil erosion. This study was to assess the effects of stability, transport distance and two hydraulic parameters on aggregate abrasion using Ultisols in subtropical China. Aggregate stability was investigated for soils from two parent materials (Shale and Quaternary red clay) with different land uses using LB methods. They were studied with a series of aggregate abrasion experiments in a 3.8m long flume with a fixed bed. Results indicated that slaking and mechanical breakdown were probably the main mechanisms of aggregate breakdown in these study soils. Two stages of aggregate abrasion process could be distinguished via the coefficient α in different transport distances. Aggregates were first rapidly abraded, became round, and was predominantly broken apart into smaller fragments, followed by weakly abrasion of smaller fragments and round aggregates, making them even light and less angular. A good multiple regression equation was obtained for estimating aggregate abrasion in overland flow with consideration of mechanical breakdown index RMI and transport distance x. From two selected Ultisols (SX3 and QX1) and under the combination of five slopes and five discharges, exponential relationships were found between aggregate abrasion and flow depth or friction factor. This research makes a good attempt at analyzing the aggregate abrasion in overland flow from simple laboratory experiments settings, and the results of the analysis could be valuable for the development of adequate soil erosion models. [Copyright &y& Elsevier]

Abstract: A rainfall simulator is an ideal tool for infiltration, soil erosion, and other related research areas for replicating the process and characteristics of natural rainfall. In this study, a laboratory-scale rainfall simulator is developed. Rainfall characteristics including the rainfall intensity and its spatial uniformity, raindrop size, raindrop velocity, and kinetic energy confirm that natural rainfall conditions are simulated with sufficient accuracy. Pressure nozzles are used to spray water corresponding to rainfall intensities ranging from 45 to 105mmh−1. The simulator produces rainfall with uniformity coefficient changing between 82 and 89%. The raindrops falling with an initial velocity from a height of 2.43m have median diameters of 2.2–3.1mm. The impact velocities of the median size raindrops deviate from their terminal velocities with a relative error between 6 and 15%. The accompanying erosion flume can be given slope up to 20% in lateral and longitudinal directions. During the experiments, flow measurement is taken from two outlets at the end of the flume to distinguish the contribution of interrill areas into rills. Experiments result in typical rainfall-induced hydrographs and sedigraphs observed under natural conditions. This shows the ability of the rainfall simulator for use in sediment transport processes over hillslopes. [Copyright &y& Elsevier]

Summary: The impact of rainfall characteristics on runoff generation and soil erosion are not fully understood despite their importance. In this study, a series of laboratory experiments, systematically considering different rainfall intensities, durations, moving directions, rainfall positions, and no-rainfall intervals, were conducted to investigate the impacts of rainfall characteristics on runoff generation and soil erosion. Significant differences, including hydrograph, sediment graph, soil water content, and infiltration depth (depth of wetting front), were observed. The following conclusions are drawn for the studied rainfall characteristics and soil from this study: (1) when compared with moving upstream rainfall scenarios (MURSs), moving downstream rainfall scenarios (MDRSs) can generally be characterized by hydrographs with a later rise and higher runoff peak for most of the rainfall events; (2) surface sealing changes the infiltration pattern so that MURS generally produce more total runoff than MDRS, and for some rainfall events MDRS generate lower runoff peak than MURS, which is different from what has been widely reported; (3) with the increase in the runoff peak, the erosion peak increases first and then decreases, indicating a switch from transport-limited erosion to detachment-limited erosion; (4) the increase ratio of underground water content for MURS is lower than MDRS; (5) rainfall duration is an important factor in soil crack occurrence. Not only does this study expand the understanding of hydrologic response and erosion, it also provides an important database for the hydrology community. [Copyright &y& Elsevier]

Abstract: We examined runoff and sediment transport associated with large-scale construction projects in Fujian Province, China. Six experimental plots, comprised of four plot types, were designed to mimic typical conditions immediately following disturbance. It was found that natural vegetative cover reduces both runoff and erosion by approximately 36 and 7457 times over bare ground, and 16 and 1801 times over typically planted grasses, respectively. The increase in erosion associated with the replacement of native vegetation with bare ground or grasses due to large-scale infrastructure projects in Fujian from 1999 to 2004, amounted to an estimated loss of 1.76×107 tonnes of top soil and 3.04×108 m3 of surface runoff from the province during the bare soil construction phase, and an additional 4.25×106 tonnes of top soil and 1.35×108 m3 of surface runoff from the province associated with the first year of operation for each project. This has implications for frequency and occurrence of landslides and other geographic hazards, the transport of chemicals into waterways, the transport of goods through shipping passages, and the fertility of land in Fujian. [Copyright &y& Elsevier]

Abstract: Water erosion is a very dynamic process with direct and indirect consequences on ecosystem functioning. While the processes of sediment (SED) and soil organic carbon (SOC) detachment and transport are well recognized, it is however difficult to assess and interpret their impact on SED and SOC detachment, transport and sedimentation within a given landscape. In this study of a tropical area of the Mekong Basin, our main objective was to evaluate sediment (SED), soil organic carbon (SOC) and runoff (R) delivery from various spatial scales from 1m² to 10km² and to interpret these results in term of erosion processes operating within the landscape. Deliveries from nested scales of microplots (1×1m²; n=12 installed at different topographic positions and soils of a hillslope), plots (1×2.5m²; n=8), hillslope (60×100m²) and catchment (30, 60, and 1000ha) were assessed during an entire rainy season. To improve understanding of soil erosion at landscape level, delivery of mobilized water, sediment and SOC from one surface area to the following one in the nested experimental design were confronted to environmental information on rainfall characteristics (rainfall intensity, I; maximum 6-min rainfall intensity, Imax; rainfall amount, R; rainfall depth Dur; cumulative yearly rainfall prior to the event, Cum), slope gradient (S), soil thickness (T) and soil crusting (Crust), antecedent soil water content (SWC), and depth to the water table (DWT). These data were finally compared to extensive mapping of the thickness and the type of the soils in an attempt to validate these results and to evaluate the longer term consequences of erosion processes on soil distribution. The mean sediment delivery from 1×1m² plots was 899gm−2 y−1 with standard error (SE) of 26gm−2 y−1. The SED delivery decreased to 275±63gm−2 y−1 on 1×2.5m2 plots and to 4.3gm−2 y−1 at the hillslope level but then increased to 16.6gm−2 y−1 at the basin level. The slight decrease in SED delivery flux from 899gm−1 y−1 on 1m long plots to 688±157gm−1 y−1 on 2.5m2 long plots and to 468gm−1 y−1 on the 100m long hillslope revealed that SED detachment and transport in slopes is mainly controlled by splash. The ratio of plot to microplot deliveries for R increased significantly as Crust increased (r=0.91) but decreased with increasing Cov (r=−0.88) while the ratio for SOC correlated the most with S (r=0.97) and Cov (r=−0.58). The R delivery ratio from hillslope to plot and from river to hillslope increased as soils get wetter and the water table rose while higher ratios for SED and SOC occurred at longer event duration and larger rainfall depth amount and at larger yearly antecedent rainfall in the case of the within catchment delivery. The large accumulations of SED and SOC at the lower parts of hillslopes confirms the observed erosion dynamics longer-term, (i.e., removal and transport of SED and SOC mainly by splash because of high infiltration occurring in slopes) thus suggesting a potential long-term sequestration of the SOC deposited in the lower parts of hillslopes while deposition in the river network appeared ephemeral. [Copyright &y& Elsevier]

Abstract: The application of polymer for controlling erosion and the associated nutrient transport has been well documented. However, comparatively less information is available on the effect of polymer application together with soil amendments. In this study, the effect of polyacrylamide (PAM) in combination with surface application of gypsum and Milorganite™ (MILwaukee ORGAnic NITtrogEn) biosolid for reducing sediment and phosphorus transport under laboratory rainfall simulations was investigated. The treatments considered were bare soil, gypsum, Milorganite™, gypsum+Milorganite™, PAM-coated gypsum and PAM-coated Milorganite™. Application rates for gypsum and Milorganite™ were 392kgha−1 (350lb/acre) and 726kgha−1 (650lb/acre), respectively. The PAM was coated on gypsum and Milorganite™ at an application rate of 11.2kgha−1 (10lb/acre) and 22.4kgha−1 (20lb/acre), respectively. Rain simulation experiments were conducted using a rainfall intensity of 6.0cmh−1 for 1h on a 10% slope. Surface runoff was collected continuously from each soil box over 10min intervals and leachate was collected continuously over the 60min simulation. The reduction in runoff or in leachate for all treatments was not significantly different from the bare soil control. The sediment loss for PAM coated Milorganite™ was reduced by 77%, when compared to bare soil. However, the sediment loss was not significantly reduced for any other treatment compared to bare soil. The PAM-coated gypsum was not effective for erosion control in our study, and there appears to be a correlation between effectiveness and prill size. However, the gypsum (coated and uncoated) contributed about half of the dissolved reactive phosphorus (DRP) export (in the runoff) compared to bare soil. The PAM-coated Milorgante™ reduced the DRP and total phosphorus (TP) export to 0.3–0.5 times that of Milorganite™ and to levels similar to bare soil. The decreased sediment and phosphorus export for the PAM-coated Milorganite™ treatment is a signal for a potential management practice for controlling erosion and nutrient transport in fertilized agricultural landscapes. [Copyright &y& Elsevier]

Abstract: The contributions and relationships of erosion by splash and overland flow over a steep slope in a Japanese beech forest in plots with different percentages of ground cover were examined. Three erosion plots (2m wide×5m long) with average understory coverage of 1%, 45%, and 94% were installed. Sediment transported by rain splash and by overland flow was sampled separately. For the plots with sparse, moderate, and high understory coverage, the average proportions of splash soil to total soil erosion during the monitoring period were 16%, 32%, and 18%, respectively. A significant correlation between the amount of splash soil and precipitation was found in the plots with 1% and 45% understory coverage, whereas no statistical relationship was identified for the plot with high understory coverage. At the sparse ground cover plot showing the largest sediment movement, the contribution of splash transport decreased with increasing precipitation. The amount of sheetwash erosion was significantly correlated with the amount of splash soil under the condition of sparse ground cover. This relationship was more pronounced during high precipitation events and the rainy season. Splash contribution to the sediment transport was in the range of 0.8%–76.7%, 2.8%–81% and 2.1%–60.8% for plot with high, moderate and low ground cover, respectively. The sparse ground cover showed the largest variation of splash and sheetwash contribution in soil erosion. This variability was due to variation in ground cover and soil surface wetness condition which led to a variation of detachment and non-linear relationship of sheetwash splash. [Copyright &y& Elsevier]

Earthworms are ecological engineers that play an important role in hydrological processes and soil erosion by their burrowing and casting activities. Little is known, however, about the ecological function of the activities of an anecic species (Metaphire guillelmi) from the Loess Plateau in China where the soil is severely eroded. We conducted rain-simulation experiments on artificial slopes (mesocosms) filled with soil from Loess Plateau. Two rain intensities (90 and 120 mm h−1) and slope gradients (5° and 15°) were used to investigate the influences of earthworm activity on runoff and soil loss under multiple conditions. Data from 15 d of earthworm activity and 1 h of rain indicated that earthworm activity significantly reduced runoff but aggravated soil erosion. Runoff initiation time increased 2.7–3.1-fold, contributing to the promotion of water infiltration, and the amounts and rates of runoff were 35.8–61.6% and 35.1–60.8% lower under earthworm activity than the controls, respectively. Earthworms greatly influenced the physical and chemical properties of the soil, and these properties were strongly correlated with runoff initiation time and cumulative runoff. The surface casts produced by the earthworms on the soil surface were completely dispersed, increasing the cumulative sediment by a maximum of 169%. Both rain intensity and slope gradient greatly influence runoff and soil detachment, but with earthworm activity, slope gradient was more influential due to its superior contribution to sediment transport. This study quantified the effects of M. guillelmi on runoff and soil erosion and provides basic data for developing a more integrated control of soil erosion on the Loess Plateau. • The increase in infiltration related to earthworm activities decreases runoff. • Soil erosion is aggravated by the low stability of surface cast under intense rainfall. • Earthworm impact on soil loss is larger at lower rain intensity and steeper slope. [ABSTRACT FROM AUTHOR]

• This paper presents new data on the intensity fluctuations in natural rainfall. • Literature review demonstrates the importance of intensity profile to rainfall simulation research. • The origin and landsurface process relevance of intensity profile are reviewed. • Recommendations are suggested that could enhance the utility of rainfall simulation research. The temporal sequence of fluctuating rainfall intensities during an event - the intensity profile or 'rainfall pattern' - is known to affect water partitioning at the ground surface and associated erosional processes. There can be large differences in runoff ratios and runoff rates between early-peak and late-peak events, and hence in the depth, speed, and sediment transport capacity of resulting overland flow. Whilst rainfall intensity may fluctuate continually during all IPs in natural rainfall, there is little information on the rates of such intensity fluctuations that can be used to guide the design of rainfall simulation experiments. This review analyses relevant data derived from published high-resolution rainfall records and also from new analyses of data from Australian ground observing stations. Both sources confirm the occurrence of rates of intensity change of greater than 500 mm h−1 min−1. It is suggested that the fluctuating intensities characteristic of natural rainfall need to be employed in rainfall simulation experiments in order to generate results applicable to natural landsurface processes like infiltration or soil removal. Constant-intensity rain, as commonly used in rainfall simulation experiments, lacks both the kinds of rapid intensity fluctuations seen in natural rainfall, as well as any representation of natural intensity profiles. These unrepresentative conditions can result in lower runoff rates and larger proportions of infiltration than when intensity fluctuations are present. There is thus a strong case for changing the design of rainfall simulation to reflect more closely natural intensity fluctuations and intensity profiles and their influence on key surface processes such as overland flow and soil erosion. [ABSTRACT FROM AUTHOR]

Abstract: Accelerated soil erosion is ubiquitous on human-modified hillslopes. A variety of erosion control products have been developed to reduce on-site soil resource degradation, and off-site transport of sediment and sediment-associated contaminants to receiving water bodies. However, limited quantitative data are available to assess erosion reduction effectiveness, and to establish the salient properties of the erosion control products. A replicated field-based rainfall simulation study was conducted to compare the runoff and erosion effectiveness of three coir (coconut) fiber rolled erosion control systems (RECSs) with a bare (control) treatment. Detailed temporal measurements of runoff and sediment transport were made during two phases of each experiment: (1) a 110-min application of rainfall via a rainfall simulator at 35mmh−1 after runoff initiation and (2) a 30-min period, at 3 times the flow rate of phase 1, applied via an overland flow generator. All coir treatments enhanced infiltration, delayed time to runoff generation, reduced intensity of rill incision, and reduced sediment output compared to bare treatments. More importantly, statistically significant differences were observed between coir RECSs of different architecture. For the two open weave coir systems tested, the most effective design had a higher mass per area, and less open space between the regularly aligned grid of fibers. The random fiber coir architecture was the most effective, having significantly lower runoff sediment concentrations, lower sediment yields, and a lower frequency of rill initiation. The differences in system architecture are examined in light of fundamental controls on runoff and erosion processes. [Copyright &y& Elsevier]

The understanding of soil erosion processes and the development of accurate erosion prediction models require understanding of detachment, deposition, and sediment transport in rills. The objectives of this study were to determine whether sediment transport capacity is a unique value for given soil, flow rate, and slope, and to determine if equilibrium sediment concentration in the rill obtained by detachment was different from that observed under depositional conditions. Experiments on a Carmi loam (fine, mixed, mesic Typic Hapludalf) simulated rill erosion under net detachment and net deposition conditions. Two discharge rates of 6 and 9 l min−1 and two sediment input regimes of 0 and excess of transport capacity were tested on soil beds with lengths of 2, 4, 6, 7, and 8 m at 7% slope. Sediment load reached steady state conditions within the 8-m distance on the rill. At 9 l min−1 discharge, 8 m length, and excess sediment added to the flow, sediment delivery was 71 g l−1 versus 31 g l−1 for the corresponding case with no sediment added. Overall, for the conditions tested, rill flow transported two times more sediment than it could detach. The flow did not reach its maximum potential transported load through detachment of soil due in part to changes in the sediment size distribution under deposition and possibly to the protective action of bedload particles moving along the rill bottom and/or changes in flow turbulence associated with sediment laden flow. [Copyright &y& Elsevier]

• Prescribed fire promoted herbaceous growth in bare interspaces. • Litter enhanced infiltration and provided protection against erosion. • Increased vegetation cover altered flow paths and reduced runoff and soil loss. • Reduced soil surface connectivity post-fire improved hydrologic function. • Hydrologic function continues to improve 9 yr after fire. Woody species encroachment into herbaceous and shrub-dominated vegetations is a concern in many rangeland ecosystems of the world. Arrival of woody species into affected rangelands leads to changes in the spatial structure of vegetation and alterations of biophysical processes. In the western USA, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.) tree species into sagebrush steppes poses a threat to the proper ecohydrological functioning of these ecosystems. Prescribed fire has been proposed and used as one rangeland improvement practice to restore sagebrush steppe from pinyon-juniper encroachment. Short-term effects of burning on the ecohydrologic response of these systems have been well documented and often include a period of increased hydrologic and erosion vulnerability immediately after burning. Long-term ecohydrologic response of sagebrush steppe ecosystems to fire is poorly understood due to lack of cross-scale studies on treated sites. The aim of this study is to evaluate long-term vegetation, hydrologic, and erosion responses at two pinyon-juniper-encroached sagebrush sites 9 years after prescribed fire was applied as a restoration treatment. Thirty-six rainfall simulation experiments on 6 m × 2 m plots were conducted for 45 min under two conditions: a dry run (70 mm h−1; dry antecedent soils) and a wet run (111 mm h−1; wet antecedent soils). Runoff and erosion responses were compared between burned and unburned plots. Overall, increases in herbaceous cover in the shrub-interspace areas (intercanopy area between trees) at both sites 9 years post-burn resulted in runoff- and erosion-reduction benefits, especially under the wet runs. While the initially more degraded site characterized by 80% bare ground pre-burn, registered a higher overall increase (40% increase) in canopy cover, greater post-fire reductions in runoff and erosion were observed at the less degraded site (57% bare ground pre-burn). Runoff and erosion for the wet runs decreased respectively by 6.5-fold and 76-fold at the latter site on the burned plots relative to control plots, whereas these decreases were more muted at the more degraded site (2.5 and 3-fold respectively). Significant fragmentation of flow paths observed at the more-degraded site 9 years post-fire, suggests a decreased hydrologic connectivity as a mechanism of runoff and erosion reduction during post-fire recovery. [ABSTRACT FROM AUTHOR]