A review of the characteristics of rainfall simulators in soil erosion research studies

Rainfall simulators are widely employed in soil erosion studies, and it is common for these simulators to be customized to address specific research questions. Nevertheless, there are certain characteristics that rainfall simulators should fulfill in the context of soil erosion studies. Rainfall simulators should simulate natural precipitation as accurately as possible. It is essential to monitor the size spectrum of generated raindrops, their maximum or terminal velocity, the uniformity of the surface distribution of rain, the kinetic energy and the overall intensity of the rain. This review aims to outline the characteristics and the corresponding measurement methods for rainfall simulators in soil erosion research. Electronic instruments like distrometers are considered more suitable for precise and comprehensive measurements than traditional instroments or literature based derivatives. By adhering to these characteristics, researchers can ensure the reliability and accuracy of their findings. Consequently, this overview serves as a valuable resource for researchers seeking to employ rainfall simulators in their investigations of soil erosion.

Experimental study of soil erosion on moraine-consolidated slopes under heavy rainfall

Surface subsidence pits formed by mining disturbance are highly susceptible to slope instability under rainfall erosion, inducing underground debris flow disasters. To prevent and control underground debris flow disasters in a subsidence area, a test model of subsidence pit slope was established in accordance with the principle of similar simulation, and the erosion-resistant performance of moraine-cured slopes with different soil-slurry ratios and the law of runoff and sand production were investigated through the simulation of artificial rainfall and a simulation test of grouting. Results show that the initial rainfall production time increases exponentially with increasing soil-slurry ratio, while sediment production intensity decreases linearly with increasing rainfall duration. The evolution of soil erosion can be divided into five stages: impact infiltration, water-filled softening, stripping cutting, migration crossing, and steady flow equilibrium. Compared with in situ moraine, moraine particles after grouting between the generation of large amounts of Si-O-Si and Si-OH hydration products become loose and porous soil medium is transformed into a dense cemented structure. The soil-slurry ratio is 5:1, the sand-fixing effect increases by 28.8 times, the resistance of permeability increases by 11.3 times, and the grouting curing effect is remarkable. This study can provide technical support for the prevention and control of geological disasters in subsidence pits.

Runoff nitrogen losses under confluence and diverging drainage systems in the sloped plot scale: A comparative study

The drainage system is a key measure for regulating runoff nutrient losses on sloping farmlands. Confluence and diverging drainage systems are two drainage layouts representing natural water network systems and are widely distributed in sloping farmlands; however, the effects of these drainage systems on runoff nutrient losses in the sloped plots remain unclear. This study investigated the effects of different drainage systems on the characteristics of runoff nitrogen (N) losses in sloped plots using laboratory rainfall simulations. Three treatments, including bare slope (without drainage system, CK), confluence drainage system (T1), and diverging drainage system (T2), were used to compare the changes in concentrations and losses of total nitrogen (TN), dissolved nitrogen (DN), and particulate nitrogen (PN), and the DN:TN ratio in runoff under a combination of 1.8 mm min-1 rainfall intensity and three slope gradients (5°, 10°, and 15°). The results showed that the time to runoff was significantly delayed in T2 compared with that in CK and T1 across all slopes (p < 0.05). Accumulated runoff depth was considerably lower in T1 and T2 than in CK across all slopes (p < 0.05). The TN and PN concentrations in T1 were markedly lower than those in T2 on the 10° and 15° slopes (p < 0.05). The DN concentration in T1 was lowest at the 5° slope (p < 0.05). TN loss in T1 was 14.7-33.9% and 17.9-30.3% lower than those in CK and T2 across all slopes, respectively (p < 0.05). The PN loss in T1 was 56.7% and 53.3% lower than that in T2 on the 10° and 15° slopes, respectively (p < 0.05). DN loss in T1 was 39.3-72.5% lower than that in CK for all slopes (p < 0.05). DN:TN in T2 was lower than that in CK and T1 at the 10° and 15° slopes (p < 0.05). Our results confirm the effectiveness of drainage systems in reducing runoff nutrient losses in a sloped plot and demonstrate that the confluence drainage system is better at reducing N losses in runoff than diverging drainage systems.

Surface and subsurface runoff generation processes and their influencing factors on a hillslope in northern China

Runoff processes are essential to the hydrological cycle in mountainous areas. However, many aspects of surface and subsurface runoff generation mechanisms and their influencing factors remain to be fully understood. In this study, rainfall simulation experiments were conducted in micro runoff plots in different slope positions on a typical hillslope to explore runoff processes and their influencing factors in the Taihang Mountain region in northern China. The surface and subsurface runoff and soil water content (SWC) variation processes were analyzed. Moreover, the impact of the soil properties, such as soil saturated hydraulic conductivity (Ks), bulk density (BD), capillary porosity (CP), non-capillary porosity (NCP), and soil organic matter (SOM), on these processes were investigated. The results revealed that the response of the SWC to rainfall was significantly different in different soil layers and slope positions. The response time was slower and the period was longer on the lower slope. However, the middle and upper slopes had a faster response time and shorter period. The surface runoff was the dominant type in the lower slope (67.26 % of the total runoff), while the subsurface runoff was the dominant type in the middle (78.83 %) and upper (83.67 %) slopes. The subsurface runoff was mainly generated in the 40 cm layer on the lower slope, 20 and 30 cm layers on the middle slope, and 30 and 40 cm layers on the upper slope. These layers exhibited good correspondence with the Ks' vertical distribution, but were inconsistent with the other soil properties. These results indicate that the Ks was the most critical factor influencing the runoff generation process. The ratio of the upper layer's horizontal Ks to the lower layer's vertical Ks controlled the subsurface runoff generation process in the hillslope. These findings provide useful information for understanding the hydrological processes in mountainous areas.

Sediment modeling using laboratory-scale rainfall simulator and laser precipitation monitor

The characterization of a rainfall simulator provides an excellent opportunity to study the potential of soil erosivity without waiting for natural rain. But, precise instrumentation is required to estimate the parameters, which is seldom available. To overcome this problem, the empirical and conceptual relationships obtained through physically-based modeling help to correlate the rain parameters contributing to soil erosion. The present laboratory study used five pressurized nozzles of different capacities and a Laser Precipitation Monitor (LPM) to generate different rain intensities (21.0-79.0 mm h-1) and to register drop size distribution, respectively. The sediment transportation induced by rain and runoff was measured with an erosion flume of 2.50 × 1.25 × 0.56 m with an adjustable longitudinal slope. The spatial uniformity, drop size distribution, drop velocity, and kinetic energy were used to evaluate the simulator's performance. The different rain erosivity parameters were correlated and tested statistically using linear and non-linear regression analysis. The rain simulation experiments of different intensities at different pressure ranges were performed on flat, 5, 10, and 15% slopes of the erosion flume to evaluate rain characteristics and record the surface runoff and sediment yield. The median drop sizes produced during the simulator ranged from 0.38 to 2.11 mm, coinciding with natural rain. The empirical relationships were developed to correlate surface discharge and sediment yield with rain intensity by optimizing the parameters for further study of experimental field plots of different slopes. The observed and estimated rain erosivity parameters showed a significant relationship (R2 = 0.75 to 0.93; P < 0.001) in multiple regression analysis, and the metrics used to test the developed regression equations showed lower MAE, MSE, and RMSE errors indicating the adequacy of the relationships. The results indicated that the simulator helps to understand the complex task of soil erosion with hydrologic and geomorphic processes in laboratory experimentation with sufficient accuracy in measuring sediment transport events.

Changes in overall and inter-variability of runoff and soil loss for a loess soil resulted from a freezing-thawing cycle

The soil freeze-thaw process is a transition phase of soil water in cold areas that influences the soil's hydrological behavior. However, dynamic phenomena and corresponding consequences have yet to be studied adequately. Therefore, the present study was planned to comparatively analyze the effects of a freezing-thawing cycle on the hydrologic behaviors of loess soil from northeast Iran. Small-size (0.5 × 0.50 m) erosion plots were subjected to a freezing-thawing cycle under governing conditions of the region of the origin soil. The plots were subjected to a freezing-thawing treatment by inducing cold air until the temperature declined to below - 20 °C and lasted for 3 days using a cooling compartment system and then were kept in the laboratory with an ambient temperature of above 10 °C for 2 days. The treated plots and untreated plots were then exposed to a simulated rainfall with an intensity of 72 mm h^-1 and 0.5 h duration while they were placed on a slope of 20%. The results indicated that the hybrid processes of freezing-thawing and splash and inter-rill erosions significantly increased runoff generation and soil loss. The time to runoff, runoff volume, and soil loss were 1.65 times less and 1.38 and 2.90 times more, respectively, compared to those reported for the control treatment with significant differences (p < 0.006). The performance of ice lenses, freezing fronts, and the creation of near-saturation moisture after completing the cycle were identified as the most critical factors affecting the different soil behaviors under the frozen-thawed cycle.

Water-related atmospheric agents and solubility: two parameters of validation in toxicological screening on clothing worn by skeletal remains

In forensic toxicology, when conventional matrices are no longer available, alternative matrices can be used to assess toxicological investigations. Clothes worn by skeletal remains may be a good unconventional matrix for toxicological analyses considering that they have absorbed decomposition fluids and blood from a body. We hypothesized a scenario in which a skeleton, wearing clothes, was discovered in an open environment. From this starting point, an experimental study was developed on different textiles (cotton, wool, and polyester) to evaluate whether water-related atmospheric agents and molecule solubility can largely influence the detection of molecules of toxicological interest on this specific matrix, together with the characteristics of different garments chosen. The experimental study was performed on blood spots, previously spiked with 6-monoacetylmorphine and morphine, accurately placed on different textiles and washed with different quantities of deionized water adjusted at pH 5.6 with formic acid to simulate different rainfall conditions. Toxicological analyses were performed via Solid-Phase Extraction and High-Performance Liquid Chromatography-Tandem Mass Spectrometry analyses (Thermo Scientific™ TSQ Fortis™ II Triple-Quadrupole Mass Spectrometer). From the experimental study morphine could not be detected on 100% cotton and 100% wool fabric after the passing of 500 mL of deionized water and in 100% synthetic polyester textile after washing with 250 mL of deionized water. In conclusion, when toxicological analyses are carried out on unconventional matrices as textiles worn by corpses exposed to different environmental conditions, it is of great importance, in using such substrates as evidence for the presence of molecules of toxicological interest, to evaluate chemical-physical characteristics of each analyte under investigation in order to correctly interpret the toxicological data obtained.

Microplastic surface retention and mobility on hiking trails

Hiking and trail running are a source of microplastic (MP) pollution on recreational trails in wilderness and conservation areas; however, the fate of MPs deposited on trails is poorly understood as MP mobility on such surfaces has not yet been examined. In this study, we simulated heavy rainfall (100 mm/h) on trail surfaces with existing MP pollution (in situ MPs) and spiked with 99 ± 2 rubber MPs (100-940 μm). Runoff was collected for 15 min and spiked and in situ MPs were quantified. Hydrological, erosional and microplastic responses were evaluated in relation to slope, bulk density, soil moisture and surface condition indicators, including amounts and types of surface cover and soil physical attributes. The MPs were largely immobile, with 85-100% of spiked MPs retained on trail surfaces. In situ MPs were detected in the trail runoff, with the majority being polyurethane, polypropylene and polyester. Microplastic movement was primarily influenced by hydrological effects, and analysis indicated the main explanatory variable was total runoff volume, followed by soil slaking. Trail sections with at least 15% herbaceous cover or a layer of loose alluvium had higher MP retention. Areas of resource accrual may be preferentially enriched, suggesting MPs from outdoor recreation may be concentrated on and adjacent to recreational trails. Microplastics deposited on trails may have long term implications for biodiversity and ecosystem functioning in wilderness and conservation areas, particularly around the trail corridor.

Evaluation of phosphorus runoff from sandy soils under conservation tillage with surface broadcasted recovered phosphates

Potential new sources of phosphorus (P) fertilizer are the recovered P from livestock wastewater through chemical precipitation and the ash from combusting animal manures. Although most of the research on P losses from conservation tillage include high water-soluble P compounds from commercial fertilizer sources, information on the use of non-conventional, low water-soluble, recycled P sources is scarce. Particularly for sandy soils of the United States (US) Southeastern Coastal Plain region, research driven information on P loss into the environment is needed to determine recommendations for a direct use of new recycled P sources as crop P fertilizers. The objective of this study is to investigate the potential P runoff from sandy soils under conservation tillage, fertilized with recovered P from liquid swine manure and turkey litter ash in comparison with commercial P fertilizer triple superphosphate (TSP). The field study included two typical sandy soils of the US Southeastern Coastal Plain region, the Noboco and Norfolk. Simulated rain corresponding to the annual 30-min rainfall in the study site (Florence County, South Carolina) was applied to plots treated with recovered P from liquid swine manure, turkey litter ash, and TSP, including a control with no P added. The runoff was monitored and sampled every 5 min during the test and composite soil samples were collected from the top (0-15 cm) and subsurface (15-30 cm) soil layers in each plot. Laboratory analyses were conducted to quantify both total P (TP) and soluble reactive P (SRP) in runoff samples, and the soil test P in the soil layers. Two-way analyses of variances show significant treatment effects on both TP and SRP runoff. The quantities of SRP runoff from plots treated with the recovered P from swine manure and turkey litter ash represent respectively 1% and 7-8% of SRP runoff from plots treated with TSP. Hence, the use of the recovered P materials as crop P fertilizers through surface broadcast application present less environmental risks compared to commercial TSP.

An experimental investigation of the erosion process and morphological characteristics of the tile-back type slope with non-uniform slopes based on a 3D reconstruction method

Tile-back type slopes comprise ephemeral gullies (EGs) and hillslopes; they are a unique and widely distributed micro-landform in the Loess Plateau region of China. Gully erosion from these landforms is a serious issue, but the micro-landform makes the erosion process and its estimation complex. Quantifying soil erosion processes and their distribution characteristics at different positions on tile-back type slopes will provide a clearer picture for ecological restoration to control further soil degradation. This study investigated the erosion process of tile-back type slope with non-uniform slopes using a 3D photo-reconstruction method during eight successive simulated rainfall events. The results showed that EG erosion began with a chain of intermittent headcuts. When the accumulated rainfall reached 76 mm, serious collapses dramatically increased the amount of sediment by 216% after the first rainfall (cumulative rainfall was about 15 mm). We quantified the sediment contribution of EG erosion (46.20%), rill erosion (35.62%), and inter-rill erosion (18.18%) to total soil loss. The erosion area of the steep slope section and extremely steep slope section accounted for 33.26% and 66.74% of the total erosion area, respectively. Moreover, sediment amounts significantly correlated with morphological parameters, particularly the amount of EG erosion and maximum gully depth, with a correlation coefficient of 0.98. Cumulative gully length and erosion area had the greatest effect on rill erosion, with a correlation coefficient of 0.97. These results provide insight into the qualitative and quantitative understanding of EG erosion process on Loess Plateau of China and an important reference for the rational arrangement of EG control measures.

Weed cover controls soil and water losses in rainfed olive groves in Sierra de Enguera, eastern Iberian Peninsula

Soil erosion is a threat for the sustainability of agriculture and severely affects the Mediterranean crops. Olive groves are among the rainfed agriculture lands that exhibit soil and water losses due to the impact of unsustainable practices such as conventional tillage and herbicides abuse. To achieve a more sustainable olive oil production, alternative, greener crop management practices need to be tested in the field. Here, a weed cover (CW) treatment is tested at an olive tree plantation that has undergone conventional mechanical tillage for 20 years and results were compared against an adjacent control plantation that maintained tillage as a weed control strategy (CO). Both plantations were under the same tillage management for centuries and macroscopic analysis confirms they are otherwise comparable. Compared to the CO, where tilled soil cover was zero, 20 years of CW (weeds cover 64%; litter cover 5%) had led to significantly higher values of soil bulk density and soil organic matter. Results from rainfall simulation experiments at 55 mm h^-1 on 0.25 m² plots under CO (N = 25) and CW (N = 25) show that as a result of the improved soil structure, CW (i) reduced soil losses by two orders of magnitude (140 times), (ii) decreased runoff yield by one order of magnitude (from 2.65 till 27.6% of the rainfall), (iii) significantly reduced runoff sediment concentration (from 18.6 till 1.43 g l^-1), and (iv) significantly delayed runoff generation (CO = 273 s; CW = 788 s). These results indicate that weed cover is a sustainable land management practice in Mediterranean olive groves and promotes sustainable agriculture production in mountainous areas under rainfed conditions, which are typically affected by high erosion rates such those found in the CO plots. Due to the spontaneous recovery of plant cover, we conclude that weed cover is an excellent nature-based solution to increase in the soil organic matter content and soil erosion reduction in rainfed olive orchards.

Coupling loss characteristics of N-P-C through runoff and sediment in the hilly region of SE China under simulated rainfall

Soil total carbon (TC), phosphorus (P), and nitrogen (N) exports from the weathered granite slopes are greatly influenced by the complex hydrological processes and terrain factors. In this study, the coupling loss characteristics of N-P-C via runoff and sediment were studied with two soil tanks under simulated rainfalls. Three soils respectively derived from the tillage layer (T-soil), laterite layer (L-soil), and sand layer (S-soil) were employed to determine the interactions of hydrology and topography on N-P-C exports under three rainfall intensities (1.5, 2.0, and 2.5 mm/min). The erosion degree of different soils displayed an order of S-soil > L-soil > T-soil. The results showed that surface flow was the main runoff form for L- and T-soil, while underground flow was predominant for S-soil. There was a linear correlation between sediment and surface flow (R² > 0.78). Surface flow was the dominant pathway of P loss via runoff with underground flow being an important supplementation, and the main P loss pattern switched between dissolved phosphorus (DP) and particle phosphorus (PP) during the experiment. However, P lost via eroded sediment accounted for more than 94% of the TP loss amount. N presented an opposite trend to P and was mainly lost via underground flow. The main N loss form in surface and underground flow was NO₃^--N. Underground flow was the predominant total nitrogen (TN) loss pathway for S- and L-soil, followed by sediment and surface flow. For T-soil, TN lost via runoff was much greater than that carried by eroded sediment. TC for S-soil was mainly lost via underground flow while that for L- and T-soil was mostly lost via surface flow. Both N-P loss loads in surface flow and P loss load in underground flow were positively correlated with TC loss load (p < 0.05), indicating that the presence of organic matter brings about more nutrient losses. These results expand our understanding of the combined effects of rainfall intensity and erosion degree on runoff and sediment yields as well as N-P-C losses from the bare weathered granite slopes of SE China.

Changes in connectivity and hydrological efficiency following wildland fires in Sierra Madre Oriental, Mexico

Fire modifies soil surface, and hence soil hydrological properties change after wildland fires. High fire severity causes partial or total removal of vegetation, reduction of soil aggregate stability and increased water repellency, which are associated with high runoff and erosion. The spatial connection among these runoff sources is an important factor to consider when evaluating fire-induced changes on hillslope and catchment hydrology, as fire generates connected areas of bare soil, which may increase hydrological connectivity and hence post-fire runoff and erosion. The aim of this study was to quantify changes in hydrological connectivity and efficiency in two burned areas in central Mexico. By integrating rainfall simulation and spatial analysis, an index of connectivity (IC) and the lateral hydrological efficiency index (LHEI) were computed based on land/cover use, fire severity and topography within 287 burned sub-basins. Post-fire IC and LHEI were compared with the pre-fire scenario, and the relationship between LHEI and the proportion of burned area was assessed at the sub-basin level. Thresholds of the burned area per fire severity needed to increase LHEI were determined by a classification tree. The index of connectivity and LHEI were higher after wildland fires. The burned area was positively related with LHEI, and at least 43.3% of area burned with high severity is sufficient to produce the highest LHEI. The results are evidence of the effect of fire on hydrological connectivity and efficiency which adds to the understanding of fire-hydrology relations and can be used for integrated catchment management, ecological restoration and risk assessment.

Interaction between ash and soil microaggregates reduces runoff and soil loss

Areas subjected to fire have a two-layer system (i.e., ash and soil), which brings enormous complexities to hydrogeomorphic processes. In addition, the combinations of variables from the ash and the soil characteristics result in several possible two-layer system contexts. Here, the interactions among ash and microaggregates (i.e., ash placed over fine soil microaggregates) and their effects on hydro-erosional processes are explored. The ash was produced by an experimental fire and collected from a field managed by a slash-and-burn agricultural system. The design of the experiment included a strategy for considering combinations in which each of the various factors of interest, i.e., ash and microaggregates, was present or absent. In addition, the study searched for interactions between the two factors when both were present. In total, 600 g m² of fine ash mixture (<0.250 mm), obtained from fire at different temperatures, and 90 g m² of microaggregates was placed over a small splash pan (0.135 m²). Next, a rainfall of 56 mm h^-1 lasting for 30 min was applied in four replicates for each treatment: 1) bare soil, 2) bare soil + microaggregates, 3) ash, and 4) ash + microaggregates. The interaction between the ash and soil microaggregates changed the soil hydrology dynamics, reducing soil moisture by 28% and surface runoff by 78%. The ash-microaggregates combination reduced soil loss by sheetwash by 20% and by rainsplash by 25%. Overall, the ash treatment increased soil loss by 47% compared to the case of bare soil. On the contrary, the ash-microaggregates interaction decreased soil loss by 26% compared to the ash treatment.

Investigation of the wash-off process using an innovative portable rainfall simulator allowing continuous monitoring of flow and turbidity at the urban surface outlet

Development of appropriate models, based on an in-depth understanding of the wash-off process, is essential to accurately estimating pollutant loads transported by stormwater, thereby minimizing environmental contamination. To this end, we developed an innovative rainfall simulator, which simulated an intense rainfall (120mm/h) and permitted the acquisition of runoff samples as well as the in situ monitoring of continuous flow and turbidity dynamics. Relationships between deposited sediments and total suspended solids in simulated runoff were thus investigated on two different types of surfaces within the Paris region in terms of loads and particle size distribution. Results demonstrate the occurrence of first flush phenomenon on the sidewalks even under constant flow. Results also show that the highest fraction conveyed by runoff consisted of fine (<16μm) and medium-sized (<100μm) particles, whose detachment was more favorable from smooth surfaces than from rougher ones. In terms of stormwater quality modelling, results suggest that the integration of a wash-off fraction based on both particle size and rainfall intensity could be an entrance for a better prediction of stormwater pollution.

Runoff initiation, soil detachment and connectivity are enhanced as a consequence of vineyards plantations

Rainfall-induced soil erosion is a major threat, especially in agricultural soils. In the Mediterranean belt, vineyards are affected by high soil loss rates, leading to land degradation. Plantation of new vines is carried out after deep ploughing, use of heavy machinery, wheel traffic, and trampling. Those works result in soil physical properties changes and contribute to enhanced runoff rates and increased soil erosion rates. The objective of this paper is to assess the impact of the plantation of vineyards on soil hydrological and erosional response under low frequency - high magnitude rainfall events, the ones that under the Mediterranean climatic conditions trigger extreme soil erosion rates. We determined time to ponding, Tp; time to runoff, Tr; time to runoff outlet, Tro; runoff rate, and soil loss under simulated rainfall (55 mm h^-1, 1 h) at plot scale (0.25 m²) to characterize the runoff initiation and sediment detachment. In recent vine plantations (<1 year since plantation; R) compared to old ones (>50 years; O). Slope gradient, rock fragment cover, soil surface roughness, bulk density, soil organic matter content, soil water content and plant cover were determined. Plantation of new vineyards largely impacted runoff rates and soil erosion risk at plot scale in the short term. Tp, Tr and Tro were much shorter in R plots. Tr-Tp and Tro-Tr periods were used as connectivity indexes of water flow, and decreased to 77.5 and 33.2% in R plots compared to O plots. Runoff coefficients increased significantly from O (42.94%) to R plots (71.92%) and soil losses were approximately one order of magnitude lower (1.8 and 12.6 Mg ha^-1 h^-1 for O and R plots respectively). Soil surface roughness and bulk density are two key factors that determine the increase in connectivity of flows and sediments in recently planted vineyards. Our results confirm that plantation of new vineyards strongly contributes to runoff initiation and sediment detachment, and those findings confirms that soil erosion control strategies should be applied immediately after or during the plantation of vines.

Rainfall simulation and Structure-from-Motion photogrammetry for the analysis of soil water erosion in Mediterranean vineyards

Soil water erosion is a serious problem, especially in agricultural lands. Among these, vineyards deserve attention, because they constitute for the Mediterranean areas a type of land use affected by high soil losses. A significant problem related to the study of soil water erosion in these areas consists in the lack of a standardized procedure of collecting data and reporting results, mainly due to a variability among the measurement methods applied. Given this issue and the seriousness of soil water erosion in Mediterranean vineyards, this works aims to quantify the soil losses caused by simulated rainstorms, and compare them with each other depending on two different methodologies: (i) rainfall simulation and (ii) surface elevation change-based, relying on high-resolution Digital Elevation Models (DEMs) derived from a photogrammetric technique (Structure-from-Motion or SfM). The experiments were carried out in a typical Mediterranean vineyard, located in eastern Spain, at very fine scales. SfM data were obtained from one reflex camera and a smartphone built-in camera. An index of sediment connectivity was also applied to evaluate the potential effect of connectivity within the plots. DEMs derived from the smartphone and the reflex camera were comparable with each other in terms of accuracy and capability of estimating soil loss. Furthermore, soil loss estimated with the surface elevation change-based method resulted to be of the same order of magnitude of that one obtained with rainfall simulation, as long as the sediment connectivity within the plot was considered. High-resolution topography derived from SfM revealed to be essential in the sediment connectivity analysis and, therefore, in the estimation of eroded materials, when comparing them to those derived from the rainfall simulation methodology. The fact that smartphones built-in cameras could produce as much satisfying results as those derived from reflex cameras is a high value added for using SfM.

Effects of soil management techniques on soil water erosion in apricot orchards

Soil erosion is extreme in Mediterranean orchards due to management impact, high rainfall intensities, steep slopes and erodible parent material. Vall d'Albaida is a traditional fruit production area which, due to the Mediterranean climate and marly soils, produces sweet fruits. However, these highly productive soils are left bare under the prevailing land management and marly soils are vulnerable to soil water erosion when left bare. In this paper we study the impact of different agricultural land management strategies on soil properties (bulk density, soil organic matter, soil moisture), soil water erosion and runoff, by means of simulated rainfall experiments and soil analyses. Three representative land managements (tillage/herbicide/covered with vegetation) were selected, where 20 paired plots (60 plots) were established to determine soil losses and runoff. The simulated rainfall was carried out at 55mmh(-1) in the summer of 2013 (<8% soil moisture) for one hour on 0.25m(2) circular plots. The results showed that vegetation cover, soil moisture and organic matter were significantly higher in covered plots than in tilled and herbicide treated plots. However, runoff coefficient, total runoff, sediment yield and soil erosion were significantly higher in herbicide treated plots compared to the others. Runoff sediment concentration was significantly higher in tilled plots. The lowest values were identified in covered plots. Overall, tillage, but especially herbicide treatment, decreased vegetation cover, soil moisture, soil organic matter, and increased bulk density, runoff coefficient, total runoff, sediment yield and soil erosion. Soil erosion was extremely high in herbicide plots with 0.91Mgha(-1)h(-1) of soil lost; in the tilled fields erosion rates were lower with 0.51Mgha(-1)h(-1). Covered soil showed an erosion rate of 0.02Mgha(-1)h(-1). These results showed that agricultural management influenced water and sediment dynamics and that tillage and herbicide treatment should be avoided.

Transport of manure-borne testosterone in soils affected by artificial rainfall events

Information is very limited on fate and transport of steroidal hormones in soils. In this study, the rainfall simulation tests were conducted with a soil slab reactor to investigate the transport of manure-borne testosterone in a silty-clay loam soil under six controllable operation conditions (i.e., three rainfall intensities and two tillage practices). The properties [e.g., rainwater volume, particle size distribution (PSD)] of the slurry samples collected in runoff and leachate at different time intervals were measured; their correlation with the distribution of testosterone among runoff, leachate and soil matrix was analyzed. The results indicated that more than 88% of the testosterone was held by the applied manure and/or soil matrix even under the rainfall intensity of 100-year return frequency. The runoff facilitated testosterone transport through both dissolved and particle-associated phases, with the corresponding mass ratio being ∼7 to 3. Soil particles collected through runoff were mainly silt-sized aggregates (STA) and clays, indicating the necessity of using partially-dispersed soil particles as testing materials to conduct batch tests (e.g., sorption/desorption). No testosterone was detected at the soil depth >20 cm or in the leachate samples, indicating that transport of testosterone through the soil is very slow when there is no preferential flow. Tillage practice could impede the transport of testosterone in runoff. For the first time, results and the methodologies of this study allow one to quantify the hormone distribution among runoff, leachate and soil matrix at the same time and to obtain a comprehensive picture of the F/T of manure-borne testosterone in soil-water environments.

Colloidal mobilization of arsenic from mining-affected soils by surface runoff

Scorodite-rich wastes left as a legacy of mining and smelting operations pose a threat to environmental health. Colloids formed by the weathering of processing wastes may control the release of arsenic (As) into surface waters. At a former mine site in Madrid (Spain), we investigated the mobilization of colloidal As by surface runoff from weathered processing wastes and from sediments in the bed of a draining creek and a downstream sedimentation-pond. Colloids mobilized by surface runoff during simulated rain events were characterized for their composition, structure and mode of As uptake using asymmetric flow field-flow fractionation coupled to inductively plasma mass spectrometry (AF4-ICP-MS) and X-ray absorption spectroscopy (XAS) at the As and Fe K-edges. Colloidal scorodite mobilized in surface runoff from the waste pile is acting as a mobile As carrier. In surface runoff from the river bed and the sedimentation pond, ferrihydrite was identified as the dominant As-bearing colloidal phase. The results from this study suggest that mobilization of As-bearing colloids by surface runoff may play an important role in the dispersion of As from metallurgical wastes deposited above ground and needs to be considered in risk assessment.

Controllability of runoff and soil loss from small plots treated by vinasse-produced biochar

Many different amendments, stabilizers, and conditioners are usually applied for soil and water conservation. Biochar is a carbon-enriched substance produced by thermal decomposition of organic material in the absence of oxygen with the goal to be used as a soil amendment. Biochar can be produced from a wide range of biomass sources including straw, wood, manure, and other organic wastes. Biochar has been demonstrated to restore soil fertility and crop production under many conditions, but less is known about the effects of its application on soil erosion and runoff control. Therefore, a rainfall simulation study, as a pioneer research, was conducted to evaluate the performance of the application of vinasse-produced biochar on the soil erosion control of a sandy clay loam soil packed in small-sized runoff 0.25-m(2) plots with 3 replicates. The treatments were (i) no biochar (control), (ii) biochar (8 tha(-1)) application at 24h before the rainfall simulation and (iii) biochar (8 tha(-1)) application at 48 h before the rainfall simulation. Rainfall was applied at 50 mm h(-1) for 15 min. The mean change of effectiveness in time to runoff could be found in biochar application at 24 and 48 h before simulation treatment with rate of +55.10% and +71.73%, respectively. In addition, the mean runoff volume 24 and 48 h before simulation treatments decreased by 98.46% and 46.39%, respectively. The least soil loss (1.12 ± 0.57 g) and sediment concentration (1.44 ± 0.48 gl(-1)) occurred in the biochar-amended soil treated 48 h before the rainfall simulation. In conclusion, the application of vinasse-produced biochar could effectively control runoff and soil loss. This study provided a new insight into the effects of biochar on runoff, soil loss, and sediment control due to water erosion in sandy clay loam soils.

Effects of vegetation on runoff generation, sediment yield and soil shear strength on road-side slopes under a simulation rainfall test in the Three Gorges Reservoir Area, China

Vegetation recolonization has often been used to control roadside slope erosion, and in this paper, four restoration models - Natural Restoration, Grass, Grass & Shrub, Sodded Strip - were chosen to recolonize the plants on a newly built unpaved roadside slope in the Three Gorges Reservoir Area. After eight months growth, eight rainfall simulations (intensity of 90 mm h(-1) for 60 min) and in-situ soil shear strength test were then carried out to identify the impacts of vegetation on roadside slope erosion and soil shear strength. The erosion on cutslopes was higher than that on fillslopes. The runoff coefficient and soil detachment rate were significantly lower on the Grass & Shrub model (4.3% and 1.99 g m(-2) min(-1), respectively) compared with the other three, which had the highest surface cover (91.4%), aboveground biomass (1.44 kg m(-2)) and root weight density (3.94 kg m(-3)). The runoff coefficient and soil detachment rate on roadside slopes showed a logarithmic decrease with the root weight density, root length density and aboveground biomass. The soil shear strength measured before and after the rainfall was higher on Grass & Shrub (59.29 and 53.73 kPa) and decreased on Grass (46.93 and 40.48 kPa), Sodded Strip (31.20 and 18.87 kPa) and Natural Restoration (25.31 and 9.36 kPa). Negative linear correlations were found between the soil shear strength reduction and aboveground biomass, root weight density and root length density. The variation of soil shear strength reduction was closely related to the roadside slope erosion, a positive linear correlation was found between runoff coefficient and soil shear strength reduction, and a power function was shown between soil detachment rate and soil shear strength reduction. This study demonstrated that Grass and Grass & Shrub were more suitable and highly cost-effective in controlling initial period erosion of newly built low-volume unpaved road.

Simulating transport of nitrogen and phosphorus in a Cambisol after natural and simulated intense rainfall

Intense rainfall adversely affects agricultural areas, causing transport of pollutants. Physically-based hydrological models to simulate flows of water and chemical substances can be used to help decision-makers adopt measures which reduce such problems. The purpose of this paper is to evaluate the performance of SWAP and ANIMO models for simulating transport of water, nitrate and phosphorus nutrients, during intense rainfall events generated by a simulator, and during natural rainfall, on a volumetric drainage lysimeter. The models were calibrated and verified using daily time series and simulated rainfall measured at 10-minute intervals. For daily time-intervals, the Nash-Sutcliffe coefficient was 0.865 for the calibration period and 0.805 for verification. Under simulated rainfall, these coefficients were greater than 0.56. The pattern of both nitrate and phosphate concentrations in daily drainage flow under simulated rainfall was acceptably reproduced by the ANIMO model. In the simulated rainfall, loads of nitrate transported in surface runoff varied between 0.08 and 8.46 kg ha(-1), and in drainage form the lysimeter, between 2.44 and 112.57 kg ha(-1). In the case of phosphate, the loads transported in surface runoff varied between 0.002 and 0.504 kg ha(-1), and in drainage, between 0.005 and 1.107 kg ha(-1). The use of the two models SWAP and ANIMO shows the magnitudes of nitrogen and phosphorus fluxes transported by natural and simulated intense rainfall in an agricultural area with different soil management procedures, as required by decision makers.

Runoff characteristics and nutrient loss mechanism from plain farmland under simulated rainfall conditions

In recent years, nonpoint source (NPS) pollution has become the main contributor to water quality problems. Research on nitrogen (N) and phosphorus (P) losses from farmland and the factors that influence these losses is very meaningful both for increasing the crop yield and for improving environmental water quality. To explore the mechanism by which N and P are lost from farmland in the North China Plain (NCP), 16 simulated rainfalls were conducted in 14 experimental fields (each of which had different conditions) in the NCP from July to August in 2010. The results showed that the rainfall intensity, the antecedent soil moisture content, and the vegetation cover status were the main factors that affected the surface runoff in the NCP. The runoff volume increased with the increasing rainfall intensity and the increasing soil moisture content, and decreased with the increasing vegetation cover. These factors also significantly affected the losses of P and N. The losses of P and N were positively correlated with the rainfall intensity and the antecedent soil moisture content, and negatively correlated with the vegetation cover. A longer and more intense rainfall resulted in a higher loss of N and P. Dissolved nitrogen was the predominant form of N loss. For phosphorous, the predominant loss form was greatly influenced by the rainfall intensity, the vegetation cover, and the antecedent soil moisture content. Most of phosphorus existed as dissolved phosphorus in Baizhuang (BZ) and as particulate phosphorus in Tangcheng (TC) and Fentai (FT). The minimum requirements for runoff occurrence in experimental regions were a rainfall depth of 5.1mm, a rainfall intensity of 50mm/h, and an antecedent soil moisture of approximately 29.6%.

Clogging evaluation of open graded friction course pavements tested under rainfall and heavy vehicle simulators

In this study a new procedure is developed to obtain core samples from field sections to assess clogging mechanisms of open graded friction course (OGFC) pavements using X-ray computed tomography (CT) imaging. The approach compared X-ray computed tomography (CT) images taken before and after: (1) rainfall simulations without trafficking to investigate particle-related clogging and (2) full-scale accelerated pavement rutting tests (APT) to investigate deformation related clogging of OGFC layers. Rainfall simulations were performed with runoff water of known total suspended solids (TSS) and particle size distributions (PSDs). Full-scale accelerated rutting tests were performed under controlled temperature and loads. Both investigations were performed for three different OGFC pavements with different layer thicknesses and mix types. The clogging of rutting test sections were also evaluated by comparing the surface permeability measurements performed before and after APT testing. The results of X-ray CT image processing revealed a significant reduction in air-void content of core samples after APT rutting tests. The highest air-void reduction was concentrated at the bottom of the OGFC layers. Permeability measurements also showed a 40%-90% reduction in permeability after APT trafficking. X-ray CT image processing of core samples tested under simulated rainfall showed that air void content reduction is concentrated in the lower part (2-6 mm from the bottom) of the OGFC layers as a result of particle accumulation. Small changes in air void contents were observed in the upper part of the OGFC layers (10-15 mm) while these reductions in air void contents were not significant to cause surface overflow and hence it is expected that the tested OGFC pavements will have sufficient permeability to infiltrate water during most average storm events.