Simulated Rainfall Research Articles

Assessment of Soil Aggregate Stability Methodologies in Calcareous Silt Loams

Highlights Three methods were used to measure soil aggregate stability in the calcareous silty loam soils of Idaho’s Magic Valley. No treatment differences were found using traditional wet sieving or SLAKES methods. Cornell Sprinkle Infiltrometer was more sensitive to the treatments compared to the other two methods. Abstract. Idaho’s Magic Valley is a highly productive agricultural region in the United States due to irrigation. The soils in this region are prone to crusting, have low organic matter, and are high in calcium carbonates, making them susceptible to erosion and water runoff. Soils need to be better managed to enhance aggregate stability to enable increased infiltration of irrigation water and decreased soil erosion in nearby waterways. However, to make management recommendations, the identification of appropriate measurements of aggregate stability needs to be identified, and few relevant studies exist. Thus, the overall goal of this project was to identify appropriate methods for the assessment of soil aggregate stability in the study region. The study sites were located in Southern Idaho and set up using common cropping rotations and agricultural management practices for the region using a variety of nutrient sources, tillage types, and cover cropping. Three methods were used to measure soil aggregate stability: wet sieving, simulated rainfall using a Cornell Sprinkle Infiltrometer (sprinkler height: 30, 90, and 150 cm), and the SLAKES mobile application. No differences in soil aggregate stability were found when the wet sieving or SLAKES methods were used at the three study sites, either due to the method or a general lack of differences between treatments. When using the Cornell Sprinkle Infiltrometer, no treatment differences were found at LT-Manure or GRACEnet; however, differences were observed between treatments at the Cover Crop study site at sprinkler heights of 30 and 90 cm. At a sprinkler height of 30 cm, the average mean weight diameter was the highest when winter forage crops (WFC) and solid dairy manure (SDM) were applied (3.73 mm) and the lowest in the control (3.12 mm). At a sprinkler height of 90 cm, the average mean weight diameter was the highest when WFC and SDM were applied (3.54 mm) and the lowest in the WFC Only treatment (2.46 mm). These results not only have implications for which methods are best for assessing progress but also for what management practices can be utilized to decrease soil erosion from irrigated cropland. This study highlighted that under these soils and management practices, simply increasing soil carbon does not increase aggregate stability, especially when root crops are included in the crop rotation with intensive tillage. In arid and semi-arid regions, the Cornell Sprinkle Infiltrometer may be a more sensitive method of measuring soil aggregate stability compared to traditional wet sieving. Keywords: Agricultural management practices, Calcareous soils, Mean weight diameter, Slake test, Soil aggregate stability.

Estimating Effective Hydraulic Conductivity (Ke) for the Rangeland Hydrology and Erosion Model (RHEM)

Highlights Effective hydraulic conductivity (Ke ) predictive equations in all RHEM versions have satisfactory performance. New Ke predictive equations were developed for RHEM applications over broader rangeland conditions. Ke values on most rangelands can be estimated through readily measurable ground cover and soil texture data. Abstract. Effective hydraulic conductivity (Ke) is an important parameter for the prediction of infiltration and runoff by the Rangeland Hydrology and Erosion Model (RHEM). Three sets of equations to predict Ke have previously been used in RHEM. These equations are mainly based on rainfall simulation data representing undisturbed sites and have not undergone comprehensive evaluation for various rangeland conditions, particularly after disturbances. The goal of this research was to evaluate these equations using independent data obtained from rainfall simulations conducted at multiple rangeland sites. Additionally, we developed and evaluated a new set of Ke predictive equations applying readily measurable cover and soils data spanning a wide range of vegetation, soil textures, and disturbance conditions. The results show that all previous Ke equations in RHEM have a “satisfactory” performance with index of agreement (d) > 0.75 and R2 > 0.4. The new Ke approach resulted in “very good” performance with d > 0.9 and R2 > 0.5. The new set of equations enhances RHEM for applications over broader rangeland conditions, including sparse vegetation cover following disturbances or community transitions. Keywords: Disturbed Rangelands, Hillslope Runoff, Infiltration.

The role of geosynthetic materials and vegetation on slope erosional control: Results of scale model tests

Geosynthetic materials for erosion control have the potential to significantly reduce the soil loss and to ensure the shallow stability of slopes. The paper presents the results of a scale model tests of a 2:3 (V:H) slope made from a very erodible soil, a sandy soil without and with 5 cm of topsoil, with and without vegetation, without and with different types of geosynthetics for erosional control. The slope models were subjected to heavy rainfall using a rainfall simulator. Results of the study show that the geosynthetics and vegetation generates a delay in the erosion process caused by the raindrops. Another result highlighted in this paper is the fact that the roots system improves the soil shear strength of the upper soil mass.

Erosion Mechanisms in Unpaved Roads: Effects of Slope, Rainfall, and Soil type

Erosion is the main cause of damage to unpaved roads. This study utilized rainfall simulators to quantify erosion on unpaved roads, controlling variables such as rainfall intensity and slope. A laboratory model of an unpaved road was utilized to evaluate soil loss in an experimental setup. A total of 72 tests were conducted to compare simulated conditions on unpaved roads for three soil types with three slope variations, and eight rainfall intensities. The impact of each variable (soil type, slope, and rainfall intensity) on soil loss was analyzed for 30-minute rainfall events. Analysis of variance (ANOVA) was employed to assess soil erosion response to terrain slope for the three soil types, revealing statistical differences in soil loss between low slopes (2%) and steep slopes (7%) with p-values of .04 (sandy soil), .00007 (sandy silt soil), and .00008 (loam silt soil). Correlation analysis demonstrated a strong relationship between rainfall intensity and soil loss ( R2 = .76) for sandy soil and sandy silt soil. Analysis of covariance (ANCOVA) indicated a linear relationship between soil loss and rainfall intensity, with significant differences ( p < .05). The findings suggest that soil loss on unpaved roads is positively correlated with slope and rainfall intensity. However, this relationship is not always linear; sandy soil exhibited a nonlinear relationship, especially with high rainfall intensities, whereas sandy silt soil showed a linear relationship with evaluated rain intensities. The type of soil influences erosion process, with higher erosion rates observed in sandy silt soils compared to loam silt soils. This paper analyzed the factors essential for addressing erosion on unpaved roads, identifying key elements to minimize soil loss.

Evaluation and correction analysis of the regional rainfall simulation by CMIP6 over Sudan

This study utilizes satellite-based rainfall CHIRPS to evaluate GCMs-CMIP6 models over Sudan from 1985 to 2014. Overall, the GCMs of BCC-CSM2-MR, CAMS-CSM1-0, CESM2, ECEarth3-Veg, GFDL-ESM4, MIROC-ES2L, and NorESM2-MM are well reproduced in the unimodal pattern of June to September (JJAS), and hence employed to calculate Multi-Model Ensemble (MME). Then, we examine the capability of the GCMs and MME in replicating the precipitation patterns on annual and seasonal scales over Sudan using numerous ranking metrics, including Pearson Correlation Coefficient (CC), Standard Deviation (SD), Taylor Skill Score (TSS), Mean Absolute Error (MAE), absolute bias (BIAS), and, normalized mean root square error (RMSD). The results show that the MME has the lowest bias and slightly overestimates rainfall over most parts of our study domain, whilst, others (ACCESS-CM2, BCC-CSM2-MR, CAMS-CSM1-0, CESM2, CNRM-CM6-1, CNRM-CM6-1-HR, CNRM-ESM2-1, FGOALS-f3-L, FGOALS-g3) consistently overestimate rainfall in referring to CHIRPS data, respectively, but FIO-ESM-2-0 underestimates bias value. Moreover, MIROC-ES2L and NorESM2-MM demonstrate better performance than the other models. Finally, we employed a bias correction (BC) technique, namely Delta BC, to adjust the GCMs model products through the annual and monsoon seasons. The applied bias correction technique revealed remarkable improvement in the GCMs against the observations, with an improvement of 0 - 18% over the original. However, MME and MIROC-ES2L show better performance after correction than other models.

The effect of paving block from plastic waste material in the urban drainage: Study case in residential areas

Large expanses of green, open land are frequently converted as a result of population growth and quick development. This phenomenon causes the decreasing of water infiltration area which has an impact on increasing runoff coefficient. In the urban drainage problem, paving blocks are often used as road pavement construction materials to reduce surface runoff. The aim of this research is to study the characteristic of flow in the paving block made from plastic waste material. The research conducted in the laboratory testing utilizing a rainfall simulator by several variations in slope of 0% to 15%. The findings indicate that paving blocks made from plastic waste have less runoff coefficient than asphalt and/or concrete pavement. There is a correlation between the slope of the land and the runoff coefficient value which the runoff coefficient value increasing as the slope of the land increases. That finding is then applied in urban drainage problem located in the Cipamokolan Village region in Bandung City with the help of SWMM program for drainage calculation. As a result, the runoff discharge is decreasing by implementing the paving block made from plastic waste.

Conservation practices reverse soil degradation in Mediterranean fig orchards

Agriculture is an important driver of soil degradation, especially where intensive practices are applied. It is essential to reduce the impact of agriculture intensification and find different solutions to halt this. This work investigates the effect of different types of treatments: 1) tillage (Tilled), 2) Grass covered (Grass), 3) olive pomace (Pomace) and 4) Hay in different seasons (Spring, Summer, and Fall) using rainfall simulations (58 mm h−1 for 30 min). Tillage reduced bulk density (BD) compared to treatments with mulch cover. Grass-covered treatments increased soil organic matter (SOM) and water-stable aggregates (WSA). Additionally, they enhanced hydrological properties, thus mitigating sediment loss (SL) and element transport. The principal component analysis (PCA) showed strong relations between SL and element losses, as well as P soil and Cu soil with SOM. Thus, implementing soil conservation practices, such as hay used as a surface cover, is crucial for fig orchards and agricultural area management to reduce soil erosion, enhance soil quality, and mitigate element transport and SL. Further on, continuous monitoring of soil properties and hydrological responses throughout different seasons should be prioritized, along with exploring alternative methods to ensure sustainable soil management.

Evaluating the influences hedgerow on soil erosion and nitrogen loss of purple soil sloping farmland under simulated rainfall

Hedgerow is a vital soil and water conservation technology for sloping farmland that can significantly reduce erosion and nutrient loss via their above- and below-ground parts. The effect of hedgerow on erosion and nutrient loss has been widely investigated, while the respective effects of their above- and below-ground parts are still unclear. Therefore, the purple soil from the Three Gorges Reservoir Area was used, and 3 slope conditions of control check, whole hedgerow and hedgerow roots only combined with 2 slope gradients (15° and 25°) were constructed and the simulated rainfall tests were researched at 3 rainfall intensities (60, 90 and 120 mm h−1). The runoff initiation time, runoff and erosion rates, and loss of nitrogen via runoff and sediment were analysed. In comparison to the control check slope condition, it was indicated that hedgerow increased the runoff initiation time by 43.38 %, decreased runoff and erosion by 15.59 % and 78.37 %, and decreased nitrogen loss via runoff by approximately 40 % and via sediment by approximately 70 % on average, respectively. The average contribution rates of the below-ground part of the hedgerow was 49.89 % for the increase in runoff initiation time, 33.99 % for runoff reduction, and 39.91 % for erosion reduction. In addition, more than 2/3 and 58.49 % of nitrogen loss reduction via runoff and sediment, respectively, was contributed by the above-ground part of the hedgerow. These results are beneficial for comprehending the control mechanism of hedgerow on soil erosion and nitrogen loss, thereby provide a scientific foundation for the sustainable and efficient utilization of soil and water resources on sloping farmland.

A Laboratory Study of the Role of Nature-Based Solutions in Improving Flash Flooding Resilience in Hilly Terrains

Nature-based solutions (NBSs) always provide optimal opportunities for researchers and policymakers to develop sustainable and long-term solutions for mitigating the impacts of flooding. Computing the hydrological process in hilly areas is complex compared to plain areas. This study used a laboratory-scaled hillslope model to study rainfall-runoff responses considering the natural hillslope conditions prevailing in hill torrents creating flash floods. The objective of this study was to estimate the impact of nature-based solutions on time-to-peak for flash flooding events on hilly terrains under different scenarios. Many factors decide the peak of runoff generation due to rainfall, like land use conditions, e.g., soil porosity, vegetation cover, rainfall intensity, and terrain slope. To reduce these complexities, the model was designed with thermopore sheets made of impermeable material. A hillslope model using NBS was designed to evaluate flood hydrograph attenuation to minimize the peak discharge (Qp) and increase time-to-peak (Tp) under varying rainfall, land cover, and drainage channel slope conditions. A rainfall simulator was used to analyze the formation of hydrographs for different conditions, e.g., from barren to vegetation under three different slopes (S0, S1, S2) and three rainfall intensities (P1, P2, P3). Vegetation conditions used were no vegetation, rigid vegetation, flexible vegetation, and the combination of both rigid and flexible vegetation. The purpose of using all these conditions was to determine their mitigation effects on flash flooding. This experimental analysis shows that the most suitable case to attenuate a flood hydrograph was the mixed vegetation condition, which can reduce the peak discharge by 27% to 39% under different channel slopes. The mixed vegetation condition showed an increase of 49% in time-to-peak (Tp) compared to the no vegetation condition. Additionally, under P1 rainfall and a bed slope of 0°, it reduced the peak discharge by up to 35% in the simulated flood and effectively minimized its potentially destructive impacts.

Impacts of Climate Change and Regional Variations on Future Rainfall Patterns in Thailand by Downscaling Method

In this study, we investigated the impacts of climate change on rainfall patterns in Thailand using the downscaling method. The simulation data was obtained from the Weather Research and Forecasting (WRF) model, using the Community Earth System Model (CCSM) as a boundary condition. The characteristics of rainfall were analyzed in terms of the total annual rainfall, rainfall intensity, the number of days with heavy rain, and the total amount of rainfall in each season in the future compared to the base periods. It was found that the simulation of the climate in upper Thailand was consistent with the reanalysis values, with TCC ranging from 0.6 to 0.9. The simulated annual rainfall amount is underestimated throughout the country. There are indications that rainfall will increase in average and extreme terms in some regions, including the eastern region of the Northeast, the western side of the North, and the upper part of the West. In the southern part of the country, the overall rainfall indices are expected to decrease with low confidence in almost the entire region.

Characterization and Application of Rice Straw-Based Polyurethane Foam Blocks for Soil Erosion Control

Soil erosion, a global problem, degrades land quality and increases pollution and sedimentation in bodies of water. This study propounds a new material to mitigate soil erosion using rice straw-based polyurethane foam (RSPF) blocks as a potential replacement for commercially available expanded polystyrene (EPS) foam in slope stabilization. RSPF was synthesized via a conventional one-shot foaming method with 15% rice straw-based polyol content. The RSPF blocks have an average density of 43.29 kg/m3, average compressive strength of 184.55 kPa, closed cell content of 88.4%, and water absorption capacity of 262% that can effectively reduce water runoff. These properties are comparable to EPS foams according to ASTM D6817, except for the high absorption capacity of RSPF. This added feature allows the foam to act as topsoil protection by reducing runoff. In slope stabilization and topsoil protection applications, the effectiveness of the RSPF blocks in reducing soil loss was tested in both simulated and natural rainfall events with different land slope degrees, rain intensities, and soil covers. Results show that the use of RSPF in the simulated setup with a heavy rain intensity of 80 mm/h reduced the soil loss by 61.5%, 22.7%, and 4.3% in 5°, 10°, and 20° of land slope, respectively. There was also a higher degree of soil loss reduction when the RSPF block was coupled with a natural vegetation soil cover by 79.6%, 70%, and 19.3% in 5°, 10°, and 20° land slopes, respectively. Moreover, in the natural rainfall events in an open field with a land slope of 20°, the recorded soil loss reduction reached 93.6–98.8% at an average rainfall intensity of 16.26 mm/h. Additionally, the relationship between soil loss and land slope was investigated to produce a best fit model that predicts the soil loss up to a 20° land slope. An interesting observation was made wherein the erosion rate increased using linear regression modeling in the simulated setup for bare soil (BS), soil with vegetation (SV), soil with RSPF (SF), and soil with RSPF and vegetation (FV), with high coefficient of determination (R2) values between 0.92 and 0.99. These findings suggest that the RSPF block is a promising alternative and sustainable material for EPS foams in mitigating soil erosion, especially under heavy rainfall conditions.

Effects of multiple factors on particle size selectivity under artificial extreme rainfall events on simulated Gobi surface

Understanding multiple-factor effects on particle size selectivity by extreme rainfall events in Ala-Shan Gobi desert is of great significance for better estimation of potential Asian dust emission sources. Artificial rainfall simulation experiments were used to investigate the particle size selectivity characteristics by extreme rainfall events under different rainfall intensities (20 mm h−1 and 40 mm h−1), slope gradients (3° and 15°) and gravel coverages (0, 30%, and 60%). Moreover, the relations of clay content (Clc), silt content (Sic), fine particle (< 50 μm) content (Fic) and enrichment ratio of fine particles (ER<50) with multiple factors were regressed and validated. Results show that rainfall intensity significantly (P < 0.05) affect runoff and sediment yield processes, but slope gradient was a dominant factor that changed particle size distribution (PSD). The selectivity of fine particles was higher at low rainfall intensity (20 mm h−1), gentle slope (3°) and moderate gravel coverage (30%), with ER<50 reaching 6.14, which dominate the potential Asian dust emission sources. The interaction were discussed and classified into ‘Synergy’ and ‘Trade-off’. Clc and Fic showed negative exponential relationship with rainfall intensity and slope gradient, but positive exponential relationship with gravel coverage. While Sic and ER<50 showed negative power function relationship with rainfall intensity, slope gradient and gravel coverage. These findings could help to understand the effects of multiple factors on potential sources of Asian dust emission under extreme rainfall events in Gobi region of northwestern China and provide basic science reference for the prediction of dust emission in this region.

Varying particle size selectivity of soil erosion along a cultivated catena

Abstract Sheet erosion is a complex multi-factor-dependent process with high spatial heterogeneity on hillslopes. Although the individual factors have been well studied, their aggregated effect on size-selective erosional processes is highly uncertain. Therefore, this study concentrates on the aggregate size distribution and effective particle size distribution (PSD) of the aggregates in the soil loss, collected from different simulated hillslope positions and surface conditions. These simulated hillslope positions combine moisture content from the extremely dry to the saturated with related slope positions of 2, 5, and 12% steepness and different surface roughness (tilled and crusted surfaces) modelled in a laboratory rainfall simulator. Using hierarchical cluster analysis, the PSD of the aggregates was separated into three groups based on the differences in the 59–116 µm range of the PSD histograms, namely, macro-aggregates, 50–250 µm sized micro-aggregates, and &lt;50 µm sized fractions were classified into distinct groups, although some micro-aggregate samples were classified into the macro-aggregate group. PSDs from the 50–250 µm aggregate size fraction were clustered into a group of macro-aggregates if the PSD changed with time (during the rainfall event), notably on rough surfaces. The role of the specified size range in the classification is believed to be due to the parallel presence of aggregates and single particles in this range. As aggregates have a lower density than mineral particles, they tend to be enriched in soil loss under low-energy runoff conditions. Moreover, all samples in the &lt;50 µm fraction clustered into the macro-aggregate group were eroded from the smooth/crusted surface, probably due to the presence of larger particles. The results indicate that the combined effect of erosional factors is not apparent, and the impact of the crust and extreme moisture content on the selectivity and size distribution of the sediment requires further investigation.

Movement of TNT and RDX from composition B detonation residues in solution and sediment during runoff

Energetics used in military exercises can potentially contaminate ground and surface waters. This study was conducted to evaluate the movement of Composition B, a formulation that includes TNT (2,4,6-trinitrotoluene), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), in runoff. Mechanisms of transport we examined include movement of energetics dissolved in runoff, as particles and adsorbed to suspended sediment, and in infiltration. Rainfall simulations were conducted under controlled conditions with two rainfall rates (approximately 30 and 50 mm h−1), two soils with different infiltration capacities, and four energetic particle sizes (4.75–9.51 mm, 2.83–4.75 mm, 2–2.83 mm, and <2 mm). Particles remaining on the soil surface after rainfall were measured as well as energetics dissolved in runoff, in suspended sediment, and in infiltration. Greater concentrations of TNT than RDX and HMX were found dissolved in runoff due to its higher solubility and dissolution rates. We also found that particle transport in runoff increased with decrease in particle size. Smaller particle sizes also led to greater transport dissolved in solution. Relationships were found relating runoff and sediment yield to the transport of RDX and TNT. The results of this study allow improved prediction of Composition B transport in runoff and therefore its contamination potential.

Combined role of ground cover management in altering orchard surface‒subsurface erosion and associated carbon-nitrogen-phosphorus loss.

The combined role of ground cover management in controlling soil erosion and nutrient loss from new orchards is still less understood. In this study, four ground cover management practices, orchard with grass cover (OG), orchard with interplant cover (OI), orchard with straw cover (OS), and orchard with bare ground (OB), were designed to identify their impacts on soil erosion and associated carbon-nitrogen-phosphorus loss in new orchards by rainfall simulation tests with rainfall intensities of 60, 90, and 120mmh-1 and 90min rainfall duration. The results showed that OS had the lowest surface flow coefficient (6.6%) and highest subsurface flow coefficient (32.5%). The highest soil loss rate occurred in the OB plot (65.4gm-2min-1), and the lowest soil loss rate occurred in the OS plot (0.5gm-2min-1). OS plot showed better effectiveness in improving soil erosion. However, the increased infiltration capacity was facilitated in terms of causing non-point source pollution. The C-N-P ratios of surface flow in different cover measures (OB, OI, OG, and OS) were 1.4:1.2:0.9:1, 1.8:1.7:1.2:1, and 2.3:1.9:1.2:1, respectively. The ratios of sediment in different cover measures were 7.3:9:2.3:1, 2:1.5:1.2:1, and 1.2:1:0.8:0.7, respectively. Cover management plots play an active role in reducing nutrient loss in surface flow and sediment, but the increased infiltration in covered management plots is associated with the risk of groundwater contamination in subsurface flow. The C-N-P ratios of subsurface flow in OB and covered managed plots (OI, OG, and OS) were 1:3.3:1.6:2.7, 1:1.5:2.2:2.4 and 1:1.2:1.5:1.3, respectively. Therefore, when managing the phenomenon of soil erosion through ground cover measures, attention should also be focused on the function of cover measures in regulating non-point source pollution underground, such as subsurface flow. This research recommends a combination of cover management measures to further mitigate erosion and the risk of groundwater contamination.

Influence of check dams on water and sediment processes and deposition patterns under simulated rainfall conditions

The Loess Plateau in China has the highest soil erosion and water loss rates in the world. Therefore, check dams, which are more useful engineering measures, have been established to improve soil and water conservation in small watershed. To determine check dam configuration pattern influence on runoff, sediment yield, erosion and deposition pattern in watershed, we conducted a rainfall simulation experiment using the qiao gully small watershed as our normal-scale model. We analysed the runoff and sediment yield characteristics and deposition patterns under four types of check dam configurations: no dams constructed, dam in first order stream channel, dam in second order stream channel, and dams in both channels. Our findings revealed that the runoff and sediment concentrations increased with time, regardless of check dam configuration. The significant effects of check dams on the evolution of storm runoff processes in a small watershed. Compared to no dams, double dams best inhibited runoff reduction and lowered sediment deposition, while construction of one dam in the primary channel was more effective than one dam in the secondary channel. In summary, check dam construction reduced channel erosion, rill erosion, and bank slope collapse at the channel head, while raising the dam-controlled watershed base level. Our findings provide a reference for designing check dams in optimal configurations on plateaus such as the Loess Plateau. The results of this study are of great practical significance in revealing the process of storm runoff and identifying key parts of soil erosion–deposition in the watershed.

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.

Potential risk, leaching behavior and mechanism of heavy metals from mine tailings under acid rain

The leaching of heavy metals from abandoned mine tailings can pose a severe threat to surrounding areas, especially in the regions influenced by acid rain with high frequency. In this study, the potential risks of heavy metals in the tailings collected from a small-scale abandoned multi-metal mine was assessed, and their leaching behavior and mechanism were investigated by batch, semi-dynamic and in situ leaching experiments under simulated and natural rainfall conditions. The results suggested that Zn, Cu, Pb, and Cd in the tailings could cause high/very high risks. Both batch and semi-dynamic leaching tests consistently confirmed that the leaching of heavy metals (particularly Cd) could lead to serious pollution of the surrounding environment. The leaching rates of heavy metals were pH-dependent and related to their chemical speciations in the mine tailings. The leaching behavior of Cu and Cd was dominated by surface wash-off, Zn was controlled by diffusion initially and then surface wash-off, and the leaching mechanisms of Pb and As varied with the pH conditions. It was estimated that acid rain could greatly elevate the release fluxes of Zn (20.8%), Cu (36.7%), Pb (49.9%) and Cd (35.3%) in the study area. These findings could improve the understanding of the leaching behavior of heavy metals from mine tailings and assist in developing appropriate management strategies.

Effects of microtopography shaping on characteristics of eroded sediment particles of a dump slope in an opencast coal mine in China

AbstractThe properties of sediment particles are crucial research areas for understanding soil erosion on dump slopes. In this study, the slope of the southern dump of the ATB opencast coal mine in the Pingshuo mining area in Shanxi Province, China, was selected to conduct microtopographical shaping and artificial rainfall simulation experiments. Three different gradients of rainfall intensity, 20, 50, and 80 mm·h−1, were set. The main component of rainwater was water (chemistry H2O) by a rainfall duration of 30 min. A Microtrac S3500 laser particle size analyzer was used to measure the collected erosion sediment particles. This study conducted level benches and fish‐scale pits microtopography shaping on the slope of the waste dump. The dimensions of the level bench design were 1, 2, and 1 m for the step width, for the step length, and between each level bench, respectively. The fish‐scale pits were 60 cm (length), 40 cm (width), and 30 cm (depth). The horizontal and row spacing of each fish‐scale pit was 1 m, and an unshaped terrain was used as the control group. Through dynamic monitoring and statistical analysis of the data, the impacts of rainfall intensity and microtopography shaping mode on the features of the eroded sediment particles were analyzed. Fine silt particles (53%) were lost as a result of the surface erosion of the slope. The mean starting periods of sediment particle loss decreased with the increase in rainfall intensity (589 s &gt; 402 s &gt; 305 s). Additionally, the clay and silt particle enrichment ratios decreased (ER &gt;1), whereas the sand particle enrichment ratios increased (ER &lt;1). The level benches had a stronger interception effect on fine sediment, whereas the fish‐scale pits had a weaker interception effect on sediment particles under heavy rain. The distribution properties of erosion sediment particles on a slope can be assessed using fractal dimension as an index. This study is significant for understanding the erosion mechanism of eroded sediment particles on dump slopes and provides a scientific foundation for soil erosion control on opencast coal mine dump slopes in the Loess Plateau. These results highlight the potential for the level bench to effectively delay the occurrence of runoff and greatly enhance the interception of sediment particles.

Fate of atrazine in soybean (Glycine max L.) and corn (Zea mays L.) succession in Brazilian subtropical conditions

This work aimed to evaluate the distribution of atrazine via surface runoff, leaching, and retention in a Rhodic Ferralsol and to analyze the effect of a succession of corn and soybean crops in Brazilian subtropical edaphoclimatic conditions on the distribution of this herbicide. The mobility of atrazine was evaluated using a drainage lysimeter under conditions of intensely simulated precipitation, carried out 24 h and 48 h after a single herbicide application at 17 days after corn emergence. Surface runoff and leaching were sampled during the rainfall simulations at intervals of 5 min until completing 1 h. Corn foliar analyses were carried out to measure the residual amounts of atrazine. In addition, laboratory studies of sorption (equilibrium and thermodynamics) and dissipation were carried out to understand the dynamics of atrazine in the soil. Freundlich's non-linear isotherms presented an excellent fit in the description of atrazine sorption in a Rhodic Ferralsol. The high content of organic matter in the soil and the temperature variation directly influences the retention of atrazine in the soil. The half-life (t1/2) of atrazine in soil under controlled conditions indicates a non-persistent pesticide, with 14.44 days. However, the herbicide can persist in deep soil layers for more than 93 days after spraying. When high-intensity rainfall occurs 24 h after application, large proportions of atrazine are lost by runoff within the first 20 min of rain. At the same time, significantly inferior losses are observed when rainfall occurs 48 h after spraying. High-intensity rainfall within 24 h of atrazine application leads to substantial losses, causing an approximate 84% reduction in its concentration in corn leaves and a 94% reduction in soil. Conservationist agronomic practices that protect the soil, especially during the initial periods of corn cultivation, are essential to reduce atrazine losses by runoff or leaching. In addition, increasing the concentration of organic matter in the soil can be extremely promising in increasing the retention of this pesticide to soil colloids, preventing its loss in soils with a low content of clay minerals.