Impact of a WWTP effluent overland flow on the properties of a mediterranean riparian soil.

In this work we aim to assess the impact of a WWTP effluent overland flow on properties and nutrient concentrations of a riparian soil, in order to explore the potential of this practice as a nature-based treatment. We set two study zones of 150 m2 on the field, one control and one that received the WWTP effluent on its surface for one month. Samples were taken before and after the effluent overland flow system, to test the impact of the effluent on soil properties through a BACI design, and after 17 months, to evaluate the recovery of the soil. Two depths were studied: 0-5 cm and 5-20 cm. The effluent overland flow triggered an increase in exchangeable sodium percentage and a decrease in nitrate concentration in both depths, and an increase in ammonium concentration in 0-5 cm depth. After 17 months, there were not found relevant differences among zones. In conclusion, this practice could be used in the purpose to reduce the nutrient concentrations of WWTP effluents. This practice could be relevant for regions where WWTP effluents are discharged in low-flow or intermittent streams, such as semi-arid regions or the Mediterranean region.

Important Role of Overland Flows and Tile Field Pathways in Nutrient Transport.

Nitrogen and phosphorus pollution is of great concern to aquatic life and human well-being. While most of these nutrients are applied to the landscape, little is known about the complex interplay among nutrient applications, transport attenuation processes, and coastal loads. Here, we enhance and apply the Spatially Explicit Nutrient Source Estimate and Flux model (SENSEflux) to simulate the total annual nitrogen and phosphorus loads from the US Great Lakes Basin to the coastline, identify nutrient delivery hotspots, and estimate the relative contributions of different sources and pathways at a high resolution (120 m). In addition to in-stream uptake, the main novelty of this model is that SENSEflux explicitly describes nutrient attenuation through four distinct pathways that are seldom described jointly in other models: runoff from tile-drained agricultural fields, overland runoff, groundwater flow, and septic plumes within groundwater. Our analysis shows that agricultural sources are dominant for both total nitrogen (TN) (58%) and total phosphorus (TP) (46%) deliveries to the Great Lakes. In addition, this study reveals that the surface pathways (sum of overland flow and tile field drainage) dominate nutrient delivery, transporting 66% of the TN and 76% of the TP loads to the US Great Lakes coastline. Importantly, this study provides the first basin-wide estimates of both nonseptic groundwater (TN: 26%; TP: 5%) and septic-plume groundwater (TN: 4%; TP: 2%) deliveries of nutrients to the lakes. This work provides valuable information for environmental managers to target efforts to reduce nutrient loads to the Great Lakes, which could be transferred to other regions worldwide that are facing similar nutrient management challenges.

Threshold migration conditions of (micro) plastics under the action of overland flow.

Surface runoff is a major pathway for the transport of plastics. However, most previous studies focus on the transport of microplastics in aquatic environment, whereas the migration of plastics from terrestrial environment to aquatic ecosystems receives limited attention. In this work, we investigated the migration of plastic on different surfaces via surface runoff. Results indicate that the threshold migration condition increases with the size and density of plastics, while decreases as the surface inclination increases. Plastics show a higher degree of mobility on smooth surfaces, but plastic films exhibit lower mobility due to the frictional forces induced by the downward pressure exerted by the water flow. Conversely, rough surfaces such as concrete and macadam can trap small fragments and rigid film plastics, and plastics can be embedded within the soil matrix under the water flow. In summary, smaller size, steeper incline, and greater water flow rate facilitate the movement of plastics on surfaces. Results from this work improve the understanding of the process of plastic migration from land to water, and are of great significance for the prevention and control of plastic pollution.

Response of sediment transport capacity to soil properties and hydraulic parameters in the typical agricultural regions of the Loess Plateau.

The sediment transport capacity by overland flow (Tc) is a key parameter in process-based soil erosion models and Tc variation is sensitive to changes in soil properties. This study was undertaken to investigate Tc variations with respect to soil properties and establish a universal relationship to predict Tc. The test soils were collected from typical agricultural regions (Guanzhong basin-Yangling (YL), Weibei Dry plateau-Chunhua (CH), Hilly and gully region-Ansai (AS), Ago-pastoral transition zone along the Great Wall-Yuyang (YY), and Weiriver floodplain-Weicheng (WC)) of the Loess Plateau, and subjected to 36 different combinations of slope gradients (S, 5.24-44.52 %) and flow discharge (q, 0.00033-0.00125 m2 s-1) in a hydraulic flume. The results showed that the mean Tc values for WC were 2.15, 1.38, 1.32, and 1.16 times greater than those for YL, CH, AS, and YY, respectively. Tc significantly decreased with clay content (C), mean weight diameter (MWD), and soil organic matter content (SOM). Tc for different soil types increased with S and q as a binary power function, and Tc variation was more sensitive to S than to q. Stream power (w) was the most appropriate hydraulic variable to express Tc for different soils. Tc for different soil types could be satisfactorily simulated using a quaternary power function of S, q, C, and MWD (R2 = 0.94; NSE = 0.94) or a ternary power function of w, C, and MWD (R2 = 0.94; NSE = 0.94). The new Tc equation can reflect the effect of soil properties on it and facilitate the development of a process-based soil erosion model.

Biochar impacts on runoff and soil erosion by water: A systematic global scale meta-analysis.

Biochar application to soil has the potential to affect soil and vegetation properties that are key for the processes of runoff and soil erosion. However, both field and pot experiments show a vast range of effects, from strong reductions to strong increases in runoff and/or soil erosion. Therefore, this study aimed to quantify and interpret the impacts of biochar on runoff and soil erosion through the first systematic meta-analysis on this topic. The developed dataset consists of 184 pairwise observations for runoff and soil erosion from 30 independent studies but 8 of which just focused on soil erosion. Overall, biochar application to soil significantly reduced runoff by 25 % and erosion by 16 %. Mitigation of soil erosion in the tropics was approximately three times stronger (30 %) than at temperate latitudes (9 %); erosion reduction in the subtropical zone was 14 %, but not significantly different from either the tropical or temperate zones. Fewer reported field observations for runoff resulted in larger confidence intervals and only the temperate latitudes showed a significant effect (i.e. a 28 % reduction). At topsoil gravimetric biochar concentrations between 0.6 % and 2.5 %, significant reductions occurred in soil erosion, with no effect at lower and higher concentrations. Biochar experiments that included a vegetation cover reduced soil erosion more than twice as much as bare soil experiments, i.e. 27 % vs 12 %, respectively. This suggests that soil infiltration, canopy interception, and soil cohesion mechanisms may have synergistic effects. Soil amended with biochar pyrolyzed at >500 °C was associated with roughly double the erosion reduction than soil amended with biochar produced at 300-500 °C, which potentially could be related to the enhancement of hydrophobicity in the latter case. Our results demonstrate substantial potential for biochar to improve ecosystem services that are affected by increased infiltration and reduced erosion, while mechanistic understanding needs to be improved.

Transport of insensitive munitions constituents, NTO, DNAN, RDX, and HMX in runoff and sediment under simulated rainfall.

Insensitive munition constituents derived from residues of low order detonations and deposited on military training grounds present environmental risks. A series of rainfall simulation experiments on small soil plots examined the effect of precipitation, soil properties, and particle size on transport of IMX-104 munition components: NTO (3-nitro-1,2,4-triazol-5-one), DNAN (2,4-dinitroanisole), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and HMX (octahydro-1,3,5,7- tertranitro-1,3,5,7-tetrazocine). The primary pathways for rainfall driven transport were subsurface infiltration, off-site transport in solution, and transport in solid form including re-adsorption onto soil particles. The transport was solubility dependent with NTO moving mostly in solution, which was dominated by either runoff or infiltration depending on soil. DNAN, RDX, and HMX, were transported primarily in particulate form. The fine energetic fraction (<2 mm) showed the highest mobility, while the coarsest fraction (>4.75 mm) remained in-situ after rainfall. A simple linear model relating energetics transport with sediment yield and energetics particle size and was proposed. These findings provide the first comprehensive mass balance of munition constituents as affected by overland flow under rainfall. They improve our understanding of environmental fate of munitions, can further be used for predictive modelling, developing mitigation strategies, and regulatory compliance.

A laboratory rill study of IMX-104 transport in overland flow.

The deposition of explosive contaminants in particulate form onto the soil surface during low-order detonations can lead to ground and surface water contamination. The vertical fate and transport of insensitive munitions formulation IMX-104 through soil has been thoroughly studied, however the lateral transport of explosive particles on the surface is less known. The objective of this research was to understand the impact of overland flow on the transport of IMX-104 constituent compounds 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The effect of overland flow was examined in a rill flume using several flow rates (165-, 265-, and 300-mL min-1) and IMX-104 particle sizes (4.75-9.51 mm, 2.83-4.75 mm, 2-2.83 mm, and <2 mm). We found that the smaller particles were transported more in solution and with the sediment compared to the larger particles, which had a higher percent mass remaining on the surface. As flow rate increased, there was an increase in the percent mass found in solution and sediment and a decrease in the percent mass remaining on the surface. NTO fate was dominated by transport in solution, while DNAN, RDX and HMX were predominantly transported with the sediment. This research provides evidence of the role of overland flow in the fate of energetic compounds.

Effects of shrub-grass cover on the hillslope overland flow and soil erosion under simulated rainfall.

Vegetation plays a vital role in regulating hydrological cycle and controlling soil erosion at multiple spatial and temporal scales. Establishing shrub-grass community is one of the widely adopted practices to increase rainfall infiltration and reduce soil erosion in water-limited and highland regions. To understand the effects of such vegetation communities on soil erosion and overland flow under different rainfall regimes at the hillslope scale, we conducted rainfall simulation experiments by setting up parallel plots at fixed slope of 15° including unvegetated (coverage 0%), shrub only (coverage 50%), grass only (coverage 50%), and shrub-grass covered (coverages 25%, 50%, 75%, and 100%) and constant rainfall intensities of 30, 60, and 90 mm h-1 rainfalls lasting 60 min each after the initiation of overland flow. Two native species Lespedeza bicolor and Carex giraldiana, distributed in the soil sampling region were planted on the plots to achieve designed coverages. We found that the overland flow and sediment load from vegetated slopes were reduced by 9%-58% and 27%-98%, respectively, compared with unvegetated slopes while the infiltration rate increased by over 45%. Shrub-grass community reduced the overland flow and sediment yield more significantly than shrub only and grass only treatments with the same coverage of 50% under three rainfall intensities. In addition, the overland flow rate linearly decreased while the mean sediment yield exponentially reduced against the increase in shrub-grass community coverage. Hydrodynamically, shrub-grass communities not only increased the critical hydrodynamic forces for the initiating soil erosion but also increased the resistance coefficient leading to reduce overland flow velocity, stream power, and thus soil erosion from the vegetative slope even under extreme rainfalls. Our research highlights the importance of developing the shrub-grass communities to reduce the quantity and energy of overland flow and control soil erosion on the hillslopes in water-limited and highland regions.

Evaluation of overland flow modelling hypotheses with a multi-objective calibration using discharge and sediment data.

Conceptual hydrological models can move towards process-oriented modelling when addressing broader issues than discharge modelling alone. For instance, water quality modelling generally requires understanding of both pathways and travel times which might not be easily identified because observations at the outlet aggregate all processes at the catchment scale. In this study we tested if adding a second kind of observation, specifically sediment data, can help distinguish overland flow from total discharge. We applied a multi-objective calibration on both discharge and suspended sediment concentration simulation performance to the World-Wide Hydrological Predictions for the Environment (HYPE) model for 111 catchments spread over the USA. Results show that in comparison to two calibrations made one after the other, the multi-objective calibration leads to a significant improvement on the simulation performance of suspended sediments without a significant impact on the performance of discharge. New modelling hypotheses for overland flow calculations are proposed and resulted in similar discharge performances as the original one but with fewer parameters, which reduces equifinality and can prevent unwarranted model complexity in data-poor areas.

Characterisation of soil erosion and overland flow on vegetation-growing slopes in fragile ecological regions: A review.

Grasses and shrubs occupy large areas of fragile ecosystems following ecological restoration. Therefore, it is increasingly important to assess and monitor the environmental safety of pastures. However, previous studies on this topic lacked systematicity and directionality. In this study, we reviewed the literature on runoff and erosion to summarise the core issues for future research, resolve the current research bottleneck, and promote the balance of soil, water, and energy in fragile ecological areas. The results of the review indicate that coverage remained the main vegetation feature considered when characterising rangeland slope erosion and runoff. Erosion energy should be comprehensively considered based on the influence of vegetation on rainfall distribution and runoff erosivity. Rangeland slope erosion and runoff changes can only be explained by integrating the above- and below-ground characteristics of vegetation. Additionally, the impact of vegetation on runoff separation and the sediment transport processes at different erosion stages under rainfall conditions vary. Therefore, studying the comprehensive indicators of vegetation at different erosion stages in response to erosion and runoff will be vital in rangeland erosion research. From the perspective of disciplinary development, this study can promote the further development of soil erosion, ecology, soil science, hydrology, hydraulics, and other disciplines.

Modeling radionuclide transport in urban overland flow: a case study.

This paper presents a case study demonstrating the process used to develop an overland flow model of radionuclide transport following an aerosol deposition from a hypothetical radiological dispersal device explosion. The process included the integration of digital elevation, building, and land cover information with hydrologic information from a calibrated Stormwater Management Model (SWMM) model. The overland flow model was used to explore the impact of washoff parameter selection and different storm events on radionuclide transport in surface flow. The range of washoff parameters used in the literature resulted in over a 7 times difference in radionuclide washoff, from a small surface removal to nearly full removal. The overland flow model illuminated the primary pathways of contaminant transport, a potentially useful tool that informs emergency response, planning, and remediation activities.

Effects of root morphological traits on soil detachment for ten herbaceous species in the Loess Plateau.

Plant root systems can greatly reduce soil loss, and their effects on soil erosion differ across species due to their varied root traits. The purpose of this study was to determine the effects of root morphology traits of herbaceous plants on the soil detachment process. Ten herbaceous plants (dominant species) in the Loess Plateau were selected, and 300 undisturbed soil samples (including living roots from the selected herbages) were scoured with flowing water to measure their soil detachment capacities under six levels of shear stress (4.98 to 16.37 Pa). Then, the root traits of each soil sample were measured, and the rill erodibility and critical shear stress were estimated based on the Water Erosion Prediction Project (WEPP) model. The results showed that root morphology traits varied greatly among the ten selected herbages. Accordingly, resulting variations in soil detachment capacity (0.030 to 3.297 kg m-2 s-1), rill erodibility (0.004 to 0.447 s m-1), and critical shear stress (4.73 to 1.13 Pa) were also observed. Plants with fibrous roots were more effective than those with tap roots in reducing soil detachment. Their mean soil detachment capacity and rill erodibility were 93.2% and 93.4% lower, respectively, and their mean critical shear stress was 1.15 times greater than that of the herbaceous plants with tap root systems. Of all the root traits, root surface area density (RSAD) was the primary root trait affecting the soil detachment, and it estimated the soil detachment capacity well (R2 = 0.91, normalized squared error (NSE) = 0.82). Additionally, an equation with few factors (soil aggregate and RSAD) was suggested to simulate the soil detachment capacity when the plant root parameters and soil properties were limited.

Nitrogen removal in an aerobic gravel filtration-sedimentation pond-constructed wetland-overland flow system treating polluted stream waters: Effects of operation parameters.

Nitrogen pollution in streams can be controlled by serially constructing natural wastewater treatment (NWT) systems inside streams. Therefore, a pilot-scale hybrid NWT system consisting of gravel filtration (GF), sedimentation pond (SP), gravel filtration-free water surface constructed wetland (GF-FWSCW), and gravel filtration-overland flow (GF-OF) was installed in order to prevent contamination in a stream (Nigde stream) that feeds and pollutes surface water source (Akkaya lake). The pilot-scale system was installed on a new 60 m-long channel which was located off the stream. Changes in ammonium (NH4+-N), organic nitrogen (Norg.), total nitrogen (TN), and biochemical oxygen demand (BOD) concentrations was routinely monitored in influent and effluent of all stages of the hybrid NWT system and the bottom sediment of the SP over a one-year operation period. According to the study results, while NH4+-N plus Norg. was reduced by an average of 75% (from 49,1 mg L-1 to 7,1 mg L-1), TN was reduced by an average of 85% (from 50,2 mg L-1 to 12,4 mg L-1). Colder seasons and higher hydraulic loading rates (HLRs) negatively affected nitrogen removal efficiency of the pilot-system. The use of vegetation and filter medium had a positive effect on the average removal efficiencies. The results showed that nitrogen pollution in polluted streams could be greatly reduced by establishing a NWT system in series within them.

[Effect of Optimized Fertilization and Biochar Application on Phosphorus Loss in Purple Soil Sloping Farmland].

Phosphorus is an essential nutrient for crop growth, but the input of excess phosphorus is a significant cause of eutrophication. This study explored the relationship between fertilization methods and phosphorus loss in actual production, providing a theoretical basis for scientific fertilization and rational reduction of fertilizer application. In the experiment, a wild-type OD flow plot was used to monitor the occurrence of multiple rainfall runoff and sediment yield in purple soil sloping farmland in 2017-2018. Four different schemes of non-fertilizer treatment, conventional fertilization treatment, optimized fertilization treatment, and reduced fertilization combined with biochar were studied. The effects of soil flow, surface runoff, and sediment phosphorus loss on purple soil sloping farmland were analyzed. The results showed that:①The total yield of each treatment was optimized (20737.23 L) > conventional (18513.17 L) > CK (18134.58 L) > biochar (13594.85 L), and the total sediment yield of each treatment was CK (1998 kg·hm-2) > biochar (1884 kg·hm-2) > optimized (1681 kg·hm-2) > conventional (910 kg·hm-2). The middle stream of soil is the main type of runoff in the rainy season, accounting for 60.14%-87.34% of the total output flow. The total amount of sediment produced by each treatment was not significantly different from that of the conventional treatment (P>0.05). ②The flux of total phosphorus loss in each treatment was characterized by sediment > surface runoff > soil middle flow. Phosphorus lost through the middle stream of soil is the least, accounting for only 2.63%-12.91% of the flux of total phosphorus loss, while the flux of sediment loss of phosphorus can reach 63.74%-78.74%, and thus is the main output route of soil phosphorus loss. ③The application of biochar can effectively reduce the abortion flow in the soil of purple soil sloping land, and the loss flux of orthophosphate in the middle stream, which are 49.94% and 56.45% lower than the conventional treatment, respectively. However, the interception effect on surface runoff is not good, and there is no significant influence on the flux loss of particulate phosphorus. At the same time, the flux of total phosphorus in surface runoff and sediment is significantly increased by 73.28% and 123.53%, respectively, compared with conventional treatment (P<0.05). Therefore, to control the loss of phosphorus in purple soil sloping farmland in southwest China, we should focus on reducing the occurrence of soil sediment loss. Bio-carbon should be further optimized in the practical application of agricultural production with the phosphorus fertilizer input ratio.

[Response of Nitrogen Loss Flux in Purple Soil Sloping Field to Reduced Fertilizer and Combining Straw].

The purple soil sloping field is considered as the main source of sediment and non-point source pollution in the Three Gorges Reservoir area. To prevent and control the non-point source pollution, it is indispensable to explore the characteristics of nitrogen loss in the overland flow and interflow of purple soil sloping field in Three Gorges Reservoir area. The purple soil sloping runoff plots, located in the Shibaozhai Experimental Station of Chengdu Institute of Chinese Academy of Sciences in Zhongxian County, Chongqing, were studied. The experiment included no fertilization treatment (CK), traditional fertilization treatment (T1), amended fertilization treatment (T2), and reduced fertilizer with straw treatment (T3). According to the data of volume of the interflow and runoff and the leach concentration and flux of nitrogen forms under rapeseed-maize rotation system, the response of nitrogen leaching flux to reduce fertilizer with straw application can be definite in purple soil sloping plots. The results show that the ratio of interflow to total runoff is 60.14%-88.56%, and the flux of nitrogen leaching in the interflow accounts for 72.88%-92.35% of total nitrogen loss flux. Ammonium was mainly leached by the overland flow. In addition, nitrate was mainly leached by the interflow and was the main form of nitrogen leaching. The fluxes of ammonium and nitrate under different treatments followed the order T1 > T2 > T3 > CK. The total nitrogen flux of T3 was 20.07 kg·(hm2·a)-1, which was 43.59% and 39.55% lower than that of T1 and T2, respectively. The reduced fertilizer with straw application significantly decreased the leaching flux of ammonium, nitrate, and total nitrogen, and weakened the effect on runoff nitrogen leaching in the purple soil sloping plots.

Micro-topographic assessment of rill morphology highlights the shortcomings of current protective measures in loess landscapes.

Due to urban expansion and the rapid development of infrastructure in the loess area of China, artificial earth-fill embankments and excavated slopes are increasingly widespread in recent years. Erosion is typical in such loess slopes; however, quantitative statistical analyses of various counter-measures that affects rill erosion are still lacking. Here, we quantified rill morphology and rill erosion development in two newly constructed slopes with different engineering protection measures. We used high-resolution digital surface models (DSMs) acquired using an Unmanned Aerial Vehicle (UAV) to analyze the case areas during two-time periods. Our results from centimeter accuracy differential DSMs demonstrated that rapid rill erosion is prevalent in the study area, expressed as rill density varying between 2.03 km-2 and 8.81 km-2 at different slope surfaces (viz., erosion protected slopes [EPS], landslide protected slopes [LPS], and unprotected slopes [US]). The slope gradient responsible for rill erosion of the EPS, LPS and US are obviously different, and such information is essential for planning preventive measures in each slope type. At the EPS, the severity of erosion is maximum at the top of the ridges, whereas the gap between reinforced concrete lattice and loess deposits are of serious concern at the LPS. The current engineering measures employed in the study area are thus found ineffective for protection against rill erosion. We therefore propose an improved design by implementing an intercepting drain to the existing design for preventing further erosion.

Determination of runoff response to variation in overland flow area by flow routes using UAV imagery.

Surface runoff can be routed to both pervious areas (PAs) and drainage systems during an overland flow. Excessive runoff from an impervious area (IA) flowing into a drainage system causes an overload, which can be relieved by diverting runoff to PAs. However, the hydrological link between IAs and PAs, especially the runoff response to variation in overland flow areas (OFAs), has not well been considered in runoff simulations due to the complexity of routing. To understand how the OFA within an IA contributes to runoff generation, a novel classification approach was applied to categorize the IA in a study area in Nanjing University, Xianlin campus, China into directly connected impervious area (DCIA) and indirectly connected impervious area (ICIA) by flow routes using high-resolution ground-based images (0.5 m) from an unmanned aerial vehicle. The OFAs then include DCIA and the total impervious area (TIA), which is the sum of DCIA and ICIA. The runoff simulations were supported by Storm Water Management Model (SWMM) calibrated with observed rainfall and runoff data. The resulting proportions of DCIA and ICIA of the study area were 34.13% and 10.99%, respectively. The spatial distributions of DCIA and ICIA are characterized by the subcatchment landscape heterogeneity resulting from vegetation, imperviousness, and slope. The observed runoff coefficients and peak flows were positively correlated with the percentages of DCIA and TIA. The runoff coefficient was significantly correlated with the DCIA in a light rainfall event of 18.4 mm (R2 =0.82) and with the TIA in a heavy rainfall event of 119 mm (R2 =0.92). Runoff generation is affected by both the characteristics of the rainfall event and the accompaning variations in OFAs. Results indicate that increasing of the flow connectivity from IAs to PAs and increasing the water retention capacity of PAs may be effective strategies for optimizing landscape patterns for stormwater management.

Effects of soil-incorporated plant litter morphological characteristics on the soil detachment process in grassland on the Loess Plateau of China.

The Loess Plateau of China is one of the most eroded areas in the world. In the past 20 years, effective vegetation restoration measures have significantly changed the near-surface characteristics of soil. In natural conditions, plant litter is widespread in the topsoil. The effects of litter incorporated into soil on the process of soil detachment, which is closely related to plant litter morphology, are still not well known. This study aimed to detect the variation of litter morphological characteristics and quantify their effects on soil detachment capacity and rill erodibility when litter is incorporated into the soil. Four plant litters (Bothriochloa ischaemum (L.) Keng., Artemisia sacrorum Ledeb., Setaria viridis (L.) Beauv., and Artemisia capillaris Thunb.) with five length levels (<0.5, 0.5-2, 2-4, 4-6, and 6-8 cm) were incorporated into soil (idle for 50 days) at the same litter biomass rate (0.7 kg m-2). Then the soil was sampled and cores were subjected to overland flow under six flow shear stress levels (5.66, 8.31, 12.21, 15.55, 19.15 and, 22.11 Pa) using a hydraulic flume (4.0 m × 0.35 m). The results showed that the litter morphological characteristics of litter length density (LLD), litter surface area density (LSAD) and litter volume ratio (LVR) differed in plant species at the same litter biomass rate. Correspondingly, soil detachment capacity (ranging from 0.414 to 2.179 kg m-2 s-1) and rill erodibility (ranging from 0.037 to 0.177 s m-1) varied significantly and mean values from the Bothriochloa ischaemum (L.) Keng. treatments were the minimums, which were 28% to 37% and 23% to 35% less than that of the other treatments, respectively. The soil detachment capacity and rill erodibility were significantly correlated with the litter morphological characteristics of LLD, LSAD and LVR (p < 0.01). The contact area between litter and soil was the most critical factor affecting soil detachment. Incorporated plant litter residue litter effect on rill erodibility could be well estimated by LSAD.

Tratamento de esgoto sanitário por escoamento superficial no solo: remoção de metais / Wastewater treatment by overland flow: removal of metals

RESUMO Com o objetivo de avaliar a remoção e a concentração dos metais cádmio (Cd), cromo (Cr), cobre (Cu), chumbo (Pb), ferro (Fe), níquel (Ni) e zinco (Zn) em águas residuais municipais, foram conduzidos ensaios de campo utilizando o método do escoamento em duas taxas de aplicação superficial, 0,30 e 0,20 m3.m-1.h-1, em uma rampa de 4,25 × 40 m, com 3,5% de declividade, plantada com Tifton 85 (Cynodon spp.). Em amostras coletadas durante o estudo de 15 meses, apenas Cu, Cr e Pb excederam os limites de lançamento de acordo com a Resolução do Conselho Nacional do Meio Ambiente (CONAMA) nº 430/2011 (BRASIL, 2011). A taxa de aplicação não influencia na remoção superficial de Cd, Cr, Cu, Fe, Ni e Pb, no entanto maior remoção de Zn ocorreu ao empregar taxas de aplicação superficial de 0,30 m3.m-1.h-1. A taxa de aplicação não influencia a incorporação de Cd, Cr, Fe, Ni e Zn na biomassa, porém maior incorporação de Pb ocorreu ao aplicar 0,20 m3.m-1.h-1.

ABSTRACT In order to evaluate the removal and concentration of the metals cadmium (Cd), chrome (Cr), copper (Cu), lead (Pb), iron (Fe), nickel (Ni) and zinc (Zn) in municipal wastewater, we conducted field tests using the method of overland flow under two rates of surface application, 0.30 and 0.20 m3.m-1.h-1, on a ramp of 4.25 × 40 m with a slope of 3.5%, planted with Tifton 85 (Cynodon spp.). In samples collected during the 15-month study, only Cu, Cr and Pb exceeded the discharge limit according to the National Environment Council (CONAMA) Resolution n. 430/2011 (BRASIL, 2011). The application rate does not influence the surface removal of Cd, Cr, Cu, Fe, Ni and Pb; however, higher Zn removal occurred by applying rates of surface application of 0.30 m3.m-1.h-1. The rate of application does not influence the incorporation of Cd, Cr, Fe, Ni and Zn in the biomass, but greater incorporation of Pb occurred when applying 0.20 m3.m-1.h-1.

Land use and climate change impacts on runoff and soil erosion at the hillslope scale in the Brazilian Cerrado.

Land use and climate change can influence runoff and soil erosion, threatening soil and water conservation in the Cerrado biome in Brazil. The adoption of a process-based model was necessary due to the lack of long-term observed data. Our goals were to calibrate the WEPP (Water Erosion Prediction Project) model for different land uses under subtropical conditions in the Cerrado biome; predict runoff and soil erosion for these different land uses; and simulate runoff and soil erosion considering climate change. We performed the model calibration using a 5-year dataset (2012-2016) of observed runoff and soil loss in four different land uses (wooded Cerrado, tilled fallow without plant cover, pasture, and sugarcane) in experimental plots. Selected soil and management parameters were optimized for each land use during the WEPP model calibration with the existing field data. The simulations were conducted using the calibrated WEPP model components with a 100-year climate dataset created with CLIGEN (weather generator) based on regional climate statistics. We obtained downscaled General Circulation Model (GCM) projections, and runoff and soil loss were predicted with WEPP using future climate scenarios for 2030, 2060, and 2090 considering different Representative Concentration Pathways (RCPs). The WEPP model had an acceptable performance for the subtropical conditions. Land use can influence runoff and soil loss rates in a significant way. Potential climate changes, which indicate the increase of rainfall intensities and depths, may increase the variability and rates of runoff and soil erosion. However, projected climate changes did not significantly affect the runoff and soil erosion for the four analyzed land uses at our location. Finally, the runoff behavior was distinct for each land use, but for soil loss we found similarities between pasture and wooded Cerrado, suggesting that the soil may attain a sustainable level when the land management follows conservation principles.