The Experts below are selected from a list of 6393 Experts worldwide ranked by ideXlab platform
Xiaomei Yang - One of the best experts on this subject based on the ideXlab platform.
-
spatial glyphosate and ampa redistribution on the soil surface driven by sediment transport processes a Flume Experiment
Environmental Pollution, 2018Co-Authors: Celia P M Bento, Meindert Commelin, Jantiene Baartman, Xiaomei Yang, Piet Peters, Hans G J Mol, Coen J Ritsema, Violette GeissenAbstract:Abstract This study investigates the influence of small-scale sediment transport on glyphosate and AMPA redistribution on the soil surface and on their off-site transport during water erosion events. Both a smooth surface (T1) and a surface with “seeding lines on the contour” (T2) were tested in a rainfall simulation Experiment using soil Flumes (1 × 0.5 m) with a 5% slope. A dose of 178 mg m−2 of a glyphosate-based formulation (CLINIC®) was applied on the upper 0.2 m of the Flumes. Four 15-min rainfall events (RE) with 30-min interval in between and a total rainfall intensity of 30 mm h−1 were applied. Runoff samples were collected after each RE in a collector at the Flume outlet. At the end of the four REs, soil and sediment samples were collected in the application area and in four 20 cm-segments downslope of the application area. Samples were collected according to the following visually distinguished soil surface groups: light sedimentation (LS), dark sedimentation (DS), background and aggregates. Results showed that runoff, suspended sediment and associated glyphosate and AMPA off-site transport were significantly lower in T2 than in T1. Glyphosate and AMPA off-site deposition was higher for T2 than for T1, and their contents on the soil surface decreased with increasing distance from the application area for all soil surface groups and in both treatments. The LS and DS groups presented the highest glyphosate and AMPA contents, but the background group contributed the most to the downslope off-site deposition. Glyphosate and AMPA off-target particle-bound transport was 9.4% (T1) and 17.8% (T2) of the applied amount, while water-dissolved transport was 2.8% (T1) and 0.5% (T2). Particle size and organic matter influenced the mobility of glyphosate and AMPA to off-target areas. These results indicate that the pollution risk of terrestrial and aquatic environments through runoff and deposition can be considerable.
-
short term transport of glyphosate with erosion in chinese loess soil a Flume Experiment
Science of The Total Environment, 2015Co-Authors: Xiaomei Yang, Fei Wang, Celia P M Bento, Sha Xue, Lingtong Gai, Ruud Van DamAbstract:Repeated applications of glyphosate may contaminate the soil and water and threaten their quality both within the environmental system and beyond it through water erosion related processes and leaching. In this study, we focused on the transport of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) related to soil erosion at two slope gradients (10 and 20°), two rates of pesticide with a formulation of glyphosate (Roundup®) application (360 and 720 mg m− 2), and a rain intensity of 1.0 mm min− 1 for 1 h on bare soil in hydraulic Flumes. Runoff and erosion rate were significantly different within slope gradients (p < 0.05) while suspended load concentration was relatively constant after 15 min of rainfall. The glyphosate and AMPA concentration in the runoff and suspended load gradually decreased. Significant power and exponent function relationship were observed between rainfall duration and the concentration of glyphosate and AMPA (p < 0.01) in runoff and suspended load, respectively. Meanwhile, glyphosate and AMPA content in the eroded material depended more on the initial rate of application than on the slope gradients. The transport rate of glyphosate by runoff and suspended load was approximately 14% of the applied amount, and the chemicals were mainly transported in the suspended load. The glyphosate and AMPA content in the Flume soil at the end of the Experiment decreased significantly with depth (p < 0.05), and approximately 72, 2, and 3% of the applied glyphosate (including AMPA) remained in the 0–2, 2–5, and 5–10 cm soil layers, respectively. The risk of contamination in deep soil and the groundwater was thus low, but 5% of the initial application did reach the 2–10 cm soil layer. The risk of contamination of surface water through runoff and sedimentation, however, can be considerable, especially in regions where rain-induced soil erosion is common.
H Ikeda - One of the best experts on this subject based on the ideXlab platform.
-
a Flume Experiment on the development of subaqueous fine gravel dunes from a lower stage plane bed
Journal of Geophysical Research, 2005Co-Authors: Paul A Carling, Keith Richardson, H IkedaAbstract:[1] Determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability. In addition, estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of, for example, oil- and gas-bearing geological strata. Consequently, a series of Experiments considered dune initiation. In these Experiments, defects and latterly incipient dunes developed from lower-stage plane gravel beds during near-threshold conditions of motion (θ/θcrit = 1.0–1.016) and long periods of marginal bed load transport rates. The three-dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters. After 17 hours of flow, incipient, low-amplitude, simple two-dimensional dunes developed from the defects, with heights ranging between 0.029 and 0.055 m, nonequilibrium wavelengths of 1–4 m and spans of 0.6–0.9 m. Continued development over several days, with θ/θcrit ratios of around 1.3, resulted in near-equilibrium two-dimensional dunes with wavelengths averaging 2.6–3.5 m and spans equal to the Flume width (4 m). The inception of incipient dunes could be predicted using bulk flow models; however, this approach was not suitable for the prediction of defect development. Near-bed turbulence, in the form of small-scale sweep events of limited breadth, controls the initiation of defects, but larger-scale, coherent turbulent structures in the outer flow are related to dune development. Significantly, both defects and incipient dunes can exist at the same time, which indicates that the effects of sweeps on the bed morphology persist at the same time as larger-scale turbulent structures are beginning to effect sediment transport.
-
a Flume Experiment on the development of subaqueous fine gravel dunes from a lower stage plane bed marine sandware and river dune dynamics
Journal of Geophysical Research, 2005Co-Authors: Paul A Carling, Keith Richardson, H IkedaAbstract:[1] Determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability. In addition, estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of, for example, oil- and gasbearing geological strata. Consequently, a series of Experiments considered dune initiation. In these Experiments, defects and latterly incipient dunes developed from lower-stage plane gravel beds during near-threshold conditions of motion (θ/θ crit = 1.0-1.016) and long periods of marginal bed load transport rates. The three-dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters. After 17 hours of flow, incipient, lowamplitude, simple two-dimensional dunes developed from the defects, with heights ranging between 0.029 and 0.055 m, nonequilibrium wavelengths of 1-4 m and spans of 0.6-0.9 m. Continued development over several days, with θ/θ crit ratios of around 1.3, resulted in near-equilibrium two-dimensional dunes with wavelengths averaging 2.6-3.5 m and spans equal to the Flume width (4 m). The inception of incipient dunes could be predicted using bulk flow models; however, this approach was not suitable for the prediction of defect development. Near-bed turbulence, in the form of small-scale sweep events of limited breadth, controls the initiation of defects, but larger-scale, coherent turbulent structures in the outer flow are related to dune development. Significantly, both defects and incipient dunes can exist at the same time, which indicates that the effects of sweeps on the bed morphology persist at the same time as larger-scale turbulent structures are beginning to effect sediment transport.
-
response of a channel with alternate bars to a decrease in supply of mixed size bed load a Flume Experiment
Water Resources Research, 1993Co-Authors: Thomas E. Lisle, Fujiko Iseya, H IkedaAbstract:The response of a channel with a topography and modeled bed material size typical of gravel bed rivers to reductions in sediment supply was investigated in a laboratory Flume filled and fed with a sand-gravel mixture. After a series of quasi-stationary alternate bars were formed under equilibrium sediment transport, feed rate was reduced in two steps to one third and one tenth the initial rate as discharge was held constant. The primary response following both reductions was an increase in bed surface particle size as a corridor of intensive bed load transport contracted and local transport rates decreased. After the first feed rate reduction, the channel incised by twice the mean water depth, on average, and caused distal bar surfaces to emerge as terracelike features. Bar roughness decreased, and mean boundary shear stress exerted on bed surface particles increased. Little incision occurred after the second feed rate reduction.
-
formation of stationary alternate bars in a steep channel with mixed size sediment a Flume Experiment
Earth Surface Processes and Landforms, 1991Co-Authors: Thomas E. Lisle, H Ikeda, Fujiko IseyaAbstract:Alternate bars were formed by sediment transport in a Flume with Froude-modelled flow and relative roughness characteristic of gravel-boulder channels with steep slopes. The Flume (0.3 m wide × 7.5 m long) was filled with a sand-gravel mixture, which was also fed into the top of the Flume at a constant rate under constant discharge. Channel slope was set at 0.03. Initially, coarse particles accumulated on incipient bar heads near one side of the Flume and diverted flow and bedload transport across the Flume toward a pool scoured against the opposite Flume wall downstream. Sorting in the pool directed coarse particles onto the next bar head downstream. Alternate sequences of pools and coarse bar heads were thereby linked down the entire Flume by interactions of sediment sorting, flow, and channel morphology. During episodes of bar construction, unsorted bedload invaded interior bar surfaces and was deposited. Persistent deposition of coarse particles on bar heads prevented downstream migration of bars by inhibiting bar-head erosion and bedload transport over bars. Likely factors leading to bar-head stabilization in modelled gravel-bed channels are coarse mixed-size sediment, steep channel gradients, and shallow depths.
Douglas M. Thompson - One of the best experts on this subject based on the ideXlab platform.
-
a Flume Experiment on the effect of constriction shape on the formation of forced pools
Hydrology and Earth System Sciences, 2010Co-Authors: Douglas M. Thompson, C R MccarrickAbstract:Abstract. A series of 18 Flume runs were conducted in a 6-m long, 0.5-m wide recirculating Flume with a bed gradient of 0.8% to determine the influence of obstruction shape on the formation and characteristics of forced pools. Six different-shaped obstructions were added to the Flume with the maximum width of the obstruction held constant at 20 cm, which equaled a 40% constriction of flow. The obstruction shapes used included a square, a rectangle, a right triangle with the hypotenuse-facing upstream, a right triangle with the hypotenuse-facing downstream, a combination of a square and triangle with the hypotenuse-facing upstream, and a rectangle and semi-circle shape. Three Flume runs were conducted with each obstruction shape. A profile of the Flume bed was taken after each Experiment and a grid measurement of bed elevations for the last run were conducted to create topographic maps of the Flume bed to compare pool-riffle morphologies. ANOVA results indicate pool depth, pool location, and the distance between the pool center and the riffle crest all vary with the obstruction shape. Obstructions with a more blunt upstream face created deeper pools, more total scour and longer pool-riffle sequence lengths than pools formed by obstructions with a more gradual narrowing of flow. The increased volume of scour associated with obstructions that rapidly narrow flow also creates larger volume riffles that cover a greater extent of the channel bed.
-
the influence of riparian vegetation on near bank turbulence a Flume Experiment
Earth Surface Processes and Landforms, 2007Co-Authors: Maeve Mcbride, Donna M. Rizzo, Cully W Hession, Douglas M. ThompsonAbstract:Measurements from a fixed-bed, Froude-scaled hydraulic model of a stream in northeastern Vermont demonstrate the importance of forested riparian vegetation effects on near-bank turbulence during overbank flows. Sections of the prototype stream, a tributary to Sleepers River, have increased in channel width within the last 40 years in response to passive reforestation of its riparian zone. Previous research found that reaches of small streams with forested riparian zones are commonly wider than adjacent reaches with non-forested, or grassy, vegetation; however, driving mechanisms for this morphologic difference are not fully explained. Flume Experiments were performed with a 1:5 scale, simplified model of half a channel and its floodplain, mimicking the typical non-forested channel size. Two types of riparian vegetation were placed on the constructed floodplain: non-forested, with synthetic grass carpeting; and forested, where rigid, randomly distributed, wooden dowels were added. Three-dimensional velocities were measured with an acoustic Doppler velocimeter at 41 locations within the channel and floodplain at near-bed and 0·6-depth elevations. Observations of velocity components and calculations of turbulent kinetic energy (TKE), Reynolds shear stress and boundary shear stress showed significant differences between forested and non-forested runs. Generally, forested runs exhibited a narrow band of high turbulence between the floodplain and main channel, where TKE was roughly two times greater than TKE in non-forested runs. Compared to non-forested runs, the hydraulic characteristics of forested runs appear to create an environment with higher erosion potential. Given that sediment entrainment and transport can be amplified in flows with high turbulence intensity and given that mature forested stream reaches are wider than comparable non-forested reaches, our results demonstrated a possible driving mechanism for channel widening during overbank flow events in stream reaches with recently reforested riparian zones. Copyright © 2007 John Wiley & Sons, Ltd.
-
The influence of riparian vegetation on near‐bank turbulence: a Flume Experiment
Earth Surface Processes and Landforms, 2007Co-Authors: Maeve Mcbride, W. Cully Hession, Donna M. Rizzo, Douglas M. ThompsonAbstract:Measurements from a fixed-bed, Froude-scaled hydraulic model of a stream in northeastern Vermont demonstrate the importance of forested riparian vegetation effects on near-bank turbulence during overbank flows. Sections of the prototype stream, a tributary to Sleepers River, have increased in channel width within the last 40 years in response to passive reforestation of its riparian zone. Previous research found that reaches of small streams with forested riparian zones are commonly wider than adjacent reaches with non-forested, or grassy, vegetation; however, driving mechanisms for this morphologic difference are not fully explained. Flume Experiments were performed with a 1:5 scale, simplified model of half a channel and its floodplain, mimicking the typical non-forested channel size. Two types of riparian vegetation were placed on the constructed floodplain: non-forested, with synthetic grass carpeting; and forested, where rigid, randomly distributed, wooden dowels were added. Three-dimensional velocities were measured with an acoustic Doppler velocimeter at 41 locations within the channel and floodplain at near-bed and 0·6-depth elevations. Observations of velocity components and calculations of turbulent kinetic energy (TKE), Reynolds shear stress and boundary shear stress showed significant differences between forested and non-forested runs. Generally, forested runs exhibited a narrow band of high turbulence between the floodplain and main channel, where TKE was roughly two times greater than TKE in non-forested runs. Compared to non-forested runs, the hydraulic characteristics of forested runs appear to create an environment with higher erosion potential. Given that sediment entrainment and transport can be amplified in flows with high turbulence intensity and given that mature forested stream reaches are wider than comparable non-forested reaches, our results demonstrated a possible driving mechanism for channel widening during overbank flow events in stream reaches with recently reforested riparian zones. Copyright © 2007 John Wiley & Sons, Ltd.
-
changes in pool size in response to a reduction in discharge a Flume Experiment
River Research and Applications, 2006Co-Authors: Douglas M. ThompsonAbstract:Management of river systems can create a reduction in flow with associated potential impacts on channel morphology. A total of 30 Flume runs were conducted with two different sediment sizes to determine the effect of a reduction in flow on pool size and depth in confined channels. The Experiments were conducted in a 6 m long, 0.5 m wide recirculating Flume. Pools were scoured adjacent to a triangular-shaped obstruction to flow from an initially flat bed. After 3 h of high flow, bed topography was measured and the flow was changed to a level of 50, 67, 80, 85 or 100% of the original flow. Changes in bed topography were then measured after 3 h under the modified flow regime. Results indicate that a reduction in flow creates smaller volume pools. With well sorted, fine-sand substrate, changes in pool volume, volume of deep habitat and depth were significant for both 50 and 80% reductions in flow level. However, development of an armor level in Experiments with poorly sorted, very coarse sand limited sedimentation at lower flows. Consequently, no changes in pool size were statistically significant with this sediment. The results suggest that data on the dimensions of pools are needed prior to any flow modifications in order to detect degradation of the physical pool habitat. Monitoring programs initiated after flow regulation may only identify changes in a limited number of cases where sediments are mobile at low flows and the reduction in flow level is severe. Copyright © 2005 John Wiley & Sons, Ltd.
-
the influence of pool length on local turbulence production and energy slope a Flume Experiment
Earth Surface Processes and Landforms, 2004Co-Authors: Douglas M. ThompsonAbstract:The influence of pool length on the strength of turbulence generated by vortex shedding was investigated in a 6 m long recirculating flume. The Experiment utilized a 38% constriction of flow and an average channel-bed slope of 0·007. The base geometry for the intermediate-length pool Experiment originated from a highly simplified, 0·10 scale model of a forced pool from North Saint Vrain Creek, Colorado. Discharge in the flume was 31·6 l/s, which corresponds to a discharge in the prototype channel of 10 m3/s. Three shorter and four longer pool lengths also were created with a fixed bed to determine changes in turbulence intensities and energy slope with pool elongation. Three-dimensional velocities were measured with an acoustic Doppler velocimeter at 31–40 different 0·6-depth and near-bed locations downstream of the rectangular constriction. The average velocity and root mean square (RMS) of the absolute magnitude of velocity at both depths are significantly related to the distance from the constriction in most pool locations downstream of the constriction. In many locations, pool elongation results in a non-linear change in turbulence intensities and average velocity. Based on the overall flow pattern, the strongest turbulence occurs in the center of the pool along the shear zone between the jet and recirculating eddy. The lateral location of this shear zone is sensitive to changes in pool length. Energy slope also was sensitive to pool length due to a combination of greater length of the pool and greater head loss with shorter pools. The results indicate some form of hydraulic optimization is possible with pools adjusting their length to adjust the location and strength of turbulent intensities in the center of pools, and lower their rate of energy dissipation. Copyright © 2004 John Wiley & Sons, Ltd.
Violette Geissen - One of the best experts on this subject based on the ideXlab platform.
-
spatial glyphosate and ampa redistribution on the soil surface driven by sediment transport processes a Flume Experiment
Environmental Pollution, 2018Co-Authors: Celia P M Bento, Meindert Commelin, Jantiene Baartman, Xiaomei Yang, Piet Peters, Hans G J Mol, Coen J Ritsema, Violette GeissenAbstract:Abstract This study investigates the influence of small-scale sediment transport on glyphosate and AMPA redistribution on the soil surface and on their off-site transport during water erosion events. Both a smooth surface (T1) and a surface with “seeding lines on the contour” (T2) were tested in a rainfall simulation Experiment using soil Flumes (1 × 0.5 m) with a 5% slope. A dose of 178 mg m−2 of a glyphosate-based formulation (CLINIC®) was applied on the upper 0.2 m of the Flumes. Four 15-min rainfall events (RE) with 30-min interval in between and a total rainfall intensity of 30 mm h−1 were applied. Runoff samples were collected after each RE in a collector at the Flume outlet. At the end of the four REs, soil and sediment samples were collected in the application area and in four 20 cm-segments downslope of the application area. Samples were collected according to the following visually distinguished soil surface groups: light sedimentation (LS), dark sedimentation (DS), background and aggregates. Results showed that runoff, suspended sediment and associated glyphosate and AMPA off-site transport were significantly lower in T2 than in T1. Glyphosate and AMPA off-site deposition was higher for T2 than for T1, and their contents on the soil surface decreased with increasing distance from the application area for all soil surface groups and in both treatments. The LS and DS groups presented the highest glyphosate and AMPA contents, but the background group contributed the most to the downslope off-site deposition. Glyphosate and AMPA off-target particle-bound transport was 9.4% (T1) and 17.8% (T2) of the applied amount, while water-dissolved transport was 2.8% (T1) and 0.5% (T2). Particle size and organic matter influenced the mobility of glyphosate and AMPA to off-target areas. These results indicate that the pollution risk of terrestrial and aquatic environments through runoff and deposition can be considerable.
-
transport of silver nanoparticles by runoff and erosion a Flume Experiment
Science of The Total Environment, 2017Co-Authors: Karrar N M Mahdi, Meindert Commelin, Ruud J B Peters, Jantiene Baartman, C J Ritsema, Violette GeissenAbstract:Silver nanoparticles (AgNPs) are being used in many products as they have unique antimicrobial-biocidal properties. After disposal of these products AgNPs can reach the soil environment possibly affecting soil organisms and disrupting plants. This work aimed to study the transport of AgNPs by water and sediment during overland flow and soil erosion. This was done in a laboratory setting, using a Flume and rainfall simulator. A low concentration of AgNPs (50 μg·kg− 1) was applied to two soil-Flumes with slope percentages of 20% and 10%. The rainfall was applied in four events of 15 min each with a total amount of rainfall of 15 mm during each event. After applying the rainfall, samples of the non-transported background soil (BS) and the transported sediment (Sf) were collected from the Flume surface. Runoff sediment (RS) and water (RW) were collected from the outlet. AgNPs were detected in all samples collected. However, concentration varied according to sample type (soil or water), time of collection (for runoff water and sediment) and the slope of the soil Flume. Higher concentrations of AgNPs in soil were detected in the BS than in the Sf likely due to the BS having more fine particles (silt and clay). The AgNPs concentration in the runoff sediments increased with subsequent applied rain events. In addition, increasing the slope of the Flume from 10% to 20% increased the total AgNPs transported with the runoff sediment by a factor 1.5. The study confirms that AgNPs can be transported by both overland flow and sediment due to erosion.
Yong Pang - One of the best experts on this subject based on the ideXlab platform.
-
simulation study on water quality based on sediment release Flume Experiment in lake taihu china
Ecological Engineering, 2011Co-Authors: Yong Pang, Hua Wang, Xianmin Wang, Kun Bao, Qi LiuAbstract:Abstract Sediments have a significant influence on the overlying water, and nutrient release from sediments is an important source for lake eutrophication, particularly in shallow lakes. Sediment resuspension is primarily driven by wind-induced currents. In this research, the correlation between release rate of suspended sediment and flow velocity was studied, and an Experiment on hydrodynamic forces was conducted in a rectangle Flume using water and sediments collected from three sites in Lake Taihu, a eutrophic lake in China. It was shown that the starting velocities of sediment in Lake Taihu at three different incipient standards gained from the Experiment were 15, 30, and 40 cm s −1 and the release rate of suspended sediment could reach up to 643.4, 5377.1, and 13980.5 g m −2 d −1 , respectively. Based on the Experiment, a water quantity and quality numerical model of wind-induced current with sediment pollution for Lake Taihu was developed. The model was calibrated and validated by applying it to the study of the water quality of Lake Taihu. The calculated values were generally in good agreement with field observations, which indicated that the developed model could represent the dynamics of sediment resuspension to a certain extent. This study provides a new approach and a practical tool for planning and management policy and operations to protect the water quality and ecosystems of shallow lakes.
-
simulation study on algal dynamics based on ecological Flume Experiment in taihu lake china
Ecological Engineering, 2007Co-Authors: Ling Ding, Yong Pang, Guang GaoAbstract:The dynamic growth of algae is influenced by the inner physiological characteristics as well as the exterior stimulating factors, including light, temperature and nutrients. The suspended sediments release nutrients driven by hydrodynamic forces, imposing significant effects on algae growth. In this research, the mechanism of algae growth was studied, and an Experiment on algae growth was conducted in an ecological Flume using water and sediments collected from Taihu lake, an eutrophic lake in China, with three water current stages: still water stage, slow water current stage, and fast water current stage. Based on the Experiment, a model was developed to quantitatively describe the relations between the release of nitrogen/phosphorous nutrients and the water flow velocity in nitrogen and phosphorus cycles. Detailed calibration and verification of the model parameters were carried out based on the results from Experiments. The predicted values fit presented the results fitting well with the measured data, which indicates that the developed model can represent the dynamics of algae growth to a certain extent. This model has the potential for forecasting algal bloom in shallow, temperate lake systems. (C) 2007 Elsevier B.V. All rights reserved.