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Rivers convey a broad range of materials, such as sediment, nutrients, and contaminants. Much of this transport can occur during or immediately after an episodic, pulsed event like a flood or an oil spill. Understanding the flow processes that influence the motion of these substances is important for managing water resources and conserving aquatic ecosystems. This study introduces a new remote sensing framework for characterizing dynamic phenomena at the scale of a channel cross-section: Hyperspectral Image Transects during Transient Events in Rivers (HITTER). We present a workflow that uses repeated hyperspectral scan lines acquired from a hovering uncrewed aircraft system (UAS) to quantify how a water attribute of interest varies laterally across the river and evolves over time. Data from a tracer experiment on the Missouri River are used to illustrate the components of the end-to-end processing chain we used to quantify the passage of a visible dye. The framework is intended to be flexible and could be applied in a number of different contexts. The results of this initial proof-of-concept investigation suggest that HITTER could potentially provide insight regarding the dispersion of a range of materials in rivers, which would facilitate ecological and geomorphic studies and help inform management. [ABSTRACT FROM AUTHOR]

This paper introduces an in-line dye tracer experiment to measure the residence time functions in continuous concrete processing. These functions quantify the material-system interdependency and can be used to compare different material-system combinations and for quality and process control. A Rhodamine B solution was used as the tracer material and detected by measuring the color intensity using a digital image processing technique. The experiment was validated on a 3D concrete printing system by comparing the results of impulse, step-up and step-down inputs with different tracer quantities. The results show that a high signal-to-noise ratio can be obtained with low tracer concentrations. For the examined combination of material and system, an impact on the original process was only observed for the step-up inputs at high tracer quantities. It is concluded that the presented method is cost-effective and non-labor-intensive and, therefore, has the potential for wide adoption and integration in automated workflows. [ABSTRACT FROM AUTHOR]

Rivers convey a broad range of materials, such as sediment, nutrients, and contaminants. Much of this transport can occur during or immediately after an episodic, pulsed event like a flood or an oil spill. Understanding the flow processes that influence the motion of these substances is important for managing water resources and conserving aquatic ecosystems. This study introduces a new remote sensing framework for characterizing dynamic phenomena at the scale of a channel cross-section: Hyperspectral Image Transects during Transient Events in Rivers (HITTER). We present a workflow that uses repeated hyperspectral scan lines acquired from a hovering uncrewed aircraft system (UAS) to quantify how a water attribute of interest varies laterally across the river and evolves over time. Data from a tracer experiment on the Missouri River are used to illustrate the components of the end-to-end processing chain we used to quantify the passage of a visible dye. The framework is intended to be flexible and could be applied in a number of different contexts. The results of this initial proof-of-concept investigation suggest that HITTER could potentially provide insight regarding the dispersion of a range of materials in rivers, which would facilitate ecological and geomorphic studies and help inform management.

Research on the scale effect of solute transport in karst conduits is very important for the correct interpretation of breakthrough curves (BTCs), but the scale effect of solute transport in a bended conduit has not been examined. In this paper, a karst conduit and a pool developed within the conduit are generalized into the transparent hose and cubic pool, respectively. Based on the previously established pool-pipe system, the bended pipes with different lengths are arranged downstream of the pool, and the tracer experiments are conducted to study the effect of the transport scale on the BTCs in conduits. We use the transient storage model to simulate the experimental curves. The results show that with the increasing pipe length downstream the pool, the peak concentration gradually decreases slowly, the rising slope of the BTCs does not change significantly, and the BTC tails gradually shorten, indicating that the longer transport distance exerts a larger effect on solute transport than the conduit bend. The coefficient of skewness (CSK), breakthrough time of posterior solute plume (tre) and breakthrough time of solute plume (td) are well negatively correlated with the length of the pipe system (R2>0.96). When the length of the pipe system with the symmetrical or asymmetrical pool increases to 154.5 m and 164.3 m, respectively, the CSK is close to zero, and the BTC is nearly symmetrical. The dispersion coefficient (D), cross-sectional area of the storage zones (As) and exchange coefficient (α) have a good negative correlation with the length of the pipe system. When the length of the pipe system with the symmetrical or asymmetrical pool increases to 159.9 m and 178.1 m, respectively, the As is close to zero. Then, the solute retention caused by the pool basically disappears. The results have certain indications for the interpretation of the BTCs in field karst conduits.

The melting treatment and isotopic tracing experiments were carried out on a self-designed plasma bench melting test with glass solidification formulas of single waste as well as mixed waste of glass fiber, concrete and soil. After melting at 1 100-1 300 ℃ for 1 h, all the four samples were turned into glass waste-forms. The density, leaching and mechanical performance of resultant glass waste-forms were tested, showing the comparable requirement with the radioactive waste glasses. The results of the tracer experiment show that the plasma melting system has high interception rate for the tracer elements Co, Cs and Sr. In addition, the glass waste-forms has higher curing capacity for Co and Sr, but lower for Cs. In engineering application, it is suggested to add a pretreatment system such as granulation at the front of the melting furnace system to reduce the proportion of material directly entering the flue gas purification system and improve the solidified efficiency of the materials.

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, we compare two different parameterisations for the wind velocity–component standard deviations. The first one is the (Hanna 1982) parameterisation, while the second is the (Scire et al. 2000) parameterisation, which provide the proper values and vertical structure for the wind standard deviations in the convective, neutral and stable layers, needed as input the Lagrangian stochastic model SPRAYWEB. The results of the model simulations carried out using the two parameterisations are compared, in terms of both mean concentration and concentration standard deviation, by evaluating some statistical indexes and trough scatter- and qq-plots. [ABSTRACT FROM AUTHOR]

Imaging subsurface small‐scale features and monitoring transport of tracer plumes at a fine resolution is of interest to characterize transport processes in aquifers. Full‐waveform inversion (FWI) of crosshole ground penetrating radar (GPR) measurements enables aquifer characterization at decimeter‐scale resolution. The method produces images of both relative dielectric permittivity (εr) and bulk electrical conductivity (σb) that can be related to hydraulic aquifer properties and tracer distributions. To test the potential of time‐lapse GPR FWI for imaging tracer plumes, we conducted a numerical tracer experiment by injecting saline water, desalinated water, and ethanol in a heterogeneous aquifer. The saline and desalinated tracers only changed σb, whereas ethanol changed both εr and σb. Tracer concentrations were retrieved from the inverted εr and σb models using information about petrophysical parameters. GPR FWI εr and σb tracer images could recover preferential paths of ∼0.2 m width, while the derived σb structures are smoother. FWI of 50 time‐lapse data sets demonstrated the potential of the FWI to derive spatially resolved breakthrough curves of the saline and ethanol tracer in the image plane between the boreholes. Thus, high‐resolution imaging with GPR FWI of tracers that produce a high permittivity contrast against the background has a great potential for characterization of heterogeneous transport in aquifers. Key Points: Time‐lapse crosshole ground penetrating radar (GPR) full‐waveform inversion (FWI) shows a potential to monitor high‐resolution of ∼0.2 m transport of tracer in aquiferStarting model strategies for FWI were tested in order to optimize plume reconstruction, to be used later for field data setsGood recovery of conductivity and especially of permittivity changes suggests to monitor adequate tracers by GPR FWI for transport imaging [ABSTRACT FROM AUTHOR]

Plant transpiration plays a significant role in the terrestrial cycles, but the spatiotemporal origins of water used by plant remains highly uncertain. Therefore, the missing link to fully characterize the water mass balance, for any control volume including significant vegetated surfaces, is identifying and quantifying the key factors that control the age of water used by plants. Here, we bring together an age‐based (tran‐SAS) and a physically based (HYDRUS‐1D) model contrasting information gleaned from soil, drainage, and xylem samples at stand scale. In particular, we focus on the relative role of advection, dispersion, and root distribution on the age of water uptake and drainage. We suggest that the interplay of advective and dispersive forces, subsumed by the local Péclet number, drives the age composition of drainage even in the case of extreme uptake rates. The vegetation influence on the age of drainage is mainly exerted by diversifying the subsurface transport pathways resulting in large dispersivity and spatial heterogeneity of soil hydraulic parameters. We introduce a uniform‐equivalent root length for vegetation and show that its ratio to the effective size of the subsurface water storage controls the age selection of water uptakes. Our results are suggestive of a route forward toward a general toolbox to upscale mass balance closures for catchments embedding large and diverse plant assemblages. Plain Language Summary: Mass balance, the fundamental tool of hydrologic analysis, cannot be closed experimentally at the scale of a hydrologic catchment without answering a simple question: what waters do plants uptake? The characterization of vegetation abstractions, subsumed by water age in the transport volume, requires detailed knowledge of suitable chemical signatures of inflows and outflows and the fate of hydrologic waters by transport. In this study, we combine two conceptually different mathematical models with high‐resolution experimental data (including tracer data from plants' xylem) to identify the main factors determining the origin of water used by vegetation. We suggest that a definition of a uniform‐equivalent root length parameter proves significant in characterizing the age of plant uptake. Key Points: We combine data in a vegetated lysimeter with results from two transport models to contrast their convergence on an age‐based mass balanceWe assess experimentally and computationally the interplay of advective and dispersive processes in driving the age of drainage watersWe suggest the key control on the age selection by vegetation is root distribution, and propose a method to characterize its bulk effects [ABSTRACT FROM AUTHOR]

• Solute transport through soil and tile drain exhibited power law tail in tracer test. • Initial pulse of solutes and particles traveled from field to stream in minutes. • Time-lapse electrical resistivity surveys confirmed lingering plume of solute in soils after 1 day. In agricultural areas with poorly drained soils, subsurface tile drains are commonly installed to improve drainage but also serve as conduits that deliver excess nutrients to adjacent streams. Our goal was to understand the transport of phosphorus (P) along these flow paths by applying a novel mixture of tracers (including 866 g of conservative chloride (Cl), 3.4 g of potassium phosphate, and approximately 3.6 × 1011 fluorescent micrometer-sized particles, or 49.5 g) to a farm field and sampling their breakthrough curves at the outlet to a stream, approximately 30 m away. Simultaneously, we performed a 26-h time-lapse electrical resistivity tomography (ERT) survey to monitor the saline tracer migration in three dimensions every 0.5 to 1 h. The initial pulse of tracers had a mean arrival time of 21 min and transported 262 g of added Cl (28 %), 0.65 g of dissolved P (17 %), and 1.4 × 1010 particles (4 %) to the tile drain outlet. A stochastic mobile-immobile model fit the anomalous (non-Fickian) solute breakthrough curves, where the mobile zone represents the macropore and tile drain network, and the immobile zone represents the soil matrix. Residence times in the immobile zone exhibited a heavy (power-law) tail. ERT images confirmed the retention of tracer mixture in soils after concentrations were no longer measurable at the tile drain outlet. Core samples suggest that 96 % of particles and 21 % of dissolved P were retained within 10.5 cm of the application location. Solutes and particles were remobilized over longer timescales during three successive storms. Exported masses of Cl and dissolved P at the tile drain outlet ranged from 1,490–12,300 g and 25.7–65.2 g, respectively, indicating flushing of older Cl and P stored in soils before the tracer experiment. Less than 0.01 % of the added fluorescent particles were flushed during these storm events. This study indicates the wide range of P travel times through the subsurface in tile drained landscapes and the need to incorporate non-Fickian transport behavior in models. [ABSTRACT FROM AUTHOR]

Trees transport gases from below ground into the atmosphere through the process of transpiration. Tracing gases transported through this mechanism continuously and under field conditions remains an experimental challenge. Here we measured gases dissolved in tree sap in-situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2, CO2) from the soil, through the trees, into the atmosphere. We constructed and inserted custom-made semi-permeable membrane probes in the xylem of a fir tree and measured gas abundances at different heights using a portable gas equilibrium membrane-inlet mass spectrometer ('miniRUEDI'). With this method we were able to continuously measure the abundances of He, Ar, Kr, N2, O2, CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of concept that trees do uptake dissolved gases in soil water, we irrigated the tree with He-enriched water in a tracer experiment, and were able to determine upwards sap flow velocity. Measurements of inert gases together with reactive species as CO2 and O2 allows to separate physical transport and exchange of gases derived from the soil or the atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in-situ measurements of gases in tree sap., (© The Author(s) 2024. Published by Oxford University Press.)

Copyright of Nonferrous Metals (Mineral Processing Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Draft rules for artificial recharge operations, which use recycled waste water as a source water, require minimum travel times to production wells in California. Deliberate tracer experiments are the accepted method for determining travel times. An example of a tracer experiment using sulfur hexafluoride is discussed at an artificial recharge site located within a regional water table depression. The study shows the complexity in interpreting travel times because of the influence of recharge rates and water production. It also demonstrates the effectiveness of recovering recharged water at spreading basins surrounded by production wells.

Conventional experiments using natural rock samples have trouble in observing rock structures and controlling fracture properties. Taking advantage of 3D printing technologies, a complex fracture network was made by using a 3D printer. This approach allowed us to control the properties of the fracture networks and to prepare identical geometries for both simulation and experiment. A tracer response curve from the flow experiment was obtained and compared with numerical simulations. The result of the computational fluid dynamics (CFD) simulation based on the Navier–Stokes equations was in good agreement with experimental result, which suggested that the results of experiment and the CFD simulation are reliable. On the other hand, comparison with an equivalent permeability model based on the cubic law showed a discrepancy from the experimental result. This validation approach enabled discussion of the limitation of the flow model. Because 3D printed fracture networks could reduce uncertainty between numerical simulation and laboratory experiment, they will be useful for understanding more detailed and more complicated phenomena in fracture networks. [ABSTRACT FROM AUTHOR]

Abstract Shellfish cultures worldwide are often located in sheltered marine bays. The Oosterschelde is such a bay in the southwestern delta of the Netherlands, harboring extensive shellfish cultures, whose yield is partly driven by seston renewal from the North Sea. Tracer experiments performed with a three-dimensional hydrodynamic model were used to study the relative influences of benthic filtration and physical processes on seston replenishment. The model exhibited good skills in reproducing observed water level, temperature, salinity, and current velocity during 2009–2010. Turnover and residence times as indicators of water renewal showed substantial gradients from the mouth to head of the Oosterschelde. Surveyed bivalve biomass and empirical filtration rates were incorporated to estimate the effects of aquaculture on the seston concentration. The filtration created strong bio-deposition suppressing the eastward seston transport and causing <10% of external seston to be delivered to the head of the Oosterschelde. The effect of biological filtration on seston transport was comparable to that of physical forcing. This simple approach combining effects of physics and benthic communities can be applied more generally in food sustainability assessments of tidal bays. Highlights • Landward seston depletion induced by bivalve filtration in a Dutch coastal bay. • Comparable biological and physical impacts on the seston dynamics. • A straightforward approach useful for shellfish culture management [ABSTRACT FROM AUTHOR]

Functional–structural root-system models simulate the relations between root-system architectural and hydraulic properties, and the spatio-temporal distributions of water and solutes in the root zone. Such models may help identify optimal plant properties for breeding and contribute to increased water-use efficiency. However, it must first be demonstrated that they accurately reproduce the processes they intend to describe. This is challenging because the flow and transport processes towards individual roots are hard to observe. In this study, we demonstrate how this problem can be addressed by combining co-registered root and tracer distributions obtained from magnetic resonance imaging with a root-system model in an inverse modeling scheme. The main features in the tracer distributions were well reproduced by the model using realistic root hydraulic parameters. By combining the functional–structural root-system model with 4D tracer observations, we were able to quantify the water uptake distribution of a growing root system. We determined that 76% of the transpiration was extracted through 3rd-order roots. The simulations also demonstrated that accurate water uptake distribution cannot be directly derived either from observations of tracer accumulation or from water depletion. However, detailed tracer experiments combined with process-based models help decipher mechanisms underlying root water uptake. [ABSTRACT FROM AUTHOR]

Highlights • Tracer experiment used for bubbling bed particle mixing characterization. • Bubbling bed mixing mostly characterized by ideally mixed flow. • Axial dispersion plug flow superimposes mixed flow at fluidization number of 4.7. • Dead spaces and short-circuit flows observed at fluidization number of 4.7. Abstract This paper reports on experiments conducted with a cold flow model utilized for the investigation of the particle residence time distribution and mixing characteristics in a bubbling fluidized bed with continuous solids exchange. The investigated system is of a rectangular cross section (0.4 × 0.2 m) with a bed height of 0.17 m. A measurement device based on an alternating current bridge circuitry coupled with lock-in amplifier technology was built in the scope of quantifying the solids residence time distribution, whereby a pulse-injected ferromagnetic tracer creates the input signal. The implementation of a profound mathematical routine ensures the reproducible calculation of the particles mean residence time and characteristic values describing particle mixing phenomena. Therefore, the E -curve was modeled by mathematical convolution of the exit age distributions available for an ideally mixed continuous stirred tank reactor and a plug flow reactor with axial dispersion. It is shown that the in-bed mixing is highly dependent on the fluidization rate as well as on the solids circulation rate. Albeit the lowest superficial gas velocity equals a fluidization number of 4.7, the formation of dead spaces and short-circuit flows was observed under these conditions. Axial dispersion coefficients in the range of 5 · 10 - 3 to 7 · 10 - 1 m2 s−1 were obtained. [ABSTRACT FROM AUTHOR]

Highlights • A new V-shaped reactor model for upgrading of biomass pyrolysis vapors was built. • The solid concentration, RTD and catalytic pyrolysis process were analyzed. • The mean residence time of catalysts in the V-shaped reactor was 2.0 s–3.0 s. • In this work the optimal gas and catalyst flow rates were determined. Abstract Catalytic upgrading of biomass pyrolysis vapors is an effective utilization technology of biomass energy. Based on the disadvantages of commonly used reactors, the V-shaped downer reactors were designed to increase gas-solid two-phase turbulent intensity, contact frequency and then increase the catalytic efficiency in short residence time. The catalytic upgrading of pyrolysis vapors in V-shaped downer reactors in terms of hydrodynamics, chemical reaction and residence time distribution were analyzed by CFD simulation and experiment. The results indicate that the solid concentration gradient decreases while flowing down. The overall mass fraction of the bio-oil vapors is around 50%. The mean residence time of catalysts in the V-shaped reactor is 2.0 s–3.0 s. The effects on product yield and residence time distribution were investigated for optimizing product selectivity and the performance of catalysts. In this paper the optimal flow rates of gas and catalysts are v g = 1.2 m s−1, v s = 0.4 m s−1. [ABSTRACT FROM AUTHOR]

Abstract Swordtip squid (Uroteuthis edulis) of various sizes are caught on an almost daily basis from early spring to late autumn in the eastern Tsushima Strait and southern Sea of Japan. In this study, we estimated the migratory routes of different sized squid jigged in the Tsushima Strait using statolith analyses, information on seawater temperature distributions and currents, and tracer experiments. Estimates of age and historic water temperatures suggested that both small and large squid hatch in the southern East China Sea and are then transported northeastward with the currents to the northern Kuroshio region. Following this, the small squid are transported north-northwestward to offshore waters, from where many of the squid enter the southern Sea of Japan and some move into coastal waters in the eastern strait, whereas large squid slowly move northward from the northernmost part of the Kuroshio region. Based on these distributions, it is likely that the small squid remain immature due to insufficient water temperatures over shorter durations, whereas the large squid mature in the Kuroshio region. Since migratory routes affect fishing ground formation, this information is important for both efficient fishing operations and stockmanagement of this species. [ABSTRACT FROM AUTHOR]

The structural characteristics of a spiral symmetry stream anaerobic bioreactor (SSSABR) contribute to its super-high-rate performance. This study investigated the structural characteristics of SSSABR, including distribution zone, spiral reaction zone, and three-phase separation zone, by computational fluid dynamics (CFD). In distribution zone, uniformity and hydraulic head loss increased with increasing number of orifices, and five-orifice is deemed optimal for distributor. In spiral reaction zone, a 45° cutting angle produced a tangential velocity strong enough to spin the granular sludge and maintain a moderate mixing intensity. A 30° installation angle produced a wide range of spiral flows. The 120° symmetrical arrangement of plates formed a strong–weak periodic spiral flow that strengthened material exchange. In separation zone, a value of 0.625 for the frustum characteristic parameter i ( i = r 1 / r 2 , where r 1 presented the bottom frustum radius of reverse cone, and r 2 presented radius of spiral reaction zone of SSSABR) provided moderate recirculation. The relative error of dead zone rate between CFD and tracer experiment was 4.66%. [ABSTRACT FROM AUTHOR]

Highlights • We propose a Lattice Boltzmann model to solve 2D fractional advection-dispersion equation. • The model is verified against the analytical solution of a benchmark problem. • We apply the model to simulate Cl− movement in a tracer experiment. • We discuss the pros and cons of the model in comparison with other numerical models. Abstract Natural soils and aquifers are inherently heterogenous and chemical transport through them is anomalous characterized by an early arrival followed by a persistent tail. How to describe such anomalous phenomena has been an interest and, as a result, a number of approaches have been proposed over the past few decades. Among others, the fractional advection-dispersion equation (FADE) is a model able to describe anomalous transport when the dispersion is regional rather than local as presumed in the classical advection-dispersion equation. Practical application of FADE needs numerical solutions, which is challenging because its spatial discretization gives rise to a full coefficient matrix. In this paper, we propose a Lattice Boltzmann model to solve the two-dimensional FADE. Given that the anomalous dispersion in soils and aquifers is hydrodynamic and caused by spatial variation in water velocity across the pore space and that the chemical plume spreads preferentially along the mean water-flow direction, the dispersion coefficient and the order of the fractional derivative should be both anisotropic. The anisotropies are solved by the two-relaxation time Lattice Boltzmann model using different relaxation parameters in different directions. Compared with existing numerical methods for the FADE, the proposed model has advantages that it is explicit, second-order accurate in both time and space, mass-conservative, and free of numerical dispersion; its stability is independent of dispersion coefficient. We verify the model against the analytical solution of a benchmark problem and then apply it to simulate Cl− movement in a tracer experiment conducted on an up-catchment hillslope. The results show that the FADE with backward skewness can reproduce the breakthrough curves measured from the experiment. [ABSTRACT FROM AUTHOR]

The numerical tool EKINOX-Zr has been upgraded to simulate oxygen tracer experiments during the high-temperature oxidation of a metal with a high oxygen solubility limit. The penetration of 18O tracer is calculated during the dynamic evolution of the ZrO2-x/αZr(O)/βzr system. The numerical approach allows to explicitly take into account the variation of the tracer diffusion coefficient through the oxide scale as a function of the vacancy concentration. A classical two-stages 16O2/18O2 tracer experiment has been simulated. It is shown that a classical fitting procedure on the 18O concentration profile obtained for short-time experiments leads to the identification of the oxygen chemical diffusion coefficient. The second type of tracer experiment is proposed using a three-stages 16O2/18O2/16O2 oxidation. It allows the direct estimation of the diffusion coefficient from the transport of 18O peak in the growing oxide scale. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we use realistic isopycnal velocities with a 3‐D eddy diffusivity to advect and diffuse a tracer in the Antarctic Circumpolar Current, beginning in the Southeast Pacific and progressing through Drake Passage. We prescribe a diapycnal diffusivity which takes one value in the SE Pacific west of 67°W and another value in Drake Passage east of that longitude, and optimize the diffusivities using a cost function to give a best fit to experimental data from the DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) tracer, released near the boundary between the Upper and Lower Circumpolar Deep Water. We find that diapycnal diffusivity is enhanced 20‐fold in Drake Passage compared with the SE Pacific, consistent with previous estimates obtained using a simpler advection‐diffusion model with constant, but different, zonal velocities east and west of 67°W. Our result shows that diapycnal mixing in the ACC plays a significant role in transferring buoyancy within the Meridional Overturning Circulation. [ABSTRACT FROM AUTHOR]

A previous study has reported that Knudsen diffusion coefficients obtained by tracer experiments conducted with a binary gas system and a porous medium are consistently smaller than those obtained by permeability experiments conducted with a single-gas system and a porous medium. To date, however, that study is the only one in which tracer experiments have been conducted with a binary gas system. Therefore, to confirm this difference in Knudsen diffusion coefficients, we used a method we had developed previously to conduct tracer experiments with a binary carbon dioxide–nitrogen gas system and five porous media with permeability coefficients ranging from 10 −13 to 10 −11  m 2 . The results showed that the Knudsen diffusion coefficient of N 2 ( D N2 ) (cm 2 /s) was related to the effective permeability coefficient k e (m 2 ) as D N2  = 7.39 × 10 7 k e 0.767 . Thus, the Knudsen diffusion coefficients of N 2 obtained by our tracer experiments were consistently 1/27 of those obtained by permeability experiments conducted with many porous media and air by other researchers. By using an inversion simulation to fit the advection–diffusion equation to the distribution of concentrations at observation points calculated by mathematically solving the equation, we confirmed that the method used to obtain the Knudsen diffusion coefficient in this study yielded accurate values. Moreover, because the Knudsen diffusion coefficient did not differ when columns with two different lengths, 900 and 1500 mm, were used, this column property did not influence the flow of gas in the column. The equation of the dusty gas model already includes obstruction factors for Knudsen diffusion and molecular diffusion, which relate to medium heterogeneity and tortuosity and depend only on the structure of the porous medium. Furthermore, there is no need to take account of any additional correction factor for molecular diffusion except the obstruction factor because molecular diffusion is only treated in a multicomponent gas system. Thus, molecular diffusion considers only the obstruction factor related to tortuosity. Therefore, we introduced a correction factor for a multicomponent gas system into the DGM equation, multiplying the Knudsen diffusion coefficient, which includes the obstruction factor related to tortuosity, by this correction factor. From the present experimental results, the value of this correction factor was 1/27, and it depended only on the structure of the gas system in the porous medium. [ABSTRACT FROM AUTHOR]

Knowledge about water flow and contaminant transport in the unsaturated zone is crucial for groundwater resource estimations and groundwater vulnerability assessments. Large field lysimeters are commonly used as physical models of the unsaturated zone. Tracer experiments conducted in lysimeters are generally applied to investigate the time scale of leaching processes in the unsaturated zone. In this paper the preliminary results of using penetrometer-based electrical resistivity profiling to follow tracer transport through the soil in a lysimeter. The measurements were made in two lysimeters (Liz A and Liz I) filled with the same sandy soil. A tracer solution was injected only into lysimeter A. The measurements in lysimeter I were treated as a benchmark reflecting the influence of temporal soil moisture variations on the soil electrical resistivity. Additionally, temperature profiling in the soil next to lysimeter column was conduceted to consider the impact of the temperature fluctuations on soil resistivity. The obtained soil resistivity profiles for lysimeter A clearly reflect the tracer breakthrough curves in the 7th and 22nd day after injection. The analysis of the curves yielded the approximated velocity of tracer transport. [ABSTRACT FROM AUTHOR]

The Zhangmu landslide is a large ancient landslide located on the China-Nepal border. Many local slope failure events occurred at this site in the past, posing a direct threat to people and property. One hundred borehole logs (total drilling length of almost 5500 m) were collected to investigate the inner structure of the landslide. Electron spin resonance (ESR) dating and width measurement of annual tree rings were used to determine the reactivation time of different parts of the landslide. A bromide tracer experiment and measurements of the distribution of borehole groundwater were combined to analyze the flow field in the study area. The alluvial stratum in the study area indicates a long-term stable deposition environment. Based on the distribution of the alluvium stratum, we identified the area least prone to landslide damage. Both the surface and underground deformation characteristics were analyzed based on displacement monitoring data from 2006, 2011, and 2013. Combining the monitoring result with the lithology and precipitation, we found that landslide reactivation is closely related to precipitation, suggesting that the reactivation began in the old shear zone. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a kind of sludge stabilization technology widely used at home and abroad. As an opaque non-Newtonian fluid, it is difficult to obtain the sludge flow characteristics in the digester exactly. Hence, it is necessary to find a sort of transparent fluid to replace it. To ensure the reliability of flow characteristics obtained from transparent analog fluid, it is indispensable to verify the flow similarity with main physical property of the fluid. The feasibility of xanthan gum transparent solution as a similarity solution of digestion sludge was analyzed according to the rheological property and density, respectively, based on the similarity criteria of fluid flow. Under the premise of satisfying the geometric similarity, the Reynolds criterion and the Froude criterion should be met simultaneously, that is, the Reynolds number and the Froude number of 2 kinds of fluids should be equal. The rheological parameter and density of 95% water content digestion sludge and xanthan gum solution at different concentrations were measured by rotating viscometer and gravimetric method severally. The rheological curve of 2 kinds of fluids was tested for a goodness-of-fit, and curve regression effect was characterized by the determination coefficient R2 on the principle of regression analysis. First, the xanthan gum solution of 13, 16, and 19 g/L was prepared. It was found that the rheological curves of the 16 g/L xanthan gum solution were similar to those of digestion sludge, and both of them were pseudo plastic non-Newtonian fluid, indicating that this xanthan gum solution could replace the sludge as a similarity solution. But, the xanthan gum solution's density was smaller than that of the target fluid in this recipe, which did not conform to the fluid flow similarity criteria. So, for adjusting the density disparity, xanthan gum solution of 14, 15, and 16 g/L was made by using KCl solution as the solvent instead of aqueous solution. Because of the fact that the salt screens the electrostatic repulsions of the trisaccharide side chains, the adoption of a helical backbone conformation is allowed, which in turn promotes the increased association of the ordered xanthan molecules in solution. With the addition of KCl, the rheological curves of 15 g/L xanthan gum solution were in reasonable agreement with those of digestion sludge, which were also typical pseudo-plastic non-Newtonian fluid. The determination coefficients of rheological curve of 2 kinds of fluids were R2=0.995 3 (viscosity curve) and R2=0.893 5 (shear stress curve), separately, showing the highest similarity. Tracing test of mixing performance displayed that tracer concentrations at the outlet in these 2 kinds of fluids had the same tendency with the change of time. The result of Welch's t-test demonstrated that there was no significant difference in the rheological parameter and density of the 2 kinds of fluids at the significant level of 0.05. Given above logical analysis, it should be pointed out that xanthan gum transparent solution used as a similarity solution of digestion sludge is acceptable, which can be used as a basis method for the flow visualization in the anaerobic digester. Generally, future work should focus on applying transparent similarity solution to validate computational fluid dynamics simulation from the perspective of reducing energy consumption and improving biogas yield. [ABSTRACT FROM AUTHOR]

Organic soils are the most important source of dissolved organic carbon (DOC) in surface water. To date, most studies have focused on natural and re-wetted peatlands, but in Central Europe a large proportion of organic soils are drained and under agricultural use. Furthermore, measures such as deep ploughing or sand addition have been conducted to improve trafficability and have resulted in topsoil horizons consisting of a peat-sand mixture. Very little is known about DOC losses from such soils. Moreover, peat soils frequently feature both mobile zones, characterised by active water and solute transport, and immobile zones, which exchange solutes with the mobile zone by diffusion. Surprisingly, however, the effects of this dual porosity on DOC transport have not yet been explored. This study investigated the physicochemical controls on DOC concentrations in a peat-sand mixture by means of a saturated column experiment with undisturbed columns. The soil came from a former bog in northern Germany where peat layers remaining after peat extraction were mixed with the underlying mineral soil by ploughing. Three pumping rates and two levels of electrical conductivity (EC) were applied. The transport properties of the soil were obtained by analysing breakthrough curves of potassium bromide using the transport model STANMOD, which is based on the two-region non-equilibrium concept. The results of the column study were compared to DOC concentrations measured bi-weekly for two years at the field site from where the columns were taken. Despite a similar texture and soil organic carbon (SOC) content, the fraction of the mobile zone in the columns varied between 51% and 100% of total porosity. Thus even heavily degraded organic soils mixed with sand still showed a dual porosity comparable to degraded peat soils. Percolating the columns with the high EC solution caused low pH values, probably due to ion exchange and cation bridging. The combination of high EC and low pH greatly decreased DOC concentrations at the outlet of the columns. DOC concentrations decreased and fluxes increased as the pumping rates increased. Taking pore water velocity in the mobile zone into account could help to explain the differences between the columns. Overall, transport of DOC did not seem to be limited by production of DOC, but by rate-limited exchange processes. In contrast to the column experiment, field concentrations of DOC were much higher and were not related to pH, but increased with higher electrical conductivity. These higher concentrations could be explained by low pore water velocities and the slightly higher SOC content in the field. This first experiment on DOC transport in peat-sand mixtures taking the dual-porosity nature of organic soils into account clearly demonstrated the importance of pore water velocity and thus the residence time for DOC concentrations. While hydrochemical conditions are frequently addressed in laboratory studies, there is a need for improved understanding of their interaction with hydrology and soil-physical properties, especially when attempting to interpret DOC data on different spatial and temporal scales. [ABSTRACT FROM AUTHOR]

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