Tracer Experiments Research Articles

Cancer EV stimulate endothelial glycolysis to fuel protein synthesis via mTOR and AMPKα activation.

Hypoxia is a common feature of solid tumours and activates adaptation mechanisms in cancer cells that induce therapy resistance and has profound effects on cellular metabolism. As such, hypoxia is an important contributor to cancer progression and is associated with a poor prognosis. Metabolic alterations in cells within the tumour microenvironment support tumour growth via, amongst others, the suppression of immune reactions and the induction of angiogenesis. Recently, extracellular vesicles (EV) have emerged as important mediators of intercellular communication in support of cancer progression. Previously, we demonstrated the pro-angiogenic properties of hypoxic cancer cell derived EV. In this study, we investigate how (hypoxic) cancer cell derived EV mediate their effects. We demonstrate that cancer derived EV regulate cellular metabolism and protein synthesis in acceptor cells through increased activation of mTOR and AMPKα. Using metabolic tracer experiments, we demonstrate that EV stimulate glucose uptake in endothelial cells to fuel amino acid synthesis and stimulate amino acid uptake to increase protein synthesis. Despite alterations in cargo, we show that the effect of cancer derived EV on recipient cells is primarily determined by the EV producing cancer cell type rather than its oxygenation status.

Patterns and drivers of atmospheric nitrogen deposition retention in global forests.

Forests are the largest carbon sink in terrestrial ecosystems, and the impact of nitrogen (N) deposition on this carbon sink depends on the fate of external N inputs. However, the patterns and driving factors of N retention in different forest compartments remain elusive. In this study, we synthesized 408 observations from global forest 15N tracer experiments to reveal the variation and underlying mechanisms of 15N retention in plants and soils. The results showed that the average total ecosystem 15N retention in global forests was 63.04 ± 1.23%, with the soil pool being the main N sink (45.76 ± 1.29%). Plants absorbed 17.28 ± 0.83% of 15N, with more allocated to leaves (5.83 ± 0.63%) and roots (5.84 ± 0.44%). In subtropical and tropical forests, 15N was mainly absorbed by plants and mineral soils, while the organic soil layer in temperate forests retained more 15N. Additionally, forests retained more than , primarily due to the stronger capacity of the organic soil layer to retain . The mechanisms of 15N retention varied among ecosystem compartments, with total ecosystem 15N retention affected by N deposition. Plant 15N retention was influenced by vegetative and microbial nutrient demands, while soil 15N retention was regulated by climate factors and soil nutrient supply. Overall, this study emphasizes the importance of climate and nutrient supply and demand in regulating forest N retention and provides data to further explore the impacts of N deposition on forest carbon sequestration.

Deciphering the Lithium-Ion Conduction Mechanism of LiH in Solid-Electrolyte Interphase.

Lithium hydride (LiH) has been widely recognized as the critical component of the solid-electrolyte interphase (SEI) in Li batteries. Although the formation mechanism and structural model of LiH in SEI have been extensively reported, the role in electro-performance of LiH in SEI is stillambiguous and has proven challenging to explored due to the complicated structure SEI and the lack of advanced in situ experimental technology. In this study, the isotopic exchange experiments combined with isotopic tracer experiments is applied to solidly illustrate the superior conductivity and Li+ conduction behavior of the LiH in natural SEI. Importantly, in situ transmission electron microscopy analysis is utilized to visualize the self-electrochemical decomposition of LiH, which is significantly distinctive from LiF and Li2O. The critical experimental evidence discovered by the work demonstrates ion transport behaviors of key components in the SEI, which is imperative for designing novel SEI and augurs a new area in optimizing the performance of lithium batteries.

Visualizing preferential flow paths using dye tracer and species diversity theory methods to explore their correlation to soil properties with random forest algorithm

The preferential flow path development is potentially the result of spatial variations in soil properties with soil depth. However, visualizing the evolution of the preferential flow path with soil depth remains a challenge. This paper presents dye tracer and species diversity theory methods for characterizing preferential flow paths. Field dye tracer experiments were performed at three sites (tree, bush, and grass) in the Yellow River Delta wetland and dye distribution diversity indices (Simpson index (Ds), Shannon-Wiener index (H), Margalef index (Dm), and Pielou index (E)) were applied to verify their availability for preferential flow assessment. The results showed that the uniformity of the shallow-infiltrated dye at the tree site, non-uniformity of the shallow-infiltrated dye at the bush site, and deep dye infiltration at the grass site were the three typical infiltration types. The average proportion of dye-stained areas (PDA) gradually decreased with increasing soil depth. The quantitative effects of soil properties on PDA changes were profound, indicating that soil clay content at 0–10 cm depth, soil sand content at 10–20 cm depth, soil drainage capacity at 20–30 cm depth, and soil bulk density at 30–40 cm depth were the most predictive factors controlling PDA changes. Our results also showed that dye-stained patches with extremely high and high dye concentrations were the most distributed; Ds, H, Dm, and E were the highest at the tree site and E was the diversity index with the greatest importance for PDA change. The findings reveal the soil properties controlling the formation of preferential flow paths, which will improve our understanding of water resource management in the vadose zones of coastal wetlands.

Experiments reveal effects of particle and pore-scale heterogeneity on thermal dispersion during porous media heat transport

The growing applications of heat transport in engineering and hydrogeology, including ground source heat pump systems and the assessment of water flow and sediment thermal properties, necessitate precise thermal dispersion modeling. Despite various factors like particle size, shape, and distribution impacting dispersion in porous media, a lack of experimental data and analysis has limited our grasp of the relationship between flow velocity and thermal dispersion. To address this gap, we conducted solute and heat tracer experiments using sands of different grain sizes, employing analytical models based on a universal power law relationship for dispersion. Additionally, we systematically compiled dispersion data from the scientific literature to assist in interpreting of the effects of particle size, shape, and pore-scale heterogeneity on dispersion. Our findings reveal that solute and thermal longitudinal dispersion align for high flow velocities in the dispersion-dominated flow regime (Pe > 5), where the velocity-dispersion relationship is linear. However, in the transition regime (advection approx. equal to diffusion, 0.1–0.3 < Pe < 5), the observed deviation from linearity (R2<0.9) is linked to increased pore-scale heterogeneity, particularly in smaller particle sizes. This study underscores the pivotal role of thermal dispersion and underscores the need for caution when estimating thermal dispersion based on solute dispersion, given the intricate nature of real-world conditions and the potential influence of factors such as grain size distribution and pore-scale heterogeneity in natural porous materials.

Spatiotemporal patterns and co-occurrence patterns of dissimilatory nitrate reduction to ammonium community in sediments of the Lancang River cascade reservoirs.

Dissimilatory nitrate reduction to ammonium (DNRA) is an important nitrate reduction pathway in freshwater sediments. Many studies have focused on the DNRA process in various natural habitats. However, the joint operation of cascade reservoirs will affect the physical and chemical properties of sediments, which may change the DNRA process and bacterial community pattern in the surface sediments of cascade reservoirs. Our study was the first to investigate the spatiotemporal distribution patterns of potential DNRA rate, nrfA gene abundances, and DNRA bacterial community diversity in surface sediments of the Lancang River cascade reservoirs. The results of slurry incubation experiments combined with the 15N isotope tracer experiment ascertained that the potential rates of DNRA were 0.01-0.15 nmol-N cm-3 h-1, and qPCR results indicated that the abundance range of nrfA was 1.08 × 105-2.51 × 106 copies g-1 dry weight. High throughput sequencing of the nrfA gene revealed that the relative abundance of Anaeromyxobacter (4.52% on average), Polyangium (4.09%), Archangium (1.86%), Geobacter (1.34%), and Lacunisphaera (1.32%) were high. Pearson and RDA correlation analysis exhibited that nrfA gene abundance was positively correlated with altitude, pH, OC, and sand concentration. Anaeromyxobacter was positively correlated with reservoir age and DNRA potential rate. The deterministic environmental selection process plays a crucial role in the formation of the DNRA bacterial community. Network analysis displayed that the dominant DNRA genus was the key population of the DNRA microbial community in the sediments of Lancang River cascade reservoirs. This study reveals that the variation of DNRA bacterial activity and community structure is largely driven by the construction of cascade reservoirs, and provides a new idea for further understanding the characteristics of the DNRA community in the cascade reservoir ecosystem.

Quantification of hydraulic characteristics and validation of CFD simulation of subsurface flow constructed wetlands using tracer

The analysis of residence time distributions (RTDs) is of great significance in the hydraulic characterization of subsurface flow constructed wetlands (SSF-CWs), and tracer experiments and simulations are generally used methods to obtain RTDs. This study developed a computational fluid dynamics (CFD) model involving two tracer tracking approaches in order to understand and quantify the flow behavior in SSF-CW. To validate the CFD model, RTDs were obtained from bench-scale impulse response tests with finite-constant injection of tracer, and the hydraulic indexes were corrected by introducing tracer injection time and nominal residence time in the formulae. The shape similarities of RTDs between the CFD model, the gamma model and observation were evaluated by a dynamic time warping algorithm, where the CFD model incorporating advection, diffusion and dispersion processes had the highest shape similarity (0.94–0.98). The proposed CFD model gave the tracer the same velocity field as the fluid, characterizing more accurate hydraulic indexes compared to the gamma model. The CFD model is appropriate for design optimization prior to full-scale construction since it saves time and is environmentally benign. It also gives visualization of the tracer trajectory, which aids in understanding contaminant fate and transport within the SSF-CW.

Improving the reliability of using rare earth elements as soil erosion tracers

Rare earth elements (REEs) have been successfully used as tracers in field-scale erosion experiments to provide spatially distributed erosion data for process-based soil erosion models. This study aimed to demonstrate how differences in the erodibility of individual REEs naturally present in the soil affect the evaluation of data from such experiments.A four-year field experiment was carried out at an experimental site used for arable farming to investigate soil erosion. The concentrations of tracer REEs (Pr, Sm, Gd, Ho, Er, and Yb) and reference REEs (all other REEs) were evaluated and compared both in the soil and eroded sediment.The tracer REE concentrations in the eroded sediments were consistently significantly higher than the average background soil concentrations. Even when compared with the maximum values of background soil concentrations, enrichment of Er, Sm, and Ho in the sediment was still evident. However, in some cases, the reference REE concentrations in the sediment were often higher than the maximum soil background concentrations by more than 10%. These enrichment differences indicate the varying erodibility of individual REEs during erosion. The elements chosen as tracers could also be enriched in the sediment from their natural background sources, thus influencing the measured concentration values in the sediment after tagging.This study demonstrated that different REEs naturally present in soil exhibit varying degrees of erodibility, which affects data evaluation in soil erosion tracing experiments using REE oxides as tracers. Therefore, the reliable application of the REE tracer method can only be suggested under certain requirements defined in this study.

Insights into the selectivity to glyceric acid and lactic acid from biomass: Reaction mechanism and temperature effect

The disclosure of the underlying reaction mechanism on biomass valorization is of significant importance but remains challenging. We here unveil the complicated reaction mechanism on the coproduction of glyceric and lactic acids from biomass (glucose as representative) in the presence of cheap but robust CaO. Interestingly, it was discovered that the selectivity to glyceric acid and lactic acid from glucose was temperature-tunable. Glyceric acid was preferentially produced at ≤70 °C, while lactic acid generation was favorable at >90 °C. Glyceric and lactic acids could be coproduced with almost 1:1 ratio at moderate reaction temperature (∼80 °C). Isotopic tracing experiment verified that at moderate temperature, glyceric acid and equivalent lactic acid were predominantly originated from glyceraldehyde and dihydroxyacetone intermediates (generated after C3-C4 cleavage), respectively. However, both glyceraldehyde and dihydroxyacetone intermediates were transformed mainly towards glyceric acid at temperature ≤70 °C, but predominantly afforded lactic acid at high temperature. Kinetic studies in combination with DFT calculation verified that glyceric acid production from both glyceraldehyde and dihydroxyacetone intermediates showed lower apparent activation energy than that for lactic acid production. This well explained the selectivity to glyceric and lactic acids via temperature control. The generated alkali in CaO aqueous solution was the major active species for glyceric acid production, while both dissolved Ca(OH)2 and solid CaO contributed to lactic acid formation. The insights into the complicated reaction mechanism will provide useful clues in biomass valorization with efficient carbon utilization.

In situ measurements of dissolved gases in xylem sap as tracers in plant physiology

Abstract Trees transport gases from the 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 the tree sap in situ and in real time, aiming to simultaneously analyse the transport of several gases (He, Ar, Kr, N2, O2 and 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 and CO2 in sap over several weeks. We observed diurnal variations of CO2 and O2 concentrations that reflected tree physiological activities. As a proof of the 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 upward sap flow velocity. Measurements of inert gases together with reactive species, such as CO2 and O2, allowed separation of the physical transport and exchange of gases derived from the soil or atmosphere from biological reactions. We discuss the opportunities that our technique provides for continuous in situ measurements of gases in the tree sap.

Experimental and numerical investigations of flow behavior in an open falling film microreactor equipped with curved flow splitting elements

This work aims the experimental and numerical characterization of gas–liquid flow in an open multichannel falling film microreactor containing 64 coated microchannels, and a split & curve structure for the flow distribution. The operating flowrate range, the flow distribution, and the residence time of the liquid in the single channels were assessed via self-designed pulse input tracer experiments.3D simulations based on Volume of Fluid (VoF) multiphase model were developed in ANSYS Fluent considering a representative section of a single microchannel. Simulation results indicate that backflow phenomena and an increase in film thickness along the channel length are the main reasons for the high film thickness observed experimentally. While the flow rate has only a marginal effect on both processes, the plate inclination angle has considerable contribution in overflow and flow stability. Finally, the numerically calculated transversal wetted area is mainly determined by the defined GLS contact angle at the sidewalls.

Nitrification in a Subterranean Estuary: An Ex Situ and In Situ Method Comparison Determines Nitrate Is Available for Discharge

AbstractSubterranean estuaries (STEs) form in the subsurface where fresh groundwater and seawater meet and mix. Subterranean estuaries support a variety of biogeochemical processes including those transforming nitrogen (N). Groundwater is often enriched with dissolved inorganic nitrogen (DIN), and transformations in the STE determine the fate of that DIN, which may be discharged to coastal waters. Nitrification oxidizes ammonium (NH4+) to nitrate, making DIN available for N removal via denitrification. We measured nitrification at an STE, in Virginia, USA using in situ and ex situ methods including conservative mixing models informed by in situ geochemical profiles, an in situ experiment with 15NH4+ tracer injection, and ex situ sediment slurry incubations with 15NH4+ tracer addition. All methods indicated nitrification in the STE, but the ex situ sediment slurries revealed higher rates than both the in situ tracr experiment and mixing model estimations. Nitrification rates ranged 55.0–183.16 μmol N m−2 d−1 based on mixing models, 94.2–225 μmol N m−2 d−1 in the in situ tracer experiment, and 36.6–109 μmol N m−2 d−1 slurry incubations. The in situ tracer experiment revealed higher rates and spatial variation not captured by the other methods. The geochemical complexity of the STE makes it difficult to replicate in situ conditions with incubations and calculations based on chemical profiles integrate over longer timescales, therefore, in situ approaches may best quantify transformation rates. Our data suggest that STE nitrification produces NO3−, altering the DIN pool discharged to overlying water via submarine groundwater discharge.

In-situ tracer experiment and solute transport characterization of a fracture in granitic rock

In-situ tracer experiment and solute transport characterization of a fracture in granitic rock

Migration and balance of 13C in the stellarator Wendelstein 7-X after 13CH[formula omitted] local injection into the island divertor

A 13C tracer experiment was carried out to investigate impurity transport and migration in the stellarator Wendelstein 7-X (W7-X). About 4.0 × 1022 molecules of 13C marked methane were injected through the divertor gas injection system during plasma operation. After the experiment, the divertor target elements were extracted to be analyzed by post-mortem methods. In particular, the results of the Nuclear Reaction Analysis are presented, and the 13C balance and predominating contributors to migration are discussed.A two-dimensional 13C deposition pattern on 12C graphite modules was obtained with over 6000 single measurements. The post-mortem analysis results extrapolations show a high local deposition of around 25% of the 13C within a 5 cm radius around the injection holes embedded in a graphite target module of one of the ten divertor units. Additionally, a striation is detected in the toroidal direction along the outer strike line and the net carbon deposition zone along the intersecting magnetic island containing about 23% of the 13C within the same divertor unit where injections were made. The residual 52% of 13C are globally migrated across the machine. In total, ∼ 90% of the injected 13C could be extrapolated by post-mortem analysis. Thus, the 13C balance is closed. The distribution indicates a non-negligible amount of global transport and the strong influence of the magnetic topology on migration. In contrast to the strike line pathway, the transport along the magnetic island only takes place counterclockwise in toroidal direction. These results are used to provide benchmark data for ERO2.0 impurity tracing simulations and to be a reference for impurity migration processes in a stellarator.

An in-line dye tracer experiment to measure the residence time in continuous concrete processing

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.

AL–AMYLOIDOSIS RELATED ADVANCED HEART FAILURE DIAGNOSED THROUGH F–18–FLUTEMETANOL PET SCAN

Abstract Background Systemic amyloidosis (SA) is a group of rare diseases in which abnormal misfolded proteins, amyloid fibrils, accumulate in tissue. The gold standard for diagnosis is tissue biopsy of the affected organ, but it is invasive and needs specific proteomic or immunohistochemistry analyses to characterize the involved protein. We report a case of a complex diagnosis of SA in an advanced heart failure (HF) patient. Methods and Results A 68–year–old woman with history of recurrent uveitis started to complain dyspnea in 2022, after Covid19. Since her symptoms worsened, in June 2023 she was diagnosed in another center with restrictive cardiomyopathy with preserved left ventricular (LV) ejection fraction. She underwent coronary angiography (unremarkable), cardiac MRI (aspecific fibrosis), and a FDG–PET scan which showed non–homogeneous LV fixation. The patient was treated with steroids for the suspicion of an immunologic–inflammatory disease, without benefit. Fourteen months after the initial presentation, she was admitted to our centre for advanced inotrope–dependent HF. She had mildly increased LV hypertrophy and severe systolic dysfunction with restrictive physiology and, notably, peri–orbital subcutaneous hemorrhages (Figure 1). Hematological screening for amyloidosis showed elevated serum free lambda light chains. Repeated cardiac MRI scan was consistent with infiltrative disease. A total–body PET scan with dual tracer was performed. The control session with F–18–FDG showed mild aspecific cardiac uptake in the basal septum and lateral wall (Figure 2), while off–label use of F–18–Flutemetanol, an Alzheimer‘s disease approved experimental tracer that binds to amyloid fibrils beta sheets with very high sensitivity and specificity, showed intense cardiac, hepatic, pulmonary and muscular uptake, with wash–out–timing diagnostic for AL–SA (Figure 3). Periumbilical fat biopsy confirmed the clinical suspicion of SA. Hematological investigations led to the diagnosis of stage I–A lambda micromolecular multiple myeloma, with systemic amyloidosis and a IIIb cardiac prognostic score. Conclusions Endomyocardial biopsy is an invasive procedure and periumbilical fat biopsy discriminates the amyloid protein type only by proteomic analysis, which is available in very few Italian centres. The off–label use of Alzheimers’ PET tracers could reduce the delay of cardiac AL–SA diagnosis, allowing early disease identification and prompting timely hematological therapy.

Tracing the contribution and fate of synthetic nitrogen fertilizer in young apple orchard agrosystems

Excessive synthetic nitrogen (N) inputs in intensive orchard agrosystems of developing countries are a growing concern regarding their adverse impacts on fruit production and the environment. Quantifying the distribution and contribution of fertilizer N is essential for increasing N use efficiency and minimizing N loss in orchards. A 15N tracer experiment was performed in a young dwarf apple orchard over two growing seasons to determine the fertilizer N transformation and fate. Fertilizer N primarily contributed to 25 % to 75 % of soil nitrate in the top 60 cm, but the contribution to soil microbial biomass N and fixed ammonium was <8 %, with the contribution to plant N ranging from 9 % to 19 %. In most growth periods, soil nitrate and fixed ammonium contents derived from native soil with N fertilization were higher than those not receiving N fertilizer. The N use efficiency of plants was only 2.6 % and 4.9 % in the first and second seasons, respectively, in contrast to 56.6 % and 54.0 % of N recovered in soil. Meanwhile, N assimilated into microbial biomass accounted for 0.8 %, and the proportion fixed by clay minerals was 3.5 %–5.2 %. One season after N fertilization, the nitrate below the 1 m soil layers accounted for 4.6 % of the applied N fertilizer, and the proportion increased to 22.5 % after two seasons. The N loss rate via N2O emission was 0.4 % over two years. The application of N fertilizer facilitated indigenous soil N mineralization, and abiotic ammonium fixation more efficiently retained synthetic N than microbial immobilization. These findings provide new insight into orchard N cycling, and attention should be given to the improvement of soil N retention and turnover capacity regulated by soil microbial and abiotic processes, as well as the potential environmental impacts of additional soil N mineralization resulting from prolonged chemical N fertilization.

A distributed-temperature-sensing-based soil temperature profiler

Abstract. Storage change in heat in the soil is one of the main components of the energy balance and is essential in studying the land–atmosphere heat exchange. However, its measurement proves to be difficult due to (vertical) soil heterogeneity and sensors easily disturbing the soil. Improvements in the precision and resolution of distributed temperature sensing (DTS) equipment has resulted in its widespread use in geoscientific studies. Multiple studies have shown the added value of spatially distributed measurements of soil temperature and soil heat flux. However, due to the spatial resolution of DTS measurements (∼30 cm), soil temperature measurements with DTS have generally been restricted to (horizontal) spatially distributed measurements. This paper presents a device which allows high-resolution measurements of (vertical) soil temperature profiles by making use of a 3D-printed screw-like structure. A 50 cm tall probe is created from segments manufactured with fused-filament 3D printing and has a helical groove to guide and protect a fiber-optic (FO) cable. This configuration increases the effective DTS measurement resolution and will inhibit preferential flow along the probe. The probe was tested in the field, where the results were in agreement with the reference sensors. The high vertical resolution of the DTS-measured soil temperature allowed determination of the thermal diffusivity of the soil at a resolution of 2.5 cm, many times better than what is feasible using discrete probes. A future improvement in the design could be the use of integrated reference temperature probes, which would remove the need for DTS calibration baths. This could, in turn, support making the probes “plug and play” into the shelf instruments without the need to splice cables or experience in DTS setup design. The design can also support the integration of an electrical conductor into the probe and allow heat tracer experiments to derive both the heat capacity and the thermal conductivity over depth at high resolution.

Pebble tracing experiment at the Promenade des Anglais (Nice, France): A contribution towards beach management efforts

In this paper, the results of a short-term tracing experiment carried out at a beach compartment along the Bay of Nice (southern France) are presented. Nice urban beach is characterized by persistent offshore sediment loss issues that force the local administration to operate frequent artificial replenishments to maintain the current configuration, which also protects the well-renown Promenade des Anglais from high-energy events. As beach refills are quite expensive, the aim of the paper is to provide novel insights about the transport processes of pebble-sized tracers, which might support the Municipality to better adjust future interventions. Pebbles were tracked by means of the Radio Frequency Identification technology, largely used in such settings because of its reliability and efficiency. In addition, the morphology of the beach was monitored during the three-days-long experiment by airborne and ground topographic surveys, as well as the shape and the size of the tracers. Finally, a wave model was produced to simulate wave propagation in the nearshore, which validates the observed transport patterns. The results documented a low recovery rate (56%) 4 h after tracer injection, which is uncharacteristic considering that it jumped to 91% after the second survey, 24 h after the injection. At the end of the experiment (48 h), the recovery rate sank to 14%. These data were adequate to identify a few trends in pebble transport: tracer recovery rate in the swash zone was very low, while many marked pebbles were found at the step crest. Although this transport pattern may corroborate the offshore movement of the sediments, the topographic surveys revealed the destruction and re-formation of the fair-weather berm overnight, which would imply the presence of a shoreward transport under low energy wave conditions. While size did not single out any tendency, shape did: spheres rolled down the beachface earlier than disks; by contrast, disk-shaped pebbles moved for longer distances than spheres. These findings will be useful for local coastal managers because next beach fills will be planned and optimized based on the observed transport patterns. Though the selection of disk-shaped pebbles implies increasing costs, replenishments would be more efficient and fine-tuned for this sector of coast, which would ultimately save resources reducing negative impacts on the environment along the way. These considerations are valid for the Bay of Nice, but they might be useful wherever coarse-clastic beaches need recurring replenishments.

Verification of Particle Tracking and In Situ Tracer Experiment for the Gravel and Cholan Formation Composite in Northwest Taiwan

This paper presents the verification results of an experimental site that employed a particle tracking algorithm to assess the transport of tracers through the composite formation of gravel and Cholan in northwest Taiwan. A suitable hydrogeological conceptual model that describes the flow characteristics of the gravel formation and Cholan formation is essential to evaluate groundwater flow and management at this site. Continuous porous medium (CPM) can be easily applied in the gravel formation, while the Cholan formation, characterized by argillaceous sandstone, is commonly treated as a porous medium. However, this study obtains its fracture distribution through geological surveys, and the key fracture parameters are also collected, analyzed, and incorporated into the model. Four hydrogeological conceptual models, including CPM, discrete fracture network (DFN), equivalent continuous porous medium (ECPM), and hybrid DFN/ECPM, are generated for this complex formation. This study combines the conceptual models of the gravel and Cholan formation into four cases to describe the characteristics of the composite formation. The groundwater flow field of four cases is simulated, and the particle tracking method is employed to model the tracer transport. Simulation results from the four hybrid models all yielded a breakthrough curve (BTC) for the first 15 h, indicating that the tracer arrived at the designated outlet within this timeframe and primarily flowed through the gravel formation, while long-time particle tracking revealed a possible flow path through the Cholan formation after 15 h. The breakthrough curve of the four cases shows that the ECPM model is more suitable for representing the heterogeneity of the Cholan formation than the common CPM model. This study provides a suitable numerical algorithm of the conceptual model of the Cholan formation based on strong evidence by considering different models and comparing them with in situ tracer tests.