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  • 550.724  (18)
  • English  (18)
  • Russian
  • 2020-2022  (18)
  • 1940-1944
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  • English  (18)
  • Russian
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  • 2020-2022  (18)
  • 1940-1944
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  • 1
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    Measuring vertical soil water content profiles by combining horizontal borehole and dispersive surface ground penetrating radar data (2021)
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    Publication Date: 2021-10-07
    Description: To investigate transient dynamics of soil water redistribution during infiltration, we conducted horizontal borehole and surface ground penetrating radar measurements during a 4-day infiltration experiment at the rhizontron facility in Selhausen, Germany. Zero-offset ground penetrating radar profiling in horizontal boreholes was used to obtain soil water content information at specific depths (0.2, 0.4, 0.6, 0.8 and 1.2 m). However, horizontal borehole ground penetrating radar measurements do not provide accurate soil water content estimates of the top soil (0–0.1 m depth) because of interference between direct and critically refracted waves. Therefore, surface ground penetrating radar data were additionally acquired to estimate soil water content of the top soil. Due to the generation of electromagnetic waveguides in the top soil caused by infiltration, a strong dispersion in the ground penetrating radar data was observed in 500 MHz surface ground penetrating radar data. A dispersion inversion was thus performed with these surface ground penetrating radar data to obtain soil water content information for the top 0.1 m of the soil. By combining the complementary borehole and surface ground penetrating radar data, vertical soil water content profiles were obtained, which were used to investigate vertical soil water redistribution. Reasonable consistency was found between the ground penetrating radar results and independent soil water content data derived from time domain reflectometry measurements. Because of the improved spatial representativeness of the ground penetrating radar measurements, the soil water content profiles obtained by ground penetrating radar better matched the known water storage changes during the infiltration experiment. It was concluded that the combined use of borehole and surface ground penetrating radar data convincingly revealed spatiotemporal soil water content variation during infiltration. In addition, this setup allowed a better quantification of water storage, which is a prerequisite for future applications, where, for example, the soil hydraulic properties will be estimated from ground penetrating radar data.
    Keywords: 550.724 ; Ground-penetrating radar ; Hydrogeophysics ; Data processing
    Language: English
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  • 2
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    Central uplift collapse in acoustically fluidized granular targets: Insights from analog modeling (2021)
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    Publication Date: 2021-10-12
    Description: Depending on their sizes, impact craters have either simple or complex geometries. Peak-ring craters such as the Chicxulub impact structure possess a single interior ring of peaks and hills and a flat interior floor. The exact mechanisms leading to the formation of a morphological peak-ring are still a matter of debate. In this study, analog modeling was used to study the flow field of a collapsing central uplift. A 3-D-printed cast was used to bring the analog material in the shape of an overheightened central uplift that was based on numerical modeling. The cast was then quickly removed and the central peak collapsed, forming a flattened broad mound that spread out onto the annular moat of the crater cavity. A subwoofer was used to fluidize the granular target material. The kinematics of the collapse were analyzed with the aid of particle image velocimetry, revealing a downward and outward collapse of the central uplift. This mode of collapse is partly in agreement with numerical models, in particular for the initial and middle phases. The overthrusting of the collapsing central peak onto the inward moving crater floor predicted by numerical modeling was observed, though to a lesser degree. A peak-ring, however, could not be reproduced since the collapse came to a halt before the central peak was completely leveled. Nevertheless, the method provides qualitative insights into the kinematics of collapse phenomena. This experimental study provides independent support of the theory of acoustic fluidization, in addition to numerical simulations.
    Keywords: 550.724 ; 551.397 ; impact craters ; morphological peak-rings ; analog modeling
    Language: English
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  • 3
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    How Dynamic Boundary Conditions Induce Solute Trapping and Quasi-stagnant Zones in Laboratory Experiments Comprising Unsaturated Heterogeneous Porous Media (2021)
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    Publication Date: 2021-10-12
    Description: The vadose zone is subject to dynamic boundary conditions in the form of infiltration and evaporation. A better understanding of implications for flow and solute transport, arising from these dynamic boundary conditions in combination with heterogeneous structure, will help to improve the prediction of the fate of solutes. We present laboratory experiments and numerical simulations of heterogeneous porous media under unsaturated conditions where controlled, temporally varying precipitation and evaporation are applied to study the effect of dynamic boundary conditions on solute transport in the presence of material interfaces. Dye tracers Eosine Y and Brilliant Blue FCF are utilized to visualize solute transport and analyze redistribution processes in a flow cell. Water and solute fluxes in and out of the flow cell are quantified. While in dynamic experiments application of small infiltration rates (significantly below the saturated hydraulic conductivities of the materials) led to a reversal of transport paths between infiltration and succeeding evaporation, larger infiltration rates altered downward transport such that flow and transport paths differed from those observed during evaporation. Differences in transport paths ultimately led to a redistribution and trapping of solute in one material which manifested as pronounced tailing in breakthrough curves. Trapping was induced not by the formation of a stagnant zone as result of large parameter contrast but by an interplay of dynamic boundary conditions and material heterogeneity. This study thereby highlights the importance to consider dynamic boundary conditions in predictions of solute leaching.
    Keywords: 550.724 ; laboratory experiment ; unsaturated porous media ; conservative solute transport ; dynamic boundary conditions
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  • 4
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    Electrification of Experimental Volcanic Jets with Varying Water Content and Temperature (2021)
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    Publication Date: 2021-10-12
    Description: Volcanic lightning—a near ubiquitous feature of explosive volcanic eruptions—possesses great potential for the analysis of volcanic plume dynamics. To date, the lack of quantitative knowledge on the relationships between plume characteristics hinders efficient data analysis and application of the resulting parameterizations. We use a shock-tube apparatus for rapid decompression experiments to produce particle-laden jets. We have systematically and independently varied the water content (0–27 wt%) and the temperature (25–320 °C) of the particle-gas mixture. The addition of a few weight percent of water is sufficient to reduce the observed electrification by an order of magnitude. With increasing temperature, a larger number of smaller discharges are observed, with the overall amount of electrification staying similar. Changes in jet dynamics are proposed as the cause of the temperature-dependence, while multiple factors (including the higher conductivity of wet ash) can be seen responsible for the decreased electrification in wet experiments.
    Keywords: 550.724 ; volcanic lightning ; atmospheric electricity ; Faraday cage ; volcanic jets ; temperature ; water content
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  • 5
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    Evaporation Study Based on Micromodel Experiments: Comparison of Theory and Experiment (2021)
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    Publication Date: 2021-10-11
    Description: Abstract Evaporation—a key process for water exchange between soil and atmosphere—is controlled by internal water fluxes and surface vapor fluxes. Recent studies demonstrated that the dynamics of the water flow in corners determine the time behavior of the evaporation rate. The internal water flux of the porous media is often described by capillary flow assuming complete wetting. Particularly, the crucial influence of partial wetting, that is, the nonlinear contact angle dependency of the capillary flow has been neglected so far. The focus of the paper is to demonstrate that SiO2-surfaces can exhibit contact angles of about 40°. This reduces the internal capillary flow by 1 order of magnitude compared to complete wetting. First, we derived the contact angle by inverse modeling. We conducted a series of evaporation experiments in a 2-D square lattice microstructure connected by lognormal distributed throats. We used an explicit analytical power series solution of the single square capillary model. A contact angle of 38° ± 1° was derived. Second, we directly measured the contact angle of the Si-SiO2 wafer using the Drop Shape Analyzer Krüss 100 and obtained an averaged contact angle of 42° ± 2°. The results support the single square capillary model as an appropriate model for the description of the evaporation process in an ideal square capillary.
    Keywords: 550.724 ; 551.5 ; evaporation ; experiments
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  • 6
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    The Impact of Wettability and Surface Roughness on Fluid Displacement and Capillary Trapping in 2-D and 3-D Porous Media: 2. Combined Effect of Wettability, Surface Roughness, and Pore Space Structure on Trapping Efficiency in Sand Packs and Micromodels (2021)
    Details
    Publication Date: 2021-10-13
    Description: A comprehensive understanding of the combined effects of surface roughness and wettability on the dynamics of the trapping process is lacking. This can be primarily attributed to the contradictory experimental and numerical results regarding the impact of wettability on the capillary trapping efficiency. The discrepancy is presumably caused by the surface roughness of the inner pore-solid interface. Herein, we present a comparative μ-CT study of the static fluid-fluid pattern in porous media with smooth (glass beads) and rough surfaces (natural sands). For the first time, a global optimization method was applied to map the characteristic geometrical and morphological properties of natural sands to 2-D micromodels that exhibit different degrees of surface roughness. A realistic wetting model that describes the apparent contact angle of the rough surface as a function surface morphology and the intrinsic contact angle was also proposed. The dynamics of the trapping processes were studied via visualization micromodel experiments. Our results revealed that sand and glass beads displayed opposite trends in terms of the contact angle dependence between 5° and 115°. Sand depicted a nonmonotonous functional contact angle dependency, that is, a transition from maximal trapping to no trapping, followed by an increase to medium trapping. In contrast, glass beads showed a sharp transition from no trapping to maximal trapping. Since both porous media exhibit similar morphological properties (similar Minkowski functions: porosity, surface density, mean curvature density, Euler number density), we deduce that this difference in behavior is caused by the difference in surface roughness that allows complete wetting and hence precursor thick-film flow for natural sands. Experimental results on micromodels verified this hypothesis.
    Keywords: 550.724 ; impact of wettability on trapping efficiency ; impact of surface roughness and pore space structure on trapping efficiency ; porous media with rough surface ; natural sand and glass ceramic micromodels ; wettability-controlled crossover from snap-off to bypass trapping ; spontaneous precursor thick-film flow (Wenzel's argument)
    Language: English
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  • 7
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    Leaching of hexavalent chromium from young chromite ore processing residue (2021)
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    Publication Date: 2021-10-13
    Description: Chromite ore processing residue (COPR) is a waste derived from the chromate extraction from roasted ores and is deposited in some countries in landfills. The objective of this study was to investigate the leaching characteristics of hexavalent Cr [Cr(VI)] from two COPR samples obtained from unlined landfills in the Kanpur area of northern India. Column experiments were conducted under water-saturated conditions to simulate Cr release from the wastes caused by tropical heavy-rain events. Leached Cr(VI) decreased from 1,800 to 300 mg L−1 (Rania site) and 1,200 to 163 mg L−1 (Chhiwali site) during exchange of 12 pore volumes, which approximately corresponds to 2 yr of monsoon precipitation. Flow interruptions for 10, 100, and 1,000 h had little effect on Cr(VI) concentrations in the leachate, suggesting that Cr(VI) leaching was not limited by slow release kinetics. Calcium aluminum chromium oxide hydrates (CAC), and highly soluble phases such as Na2CrO4 may play a role in controlling Cr(VI) concentration in the leachates. The amount of Cr(VI) leached from the columns accounted for 16% of the total Cr(VI) present in both COPR samples. A decrease in the solid-phase Cr(VI)/Crtotal ratio along the column was identified by X-ray absorption near edge structure (XANES) spectroscopy. Consistently, the smallest Cr(VI)/Crtotal ratios were found in the lower column section closest to the inflow. Our results suggest that Cr(VI) leaching from the unlined COPR landfills will continue for centuries, highlighting the urgent need to remediate these dumpsites.
    Keywords: 577.275 ; 550.724 ; Northern India ; chromite ore processing residue ; leaching ; experiments
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  • 8
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    Transport and Retention of Sulfidized Silver Nanoparticles in Porous Media: The Role of Air-Water Interfaces, Flow Velocity, and Natural Organic Matter (2021)
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    Publication Date: 2021-10-13
    Description: The sulfidation and aging of silver nanoparticles (Ag-NPs) with natural organic matter (NOM) are major transformation processes along their pathway in wastewater treatment plants and surface waters. Although soils appear to be a sink for disposed Ag-NPs, the impact of variable saturation on the transport and retention behavior in porous media is still not fully understood. We studied the behavior of sulfidized silver nanoparticles (S-Ag-NPs, 1 mg L−1) in saturated and unsaturated sand columns regarding the effects of (i) the presence of NOM (5 mg L−1) in the aquatic phase on retention, transport, and remobilization of S-Ag-NPs and (ii) the distribution and quantity of air-water and solid-water interfaces for different flow velocities determined via X-ray microtomography (X-ray μCT). Unsaturated transport experiments were conducted under controlled conditions with unit gradients in water potential and constant water content along the flow direction for each applied flux. It was shown that (i) NOM in S-Ag-NP dispersion highly increased the NP-mobility; (ii) differences between saturated and unsaturated transport were increasing with decreasing flux and, consequently, decreasing water contents; (iii) both, solid-water and air-water interfaces were involved in retention of S-Ag-NPs aged by NOM. Using numerical model simulations and X-ray μCT of flow experiments, the breakthrough of Ag-NP could be explained by a disproportional increase in air-water interfaces and an increasing attachment efficiency with decreasing water content and flow velocity.
    Keywords: 577.275 ; 550.724 ; silver nanoparticles ; X-ray tomography ; phase distribution ; air-water interface ; natural organic matter ; transport
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  • 9
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    The Impact of Wettability and Surface Roughness on Fluid Displacement and Capillary Trapping in 2-D and 3-D Porous Media: 1. Wettability-Controlled Phase Transition of Trapping Efficiency in Glass Beads Packs (2021)
    Details
    Publication Date: 2021-10-13
    Description: Fluid invasion, displacement of one fluid by another in porous media, is important in a large number of industrial and natural processes. Of special interest is the trapping of gas and oil clusters. We study the impact of wettability on fluid pattern formation and capillary trapping in three-dimensional glass beads packs (dmean = 1 mm) during fluid invasion at capillary numbers of 10−7 using μ-CT. The invading fluid was water, and the defending fluid was air. The contact angle of the glass beads was altered between 5° and 115° using Piranha cleaning and silanization. We analyzed the front morphology of the invading fluid, the residual gas saturation, the fluid occupation frequency of pores, and the morphology and statistics of the trapped gas clusters. We found a sharp transition (crossover) at a critical contact angle θc = 96°. Below θc the morphology of the displacement front was flat and compact caused by the strong smoothing effect of cooperative filling. Above θc the morphology of the displacement front was fractal and ramified caused by single bursts (Haines jumps). Across this dynamical phase transition the trapping efficiency changes from no trapping to maximal trapping. For θ 〉 θc the experimental results show that invasion percolation governs the fluid displacement. Strong indicators are the universal scaling behavior of the size distribution of large clusters (relative data error εdata 〈 1%) and their linear surface-volume relationship (R2 = 0.99).
    Keywords: 550.724 ; percolation transition ; sharp transition (crossover) at a critical contact angle θc ; below θc, the displacement front was flat and compact ; above θc, the displacement front was fractal and ramified ; trapping efficiency changes from no trapping to maximal trapping ; trapped gas clusters show universal scaling law
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  • 10
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    Laboratory and field investigations on freeze and gravity core sampling and assessment of coring disturbances with implications on gas bubble characterization† (2021)
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    Publication Date: 2021-10-14
    Description: The quantification of greenhouse gas emissions from aquatic ecosystems requires knowledge about the spatial and temporal dynamics of free gas in sediments. Freezing the sediment in situ offers a promising method for obtaining gas-bearing sediment samples, unaffected by changes in hydrostatic pressure and sample temperature during core withdrawal and subsequent analysis. This article presents a novel freeze coring technique to preserve the in situ stratigraphy and gas bubble characteristics. Nondestructive X-ray computed tomography (CT) scans were used to identify and characterize coring disturbances of gravity and freeze cores associated with gassy sediment, as well as the effect of the freezing process on the gas bubble characteristics. Real-time X-ray CT scans were conducted to visualize the progression of the freezing process. Additional experiments were conducted to determine the freezing rate to assess the probability of sediment particle/bubble migration, and gas bubble nucleation at the phase transition of pore water to ice. The performance of the freeze coring technique was evaluated under field conditions in Olsberg and Urft Reservoir (Germany). The results demonstrate the capability of the freeze coring technique for the preservation of gas-bearing sediments and the analysis of gas bubble distribution pattern in both reservoirs. Nevertheless, the obtained cores showed that nearly all gravity and freeze cores show some degree of coring disturbances.
    Keywords: 550.724 ; gas-bearing sediments ; freeze coring technique
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  • 11
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    Ice Particle Properties Inferred From Aggregation Modelling (2021)
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    Publication Date: 2021-10-14
    Description: We generated a large number 105,000 of aggregates composed of various monomer types and sizes using an aggregation model. Combined with hydrodynamic theory, we derived ice particle properties such as mass, projected area, and terminal velocity as a function of monomer number and size. This particle ensemble allows us to study the relation of particle properties with a high level of detail which is often not provided by in situ measurements. The ice particle properties change rather smoothly with monomer number. We find very little differences in all particle properties between monomers and aggregates at sizes below 1 mm which is in contrast to many microphysics schemes. The impact of the monomer type on the particle properties decreases with increasing monomer number. Whether, for example, the terminal velocity of an aggregate is larger or smaller than an equal-size monomer depends mostly on the monomer type. We fitted commonly used power laws as well as Atlas-type relations, which represent the saturation of the terminal velocity at large sizes (terminal velocity asymptotically approaching a limiting value) to the data set and tested the impact of incorporating different levels of complexity with idealized simulations using a 1D Lagrangian super particle model. These simulations indicate that it is sufficient to represent the monomer number dependency of ice particle properties with only two categories (monomers and aggregates). The incorporation of the saturation velocity at larger sizes is found to be important to avoid an overestimation of self-aggregation of larger snowflakes.
    Keywords: 551.5 ; 550.724 ; agreggation modeling ; cloud microphysics ; ice particle properties ; Lagrangian modeling ; terminal velocity
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  • 12
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    Comment on “A New One-Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a Wide Range of Reynolds Number” by F. Dioguardi et al. (2021)
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    Publication Date: 2021-10-14
    Description: With this comment we want to clarify a number of aspects of the paper recently published by Dioguardi, Mele, and Dellino “A New One-Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a Wide Range of Reynolds Number” (hereafter referred to as DMD2018). In particular, we show that contrary to the conclusions of DMD2018, the model of Bagheri and Bonadonna (2016, https://doi.org/10.1016/j.powtec.2016.06.015), hereafter referred to as BB2016, is the best model in predicting the drag and terminal velocity of particles measured by DMD2018, as demonstrated here by comparison of estimation errors. The discrepancy is mainly due to a production error (misplaced parentheses) introduced in BB2016 during the publication process and partly due to the incorrect methodology used by DMD2018 to calculate particle terminal velocity. Here we present the correct sets of equations and methodology to show that typo-free model of BB2016 outperforms all existing drag models including the new model suggested by DMD2018.
    Keywords: 550.724 ; drag coefficient ; terminal velocity ; particle shape ; non-spherical ; irregular
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  • 13
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    Lithic artifact assemblage transport and microwear modification in a fluvial setting: A radio frequency identification tag experiment (2021)
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    Publication Date: 2021-10-14
    Description: River processes are widely assumed to have impacted the integrity of lithic assemblages when artifacts are found in fluvial sediments, but the specifics of these influences remain largely unknown. We conducted a real-world experiment to determine how the initial stages of fluvial entrainment affected lithic artifact assemblages. We inserted replica artifacts with radio frequency identification tags into a gravel-bedded river in Wales (UK) for seven months and related their transport distances to their morphology and the recorded streamflow. In addition, nine artifacts were recovered at the end of the experiment and analyzed for microwear traces. In sum, our results show that in a gravel-bedded river with a mean discharge of 5.1 m3/s, artifact length and width were the main variables influencing artifact transport distances. The experiment also resulted in characteristic microwear traces developing on the artifacts over distances of 485 m or less. These results emphasize the multifaceted nature of alluvial site formation processes in a repeatable experiment and highlight new ways to identify the transport of replica Paleolithic material.
    Keywords: 550.724 ; 551.35 ; experimental archaeology ; fluvial dynamics ; Paleolithic ; RFID ; taphonomy ; use-wear
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  • 14
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    Laboratory Study on Fluid-Induced Fault Slip Behavior: The Role of Fluid Pressurization Rate (2021)
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    Publication Date: 2021-10-06
    Description: Understanding the physical mechanisms governing fluid-induced fault slip is important for improved mitigation of seismic risks associated with large-scale fluid injection. We conducted fluid-induced fault slip experiments in the laboratory on critically stressed saw-cut sandstone samples with high permeability using different fluid pressurization rates. Our experimental results demonstrate that fault slip behavior is governed by fluid pressurization rate rather than injection pressure. Slow stick-slip episodes (peak slip velocity 〈 4 μm/s) are induced by fast fluid injection rate, whereas fault creep with slip velocity 〈 0.4 μm/s mainly occurs in response to slow fluid injection rate. Fluid-induced fault slip may remain mechanically stable for loading stiffness larger than fault stiffness. Independent of fault slip mode, we observed dynamic frictional weakening of the artificial fault at elevated pore pressure. Our observations highlight that varying fluid injection rates may assist in reducing potential seismic hazards of field-scale fluid injection projects.
    Keywords: 550.724 ; fault slip ; fluid injection ; induced seismicity ; fluid pressurization rate ; stick-slip ; fault creep
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  • 15
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    Controls on the lateral channel-migration rate of braided channel systems in coarse non-cohesive sediment (2021)
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    Publication Date: 2021-10-06
    Description: Lateral movements of alluvial river channels control the extent and reworking rates of alluvial fans, floodplains, deltas, and alluvial sections of bedrock rivers. These lateral movements can occur by gradual channel migration or by sudden changes in channel position (avulsions). Whereas models exist for rates of river avulsion, we lack a detailed understanding of the rates of lateral channel migration on the scale of a channel belt. In a two-step process, we develop here an expression for the lateral migration rate of braided channel systems in coarse, non-cohesive sediment. On the basis of photographic and topographic data from laboratory experiments of braided channels performed under constant external boundary conditions, we first explore the impact of autogenic variations of the channel-system geometry (i.e. channel-bank heights, water depths, channel-system width, and channel slope) on channel-migration rates. In agreement with theoretical expectations, we find that, under such constant boundary conditions, the laterally reworked volume of sediment is constant and lateral channel-migration rates scale inversely with the channel-bank height. Furthermore, when channel-bank heights are accounted for, lateral migration rates are independent of the remaining channel geometry parameters. These constraints allow us, in a second step, to derive two alternative expressions for lateral channel-migration rates under different boundary conditions using dimensional analysis. Fits of a compilation of laboratory experiments to these expressions suggest that, for a given channel bank-height, migration rates are strongly sensitive to water discharges and more weakly sensitive to sediment discharges. In addition, external perturbations, such as changes in sediment and water discharges or base level fall, can indirectly affect lateral channel-migration rates by modulating channel-bank heights. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley & Sons, Ltd. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley & Sons, Ltd.
    Keywords: 550.724 ; 551.35 ; braided alluvial rivers ; physical experiments ; channel migration
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  • 16
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    Velocity Field Estimation on Density-Driven Solute Transport With a Convolutional Neural Network (2021)
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    Publication Date: 2021-10-06
    Description: Recent advances in machine learning open new opportunities to gain deeper insight into hydrological systems, where some relevant system quantities remain difficult to measure. We use deep learning methods trained on numerical simulations of the physical processes to explore the possibilities of closing the information gap of missing system quantities. As an illustrative example we study the estimation of velocity fields in numerical and laboratory experiments of density-driven solute transport. Using high-resolution observations of the solute concentration distribution, we demonstrate the capability of the method to structurally incorporate the representation of the physical processes. Velocity field estimation for synthetic data for both variable and uniform concentration boundary conditions showed equal results. This capability is remarkable because only the latter was employed for training the network. Applying the method to measured concentration distributions of density-driven solute transport in a Hele-Shaw cell makes the velocity field assessable in the experiment. This assessability of the velocity field even holds for regions with negligible solute concentration between the density fingers, where the velocity field is otherwise inaccessible.
    Keywords: 550.724 ; Hele-Shaw cell experiment ; density-driven active solute transport ; convolutional neural network ; velocity field estimation
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  • 17
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    Efficiency and Accuracy of Micro-Macro Models for Mineral Dissolution (2021)
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    Publication Date: 2021-12-03
    Description: Micro-macro models for dissolution processes are derived from detailed pore-scale models applying upscaling techniques. They consist of flow and transport equations at the scale of the porous medium (macroscale). Both include averaged time- and space-dependent coefficient functions (permeability, porosity, reactive surface, and effective diffusion). These are in turn explicitly computed from the time- and space-dependent geometry of unit cells and by means of auxiliary cell problems defined therein (microscale). The explicit geometric structure is characterized by a level set. For its evolution, information from the transport equations solutions is taken into account (micro-macro scales). A numerical scheme is introduced, which is capable of evaluating such complex settings. For the level-set equation a second-order scheme is applied, which enables us to accurately determine the dynamic reactive surface. Local mesh refinement methods are applied to evaluate Stokes type cell problems using P2/P1 elements and a Uzawa type linear solver. Applications of our permeability solver to scenarios involving static and evolving geometries are presented. Furthermore, macroscopic flow and transport equations are solved applying mixed finite elements. Finally, adaptive strategies to overcome the computational burden are discussed. We apply our approach to the dissolution of an array of dolomite grains in the micro-macro context and validate our numerical scheme.
    Keywords: 551.49 ; 550.724 ; porous media ; reactive flow ; dissolution processes ; modeling
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  • 18
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    Carbon release and transformation from coastal peat deposits controlled by submarine groundwater discharge: a column experiment study (2021)
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    Publication Date: 2021-12-06
    Description: Abstract Although the majority of coastal sediments consist of sandy material, in some areas marine ingression caused the submergence of terrestrial carbon-rich peat soils. This affects the coastal carbon balance, as peat represents a potential carbon source. We performed a column experiment to better understand the coupled flow and biogeochemical processes governing carbon transformations in submerged peat under coastal fresh groundwater (GW) discharge and brackish water intrusion. The columns contained naturally layered sediments with and without peat (organic carbon content in peat 39 ± 14 wt%), alternately supplied with oxygen-rich brackish water from above and oxygen-poor, low-saline GW from below. The low-saline GW discharge through the peat significantly increased the release and ascent of dissolved organic carbon (DOC) from the peat (δ13CDOC − 26.9‰ to − 27.7‰), which was accompanied by the production of dissolved inorganic carbon (DIC) and emission of carbon dioxide (CO2), implying DOC mineralization. Oxygen respiration, sulfate (SO42−) reduction, and methane (CH4) formation were differently pronounced in the sediments and were accompanied with higher microbial abundances in peat compared to sand with SO42−-reducing bacteria clearly dominating methanogens. With decreasing salinity and SO42− concentrations, CH4 emission rates increased from 16.5 to 77.3 μmol m−2 d−1 during a 14-day, low-saline GW discharge phase. In contrast, oxygenated brackish water intrusion resulted in lower DOC and DIC pore water concentrations and significantly lower CH4 and CO2 emissions. Our study illustrates the strong dependence of carbon cycling in shallow coastal areas with submerged peat deposits on the flow and mixing dynamics within the subterranean estuary.
    Keywords: 550.724 ; coastal peatlands ; coastal peatlands ; biogeochemical processes ; carbon release ; column experiments
    Language: English
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