scholarly journals A three-dimensional reactive transport model for sediments, incorporating microniches

2008 ◽  
Vol 5 (3) ◽  
pp. 218 ◽  
Author(s):  
Łukasz Sochaczewski ◽  
Anthony Stockdale ◽  
William Davison ◽  
Wlodek Tych ◽  
Hao Zhang
Keyword(s):  
Reactive Transport ◽  
Manganese Oxides ◽  
Transport Model ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Sediment Surface ◽  
Concentration Gradients ◽  
Reactive Iron ◽  
Context Modelling ◽  
D Model

Environmental context. Modelling of discrete sites of diagenesis in sediments (microniches) has typically been performed in 1-D and has involved a limited set of components. Here we present a new 3-D model for microniches within a traditional vertical sequence of redox reactions, and show example modelled niches of a range of sizes, close to the sediment–water interface. Microniche processes may have implications for understanding trace metal diagenesis, via formation of sulfides. The model provides a quantitative framework for examining microniche data and concepts. Abstract. Most reactive transport models have represented sediments as one-dimensional (1-D) systems and have solely considered the development of vertical concentration gradients. However, application of recently developed microscale and 2-D measurement techniques have demonstrated more complicated solute structures in some sediments, including discrete localised sites of depleted oxygen, and elevated trace metals and sulfide, referred to as microniches. A model of transport and reaction in sediments that can simulate the dynamic development of concentration gradients occurring in 3-D was developed. Its graphical user interface allows easy input of user-specified reactions and provides flexible schemes that prioritise their execution. The 3-D capability was demonstrated by quantitative modelling of hypothetical solute behaviour at organic matter microniches covering a range of sizes. Significant effects of microniches on the profiles of oxygen and nitrate are demonstrated. Sulfide is shown to be readily generated in microniches within 1 cm of the sediment surface, provided the diameter of the reactive organic material is greater than 1 mm. These modelling results illustrate the geochemical complexities that arise when processes occur in 3-D and demonstrate the need for such a model. Future use of high-resolution measurement techniques should include the collection of data for relevant major components, such as reactive iron and manganese oxides, to allow full, multicomponent modelling of microniche processes.

scholarly journals CHROTRAN 1.0: A mathematical and computational model for in situ heavy metal remediation in heterogeneous aquifers

2017 ◽  
Author(s):  
Scott K. Hansen ◽  
Sachin Pandey ◽  
Satish Karra ◽  
Velimir V. Vesselinov
Keyword(s):  
Heavy Metal ◽  
Reactive Transport ◽  
Transport Model ◽  
Three Dimensional ◽  
Chemical Species ◽  
Heterogeneous Aquifers ◽  
Heavy Metal Remediation ◽  
Full Coupling ◽  
Abiotic Reduction

Abstract. Groundwater contamination by heavy metals is a critical environmental problem for which in situ remediation is frequently the only viable treatment option. For such interventions, a three-dimensional reactive transport model of relevant biogeochemical processes is invaluable. To this end, we developed a model, CHROTRAN, for in situ treatment, which includes full dynamics for five species: a heavy metal to be remediated, an electron donor, biomass, a nontoxic conservative bio-inhibitor, and a biocide. Direct abiotic reduction by donor-metal interaction as well as donor-driven biomass growth and bio-reduction are modeled, along with crucial processes such as donor sorption, bio-fouling and biomass death. Our software implementation handles heterogeneous flow fields, arbitrarily many chemical species and amendment injection points, and features full coupling between flow and reactive transport. We describe installation and usage and present two example simulations demonstrating its unique capabilities. One simulation suggests an unorthodox approach to remediation of Cr(VI) contamination.

A 1-D model to explore the effects of tissue loading and tissue concentration gradients in the revised Starling principle

2006 ◽  
Vol 291 (6) ◽  
pp. H2950-H2964 ◽  
Author(s):  
Xiaobing Zhang ◽  
Roger H. Adamson ◽  
Fitz-Roy E. Curry ◽  
Sheldon Weinbaum
Keyword(s):  
Tight Junction ◽  
Tissue Concentration ◽  
Three Dimensional ◽  
Force Balance ◽  
Endothelial Glycocalyx ◽  
Surrounding Tissue ◽  
Concentration Gradients ◽  
Rat Mesentery ◽  
The Matrix ◽  
D Model

The recent experiments in Hu et al. ( Am J Physiol Heart Circ Physiol 279: H1724–H1736, 2000) and Adamson et al. ( J Physiol 557: 889–907, 2004) in frog and rat mesentery microvessels have provided strong evidence supporting the Michel-Weinbaum hypothesis for a revised asymmetric Starling principle in which the Starling force balance is applied locally across the endothelial glycocalyx layer rather than between lumen and tissue. These experiments were interpreted by a three-dimensional (3-D) mathematical model (Hu et al.; Microvasc Res 58: 281–304, 1999) to describe the coupled water and albumin fluxes in the glycocalyx layer, the cleft with its tight junction strand, and the surrounding tissue. This numerical 3-D model converges if the tissue is at uniform concentration or has significant tissue gradients due to tissue loading. However, for most physiological conditions, tissue gradients are two to three orders of magnitude smaller than the albumin gradients in the cleft, and the numerical model does not converge. A simpler multilayer one-dimensional (1-D) analytical model has been developed to describe these conditions. This model is used to extend Michel and Phillips’s original 1-D analysis of the matrix layer ( J Physiol 388: 421–435, 1987) to include a cleft with a tight junction strand, to explain the observation of Levick ( Exp Physiol 76: 825–857, 1991) that most tissues have an equilibrium tissue concentration that is close to 0.4 lumen concentration, and to explore the role of vesicular transport in achieving this equilibrium. The model predicts the surprising finding that one can have steady-state reabsorption at low pressures, in contrast to the experiments in Michel and Phillips, if a backward-standing gradient is established in the cleft that prevents the concentration from rising behind the glycocalyx.

scholarly journals Middle atmospheric changes caused by the January and March 2012 solar proton events

2014 ◽  
Vol 14 (2) ◽  
pp. 1025-1038 ◽  
Author(s):  
C. H. Jackman ◽  
C. E. Randall ◽  
V. L. Harvey ◽  
S. Wang ◽  
E. L. Fleming ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Middle Atmosphere ◽  
Transport Model ◽  
Michelson Interferometer ◽  
Three Dimensional ◽  
Peroxy Radical ◽  
Solar Proton ◽  
Proton Event ◽  
Neutral Atmosphere ◽  
D Model

Abstract. The recent 23–30 January and 7–11 March 2012 solar proton event (SPE) periods were substantial and caused significant impacts on the middle atmosphere. These were the two largest SPE periods of solar cycle 24 so far. The highly energetic solar protons produced considerable ionization of the neutral atmosphere as well as HOx (H, OH, HO2) and NOx (N, NO, NO2). We compute a NOx production of 1.9 and 2.1 Gigamoles due to these SPE periods in January and March 2012, respectively, which places these SPE periods among the 12 largest in the past 50 yr. Aura Microwave Limb Sounder (MLS) observations of the peroxy radical, HO2, show significant enhancements of > 0.9 ppbv in the northern polar mesosphere as a result of these SPE periods. Both MLS measurements and Goddard Space Flight Center (GSFC) two-dimensional (2-D) model predictions indicated middle mesospheric ozone decreases of > 20% for several days in the northern polar region with maximum depletions > 60% over 1–2 days as a result of the HOx produced in both the January and March 2012 SPE periods. The SCISAT-1 Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE) and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instruments measured NO and NO2 (~ NOx), which indicated enhancements of over 20 ppbv in most of the northern polar mesosphere for several days as a result of these SPE periods. The GSFC 2-D model and the Global Modeling Initiative three-dimensional chemistry and transport model were used to predict the medium-term (~ months) influence and showed that the polar middle atmospheric ozone was most affected by these solar events in the Southern Hemisphere due to the increased downward motion in the fall and early winter. The downward transport moved the SPE-produced NOy to lower altitudes and led to predicted modest destruction of ozone (5–13%) in the upper stratosphere days to weeks after the March 2012 event. Polar total ozone reductions were predicted to be a maximum of 1.5% in 2012 due to these SPEs.

scholarly journals Present nitrogen and carbon dynamics in the Scheldt estuary using a novel 1-D model

2008 ◽  
Vol 5 (4) ◽  
pp. 981-1006 ◽  
Author(s):  
A. F. Hofmann ◽  
K. Soetaert ◽  
J. J. Middelburg
Keyword(s):  
Reactive Transport ◽  
Water Exchange ◽  
Transport Model ◽  
Scheldt Estuary ◽  
Dispersive Transport ◽  
Comparable Amount ◽  
Carbon And Nitrogen ◽  
Reactive Transport Model ◽  
Model Features ◽  
D Model

Abstract. A 1-D, pelagic, reactive-transport model of a completely mixed, turbid, heterotrophic estuary – the Scheldt estuary – is presented. The model resolves major carbon and nitrogen species and oxygen, as well as pH. The model features two organic matter degradation pathways, oxic mineralisation and denitrification, and includes primary production as well as nitrification. Apart from advective-dispersive transport along the length axis, the model also describes O2, CO2, and N2 air-water exchange. The aim of this study is to present a model which is as simple as possible but still fits the data well enough to determine the fate and turnover of nutrients entering the estuary and their spatial patterns in the years 2000 to 2004. Nitrification is identified as one of the most important processes in the estuary, consuming a comparable amount of oxygen as oxic mineralisation (1.7 Gmol O2 y−1 vs. 2.7 Gmol O2 y−1). About 10% of the 2.5 Gmol of nitrogen entering the estuary per year is lost within the estuary due to denitrification. Nitrogen and carbon budgets are compared to budgets from the seventies and eighties, showing that nitrification activity has peaked in the eighties, while denitrification steadily declined. Our model estimates an average CO2 emission of 3.3 Gmol y−1 in the years 2001 to 2004, which is a comparatively low estimate in the context of previous estimates of CO2 export from the Scheldt estuary.

scholarly journals Characterizing Reactive Transport Behavior in a Three-Dimensional Discrete Fracture Network

2021 ◽  
Author(s):  
Thomas Sherman ◽  
Guillem Sole-Mari ◽  
Jeffrey Hyman ◽  
Matthew R. Sweeney ◽  
Daniel Vassallo ◽  
...  
Keyword(s):  
Reactive Transport ◽  
Three Dimensional ◽  
Fracture Network ◽  
Discrete Fracture Network ◽  
Transport Behavior ◽  
Discrete Fracture

Modelling uranium leaching from agricultural soils to groundwater as a criterion for comparison with complementary safety indicators

2006 ◽  
Vol 932 ◽  
Author(s):  
D. Jacques ◽  
J. Šimůnek ◽  
D. Mallants ◽  
M.Th. van Genuchten
Keyword(s):  
Soil Profile ◽  
Reactive Transport ◽  
Transport Model ◽  
Agricultural Soils ◽  
Solid Phase ◽  
Water Flux ◽  
Fertilizer Application ◽  
Mineral Fertilizers ◽  
Deep Soil ◽  
Long Time

ABSTRACTNaturally occurring radionuclides can also end up in soils and groundwater due to human practices, such as application of certain fertilizers in agriculture. Many mineral fertilizers, particularly (super)phosphates, contain small amounts of 238U and 230Th which eventually may be leached from agricultural soils to underlying water resources. Field soils that receive P-fertilizers accumulate U and Th and their daughter nuclides, which eventually may leach to groundwater. Our objective was to numerically assess U migration in soils. Calculations were based on a new reactive transport model, HP1, which accounts for interactions between U and organic matter, phosphate, and carbonate. Solid phase interactions were simulated using a surface complexation module. Furthermore, all geochemical processes were coupled with a model accounting for dynamic changes in the soil water content and the water flux. The capabilities of the code in calculating natural U fluxes to groundwater were illustrated using a semi-synthetic 200-year long time series of climatological data for Belgium. Based on an average fertilizer application, the input of phosphate and uranium in the soil was defined. This paper discusses calculated U distributions in the soil profile as well as calculated U fluxes leached from a 100-cm deep soil profile. The calculated long-term leaching rates originating from fertilization are significantly higher after 200 years than estimated release rates from lowlevel nuclear waste repositories.

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