scholarly journals Modeling the impact of soil aggregate size on selenium immobilization

2012 ◽  
Vol 9 (9) ◽  
pp. 12047-12086 ◽  
Author(s):  
M. F. Kausch ◽  
C. E. Pallud
Keyword(s):  
Reactive Transport ◽  
Temporal Dynamics ◽  
Transport Model ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Drainage Water ◽  
Rate Equations ◽  
Advective Transport ◽  
The Impact

Abstract. Soil aggregates are mm- to cm-sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-aggregate micropores. This can lead to mass transfer limitations and the formation of aggregate-scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil aggregates are thought to promote this process in otherwise well aerated soils. To evaluate the impact of soil aggregate size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se-species. The spatial and temporal dynamics of the model were validated with data from experiments and predictive simulations were performed covering aggregate sizes between 1 and 2.5 cm diameter. Simulations predict that selenium retention scales with aggregate size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5-cm-aggregates compared to 1-cm-aggregates. Under oxic conditions, aggregate size and pyruvate-concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.

scholarly journals Modeling the impact of soil aggregate size on selenium immobilization

2013 ◽  
Vol 10 (3) ◽  
pp. 1323-1336 ◽  
Author(s):  
M. F. Kausch ◽  
C. E. Pallud
Keyword(s):  
Reactive Transport ◽  
Temporal Dynamics ◽  
Transport Model ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Drainage Water ◽  
Rate Equations ◽  
Advective Transport ◽  
The Impact

Abstract. Soil aggregates are mm- to cm-sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-aggregate micropores. This can lead to mass transfer limitations and the formation of aggregate scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil aggregates are thought to promote this process in otherwise well-aerated soils. To evaluate the impact of soil aggregate size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se species. The spatial and temporal dynamics of the model were validated with data from experiments, and predictive simulations were performed covering aggregate sizes 1–2.5 cm in diameter. Simulations predict that selenium retention scales with aggregate size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5 cm aggregates compared to 1 cm aggregates. Under oxic conditions, aggregate size and pyruvate concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.

Stabilization of Soil Aggregates in Relation to Soil Redistribution by Intensive Tillage on a Steep Hillslope

2014 ◽  
Vol 955-959 ◽  
pp. 3566-3571 ◽  
Author(s):  
Yong Wang ◽  
Zhuang Xiong ◽  
Wu Xian Yan ◽  
Yue Qun Qiu
Keyword(s):  
Soil Aggregates ◽  
Geometric Mean ◽  
Aggregate Stability ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Soil Aggregate Stability ◽  
Mean Weight Diameter ◽  
Tillage Operation ◽  
Sloping Land ◽  
The Impact

The objective of this study was to investigate soil aggregate stability within landscape on hillslopes by intensive tillage. Traditional tillage by consecutive hoeing was performed 5 and 20 times on steeply sloping land of the Sichuan Basin, China, by using the methods of simulated tillage to analyze the impact of long-term tillage on soil aggregates at different slope positions. The dry-sieved method was used to determine distribution of aggregate size in the different landscape positions, and mean weight diameter (MWD) and geometric mean diameter (GMD) as indices of soil aggregate stability. The different times of tillage resulted in different soil aggregate distributions. The results showed that the MWD and GMD values of aggregates were significantly decreased (p< 0.05) after 20-tillage operation, compared with pre-tillage operation. The differences in distributions of MWD and GMD demonstrate that the choice of the tillage times can be an important factor in changing soil aggregate stability and productivity in steeply sloping fields.

Aggregate size distribution and stability of an oxisol under legume-based and pure grass pastures in the eastern Colombian savannas

Soil Research ◽  
1995 ◽  
Vol 33 (1) ◽  
pp. 153 ◽  
Author(s):  
AJ Gijsman ◽  
RJ Thomas
Keyword(s):  
Size Distribution ◽  
Soil Aggregates ◽  
Aggregate Stability ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Hot Water ◽  
Aggregate Size Distribution ◽  
Carbohydrate Concentration ◽  
Stability Measurement ◽  
Water Extractable

This study evaluated soil aggregate size distribution and stability of an Oxisol under improved grass-only or grass-legume pastures, established in previously native savanna. Three grass-legume combinations were included at various stocking rates. In all treatments and soil layers, soils were well aggregated, having more than 90% of their weight in macroaggregates (>250 �m). The addition of legumes to pastures did not affect the soil aggregate size distribution, although aggregates showed somewhat more stability against slaking. An increase in stocking rate negatively affected both average aggregate size and aggregate stability. Aggregates showed little or no dispersion of clay particles in any treatment. A positive correlation was found between wet aggregate stability and hot-water extractable carbohydrate concentration, supporting the hypothesis that these carbohydrates equate with plant-derived or microbial polysaccharides which glue soil aggregates together. It is suggested that determination of hot-water extractable carbohydrates may serve as a useful indicator of small differences in aggregate stability, even when these differences are not evident in the stability measurement itself.

Investigation of Underground Bio-Methanation Using Bio-Reactive Transport Modeling

2021 ◽  
Author(s):  
Denis Sergeevich Nikolaev ◽  
Nazika Moeininia ◽  
Holger Ott ◽  
Hagen Bueltemeier
Keyword(s):  
Carbon Dioxide ◽  
Reactive Transport ◽  
Transport Model ◽  
Porous Media Flow ◽  
Potential Candidate ◽  
Field Scale ◽  
Reactive Transport Model ◽  
Demand Fluctuations ◽  
Gas Fields ◽  
The Impact

Abstract Underground bio-methanation is a promising technology for large-scale renewable energy storage. Additionally, it enables the recycling of CO2 via the generation of "renewable methane" in porous reservoirs using in-situ microbes as bio-catalysts. Potential candidate reservoirs are depleted gas fields or even abandoned gas storages, providing enormous storage capacity to balance seasonal energy supply and demand fluctuations. This paper discusses the underlying bio-methanation process as part of the ongoing research project "Bio-UGS – Biological conversion of carbon dioxide and hydrogen to methane," funded by the German Federal Ministry of Education and Research (BMBF). First, the hydrodynamic processes are assessed, and a review of the related microbial processes is provided. Then, based on exemplary field-scale simulations, the bio-reactive transport process and its consequences for operation are evaluated. The hydrogen conversion process was investigated by numerical simulations on field scale. For this, a two-phase multi-component bio-reactive transport model was implemented by (Hagemann 2018) in the open-source DuMux (Flemisch et al. 2011) simulation toolkit for porous media flow. The underlying processes include the transport of reactants and products, consumption of specific components, and the related growth and decay of the microbial population, resulting in a bio-reactive transport model. The microbial kinetic parameters of methanogenic reactions are taken from the available literature. The simulation study covers different scenarios on conceptional field-scale models, studying the impact of well placement, injection rates, and gas compositions. Due to a significant sensitivity of the simulation results to the bio-conversion kinetics, the field-specific conversion rates must be obtained. Thus, the Bio-UGS project is accompanied by laboratory experiments out of the frame of this paper. Other parameters are rather a matter of design; in the present case of depleted gas fields, those parameters are coupled and can be chosen to convert fully hydrogen and carbon dioxide to methane. Especially the well spacing can be considered the main design parameter in the likely case of a given injection rate and gas composition. This study extends the application of the previously developed code from a homogeneous-2D to the heterogeneous-3D case. The simulations mimic the co-injection of carbon dioxide and hydrogen from a 40 MW electrolysis.

Multicomponent multiphase reactive fluid flow in viscoelastoplastic porous media: localization patterns of fluid flow and strain

2021 ◽  
Author(s):  
Lyudmila Khakimova ◽  
Nikolai Belov ◽  
Artyom Myasnikov ◽  
Anatoly Vershinin ◽  
Kirill Krapivin ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Reactive Transport ◽  
Transport Model ◽  
Shear Bands ◽  
Porous Matrix ◽  
Deformation Localization ◽  
Linear Free Energy ◽  
Constrained Minimization Problem ◽  
Spectral Finite Elements ◽  
The Impact

&lt;p&gt;This work is devoted to developing the self-consistent thermo-hydro-chemo-mechanical reactive transport model to predict and describe natural and industrial petroleum processes at different scales.&lt;/p&gt;&lt;p&gt;We develop a version of the front tracking approach for multicomponent multiphase flow in order to treat spontaneous splitting of discontinuities. We revisit the solution for the Riemann problem and systematically classify all possible configurations as functions of initial concentrations on both sides of the discontinuity. We validate the algorithm against finite volume high-resolution technics and high-order spectral finite elements.&lt;/p&gt;&lt;p&gt;To calculate the parameters of phase equilibria, we utilize an approach based on the direct minimization of the Gibbs energy of a multicomponent mixture. This method ensures the consistency of the thermodynamic lookup tables. The core of the algorithm is the non-linear free-energy constrained minimization problem, formulated in the form of a linear programming problem by discretization in compositional space.&lt;/p&gt;&lt;p&gt;The impact of the complex rheological response of porous matrix on the morphology of fluid flow and shear deformation localization is considered. Channeling of porosity waves and shear bands morphology and their orientation is investigated for viscoelastoplastic both shear and bulk rheologies.&lt;/p&gt;

scholarly journals Factors Determining Soil Water Repellency in Two Coniferous Plantations on a Hillslope

Forests ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 730 ◽  
Author(s):  
Moein Farahnak ◽  
Keiji Mitsuyasu ◽  
Kyoichi Otsuki ◽  
Kuniyoshi Shimizu ◽  
Atsushi Kume
Keyword(s):  
Soil Water ◽  
Overland Flow ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Water Repellency ◽  
Soil Aggregate ◽  
Water Infiltration ◽  
Soil Water Repellency ◽  
Tree Cutting ◽  
Coniferous Plantations

Soil water repellency (SWR) is a cause of low water infiltration, overland flow and soil erosion in mountainous coniferous plantations in Japan. The factors determining SWR intensity were investigated in two coniferous plantations of Chamaecyparis obtusa (Siebold et Zucc.) Endl. and Cryptomeria japonica (L.f.) D. Don, using intact tree plots and cut tree plots on the same hillslope. The SWR of Ch. obtusa plots was stronger than that of Cr. japonica plots. SWR intensity decreased after tree cutting. There were no significant differences in SWR upslope and downslope of individual trees/stumps for both tree species, though areas downslope of individual Ch. obtusa trees had higher SWR intensity than those upslope. SWR intensity and soil aggregate stability were positively correlated in the Ch. obtusa intact tree plot (r = 0.88, p < 0.01), whereas in the cut tree plot, this correlation was weak with no significance (r = 0.29, p = 0.41). Soil aggregate size had a non-significant influence on SWR intensity. These findings suggest that SWR intensity was not related to the soil aggregate size, but SWR intensity seemed have a role in soil aggregation in the Ch. obtusa intact tree plot. Destruction of soil aggregates could occur after tree cutting because of physical disturbances or increased input of different types of organic matter from other vegetation into soil. The presence of Ch. obtusa introduces a source of SWR, although uncertainty remains about how water repellency is distributed around soil aggregates. The distribution pattern of soil water content and soil hydraulic conductivity around Cr. japonica was related to other factors such as the litter layer and non-water-repellant soil.

scholarly journals THE EFFECT OF SOILAGGREGATE SIZE AND P DOSAGE ON AMF SPORES NUMBER IN SHORGUM (Sorghum bicolor L.)

2018 ◽  
Vol 4 (1) ◽  
pp. 20
Author(s):  
Samsu Samsu ◽  
Henry N Barus ◽  
Uswah Hasanah
Keyword(s):  
Agricultural Land ◽  
Soil Aggregates ◽  
Block Design ◽  
Aggregate Size ◽  
Arbuscular Mycorrhizal ◽  
Dry Weight ◽  
Soil Aggregate ◽  
Experimental Unit ◽  
Randomized Block Design ◽  
Infected Root

Mycorrhiza is a biological agent to help fertility of soil and plants. Application of mycorrhiza on the land in the form of inoculum is often used in agricultural land in the name of quality of inoculum that also influenced by the content of existing spores. One of them is growing medium. This study aimed to study the effect of soil aggregate size and P dosage on the number of mycorrhizal spores in sorghum plants. The research design used was Randomized Block Design consisting of 2 factors. First factor was soil aggregate size(μm) which consisted of 4 treatments: U1 = < 2000, U2 = 500 - 1000, U3 = 200 - 500, U4 = < 200, and second factor was P dosage: 100 mg/kg and 300mg/kg. Each treatment combination was repeated 3 times so that there were 24 units of experimental unit. Observation parameters included the percentage of the infected root, number of spores, plant height and dry weight of the plant. The research was conducted in Greenhouse and Agronomy Laboratory of Agricultural Faculty of Tadulako University Palu. The various sizes of soil aggregates do not affect the amount of arbuscular mycorrhizal spores in sorghum plants. P 100 mg/kg or f P 300 mg/kg dosage used do not address the effect of the mycorrhizal spores. There is no interaction between soil aggregate size and P dosage to the amount of mycorrhizal spores in sorghum plants.

Soil aggregate size affects C sequestration and microorganisms inside aggregate under straw addition

2020 ◽  
Author(s):  
Jinjing Lu ◽  
Sheng ping Li ◽  
Xueping Wu ◽  
Aurore Degre
Keyword(s):  
Large Scale ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
C Sequestration ◽  
Soil Aggregate ◽  
Basic Unit ◽  
Size Fractions ◽  
Soil Microbial ◽  
Relationship Of ◽  
The Relationship

&lt;p&gt;As the basic unit of soil, aggregates are considered as a stable soil organic ( SOC ) pool. Changes in organic subtract due to straw addition induce variations in soil microbial community or activity, which may effect the C sequestration in aggregates. Most of the previous studies on soil microorganisms assessment was done at large scale i.e. larger quantities of soil, however, few studies on SOC is known in aggregate size fractions. This study investigated the effects of soil aggregate size on the distribution of microorganism and SOC, and the relationship of microorganism and C sequestration inside aggregate size fractions with &lt;sup&gt;13&lt;/sup&gt;C-labelled straw addition. Soil samples were collected from 0-15 cm and classified into 5 aggregates sizes classes ( &amp;#65310;5 mm, 2-5 mm, 1-2 mm, 0.25-1 mm and &amp;#65308;0.25 mm ), and the graded aggregates were incubated for 180 days at 20&amp;#160;&amp;#176;C, with or without&amp;#160;&lt;sup&gt;13&lt;/sup&gt;C-labelled straw residue. The incorporation of &lt;sup&gt;13&lt;/sup&gt;C into the five aggregate size fractions was analyzed.&lt;/p&gt;&lt;p&gt;After incubation, the SOC, DOC and ROC contents were increased more rapidly and significantly in aggregate ( &amp;#65310;5 mm ) than that in aggregate ( &amp;#65308;5 mm ) under straw addition, with the same trend of new carbon derived from straw. The total PLFAs was increased most significantly in aggregate ( &amp;#65310;5 mm ), especially fungi and negative bacteria ( G- ), while the positive bacteria ( G+ ) increased slightly in aggregate ( &amp;#65308;0.25 mm ), with no significant change in total PLFAs. The proportion of bacteria in total microorganism increased gradually, as the aggregate size increased in straw treatment. The results imply that aggregate ( &amp;#65310;5 mm ) have more space for C sequestration and greater contribution to new carbon turnovering in soil than other small aggregates, and it gradually tended to be bacterial with the enrichment of carbon. In addition, the SOC contents were strongly related to the amount of fungi and G- in aggregate ( &amp;#65308;5 mm ), while related to G+ in aggregate ( &amp;#65308;0.25 mm ) under straw addition.&lt;/p&gt;

scholarly journals Impact of Cover Crop Monocultures and Mixtures on Organic Carbon Contents of Soil Aggregates

Soil Systems ◽  
2021 ◽  
Vol 5 (3) ◽  
pp. 43
Author(s):  
Daphne Topps ◽  
Md Imam ul Khabir ◽  
Hagir Abdelmagid ◽  
Todd Jackson ◽  
Javed Iqbal ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Cover Crop ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Control Treatment ◽  
Hairy Vetch ◽  
Vicia Villosa ◽  
Size Classes ◽  
Oilseed Radish

Cover crops are considered an integral component of agroecosystems because of their positive impacts on biotic and abiotic indicators of soil health. At present, we know little about the impact of cover crop types and diversity on the organic carbon (OC) contents of different soil aggregate-size classes. In this study, we investigated the effect of cover plant diversity on OC contents of different soil aggregates, such as macro- (<2000–500 μm), meso- (<500–250 μm), and micro-aggregates (<250 μm). Our experiment included a total of 12 experimental treatments in triplicate; six different monoculture treatments such as chickling vetch (Vicia villosa), crimson clover (Trifolium incarnatum), hairy vetch (Vicia villosa), field peas (Pisum sativum), oilseed radish (Raphanus sativus), and mighty mustard (Brassica juncea), and their three- and six-species mixture treatments, including one unplanted control treatment. We performed this experiment usingdeep pots that contained soil collected from a corn-soybean rotation field. At vegetative maturity of cover plants (about 70 days), we took soil samples, and the soil aggregate-size classes were separated by the dry sieving. We hypothesized that cover crop type and diversity will improve OC contents of different soil aggregate-size classes. We found that cover plant species richness weakly positively increased OC contents of soil macro-aggregates (p = 0.056), whereas other aggregate-size classes did not respond to cover crop diversity gradient. Similarly, the OC contents of macroaggregates varied significantly (p = 0.013) under cover crop treatments, though neither monoculture nor mixture treatments showed significantly higher OC contents than the control treatment in this short-term experiment. Interestingly, the inclusion of hairy vetch and oilseed radish increased and decreased the OC contents of macro- and micro-aggregates, respectively. Moreover, we found a positive correlation between shoot biomass and OC contents of macroaggregates. Overall, our results suggest that species-rich rather than -poor communities may improve OC contents of soil macroaggregates, which constitute a major portion of soil systems, and are also considered as important indicators of soil functions.

scholarly journals Reactive transport model of kinetically controlled celestite to barite replacement

2021 ◽  
Vol 56 ◽  
pp. 57-65
Author(s):  
Morgan Tranter ◽  
Maria Wetzel ◽  
Marco De Lucia ◽  
Michael Kühn
Keyword(s):  
Reactive Transport ◽  
Oil And Gas ◽  
Prediction Models ◽  
Transport Model ◽  
Solid Phase ◽  
A Priori ◽  
Dissolution Kinetics ◽  
Input Concentration ◽  
Geochemical Model ◽  
The Impact

Abstract. Barite formation is of concern for many utilisations of the geological subsurface, ranging from oil and gas extraction to geothermal reservoirs. It also acts as a scavenger mineral for the retention of radium within nuclear waste repositories. The impact of its precipitation on flow properties has been shown to vary by many orders of magnitude, emphasising the need for robust prediction models. An experimental flow-through column setup on the laboratory scale investigating the replacement of celestite (SrSO4) with barite (BaSO4) for various input barium concentrations was taken as a basis for modelling. We provide here a comprehensive, geochemical modelling approach to simulate the experiments. Celestite dissolution kinetics, as well as subsequent barite nucleation and crystal growth were identified as the most relevant reactive processes, which were included explicitly in the coupling. A digital rock representation of the granular sample was used to derive the initial inner surface area. Medium (10 mM) and high (100 mM) barium input concentration resulted in a comparably strong initial surge of barite nuclei formation, followed by continuous grain overgrowth and finally passivation of celestite. At lower input concentrations (1 mM), nuclei formation was significantly less, resulting in fewer but larger barite crystals and a slow moving reaction front with complete mineral replacement. The modelled mole fractions of the solid phase and effluent chemistry match well with previous experimental results. The improvement compared to models using empirical relationships is that no a-priori knowledge on prevailing supersaturations in the system is needed. For subsurface applications utilising reservoirs or reactive barriers, where barite precipitation plays a role, the developed geochemical model is of great benefit as only solute concentrations are needed as input for quantified prediction of alterations.

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