Structural stability of Chernozemic soils as affected by exchangeable sodium and electrolyte concentration

1994 ◽  
Vol 74 (2) ◽  
pp. 157-164 ◽  
Author(s):  
D. Curtin ◽  
H. Steppuhn ◽  
F. Selles
Keyword(s):  
Electrolyte Concentration ◽  
Clay Content ◽  
Threshold Concentration ◽  
Prairie Soils ◽  
Structural Deterioration ◽  
Soil Clays ◽  
Low Salt ◽  
Leaching Solution ◽  
The Stability ◽  
General Response

The stability of soil structure in the presence of exchangeable Na is an important factor determining the success of irrigation developments using sodic waters. Our objective was to determine the effects of sodium adsorption ratio [SAR = Na/((Ca + Mg)/2)0.5, where concentrations are expressed in mmolc L−1] and electrolyte concentration on saturated hydraulic conductivity (K) and on macroscopic swelling in a range of Brown Chernozemic soils from southern Saskatchewan. All soils showed the same general response to sodicity (SAR) and electrolyte concentration of the leaching solution, i.e., K decreased as SAR increased and as salt concentration decreased. However, major differences existed between the soils in their susceptibility to Na-induced structural deterioration. For example, at SAR 20, the electrolyte concentration needed to maintain stable structure ranged from about 5 to 30 mmolc L−1. Our results indicated that use of a generalized threshold concentration curve to partition stable from unstable structure would not be satisfactory for all irrigated prairie soils. Texture was a major source of variation between soils; the limits on acceptable irrigation water SAR should generally be decreased as clay content increases. Swelling and dispersion of soil clays both contributed to sodicity-induced K decline. Soil clays swelled appreciably when soil exchangeable Na percentage exceeded about 10. In contrast to swelling, which was relatively insensitive to electrolyte concentration, clay dispersion was only observed at low salt concentrations (≤ 20 mmolc L−1. In implementing irrigation water:soil compatibility guidelines, it will be necessary to identify soils which deviate substantially from general or average behavior because of their propensity to disperse or swell. Key words: Sodicity hazard, threshold concentration curves, clay swelling

The significance of the threshold and turbidity concentrations in relation to sodicity and microstructure

Soil Research ◽  
2001 ◽  
Vol 39 (6) ◽  
pp. 1185 ◽  
Author(s):  
J. P. Quirk
Keyword(s):  
Electrolyte Concentration ◽  
Sandy Loam ◽  
Infiltration Rate ◽  
Threshold Concentration ◽  
Diffuse Double Layer ◽  
Soil Permeability ◽  
Soil Microstructure ◽  
Discernible Effect ◽  
Irrigation Practice ◽  
The Stability

Quirk and Schofield (1955) in their paper on the effect of electrolyte concentration on soil permeability in relation to sodicity designated 2 concentrations: the threshold concentration, which related to the first discernible effect on soil structure; and the turbidity concentration, at which the dismantling of the soil microstructure is indicated by the appearance of dispersed particles in the percolate—this occurs when the electrolyte concentration is about one-quarter of the threshold concentration. This behaviour is explained in terms of clay domains, which are assemblages of many clay particles in parallel alignment. Within a clay domain, slit-shaped pores with surface separations about equal to the thickness of clay crystals exist. When calcium is the dominant exchangeable ion the clay domains are stable because where contiguous crystals overlap the surfaces reside in a potential well as a result of strong attractive forces. These attractive forces are similar to those responsible for the stability of Camontmorillonite and Ca-vermiculite crystals. A model of 3 clay crystals is used to illustrate how crystal interaction within a clay domain, in terms of classical repulsive diffuse double-layer forces and modern attractive forces, affect domain stability. Attention is drawn to a misconception, now prevalent in the literature, which does not recognise the basic significance of the turbidity concentration with respect to microstructure and wrongly contends that the concentration of electrolyte required to effect the dispersion to flocculation transition in soil suspensions can be used for predicting the level of electrolyte required to sustain soil permeability or infiltration rate in irrigation practice. It is shown that the flocculation concentration is almost 8 times the turbidity concentration. The application of the threshold concentration concept in irrigation practice is discussed. It is demonstrated that the threshold and turbidity concentration comfortably explain the behaviour of a heavy clay soil subjected to border-check irrigation and Cajon sandy loam in Arizona.

scholarly journals Electrophoretic Deposition of Copper(II)–Chitosan Complexes for Antibacterial Coatings

2020 ◽  
Vol 21 (7) ◽  
pp. 2637 ◽  
Author(s):  
Muhammad Asim Akhtar ◽  
Kanwal Ilyas ◽  
Ivo Dlouhý ◽  
Filip Siska ◽  
Aldo R. Boccaccini
Keyword(s):  
Electrophoretic Deposition ◽  
Mechanical Stability ◽  
Metallic Copper ◽  
Antibacterial Properties ◽  
Threshold Concentration ◽  
X Ray Diffraction ◽  
X Ray ◽  
Antibacterial Coatings ◽  
Elemental Analyses ◽  
The Stability

Bacterial infection associated with medical implants is a major threat to healthcare. This work reports the fabrication of Copper(II)–Chitosan (Cu(II)–CS) complex coatings deposited by electrophoretic deposition (EPD) as potential antibacterial candidate to combat microorganisms to reduce implant related infections. The successful deposition of Cu(II)–CS complex coatings on stainless steel was confirmed by physicochemical characterizations. Morphological and elemental analyses by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy verified the uniform distribution of copper in the Chitosan (CS) matrix. Moreover, homogeneous coatings without precipitation of metallic copper were confirmed by X-ray diffraction (XRD) spectroscopy and SEM micrographs. Controlled swelling behavior depicted the chelation of copper with polysaccharide chains that is key to the stability of Cu(II)–CS coatings. All investigated systems exhibited stable degradation rate in phosphate buffered saline (PBS)–lysozyme solution within seven days of incubation. The coatings presented higher mechanical properties with the increase in Cu(II) concentration. The crack-free coatings showed mildly hydrophobic behavior. Antibacterial assays were performed using both Gram-positive and Gram-negative bacteria. Outstanding antibacterial properties of the coatings were confirmed. After 24 h of incubation, cell studies of coatings confirms that up to a certain threshold concentration of Cu(II) were not cytotoxic to human osteoblast-like cells. Overall, our results show that uniform and homogeneous Cu(II)–CS coatings with good antibacterial and enhanced mechanical stability could be successfully deposited by EPD. Such antibiotic-free antibacterial coatings are potential candidates for biomedical implants.

Influence of sodium adsorption ratio on sodium and calcium breakthrough curves and hydraulic conductivity in soil columns

Soil Research ◽  
2007 ◽  
Vol 45 (8) ◽  
pp. 586 ◽  
Author(s):  
Oagile Dikinya ◽  
Christoph Hinz ◽  
Graham Aylmore
Keyword(s):  
Hydraulic Conductivity ◽  
Electrolyte Concentration ◽  
Soil Aggregates ◽  
Breakthrough Curves ◽  
Sodium Adsorption Ratio ◽  
Threshold Concentration ◽  
Critical Threshold ◽  
Soil Columns ◽  
Clay Particles ◽  
The Matrix

The paper examines the effects of electrolyte concentration and sodium adsorption ratio (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na–Ca exchange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using an agricultural Balkuling soil and a mining residue. Generally, RHC has been found to decrease with time, with increasing SAR, and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were observed in the passage of fronts of decreasing electrolyte concentrations for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at any given point in the column. Measurements at the critical threshold concentration and turbidity concentration at SAR 15 revealed structural breakdown of the pore matrix system as evidenced by decreased RHC. The increase in SAR to 15 is initially accompanied by erratic RHC, presumably due to the break up of soil aggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores.

Thermodynamic regime of greenstone metamorphism of basic volcanic rocks after experimental data

1981 ◽  
Vol 18 (8) ◽  
pp. 1303-1309 ◽  
Author(s):  
L. P. Pluysnina ◽  
I. P. Ivanov
Keyword(s):  
Stability Boundary ◽  
Salt Content ◽  
Volcanic Rocks ◽  
Fe Content ◽  
Low Salt ◽  
Thermodynamic Regime ◽  
Lower Temperature ◽  
The Stability ◽  
Basic Volcanic ◽  
Facies Transition

The stability fields of laumontite, prehnite, pumpellyite, zoisite, and tremolite-bearing assemblages were experimentally examined in the CaO–MgO–Al2O3–SiO2–H2O–CO2 system. The influence of the Fe content on the shift of the upper stability boundary towards both lower temperature and [Formula: see text] equilibrium values is shown for pumpellyite. The runs for some dehydration–carbonatization reactions in the complex H2O–CO2–NaCl fluid have revealed a decrease in the [Formula: see text] equilibrium values for even low salt content. The zeolite, prehnite–pumpellyite, and greenschist facies limits are plotted in the schematic [Formula: see text] diagram, and their possible Pfl limits are discussed. For examined P–T conditions of greenschist to amphibolite facies transition the absence of the compositional gap between tremolite and Ca-hornblende is found.

Effects of mutations at Gly114 on the stability and refolding of haloarchaeal nucleoside diphosphate kinase in low salt solution

2009 ◽  
Vol 44 (4) ◽  
pp. 361-364 ◽  
Author(s):  
Matsujiro Ishibashi ◽  
Tatsuya Iwasa ◽  
Kouko Kumeda ◽  
Tsutomu Arakawa ◽  
Masao Tokunaga
Keyword(s):  
Salt Solution ◽  
Nucleoside Diphosphate Kinase ◽  
Low Salt ◽  
The Stability

scholarly journals A Mathematical Approach to Evaluating the Influence of Various Factors on the Stability of Aggregates in Vertisols

1969 ◽  
Vol 53 (1) ◽  
pp. 57-60
Author(s):  
M. A. Lugo López ◽  
Raúl Pérez Escolar
Keyword(s):  
Organic Matter ◽  
Soil Aggregates ◽  
Aggregate Stability ◽  
Correlation Coefficients ◽  
Clay Content ◽  
Mathematical Approach ◽  
Single Factor ◽  
Additional Increase ◽  
Independent Variable ◽  
The Stability

A mathematical approach is presented in this paper to evaluate the influence of such factors as clay content, silt content, organic matter, Ca + Mg, and soluble sodium upon the stability of soil aggregates in a group of Vertisols from the Lajas Valley, P.R. The relationships between aggregate stability and silt and clay were not significant. When the percentage of organic matter was considered as the independent variable, a highly significant correlation coefficient of 0.66 was obtained. Therefore, almost 43 percent of the variability in aggregate stability could be explained on the basis of this single factor. Attempts to increase the percentage of the variability which could be explained in terms of the content of Ca + Mg, and also of soluble sodium, yielded correlation coefficients of 0.70 and 0.74, respectively. Thus, only a slight, but significant, additional increase could be explained when these variables were included.

scholarly journals Different resource allocation in a Bacillus subtilis population displaying bimodal motility

2021 ◽  
Author(s):  
Leendert W. Hamoen ◽  
Biwen Wang ◽  
Jojet Staal ◽  
Yongqiang Gao ◽  
Remco Kort ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Exponential Growth ◽  
Microscopic Analysis ◽  
Feedback Regulation ◽  
Ribosomal Gene ◽  
Threshold Concentration ◽  
Negative Feedback Regulation ◽  
Continuous Increase ◽  
Motile Cells ◽  
The Stability

To cope with sudden changes in their environment, bacteria can use a bet-hedging strategy by dividing the population into cells with different properties. This so-called bimodal or bistable cellular differentiation is generally controlled by positive feedback regulation of transcriptional activators. Due to the continuous increase in cell volume, it is difficult for these activators to reach an activation threshold concentration when cells are growing exponentially. This is one reason why bimodal differentiation is primarily observed from the onset of the stationary phase when exponential growth ceases. An exception is the bimodal induction of motility in Bacillus subtilis, which occurs early during exponential growth. Several mechanisms have been put forward to explain this, including double negative-feedback regulation and the stability of the mRNA molecules involved. In this study, we used fluorescence-assisted cell sorting to compare the transcriptome of motile and non-motile cells and noted that expression of ribosomal genes is lower in motile cells. This was confirmed using an unstable GFP reporter fused to the strong ribosomal rpsD promoter. We propose that the reduction in ribosomal gene expression in motile cells is the result of a diversion of cellular resources to the synthesis of the chemotaxis and motility systems. In agreement, single-cell microscopic analysis showed that motile cells are slightly shorter than non-motile cells, an indication of slower growth. We speculate that this growth rate reduction can contribute to the bimodal induction of motility during exponential growth.

scholarly journals Permeability Prediction of Iron Tailings Including Degree of Compaction and Structure

Complexity ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Deqing Gan ◽  
Xi Yang ◽  
Yunpeng Zhang
Keyword(s):  
Water Flow ◽  
Critical Pressure ◽  
Clay Content ◽  
Vital Role ◽  
Tailings Dam ◽  
Flow Paths ◽  
Silt Content ◽  
The Stability ◽  
Granulometric Characteristics ◽  
Water Flow Paths

The stability of iron tailings dam is affected by the permeability of tailings. Considering the influence of it, it is necessary to analyze the permeability of tailings so as to prevent the recurrence of Brazilian iron tailings dam accidents. Nevertheless, the results of iron tailings permeability from some prediction equations (Terzaghi equation, Hazen equation, and Kozeny equation) cannot be accurate. Iron tailings are various as they can be divided into three categories: (1) silt content is less than 40%; (2) silt content is more than 40%, while clay content is less than 15%; and (3) clay content is more than 15% and less than 30%. Correspondingly, three equations are proposed to calculate the disturbed and iron undisturbed tailings permeability for the three types. And more accurate results come from it. The water-flow paths of the iron tailings are blocked after compaction, and the critical pressure of iron tailings blockage is 200 kPa. Although the porosity is large, some of the pores are isolated from each other when the pressure is larger than 200 kPa. However, porosity becomes too large for permeability calculation after compaction and the calculated permeability gets larger as well (equations (24)–(26)). Correcting the permeability calculation equations is an absolute must. The calculated permeability by the revised equations becomes more accurate (equations (27)–(29)). In fact, the granulometric characteristics necessarily play a vital role in the evolution of the pore interconnections by blocking the water-flow paths and modifying the morphological parameters. More research studies are required to be done in the future.

The Environmental Fate and Mechanism of Formation of 2-Ethyl-5,5′-Dimethyl-1,3-Dioxane (2EDD) – a Malodorous Contaminant in Drinking Water

1999 ◽  
Vol 40 (6) ◽  
pp. 217-224 ◽  
Author(s):  
L. Schweitzer ◽  
J. Noblet ◽  
Q. Ye ◽  
E. Ruth ◽  
I. H. Suffet
Keyword(s):  
Waste Water ◽  
Drinking Water ◽  
Environmental Fate ◽  
Profile Analysis ◽  
Threshold Concentration ◽  
Odor Threshold ◽  
Taste And Odor ◽  
The Stability ◽  
Water Taste ◽  
Flavor Profile Analysis

A malodorous chemical, 2-ethyl-5,5′-dimethyl-1,3-dioxane (2EDD) created a drinking water taste and odor episode in Pennsylvania (USA) during 1992. The odor episode occurred as the result of a reaction between propionaldehyde and neopentyl glycol in the waste tank of a resin manufacturer. Samples of this waste water were extracted and analyzed. An in situ aqueous preparation of 2EDD was completed to demonstrate that 2EDD could have formed under the conditions found in the waste water. The stability (fate) of 2EDD was studied at different aqueous pHs (pH3, 5, 7, and 9). Some hydrolysis of 2EDD was found at pHs<7 after one week, but 2EDD appeared to be stable at pH 9. The odor characteristics and odor threshold of 2EDD were determined by the method of flavor profile analysis. The odor threshold concentration of 2EDD was found to be between 5 and 10 ng/l and was described as having a sweet, tutti fruitti odor (near the odor threshold concentration) and a burnt, sickening sweet odor at higher concentrations. This study also discovered that slight antagonism in chloraminated drinking water may occur at or near the threshold odor level of 2EDD.

Groundwater irrigation and phosphogypsum application: their influence on soil properties and pasture production in northern Victoria

2004 ◽  
Vol 44 (2) ◽  
pp. 193
Author(s):  
D. P. Burrow ◽  
A. Surapaneni
Keyword(s):  
N Uptake ◽  
Clay Content ◽  
Organic Carbon Content ◽  
Pasture Production ◽  
Groundwater Irrigation ◽  
Chemical Measurements ◽  
Physico Chemical ◽  
The Stability ◽  
Pasture Yield ◽  
Microaggregate Stability

Saline–sodic irrigation water [ECiw = 0.1, 0.8, 2.5, 4.5, 7.5 dS/m, SARiw = 3, 5, 11, 17, 29 (mmolc/L)0.5] was applied to lucerne plots over 1991–95 followed by further irrigation [ECiw = 0.1, 0.8, 4.5 dS/m, SARiw = 3, 5, 17 (mmolc/L)0.5] of perennial pasture in 1997–99 with and without added phosphogypsum (PG = 0, 5 t/ha; May 1998). The later irrigation treatments and PG did not decrease exchangeable sodium percentage (ESP) in the B horizon nor alter bulk soil physical properties. Microaggregate stability to wetting decreased with increasing�residual sodicity and decreasing soil electrolyte concentration. The stability of topsoil aggregates was explained by higher organic carbon content while subsoil aggregate instability was related to higher clay content and higher ESP. Pasture yield decreased by 2 t/ha with an associated increase in soil ESP from 9 to 15%. Pasture yield was highest for ECiw = 0.8 dS/m and this treatment marginally increased N uptake in leaves. Higher yields for this treatment could not be readily explained by soil physico–chemical measurements.

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