Dissociation Of Organic Acids Research Articles

Impact of acidity and surface-modulated acid dissociation on cloud response to organic aerosol

Abstract. Acid dissociation of the organic aerosol fraction has the potential to impact cloud-activating properties by altering aqueous-phase H+ concentrations and water activity but is currently overlooked in most atmospheric aerosol models. We implemented a simple representation of organic acid dissociation in the aerosol–chemistry–climate box model ECHAM6.3–HAM2.3 and investigated the impact on aerosol-forming aqueous sulfur chemistry, cloud droplet number concentrations, and the shortwave radiative effect. Many atmospheric organic acids are also surface-active and may be strongly adsorbed at the surface of small aqueous droplets. The degree of dissociation has recently been observed for several atmospheric surface-active organics with Brönsted acid character to be significantly shifted in the surface, compared to the bulk aqueous solution. In addition to the well-known bulk acidity, we therefore introduced an empirical account of this surface-modulated dissociation to further explore the potential impact on aerosol climate effects. Malonic acid and decanoic acid were used as proxies for atmospheric organic aerosols of different surface-active and acid strengths. Both acids were found to yield sufficient hydrogen ion concentrations from dissociation in an aqueous droplet population to strongly influence aqueous aerosol sulfur chemistry, leading to enhanced cloud droplet number concentrations and a cooling shortwave radiative effect. Further considering the surface modulation of organic acid dissociation, the impact on cloud microphysics was smaller than according to the well-known bulk solution acidity but still significant. Our results show that organic aerosol acid dissociation can significantly influence predictions of aerosol and cloud droplet formation and aerosol–cloud–climate effects and that, even for a well-known bulk solution phenomenon such as acidity, it may be important to also consider the specific influence of surface effects when surface-active acids comprise a significant fraction of the total organic aerosol mass.

Formic and acetic acid pKa values increase under nanoconfinement.

Organic acids are prevalent in the environment and their acidity and the corresponding dissociation constants can change under varying environmental conditions. The impact of nanoconfinement (when acids are confined within nanometer-scale domains) on physicochemical properties of chemical species is poorly understood and is an emerging field of study. By combining infrared and Raman spectroscopies with molecular dynamics (MD) simulations, we quantified the effect of nanoconfinement in silica nanopores on one of the fundamental chemical reactions-the dissociation of organic acids. The pKa of formic and acetic acids confined within cylindrical silica nanopores with 4 nm diameters were measured. MD models were constructed to calculate the shifts in the pKa values of acetic acid nanoconfined within 1, 2, 3, and 4 nm silica slit pores. Both experiments and MD models indicate a decrease in the apparent acid dissociation constants (i.e., increase in the pKa values) when organic acids are nanoconfined. Therefore, nanoconfinement stabilizes the protonated species. We attribute this observation to (1) a decrease in the average dielectric response of nanoconfined aqueous solutions where charge screening may be decreased; or (2) an increase in proton concentration inside nanopores, which would shift the equilibrium towards the protonated form. Overall, the results of this study provide the first quantification of the pKa values for nanoconfined formic and acetic acids and pave the way for a unifying theory predicting the impact of nanoconfinement on acid-base chemistry.

Effects of forest management on soil acidification in cedar plantation

Forest management practices such as clearcutting risk increasing the leaching loss of cations and soil acidification by increasing nitrification and reducing plant uptake. To evaluate the effect of two forest management practices, clearcutting and stem girdling, on soil acidification, we quantified proton budgets by measuring ion fluxes associated with solute leaching and plant uptake in a Japanese cedar plantation in Wakayama, Japan. In the control and girdling plots, the dissociation of organic acids was a major proton-generating process that promoted cation leaching from the organic horizon. Plant uptake of mobilized cations was a dominant soil-acidifying process in the control plot, whereas litterfall from tree dieback and loss of plant uptake led to soil alkalization via cation inputs to the mineral soil in the girdling plot. In the clearcut plot, in addition to cation removal due to harvesting, nitrification was a major proton-generating process that increased aluminum (Al) leaching in the first year following clearcutting. However, proton consumption via net mineralization (loss) of soil organic matter (SOM) could neutralize the acidity generated by nitrification. Forest management practices stimulate both proton-generating and -consuming processes. Soils under cedar plantation are affected by biological acidification of surface soil by plant uptake in the rooting zone and net cation leaching by carbonic acid below the rooting zone (subsoil and bedrock), but organic matter and Al and Fe oxides accumulated in plantation could mitigate acidification induced by disturbances.

Interpreting measurements of total alkalinity in marine and estuarine waters in the presence of proton-binding organic matter

Total alkalinity (AT) is one of four measurable cornerstone parameters for characterizing the marine carbonate system, yet its measurement by standard titration methods is subject to systematic misinterpretations in the presence of uncharacterized dissolved organic molecules in ocean and estuarine waters. A consequence of these misinterpretations may be the lack of thermodynamic consistency that is routinely observed among measured and calculated parameters of the carbonate system. In this work, a numerical model is used to illustrate (a) how proton-binding dissolved organic molecules influence the reported results of total alkalinity titrations in marine and estuarine settings and (b) how errors in interpretations of reported AT values can then propagate through carbonate system calculations, thus distorting biogeochemical interpretations of calculated parameters. We examine five distinct approaches for alkalinity measurement by titration. Ideally, the difference between the measured (reported) AT and the conventional (thermodynamic) definition of inorganic alkalinity (Ainorg) would be zero. However, in the presence of titratable organic matter, our model results show consistent non-zero differences that vary with the chemical properties of the organic matter. For all five titration approaches, the differences between reported AT and Ainorg are greatest when the negative logarithm of the organic acid dissociation constant (pKorg) is between approximately 5 and 7. The differences between reported AT and Ainorg also display previously undescribed variation among measurement approaches, most significantly when pKorg is between approximately 3 and 6 (typical of carboxylic acid groups). The measurement approaches that are most effective at limiting the unfavorable influence of these relatively low-pK organic acids on AT are closed-cell titrations and single-step titrations that are terminated at a relatively high pH. For calculated carbonate system parameters relevant to in situ conditions (e.g., pH, pCO2, calcium carbonate mineral saturation states), errors resulting from the presence of proton-binding organics are largest when calculations are based on the input pair of directly measured dissolved inorganic carbon (CT) and directly measured AT, and can vary in magnitude depending on the titration approach that is used to obtain AT. The modeling results presented in this work emphasize the importance of (a) determining AT in a manner that accounts for the ubiquity of organic alkalinity in marine and estuarine waters and (b) working toward a clearer understanding of the phenomena underlying the routine lack of internal consistency between measured versus calculated carbonate system parameters. Total alkalinity measurements should begin to incorporate either implicit or explicit evaluations of the titration characteristics of the natural organic carbon present in each sample. To that end, we recommend use of secondary titrations to directly measure organic alkalinity (sample-by-sample), characterization of relationships between total dissolved organic carbon concentrations and organic alkalinity (on local to regional scales), and/or exploration of novel curve-fitting procedures to infer the behavior of organic functional groups from titration data.

Contemporary distribution and impending mobility of arsenic, copper and zinc in a tropical (Brahmaputra) river bed sediments, Assam, India

The present study develops a correlationship among different phases of metal for developing an understanding of metal distribution and speciation, which is seldom reported in many studies. Also, the study examines the effect of sediment texture, pH, CEC, organic content and conductivity to understand the metal distribution. Bed sediment (n = 8) samples were collected from Brahmaputra river by grab sampling method to understand the spatial distribution and speciation of Cu, As and Zn. X-ray Diffraction (XRD) analysis strongly indicated the presence of arsenopyrite in Dhansirimukh site (BRS-5) sample as a dominating As containing mineral. It was found that distribution of As was relatively higher in downstream side due to increase in clay content of the sediment. Partition coefficient (kd) indicated higher mobility of Zn and Cu in comparison to As. The presence of organic matter and clay resulted in high metal content due to high CEC values, which is because of negative charge on clay and organic matter. The negative charge in clay and organic matter is due to isomorphous substitution and dissociation of organic acids, respectively. High clay content leads to Cu enrichment at BRS-4, while sandy nature of sediment at BRS-8 and absence highly active mineral leads to low Zn content. Sediment properties like organic matter and grain size were the main controlling parameters for metal concentration and its potential mobility as indicated by correlation and factor analysis. Factor analysis further revealed three probable processes governing metal enrichment and distribution viz. (i) Textural driven (ii) Metal solubility at sediment-water interface and (iii) Carbonate weathering. The study demonstrates that the textural assemblage governs metal mobility in the river sediments. Study developed a conceptual diagram for probable geochemical processes explaining the specific observations in this study, which is essential for environmental safety.

The inclusion of organic acids dissociation in the prediction of liquid-liquid equilibrium data

Advances in thermodynamic equilibrium have led to the recent development of binary, ternary and quaternary systems including electrolytes. However, a precise determination of phase equilibrium must consider the physical-chemical aspects of the components that will can to take place in a mixture. A solute is liable to dissociate hence the need to take this consideration into account. The chosen organic acids have attracted much attention in the research works but unfortunately, their dissociation into the aqueous phase has not been taken into the calculation of phase equilibrium. The present research work focuses on the development of the calculation of the phase equilibrium methods by including the dissociation of the chosen organic acids, for predicting the liquid-liquid equilibrium (LLE) data from the binary parameters for various ternary systems composed of {water-phosphoric acid-methylisobutylketone},{water-acetic acid-cumene},{water-propionic acid-cumene},{water-formic acid-isoamyl acetate} and {water-butyric acid-isoamyl acetate} at 298.15 K and normal atmospheric pressure, so as to be able to design electrolytes having specific properties. This requires a modeling framework that is based upon the fundamental laws and models of physics. Therefore, in our study, we used the Extended UNIQUAC model to predict the LLE data. We are newly investigating the effect of including the dissociation of the picked organic acids on prediction of phase equilibrium. The results have been compared with authors who consider no dissociation of organic acids, where they have been satisfactory.

13C and 1H NMR measurements to investigate the kinetics and the mechanism of acetic acid (CH3CO2H) ionization as a model for organic acid dissociation dynamics for polymeric membrane water filtration

Abstract The formation of ionic charge carriers and their transport in acetic acid (CH3COOH): water mixtures have been investigated by 13C and 1H NMR. The obtained dissociation constant from the NMR measurements is close to pKa = 4.70 in a highly diluted system which is in full agreement with literature values. The maximum molar concentration of ions (H3O+ and CH3COO−) is found at a water mole fraction around 0.5 to 0.6. Remarkably, minima in the molecular diffusion coefficients and ionic mobility are observed at this concentration. Ionic concentrations, ionic strength and the pH curve were obtained for any water content based on the 13C and 1H NMR as well as pH measurements and the numerical calculations. The data is relevant for the understanding and optimization of the properties of polymeric nanofiltration membranes for organic ion removal. They provide interesting insight into the water dependence of the viscoelastic and kinematic properties, the charge formation mechanism and the dissociation limit, especially for highly diluted systems simulating the case of ionic pollutants.

Geochemical Mixing in Peatland Waters: The Role of Organic Acids

The close interplay between hydraulic and biotic processes controls the evolution of ecosystems in large, circumboreal peatlands and the degree to which they lose, gain or sequester carbon. In peatlands, biota significantly alters surficial acid–base equilibrium and solute chemistry by releasing dissolved organic compounds into surface and pore waters, which then mix through advection and dispersion through pore water flow paths. We report herein the results of new geochemical mixing models that incorporates organic acid dissociation constants to understand how organic acids control the acid–base chemistry in mixtures of dilute acidic bog pore waters and circum-neutral groundwater (typical of carbonate terrains) that upwells or disperses into peat deposits. In our new mixing models, at least twice as much groundwater is required to neutralize bog water acidity when dissolved organic carbon concentrations exceed 10 mmol/L than in their absence. Although it remains uncertain how future climatic change will alter the composition of dissolved organic matter in peatlands, organic acids should remain an important factor with respect to potential neutralization of peatland waters by groundwater sources. The acid base equilibria in large peat basins not only has important implications for vegetation patterning but also for biogeochemical cycles in these globally important reservoirs for carbon.

Determination of sugars, organic acids and alcohols in microbial consortium fermentation broth from cellulose using high performance liquid chromatography

A high performance liquid chromatographic method was established for the determination of metabolites (sugars, organic acids and alcohols) in microbial consortium fermentation broth from cellulose. Sulfate was first added in the samples to precipitate calcium ions in microbial consortium culture medium and lower the pH of the solution to avoid the dissociation of organic acids, then the filtrates were effectively separated using high performance liquid chromatography. Cellobiose, glucose, ethanol, butanol, glycerol, acetic acid and butyric acid were quantitatively analyzed. The detection limits were in the range of 0.10-2.00 mg/L. The linear correlation coefficients were greater than 0.999 6 in the range of 0.020 to 1.000 g/L. The recoveries were in the range of 85.41%-115.60% with the relative standard deviations of 0.22% -4.62% (n = 6). This method is accurate for the quantitative analysis of the alcohols, organic acids and saccharides in microbial consortium fermentation broth from cellulose.

Membrane capacitive deionization for biomass hydrolysate desalination

Biomass hydrolysates are rapidly gaining interest as low-cost non-food renewable feedstocks for fermentation processes. However, since high concentrations of salt such as sodium and potassium can act toxic to microorganisms, there is a need to remove these salts to maintain high biochemical productivity. In this study, the electrochemical treatment of biomass hydrolysates by membrane capacitive deionization (MCDI) was considered as an auxiliary chemical free, lower cost alternative in comparison to the commonly used ion-exchange processes. Model experiments performed with a commercial bench-scale MCDI set-up and model solutions indicated that none of the most abundant hydrolysate components (sugars, organic acids and furans) prohibited the implementation of MCDI for this application, although performance was lowered by the competition for electro-sorption between the protons deriving from organic acid dissociation and the cations. Such an effect was not observed during MCDI treatment of a real biomass hydrolysate sample. Instead, the results achieved in terms of Na and K removal and energy usage were very comparable to the ones for a model solution with equal conductivity and sugar concentration. As such, this study clearly demonstrates the technical feasibility of MCDI for process streams such as biomass hydrolysates, hereby considerably broadening its potential application field.

Studies Thermodynamical Stability of Complexes of Rare Earth Metal Ions with Substituted Pyrazole

Abstract The stability constants of 1-phenyl-3-(2-hydroxy-4-methylphenyl)-5-methylpyrazole (PHMPMPz) and their complexes with Pr (III) and Sm (III) metal ions have been determined in 70% v/v dioxane-water media at different ionic strength (0.02, 0.04, 0.06, 0.08, 0.1) mol.dm -3 at 300.15K by pH metry method. The pK and logK values decreasewith increase in ionic strength of medium, which indicated the opposite charges on reacting species. The values of stability constants for Sm (III) were greater than Pr (III) metal ion. The thermodynamic stability constants at zero ionic strength have also been determined. Keywords Pyrazole, ionic strengthstability constant, , pH 1. Introduction Dissociation of organic acids and their interaction with metal ions (complex formation) may be extremely sensitive to ionic strength of the medium [1]. If charges on the reacting species are opposite then there is a decrease in the reaction rate with increasing ionic strength (IS) whereas if the charges are identical, an increase in the reaction rate will occur while one of the reactant charge is less t he reaction rate does affect by ionic strength of the medium [2]. Ionic strength measures the intensity of an electric field of solution due to the presence of ions in a solution. Ionic strength of medium affects the rate at which ions react with each other and to extent the reaction occurs [3]. High ionic strength reactions are found all around us, from industrial reactions that are carried out at high concentrations to ensure increased productivity to biochemical processes that occur at low or high pH. Indeed, practically every solution based reaction of importance deviates from ideality to some extent. The ionic strength data also used to study the correct mechanism of the complexation reaction [4]. The thermodynamic properties of electrolyte solutions can be studied from long range interactions between ion and solvent molecules. Number of workers [5, 6] reported the influence of ionic strength on the organic compounds with metal ions.

A hydrophilic/hydrophobic organic (H2O) aerosol model: Development, evaluation and sensitivity analysis

A secondary organic aerosol (SOA) model, the Hydrophilic/Hydrophobic Organic model (H2O), is presented and evaluated over Europe. H2O uses surrogate organic molecules to represent the myriad of SOA species and distinguishes two kinds of surrogate species: hydrophilic species (which condense preferentially into an aqueous phase) and hydrophobic species (which condense only into an organic phase). These surrogate species are formed from the oxidation in the atmosphere of volatile organic compounds. H2O includes several important processes, including the effect of nitrogen oxides (NOX) on SOA formation, the dissociation of organic acids in an aqueous phase, the oligomerization of aldehydes, the non‐ideality of the particle phase and the hygroscopicity of organics. Concentrations of organic aerosols were simulated over Europe from July 2002 to July 2003 for comparison with measurements of the European Monitoring Evaluation Program (EMEP). In H2O, primary organic aerosols (POA) are considered as semi‐volatile organic compounds (SVOC) present in both the gas phase and the particle phase. Taking into account the gas‐phase fraction of SVOC increases significantly organic PM concentrations, particularly in winter, in better agreement with observations. The impacts on organic aerosol formation of ideality, of the choice of the parameterization for isoprene SOA formation, and of the OM/OC ratio of the model were also investigated. Assuming ideality in H2O was found to lead to a small decrease in OM. Compared to a two‐product parameterization, the parameterization of Couvidat and Seigneur [2011] for SOA formation from isoprene oxidation leads to a significant increase in isoprene SOA by taking into account their hydrophilic properties and suggests that most models may currently underestimate isoprene SOA.

Acidification of tropical forest soils derived from serpentine and sedimentary rocks in East Kalimantan, Indonesia

Soil acidification is one of major pedogenetic processes under tropical forests, however, proton sources and weathering reactions vary from soil to soil. The dominant soil-acidifying processes, along with their spatial heterogeneity, under tropical forests were analyzed for five Indonesian soils formed from different parent materials (serpentine and sedimentary rocks). The contribution of different proton sources to soil acidification was quantified based on the theory of proton budget by measuring fluxes of solutes leaching and vegetation uptake. Excess cation accumulation in wood (3.0–8.6 kmol c ha − 1 yr − 1 ) was a dominant acidification process in all the soil profiles due to the high net primary production in this tropical region. However, the dominant proton-generating and consuming processes varied with soil horizons and parent materials. In moderately acidic soils from serpentine and mudstone, protons generated by nitrification, dissociation of carbonic and organic acids and vegetation uptake contributed to acidification of the mineral soil horizons (2.4–4.3 kmol c ha − 1 yr − 1 ), but they could completely be neutralized by basic cations. A higher acid neutralizing capacity (ANC) of these soils weakened acidity and contributed to accumulation of Al and Fe oxides through in situ weathering. In highly acidic soils from sandstone, protons generated by dissociation of organic acids and vegetation uptake in the O horizons (1.6–3.6 kmol c ha − 1 yr − 1 ) could not completely be neutralized owing to the lower ANC, which resulted in eluviation of protons, Al and Fe from the surface soil horizons. In this tropical region, parent materials influence pedogenetic acidification processes at a local scale through effects on the intensity and distribution of acids and ANC of litter and soils.

Investigation of electrostatic charging mechanism in aged oil-immersed transformers

Electrostatic charging mechanism in aged oil-immersed transformers is investigated. Sulfonium ions, which are generated by sulfoxide compounds and hydrogen ions, are identified as the prime compounds that increase electrostatic charging tendency (ECT) of mineral insulating oil. Sulfoxide compounds are generated by the oxidation of sulfide compounds that are contained in new oil. Hydrogen ions are considered to be supplied by organic acids that are generated due to the oxidation of hydrocarbons. Negative ions with low mass are generated by the dissociation of organic acids during the generation of sulfonium ions. Because these negative ions are hydrophilic, the oil is charged positively. Water is also generated by the deterioration of insulating oils and has the same effect. On the other hand, negative charging of oil is detected with the addition of sulfonic acids, which reflects the generation of positive ions with low mass and hydrophility.

Contribution of different proton sources to pedogenetic soil acidification in forested ecosystems in Japan

The contribution of different proton sources to pedogenetic soil acidification was evaluated for three Japanese forest soils, i.e. ando soil, podzolic soil and brown forest soil in relation to the respective soil forming processes. Soil acidification rate and net proton generation were quantified based on the theory of proton budget for the respective soil horizon compartments (mainly the O, A and B horizons) by measuring fluxes of solutes entering and leaving the soil horizon compartment and vegetation uptake. Protons were produced by the dissociation of organic acids and nitrification in the O horizon and then consumed by adsorption and decomposition of organic acids and nitrate uptake by vegetation in deeper soil horizons at all plots. Excess uptake of cation over anion by vegetation was highest among proton sources in the whole soil compartment at all plots. Pedogenetic soil acidification was considered to include cation leaching from surface soil horizons due to proton generation by the dissociation of organic acids and nitrification and subsequent cation excess accumulation in wood in the growth stage of forests. In ando soil, andosolization resulted from the low contribution of net proton generation by the dissociation of organic acids as well as a lower soil acidification rate and complete acid neutralization. Dissolved organic carbon (DOC) fluxes in ando soil were lower than those in podzolic soil and brown forest soil due to high adsorption capacity of amorphous materials. In podzolic soil, podzolization resulted from intensive acidification in the O horizon, which derived from net proton generation by the dissociation of organic acids and nitrification as well as cation excess uptake by vegetation due to concentrated fine root biomass in the O horizon, and subsequent high proton efflux to subsoil. The high fluxes of DOC and Al leached from surface soil horizons were considered to contribute to eluviation of Al from surface soil and illuviation in subsoil in podzolic soil. In brown forest soil, brunification resulted from a lower DOC flux from the O horizon due to high decomposition and adsorption by oxides, where podzolization was weakened by high acid neutralization. Thus, the three representative processes involved in the pedogenesis of Japanese forest soils were well characterized by quantification of the respective proton-generating and consuming processes in each soil horizon.

Buffering of recovery from acidification by organic acids

In the United Kingdom, as in other regions of Europe and North America, recent decreases in surface water sulphate concentrations, due to reduced sulphur emissions, have coincided with marked increases in dissolved organic carbon (DOC) concentrations. Since many of the compounds comprising DOC are acidic, the resulting increases in organic acidity may have the potential to offset the benefits of a decrease in mineral (sulphate) acidity. To test this, we used a triprotic model of organic acid dissociation to estimate the proportional organic acid buffering of reduced mineral acidity as measured in the 22 lakes and streams monitored by the UK Acid Waters Monitoring Network. For an average non-marine sulphate decrease of 30 μeq l − 1 over 15 years from 1988–2003, we estimate that around 28% was counterbalanced by rising strong organic acids, 20% by rising alkalinity (partly attributable to an increase in weak organic acids), 11% by falling inorganic aluminium and 41% by falling non-marine base cations. The situation is complicated by a concurrent decrease in marine ion concentrations, and the impact this may have had on both DOC and acidity, but results clearly demonstrate that organic acid increases have substantially limited the amount of recovery from acidification (in terms of rising alkalinity and falling aluminium) that have resulted from reducing sulphur emissions. The consistency and magnitude of sulphate and organic acid changes are consistent with a causal link between the two, possibly due to the effects of changing acidity, ionic strength and aluminium concentrations on organic matter solubility. If this is the case, then organic acids can be considered effective but partial buffers to acidity change in organic soils, and this mechanism needs to be considered in assessing and modelling recovery from acidification, and in defining realistic reference conditions. However, large spatial variations in the relative magnitude of organic acid and sulphate changes, notably for low-deposition sites in northwestern areas where organic acid increases apparently exceed non-marine sulphate decreases, suggest that additional factors, such as changes in sea-salt deposition and climatic factors, may be required to explain the full magnitude of DOC increases in UK surface waters.

Dissociation constants of protonated methionine species in seawater media

The dissociation constants (p K 1 ⁎ and p K 2 ⁎) for methionine have been measured in artificial seawater as a function of salinity ( S = 5 to 35) and temperature (5 to 45 °C). The seawater p K 2 ⁎ values were lower than the values in NaCl at the same ionic strength while the p K 1 ⁎ values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg 2+ complexes and Pitzer interaction parameters for Mg 2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of p K 1 ⁎ and p K 2 ⁎ between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.

Dissociation constants of protonated cysteine species in seawater media

The dissociation constants (p K 1 ⁎, p K 2 ⁎ and p K 3 ⁎) for cysteine have been measured in seawater as a function of temperature (5 to 45 °C) and salinity ( S = 5 to 35). The seawater values were lower than the values in NaCl at the same ionic strength. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been compared to those calculated from the Pitzer ionic interaction model. The lower values of p K 3 ⁎ in the Na–Mg–Cl solutions have been attributed to the formation of Mg 2+ complexes with Cys 2− anions Mg 2+ + Cys 2− = MgCys The stability constants have been fitted to log ⁡ K MgCys ∗ = − 0.144 + 0.564 ⁢ I 0.5 after corrections are made for the interaction of Mg 2+ with H +. The p K 1 seawater measurements indicate that H 3Cys + interacts with SO 4 2−. The Pitzer parameters β 0(H 3CysSO 4), β 1(H 3CysSO 4) and C(H 3CysSO 4) have been determined for this interaction. The formation of CaCys as well as MgCys are needed to account for the values of p K 2 and p K 3 in seawater. The consideration of the formation of MgCys and CaCys in seawater yields model calculated values of p K 1 ⁎, p K 2 ⁎ and p K 3 ⁎ that agree with the measured values to within the experimental error of the measurements. This study shows that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.

Non-steady-state modeling of effects of timing and level of concentrate supplementation on ruminal pH and forage intake in high-producing, grazing ewes1

A computer model was developed to predict responses of lactating ewes to concentrate supplementation, whether on pasture or stall-fed, given concentrate once per day or in multiple feedings, and suckling multiple lambs. The model considers effects of concentrate supplementation on organic acid production, saliva flow, ruminal pH, and forage intake. The user defines ewe BW, feed composition, and concentrate feeding times and amounts. The reference ewe has free access to forage and water. Upon consumption, forages and concentrates enter into lag pools for 2.0 and 0.24 h, respectively. Carbohydrates then enter ruminal pools of degradable fiber, undegradable fiber, or nonstructural carbohydrate, from which they are degraded or pass to the lower gut. Rapid dissociation of organic acids from carbohydrate fermentation and buffers from rumination are simulated to determine ruminal pH according to the Henderson-Hasselbach equation. The pH, in turn, affects fiber degradation rates. Forage intake continues during daylight hours until ruminal NDF exceeds 1.0% of BW, or organic acid concentration exceeds 130 mM. A circadian pattern of organic acid concentrations and pH of rumen contents with multiple concentrate feedings was simulated by the model with root mean square prediction error of 7.7 and 3.0 to 4.0% of the observed mean, respectively. However, ignoring fermentation of dietary protein may have caused an underestimation of organic acid production rates. The model predicted the increase in total DMI and the substitution effect on forage intake of increasing levels of concentrate supplementation. Simulations suggested that a single concentrate meal daily was best fed in the evening to minimize the substitution effect, and that there was no benefit in forage intake to feeding 2 kg/d concentrate in more than two meals per day.

Aluminium chemistry in ploughed podzolic forest soils

Mechanical site preparation has been used to ensure efficient reforestation of clear-felled areas in Finland since the 1960s. About 18% (3.94 million ha) of the total forest land in Finland (21.9 million ha) has been site-prepared, of which one-third has been deeply tilled. In the present study, long-term effects of deep tilling on the chemical properties of soil and soil solution chemistry were evaluated at two forest sites that had been ploughed 17 and 31 years ago and planted with Norway spruce (Picea abies (L.) Karst.) seedlings. Particular interest was focused on the possible mobilisation of soil aluminium in the spodic B horizons exposed upon tilling. Mechanisms controlling Al solubility in the tilled soil profiles were also examined. Decreased concentrations of soil extractable Al, mainly inorganic secondary Al, in the exposed Bs horizons of tilts and furrows and increased concentrations of organically complexed Al in the O horizons buried within the tilt indicate that some Al was mobilised at the ploughed forest sites. Accumulation of organic C on top of the tilts and furrows with the relatively high Norway spruce fine root biomass in the tilts indicated that the release of Al was mainly due to acidity produced by ecosystem internal processes such as organic acids excreted by roots or released during decomposition of aboveand belowground litter. Ploughing did not affect the processes controlling activity of Al in soil solution. In the undisturbed and disturbed Bs horizons, Al solubility was controlled by secondary minerals while in the O and Ah/E horizons, solubility control by organically bound Al was observed. Although the soil exchangeable Al pool was small, the Al Ca exchange based on the Gaines-Thomas equation succesfully described the relationship between these cations in soil solution and on exchange sites in the studied O and Bs horizons. In the O horizons, exchangeable Al had nonacidic properties similar to those of base cations, and the soil solution pH was explained by weak organic acid dissociation using the Henderson-Hasselbach equation. The changes observed in soil chemical properties in the ploughed soil were consistent with the processes determining the Al chemistry in soil solution, and in accordance with the theory of podzolization. It may be expected that soil formation processes will in the course of time result in the development of a new spodic horizon in the tilts and furrows. Although the time elapsed since ploughing was only a few decades in this study, the occurrence of changes observed suggest that plant-derived organic matter and plant-soil interactions are already modifying the properties of ploughed podzols.