Range In pH Research Articles

Spatial variation and chemical reactivity of dusts from open-pit bitumen mining using trace elements in snow

The chemical reactivity of trace elements (TEs) in dusts from bitumen mining, upgrading and related industrial activities in the Athabasca Bituminous Sands region (ABS), Alberta, Canada, was evaluated using the acid-soluble fraction of snow. Samples were collected at 14 sites along the Athabasca River (AR) and its tributaries, and at 3 remote locations. Following metal-free, ultra-clean procedures for processing and analysis, samples were leached with nitric acid (pH < 1), filtered (<0.45 μm), and analyzed using ICP-MS. Insoluble particles (>0.45 μm) were examined using SEM-EDS. Along the river, acid-soluble concentrations of TEs varied by 6 orders of magnitude, from 1 mg/L (Al) to less than 1 ng/L (Tl). Conservative (Al, Y, La, Th) and mobile (Li, Be, Cs, Sr) lithophile elements, those enriched in bitumen (V, Ni, Mo), and potentially toxic chalcophile elements (As, Cd, Pb, Sb, Tl) showed considerable spatial variation. Normalizing the concentrations of TEs in samples collected near industry to the corresponding concentrations in snow from the reference site (UTK), resulted in enrichments of V and most of the lithophile elements. Dust reactivity, quantified as the ratio of acid-soluble to total concentrations, was less than 50% suggesting limited bioaccessibility. The large differences in behaviour between Cd and Pb versus Ni and V could be due to the occurrence of the former pair in carbonate or sulfide minerals, versus acid-insoluble petcoke particles for the latter couple. Spatial variations in the reactivity of TEs most likely reflect the range in diversity and chemical stability of dust particles, and variations in their abundance in primary source areas. The leaching conditions employed here are extreme (pH < 1) and intended to identify an upper limit of chemical reactivity, with far less dust dissolution expected when these dusts encounter natural waters of the area which range in pH from 4 to 8.

Moss-associated diatoms from Malaysian montane cloud forest with a description of two new species

Although tropical montane cloud forests (TMCFs) occupy less than half of a percent of the Earth’s land surface, they are the most species-rich and species-dense ecosystems worldwide. Despite numerous studies on various organisms in this environment, diatoms remain a group that is practically unknown. Our work focused on samples of terrestrial bryophytes collected from various substrata at a single site in the Malaysian cloud forest. Despite originating from only one site, the samples contained a high diversity of diatom species and represented a wide range in pH (3.6–6.3). In our study, 62 diatom taxa were observed (8–24 per sample), of which 19 could not be identified with certainty, and were referred to established taxa of similar morphology (as cf. or aff.). Among these however, two species are described as new on the basis of their unique valve morphology: Geissleria bryophila sp. nov. and Eunotia brinchangiana sp. nov.

A baseline assessment of coastal pH variability in a temperate South African embayment: implications for biological ocean acidification research

Compared with the open ocean, knowledge of pH variability in coastal waters is rudimentary, especially in Africa. This is concerning as quantifying local pH conditions is critical when assessing the response of coastal species to future ocean acidification scenarios. The objective of this study was to capture some of the variability in pH at scales and sites relevant to coastal marine organisms in a South African temperate embayment (Algoa Bay, Indian Ocean). We used a sampling approach that captured spatial (at a resolution of ∼10 km), monthly and diel (24-hour) variability in pH and associated physical and biological parameters at offshore and shallow inshore sites in Algoa Bay. We found that pH and associated parameters (temperature, calculated pCO2, chlorophyll a) varied over space and time in Algoa Bay. The range in pH was 0.30 units at offshore sites and 0.46 at inshore sites, and the average pH was 8.10 (SD 0.06) and 8.10 (SD 0.13) at these sites, respectively, which is typical for coastal environments. Our results showed that both biological factors (at the offshore sites) and salinity (at the inshore sites) may influence temporal and spatial variability in pH. We also identified a shallow inshore site with high levels of macroalgal growth that had consistently higher average daytime pH levels (8.33 [SD 0.07]), which may serve as an ocean acidification refuge for coastal marine species. This is the first comprehensive pH-monitoring study to be implemented in a nearshore coastal area in Africa and provides recommendations for monitoring in other understudied regions.

COOH-Terminated Silicon Quantum Dots as a Highly Efficient Drug Nanocarrier for Targeted Tumor Cell Imaging.

Fluorescent silicon quantum dots (SiQDs) characterized by exceptional photostability and colloidal robustness as well as beneficial biocompatibility are fast becoming new pharmaceutical nanocarriers. With a view to efficiently loading cisplatin (CDDP) onto SiQDs, carboxylate group (COOH) terminated SiQDs were imperative because of chelate formation with CDDP. In this work, we employed a facial microwave irradiation route for rapidly synthesizing high-quality COOH-SiQDs through the use of 3-aminopropyl trimethoxy silane (APTMS) molecules to fulfil the role of silicon precursor and maleic acid (MA) as the agent for facilitating reduction. The SiQDs showed blue fluorescence with an associated photoluminescence quantum yield (PLQY) of 40.2%, the size of which was small at 3.2 ±0.6 nm, and long-lasting stability (an extensive range in pH (4-12) and concentrations of electrolytes reaching 3 Molarity of a solution of sodium chloride). As nanocarriers, carboxylic acids chelation generated a high loading of CDDP onto SiQDs (drug loading capacity, DLC up to 32.2% at pH = 9) and a drug release of CDDP up to 57.6% at pH = 5. Furthermore, the MTT assays demonstrated the non or low cytotoxicity of SiQDs and the role of the controlled release of SiQD-CDDP Finally, the prepared SiQD-CDDP were used for cell imaging, and further targeted labeling of some tumors after folic acid (FA) conjugation. These characteristics allow for the deployment of SiQDs as a highly efficient nanocarrier that facilitate the delivery of clinical drugs for the future.

Concurrence of negative in-plane piezoelectricity and photocatalytic properties in 2D ScAgP2S6 monolayers

Apart from poly(vinylidene fluoride) and its copolymers, 2D multilayered CuInP2S6 (CIPS) is experimentally known to show negative out-of-plane piezoelectric coefficient (d 33) [2019 Sci. Adv. 5 1–10], which is attributable to weak interlayer van der Waals binding. However, CIPS monolayers exhibit positive in-plane piezoelectricity (d 11) [Phys. Status Solidi RRL, 14 2000321], as per DFT calculations. We ascribe it to strong in-plane interatomic bonding. Weakening of the in-plane interatomic bonding may even induce a negative in-plane piezoelectric coefficient, which is exceptionally rare, as observed in this work based on DFT calculations. Much smaller in-plane elastic constants found in ScAgP2S6 monolayers relative to that in CIPS monolayers indicate much weaker in-plane interatomic bonding, which induces negative in-plane piezoelectric coefficient, d 22 = −2.81 pm V−1, in ScAgP2S6 monolayers. In addition to its all-around stability, ScAgP2S6 monolayer is a semiconducting showing a bandgap of 2.04 eV, thereby making it suitable for electronics and solar energy harvesting. Upon the application of 4% biaxial strain on this flexible and stretchable 2D material, d 22 has been found to be drastically increased to −591 pm V−1. The factors causing such an enhancement in d 22 have been ascertained through the maximum rise in the Born effective charges and maximum drop in the elastic constants. With the further drop in elastic constants relative to ScAgP2S6 monolayer, d 22 reaches −3.45 pm V−1 and −13.48 pm V−1 in ScAgP2Se6 and ScAgP2Te6 monolayers respectively. 2D ScAgP2S6 monolayer is found to be a promising photocatalyst as well, since its band edges straddle the water redox potential over the entire range in pH (0–14), in addition to having a high absorption coefficient (≈105 cm−1) in the visible region. It is understood that 2D ScAgP2S6 will substantially expand the scope for its applications in piezoelectricity and visible light harvesting at the nanoscale.

Controls on soil microbial carbon use efficiency over long-term ecosystem development

Carbon use efficiency—the proportion of substrate carbon that is converted to microbial biomass—is an important control on many ecosystem properties including carbon sequestration and nutrient cycling. Although CUE varies widely across terrestrial ecosystems, a coherent understanding of edaphic controls on CUE is lacking, thereby limiting the accuracy of global carbon models. The objective of this study was to determine how microbial CUE changes with long-term soil development and nutrient availability. Soil was collected across the chronosequence and fertility gradient at Jug Handle State Natural Reserve (the “Ecological Staircase”) in Mendocino County, CA. These soils exhibit a range in pH (3.29–6.59), litter quantity and quality (litter C:N, 32–70), and clay content (14.13–87.30%), while other factors such as modern-day climate, potential biota, and parent material are common to all sites. CUE varied significantly with soil and ecosystem development; the relationship was unimodal over geological time with CUE peaking at intermediate aged soils. Soil organic matter (SOM) content and pH were the most important variables each accounting for 30% of the variation in CUE across sites. Soil pH had a quadratic relationship with CUE, peaking at pH 4.7. Litter carbon to phosphorus (C:P) and nitrogen to phosphorus (N:P) ratios were also significant factors (Pearson’s r = 0.57 and 0.39 respectively). These results demonstrate that CUE changes in complex ways with soil fertility and long-term ecosystem development, and that edaphic factors such as SOM, pH, and litter quality need to be taken into account when predicting CUE for a given system.

Ipomoea aquatica roots as environmentally friendly and green adsorbent for efficient removal of Auramine O dye

This study presents Ipomoea aquatica root (“kangkong” root or KR) as a plausible environmentally friendly adsorbent. This readily available adsorbent, after oven drying, demonstrates strong adsorption characteristics toward Auramine O (AO) dye exhibiting 2.0 h equilibration time and stable efficiency within a sufficiently broad range in both pH and ionic strength. Adsorption kinetics was best described by the pseudo second order and Elovich models, indicating that chemisorption of two reactive moieties could be involved. Application of the experimentally obtained adsorption equilibrium data to investigate the conformity among many adsorption isotherm models, namely Langmuir, Freundlich, Temkin, Redlich-Peterson and Sips, together with corresponding error analyses, identified that the Sips model be the best-fit model, leading to attractive maximum adsorption capacity of 455.74 mg g−1. Further, regeneration and reuse of the spent adsorbent would be possible with ~ 75% AO dye being adsorbed even at the 5th cycle, when using base treatment. Hence, the utilization of Ipomoea aquatica root as a low-cost, effective adsorbent in wastewater treatment could be possible.

Assessment of pH dependent errors in spectrophotometric pH measurements of seawater

A recent analysis of full water column hydrographic data revealed a pH-dependent discrepancy between spectrophotometrically measured pH using purified meta-cresol purple and pH calculated from dissolved inorganic carbon (DIC) and total alkalinity (TA). The discrepancy (pHspec – pHTA,DIC) is approximately −0.018 and 0.014 at pH 7.4 and 8.2, respectively. This discrepancy has a wide range of implications for marine inorganic carbon measurements, such as establishing robust calibration protocols for pH sensors operating on profiling floats. Here, we conducted a series of lab based experiments to assess the magnitude of pH-dependent errors for spectrophotometric pH measurements in seawater by directly comparing its performance to pH measured by an Ion Sensitive Field Effect Transistor (ISFET) pH sensor known to have Nernstian behavior. Natural seawater was titrated with high CO2 seawater while simultaneously measuring pH using spectrophotometry and an ISFET sensor over a large range in pH (7–8.5) and temperature (5–30 °C). The two pH measurements were consistent to better than ±0.003 (range) at all temperatures except at 5 and 10 °C and very low and high pH, where discrepancies were as large as ±0.005. These results demonstrate that pH-dependent errors in spectrophotometric pH measurements can be rejected as the cause of the pH-dependent discrepancy between pHspec and pHTA,DIC. The cause of this discrepancy is thus likely due to our incomplete understanding of the marine inorganic carbon model that could include errors in thermodynamic constants, concentrations of major ions in seawater, systematic biases in measurements of TA or DIC, or contributions of organic compounds that are not accounted for in the definition of total alkalinity. This should be a research priority for the inorganic carbon community.

Fabrication of Tetra-Substituted Copper(II) Phthalocyanine-Graphene Modified Pencil Graphite Electrode for Amperometric Detection of Hydrogen Peroxide

In this study, tetra-substituted copper(II) phthalocyanine-graphene modified pencil graphite electrode (CuPc-Gr/PGE) was developed for the amperometric determination of hydrogen peroxide (H2O2) for the first time in the literature. The developed non-enzymatic electrode platform was electrochemically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods were also used for surface characterization of the modified electrode. The response to H2O2 at the working potential of −0.4 V is linear in the 0.1 μM to 100 μM concentration range in PBS pH 7.0. The limit of detection (LOD) and limit of quantitation (LOQ) are 0.045 and 0.15 μM, respectively. Good selectivity was observed within physiological interference species such as ascorbic acid, dopamine, uric acid, and glucose. Additionally, amount of H2O2 was determined using the novel produced non-enzymatic sensor with satisfactory results in beverage samples. These consequences imply that the CuPc-Gr/PGE displays effective electrocatalytic activity for the reduction of H2O2, indicating it has capability use for the detection of H2O2.

A novel PARAFAC model for continental hot springs reveals unique dissolved organic carbon compositions

Dissolved organic carbon in hot springs reflects a range of sources and biogeochemical processes. We evaluated ~200 continental hot spring samples, with a range in pH and temperature, collected from the Tengchong hydrothermal region, Yunnan Province, China and Yellowstone National Park, Wyoming, USA. Dissolved organic carbon concentrations ranged from 16.7 µM to 2.97 mM. Acidic springs displayed the highest values and widest range in carbon concentration. Alkaline springs had a narrower range and lower average concentrations. Carbon composition was evaluated using ultraviolet absorption and 3D-fluorescence spectroscopy. Total fluorescence was correlated (p < 0.05) with dissolved organic carbon (DOC) concentration. Fluorescence excitation-emission matrices were deconvolved using parallel factor analysis. We validated a five-component model that represented >97% of the total fluorescence. Our model includes three humic-like components, one protein-like component, and one novel component exclusively observed in highly acidic springs. The closest spectral match to the novel component is an acid-soluble lignin produced during high-temperature, acid digestion of wood pulp. Humic-like components were dominant in mid-pH springs (4 < pH < 7) indicating these springs had greater terrestrial carbon input. Acidic springs also exhibited evidence for terrestrial carbon input. Alkaline springs, in contrast, consistently had low dissolved organic carbon content and low fluorescence intensity suggesting that these springs had little terrestrial input. This absence of terrestrial carbon implies a predominantly hydrothermal fluid source. A comparison of the traditional fluorescence indices with our five model components suggest that these indices may have limited utility in continental hot springs with multiple organic matter sources and alteration processes.

Nutritional and functional properties of durum wheat bran protein concentrate

AbstractBackground and objectivesPlant industrial by‐products are relatively low cost and rich in organic material. Although these by‐products are a good source of various nutritional compounds, they represent the main disposal problem for the food industry. Wheat bran, one of the main by‐products of the wheat milling industry, contains more than 15% high‐quality proteins. However, these proteins are present in a form which is poorly digested as they are enclosed within a matrix of cell wall polysaccharides. About 15.5 million tonnes of usable protein could be recovered from bran if a commercial extraction process can be made viable. The purpose of this work was to extract protein from durum wheat bran using an alkaline acid method to study its nutritional and functional properties with the goal of using it as a fortifying material in cereal‐based foods such as pasta and bread.FindingsDurum wheat bran protein concentrate (WBPC) was prepared by using an alkaline extraction method (pH 9.5 for two hours) followed by isoelectric precipitation (pH 4.2). Chemical, nutritional, and functional properties of WBPC were obtained. WBPC had a protein content of ~61% (protein yield 20.5%–24.8%), containing also lipids, fiber, and small quantities of starch. WBPC was enriched in phytosterols compared to wheat bran (11.59 vs. 5.14 mg/g) with β‐sitosterol the predominant (4.37 mg/g). WBPC was also enriched in all the amino acids compared to bran, especially lysine and threonine. WBPC retained some phenolic acids, but at an eightfold lower quantity than in bran and retained about half the antioxidant activity (DPPH) of bran. WBPC showed excellent functional properties in terms of high solubility over a wide range in pH and good water and fat absorption capacity. The main protein components were albumin and globulin proteins.ConclusionThe extraction method used produced a protein concentrate in reasonable yield with high protein content enriched in essential amino acids and phytosterols compared to wheat bran with good functional properties and phenolic acids and antioxidant potential.Significance and noveltyThe nutritional and functional properties of WBPC make it a promising ingredient for various food products such as cereal and baked foods, processed meat, and beverages.

The effects of ultimate pH and color on sensory traits of pork loin chops cooked to a medium-rare degree of doneness.

The objective was to determine the effects of pH and color on sensory characteristics of boneless pork loin chops cooked to an internal endpoint temperature of 63 °C. Center cut loins (296 total) from barrows and gilts, 5 different sire lines, and a range in pH of 5.36 through 6.23 were used. Previously, ultimate pH was correlated with sensory characteristics of chops cooked to a medium (71 °C) degree of doneness. Additionally, increasing ultimate pH improved sensory tenderness and juiciness of loin chops cooked to a medium degree of doneness. However, in 2011, the United States Department of Agriculture Food Safety and Inspection Service reduced the recommended final internal cooking temperature of pork chops from 71 to 63 °C (followed by a 3-min rest). The effects of ultimate pH on sensory traits of pork chops cooked to a medium-rare (63 °C) degree of doneness are not known. Therefore, loins were categorized using historical categories based on ultimate pH: >5.95, n = 22; 5.80 to 5.95, n = 75; 5.65 to 5.80, n = 102; 5.50 to 5.65, n = 91; <5.50, n= 6. On 1-d postmortem, loins were evaluated for CIE instrumental L*, a*, b*, visual color, marbling, and subjective firmness. Then, loins were aged in vacuum packages at 4 °C until 16-d postmortem. After aging, loins were cut into 2.54-cm thick chops, vacuum-packaged, and frozen until sensory or instrumental tenderness analysis. One chop was also used to determine extractable lipid. Chops were weighed, cooked to 63 °C, cooled to approximately 23 °C, weighed again to determine cook loss, and then evaluated for Warner-Bratzler shear force. Another chop was cooked to 63 °C internal temperature and served warm to trained panelists to determine sensory traits. Coefficients of determination (R2) were calculated to determine the predictability of ultimate pH and instrumental color on sensory tenderness, juiciness, and flavor. A 1-way ANOVA and means separation test were used to determine specific differences among pH categories. Ultimate pH explained less than 5% of the variation in tenderness and less than 1% of the variation in juiciness or flavor. Furthermore, sensory tenderness did not differ (P > 0.05) among pH categories, except for chops with an ultimate pH > 5.95. Chops with a pH > 5.95 were at least 9.1% more tender (P < 0.05) than chops with a pH < 5.95. Visual and instrumental color were not predictive (R2 ≤ 0.03) of any sensory traits. Overall, pH does not influence sensory traits of pork chops cooked to medium-rare degree of doneness unless pH is at least 5.95.

Effects of seawater acidification on the early development of sea urchin Glyptocidaris crenularis

In this study, we evaluated the effects of CO2-induced seawater acidification on fertilization, embryogenesis and early larval development in the sea urchin Glyptocidaris crenularis, that inhabits subtidal coastal areas in northern China. The range in seawater pH used in experiments was based on the projections of the Intergovernmental Panel on Climate Change (IPCC), to the year 2100. A natural seawater treatment (pHnbs =7.98±0.03) and three laboratory-controlled acidified treatments (OA1, ΔpH nbs =-0.3 units; OA2, ΔpHnbs =-0.4 units; OA3, ΔpHnbs=-0.5 units) were used in experiments. Results show that: (1) there was a negative effect of seawater acidification on fertilization and on the percentage of abnormal fertilized eggs; (2) the size of early cleavage stage embryos decreased in a dose-dependent manner with decreasing pH; (3) both the hatching rate of blastulae and the survival rate of four-armed pluteus larvae decreased as pH declined; (4) larval abnormalities including asymmetrical development, changes in the length of skeletal elements, and corr oded spicules were observed in all seawater acidified-treatments compared with the control. These data indicate that seawater acidification has a negative impact on the early development of G. crenularis, and supports the hypothesis that the response of echinoderms to ocean acidification (OA) varies among species. Further research is required to clarify the specific cellular mechanisms involved.

Arsenic(Ⅴ) Removal by Granular Adsorbents Made from Backwashing Residuals from Biofilters for Iron and Manganese Removal

Granular adsorbents for arsenic removal (GA) made from the backwashing residuals from iron and manganese removal biofilters for groundwater were characterized and examined as an arsenate sorbent. The GA were characterized by SEM-EDS microscopy, X-ray diffraction (XRD), and BET surface area measurement. The results showed that the GA had rough surfaces, developed pores, and were mainly amorphous, with small fractions of crystalline quartz and hematite. The surface area of the GA, which consists of many mesopores, was 43.8 m2·g-1. The kinetic studies revealed that arsenate adsorption on the GA was described by a pseudo-second-order kinetic equation, and the Freundlich isotherm equation fit the arsenate adsorption well (R2=0.994). The maximum adsorption capacity calculated by the Langmuir isotherm equation for As(Ⅴ) was 5.05 mg·g-1. Further studies showed that the GA operated well for As(Ⅴ) removal over a broad range in pH from 1.1 to 9.5. The coexistence of HCO3- and SO42- had no great influence on arsenic adsorption, while the H2PO4- and SiO32- showed negative effects. The GA can be regenerated well, and 82% of the original adsorption capacity was maintained after three regeneration cycles.

Tropical tree species traits drive soil cation dynamics via effects on pH: a proposed conceptual framework

AbstractHumid tropical forests are major players in the global carbon cycle, despite evidence that cations (rock‐derived, positively charged ions) can limit or co‐limit net primary productivity (NPP). In mature forests, tight cation cycling, i.e., without leaching losses, could maintain cation stocks on site. That mechanism does not explain how regenerating tropical secondary forest trees start from seeds and accrue large cation stocks in biomass, when growing on soils depleted in available cations. We propose a new mechanism that links tree species’ traits to soil cation availability via impacts on soil pH, a master biogeochemical driver. We tested plot‐level effects of tree species on soil pH, soil extractable cations, and cation accrual in biomass in a unique, 25‐yr‐old, randomized‐complete‐block experiment in which climate, soil, and previous land‐use history were similar across four native tree species grown in mono‐dominant plantations in Costa Rica. Surface‐soil pH in this Oxisol, initially 4.52 ± 0.02 (mean ± SE (standard error)), declined to 4.14 ± 0.02 under Pentaclethra macroloba, a nodulated legume, and increased to 4.71 ± 0.08 under Vochysia guatemalensis, an aluminum (Al) accumulator. The range in pH corresponds to a five‐fold difference in proton concentrations, which is sufficient to alter dispersion of organo‐mineral colloids. Cation stocks in biomass differed across species by 1.7‐, 1.9‐, 2.8‐, 2.9‐, 3.1‐, 3.5‐, and 17.2‐fold for iron (Fe), calcium (Ca), potassium (K), manganese (Mn), strontium (Sr), magnesium (Mg), and Al, respectively. Differential acquisition of available soil cations was an unlikely explanation for measured differences among species because changes in extractable soil cation stocks were unrelated to cation accrual in biomass. Soil pH and biomass cation stocks were highly correlated, however. By our proposed conceptual framework, species traits that strongly increase proton concentrations and decrease pH in soil, e.g., support of N fixation, increase colloid aggregation, reducing cation availability. Traits that reduce soil protons and increase pH, e.g., Al+3 accumulation, disperse colloids, thereby releasing cations occluded during pedogenesis. This highlights a novel biogeochemical role for the Al‐accumulation trait, i.e., liberation of occluded soil cations. Further studies would clarify effects of soil pH on cation supply via colloid dispersion, and its importance for nutrient acquisition in cation‐depleted soils.

Calcification responses to diurnal variation in seawater carbonate chemistry by the coral Acropora formosa

Significant diurnal variation in seawater carbonate chemistry occurs naturally in many coral reef environments, yet little is known of its effect on coral calcification. Laboratory studies on the response of corals to ocean acidification have manipulated the carbonate chemistry of experimental seawater to compare calcification rate changes under present-day and predicted future mean pH/Ωarag conditions. These experiments, however, have focused exclusively on differences in mean chemistry and have not considered diurnal variation. The aim of this study was to compare calcification responses of branching coral Acropora formosa under conditions with and without diurnal variation in seawater carbonate chemistry. To achieve this aim, we explored (1) a method to recreate natural diurnal variation in a laboratory experiment using the biological activities of a coral-reef mesocosm, and (2) a multi-laser 3D scanning method to accurately measure coral surface areas, essential to normalize their calcification rates. We present a cost- and time-efficient method of coral surface area estimation that is reproducible within 2% of the mean of triplicate measurements. Calcification rates were compared among corals subjected to a diurnal range in pH (total scale) from 7.8 to 8.2, relative to those at constant pH values of 7.8, 8.0 or 8.2. Mean calcification rates of the corals at the pH 7.8–8.2 (diurnal variation) treatment were not statistically different from the pH 8.2 treatment and were 34% higher than the pH 8.0 treatment despite similar mean seawater pH and Ωarag. Our results suggest that calcification of adult coral colonies may benefit from diurnal variation in seawater carbonate chemistry. Experiments that compare calcification rates at different constant pH without considering diurnal variation may have limitations.

High temperature ultralow water content carbon dioxide-in-water foam stabilized with viscoelastic zwitterionic surfactants

Ultralow water content carbon dioxide-in-water (C/W) foams with gas phase volume fractions (ϕ) above 0.95 (that is <0.05 water) tend to be inherently unstable given that the large capillary pressures that cause the lamellar films to thin. Herein, we demonstrate that these C/W foams may be stabilized with viscoelastic aqueous phases formed with a single zwitterionic surfactant at a concentration of only 1% (w/v) in DI water and over a wide range of salinity. Moreover, they are stable with a foam quality ϕ up to 0.98 even for temperatures up to 120°C. The properties of aqueous viscoelastic solutions and foams containing these solutions are examined for a series of zwitterionic amidopropylcarbobetaines, R-ONHC3H6N(CH3)2CH2CO2, where R is varied from C12–14 (coco) to C18 (oleyl) to C22 (erucyl). For the surfactants with long C18 and C22 tails, the relaxation times from complex rheology indicate the presence of viscoelastic wormlike micelles over a wide range in salinity and pH, given the high surfactant packing fraction. The apparent viscosities of these ultralow water content foams reached more than 120cP with stabilities more than 30-fold over those for foams formed with the non-viscoelastic C12–14 surfactant. At 90°C, the foam morphology was composed of ∼35μm diameter bubbles with a polyhedral texture. The apparent foam viscosity typically increased with ϕ and then dropped at ϕ values higher than 0.95–0.98. The Ostwald ripening rate was slower for foams with viscoelastic versus non-viscoelastic lamellae as shown by optical microscopy, as a consequence of slower lamellar drainage rates. The ability to achieve high stabilities for ultralow water content C/W foams over a wide temperature range is of interest in various technologies including polymer and materials science, CO2 enhanced oil recovery, CO2 sequestration (by greater control of the CO2 flow patterns), and possibly even hydraulic fracturing with minimal use of water to reduce the requirements for wastewater disposal.

Adsorption of Antimonate by Gibbsite: Reversibility and the Competitive Effects of Phosphate and Sulfate

Core Ideas Antimonate adsorption by gibbsite is pH and ionic‐strength dependent. Antimonate adsorption is reversible in alkaline but hysteretic in acidic systems. Adsorbed Sb(V) generates a downward shift in the gibbsite isoelectric point. Both phosphate and sulfate decrease adsorbed Sb(V) concentrations. The triple‐layer model predicts Sb(V) adsorption using inner and outer sphere surface complexes. Antimony (Sb) is a potential environmental contaminant of emerging concern that occurs in soils in the Sb(V) oxidation state as the antimonate species Sb(OH)6−. In soils, metal oxyhydroxides play an important role in the immobilization of contaminants and in restricting bioaccessibility. One such mineral is gibbsite, which bears the reactive aluminol surface functional group. Both inner‐ and outer‐sphere surface complexation mechanisms have been inferred from conflicting Sb(V) adsorption findings involving aluminol‐bearing minerals. The objectives of this research are to characterize Sb(V) adsorption by gibbsite and to use the macroscopic findings to develop mechanistic adsorption models. Antimonate adsorption envelopes were developed using two equilibrium techniques: continuous pH titration and batch. The adsorption of Sb(V) decreases with increasing pH and increasing ionic strength, suggesting that outer‐sphere surface complexation is an important adsorption mechanism. However, Sb(V) retention is irreversible at pH &lt;6 but is reversible in pH &gt;7 systems, suggesting that inner‐sphere species may be significant in acidic environments. Adsorbed Sb(V) also generates a downward shift in the gibbsite isoelectric point, further supporting the formation of inner‐sphere Sb(V) surface complexes. Both PO4 and SO4 decrease adsorbed Sb(V) concentrations: PO4 throughout the pH 3 to 10 range and SO4 in pH &lt;7 systems. The triple‐layer surface complexation model successfully predicts Sb(V) adsorption by using both outer‐sphere and inner‐sphere surface species. The triple‐layer model also predicts ligand adsorption in the competitive systems without the need for reoptimization.

Interactions between soil pH, wood heavy metal content and fungal decay at Norway spruce stands

The incidence of conifer wood decay caused by pathogenic white-rot-fungi in the genus Heterobasidion increases along with increase in soil pH. To clarify factors that influence this relationship, 36 Norway spruce stands that represent a wide range in soil pH and calcium content were surveyed for frequency of H. parviporum caused decay and soil type specific differences in wood composition and fungal growth. Significantly higher concentrations of biotoxic metals were recorded for wood from soils with pH below 4.6 compared to less acidic soils. This finding is coherent with the observed generally higher oxalate concentration in decaying wood in the more acidic stands, as wood decay fungi secrete oxalic acid to detoxify excess metals. The performed in vitro inoculation experiment of wood provided no conclusive evidence that H. parviporum strains from different soil types differ in oxalate production. Further field experiments are warranted to test a hypothesis now raised: soil type—specific differences in accumulation of toxic metals in wood influence wood decomposition rate and fungal spread within and between trees, and thereby also stand decay frequency.

Microbial biomass, fungal and bacterial residues, and their relationships to the soil organic matter C/N/P/S ratios

The interrelations between the microbial biomass, total N, organic P, and organic S in the accumulation of soil organic C (SOC) and the contribution of fungal and bacterial residues to SOC, based on amino sugar data, were investigated in the current study. The soils had been developed under humid temperate, arid sub-tropical, and tropical climatic conditions and were used as arable, grass, and forest land. They covered a wide range in soil pH, in salinity as well as in the contents of clay and SOC. An increased microbial biomass C/N ratio due to nutrient limitation is not reflected by any increase in SOM elemental C/N/P/S ratio within the total nutrient pool or within the organic fraction. Increased SOC/total N and SOC/organic S ratios reduced the contribution of microbial biomass C to SOC, whereas neutral soil pH and high clay contents had positive effects. An increased formation of microbial biomass C also enlarged the contribution of microbial residue C to SOC, which accounted on average for 48% SOC in the neutral arable and moderate acidic grassland soils and for 30% in the saline arable and strongly acidic forest soils. The fungal C to bacterial C ratio increased with increasing acidity from 0.9 in the saline arable soils to 4.5 in the strongly acidic forest soils. Consequently, the relationship of the fungal C to bacterial C ratio was not simply related to the contribution of microbial residues to SOC. The lower the ergosterol to fungal GlcN ratio, the higher the contribution of microbial residues to SOC. This means the higher the contribution of arbuscular mycorrhizal fungi and the lower the contribution of saprotrophic fungi to the microbial community, the more fungal residues can be sequestered to SOC.