Acid Neutralizing Capacity Research Articles

Formulation, optimization, and evaluation of raft-forming formulations containing Nizatidine

Objective: The main objective of this research is to formulate, optimize, and evaluate raft-forming chewable tablets of Nizatidine. Various raft-forming agents were used in preliminary screening. Sodium alginate showed maximum raft strength, so tablets were prepared using sodium alginate as the raft forming agent, along with calcium carbonate (CaCO3) as antacid and raft strengthening agent, and sodium bicarbonate (NaHCO3) as a gas generating agent.Research design and methods: Raft forming chewable tablets containing Nizatidine were prepared by direct compression and wet granulation methods, and evaluated for drug content, acid neutralization capacity, raft strength, and in-vitro drug release in 0.1 N HCl. Box–Behnken design was used for optimization.Results: Two optimized formulations were predicted from the design space. The first optimized recommended concentrations of the independent variables were predicted to be X1 = 275.92 mg, X2 = 28.60 mg, and X3 = 202.14 mg for direct compression technique and the second optimized recommended concentrations were predicted to be X1 = 253.62 mg, X2 = 24.60 mg, and X3 = 201.77 mg for wet granulation technique. Optimized formulations were stable at accelerated environmental testing for six months at 35 °C and 45 °C with 75% relative humidity. X-Ray showed that the raft floated immediately after ingestion and remained intact for ∼3 h.Conclusion: Raft was successfully formed and optimized. Upon chewing tablets, a raft is formed on stomach content. That results in rapid relief of acid burning symptoms and delivering the drug into systemic circulation with enhanced bioavailability.

Physical, chemical, and surface charge properties of bauxite residue derived from a combined process

A detailed understanding of the composition, buffering capacity, surface charge property, and metals leaching behavior of bauxite residue is the key to improved management, both in reducing the environmental impact and using the material as an industrial by-product for other applications. In this study, physical, chemical, and surface charge properties of bauxite residue derived from a combined process were investigated. Results indicated that the main alkaline solids in bauxite residue were katoite, sodalite, and calcite. These minerals also lead to a higher acid neutralizing capacity of bauxite residue. Acid neutralizing capacity (ANC) to pH 7.0 of this residue is about 0.9 mol H+/kg solid. Meanwhile, the Fe-, Al-, and Si-containing minerals in bauxite residue resulted in an active surface; The isoelectric point (IEP) and point of zero charge (PZC) were 7.88 and 7.65, respectively. This also leads to a fact that most of the metals in bauxite residue were adsorbed by these surface charged solids, which makes the metals not readily move under natural or even moderately acidic conditions. The leaching behavior of metals as a function of pH indicated that the metals in bauxite residue present low release concentrations (pH > 3).

Stream geochemical response to reductions in acid deposition in headwater streams: Chronic versus episodic acidification recovery

AbstractIn the decades since dramatic reductions in acid emissions and subsequent deposition in North America and Europe, the vast majority of research on aquatic chemical recovery has focused on trends in acid–base concentrations during baseflow conditions. Missing from such assessments is consideration of higher flow periods, when flow paths and chemical concentrations change and episodic acidification may occur. Stream samples collected weekly and bi‐hourly during high‐flow storm events from 1992 to 2015 at three watersheds representing a gradient in response to acid deposition in the south‐eastern United States were used to evaluate temporal trends in acid anions, base cations, acid neutralizing capacity (ANC), and pH for each of five distinct flow exceedance regimes, as well as trends in concentration–discharge (C–Q) relationships. For the most well‐buffered watershed (mean ANC = 220 μeq L−1), ANC and pH increased at a similar rate for baseflow and storm flow conditions. Decreases in sulfate controlled ANC trends at higher flows, whereas smaller sulfate decreases in combination with base cation increases resulted in similar ANC improvements for low‐flow periods. For the most acid sensitive watershed (mean ANC = 10 μeq L−1), no trends in ANC or pH were observed for the lowest flows (>90% flow exceedance), whereas reductions in sulfate resulted in significant increases in ANC during higher flow conditions. At all sites, greater rates of sulfate decline during high‐flow, as compared with low‐flow, conditions are likely a result of a reduced capacity of near surface soils to adsorb and retain sulfur in these non‐glaciated watersheds. Overall, consistent increases in pH (~0.01–0.02 pH units year−1) during higher flow conditions (<10% flow exceedance) in contrast to the variable trends observed during lower flows (>50% flow exceedance) illustrate that episodic acidification is recovering at an equal or greater rate than chronic acidification in these watersheds.

RANITIDINE CONTROLLED RELEASE ANTI-REFLUX SUSPENSION FOR GASTRO-OESOPHAGEAL REFLUX DISEASE AND IT’S IN VITRO EVALUATION

Objective: The aim of this work was to develop triple action controlled release anti-reflux suspension of ranitidine and its in-vitro evaluation of anti-reflux and controlled release properties.Methods: The formulation was optimized using sodium alginate as a gelling agent along with calcium carbonate, sodium bicarbonate, magnesium hydroxide, aluminium hydroxide as alkalizing agents and colloidal microcrystalline cellulose (MCC) as a suspending agent at various concentrations and arrived at an optimized formulation for its best quality attributes. To avoid initial release in water before administration, ranitidine coated MCC sphere was incorporated into powder formulation and subjected to in vitro characteristics like raft strength, acid neutralizing capacity, pH, viscosity and dissolution study. The obtained results were assessed using Minitab 17 statistical software to conclude the study design.Results: Formulation containing 300 mg of ranitidine along with 750 mg alginate has shown better anti-reflux characteristics like raft strength 18±2g, acid neutralizing capacity 17±1 mEq compared to other formulations. This formulation has also shows zero-order controlled release in the simulated gastric fluid (SGF) up to 10 h compared to the formulation without alginate. Further, to this optimized formulation has shown negligible change in the assay of ranitidine even after 3 mo at 40 °C temperature and 75% RH.Conclusion: The developed stable sustained release powder for suspension has the combined therapeutic efficacy as an antacid and anti-reflux drug suitable for the management and treatment of gastro-oesophageal reflux disease (GERD) unlike the existing drugs possessing only reflux resistance action.

Probabilistic relations between acid–base chemistry and fish assemblages in streams of the western Adirondack Mountains, New York, USA

Surface waters across much of New York’s Adirondack Mountains were acidified in the late 20th century but began to recover following the 1990 amendments to the Clean Air Act. Little data, however, are available to characterize biological impacts and predict recovery of fish assemblages in streams of the region. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014–2016 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different nitrogen (N) and sulfur (S) deposition loads may affect future fish assemblages. Models for inorganic monomeric aluminum (Ali) and richness ≥1 species and for acid neutralizing capacity (ANC) and total density >400 fish/0.1 ha, total biomass >1500 g/0.1 ha, brook trout (Salvelinus fontinalis) density >0 or >200 fish/0.1 ha, and brook trout biomass >1000 g/0.1 ha were suitable for evaluating community and population responses to changes in acid–base chemistry. Anticipated changes in national (US) secondary standards for atmospheric emissions of nitrogen oxides (NOx) and sulfur oxides (SOx) to achieve target N and S deposition loads will alter acid–base chemistry and the probabilities for observing various levels of fish metrics in streams across the region and elsewhere.

Treatment of the acidic effluent from a copper smelter by flotation tailings

Since commissioning in 1961, the copper mine Majdanpek, a part of the Mining and Smelting Complex Bor (RTB Bor), produced approximately 378 million tons of flotation tailings. Semi-quantitative mineralogical analysis of the flotation tailings revealed significant content of carbonate minerals (approximately 20-25 %), indicating high acid neutralization capacity. Also, approximately 70 % of copper is in the form of the oxide mineral cuprite (Cu2O). Copper can be easily leached from cuprite by using sulphuric acid. The RTB Bor copper smelter generates 8.7 m3h-1 of extremely acidic waste effluent (142.4 kgm-3 of sulphuric acid, pH -0.464) with relatively high concentrations of dissolved metals and metalloids (Cu, Fe, Zn, Pb and As). The effluent is currently treated with hydrated lime. The present study focused on application of flotation tailings as a neutralizing agent for acidic effluents. Laboratory experiments followed by computer simulation of the industrial process showed that 99% of the acid can be neutralized with flotation tailings in a series of six reactors resulting in the final copper concentration of 1.55 gL-1. Benefits of the proposed process are: lower environmental impact of the process and reduced costs of neutralization of the acidic effluent from the copper smelter.

Two placebo-controlled crossover studies in healthy subjects to evaluate gastric acid neutralization by an alginate–antacid formulation (Gaviscon Double Action)

Objective: To investigate the intragastric acid neutralization activity of a combined alginate-antacid formulation. Significance: Published studies have investigated the reflux-suppressing alginate component of Gaviscon Double Action (Gaviscon DA; RB, UK) but intragastric acid neutralization activity of the antacid component has not been evaluated in vivo. Methods: Intragastric pH monitoring, using a custom-made 10-electrode catheter, was evaluated in a two-part exploratory study in healthy subjects; Part I (n = 6) tested suitability of the catheter using antacid tablets (Rennie; Bayer, Germany); Part II (n = 12) evaluated gastric acid neutralization activity of Gaviscon DA liquid (20 ml) versus placebo in fasted subjects using a randomized, open-label, crossover design. The primary endpoint was the percentage of time that intragastric pH ≥4 was measured during 30 min post-treatment. A confirmatory study of identical design was subsequently conducted (n = 20). Results: Monitoring pH using the multielectrode catheter was a viable approach, directly detecting changes in intragastric pH following a single dose of antacid tablets. In the exploratory study, the percentage of time that pH ≥4 during 30 minutes post-treatment was 46.8% with Gaviscon DA liquid versus 4.7% with placebo (p = 0.0004). These findings were supported by the confirmatory study, where pH ≥4 was recorded 50.8% of the time with Gaviscon DA versus 3.5% with placebo (p = 0.0051). In this study, Gaviscon DA was safe and well tolerated. Conclusions: These studies demonstrate the effective acid neutralizing capacity of Gaviscon DA versus placebo in healthy, fasted subjects. This adds to the evidence base for the combination of alginates and antacids. Trial registration: EU Clinical Trials Register identifier: 2014-003158-15. Trial registration: EU Clinical Trials Register identifier: 2016-000539-42.

Ettringite and monosulfate formation to reduce alkalinity in reactions of alum-based water treatment residual with steel slag

Aged steel slag has a potential use as a highly durable aggregate in roadway construction; however, its high capacity for creating alkaline leachates (pH > 12.4) poses a severe environmental risk. In batch and column leach tests, 10% alum-based water treatment residual (WTR) addition to aged steel slag resulted in a 67% decrease in acid neutralizing capacity of steel slag and leachate alkalinity, but this alkalinity mitigation effect was accompanied with markedly increases in dissolved Al concentrations in the leachates (<4.6 mM) compared to steel slag-only samples. Measurements of dissolved ions, saturation index evaluations, and results of geochemical modeling analysis indicated that ettringite and monosulfate formations were favored and that it is probably the responsible mechanism for the observed mitigation of alkalinity and Ca release under alkaline conditions.

Influence of wood ash pre-treatment on leaching behaviour, liming and fertilising potential

In Denmark, increasing amounts of woody biomass are being used for the production of renewable energy, resulting in more wood ashes being generated. While these materials have been mainly landfilled, wood ashes may also be utilised for fertilizing and liming purposes on top of soils. Pre-treatments involving hardening or granulation may be carried out prior to soil application. In this study, two Danish wood ash samples were hardened and/or granulated. Lab-hardening induced rapid changes in the shape of the acid neutralisation capacity curve of the ashes. Up-flow column tests, assuming local equilibrium conditions, were employed to investigate the leaching from pre-treated ashes. Granules and loose ashes demonstrated similar leaching behaviours, indicating that similar geochemical processes were governing their leaching. In comparison with untreated fresh ashes, the hardened ashes demonstrated reduced leaching of Ca, Ba, Pb and Zn with concentration levels generally below or close to the analytical limits of quantification; to the contrary, the leaching of As, P, Sb, Si, V and Mg was enhanced in the hardened ashes. The release of alkalinity was reduced by hardening. In general, all granules were barely breakable by finger-pinching and they could withstand one month of continuous leaching, preserving their overall shape. The solubility of phosphorous in neutral ammonium citrate indicated that about 30–51% of the total P content in the ash samples was released, suggesting that the ashes could be potentially valuable as P-fertiliser if applied onto soil.

Development and pharmacokinetic evaluation of alginate-pectin polymeric rafts forming tablets using box behnken design

Raft is an emerging drug delivery system, which is suitable for controlled release drug delivery and targeting. The present study aimed to evaluate the physico-chemical properties of raft, in vitro release of pantoprazole sodium sesquihydrate and conduct bioavailability studies. Box behnken design was used with three independent and dependent variables. Independent variables were sodium alginate (X1), pectin (X2) and hydroxypropyl methyl cellulose K100M (X3) while dependent variables were percentage drug release at 2 (Y2), 4 (Y4) and 8 h (Y8). The developed rafts were evaluated by their physical and chemical properties. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to study the chemical interaction and thermal behaviour of drug with polymers. Alginate and pectin contents of R9 formulation were 99.28% and 97.29%, respectively, and acid neutralization capacity was 8.0. R9 formulation showed longer duration of neutralization and nature of raft was absorbent. The raft of R9 formulation showed 98.94% release of PSS at 8 h in simulated gastric fluid. Fourier transform infrared spectroscopy showed no chemical interaction and differential scanning calorimetry indicated endothermic peaks at 250 °C for pantoprazole sodium sesquihydrate. tmax for the test and reference formulations were 8 ± 2.345 h and 8 ± 2.305 h, respectively. Cmax of test and reference formulations were 46.026 ± 0.567 µg/mL and 43.026 ± 0.567 µg/mL, respectively. AUC(0-t) of the test and reference formulations were 472.115 ± 3.467 µg × h/mL and 456.105 ± 2.017 µg × h/mL, respectively. Raft forming system successfully delivered the drug in controlled manner and improved the bioavailability of drugs.

Thirty‐year trends in acid deposition and neutralization in two headwater catchments, northwestern Massachusetts, USA

AbstractLong‐term decreases in acidic precursors have changed the chemistry of precipitation and streamflow in two moderately to well‐buffered, forested headwater catchments in the Taconic Range of western New England, USA. We report 30‐year geochemical trends from Birch Brook and annual and seasonal variations from Birch Brook and adjacent Ford Glen, which drain phyllitic and carbonate bedrock. Median pH of precipitation has increased irregularly since 1983, consistent with regional trends. Increases in precipitation pH and decreases in sulfate (SO42−) correspond with increasing stream pH and decreasing SO42− concentration and flux over at least the past 30 years. Calcium (Ca2+) concentration and acid‐neutralizing capacity (ANC) in Birch Brook began to increase about 2005, in contrast to geochemical indicators from some poorly buffered catchments in the NE USA. Point and longitudinal sampling over a range of flows show that Birch Brook chemistry is a mixture of upstream source waters (throughfall, soil water, and ground water) with different chemistries. Acidic precipitation and shallow soil water affect stream chemistry directly only in the upper reaches of Birch Brook and during periods of extremely high flow, such as snowmelt. Ford Glen has high ANC and is near saturation with calcite at most flows. Long‐term trends measured at Birch Brook and at other streams in western Massachusetts show that stream chemistry reflects changes in acidic deposition in upland catchments, even where ecosystem geochemistry is well buffered by bedrock composition.

Present status of water chemistry and acidification under nonpoint sources of pollution across European Russia and West Siberia

Acidic deposition has caused severe surface water acidification in Europe and North America, but surface water acidification has not been systematically studied in Russia. Here we present the first detailed study on regional surface water acidification in European Russia (ER) and Western Siberia (WS) based on a survey of 367 lakes in a transect from the tundra to the steppe, which were investigated to explore the status and mechanism of surface water acidification. The variability of water chemistry is documented and discussed. High pH and acid-neutralizing capacity (ANC) were observed for lakes in the southern region, indicating that surface water acidification does not occur here. Anthropogenic acidification occurs in the humid areas of both regions, being observed in 4.4% of ER and 8.2% of WS lakes. These tundra and taiga lakes are characterized by high transparency, low pH, and ANC with a high concentration of strong acid anions. The main factor leading to acidification in the ER lakes is sulfur emission from metal smelters whilst that in WS is acidification, likely associated with gas burning by oil production facilities. In the ER acid lakes, SO42− is dominant; this is in contrast to WS, where NO3− and Cl− are dominate. The influence of strong technogenic acids on the structure of organic components and their possibility to form a proton is discussed. The phenomenon of the increase in water acidification by organic acids and strong acids is explained. These results clearly show the effect of a number of factors that strengthen the acidity of water. Differences in the chemical composition of lakes of both regions, as well as differentiation by their acid properties, were statistically proved. Results of our research indicate the need to reduce emissions of acidic gases into the atmosphere.

Removal of Acidity and Metals from Acid Mine Drainage-Impacted Water using Industrial Byproducts

One of the biggest environmental impacts of mining is the generation of acid mine drainage (AMD). In the absence of proper post-mining management practices, AMD pollution can cause massive environmental damage. Current AMD management practices often fail to meet the expectations of cost, efficiency, and sustainability. The objective of this study was to utilize the metal-binding and acid-neutralizing capacity of an industrial by-product that is otherwise landfilled, namely drinking-water treatment residuals (WTRs), to treat AMD-water, thus offering a green remediation alternative. AMD-water was collected from Tab-Simco coal mine in Carbondale, Illinois. It was highly acidic (pH 2.27), and contaminated with metals, metalloids and sulfate at very high concentrations. A filter media, prepared using locally-generated aluminum (Al) and calcium (Ca)-based WTRs, was used to increase pH and to remove metals and [Formula: see text] from AMD-water. Laboratory-batch sorption studies at various WTRs (Al and Ca):AMD-water ratios were performed to optimize the filter media. WTRs:sand ratio of 1:6 provided optimal permeability, and 1:1 Al-WTRs:Ca-WTRs ratio was the optimal sorbent mix for removal of the metals of concern. A scaled-up study using a 55-gallon WTRs and sand-based filter was designed and tested. The results showed that the filter media removed more than 99% of the initial Fe (137 mg/L), Al (80 mg/L), Zn (11 mg/L), Pb (7 mg/L), As (4 mg/L), Mn (33 mg/L), and 44% of the initial [Formula: see text] (2481 mg/L) from Tab-Simco AMD-water. pH increased from 2.27 to 7.8. Desorption experiments showed that the metals were irreversibly bound to the WTRs and were not released back to the water.

Arctic charr (Salvelinus alpinus) re-established in a formerly acidified and highly dilute mountain lake under declining acidic deposition

Arctic charr in Lake Ronvatn, a mountain lake in southern Norway was re-established through stocking. The population went extinction during the early 1980s due to acidification, when the lake was highly acidified with a mean pH of 5.2-5.4 with occasional declines to 4.3-4.7. However, from the mid to late 1990s, the pH and acid-neutralising capacity (ANC) of the lake rose to 5.8-5.9 and 13-15 µeq L-1, respectively. The lake is extremely dilute with a mean conductivity and calcium concentration of 7.7 µS cm-1 and 0.35 mg L-1, respectively. The lake was stocked with 250 Arctic charr from a neighbouring lake between 1998 and 2000. These introductions were highly successful, as test-fishing in 2004, 2008 and 2012 revealed a relatively dense population of Arctic charr, and the presence of several young age groups. Water quality has remained stable since the late 1990s, or has slightly improved.

Leaching behavior of major and trace elements from sludge deposits of a French vertical flow constructed wetland

Surface sludge deposits were collected from a French Vertical Flow Constructed Wetland (French VFCW) sewage treatment plant. The objectives were to characterize the retention of major elements and trace metals within the sludge deposits particles under regular operating conditions, and the influence of extreme pH conditions on their potential release which may occur in situations when the plant malfunctions or after land application of the dredged sludge. A sequential extraction protocol was first used to assess the distribution of the elements within the sludge deposits. Results showed that most of Cu and Pb were associated to organic matter within the oxidizable fraction. Zn, Ni and Cd were distributed in several fractions, notably bound to Fe-Mn oxides and associated to organic matter. Cr was analyzed mostly in the residual fraction. Aliquot fractions of sludge deposits were also submitted to Acid and Base Neutralization Capacity tests (ANC-BNC) where the samples were suspended into acidic or alkaline aqueous solutions, and the solutions analyzed after 48 h contact time. Results showed a pH-dependent leaching profile for all monitored elements. The role of organic matter was observed for almost all metals. It was particularly dominant for Cu which was leached more extensively under alkaline than acidic conditions. Since Cu is not an amphoteric element, this leaching pattern was attributed to the leaching of organic matter which followed a similar pH-dependent profile than Cu. Spectrometric indices were used to characterize soluble organic compounds. Results showed that complex and humified dissolved organic compounds were mostly released under alkaline conditions.

Agricultural loess soils along a climosequence evidenced different susceptibility to acidification by simulated N-fertilization

Agricultural loess soils of the central region of Argentina show acidification evidences linked to both climatic conditions and N-fertilization. Because of that, simulations to estimate the future acidification trends under continuing N-fertilization, considering the different neutralization capacities of the soils in this region, were performed. An equivalent number of protons to that produced by a constant application of 180 kg urea ha−1 year−1 (84 kg N ha−1 year−1) during 1, 10, 30 and 50 years of fertilization, was added to unfertilized topsoil samples of agricultural Haplustolls, Hapludolls and Argiudolls. Mostly proton additions did not modify neither CEC nor the contents of both amorphous and crystalline Al, Mn and Fe oxides. However, the Hapludolls, located in the transition zone of the climosequence, showed decreases in their phyllosilicates crystallinity with the most acidifying treatments equivalent to 30 and 50 years of N-fertilization. This effect was less pronounced in those soils placed in both the driest (Haplustolls) and the moist (Argiudolls) environments, due to the amount and composition of the substances and/or systems with acid neutralizing capacity that prevailed. Thus, the Haplustolls were the less affected soils by acidification due to their high amount of free lime- and soil organic matter (SOM) as well as the smectitic mineralogy of their fine mineral fractions, clay and silt. The Argiudolls were the soils with stronger neutralizing mechanisms given by both their high SOM and fine mineral fractions contents, though illitic. Therefore, the Hapludolls were the most susceptible soils to being acidified if N-fertilization continues, according to the low quantity of SOM and fine mineral fractions of illitic mineralogy. From these results, the development and validation of mathematical models were assessed in order to predict the soil buffer capacity and the future pH of the soils. The soil buffer capacity was explained 78% by both the cation exchange and dissolution reactions of minerals accumulated in clays and silts, while pH values were explained 75% by the cation exchange capacity as well as by the SOM, free-lime and clay and silt contents. The pH that the soils would have in the future was predicted with an accuracy of 75% by the outcomes of the simulations, and in a 57% by the pH values of no-tilled and urea fertilized soils.

The use of mid-infrared diffuse reflectance spectroscopy for acid sulfate soil analysis

Good management of sulfide minerals and sulfuric acid in Acid Sulfate Soils (ASS) requires cost-effective rapid analytical data for their characterisation. However, the determination of properties in ASS samples using traditional laboratory techniques is expensive and time consuming. Excessive delays in analysis risks sample changes from oxidation. Mid-infrared (MIR) spectroscopy with multivariate regression offers a quicker and cheaper surrogate. This manuscript reports the prediction of some of the following key soil parameters in ASS characterisation using benchtop (Perkin Elmer) and handheld (ExoScan) diffuse reflectance MIR Fourier transform (DRIFT) spectrometers: Total Organic Carbon (TOC), Titratable Actual Acidity (TAA), Extractable Sulfate Sulfur (ESS), Reduced Inorganic Sulfur (RIS), Retained Acidity (RA), Acid Neutralising Capacity (ANC), and Lime Calculation (LC). Three sets of representative ASS soil profiles, comprising 132 samples from hyposulfidic, hypersulfidic and sulfuric materials, and covering a wide range of environments in South Australia were scanned under laboratory conditions. These were combined with reference laboratory data in partial least squares regression (PLSR) calibration models. The calibrations were validated by leave-one-out cross validation, with a further test set available for validation. Predictions with coefficient of determination (R2) > 0.75, were obtained for TOC (0.95), TAA (0.88), RIS (0.86), LC (0.76) and ANC (0.76), but models for ESS (0.66) and RA (0.41) were less satisfactory. The handheld spectrometer performed similarly to the benchtop spectrometer in terms of PLSR prediction accuracies with the potential for in-field sampling. Results thus confirmed the possibility of using MIR spectroscopy for the rapid and cost-effective characterisation of ASS.

Cation exchange capacity of biochar: An urgent method modification

Biochar, produced through pyrolysis of organic matter, is negatively charged, thus contributing to electrostatic adsorption of cations. However, due to its porous structure and contents of alkaline ashes, the determination of the cation exchange capacity (CEC) is challenging. Literature values for the CEC of biochar are surprisingly variable and are often poorly reproducible, suggesting methodological problems. Here, we modify and critically assess different steps in the existing ammonium acetate (NH4OAc) method (pH 7), where ammonium (NH4+) is displaced by potassium chloride (KCl), following removal of excess NH4OAc with isopropanol, in batch mode. We used pigeon pea biochar to develop the method and conducted a test on three additional biochars with different acid neutralizing capacity. A pretreatment step of biochar was introduced, using diluted hydrochloric acid, to decrease biochar pH to near neutral, so that 1 M NH4OAc effectively buffers the biochar suspension pH at 7. This allows the CEC of all biochars to be determined at pH 7, which is crucial for biochar comparison. The dissolution of ashes may cause relatively large weight losses (e.g. for cacao shell biochar), which need to be accounted for when computing the CEC of raw biochar. The sum of NH4OAC-extractable base cations provided a smaller and better estimate of the CEC than KCl-extractable NH4+. We hypothesize that the overestimation of the CEC based on KCl-extractable NH4+ is due to the ineffectiveness of the relatively large isopropanol molecules to remove excess NH4OAc in biochars rich in micro-pores, due to size exclusion. The amount of base cations removed in the pretreatment was about three (rice husk biochar) to ten times (pigeon pea biochar) greater than the amount of exchangeable cations. The CEC values of biochar increased from 10.8 cmol/Kg carbon to 119.6 cmol/Kg carbon. These values are smaller than reported CEC values of soil organic carbon.

Alpine catena response to nitrogen deposition and its effect on the aquatic system

Alpine areas are vulnerable to nitrogen (N) deposition because of low N-buffering capacity and limited ability to resist change. The objective of the study was to assess if >30 years of N deposition have resulted in a decline in exchangeable base cations (CB) coupled with an increase of exchangeable aluminum (Al). We used soil and stream data sampled between 1982 and 2015 at Green Lakes Valley, Colorado Front Range to evaluate the change in an alpine catena. The CB in the surface horizons of the summit position decreased significantly from 45 cmolc kg−1 in 1982 to 2.3 cmolc kg−1 in 2015, while the exchangeable Al increased from 0.09 cmolc kg−1 to 0.7 cmolc kg−1 in the summit and from 8.9 cmolc kg−1 to 10.5 cmolc kg−1 in the toeslope. Spatiotemporal distribution of soil moisture along the catena exhibited the lowest values during the winter months because the temperature was below freezing. The soil moisture increased in early spring as soil-temperature rose. A Seasonal Kendall test (SK) showed that the soil moisture decreased along the catena by −0.007 m3 m−3 yr−1(P < 0.001). The soil moisture trend coincided with a soil temperature increase from the summit to toeslope of 0.68° yr−1. Segmental SK analysis of acid-neutralizing capacity (ANC) measured in the outlet of the lake below the catena showed a decrease of −2.15 μeq L−1 yr−1 for the first monitoring period from 1982 to 1995, and an increase by 0.51 μeq L−1 yr−1 during the second monitoring period from 1995 to 2014. These trend analyses attest to the limited influence of the alpine soil system on the overall aquatic chemistry. Hence, a clear distinction should be made between the alpine soils and the terrestrial system (e.g., rock glacier, taluses, and screes). Most of the soils have little impact on the aquatic system, whereas other terrestrial features are more important in this regard.

The response of soil solution chemistry in European forests to decreasing acid deposition

Acid deposition arising from sulphur (S) and nitrogen (N) emissions from fossil fuel combustion and agriculture has contributed to the acidification of terrestrial ecosystems in many regions globally. However, in Europe and North America, S deposition has greatly decreased in recent decades due to emissions controls. In this study, we assessed the response of soil solution chemistry in mineral horizons of European forests to these changes. Trends in pH, acid neutralizing capacity (ANC), major ions, total aluminium (Altot ) and dissolved organic carbon were determined for the period 1995-2012. Plots with at least 10years of observations from the ICP Forests monitoring network were used. Trends were assessed for the upper mineral soil (10-20cm, 104 plots) and subsoil (40-80cm, 162 plots). There was a large decrease in the concentration of sulphate (SO42-) in soil solution; over a 10-year period (2000-2010), SO42- decreased by 52% at 10-20cm and 40% at 40-80cm. Nitrate was unchanged at 10-20cm but decreased at 40-80cm. The decrease in acid anions was accompanied by a large and significant decrease in the concentration of the nutrient base cations: calcium, magnesium and potassium (Bc=Ca2+ +Mg2+ +K+ ) and Altot over the entire dataset. The response of soil solution acidity was nonuniform. At 10-20cm, ANC increased in acid-sensitive soils (base saturation ≤10%) indicating a recovery, but ANC decreased in soils with base saturation >10%. At 40-80cm, ANC remained unchanged in acid-sensitive soils (base saturation ≤20%, pHCaCl2≤4.5) and decreased in better-buffered soils (base saturation >20%, pHCaCl2>4.5). In addition, the molar ratio of Bc to Altot either did not change or decreased. The results suggest a long-time lag between emission abatement and changes in soil solution acidity and underline the importance of long-term monitoring in evaluating ecosystem response to decreases in deposition.