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Background: In this study, we determined the acid-neutralizing capacity (ANC) of Mg/Al-Hydrotalcite-like compounds. The MgAl-hydrotalcites were synthesized by the co-precipitation method at room temperature using Mg/Al molar ratios 2:3. The synthesized bioactive nanomaterials were characterized by various physicochemical techniques such as TG/dTG, XRD, FT-IR spectroscopy, BET/BHJ, and SEM/EDX. The antacid activity assay was done by converting both synthesized samples into liquids, 1 g of which was added to 50 ml of deionized water at 37°C under vigorous agitation. The acid-neutralizing capacity (ANC) was evaluated with 0.1N HCl. The pH was constantly measured using a pH meter and values were recorded every minute up to 35 min. In order to improve the neutralizing power of the samples, we performed an exchange of chlorides by carbonates on the MgAl-HT3 synthesized. The exchanged Mg/Al-Hydrotalcite (MgAl- HTE) showed high acid neutralization capacity (up to 13.5 mEq/g). Objective: This study aimed to synthesize MgAl-hydrotalcite-like compounds and evaluate their acid-neutralizing capacity. In order to can be good candidates for pharmaceutical applications as antacid drugs. Methods: Following methods are used in this study: - Preparation of MgAl-hydrotalcite-like compounds was done by coprecipitation methods. - Characterization of samples was done by physico-chemical techniques such as TG/dTG, XRD, FT-IR spectroscopy, BET/BHJ and SEM/EDX. - Evaluation of acid-neutralizing capacity was done by titration procedure (Dose-titration). Results: This protocol describes the preparation of MgAl-hydrotalcite-like compounds using the classical coprecipitation method. The synthesized samples were characterized by various physicochemical techniques such as TG/dTG, XRD, FT-IR spectroscopy, BET/BHJ, and SEM/EDX. The as-synthetized samples were used for the evaluation of their acid-neutralizing capacity (ANC). Further, an exchanged of MgAl-Hydrotalcite with carbonate was done for the purpose to increase the acid-neutralizing capacity. Conclusion: In summary, this study describes a simple synthesis of MgAl-Hydrotalcites compounds by a co-precipitation method at constant pH around 10, with a ratio Mg/Al = 3:2 (referred to as MgAl-HT3 and MgAl-HT2). An exchange of the chlorides (not eliminated by washing) by the carbonates was carried out on hydrotalcite with a ratio Mg/Al = 3, and the solid obtained was named MgAl-HT3E. The materials MgAl-HT2, MgAl-HT3, and MgAl-TH3E were used to evaluate antacid activity. To this end, a study was conducted to determine the acid-neutralizing capacity (ANC). As result, the MgAl-HT3E was able to increase acid-neutralizing capacity and maintain an ideal pH. These results could be interesting to prepare novel antacid drugs (due to the low cost of synthesized materials) essentially the hydrotalcite of mg/Al ratio equal to 3 because of its relatively slow kinetics of releasing basic species and therefore of its beneficial action as an antacid.

Background and objective: Antacids are basic substances that can neutralize hydrochloric acid and reduce gastric acidity. They are over the counter drugs used to treat dyspepsia. The most commonly used antacids are sodium bicarbonate, magnesium hydroxide, aluminum hydroxide, and calcium carbonate. This study aimed to evaluate the effectiveness of antacids that are commonly used in Erbil city by finding their acid-neutralizing capacity. Methods: The method for acid-neutralizing capacity was adapted from pharmacopeia. The samples were prepared by dissolving the antacid in an excess amount of hydrochloric acid, then neutralizing the excess acid with sodium hydroxide solution by doing back titration. The number of milliequivalents that are neutralized by the antacid is the acid-neutralizing capacity of the antacid. Results: Rennie® chewable tablet showed the highest acid-neutralizing capacity, followed by AntacidAwa and Maalux® plus. The lowest acid-neutralizing capacity was for the suspensions Gaviscon® and Enoxon®. Conclusion: Acid-neutralizing capacity is an easy and quick method to evaluate the efficacy of antacids. Different combinations of salts and concentrations can affect the acid-neutralizing capacity of the antacid. The higher the neutralizing effect of the antacid, the more effective the antacid is. Keywords: Acid-neutralizing capacity; Antacid; pH; Dyspepsia; Erbil.

Hyperacidity (Amlapitta) is one of the most common disorder. It is observed by excess production of gastric acid in stomach. It is generally imbalance between offensive parameters like gastric acid and defensive factors like mucin bicarbonate secretions. Over the counter products aim at neutralizing gastric acid rather than the root cause. Ayurvedic preparations has an solution to amlapitta. It not only neutralizes acid secreted but also improves defensive properties of stomach. Once such combination is Ulsant tablets. Acid neutralizing capacity and buffering capacity was conducted in vitro. The aim of the present study was to find out safety and efficacy of Ulsant tablet. In present study total 35 patients were taken. Patients were advised with Ulsant tablet 2 tab twice a day for 45 days. Results shown significant positive results with respect to acid neutralizing capacity, buffering capacity and clinical symptoms. Keywords: Hyperacidity, Ulcer, Ayurveda, Ulsant, Natural.

Nitrogen deposition from air pollution is increasingly reaching alpine lakes where the addition of nitrate and ammonium to sensitive surface waters can cause acidification and/or eutrophication. Thirty years of sampling in the Wind River Range, WY, has shown some lakes increasing in nitrogen. We sought to (1) determine if nutrient concentrations in Deep Lake increase during snowmelt when atmospheric deposition is released from the snowpack and (2) assess if the sampling season, location, meteorological factors, and time of day samples are collected influence lake chemistry metrics, to inform monitoring. We analyzed water samples from the outlet of Deep Lake in peak snowmelt (June) and from the inlet, outlet, and middle of Deep Lake when the basin was snow free (August). In June, outlet samples were more acidic, and nitrogen content was three times August levels. Acid neutralizing capacity (ANC) declined with snowmelt. August inlet samples were higher in nutrients than outlet and mid-lake samples. Our results indicate that atmospheric pollution in the snowpack enters the lake with snowmelt. Although Deep Lake has not acidified, ANC levels indicate a risk of episodic acidification if nitrogen deposition continues to increase. When monitoring lakes at risk for episodic acidification, sampling during the late snowmelt pulse should be prioritized. Simplified sampling protocols may be used in some lakes, as epilimnion and outlet samples were nearly identical. The time of day and cloud cover did not affect lake chemistry, while wind speed and precipitation weakly increased August ANC and June pH, respectively.

Passive systems are often used for the treatment of acid mine drainage (AMD) on closed and abandoned mine sites. Metal-rich residues (solid precipitates) with variable chemical composition and physical properties can be generated. Their characterization is required to better anticipate the potential fate, including stability for disposal, potential recovery, or reuse. The present study evaluated the leaching potential of solids from a laboratory passive multi-step treatment for Fe-rich AMD (2350 ± 330 mg/L Fetot, 0.7 ± 0.4 mg/L Ni, 0.2 ± 3.0 mg/L Zn, and 5073 ± 407 mg/L SO42-, at pH 3.04 ± 0.45). To do so, post-treatment solids from three units (Fe-pretreatment reactor (50% wood chips and 50% wood ash, WA50), passive biochemical reactor, PBR for SO42- treatment (30% inorganic materials, 70% organic substrate), and polishing reactor (50% calcite and 50% wood chips, C50)) of a pilot laboratory treatment system were sampled. Physicochemical and mineralogical characterization, as well as static leaching tests were then performed. Results showed that all solids had high neutralizing potential, while high inorganic carbon was found in C50. Moreover, high metal concentrations were found in WA50. Metals and sulfates in all solids precipitated in the form of oxyhydroxides, oxy-hydroxy-sulfates, carbonates, sulfides, sulfate, and native sulfur. The Fe was not found as problematic contaminant in solids, but it was in AMD. However, a probable generation of contaminated neutral drainage by Ni and Zn could occur from WA50. The C50 had the highest acid neutralizing capacity and could better resist to acid aggression relative to solids from PBR and WA50. The PBR and C50 solids were considered as non-hazardous towards regulation's limits and a potential co-disposal with municipal wastes could be a storage option. Further studies should be undertaken by testing other leaching and kinetic tests to assess long-term metal stability.

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 (

Modeling studies project that in the future surface waters in the northeast US will continue to recover from acidification over decades following reductions in atmospheric sulfur dioxide and nitrogen oxides emissions. However, these studies generally assume stationary climatic conditions over the simulation period and ignore the linkages between soil and surface water recovery from acid deposition and changing climate, despite fundamental impacts to watershed processes and comparable time scales for both phenomena. In this study, the integrated biogeochemical model PnET-BGC was applied to two montane forest watersheds in the Adirondack region of New York, USA to evaluate the recovery of surface waters from historical acidification in response to possible future changes in climate and atmospheric sulfur and nitrogen deposition. Statistically downscaled climate scenarios on average project warmer temperatures and greater precipitation for the Adirondack by the end of the century. Model simulations suggest under constant climate, acid-sensitive Buck Creek would gain 12.8 μeq L−1 of acid neutralizing capacity (ANC) by 2100 from large reductions in deposition, whereas acid insensitive Archer Creek is projected to gain 7.9 μeq L−1 of ANC. However, climate change could limit those improvements in acid-base status. Under climate change, a negative offset relative to the ANC increases with no climate change are projected for both streams by 2100. In acid-insensitive Archer Creek the negative offset (−8.5 μeq L−1) was large enough that ANC is projected to decrease by −0.6 μeq L−1, whereas in acid-sensitive Buck Creek, the negative offset (−0.4 μeq L−1) resulted in a slight decline of the projected future ANC increase to 12.4 μeq L−1. Calculated target loads for 2150 for both sites decreased when future climate change was considered in model simulations, which suggests further reductions in acid deposition may be necessary to restore ecosystem structure and function under a changing climate.

Acid deposition, resulting from the atmospheric transport of acidifying compounds emitted during the combustion of fossil fuels, has historically resulted in stream acidification in many headwater streams in the eastern United States, including streams in Shenandoah National Park (SHEN). Though restrictions on these emissions were established by an amendment to the Clean Air Act in 1990, reductions in stream acidification have not been observed in all regions of SHEN due to variations in the geological composition of SHEN watersheds. Before the implementation of these restrictions, fish assemblages were strongly controlled by a stream’s acid neutralizing capacity (ANC), which is the ability of a watershed to buffer acid inputs. This study investigated changes in the relationship between fish assemblages and ANC within SHEN 21 years after implementation of more stringent restrictions on the emission of sulfur and nitrogen oxides in 1995. Results indicated that recovery trends in water chemistry were observed in some SHEN watersheds; however, fish species richness and total fish biomass continue to be influenced by the legacy of acid deposition in acid sensitive watersheds. Temporal trend analysis indicated little change in ANC within acid sensitive watersheds and minor decreases in stream sulfate concentrations. These findings indicate a persistent impact from previously deposited sulfur oxides and the continued influence of these compounds on fish assemblages within SHEN. Though no further loss of fish species, and in some cases, increases in species richness, suggest the early stages of recovery, many SHEN streams remain as susceptible to acidification as they were over two decades ago, highlighting the need for continued regulation of acidifying emissions and conservation efforts in headwater streams.

A bark beetle attack in a Norway spruce forest in southwestern Sweden killed most trees, which however mostly remained standing, and caused elevated nitrate concentrations and subsequent acidification in the soil water. Long-term monitoring showed very low nitrate concentrations in the soil water before the bark beetle attack. High nitrate concentrations remained throughout five years after the initiation of the bark beetle attack until the monitoring was terminated. The increased nitrate concentrations in the soil water were accompanied by a decrease in both pH and the acid neutralizing capacity, ANC. The significance for future nitrogen and acidity leakage to ground- and surface waters is discussed in relation to the expected future increase in the frequencies of bark beetle attacks in boreal and northern temperate forests.

In this study we investigated the components of organic alkalinity (AO) in pore water from marine sediments. We used absorbance and fluorescence of pore water to characterize dissolved organic matter (DOM), the source of AO. Research material was collected during growing season (September 2016) from two sites located in the eutrophic Gulf of Gdansk (southern Baltic). Concentration of AO ranged from 104 to 1505 μmol l−1 and increased with sediment depth. Our results demonstrate a clear link between AO and composition of DOM in pore water. Measurements of pore water fluorescence showed that the main source of AO is humic substances. The protein-like fluorescence, pointing to presence of freshly produced organic substances, was clearly visible in the upper layers and diminished with depth. There are changes in absorbance spectra with depth indicating decrease of molecular weight of DOM. In anoxic sediments the concentration of AO was close to the alkalinity from non‑carbonate inorganic bases (N-CIBs) and did not exceed 8% of total alkalinity (AT). In the sediments where organic matter was mineralized with the use of substances preceding sulfate in the sequence of oxidants (i.e. oxygen, nitrate, Mn, Fe), DOM was the source of up to 17% of AT. The results from this study indicate that DOM has a large effect on acid neutralizing capacity of pore water of marine sediments. We suggest the production of AO in sediment and its benthic efflux should be taken into account in modeling acid-base system in shelf seas.

In this study, cow dung was identified as a neutralizing agent for red mud (RM). Present research estimated a significant reduction in pH value of red mud (10 g) from 10.28 to 8.15 and reduction in alkalinity of ~148 mg/L from ~488 mg/L by adding 80 g of cow dung in 40 days of anaerobic condition. XRD results exhibit a high intensity of quartz and found new compound, the calcium carbide. The acid neutralizing capacity (ANC) of NRM reduces to ~0.87 from ~1.506 mol H+/kg. Based on the resultant research, present study proposes cow dung as an efficient neutralizing agent for reducing the pH and alkalinity in the red mud.

In the past, black slag from an Electric Arc Furnace was dumped or stockpiled. Nevertheless, after much controversy, slag can no longer be considered a “waste”, and bearing in mind its positive properties, reuse alternatives are being sought. In this study, a black slag was used as an alternative packing material for toluene, ethylbenzene and p -xylene biofiltration, with these pollutants being fed both individually and jointly. Ethylbenzene recorded the highest elimination capacity when the ternary mixture was fed. The electrical conductivity of the leaching solution showed that the slag did not contribute to ion release or dissolution. The acid neutralizing capacity of the slag played a major role in preventing bed acidification. All the biofilters were invaded by mites, and other meiofauna including nematodes and rotifers also developed in the bed. Under these conditions, CO 2 production was attributed not only to contaminant degradation but also to the metabolic processes of the meiofauna originating from the inoculum. Despite the favourable evolution of the operating parameters and the suitable performance of the slag bed, its high bulk density restricts the size of the bed. Slag is nonetheless recommended for use as a co-packing material.

Acidic deposition used to cause severe surface water acidification in Europe and the North America, but no damage of surface water acidification was reported under continuous heavy acid deposition in China. We present the first detailed study on regional surface water acidification in southern and northeastern China based on a survey of 255 forested headwater streams, which were investigated during 2010–2015 to explore the status and mechanism of surface water acidification. South China has a subtropical climate with high acid deposition, whereas northeast China is located in a cold temperature zone with relatively low acid deposition. High pH and acid neutralizing capacity (ANC) were observed for almost all of the streams, indicating that surface water acidification may not be a serious regional issue in China both at present and in the future. In northeast China, where soil types are similar in low weathering rate to those in Northern Europe and North America, the ANC of surface waters was lower than that in South China, indicating a higher acid-sensitivity of the surface water. In comparison, the high pH and ANC of streams in southwest China resulted from high soil weathering and atmospheric calcium (Ca) deposition, despite elevated atmospheric acid inputs due to the high sulfur (S) and nitrogen (N) deposition. Comparison of stream nitrate (NO3−) and sulfate (SO42 −) concentrations with modeled N and S deposition showed significant N and possible S sinks in the catchments in south China, probably due to denitrification of NO3− in groundwater discharge zone and SO42 − adsorption by acid soils respectively, which may also buffer the acidifying effect of S and N depositions. It seems that considerable NO3− leaching to stream waters does not occur in China unless N deposition is higher than 1.8 keq·ha− 1·yr− 1 (2.50 g N·m− 2·yr− 1) (or greater values in certain regions).

Bauxite residue, a highly alkaline solid waste, is extremely hazardous to the surrounding environment and current research approaches have largely focused on the removal and separation of alkaline substances. Natural weathering processes may be a step forward in terms of their regeneration. In this study, natural evolution of basic alkalinity, electrical conductivity, exchangeable ions and acid neutralizing capacity of residue in the disposal areas was discussed. Minerals, exchangeable cations and alkaline anions were analyzed by X-ray powder diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and titration, respectively. Acid neutralizing capacity was carried out by batch neutralization experiments. Basic alkalinity, electrical conductivity, cation exchange capacity and exchangeable sodium percentage decreased with increasing disposal duration. Sodium was the predominant exchangeable cation in fresh residue but its concentration significantly decreased with increasing time from initial disposal. The acid neutralizing capacity of bauxite residue was investigated by incubation with hydrochloric acid. Acid neutralizing capacity curves changed with disposal duration and each revealed a characteristic buffering behavior that could be controlled by its alkaline components.

Acidic deposition is comprised of sulfuric and nitric acids, and ammonium derived from atmospheric emissions of sulfur dioxide, nitrogen oxides, and ammonia, respectively. These compounds are released to the atmosphere largely by the burning of fossil fuels and agricultural activities. Atmospheric deposition delivers acids and acidifying compounds to the Earth’s surface. The adverse ecological effects of acidic deposition on forests, streams, and lakes largely occur in eastern North America, northern and central Europe, and southwestern China. Acidic deposition has altered, and continues to alter, forest soil by accelerating the leaching of calcium and magnesium and increasing concentrations of dissolved inorganic aluminum in soil waters. At high concentrations, dissolved inorganic aluminum can hinder the uptake of water and essential nutrients by tree roots. The alteration of soils by acid deposition has serious consequences for acid-sensitive forest ecosystems. Soils that are compromised by acidic deposition are less able to neutralize additional inputs of strong acids, and provide poorer growing conditions for plants and delay the recovery of surface waters. Acidic deposition has impaired, and continues to impair, the water quality of lakes and streams in eastern North America and Europe in three important ways: lowering pH levels (i.e., increasing the acidity); decreasing acid-neutralizing capacity; and increasing aluminum concentrations. Many surface waters in acid-sensitive regions impacted by acidic deposition exhibit chronic and/or episodic (i.e., short-term) acidification. Moreover, elevated concentrations of dissolved inorganic aluminum have been measured in acid-impacted surface waters. High concentrations of aluminum and increased acidity have reduced the species diversity and abundance of aquatic life in many lakes and streams draining acid-sensitive regions. Fish have received the most attention to date, but entire food webs are often negatively affected. For example, in a survey of lakes in the Adirondack region of New York, 346 lakes (24% of the total) did not contain fish. These fishless lakes had significantly lower pH and higher concentrations of dissolved inorganic aluminum when compared to those lakes with fish.

Reductions in acidic deposition following the 1990 Amendments to the Clean Air Act have led to improvements in the acid/base status of many freshwater bodies in the eastern United States, but such recovery has not been as widespread in Virginia mountain streams. In the current analysis, water chemistry trends are determined for 63 streams within Shenandoah National Park, Virginia, and surrounding national forests, where water samples have been collected on a quarterly basis from 1987 to 2019. Over this timeframe, a majority of the most acid-sensitive streams – those with watersheds underlain by siliciclastic bedrock – have experienced reductions in acid neutralizing capacity (ANC). This outcome, which differs from the modest recovery predicted by earlier modeling studies, is likely due to further depletion of soil base cations and perhaps increases in organic acids. Meanwhile, stream water pH has increased for all watershed bedrock types, averaging between 0.05 and 0.10 pH units per decade. High-flow sampling was conducted at three sites from 1992 to 2019, revealing an assessment of episodic acidification that is more encouraging than that of chronic acidification. For two of these sites, pH during high-flow conditions increased much more rapidly than pH during low-flow conditions. Steep reductions in sulfur deposition over the three decades since the 1990 Amendments have led to a “flushing” of sulfate from shallow soils, which has contributed to the improved acid/base status during episodes of high flow. The findings suggest that continued low acidic deposition rates will lead to further improvements in stream water quality, with the timescales of recovery dependent upon bedrock geology of the watersheds.

Decades of acidic deposition have adversely affected aquatic and terrestrial ecosystems in acid-sensitive watersheds in parts of the eastern United States. The national Acid Rain Program (Title IV of the 1990 Clean Air Act Amendments - CAAA) helped reduce emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) and resulted in sharp decreases in the acidity of atmospheric deposition. The decrease in acidic deposition produced a steady decline in the acidity of streams in many poorly buffered waters across the western Adirondacks and parts of the Catskill Mountains of New York. Until recently, however, there has been little evidence of biological recovery in most acid-sensitive streams in both regions. Long-term deposition and stream-chemistry records and fish-community data from quantitative surveys done during 1991–93 and again during 2012–19 at 13 sites in the upper Neversink River and its tributaries were evaluated to determine if chemical and biological recovery were evident in this Catskill Mountain watershed and if they could be linked to regional declines in acidic deposition. Between 1991 and 2019, large decreases in sulfate and nitrate deposition in the basin mirrored declines in total nationwide SO2 and NOx emissions. There were corresponding decreases in sulfate and nitrate concentrations in deposition at a National Trends Network station at Frost Valley (NY68) and coincident declines in sulfate concentrations at four long-term monitoring sites in the Neversink River watershed. Mean acid neutralizing capacity and pH increased and inorganic aluminum (Ali) concentrations from routine summertime samples decreased significantly at most moderately to severely acidified sites between the two study periods. Richness, density, and biomass of fish communities increased at most sites, while the density and biomass of brook trout Salvelinus fontinalis populations increased at fewer sites that were undergoing chemical recovery. Although recovery is far from complete, trends in deposition chemistry, water quality, and fish assemblages in streams of the upper Neversink watershed indicate that the 1990 CAAA is having positive impacts on aquatic ecosystems in the Catskill Mountain region, New York.

This paper deals with the assessment of the available insoluble calcium compounds in pond sediment and their conversion into soluble bicarbonate; its impact on the acid neutralizing capacity (ANC) or alkalinity of water and the influence of bioturbation by fish stock. The objective of the study was the assessment of the influence of different Ca contents in pond sediments of two groups of ponds: LCa (with a low content of available Ca) and HCa (with a high content of available calcium) on acid neutralizing capacity of water, conductivity and pH. In our experiments, the turbidity of water, content of chlorophyll, nutrients and natural gain of fish in general have been observed as well. The results revealed that ponds with a higher content of calcium with a mean concentration of 27.45 ± 7.9 mmol Ca/kg in dry matter reported a higher ANC (alkalinity; mean value of 2.31 ± 0.33 mmol/l); pH with smaller fluctuations (7.69 ± 0.37; p < 0.05) and higher average values of turbidity (30.9 ± 17.4 NTU) and conductivity of water (291 ± 40.5 μS/cm−1; p < 0.01). Tight relations of the content of Ca in sediments and acid neutralizing capacity, conductivity and water pH during the growing season have been proven. The natural gain of fish was higher in the ponds with a higher content of available Ca in the sediment and a higher value of acid neutralizing capacity of water. The natural gain of fish was positively influenced also by a higher content of nutrients and chlorophyll, which was observed particularly in HCa ponds.

During recent decades, increasing anthropogenic activities have affected natural ionic composition, including the strongest and most common relationship between ionic concentrations in the majority of natural global freshwaters, i.e., the Ca2+-ANC (acid neutralizing capacity) equilibrium. Using long-term monitoring data and MAGIC modelling, we evaluated effects of major present environmental stressors (synthetic fertilizers, liming, acidic deposition, forest disturbances, and climate change) on the Ca2+-ANC equilibrium. We evaluated the effects for three different types of terrestrial ecosystems, a circumneutral lowland agricultural catchment, two acid sensitive mountain forest catchments differing in forest health, and one acid sensitive alpine catchment. All catchments are in a region with the world-largest changes in fertilizing rates and acidic deposition in the 20th century, with increasing impacts until the late 1980s, and their subsequent abrupt, dramatic decreases. These strong changes resulted in a substantial disruption, followed by continuing re-establishment of the Ca2+-ANC relationship in all study waters. The shape of the disruption and the following re-establishment of its new value were dependent on the intensity, duration, and combination of stressors, as well as on catchment characteristics (bedrock composition, soil amount and composition, vegetation status, and hydrology). We conclude that a new equilibrium may deviate from its natural value due to the (1) legacy of fertilizing, acidic deposition and liming, affecting the soil Ca2+ pools, (2) forest disturbances and management practices, and (3) climate change.

This study has evaluated the acid neutralizing and buffering capacities (BC) of nine selected antacid brands (“L1-L9”) in Ghana. The active acid neutralizing ingredients were recorded and the preliminary antacid test (PAT) determined with 0.5 N HCl after 10 min. The acid neutralizing capacity (ANC) was evaluated with 1 N HCl by neutralizing the excess with 0.5 N NaOH after 15 min stirring. Buffering capacity (BC) was estimated with 0.1 N HCl and titrated with 0.1 N NaOH at 5 min interval up to 50 min. All determination were at 37±3 °C using a pH meter. All brands had as part of their active ingredients dried aluminum hydroxide and magnesium hydroxide, with 67% containing simethicone as antifoam. The PAT declared all brands to be antacids with pH range of 4.38 ± 0.21–6.43 ± 0.06. The ANC of all brands were in the range 13.16 ± 0.55–20.70 ± 0.18 mEq/g with “L4” and “L9” having the lowest and highest values respectively. “L9” further demonstrated a considerably higher BC up to 40 min whiles “L6” had the least BC up to 15 min. The ability of an antacid to have a high ANC and to resist significant changes in pH (longer BC) is crucial in assuring quality and efficacy of the brand.

The present-day acid-base chemistry of surface waters can be directly linked to contemporary observations of acid deposition; however, pre-industrial conditions are key to predicting the potential future recovery of stream ecosystems under decreasing loads of atmospheric sulfur (S) and nitrogen (N) deposition. The integrated biogeochemical model PnET-BGC was applied to 25 forest watersheds that represent a range of acid sensitivity in the Adirondack region of New York, USA to simulate the response of streams to past and future changes in atmospheric S and N deposition, and calculate the target loads of acidity for protecting and restoring stream water quality and ecosystem health. Using measured data, the model was calibrated and applied to simulate soil and stream chemistry at all study sites. Model hindcasts indicate that historically stream water chemistry in the Adirondacks was variable, but inherently sensitive to acid deposition. The median model-simulated acid neutralizing capacity (ANC) of the streams was projected to be 55 μeq L-1 before the advent of anthropogenic acid deposition (~1850), decreasing to minimum values of 10 μeq L-1 around the year 2000. The median simulated ANC increased to 13 μeq L-1 by 2015 in response to decreases in acid deposition that have occurred over recent decades. Model projections suggest that simultaneous decreases in sulfate, nitrate and ammonium deposition are more effective in restoring stream ANC than individual decreases in sulfur or nitrogen deposition. However, the increases in stream ANC per unit equivalent decrease in S deposition is greater compared to decreases in N deposition. Using empirical algorithms, fish community density and biomass are projected to increase under several deposition-control scenarios that coincide with increases in stream ANC. Model projections suggest that even under the most aggressive deposition-reduction scenarios, stream chemistry and fisheries will not fully recover from historical acidification by 2200.

This paper presents a comprehensive investigation of chemical properties, including soil pH, acid neutralizing capacity, metal leachability and chemical speciation, of a Zn, Pb and Cd contaminated site soil stabilized by KMP. The results show that the KMP stabilized soils have lower pH and higher resistance to acid attack than the untreated soil; the KMP is effective in reducing the metal leachability and changing the metal speciation, and the corresponding leached concentrations significantly below their regulatory limits; furthermore, lower acid soluble fraction contents contributes to the lower metal leachability in contaminated soils.

Acid rain, or acid deposition, was determined to be a widespread environmental problem in the late 1960s and early 1970s in eastern North America and northwestern Europe. Acid deposition is largely attributed to the burning of fossil fuels, which in turn releases the acid deposition precursors, sulfur dioxide (SO 2 ), mainly from power plants, and nitrogen oxides (NO x ), mainly from vehicles. Early signs of environmental damage from acid deposition include the loss of fish populations in remote lakes and streams, and the die back of forests in Europe and eastern North America. Scientific evidence and public outcry in these regions led to legislation to reduce emissions of SO 2 , and then NO x , which resulted in dramatic declines in acid deposition and other related pollutants (e.g., particulates), and in many areas an improvement in ecosystem and human health. Some areas have only seen minor improvements due to long-term loss of acid neutralizing capacity in soils of acid sensitive landscapes, brought about by decades of acid deposition. SO 2 and NO x emissions are increasing in Asia, where the high potential for future problems related to acid deposition still exists.

Great Smoky Mountains National Park (GSMNP) is subject to high levels of sulfur (S) and nitrogen (N) deposition, which can adversely affect forest vegetation and aquatic biota. We used multiple chemical criteria to calculate critical loads for S and N deposition (CL (S+N)) and nutrient N (CLnutN) and used the Very Simple Dynamic (VSD) model to predict the effects of deposition reduction scenarios on critical thresholds for four forested sites in GSMNP. Critical loads were exceeded for current deposition at three of four sites using critical thresholds of aluminum to base cations (Al:Bc) = 0.1 or no decrease in base saturation but were not exceeded using the chemical criteria of Al = 0.2 meq L-1, Al:Bc = 1.0, and pH = 4.2. With deposition reductions of 48 percent S and 56 percent nitrate (NO3‾), neither the critical thresholds of acid neutralizing capacity (ANC) = 20 μeq L-1 nor a decrease in base saturation was achieved. With deposition reductions of 90 percent S and 90 percent NO3‾, ANC = 100 μeq L-1 was achieved at a single site. Historical ANC values affected a site's ability to achieve ANC critical thresholds. The critical threshold for soil solution NO3‾ was exceeded for all but the most stringent deposition scenarios (–90 percent S and –90 percent NO3¯). Deposition reductions of 90 percent for NO3‾ and 80 percent for ammonium (NH4+) were not sufficient to lower deposition below the CLnutN at all sites. Data indicate that upper sites at GSMNP are N saturated; to protect these sites from acidification, the more protective chemical criteria of no decrease in base saturation and Al:Bc = 0.1 should be used when determining critical loads. When choosing chemical criteria in deposition reduction modeling, care should be taken to ensure that the criteria chosen will protect sensitive ecosystem elements.

Atmospheric acid deposition of sulfate and nitrate has declined markedly in the northeastern United States due to emissions controls. We investigated long-term trends in soil water (1984–2011) and stream water (1982–2011) chemistry along an elevation gradient of a forested watershed to evaluate the progress of recovery of drainage waters from acidic deposition at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA. We found slowed losses of base cations from soil and decreased mobilization of dissolved inorganic aluminum. Stream water pH at the watershed outlet increased at a rate of 0.01 units yr−1, and the acid neutralizing capacity (ANC) gained 0.88 µeq L−1 yr−1. Dissolved organic carbon generally decreased in stream water and soil solutions, contrary to trends observed at many North American and European sites. We compared whole-year hydrochemical trends with those during snowmelt, which is the highest-flow and lowest ANC period of the year, indicative of episodic acidification. Stream water during snowmelt had long-term trends of increasing ANC and pH at a rate very similar to the whole-year record, with closely related steady decreases in sulfate. A more rapid decline in stream water nitrate during snowmelt compared with the whole-year trend may be due, in part, to the marked decrease in atmospheric nitrate deposition during the last decade. The similarity between the whole-year trends and those of the snowmelt period is an important finding that demonstrates a consistency between recovery from chronic acidification during base flow and abatement of snowmelt acidification.

The alluvial aquifer underlying the city of Douala comprises shallow Quaternary deposits where groundwater is the main source for domestic and drinking purposes. Shallow groundwater in the area show signs of acidification with average pH range of 3.8-6.8. Long-term groundwater chemistry data (1998-2013), hydrogeochemical and R mode factor analysis were used to establish the acidification process of shallow groundwater and also determine possible origin and implications for water quality and use in the area. Twenty-six groundwater sample points, three streams and three rain sample points were studied seasonally in the 2006-2008 and the 2010-2013 study periods. The data were compared with result of a study, 7 years earlier (1998-1999). The results show evidence of acidification manifested by depletion of HCO3, a decrease in the pH and increase in SO4 and NO3 concentrations of shallow groundwater. Average groundwater pH range is 3.94-7.70 (1998-1999), 3.8-6.91 (2006-2008), and 3.7-6.8 (2010-2013). Only approximately 16 % (1998-1999), 14 % (2006-2008) and 11.11 % (2010-2013) of water samples fall within the range of pH (6.5-8.5) for potable water according to WHO (1993). The alkalinity/acid neutralizing capacity of the shallow groundwater has decreased significantly coupled with increase in the number of zero alkalinities recorded in the 2010-2013. The shallow groundwater is generally undersaturated with common carbonate minerals (calcite, dolomite), therefore providing insufficient acid buffer. Principal component analysis in combination with hydrogeochemical studies revealed that four main factors are responsible for the groundwater chemistry and acidity: (1) acid atmospheric deposition, (2) anthropogenic activities (industrial effluent discharges and acid spill, (3) chemical weathering, and (4) coastal atmospheric deposition/cation exchange. In general, the shallow groundwater is not suitable for drinking and domestic purposes with respect to the low pH and elevated nitrate concentration. In view of the implications such as increase in corrosion and increased mobilization of toxic elements (e.g. Al, Pb, Cu, Zn, Mn) as well as their possible harmful effect on health, it is recommended that the causes, rate of acidification and the mobility of trace elements be investigated with more details.

At the Kidston gold mine, Australia, the direct establishment of vegetation on tailings was considered as an alternative to the use of a waste rock cover. The tailings acid/base account was used to predict plant growth limitation by acidity, and thus methods capable of identifying tailings that would acidify to pH 4.5 or lower were sought. Total S was found to be poorly correlated with acid-generating sulfide, and total C was poorly correlated with acid-neutralizing carbonate, precluding the use of readily determined total S and C as predictors of net acid generation. Therefore, the selected approach used assessment of sulfide content as a predictor of acid generation, and carbonate content as a measure of the acid-neutralizing capacity available at pH 5 and above. Using this approach, the majority of tailings (67%) were found to be non-acid generating. However, areas of potentially acid-generating tailings were randomly distributed across the dam, and could only be located by intensive sampling. The limitations imposed by the large sample numbers, and costly analysis of sulfide and carbonate, make it impractical to identify and ameliorate acid-generating areas prior to vegetation establishment. However, as only a small proportion of the tailings will acidify, a strategy of re-treating acid areas following oxidation is suggested. The findings of the present study will assist in the selection of appropriate methods for the prediction of net acid generation, particularly where more conservative measurements are required to allow vegetation to be established directly in tailings.

Liming of acidic soils increases crop yield and farming profitability. The effectiveness of a liming material for neutralizing soil acidity depends mainly on its calcium carbonate (CaCO3) equivalent (CCE) and its fineness. The Iowa Department of Agriculture and Land Stewardship (IDALS) rules for agricultural lime (aglime) sales requires measuring Effective CCE (ECCE), which combines CCE and fineness efficiency estimates. Use of pelleted finely ground limestone has increased in recent years, but scarce field research has evaluated how ECCE evaluates the granulation effect on its acid neutralizing capacity compared with aglime. Therefore, a study was conducted at two Iowa State University (ISU) central Iowa farms to compare the effectiveness of calcium carbonate, calcitic aglime, and pelleted calcitic aglime at increasing soil pH and crop yield.

Pilot-scale successive alkalinity producing systems (SAPS) with varying amounts of mushroom compost were installed in a closed coal mine site in Korea to treat acidic mine effluent. The bioreactors were operated for 125 days and monitored for various water quality parameters to evaluate the effect of amount of mushroom compost on the performance of the reactors. The monitored parameters included dissolved oxygen (DO), oxidation–reduction potential (ORP), pH, electrical conductivity, concentrations of sulfate, sulfide and metals, and alkalinity generation. The results demonstrated that acid neutralizing capacity and metal removal efficiency were generally higher for the bioreactors containing greater amounts of mushroom compost. DO and ORP were the most sensitive parameters that readily reflected the effect of the amount of mushroom compost in the bioreactors. The effluents of bioreactors with less amount of mushroom compost consistently gave higher DO and ORP values, although the reactors maintained similar performances in removal of Fe, Al, and sulfate. However, the increase of DO and ORP values is a clear indication of performance deterioration of SAPS, especially in extended period of time. Therefore, in a practical sense, DO and ORP could be utilized as diagnostic parameters for implementation of proper corrective measures to SAPS in operation before encountering system failure.

Increased sulfate levels caused by salinisation associated with water table elevation has led to reduced sulfur accumulation in many inland (historically fresh) water bodies. Subsequent oxidation of the accumulated reduced sulfur is acid generating and, in the absence of sufficient acid-neutralising capacity, results in wetland acidification and associated toxic effects. Although alkalinity is generated during sulfate reduction, if this is not captured in a solid phase it may be removed from the reduction site via surface or groundwater exchange. This study examines the processes controlling the generation and retention of acid-neutralising capacity during the reduction phase. We use thermodynamic modelling to demonstrate that the ionic composition of a wetland’s source water, particularly the calcium to sulfate ratio, is an important factor in determining whether sufficient alkalinity can be stored (as calcium carbonate) during sulfate reduction to avoid acidification upon re-oxidation. Through controlled reactor experiments, where microbial sulfate reduction was induced in a wetland sediment suspension in the presence of a range of calcium (and magnesium) concentrations, we confirm the importance of carbonate precipitation for alkalinity storage. The reactor experiments also highlight the role of the sediment for solid-phase alkalinity storage and subsequent acid buffering and show that the extreme pH values predicted by modelling based on ionic composition alone are attenuated in the presence of natural sediment. We outline an approach in which wetland source water composition and sediment buffering properties could be coupled to a hydrologic model to allow determination of the risk of wetland acidification during a sulfate reduction–oxidation cycle.

The water chemistry of streams and precipitation in the province of Jämtland, northern Sweden has been monitored since the 1980s to study long-term trends, occurrence of acid episodes, and effects of liming. The acidity in precipitation increased in the 1970s, followed by a loss of acid neutralizing capacity (ANC) and low pH in the streams. Sulfur deposition began to decrease in the 1980s, until approximately 2000, after which the decrease levelled out. Stream water sulfate concentration followed the precipitation trend but decreased more slowly and since the late 1990s a subtle increase was observed. Sulfate concentrations in the snow typically have been higher than or equal to the stream sulfate levels. However, during the period of rapid deposition decrease and also since 2005 stream sulfate has sometimes exceeded snow sulfate, indicating desorption of stored soil sulfate, possibly because of climate-related changes in run-off routes through the soil profiles, following shorter periods of frost. From 1982 to 2000, total organic carbon (TOC) increased by approximately 0.1 mg L−1 yr−1. The mean trends in sulfate and TOC from approximately 1990 until today were generally opposite. Acidic episodes with pH 4.0 at flow peaks occurred frequently in the unlimed streams, despite relatively well-buffered waters at baseflow. To evaluate the main causes for the loss of ANC during episodes, the changes in major ion concentrations during high flow episodes were evaluated. The most important factors contributing to ANC loss were dilution of base cations (Na+, K+, Ca2+, Mg2+), enrichment of organic anions and enrichment of sulfate. Wetland liming started in 1985 after which the earlier observed extreme peak values of iron, manganese and aluminium, did not reoccur. The studied area is remote from emission sources in Europe, but the critical load of acidity is still exceeded. The long-term recovery observed in the unlimed streams is thus slow, and severe acidic episodes still occur.

While North America and Europe have been recovering from acidification, China is experiencing impacts of acid deposition. The Taihu region is a seriously impacted area by acid rain in China, with the average rainfall pH < 5. However, the acid neutralizing capacity (ANC) and pH of Taihu Lake have significantly increased over the past 60 years (p < 0.05). Analyses showed that watershed neutralization by carbonates and in-lake alkalinization by algae activities were the two major reactions responsible for the increase. In the Taihu basin, the dominant carbonate bedrocks are the major source of base cations (particularly Ca2+ and Mg2+) and act as the acidification buffer. In addition, our field measurements across the lake showed that the pH values were significantly higher in algal bloom waters than in areas without blooms. This observation was further supported by our statistical analysis showing that the Taihu ANC and pH were significantly correlated with the chlorophyll increase (p < 0.05; 1985–2015). How...

Decreased acid deposition over recent decades has led to reductions in streamwater acidity on a widespread basis throughout the U.S. and Europe. A notable exception has been the southern Appala- chian Mountains of the southeastern U.S., where declines in acid deposition have not translated into similar trends in stream chemistry in these watersheds with highly-weathered soils. To better characterize this observed behavior, streamwater samples collected at 64 sites in western Virginia on a quarterly basis from 1987 to 2011 were analyzed for chemical properties. Individual watershed response was strongly influ- enced by the dominant underlying bedrock, which affected sulfate (SO 2 ) adsorption and base cation supply. Overall, pH increased at a majority of sites across all bedrock types. However, acid neutralizing capacity (ANC) decreased at most sites underlain by base-poor bedrock, suggesting the susceptibility to episodic acidification remains a serious threat to these streams. The declines in ANC were more closely related the depletion of base cations (Ca 2? ,M g 2? ,K ? , and Na ? ) rather than increased SO 2 concentration. Sites with higher relative SO 2 adsorption exhibited little change in ANC. A mass balance analysis of sulfur at a base-poor watershed revealed that exports have recently surpassed inputs for the first time within the several-decade period of record. This pattern appears likely to continue, and if sustained, the depletion of the stored pool of sulfur signifies an important precursor for further improvements in streamwater acidity in the region.

There is detailed literature on the mobilization of aluminum (Al) from soil to surface waters as a result of elevated acidic deposition to base-poor forest watersheds. There is considerably less information on the mobilization and effects of Al from the application of alum that is used in some water supplies to control turbidity during high-flow events. We report on the results of field measurements, laboratory sediment release experiments, and chemical equilibrium calculations conducted to evaluate the potential for the mobilization of Al from alum floc deposits in sediments of Kensico Reservoir, New York. Under ambient water quality conditions, mobilization of sediment Al is not a noteworthy concern at Kensico Reservoir. However, under experimental conditions of low pH, low acid neutralizing capacity (ANC), and low temperature, the inorganic fraction of monomeric Al can be mobilized from Kensico sediments to concentrations that would likely impair the health of aquatic organisms (>2 μmol/l). Elevated concentrations of monomeric Al were observed only when ANC decreased below 50 μeq/l, which is outside the range of values observed in Kensico during the 1997-2007 interval (120-460 μeq/l). Concentrations of complexing ligands are relatively low in Kensico waters (i.e., fluoride, naturally occurring organic solutes) and do not appear to substantially contribute to potential Al mobilization. For other water supplies with low ANC, the potential for sediment release of Al may exist.

The aim of this study was to evaluate the acid neutralizing capacity and to observe surface changes of giomer in comparison with composite resin, when it comes in contact with an acidic solution. A packable giomer(Beautifil II) and a flowable giomer(Beautifil Flow F02) were used as experimental groups, while a packable composite resin(FiltekTM Z-250) was used as control group. pH values were measured after mixing the specimens of the disc and powder types with a pH 2.0 hydrochloric acid solution, respectively. Also, in the case of powder type giomers used in the earlier experiment, their pH values were measured again after mixing them with a fresh acid solution. Moreover, surface structure changes of disc type specimens were observed by using a scanning electron microscopy(SEM). In the disc type test, the pH values of packable giomer were significantly increased after 24 hours( p < 0.05). In contrast, in the powder type test, the pH values of packable and flowable giomers were dramatically increased within 30 minutes. The pH value of packable giomer, in particular, was higer than that of flowable giomer(p < 0.05). In the repeated neutralizing test, the degree of pH variation was lower than that of the previous neutralizing test(p < 0.05). Erosive changes on the surface of packable giomer were observed to be more than those on composite resin and flowable giomer as well. In conclusion, giomer has a acid neutralizing capacity, when it comes in contact with an acidic solution. Especially, packable giomer with high filler content has a greater acid neutralizing capacity than flowable giomer.

We investigated relationships among modern diatom species composition and physical and chemical characteristics of high-elevation lakes of the Sierra Nevada (California), to develop transfer functions that can be used to infer historic lake conditions. Data were collected from 50 lakes in National Parks and Forests of the central and southern Sierra Nevada. Multivariate statistical methods revealed that acid neutralizing capacity (ANC) and nitrate accounted for significant variation in diatom taxa. A training set with 242 modern diatom taxa from a subset of 41 lakes was used to develop transfer functions for ANC and nitrate using weighted averaging techniques. ANC and nitrate calibration ranges were 23.0–137 μEq/L and 0.18–9.5 μM, respectively. Coefficients of determination for the models were: ANC: R2 = 0.76, and R jackknife 2 = 0.44; NO3: R2 = 0.67, and R jackknife 2 = 0.27. The ANC model was applied to the top 50 cm of sediments in Moat Lake to reconstruct ANC from ca. AD 350 to 2005. The reconstruction suggests that ANC declined by about 40 % (101–60 μEq/L) between the 1920s and the 1960s and then recovered to pre-1920s levels during 1980–2000. The magnitude of this ANC excursion was the largest observed during the past 1,600 years. We hypothesize that temporal variations in ANC were influenced by: (1) changes in rates of acid deposition, especially nitric acid and (2) variations in the timing and magnitude of snowmelt runoff.

Throughout Europe and the USA, forest ecosystem functioning has been impacted by long-term excessive deposition of acidifying compounds. In this study, we report on trends in stand deposition and soil solution fluxes of inorganic nitrogen (N) and sulphur (S) compounds over a 17-year period (1994–2010) in five ICP Forests monitoring plots in Flanders, northern Belgium. Deposition was dominated by N, and primarily NH 4 + . Deposition of SO 4 2− and NH 4 + declined by 56–68% and 40–59% respectively. Deposition of NO − 3 decreased by 17–30% in deciduous forest plots, but remained stable in coniferous forest plots. The decrease of N and S deposition was parallelled by a simultaneous decline in base cation (BC = Ca 2+ + K + + Mg 2+ ) deposition, resulting in a 45–74% decrease of potentially acidifying deposition. Trends in soil solution fluxes of NH 4 + , NO 3 − , SO 4 2− and BC mirrored declining depositions. Nitrate losses below the rooting zone were eminent in both coniferous forest plots and in one deciduous forest plot, while net SO 4 2− release was observed in two deciduous forest plots. Critical limits for BC/Al ratio were exceeded at the three plots on sandy soils with lower cation exchange capacity and base saturation. Soil solution acid neutralizing capacity increased but remained negative, indicating that soil acidification continued, as the start of recovery was delayed by a simultaneous decrease of BC depositions and short-term soil buffering processes. Despite substantial reductions, current N deposition levels still exceed 4–8 times the critical load for safeguarding sensitive lichen species, and are still 22–69% above the critical load for maintaining ground vegetation diversity.

A regional survey of surface water acidification in Sichuan Basin was carried out during 2009–2011. Analysis of more than 90 samples revealed high pH and acid neutralizing capacity (ANC) in most surface waters, indicating that surface water acidification might not be a serious environmental issue in Sichuan Basin. However, some acidified surface water systems were present. Comparison of the results with a survey conducted 20 years ago revealed a significant decrease in ANC and increasing sulfate (SO42 ) and nitrate (NO3) concentrations. Rapid increases in sulfur dioxide (SO2 ) and nitrogen oxides (NOx ) emissions were likely the primary cause of surface water acidification, while high weathering of the purple soil in Sichuan Basin likely enabled strong buffering against acidification of surface water. However, low weathering occurred in areas of yellow earth and yellow-brown earth in the surrounding mountains, indicating that serious acid deposition could lead to acidification of surface water in these areas.

Relationships between stream chemistry and elevation, area, Anakeesta geology, soil properties, and dominant vegetation were evaluated to identify the influence of basin characteristics on baseflow and stormflow chemistry in eight streams of the Great Smoky Mountains National Park. Statistical analyses were employed to determine differences between baseflow and stormflow chemistry, and relate basin-scale factors governing local chemical processes to stream chemistry. Following precipitation events, stream pH was reduced and aluminium concentrations increased, while the response of acid neutralizing capacity (ANC), nitrate, sulfate, and base cations varied. Several basin characteristics were highly correlated with each other, demonstrating the interrelatedness of topographical, geological, soil, and vegetative parameters. These interrelated basin factors uniquely influenced acidification response in these streams. Streams in higher-elevation basins (>975 m) had significantly lower pH, ANC, sodium, and silicon and higher nitrate concentrations (p 10%) had significantly lower pH and sodium concentrations, and higher aluminium concentrations. Chemical and physical soil characteristics and dominant overstory vegetation in basins were more strongly correlated with baseflow and stormflow chemical constituents than topographical and geological basin factors. Saturated hydraulic conductivity, of all the soil parameters, was most related to concentrations of stormflow constituents. Basins with higher average hydraulic conductivities were associated with lower stream pH, ANC, and base cation concentrations, and higher nitrate and sulfate concentrations. These results emphasize the importance of soil and geological properties influencing stream chemistry and promote the prioritization of management strategies for aquatic resources. Copyright © 2012 John Wiley & Sons, Ltd.

Watershed 1 (W1) at the Hubbard Brook Experimental Forest in New Hampshire, with chronically low pH and acid neutralizing capacity (ANC) in surface water, was experimentally treated with calcium silicate (CaSiO3; wollastonite) in October 1999 to assess the role of calcium (Ca) supply in the structure and function of base-poor forest ecosystems. Wollastonite addition significantly increased the concentrations and fluxes of Ca, dissolved silica (Si), and ANC and decreased the concentrations and fluxes of inorganic monomeric Al (Ali) and hydrogen ion (H+) in both soil solution and stream water in all sub-watersheds of W1. Mass balances indicate that 54% of the added Ca remained undissolved or was retained by vegetation during the first 6 years after treatment. Of the remaining added Ca, 44% was retained on O horizon cation exchange sites. The Ca:Si ratio in the dissolution products was greater than 2.0, more than twice the molar ratio in the applied wollastonite. This suggests that Ca was preferentially leached from the applied wollastonite and/or Si was immobilized by secondary mineral formation. Approximately 2% of the added Ca and 7% of the added Si were exported from W1 in streamwater in the first 6 years after treatment. Watershed-scale Ca amendment with wollastonite appears to be an effective approach to mitigating effects of acidic deposition. Not only does it appear to alleviate acidification stress to forest vegetation, but it also provides for the long-term supply of ANC to acid-impacted rivers and lakes downstream.

Trends in precipitation pH and conductivity during 1992–2009, and in ionic compositions from January 2007 to June 2009, are reported from Lushan Mountain, one of the highest mountains in mid-east China. Annual mean pH was in the range of 4.35–5.01 and showed a statistically very significant (P

After years of adverse impacts to the acid-sensitive ecosystems of the eastern United States, the Acid Rain Program and Nitrogen Budget Program were developed to control sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions through market-based cap and trade systems. We used data from the National Atmospheric Deposition Program’s National Trends Network (NTN) and the U.S. EPA Temporally Integrated Monitoring of Ecosystems (TIME) program to evaluate the response of lake-watersheds in the Adirondack region of New York to changes in emissions of sulfur dioxide and nitrogen oxides resulting from the Acid Rain Program and the Nitrogen Budget Program. TIME is a long-term monitoring program designed to sample statistically selected subpopulations of lakes and streams across the eastern U.S. to quantify regional trends in surface water chemistry due to changes in atmospheric deposition. Decreases in wet sulfate deposition for the TIME lake-watersheds from 1991 to 2007 (−1.04 meq m−2-yr) generally corresponded with decreases in estimated lake sulfate flux (−1.46 ± 0.72 meq m−2-yr), suggesting declines in lake sulfate were largely driven by decreases in atmospheric deposition. Decreases in lake sulfate and to a lesser extent nitrate have generally coincided with increases in acid neutralizing capacity (ANC) resulting in shifts in lakes among ANC sensitivity classes. The percentage of acidic Adirondack lakes (ANC

We used data collected from 1989 to 2009 from 151 shallow (mean depth

Acid rock/mine drainage and metal leaching constitute major environmental management risks in the mining industry. This paper assesses the environmental risks due to acid rock/mine drainage, and the metal leaching potential of multiple mines of gold and manganese on the Ankobra River Drainage Basin in Southwestern Ghana. The basin is a hub of mining activity in Ghana, hosting several mines. A combination of mineralogical, and static geochemical acid drainage predictive investigation of overburden of varied geological units, complimented with hydrochemical drainage quality analysis was used to assess potential environmental risks posed by acid-generating lithologies and mine spoil. Mineralogical investigations revealed sulphide-bearing lithological units with profound compositional variations due to the incorporation of potentially toxic heavy metals and metalloids, in association with carbonates and silicates. Accounting Base Accounting (ABA) and Net acid generation potential pH (NAGpH) tests delimited two tailing sites as potentially acid generating with NAGpH of 3.5 and 4.8, respectively. Five other samples, representing specific lithological units in the stratigraphic sequence, with net acid neutralization potential ratio (NNPR) less than 5.0, were classified as being potentially acid generating according to the categorization requirement of the US Forestry Service. The rest of the samples exhibited moderate to very strong buffering capabilities. The assessment also evaluated drainage quality of the network of streams and rivers constituting the basin and identified sources of drainage contaminants. Acidic waters emanate from identified acid generating sources, while high metal load regimes were identified with both low pH waters and high pH regimes, coincident with high sulphide and carbonate alteration sites, respectively. The study results show that Zn, Cu, Ni, As, Co, Sb, SO4 2−, pH, alkalinity and conductivity are essential and adequate parameters in routine environmental risk monitoring programmes of mines in the area. Sites characterized by low pH ( 7.5), metal ions and sulphate are suggestive of net acid neutralizing.

This paper compares lake chemistry in the Adirondack region of New York measured by the Temporally Integrated Monitoring of Ecosystems (TIME) and Adirondack Long-Term Monitoring (ALTM) programs by examining the data from six lakes common to both programs. Both programs were initiated in the early 1990s to track the efficacy of emission reduction policies and to assess the full impacts of acid deposition on surface water chemistry. They now serve to inform on the emerging chemical recovery of these waters. The Adirondack TIME program utilizes a probability-based approach to assess chronic acidification in a population of lakes using one summer sample per year. The ALTM attempts to track changes in both chronic and episodic acidification across a gradient of lake types using monthly samples. The ALTM project has two important attributes that contrast with the TIME program in the Adirondacks: higher temporal resolution (monthly versus once during the summer or fall) and speciation of aluminum. In particular, the ALTM program provides inorganic monomeric aluminum (AlIM), the fraction of Al that is most toxic. The monthly sampling of the ALTM program includes the spring snowmelt period when acid-neutralizing capacity and pH are near their lowest and Al levels are near their highest. We compare chemistry trends (1992–2008) for sulfate, nitrate, base cations, dissolved organic carbon, hydrogen ion, acid neutralizing capacity, and Al for the six lakes common to both programs. We also compare relatively high springtime AlIM concentrations from the ALTM with relatively low summertime total Al concentrations from the TIME, showing that the ALTM program provides a more biologically relevant indicator of the effects of acid deposition, illustrating the value of the complementary monitoring efforts in the Adirondack region.

A field study was conducted to determine the linkage between dissolved organic matter (DOM) quality and bedrock geology. Sediment and water samples were collected from six streams, three flowing over sandstone and three flowing over limestone bedrock in the Bankhead National Forest, Alabama. Various stream water and sediment characteristics were determined by standard limnological methods and DOM quality was determined by Fourier transform ion cyclotron resonance mass spectrometry with sample introduction by electrospray ionization (ESI FT-ICR MS). Stream waters from limestone streams showed higher concentrations of calcium, magnesium, sodium, sulfate and dissolved inorganic carbon, as well as higher pH and acid neutralizing capacity, and were enriched in condensed hydrocarbons. In contrast, stream waters from sandstone streams showed higher concentrations of aluminum and iron and were enriched in tannin-like compounds. ESI FT-ICR MS analysis indicated that stream water DOM consisted of between 2950 and 3700 individual compounds ranging from 250 to 1000 Dalton. DOM compounds were grouped into 35 heteroatom (NnOoSs) classes based on molecular formula assignments and multi- variate statistical analysis was applied to reveal the patterns of variation of the DOM quality and identify environmental parameters associated with the variation. Partial redundancy analysis indicated that the variation in stream water DOM quality correlated with stream location and water chemistry parameters associated with bedrock type. A similar analysis including three previously published ESI FT-ICR MS anal- yses of stream water DOM showed similar correlations with location and stream water chemistry, indi- cating that bedrock geology via stream water chemistry influences DOM quality.

A laboratory study was conducted to investigate the ability of neutralization of red mud (RM) using carbon dioxide gas sequestration cycle at ambient conditions. The neutralized red mud (NRM) was characterized by XRD, SEM, EDX, FT-IR and auto titration method. X-ray diffraction pattern of NRM was revealed that the intensity of gibbsite was increased prominently and formed ilmenite due to dissolution of minerals. EDX analysis was showed that the %(w/w) of Na, C, O, Si were higher in the carbonated filtrate as compared to the RM and NRM. The permanently sequestered CO(2)%(w/w) per 10 g of red mud were approximately 26.33, approximately 58.01, approximately 55.37, and approximately 54.42 in NRM and first, second, third cycles of carbonated filtrate, respectively. The pH of red mud was decreased from approximately 11.8 to approximately 8.45 and alkalinity was decreased from approximately 10,789 to approximately 178 mg/L. The acid neutralizing capacity of NRM was approximately 0.23 mol H(+)/kg of red mud. The specific advantages of these cyclic processes are that, large amount of CO(2) can be captured as compared to single step.

Mean annual concentration of \({\textrm{SO}}_{4}^{2-}\) in wet-only deposition has decreased between 1988 and 2006 at the paired watershed study at Bear Brook Watershed in Maine, USA (BBWM) due to substantially decreased emissions of SO2. Emissions of NOx have not changed substantially, but deposition has declined slightly at BBWM. Base cations, \({\textrm{NH}}_{4}^{+}\), and Cl − concentrations were largely unchanged, with small irregular changes of

Studies on the chemical composition of wet precipitation were carried out from September 2005 to September 2007 at three Chinese regional background stations. All samples were analyzed for pH and major ions (F − , Cl − , NO − 3 , SO 4 2− , K + , Na + , Ca 2+ , Mg 2+ and NH 4 + ). Of the three stations, the lowest pH value was observed at Lin'an. The highest ion concentrations (SO 4 2− , NO 3 − and NH 4 + ) occurred at Shangdianzi. By referring to former studies and observations of reactive gases at the three stations, pH and chemical composition trends from 1985 to 2007 were analyzed. Compared to values from 1985 to 1997, the pH values in the precipitation of all three stations were significantly lower and [NO 3 − ] was higher. [SO 4 2− ] in the precipitation also increased at Shangdianzi and Longfengshan. Due to the neutralization of alkaline aerosols in northern China, precipitation at Shangdianzi and Longfengshan was not as severely acidified as at Lin'an. However, the neutralizing effects of the aerosols have decreased in recent years. Significant correlations between ions were found at each of the three stations. Principal component analysis was also performed to find possible sources of the major ionic species. Acid rain research in China has traditionally focused on urban sites, however the present study of background stations revealed significant effects of long-range transported air pollutants on rural areas in China.