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The relative influence of seasonal patterns in hydrological flow and seasonal differences in biological and geochemical activity on stream chemistry patterns is difficult to discern because they covary; temperate systems are characterized by lower mean flow in the summer (i.e. corresponding to deeper flow paths, elevated temperature, and biological activity), and higher mean flow in the winter (i.e. corresponding to shallower flow paths, depressed temperature, and biological dormancy). Using 2018 data, when seasonal stream flow conditions reversed, and two prior conventional water years, the relationship between monthly acid-relevant analyte concentrations and streamflow were compared within and between winter and summer to provide insight into controls on characteristic seasonal chemistry patterns at two mid-Appalachian sites with distinct geology (weatherable mafic and weather resistant siliciclastic). Acid neutralizing capacity (ANC) increased (1) with lower flow, in both seasons and (2) in summer, for all flow conditions. The compounding impacts resulted in a doubling of concentration from typical winter with high flow to summer with low flow at both sites. Base cation patterns tracked ANC at the mafic site, resulting in an ~ 60% increase of from winter with high flow to summer with low flow; distinctions between summer and winter contributed more to the seasonal pattern (72%) than changes in flow. Sulfate increased at the mafic site (1) with higher flow, in both seasons and (2) in winter, for all flow conditions, resulting in an ~ 50% increase from summer with low flow to winter with high flow; distinctions between winter and summer conditions and flow contributed similarly (40–60%) to the typical seasonal chemical pattern. The biogeochemical mechanism driving differences in stream chemistry between summer and winter for the same flow conditions is likely increased rates of natural acidification from elevated soil respiration in summer, resulting in greater bedrock weathering and sulfate adsorption. Findings highlight the significance and consistency of growing vs dormant season variations in temperature and biological activity in driving intra-annual patterns of stream solutes. This data set informs parameterization of hydro-biogeochemical models of stream chemistry in a changing climate at a biologically relevant, seasonal, timescale. [ABSTRACT FROM AUTHOR]

Excessive anthropogenic nitrogen fixation alters the nitrogen cycle and increases nitrogen deposition, leading to nitrogen saturation, which in turns leads to forest decline and nitrate leaching into stream waters. Kureha Hill in Toyama Prefecture, Japan, is considered to be in nitrogen saturation, since many streams have contained high concentrations of nitrate for more than 20 years. In this study, the latest status of nitrogen saturation was verified by comparing most recent data with 20 years observational data, focusing on various indicators of nitrogen saturation, such as stream water quality, nitrogen budget of the watershed, and soil nitrification and mineralization potential. Both the nitrogen deposition on the Hyakumakidani watershed on Kureha Hill and the amount of nitrate leaching to the stream tended to decrease. The reduction in nitrate leaching could be attributed to the reduction in nitrogen deposition and other factors, such as nitrogen pools in the soil. Despite the recent decline in nitrate concentration of the Hyakumakidani stream, the pH level has remained unchanged. This may be due to decreased concentrations of sulfate and acid neutralizing capacity (ANC). The C/N ratio of the soil ranged from 12 to 18 from 2000 to 2023, which was lower than the nitrogen saturation threshold of 25. The net nitrification rate and net mineralization rate showed no significant changes between 2002 and 2023, indicating that the potential to produce nitrate has been unchanged. Similar values in net nitrification and net nitrogen mineralization rates reflected that the Hyakumakidani watershed remained in Stage‐3 nitrogen saturation. [ABSTRACT FROM AUTHOR]

Eight pediatric oral nutritional supplements (ONSs) and 0.5% fat bovine milk were examined in vitro regarding their effect on the adhesion of three caries-related bacteria, Streptococcus mutans (strain CCUG 11877T), Lactobacillus gasseri (strain CCUG 31451), and Scardovia wiggsiae (strain CCUG 58090), to saliva-coated hydroxyapatite, as well as their pH and capacity to withstand pH changes. Bacteria were cultivated and radiolabeled. The adhesion assays used synthetic hydroxyapatite coated with whole or parotid saliva. Measurements of pH and titration of the products with HCl and NaOH were conducted in triplicate. Three ONSs promoted the S. mutans adhesion to saliva-coated hydroxyapatite (increase from 35% to >200%), supporting caries risk enhancement. S. wigssiae and L. gasseri adhered only to one and no ONS, respectively. Most supplements had limited buffering capacity to counteract acidification changes, suggesting their low capacity to neutralize acids, and one ONS showed a significant capacity to counteract basic changes, suggesting a high erosive potential. S. mutans adhesion was influenced by the ONS pH and volume NaOH added to reach pH 10. L. gasseri and S. wiggsiae adhesion was influenced by the ONSs' carbohydrate and fat content. Interdisciplinary efforts are needed to increase awareness and prevent the possible negative impact of ONSs on children's oral health. [ABSTRACT FROM AUTHOR]

Blackwater rivers and streams have stained or tea‐colored water from tannins released by decaying plant matter. Natural conditions in these waters often differ from non‐blackwater systems. For example, the pH and oxygen levels in waters can be very low, but completely natural. We examined an existing USEPA data set and found that blackwaters existed across the contiguous United States but were most common in the east. Water chemistry showed differences between blackwater and non‐blackwater sites, but differences were not consistent across ecoregions making national scale generalizations difficult. Physical habitat data analysis did not show dramatic differences between blackwater and non‐blackwater sites. Blackwater typically arises from streams that drain tannin‐rich bogs/muskeg and wetlands, so as expected blackwater sites had a shorter Euclidean distance to wetlands than non‐blackwater sites and existed in watersheds with a higher percentage of wetland habitat. Blackwaters in Northern and Temperate Plains tended to have higher acid neutralizing capacity, conductivity, and lower True Color; a visual color scale used for water purity. We posit that differences were because Color and Dissolved Organic Carbon at these sites were from buried wetland deposits rather than contemporary wetland habitats. Research needs that may increase our understanding and management of blackwaters include development of an operational definition that includes a classification framework and reference conditions for different blackwater types, identification of stressors and their associated dynamics that negatively impact blackwater systems, and development of data‐driven, consistent, and repeatable assessment methods, including development of targets, protective of unique conditions in blackwater rivers and streams. Plain Language Summary: Blackwater rivers and stream systems have stained or tea‐colored water due to tannins released by decaying plant matter. Although blackwaters exist across the contiguous United States, they are most common in the eastern United States. Beyond their distinct appearance, the chemistry of blackwater systems can be very different from other stream types. For example, the pH and amount of oxygen in the water can be very low, but completely natural. As a result of these and other characteristics, the fish, plants, and animals that live in blackwaters can also be unique. Because of these considerations, management of these systems can be challenging. To address these challenges, U.S. Environmental Protection Agency scientists are studying these systems. One of their early findings is that different types of blackwaters exist across the country. The team has highlighted the need for a classification system to distinguish among these types. Once this system exists, scientists can begin to identify what is required to protect blackwater systems and the services they supply. Key Points: There are a substantial number of blackwater rivers in multiple ecoregions of the United StatesThe water chemistry of blackwater rivers and streams is often very different than that of non‐blackwater rivers and streamsWe explore these differences and identify research needs that would contribute to their management and protection [ABSTRACT FROM AUTHOR]

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface‐water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large‐scale assessments of long‐term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid‐sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid‐sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long‐term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification. [ABSTRACT FROM AUTHOR]

Monoammonium glycyrrhizinate (MAG), a salt of glycyrrhizin, is reported for effective treatment of gastric disorders. The work was aimed to design and develop a gastro-retentive drug delivery system for MAG to delay its release in stomach by developing a stable raft with sufficient strength and acid-neutralizing potential. Preliminary, in-silico molecular docking study of MAG with the native ligand (Vonoprazan, a potential proton pump inhibitor) present in the gastric proton pump was performed. Docking studies predicted that MAG could bind to Vonoprazan binding site, indicating its ability to inhibit the gastric proton pump. The most desirable optimal formulation of raft forming tablets of MAG was anticipated with the desirability (0.819). The optimized formulation showed raft strength (8.61 ± 0.06 g), acid neutralizing capacity (11.19 ± 0.03 mEq) and in vitro release of MAG (69.11 ± 0.61% over 8h) indicating its suitability as a potential Gastro-retentive raft forming delivery system. The optimized formulation decreased gastric acid production and elevated gastric pH (p< 0.001.) in pylorus ligation induced gastric ulcers in animal model and demonstrated significant decrease in ulcer index (p< 0.001.) The developed raft-forming tablet of MAG could be a promising alternative to the existing synthetic agents to treat gastric ulcers. [ABSTRACT FROM AUTHOR]

With climate change and ongoing impacts from human development and resource extraction, US federal land management agencies are acutely concerned with managing for healthy aquatic ecosystems in the Southern Appalachian Mountain (SAM) Region. Here, we describe development of a spatial decision support application to assess the biological and ecological impacts of atmospheric S and N deposition on aquatic ecosystems of the region. We first summarize foundational published work to predict continuous maps of surface water acid neutralizing capacity (ANC) and soil base cation weathering (BCw). We use the predicted ANC and BCw maps to estimate steady‐state critical loads (CLs) of atmospheric S and N deposition. We included estimated CLs of atmospheric N to get a complete picture of CLs and potential exceedances. We then present a logic‐based decision support model for assessing effects of S and N deposition based on statistically modeled stream ANC and CL exceedance. The model is easily modified for continuous monitoring of CL exceedance patterns as new S and N deposition and ANC data become available. We present mapped model results for the SAM study area and an important subset of the region, the Great Smoky Mountains National Park. ANC modeling results revealed that predicted acid sensitivity was spatially variable, with areas of relatively low stream ANC (<50 μeq · L−1) and soil BCw (<50 meq · m−2 · year−1) predominantly found in certain critical areas. Within the Great Smoky Mountains National Park, evidence for S CL exceedance based on an ANC criterion of 50 μeq · L−1 was strong at locations where ambient S deposition was at least two times the CL. We also predicted likely impacts of CL exceedances on aquatic insect species richness and native fish abundance. Responses for insect species richness and fish impact showed variability similar to CL exceedance, with increasing impact positively correlated with elevation. Finally, we discuss ways that the decision support system can be used to prioritize management across the region. [ABSTRACT FROM AUTHOR]

Climate warming is expected to drive an upward altitudinal shift of species distributions in mountain areas. In this study, we consider how environmental variables constrain the distribution of freshwater mollusks across elevations based on an extensive survey of the entire Pyrenean range. Results show that several altitude-related variables are significantly relevant for the distribution of all mollusks (i.e., temperature, sediment organic content). Others respond more precisely to some variables: fine substrate proportion increases the probability of finding Pisidium sensu lato (mostly Euglesa species), and the latter, the macrophyte presence, and Ampullaceana balthica. Despite the low acid-neutralizing capacity in many of the lakes, only the distribution of A. balthica was significantly constrained by this factor, independent from elevation. The results confirm a likely altitudinal expansion of the distributions of all species, particularly toward lakes with a summer surface temperature increasing above 12 °C. The pace of change is expected to differ among species according to different nonlinear thresholds in thermal response, which temperature value increases from Pisidium s.l. to Ampullaceana to Ancylus, and the taxon-specific sensitivity to substrates and chemical conditions. [ABSTRACT FROM AUTHOR]

Studies focused on emissions and acid deposition of sulfur (S) and nitrogen (N) and the consequent precipitation acidity have a long history. However, atmospheric depositions of cations play a critical role in buffering precipitation acidity, and providing cationic nutrients for vegetation growth lacks sufficient studies equally. The spatiotemporal patterns of cation depositions and their neutralization potential across broad scales remain unclear. Through synthesizing the long-term data in forest sites (n = 128) derived from three monitoring networks (NADP in Northern America, EMEP in Europe, and EANET in East Asia) on wet deposition of cations (Na+, NH4-N, K+, Mg2+, and Ca2+), this study assesses the temporal changes and spatial patterns of cation depositions and their neutralization potential over the last two decades. The results showed that the depositions of cationic nutrients were considerably higher in EANET compared to NADP and EMEP. The depositions of sea salt-associated sodium exhibited a significant transition from marine (> 15 kg ha−1 year−1) to inland (< 3.0 kg ha−1 year−1) forest sites attributable to the precipitation quantity and influences of sea spray. The higher emissions of NH3 and particulate matter in East Asia explained the higher cation depositions in EANET than NADP and EMEP. The annual trends of cations revealed that only 20–30% of the forest sites showed significant changing trends and the sites widely spread across the three networks. Possibly, base cation (BC) deposition has reached a low and stable condition in NADP and EMEP, while it has high spatial heterogeneity in the temporal change in EANET. The difference in BC deposition among the three networks reflects their distinct development of economy. Our synthesis indicates that the annual trends of neutralization factor (NF) in NADP can be explained by the declining of acid potential (AP), not by neutralization potential (NP) as BC deposition has been stably low over the past two decades. Whereas, the concurrent decreases of AP and NP in EMEP or plateau period of both AP and NP in EANET have come to a standstill of acid neutralizing capacity. [ABSTRACT FROM AUTHOR]

Ocean alkalinity plays a fundamental role in the apportionment of CO2 between the atmosphere and the ocean. The primary driver of the ocean's vertical alkalinity distribution is the formation of calcium carbonate (CaCO3) by organisms at the ocean surface and its dissolution at depth. This so‐called "CaCO3 counterpump" is poorly constrained, however, both in terms of how much CaCO3 is exported from the surface ocean, and at what depth it dissolves. Here, we created a steady‐state model of global ocean alkalinity using Ocean Circulation Inverse Model transport, biogeochemical cycling, and field‐tested calcite and aragonite dissolution kinetics. We find that limiting CaCO3 dissolution to below the aragonite and calcite saturation horizons cannot explain excess alkalinity in the upper ocean, and that models allowing dissolution above the saturation horizons best match observations. Linking dissolution to organic matter respiration, or imposing a constant dissolution rate both produce good model fits. Our best performing models require export between 1.1 and 1.8 Gt PIC y−1 (from 73 m), but all converge to 1.0 Gt PIC y−1 export at 279 m, indicating that both high‐ and low‐export scenarios can match observations, as long as high export is coupled to high dissolution in the upper ocean. These results demonstrate that dissolution is not a simple function of seawater CaCO3 saturation (Ω) and calcite or aragonite solubility, and that other mechanisms, likely related to the biology and ecology of calcifiers, must drive significant dissolution throughout the water column. Plain Language Summary: The acid neutralizing capacity, or alkalinity, in the ocean surface affects how much CO2 the ocean can absorb from the atmosphere. Alkalinity is lost from the surface ocean when marine organisms make calcium carbonate (CaCO3) shells; in contrast, alkalinity is returned to seawater when shells dissolve. Both processes are not well quantified. Here, we created a model to constrain how much CaCO3 sinks out of the surface ocean, and at what depth it dissolves. We find that CaCO3 must dissolve in the upper ocean where calcite and aragonite—the two most common forms of CaCO3—are thermodynamically oversaturated. We also find that a range of CaCO3 exports—from 1.1 to 1.8 Gt PIC y−1—can match observations, as long as high export is coupled to high dissolution in the upper ocean. These results suggest that CaCO3 dissolution is not only controlled by seawater chemistry, and that other mechanisms, likely related to the biology and ecology of organisms that make CaCO3 shells, are important drivers of CaCO3 dissolution in the ocean. Key Points: Restricting calcium carbonate (CaCO3) dissolution to below saturation horizons cannot reproduce excess alkalinity observations in the upper oceanExports between 1.1 and 1.8 Gt PIC y−1 (from 73 m) can match GLODAP observations, but models converge to 1.0 Gt PIC y−1 export at 279 mIn addition to seawater CaCO3 saturation and mineral solubility, other mechanisms drive CaCO3 dissolution throughout the water column [ABSTRACT FROM AUTHOR]

To monitor recovery from acidification, water chemistry was sampled in 11 Dutch moorland pools from 1978 to 2018. Changes were assessed by visual inspection of time series and tested non-parametrically. As a net result of all inputs and outputs, the median sulphate and ammonium concentrations in the surface water dropped by about 90%. This was accompanied by increases in pH, acid neutralizing capacity, and dissolved organic matter, and decreased metals, particularly toxic aluminium. Decreases of ammonium and sulphate in the surface water are considerably higher than in deposition, indicating the importance of losses to sediments and the atmosphere. The changes were greatest in pools with relatively flat banks exposed to the air in extremely dry summers. After the extremely dry summer of 1976, the changes were dramatic due to acidification by oxidation of the reduced sulphur and nitrogen compounds stored in the moorland pool bottom. In later dry years, the changes in the pools with flat banks were less extreme, as the sulphur stock in the sediment was depleted by winterly discharge to groundwater. In pools with steep banks, the sulphur compounds are retained in the sediment and may cause eutrophication by the displacement of phosphorus from iron compounds. [ABSTRACT FROM AUTHOR]

Sustainable management of coal waste is one of the major environmental concerns for coal mining, whether active or legacy, worldwide. Coal dump deposits demand a large physical area or footprint for disposal of solid waste, change the topography, and generate both pyritic dust and acid rock drainage (ARD) where pyritic coal waste is deposited. The beneficiation of dump deposits or, preferably, of coal waste prior to its dumping can reduce or even eliminate the liabilities related to coal waste management. In this work, dense medium separation studies of coal discards, using heavy liquids, resulted in three pooled fractions from typical South African coal waste discards from the Mpumalanga region for future use: (a) a fraction of low density with increased calorific value; (b) a fraction of intermediate density, rich in ash and acid neutralizing minerals and lower in sulfur; and (c) a fraction of high density, rich in sulfidic minerals including pyrite. The fractions were characterized using particle size analysis, sink-float studies, static tests to predict ARD potential, proximateand ultimate analysis, and gross calorific value. The results showed that approximately 70% of this discard coal is composed of a material of sufficient quality for energy generation in conventional power stations. A pyrite-rich concentrate made up 2% of the total discard mass; comprising more than 45% of the sulfidic mineral present in the feed and displaying no acid neutralizing capacity (ANC). The remaining discard fraction, with intermediate density, presented potential to be used for several ends including soil fabrication, co-disposal or as aggregate material in civil engineering; additional testing to ensure applicability for the selected re-purposing option should be chosen based on proposed use. [ABSTRACT FROM AUTHOR]

Policy measures resulted in reductions in acidic emission of sulfur and nitrogen in North America. Here, we conducted trend analyses on a 37-year database for atmospheric depositions and lake (n = 78) chemistry in the provinces of Nova Scotia, New Brunswick, and Newfoundland and Labrador, in Canada. Sulfate, and particularly nitrate deposition, began to decrease strongly around the year 2000, resulting in strong pH increases in precipitation. Recovery was observed in most lakes with significant increases in pH and Gran alkalinity (AlcG). A piecewise regression approach detected coherent breaks and overlapping confidence intervals in the break years for precipitation pH and lake AlcG (to a lesser extent for lake pH), suggesting a rapid lake response to the sudden changes in acidic inputs. However, an increase in organic acid after 2000 decreases the rate of acid neutralizing capacity recovery nearly by half in about a third of the studied lakes. Despite the positive pH and AlcG trends, a significant proportion of lakes still have pH and calcium values below the recommended thresholds for aquatic life. [ABSTRACT FROM AUTHOR]

Purpose: To compare Polygel Dual (PD) and four marketed alginate-antacid combination products, with respect to raft formation and antacid properties. Methods: The pharmacopeial tests used were selected based on demonstrable performance of raftforming potential, including speed and thickness, for all selected products. Evidence-based methods were used to determine the antacid effects in terms of acid-neutralizing capacity and increase in pH. Results: Raft-forming ability was demonstrated by three products, with AF-4 and PD outperforming in speed and thickness. PD, AF-1 and AF-2 exhibited superior antacid properties. However, PD was the only product that demonstrated superior performance with respect to raft-formation and antacid potential. Raft-forming capacity was exhibited by 3 out of 5 products, viz, PD, AF-1 and AF-4. Raft formation was faster in AF-4 (15 s), followed by in PD (25 s). Similarly, raft thickness (14.79 mm) was highest in AF-4, followed by (4.39 mm) in PD. Preliminary antacid test results showed that AF-4 failed to raise pH above 3.5, but PD raised pH to 5.86, while AF-1 raised pH to 5.88. Similarly, periodic test analysis revealed that PD maintained pH above 7 for the entire test duration of 210 min, whereas AF-4 failed to raise pH to 7 during the test period. Conclusion: Polygel dual (PD) demonstrates desirable raft-forming potential and antacid properties. Moreover, it effectively raises pH and maintains it for longer duration than any of the other antacid products. Thus, PD may be considered a potentially effective treatment for acid-reflux problems. However, this claim should be validated in suitable clinical trials. [ABSTRACT FROM AUTHOR]

The Mulberry River in Arkansas is one of America's National Wild and Scenic Rivers and has been listed as impaired for low pH since 2008. Stream chemistry is directly related to land use and changes in land use can result in degradation of surface waters. Growth of conifers, through afforestation or conversion of native hardwood stands, has been attributed to basin acidification in several regions and may be contributing acid to the Mulberry River basin. The objective of this study was to examine the relationship between land use (i.e., coniferous forest, deciduous forest, mixed forest, and pasture) and stream chemistry of 11 tributaries of the Mulberry River over a 2‐year period. Coniferous forest land use was not correlated with stream pH, neither was stream pH predicted by coniferous forest land use. Acid neutralizing capacity (ANC) was negatively correlated with, and partially predicted by coniferous land use. Total organic carbon was negatively correlated with coniferous land use and positively correlated with deciduous land use. Deciduous land use was positively correlated with SO4 and negatively correlated with total N and NO3. Spearman's rank correlation and principal component analysis identified significant inverse relationships between stream pH and NO3 and between ANC and NO3, which may suggest that HNO3 may be the primary source of acidity within the Mulberry River basin. Although no relationships were observed between coniferous land use and pH, conifer growth may be affecting the stream buffering capacity of the basin which would increase the susceptibility of the river to acidification. [ABSTRACT FROM AUTHOR]

Soil acidification induced by reactive nitrogen (N) inputs is a major environmental issue in grasslands, as it lowers the acid neutralizing capacity (ANC). The specific impacts of different N compound forms on ANC remain unclear. Grassland management practices like mowing and grazing can remove a considerable amount of soil N and other nutrients, potentially mitigating soil acidification by removing N from the ecosystem or aggravating it by removing base cations. However, empirical evidence regarding the joint effects of adding different forms of N compounds and mowing on ANC changes in different-sized soil aggregates is still lacking. This study aimed to address this knowledge gap by examining the effects of three N compounds (urea, ammonium nitrate, and ammonium sulfate) combined with mowing (mown vs. unmown) on soil ANC in different soil aggregate sizes (>2000 μm, 250–2000 μm, and <250 μm) through a 6-year field experiment in Inner Mongolia grasslands. We found that the average decline in soil ANC caused by ammonium sulfate (AS) addition (−78.9%) was much greater than that by urea (−25.0%) and ammonium nitrate (AN) (−52.1%) as compared to control. This decline was attributed to increased proton (H+) release from nitrification and the leaching of exchangeable Ca2+ and Mg2+. Mowing aggravated the adverse effects of urea and AN on ANC, primarily due to the reduction in soil organic matter (SOM) contents and the removal of exchangeable Ca2+, K+, and Na + via plant biomass harvest. This pattern was consistent across all aggregate fractions. The lack of variation in soil ANC among different soil aggregate fractions is likely due to the contrasting trend in the distribution of exchangeable Ca2+ and Mg2+. Specifically, the concentration of exchangeable Ca2+ increased with increasing aggregate size, while the opposite was true for that of exchangeable Mg2+. These findings underscore the importance of considering the forms of N compounds when assessing the declines of ANC induced by N inputs, which also calls for an urgent need to reduce N emissions to ensure the sustainable development of the meadow ecosystems. [Display omitted] • (NH 4) 2 SO 4 addition caused greater decline in ANC than CO(NH 2) 2 or NH 4 NO 3 addition. • Greater ANC decline was associated with greater NH 4 + inputs, Ca2+ and Mg2+ loss. • Mowing aggravated the effect of CO(NH 2) 2 or NH 4 NO 3 by reducing SOM and base cations. • Aggregate size had no significant effect on ANC. [ABSTRACT FROM AUTHOR]

Climate warming is expected to drive an upward altitudinal shift of species distributions in mountain areas. In this study, we consider how environmental variables constrain the distribution of freshwater mollusks across elevations based on an extensive survey of the entire Pyrenean range. Results show that several altitude-related variables are significantly relevant for the distribution of all mollusks (i.e., temperature, sediment organic content). Others respond more precisely to some variables: fine substrate proportion increases the probability of finding Pisidium sensu lato (mostly Euglesa species), and the latter, the macrophyte presence, and Ampullaceana balthica. Despite the low acid-neutralizing capacity in many of the lakes, only the distribution of A. balthica was significantly constrained by this factor, independent from elevation. The results confirm a likely altitudinal expansion of the distributions of all species, particularly toward lakes with a summer surface temperature increasing above 12 °C. The pace of change is expected to differ among species according to different nonlinear thresholds in thermal response, which temperature value increases from Pisidium s.l. to Ampullaceana to Ancylus, and the taxon-specific sensitivity to substrates and chemical conditions.

This study informs the restoration and development of salmonid fisheries and aquaculture facilities regarding water quality and light effects on hatching survival in spring channels. Brook trout Salvelinus fontinalis eggs were hatched in springs from karst and silica-clastic aquifers to determine whether survival was affected by water quality in differing geological areas. Nitrogen gas saturation (N2) was highest in karst springs and impacted survival, with a negative relationship between N2 and survival during hatching (> 110% N2 corresponded to 70.5% survival). A multiple regression model was developed to predict survival that included N2, acid neutralizing capacity (ANC), and light intensity (Light) following the equation: In a follow-up experiment, brook trout eggs were fertilized and hatched in hatching boxes in high and low levels of ultraviolet light (UV), fluorescent light, and complete darkness to test the effects of UV and light intensity on survival. Logistic regression was used to model the probability of mortality as a function of UV-B intensity. Results indicated freshly fertilized eggs were more severely impacted by light and UV than post-eyed eggs, and both UV and fluorescent light treatments experienced high mortality compared to the treatment in complete darkness. Karst springs with intermediate concentrations of calcium and increased ANC provide improved water quality for salmonids as compared to silica-clastic aquifers; however, high N2 can have negative effects on survival which, could be overcome by aeration within spring channels. Furthermore, using advanced aquaculture techniques, it may be possible to develop a brood stock that is resistant to the effects of N2. Effects of UV and light intensity pose additional challenges at early life stages for salmonids which, can be overcome by shading hatch boxes in the spring channel.

Long‐term ecosystem studies are valuable for understanding integrated ecosystem response to global changes in atmospheric deposition and climate. We examined trends for a 35‐year period (1982/83–2017/18) in concentrations of a range of solutes in precipitation and stream water from nine headwater catchments spanning elevation and surficial geology gradients at the Turkey Lakes watershed (TLW) in northeastern Ontario, Canada. Average annual water year (WY, October to September) concentrations in precipitation significantly declined over the period for sulphate (SO42−), nitrate (NO3−) and chloride (Cl−), while calcium (Ca2+) and potassium (K+) concentrations increased, resulting in a significant pH increase from 4.2 to 5.7. Trends in stream chemistry through time are generally consistent with expectations associated with acidification recovery. Concentration of many stream water solutes (SO42−, Cl−, calcium [Ca2+], magnesium [Mg2+] and NH4+ generally decreased, while others (silica [SiO2] and dissolved organic carbon [DOC]) generally increased. Increases were also observed for alkalinity (six of nine catchments), acid neutralizing capacity ([ANC]; six of nine catchments) and pH (eight of nine catchments), while conductivity declined (six of nine catchments). Variability in trends among catchments are associated with differences in surficial geology and wetland cover. While absolute solute concentrations were generally lower at bedrock dominated high‐elevation catchments compared to till dominated lower elevation catchments, the rate of change of concentration was often greater for high elevation catchments. This study confirms continued, but non‐linear stream chemistry recovery from acidification, particularly at the less buffered high and moderate elevation sites. The heterogeneity of responses among catchments highlights our incomplete understanding of the relative importance of different mechanisms influencing stream chemistry and the consequences for downstream ecosystems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

The Shenandoah Watershed Study (established in 1979) and the Virginia Trout Stream Sensitivity Study (established in 1987) serve to increase understanding of hydrological and biogeochemical changes in western Virginia mountain streams that occur in response to acidic deposition and other ecosystem stressors. The SWAS‐VTSSS program has evolved over its 40+ year history to consist of a temporally robust and spatially stratified monitoring framework. Currently stream water is sampled for water quality bi‐hourly during high‐flow events at three sites and weekly at four sites within Shenandoah National Park (SHEN), and quarterly at 72 sites and on an approximately decadal frequency at ~450 sites within the wider western Virginia Appalachian region. Stream water is evaluated for pH, acid neutralizing capacity (ANC), base cations (calcium, magnesium, sodium and potassium ion), acid anions (sulphate, nitrate and chloride), silica, ammonium, and conductivity with a subset of samples evaluated for monomeric aluminium and dissolved organic carbon. Hourly stream discharge (four sites) and in‐situ measurements of conductivity, water and air temperature (three sites) are also measured within SHEN. Here we provide an overview and timeline of the SWAS‐VTSSS stream water monitoring program, summarize the field and laboratory methods, describe the water chemistry and hydrologic data sets, and document major watershed disturbances that have occurred during the program history. Website links and instructions are provided to access the stream chemistry and time‐series monitoring data in open‐access federal databases. The purpose of this publication is to promote awareness of these unique, long‐term data sets for wider use in catchment studies. The water chemistry and hydrologic data can be used to investigate a wide range of biogeochemical research questions and provide key inputs for models of these headwater stream ecosystems. SWAS‐VTSSS is an ongoing program and quality assured data sets are uploaded to the databases annually. [ABSTRACT FROM AUTHOR]

Springs are the point of origin for most headwater streams and are important regulators of their chemical composition. We analysed solute concentrations of water emerging from 57 springs within the 3 km2 Fool Creek catchment at the Fraser Experimental Forest and considered sources of spatial variation among them and their influence on the chemical composition of downstream water. On average, calcium and acid neutralizing capacity (bicarbonate‐ANC) comprised 50 and 90% of the cation and anion charge respectively, in both spring and stream water. Variation in inorganic chemical composition among springs reflected distinct groundwater sources and catchment geology. Springs emerging through glacial deposits in the upper portion of the catchment were the most dilute and similar to snowmelt, whereas lower elevation springs were more concentrated in cations and ANC. Water emerging from a handful of springs in a geologically faulted portion of the catchment were more concentrated than all others and had a predominant effect on downstream ion concentrations. Chemical similarity indicated that these springs were linked along surface and subsurface flowpaths. This survey shows that springwater chemistry is influenced at nested spatial scales including broad geologic conditions, elevational and spatial attributes and isolated local features. Our results highlight the role of overlapping factors on solute export from headwater catchments. [ABSTRACT FROM AUTHOR]

Tusen: A thousand lakes in the Norwegian landscape: This article belongs to Ambio's 50th Anniversary Collection. With low base cation concentrations, many of the lakes were sensitive to acidification resulting from high sulfate concentrations related to acidic deposition. Lakes that had the highest sulfate concentrations showed a tendency to lower levels, however, nitrate concentrations were higher, adding to the contribution of sulfate to acidity. The Norwegian lake survey in 1986 made the linkage between acid deposition and lake acidification clear. [Extracted from the article]

Acidification of inland waters: This article belongs to Ambio's 50th Anniversary Collection. This applies also to acidification - acids are deposited on land and water, transported downstream along with other chemical species that are mobilized from soils due to increased acidity, with subsequent consequences for aquatic life. Ambio volume 50. 3 Almer B, Dickson W, Ekström C, Hörnström E. Effects of acidification on Swedish lakes. [Extracted from the article]

This study informs the restoration and development of salmonid fisheries and aquaculture facilities regarding water quality and light effects on hatching survival in spring channels. Brook trout Salvelinus fontinalis eggs were hatched in springs from karst and silica-clastic aquifers to determine whether survival was affected by water quality in differing geological areas. Nitrogen gas saturation (N2) was highest in karst springs and impacted survival, with a negative relationship between N2 and survival during hatching (> 110% N2 corresponded to ≤ 70.5% survival). A multiple regression model was developed to predict survival that included N2, acid neutralizing capacity (ANC), and light intensity (Light) following the equation: % Survival = − 3.00 N 2 + 0.08 ANC − 0.01 Light + 404.5. In a follow-up experiment, brook trout eggs were fertilized and hatched in hatching boxes in high and low levels of ultraviolet light (UV), fluorescent light, and complete darkness to test the effects of UV and light intensity on survival. Logistic regression was used to model the probability of mortality as a function of UV-B intensity. Results indicated freshly fertilized eggs were more severely impacted by light and UV than post-eyed eggs, and both UV and fluorescent light treatments experienced high mortality compared to the treatment in complete darkness. Karst springs with intermediate concentrations of calcium and increased ANC provide improved water quality for salmonids as compared to silica-clastic aquifers; however, high N2 can have negative effects on survival which, could be overcome by aeration within spring channels. Furthermore, using advanced aquaculture techniques, it may be possible to develop a brood stock that is resistant to the effects of N2. Effects of UV and light intensity pose additional challenges at early life stages for salmonids which, can be overcome by shading hatch boxes in the spring channel. [ABSTRACT FROM AUTHOR]

The purpose of this research work was to formulate raft-forming chewable bilayer tablets of sodium alginate using a raft-forming agent along with gas-generating agents. Tablets were prepared by wet granulation and evaluated for raft strength, acid neutralization capacity, weight variation, % drug content, thickness, hardness, friability and in vitro drug release. Various raft-forming agents were used in preliminary screening. The amount of sodium alginate, amount of calcium carbonate and amount sodium bicarbonate were selected as variables. Raft strength, acid neutralization capacity and drug release at 30 min were selected as responses.Tablets containing sodium alginate were having maximum raft strength as compared with other raft-forming agents. Acid neutralization capacity and in vitro drug release of all factorial batches were found to be satisfactory. Prepared tablets were found to be pharmaceutically equivalent to the marketed product. It was concluded that raft-forming chewable bilayer tablets prepared using an optimum amount of sodium alginate, calcium carbonate and sodium bicarbonate could be an efficient dosage form in the treatment of gastro oesophageal reflux diseases. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Heavy metal (HM) leaching from tungsten mine tailings is a serious environmental risk. In this study, we assess the HM pollution level of tungsten tailings, determine the HM leaching patterns and mechanisms, and estimate the HM fluxes from a tailings reservoir. The results showed that the comprehensive pollution index (CRSi) values that decreased in order of the HM pollution levels in the tailings were cadmium (Cd) > tungsten (W) > lead (Pb) > copper (Cu) = zinc (Zn) > arsenic (As) > manganese (Mn). This result indicated that Cd, W, and Pb were priority pollutants in tailings. The Res fraction of all HMs was greater than 50%. Pb and Cd had similar species fractions with high Exc fractions, and tungsten had a considerable proportion of the Wat fraction. The general acid neutralizing capacity (GANC) test divides the leaching process of HMs into two stages, and each of stage is affected by different mechanisms. A neutral environment promoted tungsten leaching in the column leching test, while an acidic environment promoted Cd and Pb leaching. In addition, the pH effect was more obvious in the early stage. The kinetic fitting results showed that the second-order dynamic model well simulated the leaching of W, Pb, and Cd in most cases. Based on column kinetic leaching test results and tailings parameters, the annual W, Pb, and Cd fluxes were estimated to be 6.35 × 108, 1.3288 × 109, and 1.012 × 108 mg/year, respectively. The above results can guide the environmental management of tungsten tailing reservoirs, such as selecting suitable repair materials and estimating repair service times. [Display omitted] • CRSi was used to assess the HM pollution of tungsten tailings. • The GANC test suggests 2 stages of W leaching and controlled by different factor. • The different effects of pH and DOM on W, Cd, and Pb were assessed in kinetic leaching. • HM fluxes of tungsten tailings reservoir was estimated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Coal fly ash can be used in in various configurations (e.g. as cap, bottom liner, or blending) at a mine site, but comparative studies investigating their capacity to control acid mine drainage are limited. Batch and column leaching experiments were conducted to investigate the effects of fly ash-mine tailings mix ratios and system configurations on leachate chemistry. Acidic mine tailings (pH 2.72) were obtained from waste piles at a former gold and pyrite mine. Mixing the fly ash with the tailings in a 1:1 (w/w) ratio decreased Zn, Ni, Fe, Mn, Pb, and Cu leaching by 90 ± 6%, increased the pH from extremely acidic (2.9) to alkaline (8.0), and decreased electrical conductivity from 4 to 2.5 mS cm−1 due to solute precipitation. Using the fly ash as a 'chemical liner' beneath the tailings, applying the fly ash as both a cap and bottom liner, or blending the fly ash with tailings produced significantly less acidity, salinity, and metal leaching than using the fly ash as a cap. The capacity of fly ash to control acid generation is attributed to its acid neutralizing capacity and high pH (11.1). [ABSTRACT FROM AUTHOR]

Abstract Municipal solid waste incineration fly ash is directly landfilled after solidification in the industry. The rapid evaluation of contaminant leaching is required before the landfill of fly ash. In order to reduce the time to evaluate the effect of solidification, a set of rapid evaluation method was developed through the determination of characteristic index, heavy metal leaching analysis, principal component analysis, and mathematical model construction. It was found that f-CaO, acid neutralizing capacity, pH and soluble calcium were negatively correlated with heavy metal leaching. The soluble chlorine was positively correlated with heavy metal leaching. The effect of each feature indicators on heavy metal leaching was evaluated using principal component analysis and mathematical analysis software R.3.4.4. Furthermore, R.3.4.4 was used to detect the optimal model and the excess probability formula by stepwise linear regression and logistic regression analysis method. By introducing the measured value of feature indicator into the excess probability formula, the rate of excess-standard of heavy metals leaching can be preliminarily determined. Based on the above ideas, a rapid detection and evaluation system could be developed according to the local leaching standards and the components of fly ash selected locally. Highlights • Survey of heavy metals leaching in MSWI fly ash was conducted with its compositions. • Soluble Cl and Ca had a positive correlation with Pb and Cd leaching. • Soluble Cl and f-CaO had decisively influence on Pb leaching. • Rapid evaluation of leaching risk correlated with fly ash contents. [ABSTRACT FROM AUTHOR]

Sulfur dioxide emissions have been regulated at a global scale; sulfur (S) deposition no longer contributes to soil acidification instead of an alleviation effect in temperate regions; however, it remains unclear whether S deposition still contributes to soil acidification in the tropics. The Pearl River Delta (PRD), South China, has been suffering serious soil acidification, but the contribution of S deposition was ignored because of the regulation of S emission since 2001. Here, we chose the evergreen broadleaf forests, which are the typical forest type at the regional scale in PRD to examine the contribution of S deposition and its characteristics in this acidification, based on an established urban–rural gradient in the range of 260 km. A substantial acidification was evidenced by the significant decline of soil pH from rural to urban sites, with mean pH values decreased by more than 0.60 U through the whole 40-cm depths. However, there was no significant difference in soil pH from 0–10 cm, 10–20 cm, and to 20–40 cm at each site (P > 0.05). Acid-neutralizing capacity (ANC) showed a similar trend to soil pH, with a significant decline along the urbanization gradient and no significant effect of soil depths. Soil sulfate (SO42−), as the most abundant species in ANC, contributed greatly to soil acidification for the whole 40-cm depth, as shown by the significant positive relationships between it with soil pH and base cations. Soils also exhibited the depletion of base cations with low base saturation (< 20%) and the release of Al and Fe. Our research demonstrated that the severe soil acidification in the PRD region has extended to the subsoil level (40-cm depth), and S deposition is still an important driver to this acidification. Therefore, both recovering the acidified soils and controlling the acidifying pollutants, especially S, are particularly difficult in southern China. [ABSTRACT FROM AUTHOR]

Background: Over fertilization with nitrogen (N) is considered the main driver of agricultural soil acidification in China. However, the contribution of this driver compared to other causes of soil acidification on intensive croplands has seldom been quantified under field conditions.Methods: We measured the fate of major nutrients, and calculated the related H+ production, based on the difference between inputs and leaching losses of those nutrients for a wheat-maize rotation system on a moderate acid silty clay loam soil in a two-year field experiment.Results: Topsoil pH decreased 0.3 units in the plots with conventional (current farmer practice) high N fertilization after two years, with a proton production of 13.1 keq H+ ha−1 yr.−1. No apparent changes in topsoil pH were observed in the plots without N application, in spite of a proton production of 4.7 keq H+ ha−1 yr.−1. Crop uptake was the primary driver of H+ production, followed by N transformation processes and HCO3− leaching in both plots.Conclusions: Nitrogen fertilization had a relative small direct impact on soil acidification due to a very limited nitrate leaching, induced by large N losses to air by denitrification in this specific moderately acid soil, whereas elevated base cation uptake by crops induced by N fertilization indirectly had a relative large impact. [ABSTRACT FROM AUTHOR]

Sulphur dioxide emissions from the smelter are expected to cause an increase in sulphate (SO SB 4 sb SP 2- sp ) concentrations in surface waters as SO SB 4 sb SP 2- sp acts as a mobile anion (Reuss & Johnson, [16]), and in young, recently glaciated soils with low S adsorption capacities SO SB 4 sb SP 2- sp should pass conservatively through soils. There are many examples worldwide where high S deposition results in high SO SB 4 sb SP 2- sp leaching but does not lead to ecosystem impacts because of the low sensitivity of the catchment soils to acidification. A recent paper by Maguire et al. ([11]) reported that sulphur (S) deposition downwind of aluminum (Al) smelter in Kitimat, British Columbia, was impacting an area of up to 100 km SP 2 sp and "may contribute to effects within tributaries on benthic stream communities and regionally important juvenile Pacific salmon.". [Extracted from the article]

• Acidification in aquatic ecosystems is still a driver of biodiversity loss. • Few metrics to assess acidification impact are calibrated for lentic-lotic waters. • Few metrics assess impacts of acidification across large geographic regions. • We developed an invertebrate-based index to assess acidity impacts and recovery. • Our index enables standardized assessment in lentic-lotic water in Nordic countries. 1) Emissions of acidifying compounds have decreased over several decades, nevertheless acidification impacts on aquatic ecosystems remains as a regionally important environmental driver resulting in biodiversity loss and impaired function in many lakes and streams. 2) Many metrics based on macroinvertebrates are currently used to assess the biological impacts of acidification. However, few include measures of community composition, abundance, diversity, and the presence/absence of tolerant/sensitive taxa, and fewer still are calibrated simultaneously for both lentic and lotic waters and across large geographic regions. 3) Data on water chemistry and benthic macroinvertebrates was extracted from a database compiled by representatives from Norway, Sweden and Finland. Using lake- and stream data on water chemistry and macroinvertebrates from Norway and Sweden, we developed a Nordic macroinvertebrate-based multimetric index (MMI) for acidity (NAMI) to assess impacts of and recovery from acidity using information on measures of community structure and traits. 4) Lake and stream datasets were explored together and independently for correlation between measures of community structure and traits to acid neutralizing capacity (ANC), modified ANC regarding 1/3 of the organic acids as strong (ANCo1) and pH. Significantly correlated candidate metrics with highest correlations were chosen using forward stepwise linear regression models against ANC, ANCo1 and pH. Results showed that the combined lake and stream MMI had the highest correlation (r-squared) with ANCo1. 5) Seven metrics were included in NAMI: one measure of composition (sum of the combined relative abundance of Gastropoda, Bivalvia and Crustacea), two measures of diversity (the number of Ephemeroptera taxa excluding leptophlebiids and the number of Bivalvia taxa), one effect trait (taxa with life cycle duration > 1 year), two response traits (taxa with resistance forms: eggs and plastron respiration) and one tolerance trait (preference > 5 pH < 5.5). 6) The NAMI is a promising metric to standardize lake and stream macroinvertebrate assessments of acidity impacts and recovery across the Nordic countries, and to harmonize chemical and biological classifications of water quality, including progress towards achieving international objectives. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) is a well-known source of toxic trace metals in freshwaters. Traditional passive treatment systems rely on AMD neutralization with limestone and removal of most common toxic transition metals such as Cu and Zn with little attention to rare earth elements (REE). Alkaline waste materials now receive increasing attention as low cost AMD treatment alternatives in the circular economy. This study was set up to identify the efficiency of alkaline waste materials remediating AMD and scavenging REE in addition to other toxic trace elements. An AMD sample was collected from a lixiviate coming from pyrite heaps in the Iberian Pyrite Belt (pH = 1.8, 30 μM ∑REY). The sample was treated with either blast furnace slag (BFS) generated during smelting of iron ore in a blast furnace or biomass ashes (BA) derived from combustion of biomass, thereby using analytical grade CaCO 3 , and NaOH as reference products. The batch alkalinization experiments were conducted by adding each alkaline material at an amount to obtain an equal pH to ≈6.5. The required amounts of the products were NaOH < CaCO 3 99%) and the remaining REE concentrations in the solutions were clearly lower than values for Cu and Zn. The Zn and Cu removals were not consistently high enough (except with NaOH) to meet environmental limits in the discharge waters. The largest efficiency for REE removals was obtained with CaCO 3. Indirect evidence here suggests that gypsum is a better host for the trivalent REE than Fe(III) minerals in the precipitates. The ionic radii of trivalent REE are more similar to Ca2+ than to Fe3+, explaining the better potential of gypsum as REE host. This study showed also the potential of BFS as alkaline agent for the remediation of AMD in terms of its higher alkalinity generation potential as compared to BA, thus making BA less promising than BFS. [Display omitted] • BFS and BA were used as waste alkaline materials to remediate acid mine drainage. • Those were efficient in remediating acid mine drainage and in removing REE. • BFS has a higher alkaline generating capacity than BA. • The lowest residual REE was achieved with CaCO 3 due gypsum precipitation. • Using alkaline waste materials contributes to circular economy and sustainability. [ABSTRACT FROM AUTHOR]