The use of molecular graphics and quantum mechanically derived electrostatic potentials to visualize Brönsted acid site strength in zeolites

The use of the quantum mechanically derived electrostatic potential is introduced to visualize the variation in acidity across a series of cluster molecules corresponding to models of terminal and bridged hydroxyl groups in zeolites. The electrostatic potential is color coded onto the electron density surfaces of the molecules involved, and the variation in acid strength can be followed from the color scheme used. This simple visualization scheme is shown to mirror the experimentally observed acidity variation of terminal hydroxyls, bridged gallium hydroxyls, and bridged aluminium hydroxyls found for zeolites.From the value of the electrostatic potential near the acidic hydrogen we estimate that the acidity of terminal hydroxyls is similar to acetic acid while the bridged aluminium form is the same as sulphuric acid.     

Limnological Features of Different Acidic Drinking Water Reservoirs in the Erzgebirge (Germany)

The biological and chemical investigations of three drinking water reservoirs differing in their acidic and trophic conditions (neutral/meso-eutrophic; circumneutral/oligotrophic; acid/oligomesotrophic) and of some of their tributaries in the Erzgebirge (Germany) are presented. It is shown that the chemistry of acidic waters is very different from circumneutral ones, particularly with respect to hardness, acid neutralizing capacity, pH and aluminium. As acidity in running and stagnant waters increases, the filtrable aluminium concentration also rises. A consequence of the changed chemical and biological conditions and their direct and indirect effects on the organisms is an overall decrease in the number of species (despite the fact that also some species newly appear in the acidified waters). Furthermore, a loss of food web complexity is observed and the trophic structure changes, e.g. fish have disappeared and invertebrate predators have become more numerous. In the acidic reservoir, species well adapted to waters low in pH and hardness (e.g. Synura sphagnicola) are more abundant and commonly benthic animals (e.g. Chydorus sphaericus) are able to extend their habitat to the open waters.     

Relationships between stream acidity and bacteria,macroinvertebrates, and fish: a comparison of north temperate and south temperate mountain streams,USA

A comparative study of relationships between stream acidity and bacteria, macroinvertebrates, and fish in the Adirondack Mountains of upper New York state and in the Southern Blue Ridge Mountains of eastern Tennessee, USA, was conducted. Although the study sites in both regions spanned a pH range from approximately 4.5 to 6.4, considerably greater seasonal variability in pH and higher monomeric Al concentrations characterized the Adirondack sites. Relationships between several biological characteristics and stream water acidity were similar in both regions, including lower production of epilithic bacteria and bacteria on decomposing leaves, lower leaf decomposition rates, lower density and generic richness of scraper/grazer macroinvertebrates, particularly Ephemeroptera, and lower fish abundance and survival in more acidic streams. Densities of total macroinvertebrates and densities of macroinvertebrates and bacteria inhabiting or closely associated with stream sediments were generally not related to stream water acidity.Regional differences occur in some of the relationships between biological characteristics and stream water acidity. Negative correlations between bacterial production on rocks and pH, between bacterial production on decomposing leaves and pH, and between densities of Ephemeroptera and scrapers and pH were stronger in the Adirondacks than in the Southern Blue Ridge. Higher Al concentrations in the Adirondacks may be responsible for the stronger relationships with pH there. The steeper slopes of the relationships between Ephemeroptera density and all forms of Al in the Adirondacks compared with the Southern Blue Ridge suggests that there may be some adaptation among a few acid/aluminum-tolerant species in the seasonally more constant acidic Southern Blue Ridge streams. Fish bioassays indicated longer survival times in acidic streams in the Adirondacks compared with the Southern Blue Ridge, but these results may be an artifact associated with the use in the Southern Blue Ridge of rainbow trout as the test species which is known to be more acid sensitive compared with brook trout, the test species used in the Adirondacks.     

Genetic adaptation to soil acidification: experimental evidence from four grass species

Anthropogenic acidification has reduced soil pH and released potentially toxic aluminium (Al) ions in many regions. This investigation examines whether increased acidity has caused genetic adaptation to acidic conditions within the grass species Elymus caninus, Poa nemoralis, Deschampsia cespitosa and D. flexuosa. We sampled tussocks (genets) of each species in two regions of southern Sweden, differing in their exposure to acidifying deposition. The tolerance of the genets was tested in a solution experiment with different pH and Al concentrations. Our data suggest that species found at lower pH field locations have a greater tolerance to low pH and high Al levels than species found on less acidic soils. Analysis of variance showed a significant average effect of population and (or) genet in most species; however, we found little evidence of genetic adaptation to acidic conditions at the regional, population and micro-site level. In fact, there was no consistent change in the ranking of populations or genets with varying pH or Al concentration. Based on these results, we hypothesize that phenotypic plasticity rather than genetic adaptation has been favoured as the predominant mechanism to cope with soil acidity in the four grass species.     

The reproductive success of the dipper Cinclus cinclus in relation to the acidity of streams in south-west Scotland

1. The breeding success of dippers Cinclus cinclus was assessed in south-west Scotland over 3 years and related to the acidity of the streams along which they bred. 2. At sites of high acidity, clutch and brood sizes were significantly smaller than those at sites of lower acidity. 3. Egg weight and the incidence of second clutches increased significantly with pH, but there was no evidence to suggest an effect of acidity on hatching success. 4. The rate at which food was delivered to individual nestlings was significantly lower at acidic than non-acidic sites. Nestling weights and survival were lower at more acidic sites. 5. Reduced brood sizes, low nestling survival and the low incidence of second brooding attempts resulted in a significant reduction in total productivity (number of fledglings produced, per pair, per year) at acidic compared with non-acidic streams. 6. It is suggested that pH-related differences in the invertebrate fauna of streams result in low prey availability for dippers on acidic streams, leading to reduced productivity.     

A corrosive concoction: The combined effects of ocean warming and acidification on the early growth of a stony coral are multiplicative

Survival of coral planulae, and the successful settlement and healthy growth of primary polyps are critical for the dispersal of scleractinian corals and hence the recovery of degraded coral reefs. It is therefore important to explore how the warmer and more acidic oceanic conditions predicted for the future could affect these processes. This study used controlled culture to investigate the effects of a 1 °C increase in temperature and a 0.2-0.25 unit decrease in pH on the settlement and survival of planulae and the growth of primary polyps in the Tropical Eastern Pacific coral Porites panamensis. We found that primary polyp growth was reduced only marginally by more acidic seawater but the combined effect of high temperature and lowered pH caused a significant reduction in growth of primary polyps by almost a third. Elevated temperature was found to significantly reduce the amount of zooxanthellae in primary polyps, and when combined with lowered pH resulted in a significant reduction in biomass of primary polyps. However, survival and settlement of planula larvae were unaffected by increased temperature, lowered acidity or the combination of both. These results indicate that in future scenarios of increased temperature and oceanic acidity coral planulae will be able to disperse and settle successfully but primary polyp growth may be hampered. The recovery of reefs may therefore be impeded by global change even if local stressors are curbed and sufficient sources of planulae are available.     

Acidic precipitation increases egg survival in Neodiprion sertifer

The effects of simulated acidic precipitation on the egg viability of the European pine sawfly, Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae) were studied by spraying egg clusters with a mixture of sulphuric and nitric acid (1:1, pH 2, 3, 4, 5, 6, distilled water, natural precipitation) for a month in April–May. Egg viability analyses showed that the proportion of hatched first instar larvae increased with increasing acidity. The better survival of sawfly eggs in pine needles in more acidic conditions may be partly due to changes in needle physiology affecting egg mortality. However, when the eggs were reared without needles in Petri-dishes, the proportion of successfully hatched larvae likewise increased with increasing acidity indicating direct acid-induced changes in the eggs themselves. Acidic precipitation as a stress factor of the host plant apparently changes population dynamics of pine sawflies and may be an important factor in triggering outbreaks.     

Computer Simulation of the Beta Structure,with Different Lattice Ions and Reactivity,of Hydroperoxo-Metal Complexes Using an Embedded-Cluster Method

The chemical properties of beta zeolite are interconnected with its structure in a complicated way. In general terms, the strength of the acid sites in the beta phase depends strongly on its structure, topology and composition. The quantum chemical calculations of the beta zeolite cluster model have been carried out in order to predict how the cluster's local structure influences the geometric parameters and thus affects the chemical functionality of the beta zeolite. Computer simulations of a beta zeolite model with one lattice aluminium, or boron, or titanium or vanadium ions and of its acidic centres have been carried out. The acidity of the framework oxygen atoms in the vicinity of the lattice atom centre has been calculated and compared. The reactivity of catalytic species comprisingthe lattice ion and a hydroperoxo ligand has been studied as an oxidising site.     

Acute effects on perch (Perca fluviatilis) and long-term effects on whitefish (Coregonus lavaretus pallasi) of liming of an acidified lake

The acute effects on perch and long‐term effects on whitefish were studied after liming one side of a lake [initial pH: 4.6–5.5; aluminium (Al): 29–54 μg L^?1; Ca²⁺: 0.02–0.07 mmol L^?1] that was divided into two parts with a plastic curtain. Some Al precipitation was observed on the gill surface of perch 1 day after liming; the concentration of plasma sodium of perch females in the limed side was also higher than in the acidic side. Nearly 6 months after liming, at the spawning time of whitefish, the plasma chloride concentration of whitefish in the limed side was higher and blood glucose concentration lower than in the acidic side. Four of five whitefish males from the limed side, but only one of five males and none of the five females from the acidic side, were ready to spawn. The growth of whitefish in the limed side was also more rapid. These changes illustrate that liming had no acute harmful effects on perch, and allowed whitefish to recover from acidity‐related physiological stress.     

The role of arbuscular mycorrhizas in decreasing aluminium phytotoxicity in acidic soils: a review

Soil acidity is an impediment to agricultural production on a significant portion of arable land worldwide. Low productivity of these soils is mainly due to nutrient limitation and the presence of high levels of aluminium (Al), which causes deleterious effects on plant physiology and growth. In response to acidic soil stress, plants have evolved various mechanisms to tolerate high concentrations of Al in the soil solution. These strategies for Al detoxification include mechanisms that reduce the activity of Al³⁺ and its toxicity, either externally through exudation of Al-chelating compounds such as organic acids into the rhizosphere or internally through the accumulation of Al–organic acid complexes sequestered within plant cells. Additionally, root colonization by symbiotic arbuscular mycorrhizal (AM) fungi increases plant resistance to acidity and phytotoxic levels of Al in the soil environment. In this review, the role of the AM symbiosis in increasing the Al resistance of plants in natural and agricultural ecosystems under phytotoxic conditions of Al is discussed. Mechanisms of Al resistance induced by AM fungi in host plants and variation in resistance among AM fungi that contribute to detoxifying Al in the rhizosphere environment are considered with respect to altering Al bioavailability.     

Carry-over effects of embryonic acid conditions on development and growth of Rana temporaria tadpoles

1. Conditions experienced during the early stages of development may have carry‐over effects on performance during later life. The egg laying period and embryonic development of temperate and boreal zone amphibians often coincides with peak acidity resulting from spring snow‐melt, but the effects of acid conditions during embryonic stage on subsequent performance are unknown. 2. We investigated the potential carry‐over effects of acidity during the embryonic stage on performance up to metamorphosis in the common frog (Rana temporaria) tadpoles. There were four combinations of acid (4.5) and neutral (7.5) pH treatments applied to the egg and larval stages in a factorial laboratory experiment. In addition, we studied the difference in embryonic and larval tolerance of acidity between two populations originating from circumneutral (pH 6.6) and acidic conditions (pH 4.8). 3. The effects of acid conditions during the embryonic stage were sublethal, as indicated by delayed development and reduced size. Under acid conditions, tadpoles that had been raised in neutral water as embryos at first grew more slowly than tadpoles raised under acid conditions as embryos. At metamorphosis, no effects of embryonic acidity were detectable indicating that tadpoles were able to compensate fully for the initial reduction in growth. 4. Acid conditions during the larval period had a strongly negative effect on survival, size and age at metamorphosis. The amount of food consumed was lower under acid conditions, suggesting that reduced food consumption was at least partly responsible for the negative effects. 5. Although the two populations differed in the length of larval period, there was no indication of a differential response to the treatments in any of the metamorphic traits studied. 6. These results suggest that, although moderate acid conditions during embryonic development affect growth and development negatively, this influence does not persist after conditions have returned to normal. However, even moderately acid conditions during the larval period may have a strong negative influence on survival and performance of the tadpoles.     

Effects of acidic water on young-of-the-year smallmouth bass (Micropterus dolomieui)

Synopsis Smallmouth bass (Micropterus dolomieui) populations are declining in areas vulnerable to anthropogenic acidification. To determine if populations may be lost directly from acid effects (i.e., in isolation from synergists), we performed a laboratory study on the effects of acid exposure on growth, survival and histology of young smallmouth bass (3 to 36 d post swimup). We exposed them to declining, then fluctuating acid levels averaging pH 7.4 (control), 5.7 and 5.0. Substantial decreases in survival were observed, as well as damage to tissues. Survival declined with increasing acidity to 43% of that in controls at pH 5.7 and to 4% at pH 5.0. Histological analysis revealed severe changes in the most acidic treatment, with damage to blood, gill, and epithelial tissue. In contrast, growth was less useful as an indicator of response to acidity. Growth in both length and dry weight was greater at the lower pH levels than in controls. This was probably a reflection of lower survival at the lower pH levels, reduced density, and hence less competition for food. Our results suggest that an increase in environmental acidity is sufficient to cause losses in this species, even in the absence of synergists such as heavy metals.School of Forest Resources, University of Georgia, Athens, GA 30602, U.S.A.     

What is wrong with aluminium? The J.D. Birchall Memorial Lecture

Aluminium chemistry has features in common with two other groups of elements: (1) divalent magnesium and calcium, and (2) trivalent chromium and iron. The essential differences between the first group and aluminium are explored and it is shown that the much higher acidity of aluminium makes it such a powerful competitor for oxygen-donor ligands, opposite functions of both magnesium and calcium, in cells that its presence is damaging. By way of contrast aluminium is a weaker acid than ferric ions but it is more available. It was necessary for iron to be utilised in the presence of aluminium so special methods had to be devised to distinguish between them. In essence aluminium has always, throughout evolution, been a threat to the biological chemistry of all these three elements. We shall examine this chemistry and then explore the relationship of calcium and aluminium under acid rain conditions.     

DOES PREY BIOMASS OR MERCURY EXPOSURE AFFECT LOON CHICK SURVIVAL IN WISCONSIN?

Abstract: Past studies suggest that the productivity of common loons (Gavia immer) is lower on acidic lakes in northern Wisconsin, USA, than on neutral lakes. Two hypotheses have been proposed to explain low chick survival: (1) reduced food consumption related to changes in prey communities on lower pH lakes and (2) high mercury (Hg) exposure on lower pH lakes. To address these hypotheses, we quantified prey and Hg consumption by loon chicks on 51 lakes and survival on 55 lakes ranging in pH from 4.9 to 9.5 in northern Wisconsin in 1995 and 1996. The time adults spent providing prey to chicks was unrelated to lake pH but increased with number of chicks and chick age. The number of prey caught per provisioning time declined as lake pH declined because adults made fewer dives, not because success of prey capture declined. Chicks consumed more insect larvae on acidic lakes and more crayfish (Family Astacidae) on neutral lakes. Biomass consumed ranged from an average 1.99 ± 1.05 (SE) g/hr/chick during the first week of a chick's life to a peak of 7.93 ± 1.93 g/hr/chick during the eighth week. Biomass intake per chick body weight (g/W_g/hr) declined with lake acidity but was not related to chick survival (P = 0.25). Although the Hg concentration in the 3 major prey species was positively related to lake acidity and blood Hg level of chicks at a lake, total Hg consumption (μg/W_g/hr) was highest on moderately acidic lakes rather than on the most acidic lakes. We suggest that loon chick survival in northern Wisconsin lakes is more likely related to prey availability than to Hg exposure. When we removed from our analysis 1 lake where 2 11-day-old chicks were killed by predators, chick survival was negatively related to lake acidity but not to biomass or Hg consumption. We discuss mechanisms of Hg excretion that may allow young chicks to survive on acidic lakes in northern Wisconsin despite high Hg intake.     

Selection of Bradyrhizobium strains and provenances of Acacia mangium and Faidherbia albida: Relationship with their tolerance to acidity and aluminium

This work was designed to determine the role of the acidity and aluminium stress in the selection of partners in the Acacia symbioses with relevance to the persistence of the microsymbiont Bradyrhizobium in the soil and the growth and nodulation of the host plant respectively. Fifteen strains of Bradyrhizobium from Acacia mangium and Faidherbia albida formed a very homogenous acid tolerant group as indicated by their ability to grow better in a medium at pH 4.5 than in a medium at pH 6.8. By contrast, a growth experiment using an acid liquid media (pH 4.5), containing different concentrations of aluminium successfully identified strains sensitive to aluminium toxicity and those able to grow even in the presence of 100 M AlCl₃.Our results suggest that high amounts of aluminium in the soil rather than acidity (pH 4.5) were a major soil factor for selection of Bradyrhizobium strains capable of establishing a permanently high population under natural conditions.Unlike the behaviour of the microsymbiont, growth and nodulation of Acacia mangium and Faidherbia albida were not affected by aluminium, even at 100 M, but they might be significantly affected by medium acidity (pH 4.5) depending on plant provenances. It is therefore suggested that ability of the host plant to tolerate acidity stress should be taken into account first when screening effective Acacia-Bradyrhizobium combinations for use in afforestation trials.     

The effects of pH, aluminium concentration and temperature on the embryonic development of the European common frog, Rana temporaria

The individual and combined effects of pH, aluminium concentration and temperature, on the development of common frog ( Rana temporaria ) embryos from an upland area of northern England, were investigated in a controlled laboratory study. There was strong evidence to suggest that embryonic survival was lower at pH 4.5 compared with pH 6.0. At pH 4.5, embryonic survival was reduced at the highest aluminium concentrations. There was no strong evidence for a reduction in embryonic survival at lower aluminium concentrations.
Gastrulation and hatching appeared to be the most sensitive stages to both pH and aluminium concentration.
There was strong evidence to suggest that temperature-shocked embryos had reduced survival when compared with those kept at a constant temperature, particularly at pH 4.5.
There was substantial variation in the survival of embryos from different clutches in the same pond with respect to low pH, aluminium concentration and temperatures. Thus R. temporaria has a wide genetic base from which to tolerate environmental changes. It is suggested, however, that the lethal and sublethal effects of low pH, high aluminium concentration and low temperature, could lead to a decrease in recruitment to the adult populations of R. temporaria in upland, northern England.     

Aluminium speciation in natural water by sorption on a complexing resin

Very stable aluminium complexes may be present in natural waters, which can be detected only using appropriate methods. One of them is the resin titration based on the sorption of aluminium on a strongly sorbing resin, Chelex 100. It was here used to detect strong aluminium complexes, and to characterize them by determining their concentration, and the corresponding stability constant. High and low salinity waters were sampled in different sites in the North of Italy. In all the samples aluminium complexes with high stability constant, up to 10(17.4) M(-1) in the less acidic solution, were detected. The stability constant depends mainly on the solution acidity, increasing with increasing pH up to 7. The concentration of the ligands responsible for the strong complexation is similar to that of aluminium (from 0.5 to 1.5 microM), or somewhat lower in the case of estuarine and sea waters. A small fraction of aluminium (from 0% to 2%) in freshwaters, higher in estuarine and sea waters (14% and 10%, respectively), is present in weakly bound forms which could also be the hydrolysis products. The conditional constants of the strong complexes were determined for the different samples examined. They were found to be slightly lower in the case of the high salinity waters, in which a value of 10(16.1) M(-1) at pH 7.5 was obtained. This is probably due to the higher ionic strength in marine water, which strongly influences the complexation of trivalent metal ions, as seen for example also in the hydrolysis. It could be deduced that similar substances, but at different concentration, would be responsible for the aluminium complexation in the sea and freshwaters here examined. They could be natural organics like fulvic substances, or better some particular complexing sites in this substances with very high affinity for aluminium.     

Effect of exchangeable aluminium on the reduction of potato scab

The severity of the incidence of the fungal disease, potato scab, varies with different soil groups at the same soil pH. At a soil pH of 5.3, potato scab is easily controlled in soils of western Hokkaido (soil group A) by simply decreasing soil pH, but in soils from eastern Hokkaido (soil group B) it is not so easily controlled. The difference appears to be due to higher levels and exchangeable aluminium in Group A.Addition of sufficient aluminium or ferrous sulfate to a group B soil decreased the incidence of potato scab in a field experiment. Higher levels of aluminium sulfate depressed crop production. It is concluded that aluminium ions control the incidence of potato scab in acid soils. It is suggested that, in soils with low exchange acidity Y1, potato scab can be controlled by adding sufficient aluminium to increase their exchange acidity Y1 to above 7–8.     

Adenosine deamination increases the survival under acidic conditions in Escherichia coli

Aims: Resistance to acidic stress contributes to bacterial persistence in the host and is thought to promote their passage through the human gastric barrier. The aim of this study was to examine whether nucleosides have a role in the survival under acidic conditions in Escherichia coli. Methods and Results: We found that adenosine has a function to survive against extremely acidic stress. The deletion of add encoding adenosine deaminase that converts adenosine into inosine and NH₃ attenuated the survival in the presence of adenosine. The addition of adenosine increased intracellular pH of E. coli cells in pH 2·5 medium. Addition of inosine or adenine did not increase the resistance to acidic conditions. Conclusions: Our present results imply that adenosine was used to survive under extremely acidic conditions via the production of NH₃. Significance and Impact of the Study: It has been proposed that amino acid decarboxylation is the major system for the resistance of E. coli to acidic stress. In this study, the adenosine deamination was shown to induce the survival under acidic conditions, demonstrating that bacteria have alternative strategies to survive under acidic conditions besides amino acid decarboxylation.