Acid rain: a review of current controversy

IN 1984, there was no more body debated scientific issue than 'acid rain'—the somewhat amorphous term covering a number of industrial-based airborne pollutants that chemically alter the pH of precipitation and, thus eventually, of soil and water resources.     

Simulated acid rain: Effects on leaf quality and yield of broadleaf tobacco

Simulated acid rains of pH 5.6, 4.0, 3.5, 3.0, 2.5, or 2.0 were applied to leaves of broadleaf tobacco twice per week for 1, 2, 3, 4, or 5 weeks. Only those plants receiving rain of pH 2.0 were injured and, among those, the plants receiving fewer applications had less severe injury. Foliar symptoms resembled weather fleck (O₃ injury) at first, but become distinguishable from them with time.     

A summary of the impact of acid rain on atlantic salmon (Salmo salar) in Canada

Within the present North American range of Atlantic salmon, severe acid rain effects are limited to the Southern Upland area of Nova Scotia. In the Southern Upland, long range transport of H₂SO₄ has caused many rivers to decline in pH to the point where their Atlantic salmon stocks have been destroyed or much diminished. Chemical records show a declining pH trend in N.S. rivers since the early 1950s. Eighty % of the annual variation in H⁺ concentration can be accounted for by a multiple linear regression model on excess sulphate, total Al and organic anions. It is technically feasible to restore the acidified salmon habitat by the addition of limestone; the total cost of mounting a liming program to restore the lost habitat has been estimated at $4.75 × 10⁶ yr^?1. The pre-acidification Atlantic salmon production capacity of the Southern Upland was estimated from physical habitat surveys and tag return data to be about 45 000 fish yr^?1. Acidification has caused a 50% decline to the current production level of about 23 000 fish yr^?1. The costs of the liming program, when compared to the economic benefits of the anticipated salmon enhancement, are economically unjustifiable. The eradication of salmon from such large regions will hinder future programs to reestablish the species in their former range when pollution of the atmosphere is eventually brought under control. Present plans are for a small liming program to establish a series of refuges for the preservation of nuclei of native salmon stocks.     

Effects of acid rain on ion leaching in a danish forest soil

The mobility of major cations (H⁺, ammonium, Al, Ca, Na, Mg, K, Fe), heavy metals (Mn, Zn, Ni, Cd) and anions (chloride, sulphate and nitrate) was studied in the laboratory in an acidified brown soil from a Norway spruce forest. Lysimeters containing undisturbed soil columns of the A-horizon and the A- plus B-horizon were watered with 540 mm of throughfall precipitation collected in situ, either directly (pH 3.6) or adjusted to pH 3.3 or 2.8. The pH 3.3 treatment increased leaching of Mn and Cd from the B-horizon. The pH 2.8 treatment increased leaching of ammonium, Na, Ca, Mg, K, Mn, Zn and Cd from the A-horizon and ammonium, Al, Na, Ca, Mg, K, Mn, Zn and Cd from the B-horizon. Fe leaching from the A-horizon was decreased by both acidic treatments, and the pH of the leachates was not significantly affected. Sulphate retention was 138-161 meq m^?2 yr^?1 by all treatments. Due to experimental conditions nitrate leaching was observed in all lysimeters.     

Interaction of acid rain and global changes: Effects on terrestrial and aquatic ecosystems

Both acid deposition and changes in the global atmosphere and climate affect terrestrial and aquatic ecosystems. In the atmosphere sulphate aerosols tend to increase haze, altering the global radiation balance. Increased nitrogen deposition to N-limited systems such as boreal forests results in increased growth and increased sequestration of atmospheric CO₂, slowing the increase in CO₂ levels in the atmosphere. Future reduction in S and N emissions may result in a trade-off -- better with respect to some effects of acid deposition and greenhouse warming, but worse with respect to others. Global warming may cause the incidence and severity of drought to increase. Mineralisation of N and oxidation of organic S compounds release pulses of SO₄, acid and Al to surface waters. Effects in lakes may include reduced deep water refugia for cold stenotherms, lower nutrient concentrations, and greater penetration of harmful UV radiation. Longer water renewal times cause declines in SO₄ and NO₃, due to increased in situ removal, but increases in base cations. The net result is increased internal alkalinity production. In areas characterised by cold winters, global warming may result in a major shift in hydrologic cycle, with snowmelt episodes occurring during the winter rather than the typical pattern of accumulation in the winter and melting in the spring. Increased storm frequency predicted for the future will cause increased frequency and severity of sea salt episodes in coastal regions. Predicting the interactions of regional and global environmental factors in the coming decades poses new challenges to scientists, managers and policy-makers.     

Simulated acid rain effects on acidification of a Lexington silt loam

Intact soil cores were collected to a depth of 15 cm from a Lexington silt loam. Simulated precipitation with adjusted pH values of 3.7, 4.7 and 5.7 (control), was applied to the cores in increments of 500 mL day^?1 until totals which approximated 10, 20, 40, and 80 yr of effective rainfall in Louisiana were reached. The exchangeable acidity and Al and H₂O and KC1 pH were measured from 2.5 cm sections of the cores after treatment. Only the 3.7 treatment at the 80 yr volume significantly affected the soil pH and exchangeable acidity and Al.     

Effects of simulated rain acidified with sulfuric acid on host-parasite interactions

Wind-blown rain, rain splash, and films of free moisture play important roles in the epidemiology of many plant diseases. The effects of simulated rain acidified with sulfuric acid were studied on several host-parasite systems. Plants were exposed in greenhouse or field to simulated rain of pH 3.2 ± 0.1 or pH 6.0 ± 0.2. Simulated ‘rain’ of pH 3.2 resulted in: (1) an 86% inhibition in telia production of Cronartium fusiforme on Quercus phellos; (2) a 66% inhibition of reproduction of Meloidogyne hapla on field-grown Phaseolus vulgaris; (3) a 10% decrease in the severity of Uromyces phaseoli on field-grown Phaseolus vulgaris; and (4) an inhibition of Rhizobium nodulation of Phaseolus vulgaris and Glycine max by an average of 73%. Effects on halo blight of kidney bean (caused by Pseudomonas phaseolicola) depended upon the segment of the disease cycle in which the ‘rain’ occurred: (a) simulated rain of pH 3.2 applied to plants before inoculation stimulated disease development; (b) suspension of inoculum in ‘rain’ of pH 3.2 decreased inoculum potential; and (c) ‘rain’ of pH 3.2 applied to plants after infection inhibited disease development. Scanning electron microscopy of epicuticular waxes on leaves of Quercus phellos and Phaseolus vulgaris showed marked erosion of those surfaces by ‘rain’ of pH 3.2, indicating possible influences on the structure and function of plant cuticles. These results suggest that the acidity of rain is a new parameter of environmental concern, and underline the need for study of the consequences of prolonged exposure of both agronomic and natural ecosystems to this stress factor.     

Effects of acid rain on leaf-litter decomposition in a beech forest on calcareous soil

Summary The effects of simulated acid rain on litter decomposition in a calcareous soil (pH_{H 2 O} 5.8) were studied. Litterbags (45 m and 1 mm mesh size) containing freshly fallen beech leaf litter were exposed to different concentrations of acid in a beech forest on limestone (Göttinger Wald. Germany) for 1 year. Loss of C, the ash content, and CO₂–C production were measured at the end of the experiment. Further tests measured the ability of the litter-colonizing microflora to metabolize ¹⁴C-labelled beech leaf litter and hyphae. The simulated acid rain strongly reduced CO₂–C and ¹⁴CO₂–C production in the litter. This depression in production was very strong when the input of protons was 1.5 times greater than the normal acid deposition, but comparatively low when the input was 32 times greater. acid deposition may thus cause a very strong accumulation of primary and secondary C compounds in the litter layer of base-rich soils, even with a moderate increase in proton input. The presence of mesofauna significantly reduced the ability of the acid rain to inhibit C mineralization. The ash content to the 1-mm litterbags indicated that this was largely due to transport of base-rich mineral soil into the litter.     

The effects of acid rain on nitrogen fixation in Western Washington coniferous forests

We investigated both the current status of N₂ fixation in western Washington forests, and the potential effects of acid rain on this vital process. Even the low concentrations of SO₂ presently found in the Northwest are thought to have an adverse effect on N₂ fixation by limiting the distribution of the epiphytic N₂-fixing lichen, Lobaria pulmonaria, which is found mainly in deciduous forests. A close relative, L. oregana, was found to be the major N₂ fixer in old-growth coniferous forests. It fixes less N₂ following exposure to H₂SO₄ of pH 4 or less. A more serious threat to N₂ fixation than acid rain is the practice of deliberately suppressing red alder to keep it from competing with Douglas fir. Also, L. oregana is a late successional species and does not develop in forests where short cutting cycles are practiced.     

The effects of organic carbon on acid rain in a temperate forest in Japan

From recent studies, we noticed that stemflow had an acidity that differed from that of precipitation or throughfall. Organic substances, supplied from the tree surface, would be one of the factors that modifies the acidity of rain. The objectives of this study were to determine the DOC concentration and to clarify the influence of dissolved organic carbon (DOC) on acidity in precipitation, throughfall and stemflow. Throughfall and stemflow were measured in sugi [Cryptomeria japonica D. Don], hinoki [Chamaecyparis obutusa Endl.] and kojii [Castanopsis cuspidata (Thumb.) Schottky.] stands. All samples were analyzed for their pH, electric conductivity (EC), major inorganic anions and cations and DOC concentration.The annual average of DOC was highest in stemflow, and that of throughfall and precipitation were one-third and one-tenth of stemflow, respectively. The averages of DOC in stemflow in two coniferous, sugi and hinoki stands, were higher than that of broadleaved kojii stand. DOC concentration was low in summer and high in winter in all stands. In Stemflow, pH and DOC were negatively correlated, while EC and DOC in stemflow were positively correlated in all stands. However in throughfall, there was no evident relationship between pH, DOC and EC. This relationship was not explained by the cause of organic acid.     

Influence of acid rain on CO2 consumption by rock weathering: Local and global scales

Sulphuric and nitric acids, which are supplied by acid precipitation, take over from carbonic acid in weathering reactions, which induced a decrease of the atmospheric/soil CO₂ consumption by weathering (WCO₂). In order to quantity this disturbance, one has compared the bicarbonate fluxes determined at the outlet of 2 small catchments (one is substantially disturbed and the other is is weakly disturbed by acid precipitation). Our study shows that, under the influence of acid precipitation, bicarbonate fluxes (i.e. WCO₂) are decreased by about 73%. It has also been attempted to simulate at the continental scale, the influence of acid precipitation on WCO₂, using a Global Erosion Model (GEM-CO₂) recently developed. Several simulations have been performed corresponding to different realistic scenarios of global acid precipitation. In the most pessimistic of these scenarios, the GEM-CO₂ simulation shows that the global WCO₂ would be decreased by no more than 10%.     

A comprehensive study of risk assessment for a hazardous compound of public health concern

A comprehensive approach to risk assessment was developed by coupling an environmental fate model to the available health effects data. This approach was used to determine the risk due to an emission of 100 Mg L^?1 of 2,4,6-trichlorophenol (2.4.6-TCP) to a water body similar to Hamilton Harbour. The results indicated that a reduction in emissions to the harbour from 100 to 27.6 fig L^?1 would be required if a risk level of 1 in 10⁶ is closen.     

Changes in chemistry and mineralogy of forest soils by acid rain

The goal of the present study was a qualitative and quantitative determination of chemical and mineralogical changes in forest soils due to acid atmospheric depositions. In the NE/SE Vienna Woods soil samples were taken at 4 depths (0 to 5 cm, 5 to 10 cm, 10 to 20 cm, 20 to 30 cm) in the contaminated infiltration zone of stemflow (S) of 8 beech trees (Fagus sylvatica), strongly influenced by acid atmospheric depositions (soil-pH 2.8 to 3.0) and in their non contaminated reference areas (R) between trees, where acid imput is much smaller (soil-pH 5.0 to 6.0). The results show that intensive weathering processes took place in the contaminated soil areas, which show higher clay and silt contents and smaller aggregates, as well as clay illuviation. Moreover, in the top of the contaminated soil areas higher contents of C_t and S_t and of the heavy metals Pb, Zn and Cu could be observed, accompanied by extreme low base saturation (expecially of Ca and Mg) and high Al-saturation (50 to 80% of the CEC). These data were confirmed by analysis of the water saturation extract. Moreover, in the contaminated top soils high amounts of Fe-oxides were found, whereas no “secondary” Al-chlorite (due to its instability at pH-values <4.0) could be traced. The desilification process which took place at the same time could be shown through total element analysis. In the clay-fraction strong weathering led to a loss of layer charge and to the genesis of highly expandable three-layer-silicates which could be determined by X-ray diffraction using n-alkylammonium-chloride technics and other chemical treatments.     

Effect of anion composition of simulated acid rain on nutrient behavior in reclaimed saline soils

Abstract

Field experiments with the “Taikichi” taro cultivar were conducted in volcanic ash soil of Kagoshima Prefecture, Japan, in order to determine the effects of potassium applied with fertilizers and manures on the growth and yield of taro. The experimental design was accord ing to the L27 (3¹³) orthogonal factorial experiment, the three factors selected being the manures, nitrogen fertilizers and amount of potassium application.

“Metsubure” corm formation was infrequent in hog manured plots without potassium application, but was significantly increased by the application of potassium fertilizer. Furthermore, the occurrence of “Metsubure” corms was significantly lower in fields prepared with hog manure than in those prepared with plant residue and cattle manure.

Chemical analysis of the taro plants and manures revealed that the plants absorbed much more calcium when planted in hog manure than in other manures. The CaO/K₂O ratio was also higher. The main reason for this was assumed to be the lower content of potassium in the hog manure (0.37% K₂O on a dry basis).

The analytic results suggest that potassium disturbs the calcium uptake ability of the taro plant causing “Metsubure” corm formation.

The authors also attempted to determine the effects of several kinds of nitrogen fertilizers on “Metsubure” corm formation, but no clear results were obtained in this experiment.     

Prolonged simulated acid rain treatment in the subarctic: Effect on the soil respiration rate and microbial biomass

Humus chemistry and respiration rate, ATP, ergosterol, and muramic acid concentration as measures of chemical properties, microbial activity, biomass, and indicators of fungal and bacterial biomass were studied in a long-term acid rain experiment in the far north of Finnish Lapland. The treatments used in this study were dry control, irrigated control (spring water, pH 6), and two levels of simulated acid rain (pH 4 and pH 3). Originally (1985–1988), simulated acid rain was prepared by adding both H₂SO₄ and HNO₃ (1.9:1 by weight). In 1989 the treatments were modified as follows. In subarea 1 the treatments continued unchanged (H₂SO₄+HNO₃ in rain to pH 4 and pH 3), but in subarea 2 only H₂SO₄ was applied. The plots were sampled in 1992. The acid application affected humus chemistry by lowering the pH, cation exchange capacity, and base saturation (due to a decrease in Ca and Mg) in the treatment with H₂SO₄+HNO₃ to pH 4 (total proton load over 8 years 2.92 kmol ha^-1), whereas the microbial variables were not affected at this proton load, and only the respiration rate decreased by 20% in the strongest simulated acid rain treatment (total proton load 14.9 kmol ha^-1). The different ratios of H₂SO₄+HNO₃ in subareas 1 and 2 did not affect the results.     

Simulated acid rain and the importance of organic ligands on the availability of aluminum in soil

Equilibrium extracts from soils of different horizons at a single profile were examined. The Al species in the extract were characterized with oxine and chelex-100 exchange techniques. The amount of Al was found to depend strongly on the availability of organic ligands, especially the more strongly-binding ones, in the soil. The reaction to an acidic input to the soil was also found to be controlled by the amount and the nature of the organic ligands.     

Effect of simulated sulfuric acid rain on the chemistry of a sulfate-adsorbing forest soil

Simulated H₂SO₄ rain (pH 3.0, 3.5, 4.0) or control rain (pH 5.6) was applied for 3.5 yr to large lysimeter boxes containing a sulfate-adsorbing forest soil and either red alder (Alnus rubra Bong) or sugar maple (Acer saccharum Marsh.) seedlings. After removal of the plants and the litter layer, soil samples were obtained at 15-cm intervals to a total depth of 90 cm. Elevated SO₄ concentrations caused by the simulated H₂SO₄ rain were most pronounced for the top 15 cm, but extended down to 45 cm (maple) or 75 cm (alder). There were no effects on SO₄ concentrations at a depth of 75 to 90 em. This confirmed the existence of a sulfate front between 20 cm and 100 cm, as postulated earlier on the basis of extracted soil solutions. Decreases in Mg and Ca concentrations, base saturation, and soil pH were limited to the uppermost 15 cm and, in most cases, to the pH 3.0 treatment. Concentrations of Mg and Ca for the pH 3.0 treatments were greater than control at a depth of 15 to 30 cm, indicating transport of these cations from the soil surface. Concentrations of Na and K, and cation exchange capacity, were not affected by simulated H₂SO₄ rain. Elevated concentrations of NO₃ and extractable Zn throughout the alder systems indicated (1) either increased rates of symbiotic N-fixation or decreased rates of N immobilization; and (2) mobilization of Zn by all acid rain treatments.     

Soil chemical and microbial effects of simulated acid rain on clover and soft chess

Effects of simulated acid rain, comprised of HNO₃ and H₂SO₄ in the mole ratio of 3:1, at pH 5.6, 4.5, 4.0 and 3.0, were tested on the grass, soft chess (Bromus mollis L.) and on clover (Trifolium subterraneum L. var. Woogenellup) in a sandy soil of granodiorite parent material. Soft chess was grown in unfertilized soil, whereas clover was grown in both unfertilized soil and soil fertilized with NH₄NO₃ and CaSO₄·2H₂O at the rates of 224 kg ha^?1 N and 78 kg ha^?1 S. Two acid-spray irrigation periods of 31 and 26 weeks duration, each delivering 400 mm and separated by a dry period of 23 weeks, simulated typical rainfall of northern California rangeland. Plants were harvested after each of the two spray periods. There were very few deleterious effects of acid rain on plant growth or soil and microbial processes. No significant (p<0.05) effects were shown by soil microbial biomass, CO₂ production, nodules per unit weight of clover root, acetylene reduction, denitrification and nitrification potentials, or for soft chess plant weights, and N and P uptake. Mineralizable-N was unaffected also, except in one case. However, pH of soil to 10 mm depths was significantly lower in the pH 3.0 treatment after the first spray period, with a corresponding decrease in exchangeable soil Ca; these effects became significant at greater soil depth only after the second spray period. There were significant effects of acid treatments shown by clover, some of which may be advantageous. Treatments of intermediate acidity generally provided added N and S, which acted as fertilizers, and compensated for possible decreases in plant productivity attributable to acidity per se. There was also evidence of decreased P uptake in unfertilized soil at pH 3. In conclusion, effects of simulated acid rain were minimal, and in some cases were advantageous because of the added N and S having a fertilizer effect on plant nutrition and growth.     

Fractionation of extractable aluminum in acid soils: A review and a proposed procedure

Abstract

Different forms of soil aluminum (Al) are involved in the retention of anions and cations, phytotoxicity of Al in acid soils, CEC reduction and soil physical properties such as aggregate stability and water infiltration. Therefore it is desirable to quantify the different forms of Al in soil especially acidic soils. A rationale was developed from a literature survey to identify the following fractions of Al: (a) exchangeable quantified by 1M KC1 extraction; (b) organic bound quantified by 0.1M CuCl₂ + 0.5M KCl extraction; (c) sorhed Al extractable with 1M NE₄OAc at pH 4.0; (d) amorphous Al oxide and hydroxide and amorphous aluminosilicates (if present) extractable with 0.2M ammonium oxalate at pH 3.0; and (e) interlayered Al extractable with 0. 33M sodium citrate at pH 7.3. Pools (a), (b), and (c) are extracted sequentially. Amorphous Al oxide and hydroxide (pool d) is calculated from ammonium oxalate extractable Al minus (a + b + c). Interlayered Al is calculated from sodium citrate extractable Al minus ammonium oxalate extractable Al. The latter two extractions are done on separate subsamples of soils. From preliminary studies and data for 13 soil samples it is suggested that this fractionation of soil Al is more meaningful than that obtained by the KCl ‐> K₄P₂O₇ ‐> ammonium oxalate > citrate‐bicarbonate‐dithionite extraction sequence.     

Thermal shock and rain effects on soil surface characteristics: A laboratory approach

In addition to its direct impact on soil physical and chemical soil properties, fire produces a sudden change in plant cover. The post-fire impact of falling raindrops on unprotected soil surfaces is a major cause of detachment of aggregates, physical degradation and erosion of soils. The aim of this work was to analyse the effects of burning intensity and rain under factor-controlled conditions using unaltered soil samples. Assessed variables were soil organic carbon, aggregate stability and water repellency (0–1 cm mineral soil), as well as soil surface compaction and hydraulic conductivity. Unaltered topsoil cores were obtained in a mature Mediterranean gorse shrubland. We applied two successive treatments: burning (unburned, low and high burning levels) and rain (77 mm/h). The soil properties studied were scarcely affected by burning. However, soils showed high vulnerability to raindrop impact: a) aggregate stability and organic carbon were not significantly affected by burning; b) low intensity burning increased the frequency of samples with moderate water repellency, whereas unburned together with high burning showed more cases of low and extreme water repellency; c) the rain treatment produced a significant decrease in hydraulic conductivity although this response was independent of burning level; d) the highest reduction in hydraulic conductivity was observed in the samples with highest values prior to the rain treatment, and this was related to the highest organic carbon contents, and e) the reduction in hydraulic conductivity could be explained by the development of a thin and friable surface crust, although the cone penetrometer was not sensitive enough to detect this observed phenomenon.