Anionic constituents of acid rain and microbial activity in soil

Soil amended with 1% glucose was treated with H₂SO₄, fuming H₂SO₄, HCl, H₃PO₄, HNO₃, fuming HNO₃ or with combinations of fuming and non-fuming H₂SO₄ and HNO₃ to lower the bulk soil pH to values ranging from 5.0 to 2.0. There was a difference in the amount of toxicity caused by the different acids at the same bulk pH of soils. Acidification to pH 2.8 or 2.9 prolonged the lag phase of glucose degradation; fuming HNO₃ had the greatest effect, and fuming H₂SO₄ was only slightly more toxic than non-fuming H₂SO₄. At pH 2.3–2.4, fuming HNO₃, alone or in combination with H₂SO₄, inhibited CO₂ evolution. Both fuming and non-fuming HNO₃ also reduced the amount of C mineralized to a greater extent than did fuming and non-fuming H₂SO₄. The amounts of C mineralized from soils treated with combinations of H₂SO₄ and HNO₃ were intermediate between those from soils treated with each of these acids alone. HCl and H₃PO₄ had a similar effect on prolonging the lag as did non-fuming H₂SO₄. H₃PO₄ was less toxic than the other acids and sometimes increased the total amount of C mineralized. The “anionic effect” of acid rain must, therefore, be considered in addition to the effect of the proton. When the soil was inoculated with a suspension of microbiologically-active soil, more C was mineralized, in general, and the inhibitory effects of acidification on C mineralization were less pronounced than in soil that had not been inoculated. The addition of montmorillonite, but not of kaolinite, enhanced the growth of Aspergillus niger in soils amended with 2:1 combinations of H₂SO₄ and fuming HNO₃ however, growth was inhibited completely at pH 3.4.     

Characteristics of Raindrop Acidification by Co-Washout of SO2(G)-H2O2(G)-HNO3(G)

In order to investigate the acid rain formation under the coexistence of SO₂(g), H₂O₂(g), and HNO₃(g) in the air, a mathematical model has been built and some numerical simulations have been carried out with use of the model. The simulation reveals that SO₂(g) absorbed into a raindrop is released and then re-absorbed as the fall distance increases. The desorption and re-absorption processes of SO₂(g) are caused by: (1) the fact that the equilibrium concentration of H₂O₂(aq) and HNO₃(aq) in raindrops are much higher than that of SO₂(aq), and (2) the fact that the oxidation reaction rate of HSO₃ ^? with H₂O₂(aq) increases with H⁺ concentration in raindrops. The degree of acidification of the rainwater has been estimated by introducing a raindrop size distribution. The acidification is mainly caused by the adsorption of SO₂(g) in the usual case where the atmospheric concentration of SO₂(g) is much higher than that of HNO₃(g). With the increase in the atmospheric concentration of HNO₃(g), the concentration of H⁺ generated from SO₂(g) decreases and the contribution of HNO₃(g) to the generation of H⁺ becomes dominant.

     

The role of neutral salts in the ion exchange between acid precipitation and soil

Theory and experimental results have shown that neutral salts in the precipitation or supplied to the ground by other means reduce the acidification of soils by acid precipitation. This salt effect is caused by the cation exchange occurring after the entry of the rain water into the soil.The acid components of precipitation consist of H₂SO₄, HNO₃ and HCl and of NH₄⁺ after nitrification in the soil. The magnitude of the salt effect depends on the relative bonding energy of H₃O⁺ and of Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺ in the soil as well as on the concentrations of H₃O⁺ and the above cations in the precipitation. The salt effect may be considerable in very acid soils. It decreases with rising pH to become very small or negligible in neutral soils, chiefly due to the increasing bonding energy of H₃O⁺ in this direction.The adverse effect of acid precipitation, therefore, is likely to be less in very acid soils, such as podsols, than in slightly acid and neutral soils with low buffering capacity against pH change. Soil texture and calcite content are very important factors in this respect as fine material and calcite increase the buffering.     

Salts and acids as determinants of the solution composition of acidic forest soils — anion effects

The study aimed at evaluating whether salt-induced mobilization of acidity may be modified by the type of anion. For this purpose, the effects of different neutral salts on the solution composition of acid soils were investigated. The results were compared with those of the addition of acids. Two topsoil (E and A) and two subsoil horizons (Bs and Bw) were treated with NaCl, Na₂SO₄, MgCl₂, MgSO₄, HCl, and H₂SO₄ at concentrations ranging from 0 to 10 mmol dm^?3. With increasing inputs of Cl^? the pH of the equilibrium soil solution dropped, the concentrations of Al and Ca increased, and the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios decreased. These effects were the least pronounced when NaCl was added and the most at the HCl treatments. According to the release of acidity, the topsoils were more sensitive for salt-induced soil solution acidification whereas on base of the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios, the salt effect seems to be more important for the subsoils. Addition of S0₄^2? salts and H₂SO₄ induced higher pH and lower Al concentrations than the corresponding Cl^? treatments due to the SO₄^2? sorption, especially in the subsoils. The Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios were higher than those of the corresponding Cl^? treatments. In subsoils even after H₂SO₄ additions these ratios were not higher than those of the NaCl treatments. The results indicate (I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider the ionic strength and the cation type but also the anion type, (II) that salt-induced soil solution composition may be more crucial in subsoils than in topsoils, and (III) that in acid soils ongoing input of HNO₃ due to the precipitation load may induce an even more acidic soil solution than the inputs of H₂SO₄ of the last decade.     

The sensitivity of ecosystems to acid inputs in the Hunter Valley,Australia

This study assesses the importance of H⁺ generation in the Hunter Valley from land use and coal-fired power stations. The Hunter Valley is a temperate coastal landsystem approximately 150 km north of Sydney. Land uses include forestry and national parks, grazing and farming, coal mining, coal-fired electricity generation and manufacturing. The H⁺ generated from land use is estimated from land suitability classes. Wet deposition is estimated from 10 years' rainwater chemistry data and dry deposition is estimated from modelled SO₂ concentrations and a deposition velocity constant. The pH and pH buffer capacity of 51 soils were measured. H⁺ loads from land use ranged from 0.05 to 12 kmol H⁺/ha/year for forests and prime agricultural land, respectively. Estimated H⁺ deposition ranged from 0.27 to 0.65 kmol H⁺/ha/year, depending on the distance and direction from the power stations. The H⁺ load that will lead to critically low pH values in 50 years is 0.27, 0.60, 1.77 and 2.14 kmol H⁺/ha/year for four broad soil classes. The two most sensitive classes, with target loads of 0.27 and 0.60 kmol H⁺/ha/year, occupy 26% and 56% of the study area respectively. Although the total contribution of H⁺ from land use is larger than from deposition (970 vs. 220 Mmol H⁺/year), H⁺ deposition may be important on low fertility nonagricultural soils with low pH buffer capacity. More detailed study of the areas with sensitive soils is warranted.     

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.     

Effects of Acid Mist and Ascorbic Acid Treatment on the Growth,Stability of Leaf Membranes,Chlorophyll Content and Some Mineral Elements of Carthamus tinctorius,the Safflower

Safflower shoots were sprayed with either HNO₃,HCl and H₂SO₄ acid solutions of pH 2.0 ordistilled water as a control and then sprayed with 0and 100 mg L^-1 ascorbic acid solutions. In theabsence of ascorbic acid, membranes of leaf discsexcised from acid misted plants were more injured bydehydration (40% polyethylene glycol, P.E.G.) andheat (51 °C) stress than those taken fromunmisted plants. Safflower plants sprayed with HCl andH₂SO₄ solutions had lower contents ofchlorophyll (Chl.), soluble sugars (S.S.),hydrolysable carbohydrates (H.C.), soluble proteins(S.P.); total free amino acids (T.A.A.) and producedless biomass in their shoot and root systems than theunacidified control. The reverse held true in theplants received HNO₃ solution. Proline contentincreased with exposure to an HCl acid mist of pH 2.0.An acid spray of pH 2.0 did not affect shoot Na⁺,K⁺ and Mg²⁺ content but reduced theircontents in the root. Shoot and root Ca²⁺contents were substantially lower in acid sprayedplants than in the unsprayed analogues. Ascorbic acidtreatment counteracted the deleterious effects of acidmist on the parameters tested, effectively protectingthe plant membranes from dehydration and heat stressinjury. Ascorbic acid protection was more pronouncedin plants that received HCl solution (e.g. chlorophyllcontent was about three-fold higher than that ofascorbic acid untreated analogues) in contrast toeither HNO₃ or H₂SO₄ treated plants.The effects of single factors, acid mist (pH),ascorbic acid (A.A.) and their interaction (pH × A.A)on the parameters tested were statisticallysignificant. The coefficient of determination(η²) indicated that: (1) acid mist (pH) hada dominant role in affecting the stability of leafmembrane to dehydration stress, Chl content, shootlength and dry mass production, shoot S.P. and H.C.,and root S.S., S.P., T.A.A., Ca²⁺, and Mg²⁺contents. (2) The effect of ascorbic acid (A.A.) wasdominant for shoot Na⁺, K⁺, Ca²⁺ andproline contents as well as for root H.C. (3) Theshare of pH × AA. interaction was dominant for thestability of leaf membrane to heat stress, root dryweight, shoot S.S., T.A.A. and root Na⁺ content.(4) The role of pH and A.A. was equally dominant inaffecting root length.     

Trends of Major Inorganic Species at the Small Watershed Ecosystem in Northern Tama Hills, the Western Tokyo Metropolitan Area, Japan

Acid rain impacts on the small forested watershed in northern Tama Hills in the western Tokyo metropolitan area Japan were investigated by surveying the trends of major inorganic species in rain and spring water during the years from 1991 to 1997. The ecosystem had been stressed by the annual H⁺-deposition of around 0.43 kmol/ha. The spring water outflow corresponded to ca. 27% of the precipitation. Budgets for the precipitation input and spring water output gave good balance for Cl^?,?0.01 ±0.09 kmol/ha, net gains for H⁺, NO₃ ^? and SO₄ ^2?, and to the contrary, relatively large net losses for Na⁺, Mg²⁺, Ca²⁺, Si(as H₄SiO₄) and HCO₃ ^?, thus suggesting the dissolution of chemical weathered products of silicate minerals. Further, in spring water, some concentration relationships were found: CNa⁺ = 376.5?2.05CCl^? (R²=0.748), CNa⁺=12.69+0.5556CHCO₃ ^? (R²=0.872) and CH₄SiO₄=130.0 + 1.108CHCO₃ ^? (R²=0.816). Evidently, the spring water chemistry reflected probable geochemical changes in the soil layer of the watershed. Mass balance in the ecosystem and estimation of the spring water output of chemical weathered products were investigated     

Project rain: Changing acid deposition to whole catchments. The first year of treatment

Project Rain (Reversing Acidification In Norway) is a 5-yr international research project aimed at investigating the effect on water and soil chemistry of changing acid deposition to whole catchments. The project comprises 2 parallel large-scale experimental manipulations -- artificial acidification at Sogndal and exclusion of acid rain at Risdalsheia. Treatment at Sogndal commenced April 1984 with the acidification of the snowpack by addition of H₂SO₄ (SOG2) and a 1:1 mixture of H₂SO₄ and HNO₃ (SOG4). Preliminary results indicate rapid and significant response in runoff chemistry to the acid treatment; pH decreased (to as low as 4.1 during snowmelt in 1984); SO₄, NO₃, and labile Al increased. Response during snowmelt 1985 was modest relative to 1984. At Risdalsheia treatment began in June 1984 with the mounting of the transparent panels on the roofs at KIM catchment (treatment by deacidified rain) and EGIL catchment (control with ambient acid rain). Preliminary data for the first year indicate that most runoff samples from KIM contain much lower NO₃ concentrations, about 20 to 30% lower SO₄ levels and pH 0.1 to 0.3 units higher than runoff from EGIL catchment. The treatments continue in 1985–87. Project RAIN provides experimental evidence bearing on target loading, reversibility of acidification, and the processes linking acid deposition, soil acidification and freshwater acidification.     

Effects of acidity in precipitation on terrestrial vegetation

Over the last several decades rain in the Northeastern United States has become more acidic presumably as a result of anthropogenic inputs of SO_x and NO_x to the atmosphere and their conversion to H₂SO₄ and HNO₃. Present experimental results suggest that acidic precipitation would initially affect organisms on leaf surfaces and epidermal cells of leaves of higher plants. More internal cell layers would be affected with increasing duration or frequency of exposure. Differences in responses of plant foliage among plant species to acidic precipitation appear to be due to the degree of leaf wetting and differences in responses of leaf cells to low pH rain. Moreover, within the same plant, particular structures or cell types may be more sensitive than others. If the United States is to utilize coal reserves for electric power generation that might increase rainfall acidity in the future, an assessment of the impact that acidic rain might have on terrestrial vegetation is necessary. In one experiment, field-grown soybeans were exposed to short duration rainfalls of either pH 4.0, 3.1, 2.7, or 2.3 to provide inputs of 50, 397, 998, or 2506 μeq of H⁺, respectively, above ambient levels throughout the growing season. Control plots received only ambient rainfalls. These additional H⁺ decreased seed yield, 2.6, 6.5, 11.4, and 9.5%, respectively. A treatment response function determined between H⁺ treatments and seed yield wasy=21.06?1.01 logx had a correlation coefficient of ?0.90. Researchers must design additional experiments with adequate experimental controls to assess the impact that acidic rain, at the present pH levels of 3.0 to 4.0 or at anticipated worst-case levels, that could occur if the acidity of rain should increase. Only a holistic view of the impacts that acid precipitation may have on vegetation will enable optimal energy and environmental policy decisions to be made.     

Throughfall Chemistry in a Sitka Spruce Plantation in Response to Six Different Simulated Polluted Mist Treatments

A mixed provenance Sitka spruce plantation, planted in 1986 on a drained deep peat, has been exposed to 6 different simulated mist treatments in 4 replicated blocks since 1996. Treatments provided N and/or S at a concentration of 1.6 mol m^?3, supplying ca. 50 kg S and/or N ha^?1 yr^?1 as N (NH₄NO₃), S (Na₂SO₄), NS Acid (NH₄NO₃ + H₂SO₄ at pH 2.5), 2NS Acid (double dose by application at twice frequency), a control treatment supplied with additional rainwater only and a 'no treatment' set of plots. Throughfall, preserved with thymol in the field, was collected using gutters with a surface area of 1 m² in all the replicate plots, and was analysed for all major ions. Prior to treatment in 1999, S deposition in throughfall exceeded that in rain because of dry deposition of SO₂ and SO₄ ^2? to the canopy; NH₄ ⁺ and NO₃ ^? ions were both retained in the canopy. During treatment, only 20–40% of the applied N in the high-N treatments was retained in the canopy. Acidity in the applied mist was partly neutralised by the canopy, but not primarily through exchange of base cations, leading to the conclusion that weak organic acids, in solution or in situ in the canopy, contributed to the buffering of the H⁺ ion deposition in the acid 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.     

Chemical Characterization of Acid Fog and Rain in Northern Japan Using Back Trajectory and Oblique Rotational Factor Analysis

Fog/cloud and rain water were collected at the mountainside of Hachimantai range in northern Japan and rain water was also collected at Akita City in order to investigate the air pollutant scavenging mechanism. The concentrations of various ions in these samples were analyzed, and the fog drop size and the wind direction were measured at each fog event. The fog at Hachimantai range had a very high total ion concentration, and was considerably acidified by non sea salt (nss-) SO₄ ^2? and NO₃ ^?, compared with the rain at Akita and all sites in Hachimantai range. Using the oblique rotational factor analysis, three factors were extracted as the air pollutants; A: (NH₄)₂SO₄+H₂SO₄, B: sea salts+HNO₃+H₂SO₄, C: NH₄NO₃+OH^?. These salts are well-known as the cloud condensation nuclei (CCN). Combining the factor analysis with the 72h back trajectory at 850hPa level, the contribution of Factor A was closely connected to the long-range transportation of anthropogenic or natural aerosol in air masses of continental origin.     

Die kurzfristige pH-Pufferung von gestörten und ungestörten Waldbodenproben

Short-timed pH-buffering of disturbed and undisturbed forest soil samples The pH buffering of disturbed and undisturbed soils under spruce (podzol and podzolic cambisol derived from phyllite, eutric cambisol derived from basalt) was studied in the laboratory by adding H₂SO₄ in ecologically relevant concentrations (pH 5.6–2.0). For the cambisol with crumb structure no difference was found. 80–90% of the added protons were neutralized by release of Ca and Mg. Disturbed samples of the podzol buffer less than 70% of the applicated acid. For undisturbed samples the maximum buffering rate of 185 g H⁺/ha · h is reached with a proton load of about 500 g H⁺/ha · h (related to 4 cm soil depth). Buffering behaviour of the podzolic cambisol lies between the podzol and the cambisol. 70–90% of the proton input is buffered in the disturbed samples while the undisturbed one does not reach its maximum buffering rate, even with high proton load. In this soil Al-release is the most reactive buffer.     

The effects of acid nitrogen and acid sulphur deposition on CH4 oxidation in a forest soil: a laboratory study

Sieved soil and soil core experiments were performed to determine the potential sensitivity of forest soil CH₄ oxidation to oxidised N, reduced N and oxidised S atmospheric deposition. Ammonium sulphate was used to simulate reduced N deposition, HNO₃ oxidised N deposition and H₂SO₄ oxidised S deposition. The effects of NH₄⁺, NO₃⁻, SO₄²⁻ and H⁺ on soil CH₄ flux were shown to be governed by the associated counter-anion or cation of the investigated ions. Ammonium sulphate, at concentrations greater than those that would be experienced in polluted throughfall, showed a low potential to cause inhibition of CH₄ oxidation. In contrast, HNO₃ strongly inhibited net CH₄ oxidation in sieved soils and also in soil cores. In addition, soil CO₂ production was inhibited and the organic and mineral soil horizons acidified in HNO₃ treated soil cores. This suggested that the HNO₃ effect on CH₄ flux might be indirectly mediated through aluminium toxicity. Sulphuric acid only inhibited CH₄ oxidation when added at pH 1. At concentrations more representative of heavily polluted throughfall, H₂SO₄ had no effect on soil CH₄ flux or CO₂ production from soil cores, even after 210 days of repeated addition. In contrast to HNO₃ additions, acidification of the soil was not marked and was only significant for the mineral soil. The findings suggest that the response of forest soil CH₄ oxidation to atmospheric acid deposition is strongly dependent on the form of acid deposition.     

Forest decline in the boreal montane ecosystems of the southern Appalachian Mountains

Research was initiated in 1984 in an attempt to quantify and test possible hypotheses for the systematic decline and mortality of red spruce (Picea rubens Sarg.) observed in the southern Appalachian Mountains. Field surveys have documented increases in decline symptoms. By 1986, 7% of all tagged red spruce trees in permanent plots were dead. This number, partially due to the effects of severe weather, increased to 41% in 1987. An insect and disease survey initiated in 1985 on 100 permanent plots has yielded little significant pathology or insect infestation. With the exception of the balsam wooly adelgid (Adelges picea (Ratz)), few signs or symptoms of disease or insect attack were noted on either Fraser fir (Abies fraseri) (Pursh Poir) or red spruce populations. Cultures from destructively-sampled root systems yielded few significant pathogens that could contribute to decline symptoms. Measurements of throughfall in 1986 yielded estimates of total wet deposition for NO₃ ^? and SO₄ ^2? of 25 and 75 kg ha^?1 yr^?1 respectively. Using net throughfall quantities, we estimate that between 40 and 60% of this input was due to cloud impact. Mean-volume-weighted pH per cloud event was 3.5. Over 75% of the cloud events sampled had a pH < 4.0. Cloud and rain water was dominated by H⁺, NH₄ ⁺, NO₃ ^?,, and SO₄ ^2? ions. Interaction with the forest canopy resulted in an enrichment of throughfall with base cations (K⁺, Ca²⁺, and Mg²⁺) and a loss of H⁺ and NH₄ ⁺. Mean-volume-weighted pH for throughfall was 3.9. The effects of simulated acidic cloud water on the epicuticular waxes of red spruce needles were studied during the summer of 1987. The cuticle proper of both 1986 and 1987 needles did not appear to be damaged by the treatments. The wax crystals which constitute the stomatal wax plugs, however, exhibited substantial degradation by simulated treatments at or below pH 3.5.     

酸和氧化还原剂对二氧化锰溶解度的影响

由于土壤中锰的有效性随pH和Eh的变化而变化,利用土壤测试方法得到的锰素营养丰缺指标,通常难以代表田间锰素营养的实际状况.然而,在应用土壤pH和氧化锰溶解度的关系时,某些文献的不确切解释,引起一些误解.本实验研究了在浓HCl、HNO3和H2SO4及其稀溶液的不同浓度情况下对二氧化锰-水钠锰矿(MnO2)的溶解能力和机理,以及三种卤素还原剂(KCl、KBr和KI)在两种pH值条件下对MnO2的还原能力,从实验上和理论上进一步阐明了pH和Eh对MnO2溶解度的影响.实验结果表明,在浓HCl中,MnO2能被Cl-迅速还原而溶解.而在浓HNO3和H2SO4溶液中,MnO2不能被酸所直接溶解,只能被酸中的H2O缓慢还原,放置两年后反应仍未到达终点.在稀酸溶液中,当H+强度小于0.5 mol L-1(pH＞1.0)时,三种强酸对MnO2都无明显的溶解能力;当H+强度＞1.0 mol L-1时,HCl对MnO2的溶解能力显著地高于HNO3和H2SO4.三种卤盐溶液对MnO2的还原能力为KI＞KBr＞KCl,并随pH的降低和浓度的升高而增强.当pH＞3时,KCl对MnO2的还原能力极弱;而无论pH高低(pH3或pH5),KI在很低浓度(0.001 mol L-1)时都能有效地还原MnO2.上述结果说明,如果二氧化锰不被还原,仅改变pH则很难被溶解.然而,在较高pH条件下,如有强还原剂存在,也有相当量的MnO2被还原.低Eh和pH条件下最有利于MnO2的还原.     

Lysimeter study with a cambic Arenosol exposed to artificial acid rain: I. Concentrations of ions in leachate

The effects of artificial acid rain on soil leachate composition were studied in a lysimeter experiment. Cambic Arenosol (Typic Udipsamment) in monolith lysimeters was treated for 6 1/2 yr with 125 mm yr^?1 artificial rain in addition to natural precipitation. Artificial acid rain was produced from groundwater with H₂SO₄ added. pH levels of 6.1, 4 and 3 were used. Increasing content of H₂SO₄ in the artificial rain increased the concentration of Ca²⁺ and Mg²⁺ in the leachate significantly. The pH of the leachate was slightly reduced only by the most acidic treatment (pH 3). The H^+? retention was not accompanied by a proportionate increase in the Al ion concentration. A slight increase in the Al ion concentration was only observed in the leachate from the pH 3-treated lysimeter. We conclud that cation exchange and/or weathering were the main buffer mechanisms in the soil. The study supports conclusions from other acidification studies, that acidic precipitation is likely to increase the leaching of Ca²⁺ and Mg²⁺ from soils.     

Lysimeter study of effects of acid deposition on properties and leaching of gleyed dystric brunisolic soil in Norway

The effects of artificial rain of various acidities were studied in a lysimeter experiment. Lysimeters, 29 cm in diameter, and 40 cm deep contained a Gleyed Dystric Brunisol. Natural structure, stratification and original vegetation were maintained. Artificial rain was produced from groundwater with “high” concentrations of neutral salts and from rainwater with lower concentrations. pH levels of 6, 4, 3 and 2 were established by adding H₂SO₄. Effects of dilution with given amounts of acid were examined by comparing the effects of 50 mm “rain” month^?1 of pH 3 and pH 2 with 500 mm “rain” month^?1 of pH 4 and pH 3, respectively. The study continued for 5 yr. Totals of 1250 or 12500 mm “rain” were applied in addition to a natural input of 2773 mm. Increased input of SO₄ ^2? increased the output of SO₄ ^2? but, as concentration increased, sorption of SO₄ ^2? in the soil also increased. Concentrations of base cations in the leachate increased parallel to the output of SO₄ ^2?. However, significant effects on leaching of base cations and on the content of exchangeable cations in the soil, was only found in the pH 2 treatment with 1250 mm of “rain” and in the pH 4 and pH 3 treatment with 12500 mm of “rain”.     

Lysimeter study with a cambic arenosol exposed to artificial acid rain: II. Input-output budgets and soil chemical properties

The effects of artificial precipitation with different pH levels on soil chemical properties and element flux were studied in a lysimeter experiment. Cambic Arenosol (Typic Udipsamment) in monolith lysimeters was treated for 6 1/2 yr with 125 mm yr^?1 artificial rain in addition to natural precipitation. Artificial acid rain was produced from groundwater with H₂SO₄ added. pH levels of 6.1, 4 and 3 were used. ‘Rain’ acidity was buffered, mainly due to cation exchange with Ca²⁺ and Mg²⁺, which were increasingly leached due to the acid input. The H⁺ retention was not accompanied by a similar increase in the output of Al ions, but a slight increase in the leaching of Al ions was observed in the most acidic treatment. The net flux of SO₄ ^2? from the lysimeters increased with increasing input of H₂SO₄, but in the most acidified lysimeters significant sorption of SO₄ ^2? was observed. The sorption was, however, most likely a concentration effect. The ‘long-term’ acidification effects on soil were mainly seen in the upper O and Ah-horizons, where an impoverishment of exchangeable Ca²⁺ and Mg²⁺ was observed. An increased proportion of Al ions on exchange sites in the organic layer was observed in the pH 3-treated soil. By means of budget calculations the annual release of base cations due to weathering was estimated to be between 33 and 77 mmol_c m^?2.