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1.
As the acidity of rain diminishes, changes in the pH, ionic strength, and ion activities of the soil solution will influence the charge characteristics of soil. We have investigated the response of cation exchange capacity (CEC) of three acid forest soils of variable charge to small changes in pH, ionic strength, and SO2?4 concentration. The variable charge for these temperate soils has the same significance as for tropical soils and those from volcanic ash. Maximum absolute increase in CEC on increasing pH by 0·2–0·5 units reached 5 cmolc kg-1 in O horizons. The increase in CEC on doubling ionic strength in EA and Bsh horizons of a Cambic Podzol was about half that amount, but relative gains compared to effective CEC were 65 and 46%, respectively. For other soil horizons, absolute changes were smaller, and relative changes were between 10 and 30%. Halving the SO2?4 concentration significantly influenced CEC only in some samples. Both pH and ionic strength must be adjusted with care when determining CECc of acid forest soils. Decreasing acid deposition will not inevitably increase CECc because in some soils pH effects may be balanced by simultaneous decrease in ionic strength.  相似文献   

2.
Potential vitiative effects of Millipore 0.45-, 0.22-, 0.05- and 0.025-pm filter elements on aqueous samples were investigated. All the filter elements evaluated exhibited a cation exchange capacity (CEC); in the case of 0.025-pm filter elements, the CEC increased with pH. Filtration of 20 μM AlCl3/1.65 mM CaCl2, solutions (I～0.005 M) to 0.45, 0.22 and 0.05 pm resulted in no significant change in solution A1 concentration. Filtration through 0.025-μm filter elements significantly reduced the total A1 present in solutions adjusted to pH 4.5 and 5.0; the A1 concentration of solution adjusted to pH 4.0 was not altered. The removal of A1 from pH 4.5 and pH 5.0 solutions was attributed to the retention of A1 hydroxide micro-particulates formed during pH adjustment of the AlCl3/CaCI2, solution. Adsorption of A1 by the filter element was not significant. Soil solutions were analysed without filtering and after filtration to 0.45,0.22,0.05 and 0.025 pm. Filtration had no effect on the concentration of the major anions (Cl?, SO24 -, NO13) or cations (Ca++, Mg++, Na+, K+). However, filtration to 0.05 and 0.025 pm resulted in significant reductions in the concentration of Al, Fe, Si and organic C in some samples. In soil solutions for which filtration resulted in the removal of large amounts of particulate material, the solution appeared less coloured after filtration and exhibited lower absorbance in the visible spectrum (4O(MOO nm). However, the absence of colour did not preclude the presence of colloidal particles.  相似文献   

3.
In the absence of SO infin4 sup= and NO inf3 su? in precipitation, the pH of precipitation is primarily a function of CO2?20 equilibria. Soil CO2 and organic acids, acquired during descent through soil profiles, augment the dissolving capacity of the solutions which initially may have a pH of 4 or lower. The recent man-related increase of H2SO4 and HNO3 in rainfall results in a significant lowering of pH in incident precipitation and an increase in corrosiveness of soil solutions. H2SO4 and HNO3 may contribute some Eh buffering capacity. Particularly susceptible to these changes are clay minerals and redox sensitive elements such as Fe, Mn, Ni, and Co. The overall chemical weathering trends associated with increased acidity of rainfall will be de-stabilization and eventual solution of clay minerals (and the loss of their cation exchange capacity), increased rates of chemical denudation, and solution of illuvial Fe and Al oxides and hydroxides. The latter results in the loss of the adsorbed and coprecipitated metal trace elements associated with these highly reactive phases. The general result in soils developed on non-carbonate substrates is a tendency toward extensive podsolization, with associated decrease in clay minerals, loss of cation exchange capacity, and decrease in fertility.  相似文献   

4.
Abstract

Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH4OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH4OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH4OAc at pH 7.0 (summation of basic cations plus exchangeable H+), (4) 0.1M BaCl2 (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H+), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H+). The 0.1M BaCl2 was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH4OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl2 method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H+ should be included in the computation.  相似文献   

5.
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 mmolc m?2.  相似文献   

6.
Abstract

Al toxicity in plants is related to the activity of Al3+ and Al‐hydroxy monomers in the soil solution, whereas Al complexed with ligands such as fluoride (F), sulphate (SO4 2‐), and oxalate is not toxic. Estimation of toxic Al relies on measurement of “labile”; Al after short contact times with colorimetric reagents or cation‐exchange resins. However, shifts in equilibrium may result in non‐toxic forms of Al reacting with the complexing agent or resin.

A series of laboratory experiments tested the degree to which labile Al is related to Al3+ in simplified media and compared methods of estimating labile Al in the presence of organic ligands and in soils. Cation‐exchange resins extracted more than the theoretical concentration of Al3+ from solutions containing a range of concentrations of OH‐ and SO4 2‐. More Al was extracted in 15 s by 8‐hydroxy‐quinoline than by Chelex‐100 from solutions of Al‐humate at pH 4. In sands which had been spiked with Al and organic matter, the estimation of labile Al varied with both the method of measurement and type of extract. The cations present in commonly used soil‐extracting chloride solutions can decrease the proportion of organically complexed Al.  相似文献   

7.
A soil's cation exchange capacity (CEC) is expected to be relatively inert against changes in cation loading. In this study, we treated a soil sample originating from the organic layer of a forest soil with various bivalent cations after removing the native cations. Sorption isotherms and cation exchange capacity were determined, the latter using the BaCl2 method. Sorption showed Langmuir characteristics, with the maximum coverage (Qmax) increasing in the order Ba2+ < Ca2+ < Mg2+, but being clearly smaller than the initial load of native exchangeable cations. The Langmuir coefficient, kMe, depended oppositely to the order obtained for Qmax. CEC increased upon cation treatment and it varied by a factor of almost two. The unexpected variation of CEC was explained by the low cation exchange capacity of the organic matter such that not all functional groups are close enough to be bridged and the second charge of a bivalent cation is not neutralized by the organic functional group. The Langmuir sorption type, and Qmax being smaller than the content of sorption sites and being largest for Mg, suggested that only a part of the sites can be cross‐linked and at least part of the cross‐links are formed by hydrated cations. Thermodynamic considerations allowed reconstruction of two contrasting processes during CEC determination by Ba2+: Case A: the disruption of cross‐links, which increases with the cationic strength and the cation load before CEC determination, but does not require structural re‐orientation in the SOM matrix, and Case B: the formation of new cross‐links during CEC determination, depending only on the content of unoccupied sites before CEC determination and requiring structural re‐organization of the matrix and thus a minimum matrix flexibility. The use of bivalent cations for CEC determination may thus result in an overestimation of CEC for organic matter with low CEC. This has, however, promising potential when comparing CEC determined with monovalent cations and bivalent cations. Using a set of bivalent cations, may allow probing distribution of distances between functional groups in the organic matter and even characterize the matrix rigidity of the cation‐cross‐linked network.  相似文献   

8.
Abstract

Single values of the cation exchange capacity (CEC) are widely used in modeling soil solution chemistry in soil and water ecosystems. Our aim was to determine the CEC as a function of pH and ionic strength in an acidic forest soil. We examined the cation exchange of two Humo‐Ferric Podzols (Haplorthods) equilibrated with artificial soil solutions of different concentrations. Aliquots of acid (HC1) or base (NaOH) were added to generate a pH range of 3 to 6. The CEC, determined by displacement with BaCl2 showed little or no increase with increasing pH and a definite increase with lower pH. This anomalous behavior was attributed to the precipitation of aluminum (Al) at high pH and to its dissolution at low pH.  相似文献   

9.
In upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba2+ as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined with m NH4OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg2+ and Ba2+ chlorides than K+ and NH4+ chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH4+ and K+, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al-chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K+ and NH4+, than with Mg2+ and Ba2+, chlorides. The implication of the results for CEC measurements is discussed.  相似文献   

10.
The fine earth (<2 mm) and rock fragments (>2 mm) fractions of two soils derived from Oligocene sandstone have been examined to assess the origin of the discrepancies between cation exchange capacity (CEC) and effective CEC (ECEC). The soils differ in terms of acidity: soil A is more acid than soil B. When the A samples are treated with BaCl2, the solution became sufficiently acid (pH < 4·5) to dissolve and to maintain Al in solution. From these samples more Al is released than base cations. Aluminium was continuously replenished even after 192 h, so that the ECEC was always larger than the CEC. Samples from soil B contain less H and Al ions, and the BaCl2 solution could not lower the pH below 5·0. In these samples little Al is released, and the base cations dominate the exchangeable pool of ions. This Al can be considered to be exchangeable, and a good agreement exists between the ECEC and the CEC. The source of non-exchangeable Al in the A samples is the OH-Al polymers of the hydroxy-interlayered vermiculite (HIV) and hydroxy-interlayered smectite (HIS) that tend to dissolve during the BaCl2 treatments. In the less acid B samples the Al polymers are not affected by BaCl2 treatment. Different results were obtained when the clays, extracted from an Na-dispersed suspension, were treated with BaCl2 solution. Because the clays are no longer acid, no H+ is released, and the OH-Al polymers are not dissolved. Therefore, the saturating ions play an important role in the dissolution of the OH-Al polymers and cause differences between the CEC and ECEC. We discount organic matter and specifically Al-organo complexes as a source of non-exchangeable Al. Both A and B soils contain very similar pyrophosphate-extractable Al, but show substantial differences in the amount of exchangeable Al.  相似文献   

11.
Comparisons among 4 peatland sites representing a gradient of increasing Fe, Al, Mn, and S loading revealed significant accumulation of total Fe, Al, and S, but not Mn, in surface (0 to 20 cm deep) peat along the gradient. Iron and Al accumulation were contributed mainly by organically bound fractions, with oxides contributing to a lesser extent. Although SO4 2? and Fe sulfides showed significant increases in concentration along the gradient, most of the accumulation of total S was contributed by organic, rather than inorganic S. Laboratory studies of Fe2+ adsorption by peat indicated that increasing the pH of added Fe2+ solutions (pH values of 3, 4, 5, and 6) did not significantly affect Langmuir equation estimates of either maximum Fe2+ adsorption capacity or the affinity of peat for Fe2+. Regardless of the pH of the added Fe2+ solutions, final solution pH values were relatively uniform, averaging about 3.4, reflecting a considerable bufferring capacity of Sphagnum peat. Factors affecting the accumulation of metals and S in peat remain topics for further investigation.  相似文献   

12.
This paper presents the results of an acidification experiment, consisting of seven consecutive equilibrations of repesentative soils of Galicia with a H2SO4 solution (pH 3). Different responses to soil acidification, such as SO4 retention and cation release, were evaluated. In soils derived from gabbro and amphibolite, SO4 retention and Al release were the principal acid neutralization mechanisms, whereas in soils derived from granite, schist, shale and sandstone Al release was the main process. The SO4 retention was significantly correlated with Al and Fe extracted with dihionite-citrate-bicarbonate and crystalline Fe. The released base cations came mainly from exchange sites, though sometimes also from other sources, probably by mineral weathering. The major sources of Al in these soils were metalorganic complexes and weatherable minerals. Solutions with pHs close to 4 are in equilibrium with gibbsite, kaolinite, jurbanite and alunite; at lower pH values, with jurbanite and alunite.  相似文献   

13.
The relations between pH, different fractions of Fe and A1 and Na4P2O7-soluble C and the amount of adsorbed SO2-4 were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of adsorbed SO2-4 was significantly better correlated with the calculated amount of the inorganic fraction of Fe and A1 oxides obtained by subtracting Na4P2O7-soluble Fe and A1 from oxalate-soluble Fe and Al than with the oxalate extraction alone. There was a close correlation between C and organically-bound S in the Na4P2O7 extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically-complexed Fe and Al increases, the ability of the soil to adsorb SO2-4 decreases. The amount of adsorbed SO2-4 expressed on the basis of the amounts of oxalate-soluble Fe and Al was generally smaller in areas with low S deposition (< 60 mmol m-2 a-1). The ratio between pyrophosphate-soluble C and oxalate-extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic matter cannot adsorb SO2-4 and that the degree of this association is pH dependent. These observations have important implications regarding the effects of anthropogenic acidification.  相似文献   

14.
The results of physico-chemical investigations of an Ultisol subsoil under a 2-year old fallow in eastern Amazonia are presented. Subsoil chemistry was studied using 4 different approaches: i) concentrations of H, Na, K, Ca, Mg, Mn, Al, and Fe in seepage water were measured under field conditions, ii) the equilibrium soil chemistry was studied in sequential batch experiments where the soil was treated with different solutions, iii) results of batch experiments were simulated with a chemical equilibrium model, and iv) the seepage data were calculated using selectivity coefficients obtained by modelling the batch experiments. The model included multiple cation exchange, precipitation/dissolution of Al(OH)3 and inorganic complexation. Cation selectivity coefficients were pKx/Casel: X = Na: 0.3, K: 0.8, Mg: ?0.1, and Al: 0.4. The amount of cations sorbed ranged from ?0.2 to 2.0 (K), ?0.7 to 2.3 (Mg), ?1.6 to 1.8 (Ca), ?4.8 to 3.6 (Al) and 0.0 to 8.5 (Na) mmolc kg?1. The model predictions were good with values lying within 0.3 pH units (for the pH range 3.7 to 7.2), and 3% of CEC for individual cations. The most important proton buffer reaction seemed to be the dissolution of gibbsite and a large release of Al into the soil solution. When selectivity coefficients obtained by the modelling procedure were used to predict the field data for cation concentrations in the seepage water, they decreased in the following order: Na > K > Ca > Mg > Al. These calculated values were similar to the measured order: Na > Ca > K ≈ Mg > Al. Thus the options for managing these soils should be carefully chosen to avoid soil acidification which may result from inappropriate use of fertilizer during the cropping period.  相似文献   

15.
In the present paper, α-FeOOH and α-Fe(Al)OOH were prepared, and the adsorption of Cr(VI) on the two samples was investigated. The influence of pH, initial concentration, and some anions such as SO4 2?, H2PO4 ?, C2O4 2?, CO3 2?, and SiO3 2? on the adsorption of Cr(VI) on α-FeOOH and α-Fe(Al)OOH was studied by batch techniques. The results show that the adsorption capacity of Cr(VI) on α-Fe(Al)OOH increases with the introduction of aluminum, but decreases with the increase of pH. The adsorption irreversibility of Cr(VI) on α-Fe(Al)OOH is much higher than that on pure α-FeOOH. The adsorbed Cr(VI) species mainly exists in the form of *Fe(wk)-OHCrO4 2? on the surface of the samples. With the presence of SiO3 2?, CO3 2?, C2O4 2?, SO4 2?, and H2PO4 ?, the binding of Cr(VI) is inhibited by different degree. The inhibition of those anions is larger in the pure goethite than that in the Al-substituted goethite system. After Al was introduced into α-FeOOH, Cr(VI) ions are preferentially adsorbed on Al sites rather than Fe sites on α-Fe(Al)OOH.  相似文献   

16.
Retention of S04 2? was investigated in Galician soils throughout an intense regime of acidification. Experiments consisted of the addition of an H2SO4 solution (pH 2.7) to columns of 6 soils of contrasting properties over 1, 2, or 5 months. Leachates were obtained continuously throughout the experiment for analysis, and analysis made of the solid fractions after 1, 2 or 5 months. The greatest capacities for retention of S04 2? were found in soil developed from serpentine and micaschist; the lowest in soils from granite, slate and sandy sediments. The surface horizons, especially those rich in organic matter, displayed low retention of 5042-. The amount of S04 2? adsorbed throughout the experiment depended on the content of crystalline forms of Fe and with the Fe and Al extracted with dithionite-citrate.The low retention of S04 2? in the organic horizons and the slightly negative relation with the organic matter suggest an inhibitory effect of the organic matter on the S04 2? retention process. Results of the study show, that under conditions of moderate acidity, SO4 2? retention occurs in the form of adsorption; in strongly acidic conditions, the precipitation of aluminium-sulphate minerals may provide an additional retention mechanism.  相似文献   

17.
To investigate the potential of synchrotron‐based X‐ray Absorption Near‐Edge Structure spectroscopy (XANES) at the sulphur (S) K‐edge for a discrimination of adsorbed and precipitated sulphate in soils and soil particles, XANES spectra of ionic sulphate compounds and Al/Fe hydroxy sulphate minerals were compared with spectra of SO42? adsorbed to ferrihydrite, goethite, haematite, gibbsite or allophane. Ionic sulphate and hydroxy sulphate precipitates had broader white‐lines (WL) at 2482.5 eV (full width at half maximum (FWHM) of edge‐normalized spectra, 2.4–4.2 eV; Al hydroxy sulphates, 3.0 eV) than SO42? adsorbed to Al/Fe oxyhydroxides or allophane (FWHM, 1.8–2.4 eV). The ratio of the white‐line (WL) height to the height of the post‐edge feature at 2499 eV (WL/PEF) was larger for SO42? adsorbed to Al/Fe oxyhydroxides or allophane (8.1–11.9) than for Al/Fe hydroxy sulphates and ionic sulphates (3.9–5.7). The WL/PEF ratio of edge‐normalized S K‐edge XANES spectra can be used to distinguish adsorbed from precipitated SO42? in soils and also at microsites of soil particles. The contribution of adsorbed and precipitated SO42? to the total SO42? pool can be roughly quantified. Adsorbed ester sulphate may result in overestimation of precipitated SO42?. The spectra of most soils could be fitted by linear combination fitting (LCF), yielding a similar partitioning between adsorbed and precipitated SO42? as an evaluation of the WL/PEF ratio. The SO42? pool of German forest soils on silicate parent material in most cases was strongly dominated by adsorbed SO42?; however, in three German forest soils subject to elevated atmospheric S deposition, a considerable portion of the SO42? pool was precipitated SO42?, most likely Al hydroxy sulphate. The same is true for Nicaraguan Eutric and Vitric Andosols subject to high volcanogenic S input. In the subsoil of the Vitric Andosol, adsorbed SO42? and Al hydroxy sulphate coexist on a micron scale.  相似文献   

18.
In Saxony‐Anhalt, Germany, an area of about 6000 ha is covered by lignite‐ash‐derived substrates. In some cases, pollutants like heavy metals or toxic organic compounds had been disposed of together with the lignite ashes. For this reason, we assessed factors influencing the cation exchange capacity (CEC) of lignite‐ash substrates exposed to natural weathering. We chose four research sites reflecting the different methods of disposal: two dumped landfills and two lagooned ashes of different ages. After determining the CEC at pH 8.1 (CECpot), we evaluated the influence of the content of silt and clay and the content of total organic C. As lignite‐ash‐derived substrates are rich in oxalate‐extractable Si, Al, and Fe, we performed an oxalate extraction and determined afterwards the CECpot to assess the contribution of oxalate‐soluble compounds to the CECpot. Moreover, we determined the variable charge of selected samples at pH values ranging from 4 to 7. The lignite‐ash‐derived soils had a high CECpot with means ranging from 25.1 cmolc kg–1 to 88.8 cmolc kg–1. The influence of the parent material was more important than the degree of weathering. The content of total organic C consisting of pedogenic organic matter and coked lignite particles together with the content of silt and clay played a statistically significant role in determining the CEC. Another property that influenced the amount of CEC in medium textured lignite ashes was the content of oxalate‐soluble silica and aluminum. After oxalate extraction, they lost about 30% of their CEC due to the dissolution of oxalate‐soluble compounds. In coarse textured lignite ashes, oxalate extraction led to higher amounts of CEC, probably due to an increase of surface area resulting either from the disintegration of particles or from etching caused by insufficient dissolution of magnetite and maghemite. Moreover, lignite‐ash‐derived substrates exhibit a high amount of pH‐dependent charge. The CEC decreased by 40% in a topsoil sample and by 51% in a subsoil sample as the pH declined from 7 to 4.  相似文献   

19.
Abstract

Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl2 ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)2 (pH 7.0) saturation with Mg(OAc)2 (pH 7.0) displacement of Ca2+; (3) N NH4OAc (pH 7.0) saturation with NaCl displacement of NH4 +; (4) N MgCl2 saturation with N KCl displacement of Mg2+; (5) compulsive exchange of Mg2+ for Ba2+; and (6) summation of N NH4OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH4OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH4OAc exchangeable cations plus BaCl2 ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl2 were consistently greater than values for the N NH4Oac (pH 7.0) extractions. The Ba2+ ion is apparently a more efficient displacing agent than the NH4 + ion. Also, the potential for dissolving unreacted limestone is greater for the Ba2 + procedures than in the NH4 + extraction.  相似文献   

20.
Cores of podzolic soil (monolith lysimeters) were treated for 4.8 yr with 1500 mm yr?1 of either 0.5 mM H2SO4 at pH 3, equivalent to 24 g S m?2 yr?1 (acid treated) or distilled water (controls). The acid treatment was about 37 times greater than the average annual input of H3O+ from rain at the site from which the monoliths were taken. Acid treatment acidified the litter (from pH(CaCl2)3.4 to pH(CaCl2)2.6) and the mineral soil to a depth of 80 cm (mean pH(CaCl2) decrease of 0.2 unit). In the litter and upper A horizon, ion-exchange reactions provided the main neutralizing mechanism, resulting in a decrease in the reserves of extractable (in 2.5 % acetic acid) Ca, Mg, and Mn of about 70 to 80 %. Dissolution of solid phase Al from hydrous oxides provided most neutralization below this depth. Al3+ was the principal soluble Al species throughout the profile. In the litter and upper A horizon, some of the mobilized Al3+ was retained on cation exchange sites resulting in an increase in exchangeable Al. Deeper in the profile, where the exchange sites were effectively saturated with Al3+, no increase in exchangeable Al occurred, and Al3+ was, therefore, available for leaching. Some reversible adsorption of SO4 2?, associated with hydrous Al oxides, occurred in the Bs and C horizons. The results are discussed in relation to possible effects of acid deposition over regions of Europe and N. America.  相似文献   

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