The effects of leaching surface‐applied amendments on subsoil aluminum and alfalfa growth in a Louisiana Ultisol

Abstract

A greenhouse leaching column study was conducted to compare the effects of surface‐applied langbeinite (LB), phosphogypsum (PG), Ca‐ silicate slag (SS), and calcitic lime (CL) on subsoil Al and growth of alfalfa (Medicago sativa L. ‘Florida 77') in Toula silt loam soil (Typic Fragiudult). Langbeinite was found to be more effective than PG in the reduction of subsoil exchangeable Al, apparently through SO₄ ^2‐‐induced Al precipitation. This study demonstrated that high exchangeable Al levels are not always indicative of Al toxicity in the soil solution phase. The primary factors limiting alfalfa growth in the Toula soil were found to be surface soil pH and Mn toxicity rather than subsoil Al toxicity. The liming materials, SS and CL, effectively corrected the surface soil Mn and pH problems, but had no effect on subsoil chemical properties.     

Specific sorption of antimony (III) by the hydrous oxides of Mn,Fe, and Al

The hydrous oxides of Mn, Fe, and Al avidly sorbed Sb from μM Sb(OH), solutions, with uptake levelling off as initial Sb concentration increased. Capacity values decreased along the sequence MnOOH > Al(OH)₃ > FeOOH. The amount sorbed by each substrate decreased gradually at pH values > 6. Addition of 0.4M CH₃COONa to the aqueous phase (to minimise retention of weakly bound Sb) had little effect on MnOOH uptake capacity (～160 mmol, kg^?1 at pH < 7) but retention dropped rapidly at higher pH. With the other two substrates (pH 6–7) the calculated capacity values for specific Sb sorption were ～ 45 mmol kg^?1 FeOOH and ～ 33 mmol kg^? Al(OH)₃; about a third of the total capacity values. On these substrates specific Sb sorption tended to peak in the pH 7 to 8 region. The pH response pattern was modified using Sb tartrate sorbate solutions. Factors influencing Sb sorption included substrate surface charge, chemical form of Sb and surface interactions. Formation of a sparingly soluble metal coating was indicated by the uptake plateaus observed when increasing amounts of solid were added to Sb solutions containing acetate.     

Chemical Characteristics and Acid Buffering Capacity of Surface Soils in Japanese Forests

To determine the geological distribution of acid buffering capacity and exchangeable Al of forest soils in Japan, surface soils under forest vegetation were collected nationwide from a total of 1,034 sites. Generally, surface soils in Japanese forests are mostly acidic and low in both exchangeable cation content and exchangeable Al. The median of soil pH(H₂O), total exchangeable cations, and exchangeable Al are 5.1, 76 mmol₍₊₎Kg^?1, and 19.6 mmol₍₊₎kg^?1, respectively. Acid buffering capacities of selected soils were determined using a soil column, which was comparable to the capacity that resulted from cation exchanges with protons. Soils with high buffering capacity and low exchangeable Al are widely distributed in Japan, and overlap with the areas of Andisol distribution. Volcanogenic materials seem to mask soil characteristics derived from underlying geology even though they are not Andisols. However, central to western Honshu Island, Shikoku Island, and northern Kyushu Island showed weak acid buffering capacities with high exchangeable Al potential in surface soils.     

Assessing the contribution of individual dissolved ions to depressions in acid neutralising capacity of streams in the adirondack and Catskill Mountains,New York

Methods for quantifying the influence of different ions on depressions in ANC, based on those used by Molot et al. (1989), have been employed on streams in the Adirondack and Catskill Mountains of New York. Streams were intensively monitored during the Episodic Response Project of the US EPA Baseflow values were determined for each variable, and for each low-ANC sample the proportion of ANC depression (relative to baseflow) contributed by each ion was calculated, In the Catskill streams Ca²⁺ dilution and NO₃ ^– increases were major causes of ANC depression; SO₄ ^2– dilution and Al mobilisation increased ANC. In the Adirondack streams Ca²⁺ and Na⁺ dilution, and NO₃ ^– and SO₄ ^2– increases, all contributed to ANC depressions. Inter-stream differences in results were linked to differences in stream acidity; in both regions Ca²⁺ dilution dominated ANC depressions in circumneutral streams, whereas NO₃ ^– increases were dominant in acidic streams. Organic anions contributed more to ANC depressions in acidic streams. Al buffering, was negligible in circumneutral streams, but more than halved ANC depressions in the most acidic stream. Individual base cation behaviour differed widely, suggesting that caution should be used when treating them as a uniform group.     

Simulating acidification and recovery processes in experimental catchments with the ILWAS model

The Integrated Lake Watershed Acidification Study (ILWAS) model was used to simulate soil discharge chemistry at two neighboring experimental catchments. One catchment underwent deacidification because of the artificial application of deacidified precipitation whereas the other catchment received unaltered acidic precipitation. Simulated results reproduce the observed seasonal dynamics in the concentrations of base cations, NO ₃ ^? , Al, and H₄SiO ₄ ⁰ in soil discharges for both catchments. Simulated results also indicate that the export flux of base cations was decreased by 30% at the deacidification catchment in response to the decrease in acid deposition. However, simulated SO ₄ ^2? concentrations show decreases that are about 40% more rapid than were observed. Simulated organic acid concentrations were also substantially lower than those observed at the deacidification catchment, indicating that organic matter decomposition processes were not correctly simulated. Acid-base budgets for both 5 and 50-yr simulations indicate that acid displacement by base cations through ion exchange is the principal process delaying recovery of runoff alkalinity, whereas SO ₄ ^2? desorption has a minor role. Silicate weathering is the dominant acid-consuming process at both catchments. Criteria proposed here for assessing forecast reliability include reproducing seasonal dynamics in discharge chemistry, providing numerically accurate chemical concentrations when compared to monitoring data, and correctly predicting deacidification rate and extent. The ILWAS model generally meets these criteria, indicating that the model can produce a reliable forecast of the effects of acid deposition on the acid-base chemistry of surface waters given sufficient temporal data for confident optimization of the calibrated variables in the model.     

Localization of aluminum in tissues of fish

The concentrations of Al in fish gills has been used as a measure of fish exposure to this metal in acidified waters. This experiment was designed to determine if other fish tissues also accumulate Al and thus possibly contribute to the cause of death. Rainbow trout (Salmo gairdneri) were exposed to the following fours test conditions for 48 hr or until death: (1) pH 6.8, <0.001 mg.L^?1 Al (n=6); (2) pH 5.2, <0.001 mg₁L^?1 Al (n=2);(3) pH 5.2,1.0 mg.L^?1 Al (n=5); (4) pH 6.8, 1.0 mg.L^?1 Al (n=3). The trout were held in synthetic, low Ca water prior to, and during, experimentation. Esophagus-stomach, gonad, gall bladder, gill (left and right), heart, intestine, kidney, liver, muscle (epaxial), and spleen were digested in a 4:1 mixture of HNO₃:HClO₄ and analyzed by Inductively Coupled Plasma Emission Spectrophotometry. Elevated Al concentrations were found in gill and gastrointestinal tissues. Left and right gills of fish exposed to pH 5.2, 1.0 mg.L^?1 Al were the only tissues found to be significantly different (p<0.01) between the test conditions. The mean total Al concentrations of these test 3 fish, for the left and right gill were 3.61 and 4.33 mg.g^?1 Al dw. The Al concentration in thle gastrointestinal tissues of the fish exposed to pH 6.8 at 1.0 mg.L^?1 Al was greater than that of the control fish, but not statistically significant. These results suggest that the analysis of whole gill remains an effective indicator of Al exposure in fishes at low pH.     

The Contribution of Various Components to pH Buffering Capacity of Acrisols in Southeastern Vietnam

This paper examined the contribution of various soil components to pH buffering capacity (pH_BC) of haplic Acrisols in an upland area of Southeastern Vietnam. Sampling was conducted in 2016 in Tan Bien district, Tay Ninh province at seven sites from the surface to 60-cm depth. Soils were very acidic (pH_H2O 4.53 ± 0.05). The pH_BC were very low, 0.46 ± 0.04 and 0.44 ± 0.05 cmol H⁺ kg^?1 pH^?1, respectively, for original samples and those from which soil organic carbon (SOC, 0.52 ± 0.09%) were removed. The contribution of Al³⁺ to pH_BC was remarkable while that of SOC was of little significance. The contribution of clay minerals to pH_BC was unclear due to the low (9.37 ± 0.76%) and kaolinite-dominated clay content. The current soil conditions indicated a potential for further soil acidification. Liming would be one of the measures to remediate soil acidity in the research area.     

Effects of fertilization practices on aluminum fractions and species in a wheat soil

Purpose

To better understand the effect of fertilizer practices on soil acidification and soil organic matter (SOM) stocks in a rice-wheat system, a field experiment was conducted to (i) investigate the influence of fertilizer practices on the Al forms in solid phases and the distribution of Al species in water extracts and (ii) explore the relationship between the Al forms, the quantity and composition of SOM, and soil acidity.

Materials and methods

Seven fertilizer treatments including CL (no fertilizer), NK, PK, NPK, N₂PK (PK and 125 % of N), NP₂K (NK and 125 % of P), and organic fertilizer (OF) were applied to induce various changes in pH and SOM composition (i.e., total C and N contents, C/N ratio, and SOM recalcitrant indices) in a rice-wheat system. After 6-year cultivation, different pools of Al forms (i.e., amorphous Al; organically bound Al of varying stability; exchangeable Al; water-soluble inorganic Al³⁺, Al-OH, Al-F, Al-SiO₃, and Al-SO₄; and organic Al monomers) were quantified and related with SOM composition and soil pH during the wheat phase.

Results and discussion

Fertilizer types significantly changed soil pH and SOM composition and which explained 84 % of the variance of Al forms using redundancy analysis. An interaction between soil pH and SOM quality on Al forms also existed but only accounted for a very small (6 %) portion of the variation. Compared to CL and chemical fertilizer, OF practice with relative low SOM stabilization is likely to favor the formation of amorphous Al in order to bind more SOM. The decrease in exchangeable acidity and water-extractable Al via hydroxyl-Al precipitation but not in the form of organo-aluminum complexes evidenced this phenomenon. In contrast, chemical fertilizer input increased exchangeable Al and water extract Al (especially Al³⁺), partly at the expense of organically bound Al. The destabilization of organic-aluminum complexes was a mechanism of pH buffering evidenced by the increased soluble Al-dissolved organic matter (DOM) as soil pH decreases. Further, the magnitude of this trend was much greater for elevated N input compared with P input.

Conclusions

Chemical fertilizer with relative high SOM stabilization favored the formation of exchangeable Al and soluble Al resulting in soil acidification, whereas OF with relative low SOM stabilization tended to transform exchangeable Al and soluble Al to amorphous Al, thereby alleviating soil acidification and enhancing C stocks in a rice-wheat system.

     

Effect of bone chars on phosphorus‐cadmium‐interactions as evaluated by three extraction procedures

Foreseen P shortage and contamination problems have stimulated the search for renewable and contaminant‐free P‐fertilizers and amendments that immobilize Cd. We investigated the P‐dissolution and Cd‐immobilizing effect of bone char (pyrolyzed de‐fatted bone chips; BC) and bone char with added reduced S compounds (BC^plus). Five soils varying in pH and low to high Cd‐contamination were incubated with slow‐release P‐fertilizers (BC and BC^plus) and the fast P‐release diammonium phosphate (DAP), and extracted with NH₄NO₃‐, NaHCO₃‐solutions, and H₂O. The P‐concentrations obtained by the three extractants were well correlated and NH₄NO₃ well suited to simultaneously assess the P‐ and Cd‐solubility. The addition of BC increased pH in all soils whereas BC^plus and DAP lowered the pH in soils with pH > 5. Similar trends for NH₄NO₃‐P differences between treatments and control were observed for BC and BC^plus during the incubation period, although BC^plus resulted in much larger P‐concentrations. The highest Cd‐immobilization efficiency was obtained in BC‐treated soils. The addition of BC^plus and DAP decreased the Cd‐concentrations until 34 d of incubation in all soils and remained effective in Cd‐immobilizing in soils that showed a pH raise over 145 d of incubation. Thus, the results indicate that surface modification of BC may promote the P‐dissolution along with a concomitant Cd‐immobilization largely through its pH‐effect but this must be confirmed in studies under non‐equilibrium conditions.     

Determination of unsaturated soil hydraulic properties at different applied tensions and water qualities

Irrigation with low-quality water may change soil hydraulic properties due to excessive electrical conductivity (EC_w) and sodium adsorption ratio (SAR_w). Field experiments were conducted to determine the effects of water quality (EC_w of 0.5–20 dS m^?1 and SAR_w of 0.5–40 mol^0.5 l^?0.5) on the hydraulic properties of a sandy clay loam soil (containing ～421 g gravel kg^?1 soil) at applied tensions of 0–0.2 m. The mean unsaturated hydraulic conductivity [K(ψ)], sorptive number (α) and sorptivity coefficient (S) varied with change in EC_w and SAR_w as quadratic or power equations, whereas macroscopic capillary length, λ, varied as quadratic or logarithmic equations. The maximum value of K(ψ) was obtained with a EC_w/SAR_w of 10 dS m^?1/20 mol^0.5 l^?0.5 at tensions of 0.2 and 0.15 m, and with 10 dS m^?1/10 mol^0.5 l^?0.5 at other tensions. Changes in K(ψ) due to the application of EC_w and SAR_w decreased as applied tension increased. Analysis indicated that 13.7 and 86.3% of water flow corresponded to soil pore diameters <1.5 and >1.5 μm, respectively, confirming that macropores are dominant in the studied soil. The findings indicated that use of saline waters with an EC of <10 dS m^?1 can improve soil hydraulic properties in such soils. Irrigation waters with SAR_w < 20 mol^0.5 l^?0.5 may not adversely affect hydraulic attributes at early time; although higher SAR_w may negatively affect them.     

Characterization of phytotoxic aluminum in soil solutions from phosphogypsum amended soils

Phosphogypsum (PG), an industrial by-product from phosphoric acid plants, is being used as an ameliorant for acid soil infertility. Phosphogypsum is primarily CaSO₄ and contains F among several impurities. An increase in SO₄ ^2– and F^– ligands in soil solutions following amendment with PG is important for the alleviation of Al toxicity. In soil solutions containing abundant SO₄ ^2– and F^–, a measure of Al that is not complexed with either of the ligands represents phytotoxic Al. Alleviation of Al toxicity by SO₄ ^2– in some instances is due to SO₄ ^2–-induced precipitation and/or sorption of Al. Some studies have demonstrated a decrease in Al toxicity by SO₄ ^2– even though precipitation of Al was not evident.In such cases, formation of the Al-SO₄ ⁺ ion-pair (predicted by speciation models) has been attributed as the reason for alleviation of Al toxicity. Recent evidence has indicated that the proportion of Al complexed with SO₄ ^2– was much greater than that predicted by using speciation models, which suggests that alleviation is not fully attributable to the formation of AlSO₄ ⁺ species. The existing colorimetric Al assay techniques have failed to discriminate Al complexed with SO₄ ^2– and have therefore, proved to be unsuitable for determination of phytotoxic Al in solutions containing SO₄ ^2–. Fractionation of Al complexed with SO₄ ^2– by size exclusion chromatography (SEC) has permitted a more precise characterization of Al complexed with SO₄ ^2– which has been demonstrated as less phytotoxic than the uncomplexed Al. Therefore, size exclusion chromatography is a promising technique for characterization of phytotoxic Al in solutions in the presence of SO₄ ^2–. In solutions containing F^–, alleviation of Al toxicity is due to formation of Al-F complexes which are less phytotoxic. The 8-hydroxyquinoline method with a 15 second reaction time excludes Al-F complexes and, therefore is a measure of phytotoxic Al in solutions containing F^–.     

Stream chemistry impacts of conifer harvesting in welsh catchments

Hydrochemical data have been collected for between 6 and 9 years from forest harvesting experiments in small catchments (>10 ha) at Plynlimon and Beddgelert, Wales, UK. Felling resulted in rapid increases in NO ₃ ^? and K⁺ concentrations at both sites. A maximum of 3.2 mg N L^?1 was observed at Plynlimon about one year after the start of felling. Concentrations declined to control stream values (0.5 mg N L^?1) after 5 years. At Beddgelert, NO ₃ ^? concentrations in the manipulated catchments remained above those in the unfelled control catchment for three years, before declining below control values. The NO ₃ ^? pulse was related to increased rates of mineralization and nitrification in the soil after felling. The initial increase in K⁺ concentration after felling at Plynlimon was followed by a slow decline, but concentrations were still above those in the control stream after 5 years. From 4 to 8 years after felling at Beddgelert, K⁺ concentrations fell below and then generally remained lower than control values. The NO ₃ ^? pulse after felling at Plynlimon sustained inorganic anion concentrations above those in the control stream for the first 18 months after felling. As the NO ₃ ^? pulse declined, inorganic anion concentrations decreased to below those in the control stream about 4 years after felling. At Beddgelert, the smaller increase in NO ₃ ^? concentrations had less of an effect on inorganic anion concentrations which decreased after felling relative to values in the control stream. The increase in NO ₃ ^? was associated with temporary streamwater acidification in the felled catchments due to the increased rates of nitrification and nitrate leaching. At Plynlimon, streamwater filterable Al concentrations declined after felling, but controls on Al behaviour are complex and not explained by simple equilibrium relationships with Al(OH)₃ or by variations in inorganic anion concentrations. At Beddgelert, felling had no effect on stream water filterable Al concentrations. Felling at Plynlimon led to a large reduction in streamwater Cl^?, Na⁺ and SO ₄ ^2? concentrations. At Beddgelert reductions in SO ₄ ^2? and ‘sea salt’ ion concentrations were less clear, reflecting the smaller proportions of the catchments which were harvested. Felling had no deleterious effects on water quality, apart from a temporary slight further decline in stream pH at Beddgelert. Increases in NO ₃ ^? concentrations were short-lived and concentrations were well below drinking water standards. Filterable Al concentrations were already higher than statutory standards, but were not increased or decreased through felling.     

Investigation of Lake Ontario water quality near Port Granby radioactive waste management site

The concentrations of²²⁶Ra, As, and NO ₃ ^? have been measured in Lake Ontario waters off Eldorado Nuclear Limited's Port Granby radioactive waste management site. Only one sample gave a²²⁶Ra value higher than the Ontario criterion for public surface water supplies. The highest levels of As and NO ₃ ^? were below the Ontario criteria. The leachate plume appears to move parallel to the shoreline in the direction of the prevailing wind but disperses rapidly reaching ambient levels within 150 m of the source. The leaching of these pollutants has only a minor effect on the lake water quality.     

Biogeochemistry of aluminum in a forest catchment in the Czech Republic impacted by atmospheric inputs of strong acids

The Lysina catchment in the Czech Republic was studied to investigate the biogeochemical response of Al to high loadings of acidic deposition. The catchment supports Norway spruce plantations and is underlain by granite and podzolic soil. Atmospheric deposition to the site was characterized by high H⁺ and SO₄ ^2– fluxes in throughfall. The volume-weighted average concentration of total Al (Al_t) was 28 mol L^–1 in the O horizon soil solution. About 50% of Al_t in the O horizon was in the form of potentially-toxic inorganic monomeric Al (Al_i). In the E horizon, Al_t increased to 71 mol L^–1, and Al_i comprised 80% of Al_t. The concentration of Al_t (120 mol L^–1) and the fraction of Al_i (85%) increased in the lower mineral soil due to increases in Al_i and decreases in organic monomeric Al (Al_o). Shallow ground water was less acidic and had lower Al_t concentration (29 mol L^–1). The volume-weighted average concentration of Al_t was extremely high in stream water (60 mol L^–1) with Al_i accounting for about 60% of Al_t. The major species of Al_i in stream water were fluorocomplexes (Al-F) and aquo Al³⁺. Soil solutions in the root zone were undersaturated with respect to all Al-bearing mineral phases. However, stream water exhibited Al_i concentrations close to solubility with jurbanite. Acidic waters and elevated Al concentrations reflected the limited supply of basic cations on the soil exchange complex and slow weathering, which was unable to neutralize atmospheric inputs of strong acids.     

Forms and buffering potential of aluminum in tropical and subtropical acid soils cultivated with Pinus taeda L

Purpose

Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.

Materials and methods

Organic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L^?1 pH 2.8 CuCl₂–Al complexed in organic matter; 1.0 mol L^?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO₃ concentrated?+?H₂O₂ 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L^?1 sodium pyrophosphate; 0.1 and 0.2 mol L^?1 ammonium oxalate; 0.25 and 0.5 mol L^?1 NaOH. Samples of clay were also analyzed by XRD.

Results and discussion

There was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl₂ method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl₂. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).

Conclusions

The worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.

     

Evaluation of water flux prediction with heat-pulse technique in saturated soils

Heat-pulse technique (HPT) has shown promise for predicting soil water flux (J_w). This study evaluated the accuracy of HPT in predicting J_w in packed saturated columns of quartz, sand, silt loam, and sandy clay loam. J_w was predicted using the maximum dimensionless temperature differences (MDTD), ratio of downstream to upstream temperature increases (T_d/T_u), and an improved T_d/T_u method. Results indicated that J_w predictions had a good linear relationship with measurements (R² > 0.93). The HPT underestimated J_w to varying degrees, and the underestimations increased as J_w increased and soil texture became fine. The T_d/T_u method outperformed the MDTD and the improved T_d /T_u because of its higher accuracy, fewer parameters, and simpler calculations. The MDTD exhibited the poorest performance. In coarse-textured soil materials (e.g. quartz and sand), J_w predictions by the T_d/T_u method were most accurate, and even with high J_w (up to 72.4 μm s^?1), relative errors still remained within 9.8%. However, in fine-textured soil materials, J_w was underestimated significantly by 16.9% in silt loam and by 23.3% in sandy clay loam. The lower J_w limits were 1.0, 2.3, 2.4, and 4.0 μm s^?1 for quartz, sand, silt loam, and sandy clay loam, respectively (P > 0.05).     

Chemical Composition of Precipitation in Beijing Area, Northern China

Variations of anions (SO₄ ^2-, NO₃ ^-,NO₂ ^-, Cl^- and F^-),cations (K⁺,Na⁺, Ca²⁺, Mg²⁺ and ⁺) and pH values in precipitation, througfall and stemflow samples collected overa four-year period (1995–1998) in Beijing (two sitesZhongguancun and Mangshan) are presented. The annualvolume-weighted range of pH values were 6.57–7.11 inprecipitation, 5.46–6.86 in thoughfall and 5.32–6.41 instemflow. The fominant anion was , while Ca⁺and NH₄ ⁺ were the main cations in precipitation,throughfall and stemflow. Most of ion concentrations with precipitation, throughfall and stemflow volume showed negative correlation, except for some ones. Significant correlationvalues were also found between ions (SO₄ ^2-,NO₃ ^-, Cl^-, F^-, Ca²⁺,Mg²⁺ andNa⁺) in precipitation, throughfall and stemflow indicatedthe common sources of these ions such as coal combustion,automobile emission and fertilizers application. Compared toprecipitation, there was an increased ion concentration inthroughfall or in stemflow. Changes of ion concentrations werein Quercus liatungensis Koiz. and Pinus tabulaefornisCarr. throughfall (or stemflow) because of different crown andbark qualities of tree species.     

Soil properties that affect sulphate adsorption by palexerults in western and central Spain

Abstract

The beneficial action of gypsum in suppressing aluminum (Al) toxicity in Bt horizons of Ultisols is related to the self‐liming effect of the adsorption of sulphate (SO₄ ^2‐) ion. The relationship between SO₄ ^2‐ adsorption by gypsum‐amended soils and some components and properties of 38 surface and subsurface horizons from seven Palexerults in western and central Spain was analyzed. The highest correlations of maximal SO₄ ^2‐ adsorption as determined from langmuir isotherms were with clay, free iron oxyhydroxides (Fe_dcb), and exchangeable Al contents, and pH. Liming reduces SO₄ ²’ ion adsorption; consequently, the joint application of limestone and gypsum to the surface of these soils results in increased availability of gypsum for the subsurface horizons.     

Contrasting the geochemistry of aluminum among peatlands

Aluminum concentrations were measured in surface waters, pore waters and surface peats of 15 wetlands in south-central Ontario. Wetlands were grouped floristically and chemically as mineralpoor, moderately-poor or mineral-rich fen. Mineral-poor fens were dominated bySphagnum, were low in alkalinity (0.31μeq L^?1) and pH (4.5–6.3). Moderately-poor fens had a mixture of vegetation (Sphagnum, sedges and grasses), mid-alkalinity (23–91μeq L^?1) and pH (5.8–6.4). Mineral-rich fens were dominated by sedges and grasses, had high alkalinity (104–181μeq L^?1) and circumneutral pH (6.2–6.3). Surface water Al concentrations were less in mineral-poor versus moderately-poor and mineral-rich fens (F=32.0; P<0.05). Pore water Al concentrations were lower in 4 of 5 mineral versus the mineral-rich fens (F=92.15; P<0.05). In all but two cases pore water Al (all species <0.2μm) were greater within the fen peats versus the overlying surface waters suggesting that peats could act as a source of Al to the overlying waters. In all wetlands, 70 and 30% of peat Al was recovered by a hydroxylamine hydrochloride/acetic extract (primarily inroganic) and an ammonium hydroxide extract (primarily organic), respectively. Differences in “extractable” Al recovered by the two reagents (i.e., inorganic+organic Al) among the 15 wetlands were independent of wetland type. Distribution coefficients, k _d , were different among the 3 types of wetlands (F=25.0; P<0.05) with theSphagnum dominated mineral-poor fens containing higher values versus the sedge and grass dominated mineral-rich fens. Lower surface and pore water concentrations of Al in mineralpoor versus mineral-rich fens may in part be a result of differences in the degree of minerotrophic influences between the two types of peatlands. As well, the greater binding capacity ofSphagnum peat as indicated by higher k _d 's in the mineral-poor fens, may have contributed to the observed lower pore water and surface water Al concentrations in mineral-poor versus mineral-rich fens. It has been postulated that anthropogenic acidification of peatlands will accelerate the transformation of a mineral-rich fen to that of a mineral-poor fen and ultimately to bog. Changes in Al geochemistry that may ensue as this transition occurs include decreases in pore and surface water Al concentrations with concurrent increases in peat bound Al.