Aluminium chemistry and acidification processes in a shallow podzol on the Swedish westcoast

Processes pertinent to soil acidification with special emphasis on the solution chemistry of A1, were studied in three adjacent small catchments on the Swedish westcoast, with mixed coniferous forest and shallow podzols (average soil depth 50 cm). Soil solution from different depths, groundwater and stream-water were sampled. Separation of organic and inorganic Al species was done with an ion exchange technique. The concentration of organic A1 species was linearly correlated with the concentration of dissolved organic C (r,², varied from 0.38 to 0.69 with p, < 0.001). In the A horizon 83 to 97 % of the dissolved A1 consisted of organic species. The average concentration of total A1 varied from 3.3 to 9.8 μmole 1^?1, in soil leachates collected below the A₀, horizon, and from 29.3 to 47.0 pmole 1^?1, in leachates collected below the A₂, horizon. The organic Al species decreased in importance with increasing soil depth. Leachates collected below the B horizon had average total A1 concentrations ranging from 95.3 to 115 pmole 1^?1, with a contribution of organic species varying between 8 and 20% of the total concentration. Activity calculations indicated an equilibrium with A1(OH)SO₄, (pK _S = 17.23) in the lower part of the B horizon, while groundwater together with some of the leachates from the upper B horizon showed a better fit with A1₁₄(OH)₁₀SO₄ (pK₁ = 117.51). Streamwater was obviously influenced by the soil organic matter in the outflow areas in terms of A1- organic matter complexes and protolysis of dissolved organic acids. There was a net outflow of Al and sulphate from the lower part of the B horizon compared to input in throughfall precipitation. The relative concentration increase varied from 64.4 to 78.0 (A1) and from 1.52 to 1.92 (sulphate). The relative increase due to evapotranspiration was estimated to be 1.4. The corresponding concentration factors for Mg and Ca were from 2.06 to 2.38, and from 0.81 to 1.07, respectively, indicating a very low Ca weathering. Data were compared with other studies, both recent and older ones. The possible influence from present-day levels of H⁺ and sulphurous compounds in the atmospheric deposition is evaluated.     

Aluminum compounds in calcium chloride extracts from podzolic soil and their possible sources

Aluminum concentrations in organoaluminum complexes, mineral polymers, Al(H₂O) ₆ ³⁺ , Al(OH)(H₂O) ₅ ²⁺ , Al(OH)₂(H₂O) ₄ ⁺ , AlH₃SiO ₄ ²⁺ , and Al(OH)₃(H₂O) ₃ ⁰ extracted with 0.001 M CaCl₂ from the main genetic horizons of a podzolic soil on two-layered deposits were determined experimentally and calculated from thermodynamic equations. It was found that aluminum bound in organic complexes was predominant in extracts from the AE horizon, and mineral polymer aluminum compounds prevailed in extracts from the E and IIBD horizons. In the AE horizon, organoaluminum compounds were a major source of aluminum, which passed into solution predominantly by exchange reactions. In the E horizon, aluminum hydroxide interlayers in soil chlorites were the main source of aluminum, which passed into solution by dissolution reactions. In extracts from the IIBD horizon, aluminum was solubilized by the dissolution of aluminosilicates inherited from the parent rock.     

Use of a coupled equilibrium model to describe the buffering of protons and hydroxyl ions in some acid soils

The buffering of protons and hydroxyl ions in acid soils was studied by the addition of small amounts of HCl, H₂SO₄, and NaOH in consecutive batch experiments using surface soils and subsoils from two Cambisols and one Podzol. A chemical equilibrium model was used to study the main buffer processes. The model included inorganic complexation and multiple cation exchange, and also the solubility of jurbanite and Al(OH)₃ for the subsoils. Buffering of protons was predicted quite well by the model for the surface soil of the Spodi-Dystric and Spodic Cambisols, suggesting that multiple cation exchange was the main buffer process. For the Podzol surface soil, however, the model overestimated proton buffering by cation exchange considerably. Hydroxyl buffering in acid surface soils could be described well by the model for the Podzol soil only. For the Cambisols, hydroxyl buffer reactions included not only cation exchange, but also solubilization of large amounts of organic matter and presumably deprotonation of dissolved organic carbon (DOC). Modelling proton and hydroxyl buffering in subsoils suggested that equilibrium with AJ(OH)₃ was not maintained for the Podzol and spodic Cambisol. Sulphate sorption had to be considered to describe titration experiments in all three soils. The assumption of jurbanite being in equilibrium with soil extracts was useful only for the Spodi-Dystric Cambisol.     

Soil solution aluminium activity related to theoretical A1 mineral solubilities in four Australian soils

Four soils were treated with HNO₃, CaCO₃ and K₂SO₄ to enable observation of the response of the soil solution composition and the solution A1 ion activity (Al³⁺) to the treatments and to time. The clay fraction of three of the soils was dominated by illite, kaolinite and quartz. The fourth was minated by kaolinite and iron oxides. The initial pH in 0.01 M CaCl₂ varied between 4.0 and 5.0 and the organic carbon content from 0.7 to 1.1%. The soil solutions from soils dominated by kaolinite, illite and quartz were generally supersaturated with respect to quartz and well ordered kaolinite, and unsaturated with respect to illite. The soil solutions from the soil dominated by kaolin and iron oxide were generally unsaturated with respect to quartz but still saturated with respect to ell crystallized kaolin. Within mineral groups such as Al₂SiO₅ compounds, A1₂Si₂O₅(OH)₄ (kaolinite group), and Al(OH)₃ (A1 oxide) minerals, the more soluble forms became less supersaturated or unsaturated with time for many treatments. Lime treatment usually increased the ion activity product of AI(OH)₃ in all soils, and of minerals with the composition, Al₂SiO₅, in the illite/kaolinite soils. Acid treatment reduced the apparent solubility of Al(OH)₃, and the A1 silicates in the Al₂SiO₅, and Al₂, Si₂, O₅,(OH)₄, mineral groups on all soils. These results are interpreted to indicate that lime treatment led to the formation of trace quantities of more soluble A1 minerals that subsequently controlled (Al³⁺), whereas acid treatment dissolved trace quantities of such minerals leaving less soluble minerals to control (Al³⁺). The results suggest that, in mineral soils such as these, (Al³⁺) is under the control of inorganic dissolution and precipitation processes. These processes conform to expectations given the free energy of various inorganic aluminium compounds. Furthermore the sequence of dissolution and formation processes appears to be governed by the Gay-Lussac—Ostwald step rule.     

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.

     

在实验酸性硫酸盐条件和酸性硫酸盐土壤上可溶性铝的控制

The controls of soluble Al concentration were examined in three situations of acid sulfate conditions:1) experimental acid sulfate conditions by addition of varying amounts of Al(OH)3(gibbsite) into a sequence of H2SO4 solutions;2)experimental acid sulfate conditions by addition of the same sequence of H2SO4 solutions into two non-cid sulfacte soil samples with known amounts of acid oxalate extractable Al; and 3) actual acid sulfate soil conditions.The experiment using gibbsite as an Al-bearing mineral showed that increase in the concentration of H2SO4 solution increased the soluble Al concentration,accompanied by a decrease i the solution pH, Increasing amount of gibbsite added to the H2SO4 solutions also increased soluble Al concentration,but resulted in an increase in solution pH.Within the H2SO4 concentration range of 0.0005-0.5mol L^-1 and the Al(OH)3 range of 0.01-0.5g(in 25 mL of H2SO4 solutions),the input of H2SO4 had the major control on soluble Al Concentration and pH .The availability of Al(OH)3，however,was responsible for the spread fo the various sample points,with a tendency that the samples containing more gibbsite had a higher soluble Al concentration than those containing less gibbsite at equivalent pH levels.The experimental results from treatment of soil samples with H2SO4 solutions and the analytical results of acid sulfate soils also showed the similar trend.     

Aluminosilicate phases during initial clay formation: H+-Al3+–oxalic acid–silicic acid–Na+ system

The solid phases and the precipitation boundary characterizing the system H⁺-Al³⁺-oxalic acid-silicic acid-Na⁺ are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science. pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)₄, H₄SiO₄ (phase Vi^a), Al₂, (OH)₆.H₄SiO₄ (phase VI^b) and NaAl(OH)₄.(H₄SiO₄), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)₄.H₄SiO₄ (phase VII precipitates at 0.4pH units above NaAl(OH)₄.(H₄SiO₄)₂. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced: Phases VI^a and VI^b are described as end-members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VI^b was identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH < 4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes. It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe the process.     

Inorganic and organic sulfur profiles in nine Sphagnum peat bogs in the United States and Czechoslovakia

Depth profiles of total S, organic S, soluble SO ₄ ^2? -S, FeS, and FeS₂ were characterized for Sphagnum-derived peat cores collected from 9 sites. Marcell S-2 Bog (MN), Tamarack Swamp (PA), Cranesville Swamp (MD/WV), and Big Run Bog (WV) receive water from precipitation and upland runoff; atmospheric S deposition is 13, 47, 54, and 114 mmol m^?2, yr^?1, respectively. McDonald's Branch Swamp (NJ) is predominantly groundwater fed. Tub Run Bog (WV) and Allegheny Mining Bog (MD) receive augmented SO ₄ ^2? inputs through acid coal mine drainage. Jezerní slat' and Bo?í Dar Bog in Czechoslovakia receive atmospheric S inputs of 33 and 243 mmol m^?2 yr^?1, respectively. In the peat from all sites except Allegheny Mining Bog, where the substantially augmented SO ₄ ^2? input was reflected in an unusually high dissolved SO ₄ ^2? pool in the surface peat, organic S (probably mostly carbon bonded S) was the dominant S fraction; FeS₂ was generally the dominant inorganic S fraction. Subsurface peaks in total S, organic S and FeS₂-S in peat from the runoff water fed sites were interpreted as indicative of depth-dependent patterns in S reduction/oxidation and in S immobilization/mineralization. Unless SO ₄ ^2? inputs to a site are tremendously augmented (e.g., Allegheny Mining Bog), the rapid turnover of the dissolved SO ₄ ^2? pool combined with the relative stability of the other inorganic and organic S pools, apparently functions as an effective buffer against site differences in S inputs, leading to a general similarity in vertical S profiles in the peat deposits.     

Alteration of secondary minerals along a time series in young alkaline soils derived from carbonatic wastes of soda production

Industrial activities result in increasing amounts of technical substrates being deposited in landfills. These substrates are subject to weathering and pedogenic processes. We studied the chemical and mineralogical transformations on naturally weathered waste deposits of soda industry. Four sites differing in age (15, 19, 57, and 70 years) and derived from carbonatic slurry (mainly CaO^.H₂O, CaCO₃, NaCl) were selected. The formed soils, calcareous spolic Regosols, are weakly to strongly alkaline with pH values ranging from 8 to 12. Within 15 years, the substrate's initial pH of 12 drops rapidly in the topsoil due to the reaction of dissolved Ca either with CO₂ from the atmosphere or evolved by microbial respiration and finally stabilizes at around 8.1. All soils show high electrical conductivity, up to 12.3 mS cm^− 1 at the youngest site. The electrical conductivity strongly decreases within 70 years of weathering due to leaching processes and the formation of less soluble secondary minerals. The content of organic C in the studied soils ranges from 2.4 to 70.8 g kg^− 1 and stocks increase with site age. Soil structure and soil color change distinctly. The binding of CO₂ results in large amounts of carbonate, increasing with time. Seventy years after deposition, calcite [CaCO₃] dominates the topsoil (0–30 cm depth), comprising about 80% of the soil material. The mineral composition was characterized by X-ray diffraction. Besides calcite, we found different quantities and different distributions of the less common minerals ettringite [Ca₆(Al(OH)₆)₂(SO₄)₃  26H₂O], thaumasite [Ca₆(Si(OH)₆)₂(CO₃)₂(SO₄)₂  24H₂O], hydrocalumite [Ca₂Al(OH)₇  2H₂O] and hydrotalcite [Mg₆Al₂(CO₃)(OH)₁₆  4H₂O]. Formation and alteration of these minerals are basically influenced by changes in the soil pH. With progressing weathering neither thaumasite nor ettringite are stable due to the non-favorable soil reaction (pH  8.1). In contrast, hydrocalumite and hydrotalcite exist in all investigated soils. They are stable also under weakly alkaline conditions and thus may exist in all carbonatic soils. Results indicate a surprisingly rapid soil development driven by the highly dynamic formation and alteration of minerals in carbonatic substrates under alkaline conditions.     

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.     

Controlling Acid Drainage in a Pyritic Mine Waste Rock. Part II: Geochemistry of Drainage

Mine waste rock can produce acid rock drainage (ARD) when constituent sulphide minerals (for example, pyrite) oxidize upon exposure to the atmosphere. Outdoor experiments were performed to test techniques for preventing and controlling ARD in a pyritic mine waste rock. The experiments involved lysimeter (plastic drum) experiments in which the crushed (25–50 mm particle sizes), amended and unamended waste rock was exposed to natural weather conditions (rain, drying, freezing and thawing) for 125 weeks. The amendments consisted of separately covering the waste rock with compacted soil, wood bark and water and mixing with limestone and phosphate rock at 1 and 3%. Waters draining the various rocks were collected and analyzed for acidity, pH, sulphate and metals. In general, concentrations of SO₄ ^2-, Fe, As, Cu, Al and Mg in the drainage from the control rock increased gradually in the first year, peaked in the second year and increased further in the third year, reflecting increasing acid generation with time. SO₄ ^2- displayed strong positive correlation (0.91 to 0.98) with Al, As, Cu, Fe and Mg.Concentrations of Zn, Mn and Cd reached their maximumin the second year. Geochemical analysis of thecomplete water quality data using the equilibriumspeciation model WATEQ4F suggested waste rockoxidation was most likely controlled by Fe³⁺. Al, SO₄ ^2- and Fe concentrations in thecontrol rock appeared to be controlled by alunite(KAl₃(SO₄)₂(OH)₆), jarosite(KFe₃(SO₄)₂(OH)₆) and amorphousferric hydroxide [(am)Fe(OH)₃] during the firstyear. Ion activity product data (log IAP) forFe³⁺ and OH^- generally ranged between –37and –34 in the first two years but decreased to –39and –40 in the third year, suggesting that amorphousferric hydroxides were beginning to crystallize intomore stable forms such as ferrihydrite (Fe[OH]₃)and goethite (FeOOH) in the third year. The addedlimestone lost its effectiveness after a while,probably because of precipitation of secondaryminerals on the limestone particles. The phosphaterock could not sustain the drainage pH above 6 andlost its effectiveness before the limestone did. Underthe conditions of the experiments, the soil cover didnot work as expected, probably because of sidewallpassage of oxygen and water. The water cover was themost effective control method, reducing the acidproduction rate data from 41 to only 0.08 mgCaCO₃ week^-1 kg^-1 waste rock. The wood bark was theworst performer and accelerated acid production by 170%.     

Dynamics of aqueous aluminum species in a podzol affected by experimental MgSO4 and (NH4)2SO4 treatments

Chemistry of aqueous Al in a podzol on a Norway spruce (Picea abies [L.] Karst.) site in the Black Forest (SW Germany) and changes induced by experimental applications of MgSO₄ were studied. Soil solution taken from the O, E and BC horizons were analyzed for the fractions ‘labile monomeric Al’, ‘non-labile monomeric Al’, and ‘acid-reactive Al’. The activities of ‘inorganic monomeric Al’ species and the saturation indices (SI) of the soil solution with respect to Al-bearing minerals were calculated using the equilibrium speciation model WATEQF. On the untreated plot, soil leachates are characterized by Al_tot concentrations of 0.1 mg L^?1 (mineral soil). In the O horizon, the fractions ‘acidsoluble Al’ and ‘non-labile monomeric Al’ (mainly organically complexed Al) together comprise 80% of Al_tot. In the leachates from the mineral soil Al³⁺ prevails, being 50% of Al_tot. Al-F-complexes make up 5 to 10% in all horizons. MgSO₄ and (NH₄)₂SO₄ treatments resulted in an intense Al mobilization up to 50 mg L^?1. In this situation, 60% of Al_tot is covered by Al³⁺ and 40% by non-phytotoxic Al-SO₄-complexes. After rainfall events, mobilized Al is quickly translocated into the subsoil, with water flow through macropores then appearing to be an important mechanism. In both treatments, soil solution chemistry was favorable for the precipitation of the Al(OH)SO₄-type minerals alunite and jurbanite. However, a control of Al solubility by this process is not likely due to kinetic restraints. Application of MgSO₄ was followed by an increase of the Mg/Al molar ratio in the soil solution, whereas the Ca/Al ratio decreased. After treatment with (NH₄)₂SO₄ both the Ca/Al and the Mg/Al ratios deteriorated.     

Metal ion interaction with the hydrous oxides of aluminium

Suspensions of Al(OH)3 gel, gibbsite or alumina were loaded with varying amounts of Cu, Cd, Zn, or Pb ions by varying the system pH. A complex relationship between metal uptake and equilibrium pH was noted (due to substrate buffering) but total loss of metal ion from solution was observed at pH > 6.5. The pre-loaded particles were back-extracted with fifteen different chemical solutions and the percentage of sorbed ion retrieved generally varied along the sequence NaCl, CaCl₂ < MgCl₂, NH₄NO₃ < CH₃OOONH₄, Na citrate, Na₄P₂O₇, EDTA, DTPA ≈ CH₃OOOH, H₂C₂O₄, HCI, HN0₃. The recovery value varied with initial surface loading and an observed minimum around 1 gruel M²⁺ per 20 mg solid is considered to reflect changes in metal species nature (e.g., bonded M²⁺, MOH⁺, precipitated M(OH)₂) and substrate surface charge. In the ‘minima’ region less than 10% of metal ion was displaced by many reagents. With different loadings up to 40% was displaceable by salts (i.e., weakly sorbed) while acids or complex formers at times released over 90 % of the pre-sorbed metal species. It was concluded that the degree of metal ion interaction varied with the initial system pH, with retention being due to a combination of weak adsorption, occlusion in gels, chemi-sorption and precipitation of M(OH)₂.     

Biosynthesis of schwertmannite by <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> and its application in arsenic immobilization in the contaminated soil

Purpose

Soil contamination with arsenic (As) is an increasingly worldwide concern. Immobilization is a potentially reliable, cost-effective technique for the reclamation of As-contaminated soils. The aim of this study is to develop new soil amendments with high As immobilization efficiency, cost-effective, environmental-friendly, and without soil acidification for As-contaminated soil remediation.

Materials and methods

Biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans has been conducted, and two types of biogenetic schwertmannites SCH and A-SCH were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), etc. The A-SCH was formed through pretreating SCH by acidic and alkaline activation. The potential of SCH and A-SCH in As immobilization in contaminated soil was evaluated. The effect of ferrous sulfate and A-SCH on soil pH and immobilization of NaHCO₃-extractable As were also investigated for comparison.

Results and discussion

The chemical formula of SCH and A-SCH can be expressed as Fe₈O₈(OH)_4.89(SO₄)_1.55 and Fe₈O₈(OH)_5.19(SO₄)_1.41, respectively. Compared to SCH, A-SCH exhibits much higher specific surface area of 74.99 m² g^?1 and contains more hydroxyl groups and inner-sphere sulfate complexes. Immobilization efficiency of water-soluble As above 99.5 % can be achieved with A-SCH dosage of 5 % and SCH dosage of 10 %, respectively. The immobilization percentages of NaHCO₃-extractable As increased from 31.5 to 90.4 % and from 40.2 to 93.8 % with increasing dosage from 0.5 to 10 wt % for SCH and A-SCH, respectively. In general, both SCH and A-SCH immobilize As in contaminated soil effectively, and the immobilization performance of A-SCH was better than that of SCH, especially at lower dosage.

Conclusions

Biogenetic schwertmannite could be used as a potential effective soil amendment for As immobilization in contaminated soil. Our findings in this study also have important implications for in situ immobilization of As in contaminated soils, especially the soils related to acidic iron and sulfate-rich environments.

     

Fracht an chemischen Elementen in den Niederschlägen im Solling

Loading of chemical elements in precipitation at the Solling For the period 1969–1976 (NH₄, NO₃: 1971–1976) monthly values of concentrations and flows of the ions NH₄, H, Na, K, Ca, Mg, Fe, Mn, Al, Cl, NO₃, SO₄, P and organic bound N in precipitation are passed on. From the correlations between elements the following main ion sources are concluded: sea water (Na, Cl), combustion processes (SO₄, NO₃, NH₄), lime dust after dissolution by H₂SO₄ and HNO₃ (Ca, Mg), soil dust after dissolution by H₂SO₄ and HNO₃ (Al, Fe), leaching from plants (K, NO₃, SO₄, Mg, Ca), biogenic contaminations (P, organic N, K, NH₄, NO₃). Seasonal variations in the concentrations are most evident for Na and Cl, less for NH₄, SO₄ and NO₃. During the measuring period the flux of NH₄ is significantly increased; for H and SO₄, less for NH₄, Mg, Ca and Fe, the increasing trend was interrupted in winter 1973/74 (oil crisis). Consequences for sampling are discussed.     

Synthesis of 15N-labelled microbial biomass in soil in situ and extraction of biomass N

Summary A Pakistani soil (Hafizabad silt loam) was incubated at 30°C with varying levels of ¹⁵N-labelled ammonium sulphate and glucose (C/N ratio of 30 at each addition rate) in order to generate different insitu levels of ¹⁵N-labelled microbial biomass. At a stage when all of the applied ¹⁵N was in organic forms, as biomass and products, the soil samples were analysed for biomass N by the chloroform (CHCl₃) fumigation-extraction method, which involves exposure of the soil to CHCl₃ vapour for 24 h followed by extraction with 500 mM K₂SO₄. A correction is made for inorganic and organic N in 500 mM K₂SO₄ extracts of the unfumigated soil. Results obtained using this approach were compared with the amounts of immobilized ¹⁵N extracted by 500 mM K₂SO₄ containing different amounts of CHCl₃. The extraction time varied from 0.5 to 4 h.The amount of N extracted ranged from 27 to 270 g g^–1, the minimum occurring at the lowest (67 g g^–1) and the maximum at the highest (333 g g^–1) N-addition rate. Extractability of biomass ¹⁵N ranged from 25% at the lowest N-addition rate to 65%a for the highest rate and increased consistently with an increase in the amount of ¹⁵N and glucose added. The amounts of both soil N and immobilized ¹⁵N extracted with 500 mM K₂SO₄ containing CHCl₃ increased with an increase in extraction time and in concentration of CHCl₃. The chloroform fumigation-extraction method gives low estimates for biomass N because some of the organic N in K₂SO₄ extracts of unfumigated soil is derived from biomass.     

Agronomic Implications of the Application of Lime plus Gypsum By‐products to a Hyperdistric Acrisol from Western Spain

Abstract: A laboratory experiment involving the use of leaching columns reproducing the topmost portion of a Hyperdystric Acrisol (FAO 1998 FAO. 1998. World reference base for soil resources, Rome: FAO, ISRIC, and ISSS. (World Soil Resources Report No. 84) [Google Scholar]) or plinthic Palexerult (Soil Survey Staff 2003 Soil Survey Staff. 2003. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys, Washington, D.C.: U.S. Government Printing Office. (Agriculture Handbook No. 436) [Google Scholar]) treated in its Ap horizon with sugar foam wastes and phosphogypsum was conducted. The amendments increased the contents in exchangeable calcium (Ca) of the Ap horizon and, to a lesser extent, also that of the AB horizon. However, the contents in exchangeable magnesium (Mg) and sodium (Na) decreased as much in Ap as they did in AB; by contrast, the potassium (K) content exhibited a less marked decrease. The potassium chloride (KCl)–extractable aluminium (Al) of the Ap horizon was dramatically decreased much more than that of the AB horizon by the amendments. In the soil solution from Ap, the amendments raised the pH and decreased the Al concentration; in that from AB, however, they caused an initial pH decrease, a tendency that reversed as the gypsum was leached and eventually led to the pH exceeding that in the soil solution from control. The first few water extractions exhibited increased Mg concentration. This trend was reversed in the second leaching cycle, where the concentrations of Mg in the amended columns were lower than those in the controls. In the soil solution, the variation of the Ca and sulphate (SO₄ ^2–) concentrations was influenced by the salt‐sorption effect. The total Al content in soil solution from AB increased during the first leaching cycle and then decreased during the second. The amendments decreased the activities of Al³⁺, AlOH⁺², and Al(OH)₂ ⁺ in the Ap horizon and increased those of Al³⁺, AlSO₄ ⁺, Al(SO₄)₂ ^?, and AlF⁺² in the first leaching cycle in the AB horizon. The productivity of the Ap horizon after the treatments was assessed using a wheat crop (T. aestivum, var. ‘Jabato’) in a greenhouse.     

Effect of Fe,Mn or Al Compounds on Humification of Three Types of Plant Residues during Thermal Incubation

The effect of three inorganic minerals on the humification of three types of plant residues was determined by employing a model thermal incubation experiment. The plant residues consisiting of rice (Oryza sativa) straw, broadleaf tree (a mixture of oak/beech, Quercus serrata, Q. dentata, Q. acutissima etc.) sawdust and Japanese cedar (Cryptomeria japonica) sawdust were each mixed with Fe, Mn and Al in the form of hydroxides, oxides and sulfates. Humic materials were extracted after incubation and their composition was analyzed using a mixed solution of 0.02 M Na₄P₂O₇ and 0.1 M NaOH. The pH values of the samples after a longer duration of the incubation period were all less than 5.0, with the lowest value of 2.16 for a sample incubated with Al₂(SO₄)₃, except for the values of the samples incubated with MnO₂, which ranged from 4.75 to 6.0. The ΔlogK values decreased with the increase of the duration of the incubation period, whereas the RF values increased, as well as the amount of humus extracted (HE) and percentage of humic acid (PQ). Whereas most of the samples were identified as Type B and Type Rp humic acids, Type A humic acid was formed in all the plant residues incubated with Al₂(SO₄)₃, FeO(OH) and MnO₂ after ?180 d of incubation period. Moreover, the degree of humification of the plant residues was observed in the order of broadleaf tree > rice straw > Japanese cedar. It can be concluded that the inorganic compounds Al₂(SO₄)₃, FeO(OH) and MnO₂ contributed to the acceleration of the humification process of plant residues during the thermal incubation. The effect of Al₂(SO₄)₃ may be associated with the increase in the reactivity with other components in the system due to its high solubility, whereas FeO(OH) and MnO₂ may be involved in a reduction-oxidation reaction during the incubation. The browning and/or blackening of the plant residues were similar to the production of melanoidin which led us to consider that the mechanism involved in the study was similar to that of the Maillard reaction.     

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.     

Amorphous Aluminum Hydroxide Control on Sulfate and Phosphate in Sediment-Solution Systems

We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)₃ for SO₄ and PO₄. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO₄ prior to acidification experiment; this sorbed PO₄ was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)₃ appears to be an important control on dissolved PO₄ concentration in surface waters, unless there is a large excess of PO₄. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO₄. Maximum SO₄ adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO₄ ⁺ inhibited the increasing SO₄ adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)₃ substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)₃, or in Al(OH)₃-rich sediment, PO₄ mobility will be severely restricted. Suspended Al(OH)₃ in acidified surface waters cannot strongly influence SO₄ concentrations because of the considerably higher total SO₄ concentrations compared to the available surface area.