Acids In Soil Solution Research Articles

Determination of aluminium complexes of low molecular organic acids in soil solution from forest soils using ultrafiltration

Ultrafiltration (<1000D) was evaluated as an analytical method for determination of Al bound to low molecular weight organic acids (LMWOA) in soil solutions from podzolised forest soils. The results were compared to those obtained by two chemical equilibrium models and a size exclusion chromatography method. The percentage of Al bound to LMWOAs was highest in the O horizon solutions (15–44%) and decreased in the deeper horizons. Citric acid was found to be the most important complex former. Generally the ultrafiltration method and modelling showed acceptable agreement. The method showed acceptable precision and good recovery of Al in the samples.

Kinetics of soil microbial uptake of free amino acids

Amino acids and proteins typically form the biggest input of organic-N into most soils and provide a readily available source of C and N for soil microorganisms. Amino acids can also be taken up directly by plant roots, providing an alternative source of available soil N. However, the degree to which plants can compete against the soil microbial population for amino acids in soil solution remains poorly understood. The aim of this study was to measure the rate of microbial uptake of three contrastingly charged 14C-labelled amino acids (glutamate1–, glycine0, lysine0.9+) over a wide concentration range (0.1–5 mM) and in two contrastingly managed soils varying in their degree of erosion, organic-C content and microbial biomass. Amino acid uptake was concentration dependent and conformed to a single Michaelis-Menten equation. The mean maximum amino acid uptake rate (Vmax) for the non-eroded (control) soil (high organic-C, high biomass) was 0.13±0.02 mmol kg–1 h–1, while half maximal uptake occurred at a concentration (Km) of 2.63±0.07 mM. Typically, Vmax was fourfold lower and Km twofold lower in the eroded soil (low available organic-C, low biomass) compared to the non-eroded (control) soil. Amino acid substrate concentration had little effect on the proportion of amino acid utilized in catabolic versus anabolic metabolism and was similar for both. While the results obtained here represent the summation of kinetics for a mixed soil population, they indicate that amino acid uptake is saturated at concentrations within the millimolar range. Because the affinity constants also were similar to those described for plant roots, we hypothesized that competition for amino acids between plants and microbes will be strong in soil but highly dependent upon the spatial distribution of roots and microbes in soil.

Consideration on the occurrence of the Al 13 polycation in natural soil solutions and surface waters

Equilibrium speciation calculations were performed (1) for soil solutions and streamwaters collected in central and eastern France and (2) for simulated waters at 0 and 25°C, to assess the highest concentration of Al 13 that could be reached in waters in the absence of complexing ligands other than OH −. A comprehensive and updated set of aqueous Al species, including polymeric hydroxyaluminosilicates (HAS), and their corresponding thermodynamic formation constants, were used. Results suggest that the concentration of the Al 13 polycation in natural waters has been largely overestimated in some past studies using equilibrium models to calculate Al speciation, owing to oversimplification (many Al ligands not considered) and the unrecognised temperature dependence of some formation constants. The Al 13 concentration in mildly acidic natural waters may not exceed a few μmol l −1 at Al T on the order of 10 −4 mol l −1 and should be less than 1 μmol l −1 at Al T=10 −5 mol l −1. Monomeric Al–Si species may not significantly interfere with the formation of Al 13, but the formation of both HAS polymers (proto-imogolite precursors) and organo-Al complexes have a marked detrimental effect on the Al 13 concentration. The maximum concentration of Al 13 decreased upon increasing temperature from 0 to 25°C. In contrast, the pH range wherein Al 13 may occur increases slightly with temperature and the most acidic pH value above which Al 13 may be formed has been underestimated. At T=25°C, the Al 13 polycation may be a significant Al species (4 to 5% of Al T) at pH < 4.5 if Al T > 10 −4 mol l −1. The results of this study and the use of HAS polymers to calculate Al speciation in moderately natural acidic soil solutions were in better accordance with soil mineralogy. This research suggests strongly that Al 13 should be negligible in natural soil and surface waters and may not control either Al 3+ activity or Al-trihydroxide formation through polymerisation/depolymerisation steps. Also, from a biological point of view, the toxicity of Al 13 to plants and aquatic organisms in natural conditions may be considered to be very low.

Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE—Bavaria, Germany

The decrease in anthropogenic deposition, namely SO42- and SO2, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate if the long term data of element concentrations at the Fichtelgebirge (NE-Bavaria, Germany) monitoring site indicates a relationship between the nutrient content of needles and the state of soil solution acidity. The soil at the site is very acidic and has relatively small pools of exchangeable Ca and Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H+ and SO42- concentrations. Soil solution concentrations of SO42-, Ca and Mg generally decreased while the pH value remained stable. Aluminum concentrations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was observed. Ca and Mg contents in the spruce needles decreased, emphasizing the relevance of soil solution changes for tree nutrition. The reasons for the delay in ecosystem recovery are due to a combination of the following two factors: (1) the continued high concentrations of NO3— and SO42— in the soil solution leading to high Al concentrations and low pH values and, (2) the decreased rates of Ca and Mg deposition cause a correlated decrease in the concentration of Ca and Mg in the soil solution, since little Ca and Mg is present in the soil's exchangeable cation pools. It is our conclusion that detrimental soil conditions with respect to Mg and Ca nutrition as well as to Al stress are not easily reversed by the decreasing deposition of H+ and SO42—. Thus, forest management is still confronted with the necessity of frequent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.

The role of low molecular weight organic acids from decomposing rye in inhibiting root-knot nematode populations in soil

Organic soil amendments have been employed as an alternative to or in combination with, chemical nematicides and cultural practices to control plant-parasitic nematodes. Rye ( Secale cereale L.) has been shown to be effective in minimizing the damage caused by root-knot nematodes ( Meloidogyne incognita (Kofoid and White) Chitwood) when grown as a cover crop and then incorporated into the soil prior to planting. It has been suggested that the release of low molecular weight organic acids during the decomposition of rye is the cause of the nematicidal effects. This study was conducted to quantify the concentration and persistence of formic, acetic, propionic, butyric, and valeric acids in soil solution following the incorporation of fresh rye foliage. Formic and acetic acids were detected by means of ion exclusion chromatography, primarily in the first 24 h following addition of rye, and at concentrations <450 μmol/l. The effect of the rye treatment on the root-knot nematode population was determined by growing tomato plants ( Lycopersicon esculentum Mill.) in the rye-amended soil and assessing the nematode damage to the root systems. Despite the low concentrations of organic acids detected, the rye treatment resulted in a significant suppression of root-knot nematode activity. To determine the fate of these acids in soil, an addition of each acid was made to a field soil resulting in a soil water concentration of 1500 μmol/l for each acid. Soil solution samples were collected every 2 h for 10 h and analyzed for the five added organic acids by means of ion exclusion chromatography. The concentration of all acids declined by 54–97% over the 10 h incubation. Although low molecular weight organic acids may be one of many factors that contribute to restriction in root-knot nematode damage, these acids do not appear to be solely responsible for the nematicidal effect of the rye.

The acid–base properties of high and low molecular weight organic acids in soil solutions of podzolic soils

The acid properties of the organic acids and identified low molecular weight (LMW) organic acids in soil solutions of podzolic soils were determined using proton affinity spectra, based on EMF titration data, and Gran titrations. The proton affinity spectra showed apparent p K a values of 2.6, 4.1, 5.4 and 6.7 for the dissolved organic material. The LMW organic acids had similar p K a values. The average specific buffer capacity as determined by Gran titrations was 8.8±0.5 μmol H +/mg DOC. The specific buffer capacity for the identified low molecular acids was 40±2 μmol H +/mg DOC.

Equilibrium models of aluminium and iron complexation with different organic acids in soil solution

The percentage of Al and Fe bound to identified low molecular weight (LMW) organic acids and phosphate in soil solution was calculated using a chemical equilibrium model. The highest fractions were obtained for the O1 horizon solutions with median values between 38–49% for Al and 18–29% for Fe. Generally the percentage declined in the deeper horizons Acceptable agreement with experimental values using ultrafiltration (<1000 D) was found especially for the spring and summer samplings. In the autumn samples, larger deviations between the modelled and ultrafiltered fractions were found. The major part of the remaining Al and Fe in solution was calculated to be bound to undefined organic acids most likely of higher molecular weight. Speciation studies of some individual organic acids are presented. Citric acid proved to be the most important complex former of the LMW acids in the O and E horizons while oxalic acid was dominant in the B horizon solutions. The total level of organic complexation of Al, Fe, Ca and Mg was also studied. It was found that >85% of the Al and >95% of the Fe were organically bound. The opposite was seen for Ca and Mg for which >85% was modelled to occur as inorganic ions. The modelling results support the theory that LMW organic acids contribute to the translocation of Al and Fe in the podzolization process.

Aluminium chemistry in two contrasted acid forest soils and headwater streams impacted by acid deposition, Vosges mountains, N.E. France.

Al chemistry was studied in two acidic watersheds, one with a podzol, the other with an acid brown soil, in the Vosges mountains (N.E. France), by analysing both leaching and centrifugation soil solutions and spring waters over 3 yr. In the podzol, Al was mobilized in the eluvial horizons under the predominant influence of organic acidity, then leached down the profile as organic and F-bound Al. Strong undersaturation with respect to proto-imogolite and imogolite showed that the proto-imogolite theory of podzolization could not apply. Al was transferred from the soil to spring water mostly as Al3+ and Al-F. Al3+, as well as additional minor species (AlOH2+, AlSO4 +), originated from the redissolution of the top of the spodic horizons under the influence of both soil solution acidity and the occurrence of mobile anions derived from atmospheric deposition. Conversely, in the acid brown soil, Al mobilization was regulated by nitrate and occurred mainly as Al3+. Most of Al was retained in the deep soil and only traces of monomeric Al reached spring water. In the podzol eluvial horizons, soil solutions were undersaturated with respect to all relevant mineral phases and their chemical composition agree with the concept of a mobilization of Al from the solid soil organic Al and a control of Al3+ activity by complexation reaction with the solid and soluble soil organic matter and F. In the acid brown soil, soil solutions were found to be in equilibrium with natural alunite, and the formation of this mineral, if confirmed, would account for the occurrence of 'open' vermiculites instead of the expected hydroxy-Al interlayered vermiculites. Al solubility control in surface water of both watersheds remains unclear. The Al-F species in both watersheds and the likely control of Al solubility by alunite in the acid brown soil emphasize the influence of acid deposition on Al chemistry in acid watersheds.

Acid mist and soil Ca and Al alter the mineral nutrition and physiology of red spruce.

We examined the effects and potential interactions of acid mist and soil solution Ca and Al treatments on foliar cation concentrations, membrane-associated Ca (mCa), ion leaching, growth, carbon exchange, and cold tolerance of red spruce (Picea rubens Sarg.) saplings. Soil solution Ca additions increased foliar Ca and Zn concentrations, and increased rates of respiration early in the growing season (July). Soil Al treatment had a broad impact, reducing foliar concentrations of Ca, Mg, Mn, P and Zn, and resulting in smaller stem diameters, sapling heights and shoot lengths compared with soil treatments with no added Al. Aluminum treatment also reduced respiration when shoots were elongating in July and decreased net photosynthesis at the end of the growing season (September). Three lines of evidence suggest that Al-induced alterations in growth and physiology were independent of foliar Ca status: (1) Ca concentrations in foliage of Al-treated saplings were within the range of sufficiency established for red spruce; (2) mCa concentrations were unaffected by Al treatment; and (3) no Al x Ca interactions were detected. Acid mist treatment increased foliar Fe and K concentrations and increased leaching of Ca, Mg, Mn, Zn, Fe, and Al from foliage. Leaching losses of Ca were more than twice those of the element with the next highest amount of leaching (Zn), and probably led to the reductions in mCa concentration and membrane stability of acid-treated saplings. Acidic mist resulted in enhanced shoot growth, and consistent reductions in foliar cold tolerance in the fall and winter. Of the few significant interactions among treatments, most involved the influence of mist pH and Al treatment on foliar nutrition. In general, reductions in cation concentration associated with Al addition were greater for pH 5.0-treated saplings than for pH 3.0-treated saplings. We propose that H(+)-induced leaching of mCa from mesophyll cells is the mechanism underlying acid-induced reductions in foliar cold tolerance of red spruce.

Influence of the ionic strength of nutrient solutions and tropical acid soil solutions on aluminum activity

Aluminum (Al) activity was determined in nutrient solutions and in acid soil solutions. Aluminum concentrations in the solutions ranged from 7.4 μM to 370.3 μM giving values of ionic strength of nutrient solutions higher than the values of acid soil solutions. The increase of ionic strength values was due to the increase of Al concentrations. The values of Al activities of 20 uM in the acid soil solutions were noticed when Al concentrations were lower than 70 μM. On the other hand, these values of Al activities in nutrient solutions were noticed only when the Al concentrations were higher than 70 μM. This study demonstrates why it is important to use higher Al concentrations in nutrient solutions to obtain Al toxic effects.

Spatial variability of soil solution chemistry under Hinoki cypress (Chamaecyparis obtusa) in Tama Hills

A monitoring study on precipitation and soil solution was conducted to analyze soil acidification processes at the Rolling Land Laboratory (RLL), Hachioji, Tokyo based on the spatial variability of the soil solution chemistry around the Hinoki cypress (Chamaecyparis obtusa) trunk. Soil solution samples were taken at various distances from the tree trunks and at various depths. Soil solution pH at the depth of 10 cm decreased to 4.1–4.2 on the downslope side of large tree trunks, presumably due to the heterogeneity of throughfall input and extensive infiltration of acidic stemflow. Ammonium ions brought by throughfall and stemflow were nitrified and provided large amounts of H+. Protons were replaced with exchangeable cations. When base cations were depleted, aluminum ion became the dominant cation species. On the average, Ca2+ concentration in the soil solutions at the depth of 10 cm decreased from 0.28 mmolc L-1 at the reference site to 0.18 mmolc L-1 on the downslope side and Mg2+ concentration decreased from 0.30 mmolc L-1 to 0.15 mmolc L-1. Arithmetic mean aluminum concentration at the depth of 10 cm on the downslope side was 0.35 mmolc L-1. Here aluminum dissolution was the main acid sink. Based on the spatial variability of the soil solution chemistry, soil solution acidification processes were divided into four stages.

The effect of liming and correction fertilisation on heavy metal and macronutrient concentrations in soil solution in heavy-metal polluted scots pine stands

Two experiments were established in 1992 in Scots pine stands ( Pinus sylvestris L.) on relatively infertile sites at distances of 0.5 and 8 km to the SE of the Cu–Ni smelter at Harjavalta, SW Finland, in order to investigate the effects of liming, correction fertiliser and site-specific fertiliser treatments on heavy metal and nutrient concentrations in the soil solution. Liming decreased soil solution acidity at 8 km, but increased it at 0.5 km. At 8 km liming brought about a long-term increase in the Ca and Mg concentrations, and correction fertilisation a corresponding long-term increase in the K concentrations. The situation at 0.5 km was the opposite; despite the increase immediately after application, there was a long-term reduction in the Ca concentrations as a result of the liming, and correction and stand-specific fertilisation. At 0.5 km all the treatments containing varying doses of limestone clearly decreased the Cu, Ni and Zn concentrations in soil solution during 1993–1995 compared to the control.

Determination of low molecular weight organic acids in soil solution by HPLC

An HPLC method employing an ion exclusion column was developed for the determination of low molecular weight organic acids in soil solution. The method includes extensive sample pretreatment using ultrafiltration and cation exchange. The method showed linear calibration graphs ( r>0.99) and the limits of detection in the range 0.1–26 μM. The recovery of eleven added acids ranged from 89 to 102%. Soil solutions of five horizons of a podzolised soil were analysed. The results showed that these compounds made up 1–3% of the dissolved organic carbon and 0–14% of the acidity. Identification of the major acids was also carried out by capillary zone electrophoresis.

Low-molecular-weight aliphatic carboxylic acids in soil solutions under different vegetations determined by capillary zone electrophoresis

Concentrations of low-molecular-weight aliphatic carboxylic acids in soil solution were determined by a newly developed capillary zone electrophoresis method. Soil solution samples were collected by centrifugation of soil from the A horizon of a Danish, homogeneous, nutrient-rich Hapludalf in adjacent forested and arable plots. The forested plots of 0.5 ha were 33-year old stands of beech (Fagus sylvatica L.), oak (Quercus robur L.), grand fir (Abies grandis Lindl.), and Norway spruce (Picea abies (L.) Karst.), while sugar beet (Beta vulgaris L.) and winter wheat (Triticum aestivum L.) were the agricultural crops this year. High variability in soil solution concentrations of metal cations (Al, Ca, K, Mg, Na), monocarboxylic acids (formic, acetic, lactic, and valeric acids), and di- and tricarboxylic acids (oxalic, malic, succinic, and citric acids) were found within each plot. Despite this short-range within-plot variability, higher concentrations of di- and tricarboxylic acids were found in the forested soils than in the arable soils. The vegetation seemed to favour some monocarboxylic acids, but the total monocarboxylic acid concentrations showed little relation to the vegetation. Probably due to much less soil water in the Norway spruce plot, the low-molecular-weight aliphatic carboxylic acid concentrations in the samples from that plot were much higher than those found in samples from the other plots. Carbon in low-molecular-weight aliphatic carboxylic acids only accounts for a few percent of dissolved organic carbon, and no general relation was found between carbon in low-molecular-weight aliphatic carboxylic acids and dissolved organic carbon, although the correlation between carbon in di- and tricarboxylic acids and dissolved organic carbon was significant.

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

AbstractThe 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 S042− salts and H2SO4 induced higher pH and lower Al concentrations than the corresponding Cl− treatments due to the SO42− 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.

Nitrogen response of herbs and graminoids in experiments with simulated acid soil solution

Sand-solution experiments involving 15 herbs and 13 graminoids were performed to study how biomass was effected by N concentrations of 50, 250 and 1250 μM, respectively, in a simulated acid forest soil solution. The concentrations of the various components corresponded with those found in soil solutions in deciduous forests of southern Sweden. The experiments were undertaken to study the extent to which species are affected differently by increases in the concentration of N as compared with that of the other nutrients. The underlying hypothesis was that species with a high demand for N and a lesser demand for other nutrients are particularly competitive in areas with acidic soil and a high degree of N deposition. The graminoids were found to be favoured more than the herbs by the addition of N, 46% displaying a significantly greater biomass at 250 than at 50 μM N as compared with only 7% for the herbs. Some species attained their highest biomass at 1250 μM N and others at 50 μM N. It is concluded that at the highest N concentration, growth was limited for most species by the supply of other nutrients and that at the intermediate N concentration the graminoids were more efficient than the herbs in utilising N. It was found that the Ellenberg N indicator values could not be used to predict biomass production under the conditions studied since they failed to adequately explain the response to treatment by N.

Neutralization of atmospheric acid inputs in small spring catchments in the Frankenwald mountains, Germany

Investigations on soil and freshwater acidification are usually focused on well-aerated systems. This study deals with the role of reductive processes for the neutralization of acid soil solution within helocrene springs. Two toposequences consisting each of three profiles (forest soil, margin of fen, fen) were established to study the chemistry of the solid phase (soil pH, CEC, pedogenic Fe- and Al-oxides) and the soil solution in two small spring catchments on three dates during 1991 and 1992. Despite high acid inputs and acidified forest soils the pH of the spring outflow is near neutral, and the soil solid phases of the spring fens are not acidified. The results support the following hypothesis: Aluminum with its corresponding anion sulfate is leached with the soil solution into the water-saturated fens. Dissimilatory iron and sulfate reduction take place within the fen and generate alkalinity. Reduced iron either reacts with sulfide to form pyrite or migrates within the fen profile and precipitates in the uppermost, oxic horizons, consuming part of the generated alkalinity. Due to the higher pH values in the fens the incoming aluminum precipitates releasing acidity. The alkalinity generated exceeds the amount of acidity released by oxidation and precipitation of iron and the precipitation of aluminum. A balance of alkalinity consuming and alkalinity generating processes based on solid phases showed that iron and sulfate reduction can account for at least 67% of the neutralization of acidity entering the fen of one of the catchments. Due to shorter water retention times and higher discharge these processes are of minor importance in the other catchment.

Tolerance of eastern gamagrass to excess aluminum in acid soil and nutrient solution

Eastern gamagrass, Tripsacum dactyloides L., has been reported to tolerate a wide variety of soil conditions, including drought, flooding, and acidity, but its specific tolerance to aluminum (Al) has not been tested. One strain of this species, PMK Select Lot 94 SFG‐1, was tested for its tolerance to excess Al in an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) and in nutrient solutions containing Al. Roots were able to penetrate unfertilized Tatum subsoil at pH levels as low as 4.1–4.2 (1:1 soil‐water), at Al saturations of 64 to 77% of CEC, and to tolerate Al concentrations in nutrient solution that would be lethal for many crop plants. For example, with 4 mg Al L‐1 and a final solution pH of 4.67, shoot and root dry weights were 75 and 76%, respectively, of those with no Al. Even with 24 mg Al L‐1 and a final solution pH of 4.13, shoot and root dry weights were 45 and 46%, respectively, of those for the no Al check treatment. Hence, this strain of gamagrass shows promise for use on soils having acidic, Al‐toxic subsoil layers that act as root barriers and predispose plants to injury by drought. Roots of gamagrass are also reported to penetrate hard clay pans and to create root channels for subsequent crops that lack this ability. Current studies indicate that the strain tested was susceptible to a chlorosis resembling iron (Fe) deficiency when grown in a Jiffy Mix potting mixture or with excess Al in nutrient solutions. Hence, gamagrass is tentatively being classified as a calcifuge [Al tolerant‐Fe‐inefficient]. In the current experiment, considerable plant to plant variability was noted regarding susceptibility to this chlorosis factor and to a purpling symptom resembling phosphorus (P) deficiency. Results indicate that an exhaustive screening of gamagrass populations could identify strains that are more suitable for specific soil situations.

Soil Solution Response to Experimentally Reduced Acid Deposition in a Forest Ecosystem

In order to measure and predict reversibility of soil solution acidification under experimentally reduced acid input, a manipulation study with artificial 'preindustrial' throughfall was established. A roof was installed underneath the canopy in a Norway Spruce stand (Picea abies [L.] Karst.) of the German Selling area. Water falling onto the roof was adjusted to clean rain concentrations before redistribution. Soil solutions were collected with suction cup lysimeters at various depths and were analyzed for major ions. The response of soil solution chemistry in the upper soil (10 cm depth) to a reduction of N, SO4, and H input was rapid. While NO3 concentration in deeper soil layers reached input levels after 2 yr of treatment, SO4 concentration in the seepage water at Im depth remained high relative to the reduced input due to a release of formerly stored S from the soil. Aluminum concentrations followed a similar pattern as the SO4 concentrations. The ion concentrations in soil leachate were predicted reasonably well using the MAGIC model (Cosby et al., 1985) with the measured SO4 sorption Isotherms and the throughfall fluxes as model input. Although the parameters of the Langmuir isotherm had no significant influence on the prediction of SO4 concentration in the upper soil layer, they were crucial for the prediction of SO4 dynamics in deeper soil layers. The model predicted that the reversibility of soil acidification at the Selling area is delayed for decades due to the release of soil SO4.

Separation of organic low molecular weight aluminium complexes in soil solution by liquid chromatography

A size exclusion chromatography method was developed for the separation of Al complexes of low molecular weight organic acids in soil solution. Bio-Gel P2 was used in a 1.6 x 30 cm column and the mobile phase consisted 0f 0.l M NaSCN of pH 4. The low molecular weight acids were determined by HPLC. The results show that 28–37% of the Al in the soil solution of the 0-horizon was bound t0 these acids. In the lower horizons Al coincided with the UV-trace at 400 run indicating organic complexes. Si was found in one major peak which was assumed to be a low molecular weight compound possibly silicic acid. As a compliment ultrafiltration was employed for characterisation