Chemical Composition Of Soil Solutions Research Articles

Transport and Model Calculation of Microplastics Under the Influence of Ionic Type, Strength, and Iron Oxide

Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

Chemical Composition of Soil Solutions of Technosols from a Coal Mine Region in South-Eastern Europe

Chemical Composition of Soil Solutions of Technosols from a Coal Mine Region in South-Eastern Europe

Effects of seasonal rainfall and water table movement on the soil solution composition of tropical peatland

ABSTRACTUnderstanding the composition of the soil solution of tropical peatlands is important because it directly affects nutrient availability and environmental degradation. The objectives of this study were to investigate temporal fluctuations in the soil solution composition in tropical peatlands in West Kalimantan and Riau, Indonesia and identify the factors controlling these fluctuations. In each site, we established four study plots consisting of three plots under oil palm (Elaeis guineensis Jacq.) plantation and one plot under uncultivated land as the control. Triplicate soil solution samples were collected at 50 and 200 cm depths, fortnightly. During the drought, the pH at 50 cm was low (3.7–4.0), which was influenced by oxidation reactions such as organic acids and NO3− generations. The pH at a depth of 200 cm was high (5.9–6.8), due to reduction reactions such as denitrification. High cation concentrations at both depths would result from organic matter decomposition and the limited downward movement of water. Rewetting the West Kalimantan peatland caused a sharp decrease in pH and ionic concentrations at 50 and 200 cm depths, because of the transportation of ions from the upper acidified layer. However, the lower rainfall levels in Riau than West Kalimantan resulted in a gradual decrease in pH and Ca2+ concentration. The higher pH levels and ion concentrations in West Kalimantan than in Riau would be influenced by the enhanced microbial activity due to water supply from the risen water table in this site. This study showed that seasonal rainfall and water table movement were the main factors controlling the fluctuations in the chemical composition of soil solutions.

Factors controlling the chemical composition of colloidal and dissolved fractions in soil solutions and the mobility of trace elements in soils

The objectives of this study were to determine the processes and physico-chemical conditions that affect the composition of the soil solutions of a forest soil and to elucidate their impact on the transport of major and trace elements through the colloidal (0.2μm to 5kDa) and dissolved (<5kDa) fractions in the first meter of soil. All experiments were performed with soil solutions obtained using lysimeter plates situated on an experimental spruce parcel of the Strengbach catchment (Northeastern France). The surface samples filtered at 0.2μm facilitated the examination of the influence of litter decomposition on the chemical composition of the upper soil solutions. The impact of the soils biogeochemical conditions (pH, moisture, temperature, oxic or anoxic conditions) on litter decomposition was also examined. More particularly, the increase in NH4+ and NO2− compounds in some of the soil solutions points to denitrification processes in an anoxic environment. Thus, under anoxic conditions, the soil solution is enriched in Ca, P, Mn and Zn, whereas under oxic conditions it is enriched in Al and Fe. The physico-chemical conditions are more seasonally dependent in the upper soil horizons than in the deeper ones and have an impact on the variability of the chemical composition of the soil solutions. The colloidal and dissolved fractions of the soil solutions were obtained by tangential flow ultra-filtration. The experimental results reveal that nutrients, such as NO3− and P, are primarily in the dissolved fraction and consequently bioavailable; secondary minerals may be dissolved and/or precipitate in the colloidal fraction, such as pyromorphite (Pb5(PO4)3(OH, Cl, F)). The results further indicate that microbial activity influences the composition of the colloidal and dissolved fractions, and possibly enriches the colloidal fraction in Ca, Mn and P, diminishes the concentrations of Pb, V, Cr and Fe in the dissolved fraction, and changes the structure of organic carbon (OC). These results are important for a better understanding of the role of the colloidal and dissolved (<5kDa) fractions in the transport of the major and trace elements in soil solutions and, more particularly, the mobility of pollutants and the bioavailability of nutrients for forested ecosystems.

Comparison of soil solution sampling techniques to assess metal fluxes from contaminated soil to groundwater.

The unsaturated zone plays a major role in elemental fluxes in terrestrial ecosystems. A representative chemical analysis of soil pore water is required for the interpretation of soil chemical phenomena and particularly to assess Trace Elements (TEs) mobility. This requires an optimal sampling system to avoid modification of the extracted soil water chemistry and allow for an accurate estimation of solute fluxes. In this paper, the chemical composition of soil solutions sampled by Rhizon® samplers connected to a standard syringe was compared to two other types of suction probes (Rhizon® + vacuum tube and Rhizon® + diverted flow system). We investigated the effects of different vacuum application procedures on concentrations of spiked elements (Cr, As, Zn) mixed as powder into the first 20cm of 100-cm columns and non-spiked elements (Ca, Na, Mg) concentrations in two types of columns (SiO2 sand and a mixture of kaolinite + SiO2 sand substrates). Rhizon® was installed at different depths. The metals concentrations showed that (i) in sand, peak concentrations cannot be correctly sampled, thus the flux cannot be estimated, and the errors can easily reach a factor 2; (ii) in sand + clay columns, peak concentrations were larger, indicating that they could be sampled but, due to sorption on clay, it was not possible to compare fluxes at different depths. The different samplers tested were not able to reflect the elemental flux to groundwater and, although the Rhizon® + syringe device was more accurate, the best solution remains to be the use of a lysimeter, whose bottom is kept continuously at a suction close to the one existing in the soil.

Impact of Waste Coal on Chemical Composition of Soil Solutions in Industrial Areas of Abandoned Coal Mines (Evidence from Avangard Mine, South of the Russian Far East)

Waste coal impact degree on chemical composition of soil solutions were studied by key hydrochemical parameters in the industrial area of abandoned Avangard coal mine. It was found that the impact of waste coal and mine waters is seen in accumulation of sulfides and silicon compounds in humus soil horizons; iron, chrome and copper in mineral horizons. Close correlation between chemical composition of mine waters and composition of soil solution was found.

Preliminary assessment of the ecochemical condition of soils after fertilization of younger spruce Picea abies (L.) H. Karst. stands in the Beskid Slaski and Zywiecki Mts.

The experimental plots were located in the middle forest zone (900– 950 m) on two nappes of the flysch Carpathians: Magura (the Ujsoly Forest District) and Silesian (the Wisla Forest District) in the spruce stands of age class 21– 40 years. Serpentinite was introduced in the autumn of 2008 on all plots while other fertilizers (N, P, NP and NPK) in the spring of 2009. Based on the chemical composition of soil solutions collected in lysimeters placed at the depth of 20 cm in the autumn 2008 and the spring and autumn 2009, ecochemical parameters were calculated: acid neutralization capacity (ANC aq ) , alkalinity (ALK), the degree of soil acidity (Ma%), acidic cations (Ma), saturation of the exchangeable complex of the soil solid phase (Mb) with alkalis, saturation with alkalis (BS), molar relations Ca/Al, Mb/Al, BC/Al. After the winter, soil solutions became acidic, especially in the Wisla Forest District. The saturation of the studied soils demonstrates moderate flexibility of soils in the Wisla Forest District in relation to acid load, and high flexibility of the Ujsoly soils. The opposite trend was observed for the degree of acidity of soils. Acid neutraliza tion capacity and alkalinity of the waters showed significant variations in soil pH even in the case of small variations in the composition of the solution, if they were caused by the inflow of the anions of NO 3 - and SO 4 2- . After application of the fertilizers, an increase of Mg, Ca and Mb was noted in the soil solution, determined in the overlaying highly acidic organic horizons trough the ion-exchange buffering mechanism of highly protonated functional groups with high buffering capacity. Highly improved content of Mg in a soil, and in some cases – also the content of N, P and K, present potential improvement of forest growth capacity without the hazard of adverse side-effects of liming. Aluminum stress in the spruce is unlikely, while trees in the control plots in the Wisla Forest District may already be sensitive.

Ionic deposition and chemistry of soil solutions in a forested study area in the Chojnów Forest District in the years 2004-2007

The study was carried out in the years 2004-2007 in a permanent observation plot established in a pine tree stand growing in a mixed fresh coniferous forest habitat of the Chojnow Forest District. Analyses pertained to the deposition of mineral compounds delivered to soil with bulk precipitation in the open field and throughfall and to chemical compositions of soil solution at a depth of 25 cm and 50 cm. pH, electrical conductivity and concentrations of Ca, Mg, Cl, NO₃, SO₄, Na, K, Fe, Mn, NH₄, PO₄, Zn, Cd, Cu, and Pb were analysed in precipitation and in soil solution samples.Total load of ions under the canopy of pine trees ranged between 47 and 61 kg·ha⁻¹·year⁻¹. Acidifying ions (N + S + Cl) contributed in 51% to the total ionic load (in molc·ha⁻¹·year⁻¹) while base ions (Ca + Mg + Na + K) in only 36%. Respective percentage contribution in bulk precipitation was 69% and 19%.No relationship was found between the chemical composition of soil solutions (at both depths) and the chemical composition of precipitation waters. Analysed soil solutions were acidic (average pH at the depth of 25 cm and 50 cm was 4.3 and 4.4, respectively) and the molar ratio of the sum of base cations (Ca, Mg, and K) to Al in the majority of examined samples from the upper soil layer, was much lower than 1. This is the evidence of low buffering capacities of analysed soil in relation to acidifying loads and indicates a potential threat for the pine stand stability.

Effects of storm Lothar (1999) on the chemical composition of soil solutions and on herbaceous cover, humus and soils (Fougères, France)

Examination of the effect of the 1999 storm on soil solution quality in an 81-year-old monitored plot in Fougères forest has not only made it possible to gain a better understanding of the impact of intensive silviculture in this ecosystem with low mineral fertility, but also to show that the cessation of internal recycling of chemical elements can be prevented by the presence of vegetation. The storm in December, 1999 resulted in several sudden openings in the forest cover, resulting in humus mineralization; the moder humus present before the storm was transformed rapidly into an oligomull. In the absence of any vegetation, the nitrates produced at the surface migrated down the profile by slow convective flux and the concentrations at depths of −10 and −30 cm increased during 2000. Herbaceous vegetation gradually replaced the arborescent strata present before the storm, taking-up the nitrate at the surface and thus limiting leaching into the deeper horizons. As convective transport is a slow process, the concentrations of nitrate in the soil solutions at depths of −55, −80 and −120 cm increased for about a year after the storm; then they decreased and stabilised in 2002. Nitrate leaching was accompanied by the migration of Al, Mg, K and Ca down the soil profile, depending on their relative availability. After the definitive installation of the herbaceous strata, the concentrations of elements in soil solutions returned to levels below those measured before the storm.

Effects of the clear-cutting of a Douglas-fir plantation (Pseudotsuga menziesii F.) on the chemical composition of soil solutions and on the leaching of DOC and ions in drainage waters

The effects of the clear-cutting of a 70-year-old Douglas-fir plantation on the chemical composition of soil solutions and on leaching of nutrients in drainage waters were observed by a continuous monitoring, six years before and three years after the cutting. Forest harvesting was made with very limited soil disturbances. Results showed that the concentration of weakly fixed solutions did not change but that the concentration of gravitational solutions of the upper soil layers drastically fell down after the cutting. The limited increase in nutrients leached with drainage waters was only due to the increase in the water flux, which is difficult to quantify because of the presence of ground vegetation. The monitoring of numerous fluxes before and after the clear-cutting could explain the specific behaviour of the soil solutions. The limited losses of nutrients the after clear-cutting in a potentially responsive ecosystem were unexpected. The initial hypothesis was that the decrease in the mineralization and nitrification rates observed after the cutting was related to a stimulating effect of Douglas-fir on the activity of soil nitrifyers.

Short-term alleviation of aluminum phytotoxicity by urea application in acid soils from south China

A laboratory experiment was conducted to study effects of urea fertilizer on the chemical composition of soil solutions over time, and to determine Al toxicity as a function of rates of urea application. The experiment revealed that addition of urea fertilizer to soils caused drastic changes in soil pH during the hydrolysis and nitrification stages of urea transformation in the experiment. These pH changes, depending on the N rate of urea application and time courses, had variable effects on soil exchangeable Al, extracted with artificial solutions containing 1 mol l −1 KCl. The Al mobilization rate could be resolved into two phases: A declining phase for Al was attributed to the urea-induced hydrolysis while a second rising phase was dependent with the nitrification of added N fertilizer. The decreases in exchangeable Al reached the greatest in 4–7 days after fertilization, consistent with soil pH increase. Decreased Al availability had been observed as a consequence of increasing urea addition and soil pH when using Root elongation of maize seedlings as the estimators. Results from the present study demonstrate that urea fertilizer to the surface of soils may lead to a temporary immobilization of Al and, therefore, alleviated Al toxicity to plant seedlings.

Soil chemical changes under irrigated mango production in the Central São Francisco River Valley, Brazil.

Irrigated areas in Brazil's Central São Francisco River Valley have experienced declines in productivity, which may be a reflection of changes in soil chemical properties due to management. This study was conducted to compare the chemical composition of soil solutions and cation exchange complexes in a five-year-old grove of irrigated mango (Mangifera indica L. cv. Tommy Atkins) with that of an adjacent clearing in the native caatinga vegetation. A detailed physiographic characterization of the area revealed a subsurface rock layer, which was more undulating than the current land surface, and identified the presence of a very saline and sodic (1045 microS cm(-1), sodium adsorption ratio [SAR] = 5.19) ground water table. While changes in concentrations of Ca, Mg, and K could be attributed to direct management inputs (fertilization and liming with dolomite), increases in Na suggested average annual capillary rise from the ground water table of 28 L m(-2). Accordingly, soil salinity levels appeared to be more dependent on surface elevation than the elevation of the rock layer or sediment thickness. The apparent influence of land surface curvature on water redistribution and the solution chemistry was more pronounced under irrigated mango production. In general, salinity levels had doubled in the mango grove and nearly tripled under the canopies, after only five years of irrigation. Though critical saline or sodic conditions were not encountered, the changes observed indicate a need for more adequate monitoring and management of water and salt inputs despite the excellent water quality of the São Francisco River.

Nutrient cycling in a clonal stand of Eucalyptus and an adjacent savanna ecosystem in Congo : 2. Chemical composition of soil solutions

The dynamics of nutrients were compared over three years in a clonal Eucalyptus plantation and in a native savanna in Congo. This paper focuses on the changes in the chemical composition of solutions during their transfer through the soil in both ecosystems. The main characteristics of the soil (Ferralic Arenosol) were similar in the two ecosystems, and the low inter-stand variability allowed reliable comparisons of the influence of afforestation on the soil solution chemistry. Rainfall amounted to about 1400 mm per year during the experimental period. In both ecosystems, an enrichment was observed for most elements during the transfer of solutions through the foliage, but N uptake occurred. Concentrations of H + and dissolved organic carbon (DOC) in solutions increased through the litter layer in both stands. In the Eucalyptus ecosystem, a quick uptake of nutrients by a dense root mat inside the forest floor likely explained why the concentrations of gravitational waters were not enhanced markedly for ‘base cations’, despite the mineralization of high amounts of nutrients during the litter decay. Soil solutions were collected by zero tension lysimeters (ZTL) at a depth of 15 cm, but these lysimeters were inefficient at collecting gravitational solutions beyond this depth. By contrast, tension lysimeters (TL) maintained at a suction of −60 kPa, collected soil solutions at the depths of 15, 50 cm, 1, 2, 3, 4 m in both ecosystems and 6 m in the plantation. In the topsoil of both stands, the nutrient concentration decreased sharply when the time of residence of solutions increased. This pattern highlighted the crucial role of the inputs by throughfall, stemflow and mineralization of the litter layer for the nutrition of these stands. A combination of high nutrient requirements of the stands and low availability of exchangeable cations in this highly weathered soil might account for the extremely low nutrient concentrations in solutions collected by TL, regardless of the depth.

Evaluation of porous cup soil‐water samplers under laboratory conditions: Comparison of ceramic and PTFE cups

Three different types of soil solution samplers (two ceramic cups and PTFE) were tested in the laboratory to validate their use for collecting soil‐water samples and for monitoring the chemical composition of soil solutions. Interactions between porous materials and chemical solutions were examined under different experimental conditions for several major cations (Ca2+, Mg2+, Na+ and K+) and anions (HCO‐ 3, NO‐ 3, SO4 2‐ and Cl‐) and for several minor ions (NH+ 4, NO‐ 4, PO4 3‐and B). The results show that ceramic cups are not inert for bicarbonate, calcium and phosphate ions. Their use is only valid for a limited number of ions such as chloride and nitrate which, however, are the most studied ions in field experiments. PTFE cups have less restrictions although their use in measuring sulphates, phosphates and ammonium presents some problems. Choosing the appropriate type of cup depends on the objectives. In any case, laboratory experiments must be performed before installation.

Dynamic of soil chemical parameters in shifting agriculture in the Eastern Amazon

In Northeast Pará, Brazil, shifting agriculture by land settlers has been practiced for around 100 years. After a common cropping period of 2 years the fields are left fallow for 4 to 8 years. Changes in extractable cations and C, N, and P of soils were studied on six fields which were under different phases of the rotational cycle. The chemical composition of soil solutions was also monitored for a period of 19 months. In topsoils, the differences in C and N contents and extractable Ca and Al could be related to the landuse history expressed as time elapsed since last burn. Repeated sampling on two ‘slash and burn’ plots, showed significant increases in pH, CEC, extractable K, Ca and Mg, but decreases in extractable Na and Al, C and N content in the plots from 7-year old fallow to the first-year cropping field. Soil solution chemistry at 105 cm depth did not change with increasing fallow age. On the ‘slash and burn’ field, big variations in solute composition at 10 cm depth were observed during the initial months of the cropping period. In the soil solutions after burning, Ca concentrations ranged from 4.8 to 30.1 mg l −1, but decreased to values between 1.2 and 2.7 mg l −1 within 2 months. Slash burning and subsequent cropping lead to increases of Cl − and NO − 3 in the soil solution at 105 cm depth. A small dose of NPK fertilizer (11 kg N ha −1, 13 kg P ha −1 and 17 kg K ha −1) did not increase NO − 3 concentration and chloride concentrations at this depth increased to a small extent. After the harvest of cassava, high nitrate concentrations of 11 mg N l −1 were observed. NO − 3 and Cl − concentrations on the cropping fields were significantly correlated ( n = 350) with the sum of the concentration of the M b cations (Na, K, Ca, Mg), (NO − 3M b, r = 0.82; Cl −M b, r = 0.81). Nitrate also showed significant correlations with protons ( r = 0.59) and Al ( r = 0.47) concentrations. Ion concentrations in the soil solution can be reduced by agricultural management. During harvest, the aboveground vegetation should not be removed completely in one single step. If clear cutting cannot be avoided, the timing should be chosen as to keep some vegetation with high uptake potential at the beginning of the rainy season. A small dose of NPK-fertilizer stimulated the nutrient uptake by the vegetation and did not enhance nutrient concentrations in the seepage water.

Comparison of chemical composition of soil solutions collected by zero‐tension plate lysimeters with those from ceramic‐cup lysimeters in a forest soil

SummaryWe analysed the chemistry of solutions collected from soil by zero‐tension plate lysimeters and cup lysimeters connected to a constant suction (600 hPa) under Douglas fir in the Beaujolais mountains (France). The chemistry of zero‐tension lysimeters' (ZTL) and tension lysimeters' (TL) solutions differed enormously: TL solutions were most concentrated in Si, NH4‐N, NO3‐‐N, Cl−, Mg2+ and A13+ and TOC, whereas Ca2+ and K+ concentrations were greater in ZTL solutions. Organic matter (OM) greatly influenced the solution chemistry in both ZTL and TL. The chemistry of ZTL solutions was affected mainly by OM mineralization in the forest floor and upper soil horizon, and that of TL solution seemed to be related to destabilization of humified compounds under the new vegetation. Nitrification was important: residual nitrification led to excess protons neutralized in weathering or ion exchange reactions, mobilized cations, mainly A13+. Selectivity coefficients calculated both for ZTL and TL solutions formalized the differences between the two types of solutions. Nevertheless, these coefficients remained most often within the same order of magnitude indicating relations between them. Solutions from the two devices provided different information and should not be used for the same objectives. Solutions from ZTL are suited for ecosystem input‐output budgets, whereas TL solutions are more useful when equilibrium between the solution and solid phase or when plant nutrition are considered.

Comparing modelled and observed effects of ash additions on chemistry of a highly acid soil

The chemical composition of soil solutions (field percolates collected in situ and laboratory saturation extracts) and the amount of salt-extractable cations were measured at several microsites (unburnt, moderately burnt, and intensely burnt ashbeds) after a fuel reduction burning in a subalpine Eucalyptus pauciflora forest. Soil samples were collected 1, 58, 375, 745, and 1095 days after the fire, and soil percolates were obtained on 17 occasions during the initial year. A model of coupled equilibria, which includes insoluble salts, multiple cation exchange, and inorganic complexation, was used to describe soil chemical changes after fire and ash addition. The model was able to describe temporal changes in cation concentrations of held percolates and soil exchangeable cations. Measurements of extractable cations using unbuffered salt solution on samples taken immediately after fire suggest immediate changes in exchangeable cations which were related to solubilisation of cations from ash, and not to changes in exchangeable cations in soils. Modelling suggests that under natural conditions the differences in solubility of cations in ash result in slow changes in exchangeable cations extending over a period of 6 years or more. The time required to reacidify the surface layer of ashbed soil was estimated to be 45 years when annual acid input was 0.5 kmol H+/ha.

Reversibility of damages to forest floor plants by episodes of elevated hydrogen- and aluminium-ion concentrations in the soil solution

Herbs and grasses may episodically be exposed to elevated concentrations of potentially toxic elements as H+ and Al3+ due to considerable temporal variability in the chemical composition of soil solutions in the uppermost layer of the soil profile. Greenhouse experiments were performed to test the effect of episodes of different length (1 and 2 weeks) and concentrations of H+ and Al3+ (pH 3.8, 4.0, 4.2 and 4.5; 0, 20 and 70 μM Al) on root and shoot growth, designed to elucidiate the reversibility of growth inhibition. Three forest floor species were studied-Galium odoratum and Lamium galeobdolon, having similar pH distribution ranges in the field and Poa nemoralis which also occurs at slightly lower pH. The plants were grown for 5 weeks (episode and recovering time) in a synthetic soil solution in a flowing solution system without recirculation. The species reacted in three different ways. Galium odoratum was the most sensitive species and seemed to be irreversibly damaged (ceased growth) by 2 week episodes of pH≤4.0 and Al≥20 μM at pH≤4.2. Lamium galeobdolon was about equally sensitive during the episodes but it had a much greater ability to recover. Poa nemoralis was rather insensitive to the episode treatments tested. It is concluded that episodes of elevated H+ and Al3+ concentrations may be decisive for plant performance. It is therefore important to consider the extreme environmental conditions which plants may be exposed to in the field, in addition to long-term averages of e.g. soil solution concentration of potentially toxic elements, when studying species distribution and performance in relation to soil chemical properties.

Chemical composition of soil solutions extracted from New Zealand beech forests and West German beech and spruce forests

Concentrations of ions were measured in soil solutions from beech (Nothofagus) forests in remote areas of New Zealand and in solutions from beech (Fagus sylvatica) and Norway spruce (Picea abies) forests in North-East Bavaria, West Germany, to compare the chemistry of soil solutions which are unaffected by acid deposition (New Zealand) with those that are affected (West Germany). In New Zealand, soil solution SO4 2− concentrations ranged between <2 and 58 μmol L−1, and NO3 − concentrations ranged between <1 and 3 μmol L−1. In West Germany, SO4 2− concentrations ranged between 80 and 700 μmol L−1, and NO3 − concentrations at three of six sites ranged between 39 and 3750 μmol L−1, but was not detected at the remaining three sites. At all sites in New Zealand, and at sites where the soil base status was moderately high in West Germany, pH levels increased, and total Al (Alt) and inorganic monomeric Al (Ali) levels decreased rapidly with increasing soil depth. In contrast, at sites on soils of low base status in West Germany, pH levels increased only slightly, and Al levels did not decline with increasing soil depth. Under a high-elevation Norway spruce stand showing severe Mg deficiency and dieback symptoms in West Germany, soil solution Mg2+ levels ranged between 20 and 60 μmol L−, and were only half those under a healthy stand. Alt and Ali levels were substantially higher the healthy stand than under the unhealthy stand, indicating that Al toxicity was not the main cause of spruce decline.

Aluminium contamination and other changes of acid soil solution isolated by means of porcelain suction‐cups

SUMMARYComparison was made between the chemical composition of soil solutions isolated by means of a suction method using porcelain cups and by centrifugation. The soil solutions were isolated from three depths of field plots, where the soil (Typic Haplohumod) had been subjected to various pretreatments.The cups were made of mullite and corundum as shown by X‐ray diffraction analysis. The material when powdered had a cation exchange capacity of about 10meq kg−1. Solutions with similar ionic strengths were obtained by the two methods, but the cups were found to release substantial amounts of Al and to adsorb H, Ca, K, Na and organic matter.After the cups had been placed in the soil for more than 7 months, calculations suggested that the Al activity in cup solutions was controlled by amorphous gibbsite. This amorphous material was probably produced by proton‐induced decomposition of part of the cup material. It is concluded that such cups are improper for isolation of soil solution from acid soils.