Acid Forest Soils Research Articles

Analysis of forest soil acidification processes in the area of NP 'Kopaonik'

In the last two decades, S and N critical loads have been used as indicators of ecosystem sustainability to soil acidification. The effect of acidification on the soil in forest ecosystems and their further development was the subject of numerous studies, based on which several mathematical models were developed. This paper presents the results of the analysis of acidification processes in brown podzolic soil on granodiorites in the stands of spruce and spruce and fir in the area of NP 'Kopaonik'. Critical loads of sulphur and nitrogen in these soils are presented using VSD model.

Experimental study of DOC, nutrients and metals release from forest floors developed under beech ( Fagus sylvatica L.) on a Cambisol and a Podzol

Forest floor in acid forest soils is a major source of dissolved organic carbon (DOC), nutrients and metals. We studied the release of DOC, nutrients and metals from two forest floors under beech stands (a moder from a Cambisol and a mor from a Podzol). We analyzed the composition of the solid phase, and we monitored the chemical properties of forest floor leachates through incubation-leaching experiments at 4 and 20 °C. Our data show that the release of DOC, nutrients and metals strongly differed between both forest floors. Whatever the temperature, the release of DOC, DIN, divalent cations and heavy metals, as compared to initial stocks of corresponding elements, were the largest in moder leachates. Instead, the release of K +, Na +, Si, Al and Fe were the largest in mor leachates at 20 °C, and were generally similar for both forest floors at 4 °C. The ionic signature of the leachates was strongly affected by DOC release and nitrogen mineralization, which was mostly directed towards the production of ammonium in mor, and of nitrate in moder. In moder leachates at 20 °C, Ca 2+ was the dominant cation, and nitrate the major anion. Instead, in mor leachates, NH 4 + was the major cation, and organic anions dominated the anionic charge. Despite the dominance of organic anions in mor leachates, the concentrations of cations and Si were strongly correlated to the concentrations of inorganic anions in leachates from both forest floors. The concentration of Al, Fe, Cu and Pb were strongly correlated to the concentration of organic anions, whereas Zn concentration was poorly correlated with either organic or inorganic anions.

Stabilization of dissolved organic matter by aluminium: a toxic effect or stabilization through precipitation?

SummaryCarbon mineralization in acidic forest soils can be retarded by large concentrations of aluminium (Al). However, it is still unclear whether Al reduces C mineralization by direct toxicity to microorganisms or by decreased bioavailability of organic matter (OM) because dissolved organic matter (DOM) is precipitated by Al. We conducted an incubation experiment (6 weeks) with two DOM solutions (40 mg C litre−1) derived from two acidic forests and possessing large differences in composition. Aluminium was added to the solutions in realistic ranges for acidic soils (1.6–24 mg Al litre−1) at pHs of 3.8 and 4.5, to achieve differences in Al speciation. We determined different Al species, including the potentially toxic Al3+, by Diffusive Gradients in Thin Films (DGT) to evaluate toxic effects on microorganisms. Precipitation of OM increased with larger amounts of added Al and higher pH, and we measured a larger fraction of dissolved ‘free’ Al at pH 3.8 than at pH 4.5. Organic matter degradation decreased significantly with Al addition, and we found more organic matter degraded at pH 3.8 than at pH 4.5 for the respective Al additions. Consequently, the observed reduction in OM degradation (i.e. stabilization) cannot be explained by toxic effects of ‘free’ Al. However, C stabilization correlated significantly with C precipitation. The pH did not influence C stabilization directly, but determined the amount of C being precipitated. Phosphorus was removed along with OM by precipitation, which possibly also affected C stabilization. We conclude that C stabilization upon Al addition did not result from toxic effects, but was caused by reduced bioavailability of OM after its precipitation. The reduction in OM degradation by 65% is of great relevance for the overall C stabilization in acidic forest soils. Increasing pH and decreasing Al concentrations upon recovery from acidic deposition should therefore not result in decreased stabilization of precipitated OM.

Cation exchange in forest soils: the need for a new perspective

SummaryThe long‐term sustainability of forest soils may be affected by the retention of exchangeable nutrient cations such as Ca2+ and the availability of potentially toxic cations such as Al3+. Many of our current concepts of cation exchange and base cation saturation are largely unchanged since the beginnings of soil chemistry over a century ago. Many of the same methods are still in use even though they were developed in a period when exchangeable aluminium (Al) and variable charge were not generally recognized. These concepts and methods are not easily applicable to acid, highly organic forest soils. The source of charge in these soils is primarily derived from organic matter (OM) but the retention of cations, especially Al species, cannot be described by simple exchange phenomena. In this review, we trace the development of modern cation exchange definitions and procedures, and focus on how these are challenged by recent research on the behaviour of acid forest soils. Although the effective cation exchange capacity (CECe) in an individual forest soil sample can be easily shown to vary with the addition of strong base or acid, it is difficult to find a pH effect in a population of different acid forest soil samples. In the very acidic pH range below ca 4.5, soils will generally have smaller concentrations of adsorbed Al3+. This can be ascribed to a reduced availability of weatherable Al‐containing minerals and a large amount of weak, organic acidity. Base cation saturation calculations in this pH range do not provide a useful metric and, in fact, pH is modelled better if Al3+ is considered to be a base cation. Measurement of exchangeable Al3+ with a neutral salt represents an ill‐defined but repeatable portion of organically complexed Al, affected by the pH of the extractant. Cation exchange in these soils can be modelled if assumptions are made as to the proportion of individual cations that are non‐specifically bound by soil OM. Future research should recognize these challenges and focus on redefining our concepts of cation retention in these important soils.

Nutrient Sorption Dynamics of Resin Membranes and Resin Bags in a Tropical Forest

Plant root simulator (PRS) probes, a resin membrane technology, are increasingly used to measure soil nutrient availability in agricultural and nonagricultural systems. Like other resin technologies, the charged surface is meant to sorb nutrients until saturation; however, there is evidence that it acts as a dynamic exchanger in soils with low nutrient availability. This study compared the nutrient sorption dynamics of PRS probes during an 8‐wk period in a young Andisol forest soil on the island of Hawaii with and without P fertilization. Resin bags, a more established technology, were used to measure nutrient availability as a comparison. The PRS probe sorption dynamics differed for the six nutrients measured. Except for NO3, nutrient sorption appeared to reach equilibrium with the soil labile pools after 4 wk. Resin bags acted as an infinite sink for NH4+, NO3−, and PO43− and sorbed more than the PRS probes. Both technologies detected an increase in P availability due to fertilization. A comparison of nutrient availability from PRS probes and resin bags correlated poorly. Isolation of the PRS probes and resin bags from root activity did not improve measurements of labile nutrients. More research is required to understand the processes behind the apparent desorption of nutrients from the PRS probes in acidic forest soils. If used for a minimum of 4 wk, however, the PRS probes appear to provide an equilibrium measure of labile soil nutrients with high sensitivity to treatment differences.

Acid properties of fulvic and humic acids isolated from two acid forest soils under different vegetation cover and soil depth

SummaryWe studied the acid‐base properties of 16 fulvic acids and 16 humic acids isolated from the surface (3–15 cm) and subsurface (> 45 cm) horizons of two types of acid forest soils, derived respectively from amphibolite and granite rocks, under five different types of vegetation. The observed differences between the contents of humic substances in the two types of soils were related to the degree of Al‐saturation of the soil organic matter, as indicated by the molar ratio between pyrophosphate extractable Al and C. Humic fractions were characterized in terms of elemental composition, and CPMAS 13C NMR spectrometry. The contents of carboxylic and phenolic groups were estimated by potentiometric titrations conducted in 0.1 m KNO3 in a nitrogen atmosphere. The fulvic acids contained more carboxylic groups but less phenolic groups than the humic acids: the ratio of phenolic to carboxylic groups in the humic acids was 0.48 ± 0.10 and in the fulvic acids 0.23 ± 0.05. The mean values of the protonation constants of each of the humic substance fractions can be used as generic parameters for describing the proton binding properties. The fulvic acids isolated from the subsurface horizon of the soil contained between 2.6 and 23% more carboxylic groups, and the humic acids between 8 and 43% more carboxylic groups than those isolated from the surface horizon of the same soil.

Results of a 30-year-old fertilisation experiment

The long-term mineral fertilisation experiment set up on acidic brown forest soil in Gödöllő in 1972 has made it possible over the years to answer a number of questions. It became clear that, in general, increasing rates of NPK fertilisation only caused a significant increase in the yields obtained in the crop rotation at lower rates (150–300 kg NPK/ha). As time went on, rates higher than this caused yield depression. The continuous application of high fertiliser rates led to a substantial increase in the P and K contents of the ploughed layer and in the quantity of nitrate accumulating in the 3 m soil profile. An increase in the quantity of nutrients was associated with a reduction in the pH and in the content of Ca and Mg. When mineral fertilisation was omitted for six years, there was a substantial reduction in the P and K contents of the ploughed layer.

Soil organic matter stabilization in acidic forest soils is preferential and soil type‐specific

SummaryMinerals with large specific surface areas promote the stabilization of soil organic matter (SOM). We analysed three acidic soils (dystric, skeletic Leptic Cambisol; dystric, laxic Leptic Cambisol; skeletic Leptic Entic Podzol) under Norway spruce (Picea abies) forest with different mineral compositions to determine the effects of soil type on carbon (C) stabilization in soil. The relationship between the amount and chemical composition of soil organic matter (SOM), clay content, oxalate‐extractable Fe and Al (Feo; Alo), and dithionite‐extractable Fe (Fed) before and after treatment with 10% hydrofluoric acid (HF) in topsoil and subsoil horizons was analysed. Radiocarbon age, 13C CPMAS NMR spectra, lignin phenol content and neutral sugar content in the soils before and after HF‐treatment were determined and compared for bulk soil samples and particle size separates. Changes in the chemical composition of SOM after HF‐treatment were small for the A‐horizons. In contrast, for B‐horizons, HF‐soluble (mineral‐associated) and HF‐resistant (non‐mineral‐associated) SOM showed systematic differences in functional C groups. The non‐mineral associated SOM in the B‐horizons was significantly depleted in microbially‐derived sugars, and the contribution of O/N‐alkyl C to total organic C was less after HF‐treatment. The radiocarbon age of the mineral‐associated SOM was younger than that of the HF‐resistant SOM in subsoil horizons with small amounts of oxalate‐extractable Al and Fe. However, in horizons with large amounts of oxalate‐extractable Al and Fe the HF‐soluble SOM was considerably older than the HF‐resistant SOM. In acid subsoils a specific fraction of the organic C pool (O/N‐alkyl C; microbially‐derived sugars) is preferentially stabilized by association with Fe and Al minerals. Stabilization of SOM with the mineral matrix in soils with large amounts of oxalate‐extractable Alo and Feo results in a particularly stable and relatively old C pool, which is potentially stable for thousands of years.

Monitoring heavy metal concentrations in leachates from a forest soil subjected to repeated applications of sewage sludge

The aim of the study was to establish whether the repeated application of sewage sludge to an acid forest soil (Dystric Cambisol) would lead to short-term groundwater contamination. Sludge was applied at four loading rates (0, 2.4, 17 and 60 Mg ha(-1)) in two consecutive years and leachates were analysed. Heavy metal inputs to soils at the lowest dose were below EC regulations but, at higher doses, limits for Zn, Cd, Cr and Ni were exceeded. Repeated application of sludge at 60 Mg ha(-1) resulted in significantly (P<0.05) higher concentrations of Zn, Cd, Cr and Ni in the leachates than with other treatments. The drinking water standards for Cd and Ni were surpassed in all treatments. Control plots were contaminated by groundwater flow despite the existence of buffer zones between plots. This complicated interpretation of the results, highlighting the importance of careful design of this type of experiment.

Relationship between Aluminum in Soils and Soil Water in Mineral Horizons of a Range of Acid Forest Soils

Previous studies suggest that the solubility of Al in acid forest soils may be expressed as the log Al3+ activity = −n pH + log KH‐Al + log Alp/Cp concentration ratio, with Alp and Cp representing pyrophosphate‐extractable Al and C, respectively, and KH‐Al is the binding constant of Al to protonated complexation sites on soil organic matter (SOM). We show that a slightly modified model, in which Alp is replaced by Alorg (= Alp − KCl‐extractable Al), successfully describes the concentration of Al in A and B horizons of a wide range of acid forest soils (Typic Dystochrepts) developed in different parent materials from a large number of spruce [Picea abies (L.) Karst.] and mixed forest stands in southern Poland. Analysis of the data suggests a reaction stoichiometry of n = 1.27 and log KH‐Al = 1.98 with R2 = 0.76. Furthermore, statistical analysis of a large set of published data, in addition to our own data from the Polish soils, indicates that log[Alorg/Cp] is significantly correlated with soil pH measured in 1 mol L−1 KCl (pHKCl), suggesting that the Al binding to SOM is less at small pHKCl due to increased competition with H+: log[Alorg/Cp] = 0.82 pHKCl − 4.16 (R2 = 0.77, n = 276). Combining the two equations gives a simple Al solubility model for mineral horizons in acid forest soils: log Al = −1.27pH + 0.82pHKCl − 2.18 (R2 = 0.82, n = 127). In this equation, pHKCl relates to chemical soil properties, whereas the pH of soil water also depends on solution characteristics like ionic strength. The equation may be applied to acid forest soils having a soil solution pH in the range of 3.0 to 4.2. Such conditions are rather common in surface horizons (A, E, and upper B) of acid forest soils of the temperate and boreal zones.

Properties of organic matter precipitated from acidic forest soil solutions

From solutions of acidic forest soils, up to 90% of the organic matter (OM) can be precipitated by Al. Precipitation of the OM contributes to its resistance to microbial decay, so the process should be of relevance for C cycling and sequestration. However, little is known about the properties and the composition of the precipitated OM. Therefore, we investigated the size of precipitated OM flocs and determined the chemical components which were preferentially precipitated. We used four different OM solutions and precipitated OM at different Al/C ratios and pH values. Results of 13C NMR (nuclear magnetic resonance), 1H NMR and UV/vis spectroscopy clearly showed preferential precipitation of aromatic components with a high content of carboxylic groups at all pH and Al/C ratios. This selective precipitation was supported by FTIR measurements which additionally revealed that binding mechanisms between OM and Al were independent of pH and Al/C values. However, we observed greater Al/C ratios for OM precipitated at pH 4.5 than at 3.8, which could be related to the amount of Al(OH) 2+ cations in solution or the formation of small Al-hydroxide primary particles. The diameter of precipitated OM flocs ranged from 3 to 110 μm, with smaller size at pH 3.8 (ave. 16.6 μm) than at pH 4.5 (ave. 27.6 μm). We observed that the Al cations formed on average 2–3 bonds to the organic molecules. As a consequence, the spatial accessibility of the OM should be considerably reduced in these flocs, leading to additional stabilization, besides the intrinsic stability of the precipitated organic compounds. We conclude that the fate of precipitated OM might be similar in many soils, regardless of the parent dissolved organic matter (DOM) because of equalization of OM properties upon precipitation.

Impact of rainfall, liming, nitrogen (N), phosphorus (P2O5), potassium (K2O), calcium (CaO), magnesium (MgO) mineral fertilization on triticale (×TriticosecaleWittmack) yield in a monoculture in Hungary

The natural climate variability may be masked by the anthropogenic made global warming, today. With a warmer climate, drought and excess rainfall conditions could become more frequent and longer lasting. The potential increase of the hazards result stresses and high costs in cereal production. For this reason a long-term study was conducted on a sandy acidic lessivated brown forest soil; WRB: Haplic Luvisol in the 44 year old Nyirlugos Field Trial (NYFT) in a Hungarian fragile agroecosystem in Nyirseg region (N: 470 41’ 60, and E: 220 2’ 80,) on triticale (× Triticosecale Wittm.) yield between 1999 and 2006. In 1962, at the trial set up the soil had the following agrochemical properties: pH (H 2 O) 5.9, pH (KCl) 4.7, hydrolytic acidity 8.4, hyl 0.3, humus 0.7%, total N 34 mg kg −1, ammonlactate (AL) soluble-P 2 O 5 43 mg kg −1, AL-K 2 O 60 mg kg −1 in the plowed (0–25 cm) layer. The trial consisted of 32 × 4 = 128 plots in randomised block design. The gross plot size was 10 × 5 = 50 m 2. The average fertilizer rates in kg ha −1 year −1 were nitrogen 75, phosphorus 90 (P 2 O 5), potassium 90 (K 2 O), calcium 437.5 (CaCO 3) and magnesium 140 (MgCO 3). The groundwater table had at a depth of 2–3 m below the surface. During drought conditions the respective yield of the control areas was −25% less than for average years. The application N alone or NP and NK treatments led to yield reduction of −19.7%, while that of NPK, NPKCa, NPKMg and NPKCaMg caused an −28.3% yield drop. In the wet years the yield decreased by −22.2% on the unfertilized soils; in case of the N, NP and NK nutrition the yield dropped with an −14.1%; and the yield increased at 13.8% on NPK, NPKCa, NPKMg and NPKCaMg treated plots. Yield dropped in the very wettest year −43.1% on control soils; −39.3% of N, NP and NK loadings, and −35.8% on NPK, NPKCa, NPKMg and NPKCaMg treatments to those in the average year. The relationship between rainfall quantity during the vegetation period and N, P, K, Ca, Mg nutrition and yield was characterised by polynomial correlation (control: R = 0.7212***, N: R = 0.7410***, NP: R = 0.6452***, NK: R = 0.6998***, NPK: R = 0.5555***, NPKCa: R = 0.5578***, NPKMg: R = 0.4869**, NPK CaMg: R = 0.4341**). However, total regression coefficients ranged from 0.43 to 0.74 in depence on the different nutrient application. Maximum yields of 5.8–6.0 t ha −1 were achieve in the rainfall range of 580–620 mm. At values above and below this domain of the precipitation the grain yield reduced quadratically. So, it can be stated that both drought and excess rainfall conditions resulted dramatically significant negative effects between fertilization (N, P, K, Ca, Mg) and triticale yield.

Temporary storage of soil organic matter and acid neutralizing capacity during the process of pedogenetic acidification of forest soils in Kinki District, Japan

Pedogenetic acidification processes in forest soils derived from sedimentary rocks under mesic and thermic soil temperature regimes (MSTR and TSTR; corresponding to mean annual soil temperatures of 8–15°C and 15–22°C, respectively) in the Kinki District were investigated based on titratable alkalinity and acidity characteristics and soil solution composition. According to statistical analyses of the soil properties, the titratable alkalinity required to acidify soils to pH 3.0 was considered to be derived from reactions occurring at the surface of amorphous Al oxides, while titratable acidity at a pH ranging from 5.5 to 8.3 results from dissociation of acidic functional groups of soil humus and/or deprotonation of oxide surfaces. These reactions were generally more prevalent in MSTR soils. Based on the soil solution composition and titratable alkalinity and acidity in the soil profiles, two processes were postulated for pedogenetic acidification, that is, eluvi-illuviation of inorganic Al followed by subsequent adsorption of dissolved organic carbon (DOC) onto the precipitates of Al hydroxides and comigration of Al and DOC in the form of organo-mineral complexes. Both processes were conspicuous in MSTR soils and significantly contributed to soil organic matter storage in the subsoil layers. Pedogenetic acidification in forest soils with MSTR was characterized by an accumulation of acidity in the form of amorphous compounds and/or organo-mineral complexes in the B horizon. It seems, to some extent, similar to podzol formation, at least in terms of Al translocation. Amorphous Al hydroxides protect against further acidification through protonation and/or partial monomerization and can, thus, be regarded as a temporary storage of acid neutralizing capacity of the soil, which would be otherwise leached out directly from the soil profile. In contrast, the acid-buffering reactions of TSTR soils seemed to occur, if at all, mostly at or near the soil surface and the contribution of the B-horizon soils was limited.

Responses of two closely related oak species, Quercus robur and Q. petraea, to excess manganese concentrations in the rooting medium

Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field.

Identification of dominant bacterial phylotypes in a cadmium-treated forest soil

The presence of heavy metals in soils can lead to changes in microbial community structure, characterized by the dominance of groups that are able to tolerate contamination. Such groups may provide good microbial indicators of heavy-metal pollution in soil. Through terminal restriction fragment length polymorphism (T-RFLP) profiling, changes in the bacterial community structure of an acidic forest soil that had been incubated with cadmium (Cd) for 30 days were investigated. T-RFLP revealed, in particular, three operational taxonomic units (OTUs) strongly dominating in relative abundance in the contaminated soil. By cloning of the amplified 16S rRNA genes and partial sequencing of 25 clones, these three dominant OTUs were phylogenetically characterized. One dominant OTU in the cadmium-contaminated soil was derived from Betaproteobacteria, genus Burkholderia, and the other two were from uncultured members of the class Actinobacteria, closely related to the genus Streptomyces. To confirm T-RFLP data, four primers were designed on the basis of this study's dominant sequences, targeting the OTUs corresponding to Burkholderia or Actinobacteria. Real-time PCR showed that Burkholderia target sequences were more abundant in cadmium-treated soil (7.8 x 10(7)+/- 3.0 x 10(7) targets g(-1) soil) than in untreated soil (4.0 x 10(6)+/- 8.9 x 10(5) targets g(-1) soil). It was concluded that the genus Burkholderia includes species that may be particularly dominant under cadmium contamination.

Sensitivity to Acidification of Forest Soils in Two Watersheds with Contrasting Hydrological Regimes in the Oil Sands Region of Alberta

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds (Lake 287 and Lake 185) with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine ( Pinus banksiana) or aspen ( Populus tremuloides). Soils in the two watersheds were extremely to moderately acidic with pH (CaCl 2) ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor > subsurface mineral soil > surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.

Relationships between soil properties and feeding activity of soil fauna in acid forest soils

AbstractWe investigated the relationships between soil chemical properties, humus form, and feeding activity in eight forest sites in Northrhine‐Westphalia, Germany. The study sites varied in forest type (oak, oak‐hornbeam, spruce, and pine). Three study sites were located under the same climatic conditions, and five study sites were distributed all over Northrhine‐Westphalia. We determined humus form, soil chemical properties, and feeding activity in three replication plots per site. We used the bait‐lamina test to determine feeding activity of soil fauna. Independent of forest type, all study sites were very acid with pH(CaCl2) values in the Ah horizon between 2.8 and 4.0. The three study sites located under the same climatic conditions showed very homogenous soil chemical properties (pH in Ah: 2.9–3.0), whereas the five other sites varied significantly due to their soil chemical parameters (pH in Ah: 2.8–4.0). All single sites presented feeding activities with a very low spatial heterogeneity. Forest types and climatic conditions were not related to activity of soil fauna. Feeding activity and thickness of the O layer were strongly negatively correlated, whereas the activity was strongly positively correlated to soil pH in the five study sites with a wide range of soil chemical parameters. The three extremely acid forest sites presented significant differences in feeding activities that were not related to soil chemical properties.

Assessment of single extractions for the determination of mobile forms of metals in highly polluted soils and sediments—Analytical and thermodynamic approaches

Highly polluted forest/tilled soils and stream sediments from a mining and smelting area were subjected to single-extraction procedures to determine the extractable contents of Cd, Cu, Pb, and Zn. The results obtained from four widely used operationally defined single extraction tests were compared: deionised water, 0.01 mol L −1 CaCl 2, 1 mol L −1 NH 4NO 3 and 0.005 mol L −1 DTPA. The analytical data were coupled with measurement of the pH and Eh in extracts, mineralogical investigations and thermodynamic modelling using the PHREEQC-2 code. The changes in the pH of the equilibrated suspensions significantly influenced the metal extractabilities, with higher values in the lower pH regions. Although the DTPA procedure generally extracted the highest amounts of metals, it was found to be unsuitable for highly organic acidic forest soils, where anionic metal–DTPA complexes are assumed to be re-adsorbed on the positively charged surfaces of soil organic matter and oxides. The NH 4NO 3 extraction was also unsuitable due to the high ionic strength (1 mol L −1), limiting the use of the thermodynamic speciation model and the formation of the Cu(NH 3) 2+ complex, leading to acidification of the suspension. 0.01 mol L −1 CaCl 2 can be proposed as the most appropriate extraction medium, suitable for speciation modelling and analytical determinations using ICP-techniques and having an ionic strength similar to that of the soil solution. The metals are present in free ionic forms or chlorocomplexes in the CaCl 2 extracts, preventing their re-adsorption on the positively charged surfaces of soil solids (organic matter, Fe- and Mn-oxides) in acidic and circum-neutral conditions.

Comparative migration behaviour of 90Sr, 239+240Pu and 241Am in mineral and organic soils of France

The vertical migration of 90Sr, 239+240Pu and 241Am has been studied in two types of soils in France (acid forest soil in the Vosges Mountains and organic-rich alkaline wetland in the Mercantour area). In order to interpret the different migration behaviour of radionuclides, the combination of two approaches are proposed – a statistical study of the evolution of radionuclide ratios ( 241Am/ 239+240Pu, 90Sr/ 239+240Pu) with depth and a calculation of the radionuclide migration rates. Migration behaviour of 90Sr, 239+240Pu and 241Am is significantly different in the Vosges and Mercantour soils. In the Mercantour soil 241Am was found to be less mobile than 239+240Pu. In both profiles 90Sr is more mobile than 239+240Pu. The high sand content (55–60%) and weathering processes of cations in the Vosges soil are thought to be responsible for the larger migration rates of radionuclides in depth, while the high organic matter content (>70%) of Mercantour soil is thought to be responsible for the stronger retention of 241Am in the first 10 cm of the soil.

Forest soil acidification assessment using principal component analysis and geostatistics

Soil acidification and consequent Al release is a problem particularly under forests in mountainous areas of the Czech Republic. It is controlled by a number of factors, like acid deposition, forest type, parent rock, altitude, etc. The Jizera Mountains region presents an area heavily influenced by acidification and forest decline. This paper focused on the effect of stand factors on spatial distribution of soil characteristics of the surface organic (O) and sub-surface (B) horizons from 98 sites using a combination of principal component analysis (PCA) and geostatistics. In the PCA, five principal components (PC) describing more than 70% of total variation were selected. The properties of the O and B horizons (pH, C, N, and S content, potentially dangerous Al forms) were in most cases separated, suggesting different processes and effects in each horizon. Spatial variation of PC scores was analysed using variograms, maps of their distribution were created using kriging. Spatial correlation with stand factors (altitude, slope aspect, forest type and age, soil unit, liming, and grass cover) was analysed using cross-variograms. The surface horizons are more sensitive to external influence (acid deposition, liming, grass expansion) and their spatial variation is stronger. The B horizons are more influenced by forest type (beech vs. spruce) and age, and by soil units (cambic vs. spodic horizons). The effect of stand factors is complex and often indirect. Nevertheless, used combination of pedometrical methods provided concise information about spatial variation and relationships between soil characteristics and the effect of stand factors.