Verhalten einiger radioaktiver Nuklide (freigesetzt durch den Reaktorunfall in Tschernobyl) in typischen Böden Norddeutschlands

Behavior of Some Radioactive Nuclides (Released During the Tchernobyl Disaster) in Typical North German Soils Initial studies carried out after the Tchernobyl disaster on the behavior of radionuclides J-131, Cs-134, Cs-137, Ru-103 and Ru-106 on typical north german soils (podzol both rich and poor in humus, gleysol and fluvisol) showed that after initial distribution, no further shifting of the nuclides took place. Generally, Cs-134 remained in the upper 4–6 cm of the soils; the same was found for Ru-103 in gleysol and podzol rich in humus. In podzol poor in humus and fluvisol, Ru-103 was more detectable in deeper soil sections than the radionuclide Cs-134. During the period of investigations it was found that over 90% Cs-134 was present in the top subsamples of the analyzed soils. Over 90% Ru-103 was detectable in the top sub-samples of the podzol rich in humus and gleysol, while in the top sub-samples of the humus-poor podzol and fluvisol, only 70% or 76% Ru-103 was discovered.     

Evidence for microbial decomposition of organic acids during podzolization

Microbial aspects of podzolization were studied by percolating organic acids through sterile and non-sterile soil in columns. Six columns containing sand from a fluvioglacial sediment were percolated (90 mm d^?1) with mor extract and an oxalate-citrate solution. In three of these, sterilized soil solutions were used. Weathering was enhanced by organic acids which formed complexes with aluminium and iron. In the non-sterile soil columns weathering by organic acids was inhibited at 7–8 cm because the acids were degraded by microorganisms. Weathering was evident from colour change, contents of extractable aluminium and iron, and the micromorphology. Enhanced weathering in the sterile columns was also suggested by larger amounts of aluminium, iron, silica and base cations leached from the columns. Comparison of the output of aluminium, iron and silica from the sterile soil with that from the non-sterile soil, suggests that probably an aluminium-iron-silicate phase was formed in the deeper parts of the non-sterile columns.     

Genetic relationships between ferralsols,podzols and white kaolin in Amazonia

White kaolin has frequently been observed to be associated with ferralsol‐podzol soil systems in Amazonia. In order to evaluate whether such systems favour kaolin genesis and to identify the associated genetic processes, we studied soil organization, mineralogy and groundwater properties of a ferralsol‐podzol soil system with white kaolin located in the High Rio Negro Basin, Brazil. We found that the kaolin was situated near the ferralsol‐podzol transition and that its thickness was related to the depth of landscape incision by regressive erosion. The kaolin was characterized by silicon, iron and titanium (Ti) leaching and aluminium (Al) absolute accumulation. The groundwater that percolates from the podzol to the kaolin can enhance kaolinite precipitation, by supplying Al originating from kaolinite dissolution in the overlying Bh, and kaolin bleaching, by low pH and Eh of the percolating waters favouring iron reduction. The system dynamics imply that the quartz dissolution rate in the kaolin is of at least the same order of magnitude as the kaolinite dissolution rate in the overlying Bh. Within the whole system, Ti appeared to be very mobile.     

Terrestrial sources of methylmercury in surface waters: The importance of the riparian zone on the Svartberget Catchment

The runoff of methylmercury (MeHg) from forested catchments to surface waters has been identified as a potentially significant input of MeHg to the aquatic ecosystem. Little, however, is known of the processes which control the transfer of MeHg from soils to surface waters. This study investigated the potential terrestrial sources of MeHg in runoff by sampling profiles of soil solution chemistry and determining the flux of water through those profiles into two tributaries on the Svartberget Catchment in northern Sweden. One study profile was from the podzol soil that covers most of the catchment area. The other profiles were taken in the riparian zone of each of the two tributaries. Soil solution was extracted from the soils by centrifugation. High catchment soil solution concentrations of MeHg (>1 ng l^?1) occur in the surface layers of the soil, but overland flow on the catchment is rare. MeHg concentrations in the podzol profile dropped to less than 0.2 ng l^?1 in the mineral soil just 5 cm below the mor layer. In the riparian soil profiles sampled in October, MeHg concentrations were higher (ca. 0.4 ng l^?1), but in a July sampling the concentrations in the riparian profiles were comparable to those in the podzol (i.e. < 0.2 ng l^?1). Very high concentrations of MeHg were found in the streambank sphagnum mosses (>2 ng l^?1) partially submerged within the stream. The concentrations of MeHg observed under the podzol soil were insufficient to sustain the concentration of MeHg in runoff from the forested subcatchments where podzol profiles cover more than 70% of the surface area. The only sources of additional MeHg that lie along major runoff flow pathways are the riparian soils and mosses on the streambanks. It is therefore hypothesized that output of MeHg from the forest areas of the catchment is controlled by the biogeochemical processes in the riparian zone.     

Weathering of Karroo argillite under equatorial conditions

The mineralogical composition of a soil catena from Karroo argillite (shale) from Bengamisa, in oriental Zaire is reported in relation to the particle size distribution and to the extent of quartz enrichment as a measure of weathering. Chemical properties such as exchangeable Al³⁺ and base saturation were strongly influenced by the relief. Of the free citrate-bicarbonate-dithionite (CBD) iron oxides, less than 5 to 10% were mobile in pH 3 ammonium oxalate. The proportion of aluminum mobilized in the latter was 17 to 44%, whereas only 0.1 to 1% of the SiO₂ was. Feldspars were almost entirely altered by the weathering process and the weathering of mica resulted in increased mica contents in the clay and fine silt fractions and in labile expanded mixed-layer complexes containing mica, vermiculite and montmorillonite. The kaolinite content increased with depth of solum, presumed to reflect degree of soil development.     

Aluminium Mobility at an Acid Sensitive Site with High S-Deposition

Soil water at an acid-sensitive forested catchment in southwestern Poland has been studied for four years. Median base saturation (BS) is only 5% in the podzol B-horizons. Very low pH values in the soil water from the O-horizons (10- and 90 percentiles pH 3.5 and 4.3) increased to a typical median pH in the B-horizons of 4.4, mainly by release of inorganic labile aluminium (Al_i). Median concentrations in the B horizons were 3.4mg Al_i L^?1. Al-soil/soilwater interactions were studied over a large span of sulphate concentrations resulting from both a generally decreasing S-deposition during the last decades and an increase in precipitation during the study period. These changes led sulphate to leach from the mineral soil. Aluminium mobilisation is better described by jurbanite- than by gibbsite solubility. For the soils with aluminium saturation (AlS) >90%, there is a tendency that the concentration of Al³⁺ decreases less than divalent base cations with a decrease in SO₄ ^2? concentration. This causes the critical load molar ratio (R_CL={Al³⁺}/{Ca²⁺+Mg²⁺}) to increase with a decrease in the sulphate concentration in soil water, which is not in agreement with a simple cation-exchange model.     

SANDSTONE-DERIVED SOILS OF A CATENA AT IPERU, NIGERIA

Chemical and mineralogical properties of five soil profiles of a catena in Iperu, Western State of Nigeria, are reported. The pH values of the subsoils are extremely acid. Acidity decreases with improved drainage in the subsoils (pH 4.0–5.8). The cation exchange capacity (C.E.C.) of the soils range from 3.0 to 16.2 me/100g of soil. The silt: silt+clay ratio, calcium: magnesium ratio and Fe₂O₃:Al₂O₃ ratio are used as weathering indices. The low values of the silt: silt + clay index indicate that the soils must have undergone advanced weathering. The magnitude of the Ca: Mg ratio indicates that more calcium than magnesium is available in the soils. The values for sodium and potassium are extremely low. More iron than aluminium was extracted from the soils by the dithionite-citrate method. Kaolinite is the most abundant clay mineral. Halloysite, interstratified clay materials, vermiculite, quartz, and mica are present in considerable amounts. The silt fraction in which quartz is the most abundant mineral, also contain some kaolinite and mica.     

Proto-imogolite and the process of podzol formation: a critical note

The presence of imogolite or other poorly crystalline aluminosilicates in the lower B horizons of podzols can be explained by neoformation from silica in the percolating soil solution and aluminium species liberated from their organic bond by activity of micro-organisms. There are physicochemical arguments refuting the alternative concept that iron and aluminium are transported down the profile as short range order aluminosilicates such as proto-imogolite which would thus play an important role in podzol formation. There is ample evidence to attribute the mobilization, translocation and precipitation of sesquioxides to complexing organic compounds.     

The weathering of ferruginous chlorite in a podzol from argyllshire,Scotland

The dominant mineral in the clay fractions from the basal horizons of a podzol developed on till derived mainly from chlorite-schists in Argyllshire is oxidized, iron-rich chlorite. Towards the profile surface, the chlorite decreases in amount, becoming absent in the A₂ horizon in which the dominant mineral is a complex dioctahedral interstratified phase formed from dioctahedral mica and composed of mica and vermiculite. The absence of any trioctahedral mineral in the A₂ horizon together with the marked loss of iron and magnesium from the clay fraction from this horizon indicates that the chlorite, a thuringite, has been destroyed, the only detectable product being goethite. In other apparently similar soils chlorite persists throughout the profiles. As the Eredine podzol contains translocated humus in the B₂ horizon, it is suggested that during podzolization, organic solutions percolated downwards from the surface, formed complexes with iron and aluminium from the chlorite structure, removing them to the B₂ horizon, and thus eventually dissolved out the chlorite from the A₂ horizon.     

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.     

Characterization of iron in alkaline EDTA and NH4OH extracts of podzols

Mössbauer and ESR spectroscopy have shown that the iron extracted from the Bh horizons of an iron humus podzol and an iron podzol by EDTA at pH 9.1 is predominantly in the form of complexes * 1 The use of the word ‘complex’ in this paper in the context of polymeric iron species and organic matter is not intended to imply any single specific type of complex, such as exists in Fe(II1) EDTA, for example, but to embrace many possible modes of association including salt formation, direct coordination, Van der Waal's adsorption, and electrostatic attraction.
of polymeric Fe(III) hydroxide and oxide with organic matter (O.M.). Small amounts of monomeric Fe(III)-O.M. and Fe(III)-EDTA complexes also occur. In contrast EDTA at pH 7 extracts iron from these podzols predominantly in the form of iron-EDTA complexes. Some monomeric Fe(III)-O.M. complex also occurs in a pH 9.1 NH₄ OH extract of these horizons and in a pH 9.1 EDTA extract of the B₃ horizon of a peaty podzol. Dialysis experiments show that the particle dimensions of the polymeric hydroxy Fe(III)-O.M. complex, which accounts for about 66% of the Fe extracted from the iron humus podzol and about 36% of that from the iron podzol, are greater than 2.4 nm. The thermal behaviour of the Mössbauer peaks indicated that the size of the iron cores was of the order of 5 nm, thus suggesting that the complex probably consists of hydroxyiron cores surrounded by large organic molecules. Results from XRD and IR suggest that these hydroxyiron cores may have structural organizations similar to those of goethite and ferrihydrite. The relationship between these forms of iron in the extracts and those in the soil is briefly discussed.     

13C/12C Ratios of soil organic matter as indicators of vegetation changes in the congo

The ¹³C/¹²C ratios were determined for the organic matter of all horizons of a podzol profile and of the A₁ horizons of some ferrallitic soils, in some grass shoots and in a fossil root fragment from the B_2h horizon of the podzol. The isotope ratio in the organic matter of the A₁ horizon of the podzol matches those in grass shoots from the present savanna vegetation. The ratios in the lower horizons match those of organic matter in the A₁ horizons of soils under forest and that of the fossil root fragment in the B_2h horizon. The ratios thus demonstrate that the humus enrichment of the B_2h horizon of the podzol occurred while it was under forest vegetation and that the present grass vegetation did not take part in the podzolization process. The differences also indicate that savanna replaced forest vegetation after the profile had been formed.     

A 13C-NMR study of the interactions of soil organic matter with aluminium and allophane in podzols

The stabilization of organic matter in soil by interaction with aluminium (Al) or allophane is important in maintaining soil quality, and in retarding the decomposition of soil organic matter. Complexation of Al by soil organic matter may also ameliorate Al toxicity. Here we use ¹³C-NMR spectroscopy to assess the interaction of soil organic matter with both Al and allophane in two poorly drained podzols containing only trace amounts of iron. The ¹³C-NMR spectrum of the subsoil of the allophane-rich One Tree Point podzol shows an intense peak at 179 p.p.m., assigned to carbon in carboxylic acids. This peak shifts to 177 p.p.m. after removal of allophane (11% of the soil mass) by treatment with HF. We infer that the carboxyl groups in the organic matter are bonded to structural Al on the surface of allophane spherules. In the non-allophanic Te Kopuru podzol, on the other hand, the organic matter apparently interacts with Al ions in the soil solution. This soil also has more aromatic carbon and fewer carbons in carboxyl and carbohydrate structures than the allophanic sample. There is an indication that allophane stabilizes carbohydrate groups as well as carboxyl groups.     

Assessment of the Regional Variation in Weathering Rates of Loess and Clay Soils in The Netherlands

To calculate critical acid loads or to predict elementconcentrations in the soil solution, information on weatheringrates is essential. Several studies have taken place in theNetherlands to obtain weathering rates for non-calcareous sandysoils. Recently information on weathering rates in less vulnerable loess and clay soils have become available. However,up to now no system is available to estimate weathering rates ona regional scale by relating them to regionally available soilproperties.To obtain weathering rates of loess and clay soils on a regionalscale for the Netherlands, the applicability of a statisticalregression model and the process based PROFILE model have beenevaluated. Both models were calibrated on a set of laboratoryexperiments. To evaluate their predictive power, both methodswere validated on a number of sites for which field weatheringrates were available.Predictions with the statistical model, for the individual basecations, were generally within a factor 2 of the calculatedhistorical weathering rates, except for Ca, which wasoverestimated, by a factor 3 to 4. PROFILE stronglyoverestimated all weathering rates using both standard parameters and in particular after calibration on the laboratoryrates. However, PROFILE predicted weathering rates of the loesssoils quite good after calibration on historical weatheringrates, indicating that the downscaling procedure used in PROFILEto translate laboratory to field weathering rates is inadequatefor the considered soils.The statistical model was applied to predict weathering rates,for the Netherlands on a 1 × 1 km grid scale. Weathering rates at the present pH values in forested loess and clay soilsranged from 135 to 6000 mol_c ha^-1 a^-1 in loesssoils and from 100 to 1750 mol_c ha^-1 a^-1 in claysoils.     

The Weathering of Mineral Soil by Natural Soil Solutions

Chemical weathering is an important neutralisation process and sourceof cations in forest soil. The presence of dissolved organic matter in the soil solution can have a considerable influence on weathering release. The aim of this study is to compare the weathering potentialof natural soil solutions, collected from Norway spruce, Scots pine and birch sites, to release Al, Ca, Mg, K, Na, and Si from the fine fraction in the C horizon of a podzol. Residual organic matter in the mineral soil was removed with H₂O₂. The <0.06 mm fraction of the mineral soil was suspended in soil solution, collected from the three sites, for 11 days with continuous agitation. Ultrapure water was used as a control. The pH of the suspensions was maintained at 5.4 by bubbling with CO₂. The initial mean DOC concentrations in the soil solutions were 65, 56 and 40 mg L^-1 for the spruce, pine and birch sites, respectively. The presence of DOM in the soil solution did not significantly enhance the capacity to weather mineral soil material, and no systematic differences were found between the three sites. However, Al release from the mineral soil was slightly higher in the soil solutions containing DOM compared to the control solution with no DOM. The proportions of DOM fractions capable of enhancing weathering were comparable with those reported in earlier studies. The weathering of metals was found to be primarily due to pH-driven processes. The lack of considerable weathering enhancement by DOM could be due to the fact that the cation-binding sites of the organic ligands were already saturated by e.g. Al and Fe in the soil solution derived from these podzolic, Al- and Fe-rich soils.     

The role of organic acids in the soil solution chemistry of a podzolized soil

The soil solution chemistry of a podzolized soil in the north of Sweden was monitored for four years using percolation lysimeters. Weak organic acids were a major constituent of the soil solution and are important because of their ability to form complexes with aluminium. Dissolved organics leached from the mor layer enhance the weathering rate in the eluvial horizon by forming complexes with aluminium, especially during the autumn when the leaching of dissolved organics was greatest. The weak organic acids were titrated and their pK_a values were evaluated. Aluminium was speciated with an ion-exchange method and by applying equilibrium calculations. Formation constants for the organic aluminium complexes were calculated to be log K_Along=5.42±0.32 m ^?1 (n=13) in spring and summer and log K_Alorg=4.87±0.14 m ^?1 (n=6) in autumn. Equilibria of Al³⁺ with solid phases were also examined using solubility constants. Percolation lysimeters below undisturbed and cut-off mor layers were compared.     

Estimating dissolved organic carbon in natural waters by UV absorbance (254 nm)

A close correlation exists between dissolved organic carbon (DOC) concentration and UV absorbance at 254 nm (A₂₅₄) in natural waters. DOC and A₂₅₄ were measured for soil solutions, throughfall, stemflow, and surface waters collected from a forested site located in eastern Austria. The slopes of lines determined by linear regression of DOC versus UV absorbance were very similar to those determined for wet deposition and throughfall samples collected in Nordrhein-Westfalen, Germany by Bartels (1988). The intercept of the regression line in the current study indicates that approximately 1 mg L¹ of non-UV-absorbing DOC is present; it is suggested that this is due to saturated aliphatic compounds such as acetate or formate.     

The influence of increased NH4+ deposition rates on aluminium chemistry in the percolate of acid soils

The influence of different NH₄⁺ loads on aluminium speciation in percolating water was studied on acid luvisols with similar soil-pH values but with different soil adsorption surface characteristics. All of the applied NH₄⁺ was nitrified and therefore led to proton production. Thus, Al displacement in the percolate was increased. The extent of this enhanced translocation was found to be chiefly a function of the amount of exchangeable base cations which buffered the protons produced by nitrification. The proportion of the different Al species in the percolate was altered at large NH₄⁺ loads. Very large A1³⁺ concentrations eliminated Al species bound to dissolved organic matter and particles, presumably because of flocculation and precipitation of organic ligands. Furthermore, increased NO₃^? and A1³⁺ concentrations enhanced the desorption of F^? giving rise to an additional increase in Al displacement by the formation of Al fluoro complexes in the aqueous phase.     

Die kurzfristige pH-Pufferung von gestörten und ungestörten Waldbodenproben

Short-timed pH-buffering of disturbed and undisturbed forest soil samples The pH buffering of disturbed and undisturbed soils under spruce (podzol and podzolic cambisol derived from phyllite, eutric cambisol derived from basalt) was studied in the laboratory by adding H₂SO₄ in ecologically relevant concentrations (pH 5.6–2.0). For the cambisol with crumb structure no difference was found. 80–90% of the added protons were neutralized by release of Ca and Mg. Disturbed samples of the podzol buffer less than 70% of the applicated acid. For undisturbed samples the maximum buffering rate of 185 g H⁺/ha · h is reached with a proton load of about 500 g H⁺/ha · h (related to 4 cm soil depth). Buffering behaviour of the podzolic cambisol lies between the podzol and the cambisol. 70–90% of the proton input is buffered in the disturbed samples while the undisturbed one does not reach its maximum buffering rate, even with high proton load. In this soil Al-release is the most reactive buffer.