Schwermetallgehalte in Waldböden Nordrhein-Westfalens -Klassifizierung und kartographische Auswertung

Heavy metal contents in forest soils of North Rhine-Westphalia - classification and cartographic evaluation Many forest areas in North Rhine-Westphalia (Germany) are contaminated with heavy metals. To evaluate this pollution of forest soils and its geographical distribution all available literature data on total heavy metal contents in forest soils of North Rhine-Westphalia were included in this study. The results show that an accumulation of heavy metals, especially of Pb, occurred in the litter layer and in the litter layer and in the topsoil. The highest values were measured in the vicinity of industrial areas and at elevated locations such as Egge Mountains and Teutoburger Forest. About 50 % of the samples from the litter layer and the topsoil have pH values below 3. 4. Since the translocation of heavy metals in the soil profile at this low pH increases, potential risk from the mobilization of high stores in the litter layer was estimated for several locations of North Rhine-Westphalia.     

Verhalten von Schwermetallen in Böden 1. Untersuchungen zur Schwermetallmobilität

Behaviour of heavy metals in soils. 1. Heavy metal mobility 158 soil samples with widely varying composition were analysed for their total, EDTA, DTPA and CaCl₂ extractable contents of Cd, Zn, Mn, Cu and Pb. By means of single and multiple regressions the relations between the different heavy metal fractions and the pH, organic carbon and clay content were considered. The correlations between the total, EDTA and DTPA extractable contents are very close, whereas the CaCl₂ extractable contents are not or only weakly correlated with these fractions. According to these statistical results the former fractions are considered to be the total quantity (total content) and the reactive quantity (EDTA and DTPA extractable contents) of the heavy metals, whereas the CaCl₂ extractable fraction represents the mobile fraction of the heavy metals in soils. The multiple regressions show that the mobile content of heavy metals is closely correlated with each of the quantity fractions and with soil pH. In the same way the proportion of the mobile fraction (in %) of the total, EDTA and DTPA extractable heavy metal content of the soil samples is closely related to the soil pH. Hereby the proportion of the mobile content of the various elements increases in the pH range 6,5 - 3 below element-specific threshold pH values (in brackets) in the order Cd (6,5) > Mn (5,7) > Zn (5,3) > Cu (4,5) > Pb (3,5). In the pH range 6,5 - 7,5 mainly Cu and to a lesser degree also Pb show an increasing mobility due to the influence of soluble organic substances.     

Use of Reference Soils in Determinations of 0.01 M Calcium Chloride Available Metals

There are few readily available standard reference soils for which 0.01 M calcium chloride (CaCl₂) soil extraction available metals data are available. This study assessed the ease with which new available metals data could be generated for reference soils. Data on 0.01 M CaCl₂ available elements for four reference soils from the Wageningen Evaluating Programs for Analytical Laboratories and three reference soils from the Australasian Soil and Plant Analysis Council proficiency testing program are presented. It is difficult to generate new 0.01 M CaCl₂ available metal values for standard reference soils, because trace element concentrations are low and measurements have relatively high variability. We suggest that laboratories can use reference soils as quality control samples in the analysis of 0.01 M CaCl₂ available metals by reporting recoveries for major elements (e.g., potassium [K], magnesium [Mg], and sodium [Na], for which reference values are of high reliability) to provide assurance of acceptable extraction efficiency.     

Distribution of major elements and trace metals as indicators of technosolisation of urban and suburban soils

Purpose

Can geochemical characteristics indicate the human impact on soil formation (technosolisation) for urban and suburban soils? This question is assessed for the city of Marrakech located in one of the main agricultural areas of Morocco and characterized by a very rapid rate of expansion. The aim of this work is to assess geochemical properties of surface horizons of urban and suburban soils and to compare them with land use types.

Materials and methods

Fifty-eight surface soil samples were collected in different sectors of the city with different land use histories. As land use can be defined as the human use of land, these sampling sites were selected according to the current human activity (e.g., residential districts, agriculture, market-gardening, traditional, or industrial activities) and according to the superposition of the land use over time. All samples were air-dried, disaggregated, homogenized, and then sieved through a 2-mm mesh. Major elements and trace metals were measured in the soil using X-ray fluorescence spectroscopy. For technical limits, Cd was measured using atomic adsorption spectrometry.

Results and discussion

Urban and suburban soils of Marrakech present generally similar geochemical compositions for many elements. Siliceous (SiO₂) compounds related to the parent material are dominant in these soils. However, the significant concentrations of P₂O₅ and CaO, measured in some of the urban soils studied, can be attributed to anthropogenic inputs of phosphorus (P) and technic materials, mainly building materials composed of cement and gypsum (plaster). Soils collected from agricultural areas irrigated with urban wastewater and soils developed on rubbish dumps are the most contaminated by metals (e.g., Cu, Zn, and Pb). Therefore, the distribution of major and trace elements in soils underlines the considerable impact of urban land uses.

Conclusions

Human activities determine the type of land use, impact the urban environment, and cause a wide spatial diversity of soil quality. The urban and suburban soils of Marrakech contain similar major element distributions except for strongly anthropised soils (soils developed on rubbish dumps and agricultural soils irrigated with urban wastewater). Unlike major elements, trace elements present systematically significantly higher concentrations in urban soils than those measured in control soils. In these conditions, the highest concentrations exceed international clean-up standards and are correlated with land use type. Phosphorus, Ca, and several heavy metals are proposed as indicators of human impacts on soil characteristics in urban and suburban environments.     

Chloroform-labile trace elements in soil via fumigation-extraction: Steps towards the soil microbial ionome beyond C:N:P

Secondary and trace elements may be limiting soil microbial functioning, albeit microbial demand and content remain largely unknown and methods for their in situ detection are limited. Thus, the objective of the present study was to take the first step towards the method development for the assessment of the soil microbial ionome, that is, the elemental composition of soil microbial communities. Chloroform (CHCl₃) fumigation extraction was used for the detection of microbial CHCl₃-labile secondary and trace element concentrations in soils. The suitability of two extractants (NH₄NO₃, CaCl₂) for the quantification of CHCl₃-labile concentrations of phosphorus, sulphur, potassium, sodium, and magnesium, as well as selenium, iron, zinc, manganese, copper, cobalt, nickel, molybdenum, vanadium, boron, silicon, barium, arsenic, and cadmium, were tested in six agricultural soils. Additionally, three soil to extractant ratios (1:5, 1:10, and 1:20) and two extraction durations, 1 or 2 h, were tested in a subset of two soils. Out of the two extractants tested, 0.01 M CaCl₂ was found to be the best-suited extractant. For CaCl₂, a soil-to-extractant ratio of 1:20 with an extraction time of 1 h was best for the majority of elements in the two soils tested. In a limited number of agricultural soils, we were able to show that CHCl₃ fumigation extraction can successfully be applied to the elements phosphorus, sulphur, potassium, sodium, magnesium, zinc, manganese, copper, nickel, vanadium, boron, silicon, and barium to yield a CHCl₃-labile element fraction. Conversion values to microbial biomass, accounting for elements contained in the cell envelope components, which are mostly not extractable, and to account for adsorption to soil colloids during extraction are yet to be determined in a larger variety of soils. To overcome some of the limitations of the fumigation extraction approach for secondary and trace elements, a pre-extraction step may provide a suitable solution.     

Blei- und Cadmium-Status Berliner Böden

Lead an cadmium conditions of Berlin soils Pleistocene sediments of Berlin contain 10 mg/kg Pb and 0.1 mg/kg Cd, but debris of the city 80 mg/kg Pb. The topsoils are enriched with 60–100 mg/kg of anthropogenous Pb, near roads more than 200 mg/kg, and with 0.3–0.6 mg/kg Cd. Only low quantities of both elements were soluble in NH₄-acetate, but half of the polluted elements was extractable with AEDTA, the unextractable part being enriched in the clay fraction. Exchange experiments show very high sorption rates of soluble lead, but in case of cadmium sorption was much lower so that this element can percolate especially sandy acid soils with low humus contents in higher amounts.     

Über die Magnesiumverarmung der Böden in den Hochlagen des Inneren Bayerischen Waldes

On the depletion of magnesium in soils of high altitudes of the Inner Bavarian Forest A widespread magnesium deficiency in stands of Norway spruce, growing at high altitudes of the Bavarian Forest, was the reason for an extensive soil survey and for hydrological-hydrochemical studies of these areas. The prevailing soils are Fragiorthods and Fragiumbrepts (great soil groups after US Soil Taxonomy). Total element contents of soils show clear relation to the respective parent rock. These relations are missing for exchange capacity (CEC_e) and exchangeable elements. This fact can be explained by a consolidated layer in the upper soil and high annual precipitations, which favor episodic interflow with low pH (about 4,0) and high SO₄- respectively NO₃-concentrations. Water of the deeper ground (baseflow) however, shows high pH-values (about 6,5) and low SO₄-concentrations. Increased concentrations of SO₄ and NO₃ in seepage water (interflow) show relation to considerable atmospheric S- and N-input. Furthermore the qualitative evaluation of the nutrient balance in these forest ecosystems revealed a release of SO₄ and NO₃ in soils of the high elevations, which must be followed by an equivalent removal of cations. The balance of element translocations in soil profiles shows, that magnesium is mostly affected by these depletion processes.     

Bestimmung von Mikronährstoffen und Schwermetallen in Böden mit dem Verfahren der Elektro‐Ultrafiltration (EUF) durch Zugabe von DTPA

With the electro–ultrafiltration (EUF) technique, the plant availability of several plant nutrients in soils can be characterized. The basic principle of EUF is that an electric field is induced using platinum electrodes. Ions in the soil suspension move either to the cathode or to the anode and are filtrated through ultra‐membrane filters. In the standard EUF procedure, two extractions steps are used: 30 min at 20°C and 5 min at 80°C. However, the determination of micronutrients and heavy metals with the standard EUF procedure is not possible, because the solubility of these elements in water is low and most of the watersoluble elements are precipitated when passing the platinum electrodes. The addition of DTPA, a well known complexing agent, during a third EUF fraction (5 min at 80°C) enables extraction of micronutrients and heavy metals. Highest concentrations in the 33 soils of the study were found for iron, followed by zinc, manganese, lead, copper, and nickel. Lower concentrations were obtained for cobalt, chromium, cadmium, and molybdenum. For two soils, the EUF/DTPA procedure was compared to CaCl₂/DTPA and EDTA soil extraction methods, showing that higher or comparable amounts were found with CaCl₂/DTPA and much higher amounts with the EDTA method. These results reveal that the EUF/DTPA technique in principle can be used for the determination of plant‐available micronutrients and heavy metals. However, in a next step the relationship between EUF/DTPA‐extractable elements and their availability for plants needs to be quantified.     

Comparison of methods for measuring heavy metals and total phosphorus in soils contaminated by different sources

The relationships between the concentrations of zinc (Zn), lead (Pb), copper (Cu), nickel (Ni) and chromium (Cr) as measured by X-ray fluorescence analysis (XRF), aqua regia, and HNO₃ pressure digestion were studied in soil samples covering a wide range of heavy metal concentrations. The soils were contaminated by sewage sludge, exhaust depositions, river sediments of mining residues, and dump material. The question was addressed whether the source of heavy metals or other soil properties affect the relationship between these three methods. The aqua regia-digestible fraction of the five heavy metals reached on average 64% of the XRF-detectable content. The pressure accelerated HNO₃-digestible fraction of the five heavy metals was on average 71% of the XRF-detectable content; the respective phosphorus (P) fraction reached a median of 75%. This suggests that HNO₃ pressure digestion can also be used for characterizing the total P content of soils. Aqua regia extraction and HNO₃ pressure digestion gave similar values for Zn, Pb, and Cu, which dominate the heavy metal load of most contamination sources. Significantly higher Cr values were obtained by HNO₃ pressure digestion than by aqua regia extraction. Additionally, the Cr contents were affected by the source, e.g. sewage sludge had relatively high contents of aqua regia and HNO₃ pressure extractable contents in comparison to the XRF values. The element-specific relationships between the three methods were all highly significant. However, the respective multiple linear regression models were in most cases affected by soil organic carbon (C), in some cases by clay or soil pH.     

The risk element contamination level in soil and vegetation at the former deposit of galvanic sludges

Purpose

Hazardous waste deposits with high contents of risk elements can represent a potential environmental hazard via penetration of these elements into soil and vegetation. In this case, the former deposit of galvanic sludges in Dolní Lipka, Czech Republic, was investigated. The deposit was temporarily remediated by a thick soil layer cover. The total and mobile risk element contents were determined within the profile of the soil cover as well as the element contents in the vegetation growing on the cover to assess the potential environmental threat of the deposit

Materials and methods

The plant samples were collected from nine sampling areas, each of 3?×?3 m. The stratification of risk elements within the soil profile was determined where the soil samples were collected in depths of 0–10, 10–40, 40–70, 70–100, and 100–140 cm. The total element contents were determined in aboveground biomass and roots of selected plant species and pseudo total content (extractable with aqua regia) in soils. The mobilizable pool of elements in soils was determined after extraction with a 2 mol L^?1 solution of HNO₃ and a plant-available pool of elements after extraction with 0.11 mol L^?1 solution of CH₃COOH.

Results and discussion

From the perspective of the vegetation and soil’s risk elements content, the dump did not meet criteria for a safe hazardous waste landfill in any way during the sampling time. According to the results, the elements can be divided into three groups: (i) low levels of elements within whole profile—As and Cr; (ii) high levels of elements concentrated in the deepest layer of the soil without significant penetration of the upper layers—Cu, Mo, Pb, Ni, and Zn; and (iii) the elements penetrating the upper layers of the soil—Cd and Hg.

Conclusions

The third case poses a serious environmental risk requiring more intensive investigation on the bioavailability of these elements at the site, and subsequently, permanent remediation of the deposit.

     

Distribution Assessment and Source Identification Using Multivariate Statistical Analyses and Artificial Neutral Networks for Trace Elements in Agricultural Soils in Xinzhou of Shanxi Province, China

Multivariate statistical analyses were used to assess the contents and distributions of trace elements in agricultural soils in Xinzhou of Shanxi Province, China, and to identify their sources. Samples with high levels of trace elements were concentrated in eastern Xinzhou, with contents declining from the east to west. Principal component and redundancy analyses revealed strong correlations among Co, Cu, Mn, Ni, Se, V, and Zn contents, suggesting that these elements were derived from similar parent materials. There were also strong correlations between the contents of these elements and soil properties. Contents of Cd and Pb were significantly higher in the agricultural soil samples than in the background soil samples (P < 0.05), and were higher in areas with higher levels of gross domestic product but decreased with distance to the nearest road. Therefore, human activities appear to have a strong influence on the Cd and Pb distribution patterns. A novel artificial neural network (ANN) model, using environmental input data, was used to predict the soil Cd and Pb contents of specified test dates. The performances of the ANN model and a traditional multilinear model were compared. The ANN model could successfully predict Cd and Pb content distributions, projecting that soil Cd and Pb contents will increase by 128% and 25%, respectively, by 2020. The results thus indicated that the economic condition of an area has a greater effect on trace element contents and distributions in the soil than the scale of the economy itself.     

Soil Extraction of Readily Soluble Heavy Metals and As with 1 M NH4NO3-Solution - Evaluation of DIN 19730 (6 pp)

Background, Aims and Scope   The German DIN 19730 (1997) describes a method for the extraction of readily available trace elements from soil by shaking the soil with 1 M NH4NO3-solution. Based on this method trigger and action values for the transfer of heavy metals and arsenic from soils to plants have been published in the German Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV 1999). The chemical mechanisms involved in this soil extraction procedure were evaluated in some detail to create requirements to improve environmental risk assessment for soil contaminations.Methods   The chemical mechanisms involved when soil is extracted with 1 M NH4NO3-solution were evaluated. This was followed by a laboratory experiment to quantify the formation of soluble metal ammine complexes during the extraction. Cd, Zn, Ni, Cu, Co and Hg were extracted from 16 soils by 1 M NH4NO3, 1 M KNO3 and water. pH was adjusted in 5 steps between 5.0 to 7.5. The potassium cation (K+) and the ammonium cation (NH4+) behave similarly when cations from soil surfaces are desorbed, because they have almost identical ion radii (e.g. 0.133 and 0.143 nm). K+ does not form ammine complexes with other ions, whereas, due to the increasing formation of NH3 from NH4 by dissociation with rising pH, metal ammine complex formation is an important process in soil extraction when using ammonium salt solutions. A difference in the extraction efficiency of 1 M NH4NO3- and 1 M KNO3-solution for a given soil can therefore be attributed to the formation of soluble metal ammine complexes. Conclusion   Our experiments resulted in considerably higher extraction rates of Cu, Cd and Hg by 1 M NH4NO3-solution as compared to 1 M KNO3-solution. This effect, caused by the formation of soluble metal ammine complexes, was only evident in soils with higher readily soluble heavy metal contents and a soil pH above 6 – 6.5 for Cu and 7 – 7.5 for Cd. Further chemical mechanisms involved when soils are extracted with 1 M NH4NO3 are a moderate decrease in pH and an increase in ionic strength. Most of the colloids and parts of soluble metal-organic complexes are precipitated due to the high ionic strength. High ionic strength also decreases the activity of metal-OH+ species and the electrostatic potential of the particle surfaces, which in turn, increases the desorption of heavy metal cations from negatively charged soil surfaces. In contrast, the adsorption of anions like arsenate is favoured by the decreasing electrostatic potential. The prediction of heavy metal uptake by plants from the results of the 1 M NH4NO3-solution extraction fits well for elements, which are mainly bound by low strength electrostatic forces to the soils. Such conditions are found in acidic soils for Cd and Tl, which have a low tendency for hydrolysis compared to other heavy metals. The correlation between 1 M NH4NO3 soil extraction and plant uptake is less significant for Ni and Zn. Only low positive correlation coefficients have been found for Pb, As, Hg and for the Cu-uptake by wheat. Imprecise prediction of plant uptake of heavy metals by the extraction with 1 M NH4NO3-solution is mainly caused by conditions leading to an overestimation of plant availability such as elements are strongly bound to soils, or low soluble trace element contents in soils. Neutral to alkaline soil pH can also lead to imprecise prediction due to increasing formation of soluble metal-organic (Cu, Pb, Hg) and metal ammine (Hg, Cu, Cd) complexes and less importantly due to the formation of colloids. Therefore, at low 1 M NH4NO3-extractable soil contents usually no high plant contents are to be expected. Recommendation and Outlook   Extraction of soil with 1 M NH4NO3-solution is a suitable method for the determination of readily soluble and plant available trace element contents. The chemical soil extraction process may cause misleading predictions of the transfer of trace elements to plants for some soil properties. This knowledge should be used to improve risk assessment of soil contaminations. It has to be considered, that the processes involved in plant uptake of trace elements are too complex to expect that just one soil extraction method can always guarantee a correct prognosis of toxicological significant element contents in plants. Soil analyses may be used for the preliminary examination of suspicious areas and the demarcation of contaminated areas. The results of soil analyses should be checked additionally by plant analyses especially under conditions with a high probability for misleading results by the 1 M NH4NO3-extraction. Alternatively, extraction with 1 M KNO3-solution can be performed to exclude the effect of metal ammine complex formation.     

Die Bedeutung von hohen Aluminiumgehalten für die Humusanreicherung in sauren Waldböden

The role of aluminium on humus accumulation in acid forest soils The impact of soil-borne aluminum on humus accumulation was investigated in a forest soil of the chestnut zone (Castanea sativa) in southern Switzerland (Ticino). Soil samples of two soils formed on bedrocks which differ mainly in their aluminum content were extracted with HNO₃, NH₄Ac.-EDTA, NH₄Cl, KCl, and NH₄F-HCl and analyzed for the most abundant elements. On gneiss which contains up to about 10% of total aluminum the common soil type in this area is a Cryptopodzol. This soil is similar to the nonallophanic Udands. It is rich in wellhumified organic matter and shows dark-colored A_h-, A(E)- and B_h-horizons. The soil samples of these horizons are extremely rich in nonexchangeable aluminum which is, however, extractable with NH₄Ac.-EDTA. It is assumed that this Al is intimately bound to the organic matter. The soil samples of these horizons contain large amounts of HNO₃-extractable phosphorus. Up to 90% of this P appears in the organic fraction. The content of NH₄F-HCl-extractable P is only 0.7 to 3.4 mg/kg. It is concluded that due to excessive Al in the organic matter the humus mineralization is inhibited compared to the Haplumbrepts of the region.     

Schwermetallverteilung und Tongehalte in Böden

Heavy metal distribution and clay contents in soils . In soil profiles differing considerably in horizon pattern and parent material the contents of Mn, Zn, Cu and Co were correlated with those of clay (and CEC), of total Fe (and dithionite soluble Fe) and - after relation to clay - with C. The correlations with clay, CEC, Fe_t and Fe_d were in all cases positive and highly significant, though differing between the different metals and between the references. Deviations for all elements are due to lithogenic differences in soils from mesozoic sediments and for Mn also due to its lower pedogenic stability. The correlations with C were not significant, since O horizons were not yet investigated. The ‘mobility’ of the heavy metals ( = EDTA + NH₄O Ac-extractable in relation to total amount) in topsoils could be more correlated (negative) with the reserves than with other soil features. Relating the ‘immobile’ heavy metal contents to the other soil features considerably improved the correlations.     

Einfluß langjähriger Gülledüngung auf den Nährstoffhaushalt des Bodens. 1. Mitteilung: N-Akkumulation und N-Nachlieferungsvermögen

Influence of long-term slurry application on soil nutrients. 1. N accumulation and N mineralization potential The influence of longterm slurry applications on the total N content, N fractions and N mobilization potential of the soil was investigated. The following results were obtained:

• – Application of high amounts of slurry over a long period of time resulted in higher total N contents not only in the upper soil layers but also in the layer 60–90 cm.
• – In two sites the higher total N contents are mainly resulting from higher contents of hydrolyzable organic N compounds and in one site of higher contents of non hydrolyzable organic N compounds.
• – The influence of the slurry application on the content of non exchangeable NH₄⁺ is depending on the K saturation of the clay minerals.
• – In incubation experiments N mobilization of the soils supplied with slurry was higher as compared to soils supplied with mineral fertilizer.
• – A highly significant correlation is existing between N mobilization and the content of hydrolyzable organic N compounds and the N_org fraction, determined by means of EUF, respectively.
• – The N_min content of the soils supplied with slurry was higher during the whole growing season.

     

Vereinfachte Bestimmung der Basenneutralisationskapazität (BNK) stark saurer Böden

Simplified method to determine the base-neutralizing capacity of strongly acidified soils The base-neutralizing capacity (BNC) is an important property to characterize acid soils. The BNC can be reliably determined by soil-base titrations (BNC_tit). But these methods are work-expensive, and a large amount of soil material is needed. Such a large amount of soil material is not available if the soil is sampled by a hand-auger (e.g. mapping, areal investigations). Known buffer methods require less soil material, but have some shortcomings. Therefore, the well known Schachtschabel-method with calcium acetate buffer was developed for the application to strongly acidified soils. BNC values measured by the developed calcium acetate method (BNC_ac) agreed nearly perfectly with BNC_tit values of 59 mineral soils. The BNC_ac slightly overestimated (< 10%) the BNC_tit of 10 samples of humus layers. Furthermore, small soil samples (down to 1 g soil), wide soil:solution ratios, and integration of pH (H₂O) measurements into the determination of the BNC_ac yielded reliable BNC_ac values. Thus, the BNC_ac-method may be recommended as a simple and reliable method to determine the BNC of acid soils, especially if only a small amount of soil material is available.     

外源砷、铅在三类紫色土中形态分配与其化学、生物有效性研究

对比研究了酸、中、石灰性紫色土添加砷、铅后其形态分配变化及化学、生物有效性特征。试验表明：砷、铅在三种紫色土中形态分配不同，外源砷、铅分配与原始土样本底值有较大差异。从提取能力、生物效应方面比较了几种浸提剂效果，认为：用0.5N NaHCO₃提取As、2.5%HAc提取Pb可以较好地表征3种紫色土砷、铅的有效量。植物吸收砷、铅与土壤有效量有较好的相关性，但吸收形态却因土而异。试验还证明，As的形态分级中H₃BO₃可以很好地掩敝F-对比色的干扰。     

热带地区玄武岩发育土壤中的生物硅及其发生学意义

运用重液分离法对海南岛北部不同喷发期玄武岩发育的7个土壤剖面生物硅进行了分离和测定,发现生物硅的含量变幅为2.9～54.0 g kg-1,其中最小值出现在发育时间较长的HE11剖面的B2层,最大值出现在发育时间较短的HE09剖面的表层。生物硅的剖面分布特征和有机碳、总氮比较相似,呈现出随土壤深度的增加含量逐渐降低的趋势,在0～40 cm范围之内这种现象更明显。生物硅和总硅之间极显著相关性表明生物硅土壤硅循环中起着主要作用。随着风化强度的提高,黏粒含量的增加,土壤pH逐渐降低,土壤中的生物硅含量有逐渐下降的趋势。初步认为:在土壤发育的初期阶段,来自原生矿物的直接风化释放的溶解硅有利于生物硅在土壤中保存和积聚。而随着土壤的进一步发育,原生矿物的逐渐被分解,土壤的pH下降和黏粒含量进一步增加,土壤中的生物硅也会被溶解、利用,结果是其含量逐渐下降。至发育的高级阶段,土壤中的硅进一步淋失,pH和黏粒含量逐渐趋于稳定。在陆地生物"泵"作用下,生物成因硅会被植物循环利用并维持在一个含量相对稳定的状态。     

Background levels of trace and ultra-trace elements in soils of Japan

Five hundred and fourteen soil samples collected from 78 sites in Japan were analyzed for their contents of trace and ultra-trace elements. We estimated the background levels (natural abundance) of 57 elements in soils. The concentration ranges were so wide that the ratios of the highest values to the lowest values were more than 100 for all the elements, with the exception of Be, Ga, Mo, Ag, In, Sn, and Ba. While the concentrations of the first transition elements (₂₁Sc to ₃₀Zn in atomic numbers) were higher than the concentration of the other elements, those of lighter (₃Li and ₄Be) and heavier elements tended to decrease, with an increase or decrease of atomic numbers, with the apparent exception of Pb, Th, and U. Concentrations of elements with even atomic numbers were, in most of the cases, higher than the concentrations of both adjacent elements with odd atomic numbers. Frequency distribution of most of the elements was strongly positively skewed. Markedly positive correlation coefficients (r>0.9) were observed among the elements within the same group in the Periodic Table in many combinations. The dendrogram obtained by cluster analysis showed that the occurrence and distribution of the elements in soils were mostly controlled by the chemical properties of each element, rather than by the nature and properties of individual soil samples. The total contents of the elements in soils were strongly dependent on the chemical composition of the parent rocks from which respective soils were derived.     

Use of factor analysis to differentiate pollutants from other trace metals in surface soils of the mineralized area of Madison County,Missouri, U.S.A.

Barium, Be, Co, Cr, Cu, Li, Mn, Ni, Pb, Sr, and V concentrations were determined in 97 surface soil samples collected 1000 m apart on a regular grid in Madison county, Missouri, U.S.A. The data were normalized by a log₁₀ transformation and a matrix of correlation coefficients computed. Strong correlations were observed between several metals and statistically significant correlations were found between others. The data were then analyzed by R-mode factor analysis. Three factors satisfactorily explained the data variance and were interpreted as follows. Factor 1 (55% variance) comprised a group of elements which contaminated local soils as a consequence of operations connected with non-ferrous metal mining. Factor 2 (33 % variance) contained elements which accumulate in soils during weathering. The remaining elements were grouped together in factor 3 (12% variance) and here soil contents appeared to be controlled by rock composition.