Soil quality in east coastal region of China as related to different land use types

Purpose

The impacts of different land use practices on soil quality were assessed by measuring soil attributes and using factor analysis in coastal tidal lands. The study provided relevant references for coastal exploitation, land management and related researches in other countries and regions.

Materials and methods

Measured soil attributes include physical indicators [bulk density (ρ _b), total porosity (? _t) and water-holding capacity (WHC)], chemical indicators [pH, electrical conductivity (EC), total nitrogen (TN), soil organic matter (SOM), available N, available P and available K] and biological indicators (urease activity, catalase activity and phosphatase activity), and 60 soil samples were collected within five land use types [(1) intertidal soils, (2) reclaimed tidal flat soils, (3) farmland soils, (4) suburban vegetable soils, (5) industrial area soils) in Jianggang village of Dongtai county, Jiangsu province of China.

Results and discussion

The results from the investigation indicated that selected soil properties reduced to three factors for 0–20-cm soil depth; “Soil fertility status” (factor 1), “Soil physical status” (factor 2) and “Soil salinity status” (factor 3). For the first factor, the measured soil attributes with higher loadings were TN and SOM, which represented soil fertility feature, and for the second and third factors, the measured soil attributes with higher loadings were ρ _b and available K as well as EC, which reflected soil physical properties and soil salinity feature, respectively.

Conclusions

Changes in different land use types due to plants (corn, wheat and green vegetable) and application of fertilizers were characterized by promoted soil quality, including improvements in chemical properties (increasing SOM concentration, TN and nutrient available to plants; decreasing EC), improvements in soil physical properties (decreasing ρ _b; increasing ? _t and WHC) and enhancements in soil enzyme activities. Judging from the soil quality indices, the soil quality was affected by different land use practices and decreased in sequence of suburban vegetable soils, farmland soils, industrial area soils, reclaimed tidal flat soils and intertidal soils in the study area.     

Defining soil geochemical baselines at small scales using geochemical common factors and soil organic matter as normalizers

Purpose

The establishment of geochemical baselines is essential for accurate evaluation of the present state of surface environments. In this study, normalization procedures (NP), which can improve the explanation of the natural variation of elements, were conducted using geochemical common factors (GCF) and soil organic matter (SOM) as normalizers to define the geochemical baselines of soil trace elements.

Materials and methods

Soil samples (n?=?345) were collected in Luhe County, Jiangsu, China, a county with a complex geologic setting and intensive anthropogenic influence. Conservative elements, Al, Ca, Fe, K, Mg, Mn, Na, P, and Ti; trace elements, As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn; and SOM were measured. Normalization procedures were conducted using multiple linear regressions between soil trace elements and SOM and GCFs, acquired from factor analysis of the soil major elements. Normalization procedures using univariate linear regressions between soil trace elements and conservative elements Al, Fe, and Ti were also conducted for comparison.

Results and discussion

Comparison of NPs using GCFs and SOM as normalizers with NPs, which use single conservative elements as normalizers, shows that the former is more accurate than the latter for As, Pb, and Zn and is as accurate for Cd, Cr, Cu, Hg, and Ni, when the most appropriate single conservative element is chosen. Small-scale geochemical baselines in the county are significantly different from regional-scale geochemical baselines for Jiangsu Province, China.

Conclusions

The application of regional-scale geochemical baselines at small scales may lead to estimation errors in determining anomalies and assessing environments. Baselines obtained from the NPs using GCFs and SOM as normalizers are more accurate.     

Soil pollution by mining activities in Andalusia (South Spain)—the role of Mineralogy and Geochemistry in three case studies

Purpose

Geochemical and mineralogical studies of soils potentially polluted by trace elements are basic to find the source of pollution, to understand the behavior of the contaminants in the environment, and to propose remediation and reclamation actions. This work reviews the role of the Mineralogy and Geochemistry to assess the hazard of soil contamination by trace elements in mining areas, focusing on three different case studies carried out in the Andalusian community (South Spain), with a Mediterranean temperate climate.

Materials and methods

Two significant mining districts were selected for this work: the Linares-La Carolina (Pb-Zn ores) and the Riotinto (Iberian Pyrite Belt, IPB) mining areas. Another case study was the Guadiamar basin, which soil was polluted by the spill produced in 1998 by the breakage of a mine tailing impoundment in Aznalcóllar mines (IPB). Soils, mine waste, and secondary precipitates were studied to approach the source of the pollution and the fate of the contaminants. Chemical composition (major and trace elements), soil parameters, and mineralogy of all materials selected were studied. In addition, the bioavailability of trace elements was determined by different methods.

Results and discussion

Pyrite and secondary phases are the main sources of pollution in the Riotinto area. Their stability is a key factor in the release of trace elements. The availability of trace elements in soils was lower in unpolluted leptosols than in contaminated orchards. In Linares-La Carolina, a severe pollution by Pb and a high availability (10–70% extracted with EDTA) were found. In Guadiamar basin, the residual pyrite sludge continues releasing trace elements to soil. Cd and Zn were mobile at pH <?6 and As at pH >?8, and Pb was quite immobile. Cd, Zn, and Pb can be coprecipitated by carbonates while As is mainly adsorbed by clays and iron oxyhydroxides.

Conclusions

The geochemical studies of soils polluted by mining activities allow to evaluate the availability of trace elements and their retention in soils. Therefore, geochemical and mineralogical studies are necessary for the assessment of soil pollution and remediation actions.

     

Spatial variability of trace elements in allotment gardens of four European cities: assessments at city,garden, and plot scale

Purpose

Urban allotment gardens (UAGs) are expanding worldwide, especially in large cities. Environmental pressures (direct and diffuse pollution, gardener practice, geogenic contamination) often result in the accumulation of potentially harmful trace elements in garden soils. The objectives of this study were to assess the spatial variability of trace element distribution in UAGs from city, garden, and plot scale in four European cities; to provide a baseline understanding and identify abnormal values under environmental pressures; and to evaluate the potential of portable X-ray fluorescence screening as a useful tool in soil management.

Materials and methods

The four cities (Ayr and Greenock (Scotland), Lisbon (Portugal), Nantes (France)) provided a wide range of environmental pressures on soils. The locations of the 14 allotment gardens were identified in consultation with the local municipality in each city to reflect various land uses or according to previous evaluation of soil quality. Soil sampling was carried out in 66 plots in total, from which 3 datasets were produced: (i) basic soil properties and trace element concentrations from a composite sample of topsoil for each plot (trace elements quantified by inductively coupled plasma–optical emission spectrometry/mass spectrometry (ICP-OES/MS) or using in-lab portable X-ray fluorescence (PXRF); (ii) in situ PXRF measurement on composite samples (263 plots in Nantes); and (iii) composite samples from 32 small areas within 4 plots in one garden of Nantes.

Results and discussion

The results were analyzed to assess the spatial variability of soil properties. At city and garden scale, the variability observed for basic soil properties and major elements is dominated by local geology/parent material (pH, CaCO₃, Fe) and gardening practice (OM, CaCO₃), which vary between each country. The range of trace element concentrations is similar between each city except for Greenock. Extreme values are observed for Cu, Pb, and Zn reflecting human disruption. In most situations, the trace element contamination was explained through the historical and environmental situations of the site. The PXRF screening method proved useful in providing detailed mapping for hot spot detection or delineation, providing support for soil management at plot and garden scale.

Conclusions

As anticipated, basic soil properties appear to be controlled by the parent material. At plot and garden scale, the trace element variability shows the influence of land use history and background and strong inputs from external factors (e.g., by industrial activity or traffic emission). The PXRF screening method appears to be an efficient solution for soil management as it can be used to discriminate zones which may require restriction on cultivation.

     

Distribution of heavy metals in soils of the Yellow River Delta: concentrations in different soil horizons and source identification

Purpose

The Yellow River Delta, an active land-ocean interaction area, will develop into a large eco-economic region in East China during the coming decade. It is necessary to assess the geochemical features of heavy metals in the soils. The objectives of this research were to evaluate the concentrations and distribution of heavy metals (Cr, Ni, Cu, Zn, Pb, and Cd) in soil profiles of the area and to identify their sources.

Materials and methods

Horizon samples were collected based on pedogenic features from bottom to top in each profile to a depth of 120 cm and a total of 92 samples were collected. The sampling sites were grouped into four lines from inland to coastal area with three land use types (cotton field, cereal field, and wetland). The concentrations of Cr, Ni, Cu, Zn, Pb, and Cd were measured by inductively coupled plasma-mass spectrometry. Iron oxide fractions in the soil were extracted by oxalate-oxalic acid and dithionite-citrate-bicarbonate. X-ray diffraction (XRD) was used to determine the mineral composition of the soils. Multivariate statistical analysis and historical data were employed to identify the possible sources of these heavy metals.

Results and discussion

The mean concentrations of heavy metals were elevated along the Yellow River region and in the southern part of the delta; however, they were generally lower than the Chinese guideline values. As for the depth distribution of heavy metals in soil profiles, the maximum values of Cr, Ni, Cu, Zn, and Cd in middle horizon of cotton field were almost twice than those in surface horizon. The iron oxides and XRD analysis indicated that the trace elements accumulation appeared to be related with the contents of crystalline iron oxide and layer silicates. Historical data from suspended sediments of the Yellow River and principal component analysis (PCA) implied that most of the metals (Cr, Ni, Cu, and Zn) were sourced from natural alluviation and sedimentation.

Conclusions

The Yellow River Delta soils were slightly polluted by heavy metals the Yellow River Delta. The special pedogenic horizon characterized by higher iron oxides and layered silicates minerals in the middle and lower part of the soil profile was found with heavy metals enrichment, which required to be studied further. Suspended sediments transported by the Yellow River were suggested to be one of the major sources for the heavy metals accumulation in the basal soils of this region.     

Grass-induced changes in properties of soils in urban green areas with emphasis on mobility of metals

Purpose

Green areas in urban parks are special ecosystems because of social and ecological benefits.

Materials and methods

We investigated the ecological impacts of green spaces by comparing the properties of soils, with emphasis on metals, in green spaces and bare soil playgrounds in four urban parks in Murcia City (SE Spain).

Results and discussion

Organic matter (OM) contents in green areas are higher than playground soils due to litter decomposition from grass. Cation exchange capacity in green areas ranged from 10 to 14 compared to 2 cmol₊kg^?1 in playground soils, showing the effect of OM (and clay) contents in green areas due to the presence of vegetation. Soil total metal contents in urban parks are below the environmental threshold values for soils in Spain and other European countries, and come from atmospheric deposition and fertilizers application. Diethylenetriaminepentaacetic acid (DTPA)-extractable soil Cd in green areas (4% of total Cd) is lower than in playground soils (58% of total Cd). We attributed the reduced DTPA- and water-extractable Cd, Co, Cr, Mn, and Mo to the formation of stable complexes between metals and OM produced from the continued decomposition of roots of grasses in green spaces.

Conclusions

Grasses accumulate less metal than soils except in roots where Cr and Zn are higher than soils by as much as 31 and 17%, respectively. We conclude that grasses increased (up to 8×) soil OM content in green areas to significantly increase the ability of soils to accumulate nutrients for plants, and to retain and reduce the mobility and toxicity of metals in soils in urban parks.     

Contribution of bricks to urban soil properties

Purpose

Bricks are regularly found in urban soils where they can strongly impact soil properties. The purpose of this study is to investigate abundance, especially in the fine earth fraction, and properties of bricks in urban soils, focusing on rooting, plant nutrition and contamination.

Materials and methods

Three different urban soils from the city of Berlin have been studied for their brick contents in the coarse and fine earth fractions by hand sorting. Light (LM) and scanning electron microscopy (SEM) was employed to investigate bricks for proofs of rooting. Third, CEC, pH, EC, C_org, nutrient and contaminant storage and availability have been investigated for bricks and the fine earth fractions of the corresponding soil horizons.

Results and discussion

The fine earth fractions of the investigated soils contain 3 to 5 % of bricks, while the coarse fractions contain up to 50 %. The LM and SEM micrographs made the proof that roots enter brick pores or attach to brick surfaces. Therefore, they can use the water and nutrients stored in bricks and bypass pore system discontinuities between bricks and surrounding soil. The CEC of bricks is grain size dependent and reaches a maximum of 6 cmol_c kg^?1 for particles smaller than 0.063 mm. This dependency is the result of the restricted diffusion into the brick pore system due to the short shaking time in the CEC analysis protocol and of the rising surface with decreasing particle size. From the nutrient storage and availability, we conclude that bricks can better supply plants with K, Mg, Ca and S than the investigated sandy bulk soil.

Conclusions

The nutrient availability from bricks is low compared to control soils, except for Ca and S. Because of the water and nutrient storage, low contamination status and the possible rooting of bricks, they can be used for amelioration of poor sandy soils and for constructed Technosols, preferably employed in small grain sizes.     

Adaptation, tolerance, and evolution of plant species in a pyrite mine in response to contamination level and properties of mine tailings: sustainable rehabilitation

Purpose

The impacts of mining contaminations and physico-chemical properties and geochemistry of mine tailings on the density, richness, biodiversity, evolution and succession of plant species and vegetation recovery in the mining area is very poorly reported in the literature. Therefore, the present study conducted an investigation on vegetation development and succession of plant communities at the abandoned São Domingos pyrite mining area.

Materials and methods

We conducted the field survey to estimate the vegetation development and succession of plant communities, collect vegetation (plant species, lichen and moss) and tailing (and soil) samples, and finally analyzed the physico-chemical and geochemical properties and metal levels in mine tailings, soil and vegetation samples.

Results and discussion

The results showed that the communities of low height and biomass like grass, legume, shrub, moss and lichen were dominating on the mine tailings and waste dumps at the inner sites and center of the mine, and the vegetation coverage was explicitly very poor. The reddish brown colluvia had poor soil quality, but high acidity and metal concentrations. However, at the outer edge of the mine the loamy soil and relatively lower acidity and metal contamination favored the higher vegetation cover and a gradual increase in the number of species and plant succession, where the taller, higher biomass and broad leaf trees were abundantly grown forming a dense forest and canopy. The succession of several plant communities dominating in the mining area, vegetation coverage and species richness were strongly related to the different levels of contamination, soil properties and adverse factors of mine tailings.

Conclusions

Although the high concentrations of toxic trace elements and low pH soil are important factors for limiting the plant growth, however, proper soil development with enriched nutrients and properties on mining wastes, by either natural or external soil aided process, can help to promote the high vegetation growth, mine rehabilitation and ecological restoration of the mining degraded lands.     

Acidification and salinization of soils with different initial pH under greenhouse vegetable cultivation

Purpose

Field survey and sampling of vegetable greenhouse soils were conducted in Shouguang, Shandong Province, and Ningbo, Zhejiang Province to study the acidification and salinization characteristics of soils with different initial soil pH values and greenhouse cultivation time.

Materials and methods

The pH, electrical conductivity (EC), and ion composition of 74 composite soil samples were analyzed to evaluate their relation to soil acidification and salinization.

Results and discussion

Compared with their corresponding open-field soils, acidification and salinization of the greenhouse soils occurred in both 0-20 cm and 20-40 cm soil layers for the Shouguang and Ningbo soils. The soil pH decreased gradually at different rates as greenhouse cultivation time increased in the two surveyed regions, but the opposite trend was observed for soil EC. For the Shouguang soils, while the percentages of K⁺ and NO₃ ^? increased dramatically and Ca²⁺ and HCO₃ ^- decreased significantly after the soils were converted to greenhouse use, the correlation between soil pH and EC was significant, and the stepwise multiple regression analysis further showed that there was a significant correlation between pH and the percent of Ca²⁺ and HCO₃ ^?.

Conclusions

Soil acidification and salinization are common in greenhouse soils with different initial soil pH. Soil acidification in the Shouguang soils is a result of decrease in the percent of Ca²⁺, HCO₃ ^? due to over application of N and K fertilizers. Future research should be devoted to understanding the relevant mechanisms in greenhouse soils with lower initial soil pH values to assess if there are correlations between soil acidification and salinization under greenhouse cultivation.     

Review of denitrification in tropical and subtropical soils of terrestrial ecosystems

Purpose

Denitrification has been extensively studied in soils from temperate zones in industrialized countries. However, few studies quantifying denitrification rates in soils from tropical and subtropical zones have been reported. Denitrification mechanisms in tropical/subtropical soils may be different from other soils due to their unique soil characteristics. The identification of denitrification in the area is crucial to understand the role of denitrification in the global nitrogen (N) cycle in terrestrial ecosystems and in the interaction between global environmental changes and ecosystem responses.

Materials and methods

We review the existing literature on microbially mediated denitrification in tropical/subtropical soils, attempting to provide a better understanding about and new research directions for denitrification in these regions.

Results and discussion

Tropical and subtropical soils might be characterized by generally lower denitrification capacity than temperate soils, with greater variability due to land use and management practices varying temporally and spatially. Factors that influence soil water content and the nature and rate of carbon (C) and N turnover are the landscape-scale and field-scale controls of denitrification. High redox potential in the field, which is mainly attributed to soil oxide enrichment, may be at least one critical edaphic variable responsible for slow denitrification rates in the humid tropical and subtropical soils. However, soil pH is not responsible for these slow denitrification rates. Organic C mineralization is more important than total N content and C/N in determining denitrification capacity in humid subtropical soils. There is increasing evidence that the ecological consequence of denitrification in tropical and subtropical soils may be different from that of temperate zones. Contribution of denitrification in tropical and subtropical regions to the global climate warming should be considered comprehensively since it could affect other greenhouse gases, such as methane (CH₄) and carbon dioxide (CO₂), and N deposition.

Conclusions

Tropical/subtropical soils have developed several N conservation strategies to prevent N losses via denitrification from the ecosystems. However, the mechanisms involved in the biogeochemical regulation of tropical and subtropical ecosystem responses to environmental changes are largely unknown. These works are important for accurately modeling denitrification and all other simultaneously operating N transformations.     

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu,Cr, Ni,and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

Purpose

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT).

Materials and methods

Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha^?1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals.

Results and discussion

The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvín, this increase peaked at an application rate of 90 Mg ha^?1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha^?1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C _E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil.

Conclusions

The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C _E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C _E for soil Cu was not related to plant Cu for all soils studied.     

Influence of pH on the redox chemistry of metal (hydr)oxides and organic matter in paddy soils

Purpose

The primary purpose of this study was to determine how flooding and draining cycles affect the redox chemistry of metal (hydr)oxides and organic matter in paddy soils and how the pH influences these processes. Our secondary purpose was to determine to what extent a geochemical thermodynamic equilibrium model can be used to predict the solubility of Mn and Fe during flooding and draining cycles in paddy soils.

Material and methods

We performed a carefully designed column experiment with two paddy soils with similar soil properties but contrasting pH. We monitored the redox potential (Eh) continuously and took soil solution samples regularly at four depths along the soil profile during two successive flooding and drainage cycles. To determine dominant mineral phases of Mn and Fe under equilibrium conditions, stability diagrams of Mn and Fe were constructed as a function of Eh and pH. Geochemical equilibrium model calculations were performed to identify Mn and Fe solubility-controlling minerals and to compare predicted total dissolved concentrations with their measured values.

Results and discussion

Flooding led to strong Eh gradients in the columns of both soils. In the acidic soil, pH increased with decreasing Eh and vice versa, whereas pH in the alkaline soil was buffered by CaCO₃. In the acidic soil, Mn and Fe solubility increased during flooding due to reductive dissolution of their (hydr)oxides and decreased during drainage because of re-oxidation. In the alkaline soil, Mn and Fe solubility did not increase during flooding due to Mn(II) and Fe(II) precipitation as MnCO₃, FeCO₃, and FeS. The predicted levels of soluble Mn and Fe in the acidic soil were much higher than their measured values, but predictions and measurements were rather similar in the alkaline soil. This difference is likely due to kinetically limited reductive dissolution of Mn and Fe (hydr)oxides in the acidic soil. During flooding, the solubility of dissolved organic matter increased in both soils, probably because of reductive dissolution of Fe (hydr)oxides and the observed increase in pH.

Conclusions

Under alternating flooding and draining conditions, the pH greatly affected Mn and Fe solubility via influencing either reductive dissolution or carbonate formation. Comparison between measurements and geochemical equilibrium model predictions revealed that reductive dissolution of Mn and Fe (hydr)oxides was kinetically limited in the acidic soil. Therefore, when applying such models to systems with changing redox conditions, such rate-limiting reactions should be parameterized and implemented to enable more accurate predictions of Mn and Fe solubility.     

Stability of soil organic matter in two northeastern German fen soils: the influence of site and soil development

Purpose

Peatland soils play an important role in the global carbon (C) cycle due to their high organic carbon content. Lowering of the water table e.g. for agricultural use accelerates aerobic secondary peat decomposition and processes of earthification. Peatlands change from C sinks to C sources. We characterized soil organic matter (SOM) with special attention to human impact through drainage. Our aim was to gain knowledge of SOM quality and soil-forming processes in drained fen soils in northeastern Germany.

Materials and methods

Through techniques of representative landscape analysis, we identified two typical and representative sampling sites in different stages of land use, representing the most important hydrogenetic mire types in northeastern Germany. We adapted chemical fractionation procedures which include hot water extraction (C_hwe and N_hwe) for determination of the labile fraction. Furthermore, a stepwise acid hydrolysis procedure was performed to measure the chemical recalcitrant part of SOM as it is more resistant to biodegradability.

Results and discussion

Total organic C decreased with increasing human impact and intensity of drainage. Conversely, C_hwe and N_hwe concentrations increased with increasing drainage and human impact. In contrast, the more recalcitrant fractions increased with soil depth.

Conclusions

Generally, there is a lack of existing data about SOM quality and the factors controlling its stability and decomposition in fen soils. For northeastern German fen soils, the data are even more inadequate. Influence of drainage seems to overlap natural influences of site on SOM quality. The used extraction scheme was suitable for the chemical fractionation of SOM into labile and more recalcitrant parts.     

Concentrations and geochemical fractions of rare earth elements in two different marsh soil profiles at the North Sea,Germany

Purpose

The purpose of this study was (1) to determine the vertical distribution of rare earth element (REE) concentrations, stocks, and geochemical fractions in two different marsh soil profiles and (2) to quantify the relations between REEs and soil properties.

Materials and methods

A sandy Fluvisol recently flooded by tidal water and a clayey Gleysol landward the dike impacted by fluctuating groundwater levels served as reference marsh soils. An aqua regia extraction was used to determine the concentrations of REEs; additionally, a sequential extraction procedure developed by the Commission of the European Communities Bureau of Reference was conducted to assess the geochemical fractions (exchangeable, reducible, oxidisable, residual fraction) of REEs. Both extractions were carried out according to genetic horizons. The stocks of REEs were calculated and the relations between physico-chemical soil properties and concentrations/mobility of REEs were quantified via correlation analysis.

Results and discussion

The aqua regia extractable REE concentrations and stocks of the Gleysol were about two times higher compared to the Fluvisol since the Gleysol was more clayey and REEs might adsorb onto clay minerals. We have detected small differences of REE concentrations and geochemical fractions between the horizons of the single profiles. Rare earth elements existed mainly in residual or reducible fraction, followed by oxidisable, and water soluble/exchangeable/carbonate bound fraction. The most striking difference between the two marsh soil profiles regarding the geochemical fractions was the higher residual fraction in the Fluvisol than in the Gleysol what seemed to be due to the lower aqua regia extractable concentration in the former.

Conclusions

The aqua regia extractable concentration as well as reduction and oxidation processes of (amorphous) iron and manganese complexes seemed to have the most important impact on the geochemical fractions of REEs in the studied marsh soil profiles. In future, those findings should be verified in further marsh soils worldwide. In particular, future studies should elucidate the specific release kinetics of REEs and their determining factors.     

Mutual relations between PAHs derived from atmospheric deposition,enzymatic activity,and humic substances in soils of differently urbanized areas

Purpose

The aim of this study was to determine the mutual relations between polycyclic aromatic hydrocarbons (PAHs) originated from atmospheric emissions and enzymatic activity and humic substances in soils at differently urbanized area, on an example of the Lublin city, east Poland.

Materials and methods

The chosen areas represented three differently urbanized environments: old tenement houses and modern residential blocks, mixture of different building and rural landscape, and typical rural environment with smallholding farms, respectively. On each of the urban, suburban, and rural areas, one representative plot was chosen on fallow lands classified as luvisol derived from loess. The soil samples were collected from the top 25 cm layer. The following properties were determined: pH, organic carbon, total nitrogen, humic and fulvic acids, PAHs content (14 PAHs from US EPA list), and the activities of the following enzymes: dehydrogenases, acid phosphatase, alkane phosphatase, protease, and urease.

Results and discussion

Higher contents of organic C and total N were found in the rural soil samples. The share of humic acid was similar in all soils investigated, ranging from 19.38 to 25.27%, while fulvic acid values differ significantly between urban and rural areas. The urban soils indicated much lower share of fulvic acids (9.78–10.99%) than those of rural (29.02–29.32%). Consequently, the values of the C_HA:C_FA ratio of the urban soil were approximately two times higher than those of the rural soil. The results showed that both the rate of humification and the activity of dehydrogenases, acid phosphatase, alkaline phosphatase, and proteases in the soils increased in the following sequence: urban < suburban < rural.

Conclusions

The results showed that an increase of PAHs in the urbanized areas affect other soil properties. The phenanthrene/anthracene and fluoranthene/pyrene ratios pointed to coal combustion as the principal source of PAHs in the investigated soils. The PAH content in the urbanized area inhibit humification processes in the soil and the activity of dehydrogenases, acid phosphatase, alkaline phosphatase, and proteases.

     

Geogenic and agricultural controls on the geochemical composition of European agricultural soils

Purpose

Concern about the environmental impact of agriculture caused by intensification is growing as large amounts of nutrients and contaminants are introduced into the environment. The aim of this paper is to identify the geogenic and agricultural controls on the elemental composition of European, grazing and agricultural soils.

Materials and methods

Robust factor analysis was applied to data series for Al, B, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Se, Sr, U, Zn (ICP-MS) and SiO2, K2O, Na2O, Fe2O3, Al2O3 (XRF) based on the European GEMAS dataset. In addition, the following general soil properties were included: clay content, pH, chemical index of alteration (CIA), loss on ignition (LOI), cation exchange capacity (CEC), total organic carbon (TOC) and total carbon and total sulfur. Furthermore, this dataset was coupled to a dataset containing information of historic P₂O₅ fertilization across Europe. Also, a mass balance was carried out for Cd, Cu and Zn to determine if concentrations of these elements found in the soils have their origin in historic P₂O₅ fertilization.

Results and discussion

Seven geogenic factors and one agricultural factor were found of which four prominent ones (all geogenic): chemical weathering, reactive iron-aluminum oxide minerals, clay minerals and carbonate minerals. Results for grazing and agricultural soils were near identical, which further proofs the prominence of geogenic controls on the elemental composition. When the cumulative amount of P₂O₅ fertilization was considered, no extra agriculture-related factors became visible. The mass balance confirms these observations.

Conclusions

Overall, the geological controls are more important for the soil chemistry in agricultural and grazing land soils than the anthropogenic controls.     

Electron transfer capacity of soil dissolved organic matter and its potential impact on soil respiration

Purpose

Soil dissolved organic matter (DOM) as the labile fraction of soil organic carbon (SOC) is able to facilitate biogeochemical redox reactions effecting soil respiration and carbon sequestration. In this study, we took soil samples from 20 sites differing in land use (forest and agriculture) to investigate the electron transfer capacity of soil DOM and its potential relationship with soil respiration.

Materials and methods

DOM was extracted from 20 soil samples representing different land uses: forest (nos. 1–12) and agriculture (nos. 13–20) in Guangdong Province, China. Chronoamperometry was employed to quantify the electron transfer capacity (ETC) of the DOM, including electron acceptor capacity (EAC) and electron donor capacity (EDC), by applying fixed positive or negative potentials to a working electrode in a conventional three-electrode cell. The reversibility of electron accepting from or donating to DOM was measured by applying switchable potentials to the working electrode in the electrochemical system with the multiple-step potential technique. Carbon dioxide produced by soil respiration was measured with a gas chromatograph.

Results and discussion

Forest soil DOM samples showed higher ETC and electron reversible rate (ERR) than agricultural soil DOM samples, which may be indicative of higher humification rate and microbial activity in forest soils. The average soil respiration of forest soil (nos. 1–12) and agricultural soil (nos. 13–10) was 26.34 and 18.58 mg C g^?1 SOC, respectively. Both EDC and EAC of soil DOM had close relationship with soil respiration (p?<?0.01). The results implied that soil respiration might be accelerated by the electroactive moieties contained in soil DOM, which serve as electron shuttles and facilitate electron transfer reactions in soil respiration and SOC mineralization.

Conclusions

DOM of forest soils showed higher ETC and ERR than DOM of agricultural soils. As soil represents one of the largest reservoirs of organic carbon, soil respiration affects C cycle and subsequently CO₂ concentration in the atmosphere. As one of the important characteristics of soil DOM related to soil respiration, ETC has a significant impact on greenhouse gas emission and soil carbon sequestration but has not been paid attention to.     

Heavy metal contamination of urban topsoils in a typical region of Loess Plateau,China

Purpose

Heavy metals pollution of city soil has become a serious environmental issue. Attention has been given to the issue of soil contamination in big cities, but little research has been done in the Loess Plateau, which is the largest loess deposition area in the world. The aim of this study was to assess the contamination of topsoil.

Materials and methods

Forty soil samples were collected from different districts and sieved through nylon sieves. The coarse particles (2 mm) were used to determine pH and electrical conductivity using a suspension of 1:5 soil to deionized water. The fine particles (150 μm) were used to determine soil organic matter and selected heavy metals. Metals were measured in digested solutions by a flame atomic absorption spectrophotometer.

Results and discussion

The mean concentrations of heavy metals in urban soils in the study area are significantly lower than the mean concentrations across China. The integrated pollution index was determined to be 1.13, indicating moderate pollution. Weathering of parent material, the use of pesticide and fertilizer, discharge of waste from traffic, wastes from commodities and industry, and coal combustion are considered to be the main sources of heavy metal pollution in the study area.

Conclusions

The results indicate that, at least in the study area, land use greatly influences the soil quality and heavy metal contents in urban topsoils. Soil backfill may change heavy metal contents to some extent. Deep digging and backfill can be effectively used for the remediation of heavy metal contaminated soil and sediments.     

Evaluation and source identification of trace element contamination of soils in the Qixia lead-zinc mining area,Jiangsu, China

Purpose

The Qixia mine is one of the largest lead-zinc mines in Eastern China and has been operational for approximately 60 years. Source identification for trace element contamination of soils in the Qixia mining area has been lacking. This report details the evaluation and source identification of trace element contamination (including Cu, Zn, Pb, Cd, Hg, Cr, As, and Ni) of soils in this area.

Materials and methods

Thirty-three soil samples from roadsides and fields in the study area were collected and analyzed. The index of geo-accumulation (I _geo) was employed to evaluate contamination. Methods of multivariate statistical analysis were used to determine the probable sources of the pollutants.

Results and discussion

The analysis showed that the levels of contamination ranked in the following order: Cd > Pb/Zn> > As/Cu> > Hg > Cr/Ni. In the sampling area nearest the mine, soil samples collected from roadsides showed much higher levels of contamination than those collected from fields away from the roadways. Trace element contamination decreased as the distance from the mine increased. Contamination extended to a distance of approximately 700 m from mineral transportation routes, with the area of greatest impact at 200 m or less. Multivariate statistical analysis and ore composition data suggest that the Cu, Zn, Pb, Cd, and As found in the soil samples originate from anthropogenic sources. Ni and Cr are considered to be at natural background concentrations.

Conclusions

This study distinguished between natural and anthropogenic sources of trace element contamination in the soils of the Qixia mining area. The contamination of Cu, Zn, Pb, Cd, and As is linked to the mining activities and is likely due to the transportation of ore concentrates and tailings.