Methane emission from two Indian soils planted with different rice cultivars

In a greenhouse study, methane emissions were measured from two diverse Indian rice-growing soils planted to five rice cultivars under similar water regimes, fertilizer applications and environmental conditions. Significant variations were observed in methane emitted from soils growing different cultivars. Total methane emission varied between 8.04 and 20.92gm^–2 from IARI soil (Inceptisol) and between 1.47 and 10.91gm^–2 from Raipur soil (Vertisol) planted to rice. In all the cultivars, emissions from IARI soil were higher than from Raipur soil. The first methane flux peak was noticed during the reproductive phase and the second peak coincided with the grain-ripening stage of the rice cultivars. Received: July 7, 1996     

Methane fluxes on agricultural and forested boreal organic soils

Abstract. Annual methane fluxes from an organic soil in eastern Finland, originally drained and planted with birch ( Betula pendula ) and then later cultivated, were studied for two years using a chamber technique. The agricultural soils growing grass or barley or without vegetation, generally acted as sinks for CH₄. Surprisingly, the agricultural soils emitted CH₄ during a warm dry summer. The CH₄ oxidation capacity and CH₄ uptake rate of the forested site was three times that of agricultural soils. Also, the forest soil better retained its capacity to take up CH₄ during a dry summer. Despite periods of CH₄ emission, the agricultural soils were annual sinks for CH₄, with uptake rate of CH₄-C varying from 0.1 to 3.7 kg ha⁻¹ yr⁻¹. The forested soil had a methane uptake rate of 3.9 kg CH₄-C ha⁻¹ yr⁻¹. All the soils acted as sinks for CH₄ during winter, which contributed up to half of the annual CH₄ uptake. The capacity of soils to transport gases did not explain the larger CH₄ uptake rate in the forest soil. At the same gas filled porosity, the forest soil had a much larger CH₄ uptake rate than the agricultural soil. Neither the soil acidity (pH 4.5 and 6.0) nor high ammonium content appeared to limit CH₄ uptake. The results suggest that CH₄ oxidation in agricultural organic soil is more sensitive to soil drying than CH₄ oxidation in forested organic soil.     

Evaluation of alternative substrates for determining methane-oxidizing activities and methanotrophic populations in soils

The magnitude of methane emission is a net result of methane production and the oxidation rate. The possibility of measuring oxidized products of alternative substrates of methane monooxygenase was examined to determine methane-oxidizing ability of soils, and to count methanotrophic populations in soils. Wetland rice soils were incubated under methane containing air to enirch the methanotrophs. Methane loss and oxygen uptake were inhibited by acetylene, dimethylether, and nitrapyrin (N-Serve). Acetylene was used routinely, because it inhibited methane oxidation even at a low concentration of 0.03 to 0.06 l ml^-1 in the incubation headspace. Propylene at 10 kPa was used as an alternative substrate of methane monooxygenase, and the formation of propylene oxide was measured. When soils were incubated under methane, their methane-oxidizing activity increased. Propylene oxide formation increased simultaneously. Acetylene also blocked propylene oxidation. The results of several experiments and propylene oxide formation (r=0.87 after long-transformation). These results indicate that propylene oxide formation can be used as a semiquantitative measure of the methane-oxidizing activity of soils. The colonies of soluble methane monooxygenase-forming methanotrophs were counted on Cu-deficient methanotroph agar medium by the formation of naphthol from haphthalene. The counts increased from 10⁴ (0 days) to 10⁷ (21 days) g^-1 soil during oxic incubation under methane.     

Methane turnover and temperature response of methane-oxidizing bacteria in permafrost-affected soils of northeast Siberia

The abundance, activity, and temperature response of aerobic methane-oxidizing bacteria were studied in permafrost-affected tundra soils of northeast Siberia. The soils were characterized by both a high accumulation of organic matter at the surface and high methane concentrations in the water-saturated soils. The methane oxidation rates of up to 835 nmol CH₄ h⁻¹ g⁻¹ in the surface soils were similar to the highest values reported so far for natural wetland soils worldwide. The temperature response of methane oxidation was measured during short incubations and revealed maximum rates between 22 °C and 28 °C. The active methanotrophic community was characterized by its phospholipid fatty acid (PLFA) concentrations and with stable isotope probing (SIP). Concentrations of 16:1ω8 and 18:1ω8 PLFAs, specific to methanotrophic bacteria, correlated significantly with the potential methane oxidation rates. In all soils, distinct 16:1 PLFAs were dominant, indicating a predominance of type I methanotrophs. However, long-term incubation of soil samples at 0 °C and 22 °C demonstrated a shift in the composition of the active community with rising temperatures. At 0 °C, only the concentrations of 16:1 PLFAs increased and those of 18:1 PLFAs decreased, whereas the opposite was true at 22 °C. Similarly, SIP with ¹³CH₄ showed a temperature-dependent pattern. When the soils were incubated at 0 °C, most of the incorporated label (83%) was found in 16:1 PLFAs and only 2% in 18:1 PLFAs. In soils incubated at 22 °C, almost equal amounts of ¹³C label were incorporated into 16:1 PLFAs and 18:1 PLFAs (33% and 36%, respectively). We concluded that the highly active methane-oxidizing community in cold permafrost-affected soils was dominated by type I methanotrophs under in situ conditions. However, rising temperatures, as predicted for the future, seem to increase the importance of type II methanotrophs, which may affect methane cycling in northern wetlands.     

沈阳城郊温室土壤特性调查研究

对城郊于洪区有代表性的 1 1 0个温室土样进行了研究 .结果表明 ,与原耕作土壤相比 ,碱解氮、有效磷增幅较大 ,pH值呈下降趋势 ,电导率呈升高态势 ,有效铜呈降低而有效锌呈升高趋势 .电导率与硝态氮呈正相关 ,表明温室土壤存在酸化和次生盐渍化倾向 .蔬菜产量与土壤全氮、有效磷呈正相关 ,而与碱解氮呈负相关 .优化施肥、注重有机肥施用 ,控制氮肥用量 ,有针对性地施用石灰 ,注意灌水方法是城郊温室土壤管理的重点 .     

Methanotrophic bacteria in the rhizosphere of rice microcosms and their effect on porewater methane concentration and methane emission

CH₄ emission from irrigated rice field is one of the major sources in the global budget of atmoshperic CH₄. Rates of CH₄ emission depend on both CH₄ production in anoxic parts of the soil and on CH₄ oxidation at oxic-anoxic interfaces. In the present study we used planted and unplanted rice microcosms and characterized them by numbers of CH₄-oxidizing bacteria (MOB), porewater CH₄ and O₂ concentrations and CH₄ fluxes. Plant roots had a stimulating effect on both the number of total soil bacteria and CH₄-oxidizing bacteria as determined by fluorescein isothiocyanate fluorescent staining and the most probable number technique, respectively. In the rhizosphere and on the root surface CH₄-oxidizing bacteria were enriched during the growth period of tice, while their numbers remained constant in unplanted soils. In the presence of rice plants, the porewater CH₄ concentration was significantly lower, with 0.1–0.4mM CH₄, than in unplanted microcosms, with 0.5–0.7mM CH₄. O₂ was detected at depths of up to 16 mm in planted microcosms, whereas it had disappeared at a depth of 2 mm in the unplanted experiments. CH₄ oxidation was determined as the difference between the CH₄ emission rates under oxic (air) and anoxic (N₂) headspace, and by inhibition experiments with C₂H₂. Flux measurements showed varying oxic emission rates of between 2.5 and 29.0 mmol CH₄m^-2 day^-1. An average of 34% of the anoxically emitted CH₄ was oxidized in the planted microcosms, which was surprisingly constant. The rice rhizosphere appeared to be an important oxic-anoxic interface, significantly reducing CH₄ emission.     

Methane production potentials of twenty-eight rice soils in China

 Soil CH₄ production potentials were investigated by incubating air-dried soils under anaerobic conditions in the laboratory. Twenty-eight soils from different fields and locations were collected for this study. Soil CH₄ production during a 100-day incubation differed greatly and were significantly correlated with soil organic content (r=0.61, P<0.01). The statistical significance increased when soils were grouped according to soil reduction rates. A significant correlation was also found between CH₄ production and total N content (r=0.64, P<0.01) and between CH₄ production and soil particle sizes of 0.25–0.05 mm (r=0.48, P<0.05). A negative exponential correlation was found between CH₄ production and aerobic soil pH (r=–0.74, P<0.01). The 28 soils were stratified into four groups on the basis of variation in CH₄ production rates which were associated with the soil reduction rate and soil organic content. The faster the Eh of soil fell, the more CH₄ was formed. Adding rice straw to Hangzhou and Beijing soils increased CH₄ production. The increase in CH₄ production was more pronounced in the soil with the lowest organic matter content and slowest reduction rate than in the soil with highest organic matter and fastest reduction rate. Inorganic fertilizer had no significant influence on CH₄ production potentials of either type of soil. Received: 26 November 1997     

Methane emission and entrapment in flooded rice soils as affected by soil properties

Laboratory incubation experiments were conducted to study the effects of soil chemical and physical properties on CH₄ emission and entrapment in 16 selected soils with a pH range of 4.7–8.1, organic matter content of 0.72–2.38%, and soil texture from silt to clay. There was no significant correlation with CH₄ emission for most of the important soil properties, including soil aerobic pH (measured before anaerobic incubation), total Kjeldahl N, cation exchange capacity, especially soil organic matter, and soil water-soluble C, which were considered to be critical controlling factors of CH₄ emission. A lower CH₄ emission was observed in some soils with a higher organic matter content. Differences in soil Fe and Mn contents and their chemical forms contributed to the this observation. A significant correlation between the CH₄ emission and the soil organic C content was observed only after stratifying soils into subgroups according to the level of CH₄ emission in soils not amended with organic matter. The results also showed that the soil redox potential (Eh), anaerobic pH, anerobic pH, and biologically reducible Fe and Mn affected CH₄ emission significantly. Urea fertilization promoted CH₄ emission in some soils and inhibited it in others. This result appeared to be related to the original soil pH. CH₄ entrapment was positively correlated with soil clay content, indicating the importance of soil physical characteristics in reducing CH₄ emissions to the atmosphere.     

滇池富磷区土壤中溶磷真菌的筛选及其对油菜的促生作用

从滇池富磷区的89份土样中筛选出48株溶磷真菌,采用钼蓝法测定这些真菌溶解Ca3(PO4)3的能力。结果表明培养液中可溶性磷含量在14.45～64.87?mg/L,其中菌株SPF46、SPF47和Mo-Po的溶磷能力最强,其培养液中可溶性磷含量分别达到55.44、59.78和64.87?mg/L。结合形态特征及ITS rDNA 系统亲缘关系分析,将PSF46鉴定为黄暗青霉（Penicillium citreonigrum）,PSF47菌株鉴定为黑曲霉（Aspergillus niger）,Mo-Po菌株鉴定为草酸青霉（Penicillium oxalicum）。在Ca3(PO4)3、FePO4.4H2O和AlPO4 3种磷源中,这3种溶磷真菌对Ca3(PO4)2的溶磷效果最好。通过盆栽试验表明这3种溶磷真菌对油菜具有较好的促生效果,单一菌株处理,根系增长率在10.16%～294.7%,株高增长率在32.19%～134.5%;叶片直径增长率在35.53%～170.5%;鲜质量和干质量增长率分别在30.71%～189.5%,56%～224%。3种溶磷真菌混合处理,根系增长129.4%,株高增加60.41%,叶片直径增加170.5%;鲜质量和干质量分别增加246.1%、272.2%。     

Methane production in unamended and rice-straw-amended soil at different moisture levels

 CH₄ production in an alluvial soil, unamended or amended with rice straw (1% w/w), was examined under nonflooded [–1.5 MPa, –0.01 MPa and 0 MPa (saturated) and flooded (1 : 1.25 soil to water ratio)] conditions during a 40-day incubation in closed Vacutainer tubes. CH₄ production was negligible at –1.5 MPa, but increased with an increase in the moisture level. Addition of rice straw distinctly increased CH₄ production in the soil at all moisture levels including –1.5 MPa. Evidence, in terms of the drop in redox potential and Fe²⁺ accumulated, suggested that the addition of rice straw hastened the reduction of the soil, even under nonflooded conditions; thus its addition stimulated even the nonflooded soil to produce CH₄ in substantial amounts. Our results indicate that many currently unidentified sources of CH₄, possibly including organic-amended nonflooded soils, may make a significant contribution to the global CH₄ budget. Received: 10 July 1997     

The effect of soil type on phosphorus sorption capacity and desorption dynamics in Irish grassland soils

Abstract. The phosphorus (P) sorption and desorption dynamics of eleven major agricultural grassland soil types in Ireland were examined using laboratory techniques, so that soils vulnerable to P loss might be identified. Desorption of P from soil using the iron-oxide paper strip test (Pfeo), water extractable P (Pw) and calcium chloride extractable P (Pcacl₂) depended on soil P status in all soils. However, soil types with high organic matter levels (OM), namely peat soils (%OM >30), had lower Pfeo and Pw but higher Pcacl₂ values compared to mineral soils at similar soil test P levels. Phosphorus sorption capacity remaining (PSCr) was measured using a single addition of P to soils and used to calculate total P sorption capacities (PSCt) and degree of P saturation (DPS). Phosphorus sorption capacities correlated negatively with % OM in soils indicating that OM may inhibit P sorption from solution to soil. High organic matter soils exhibited low P sorption capacities and poor P reserves (total P, oxalate extractable P) compared to mineral soils. Low P sorption capacities (PSCt) in peat soils were attributed to OM, which blocked or eliminated sorption sites with organic acids, therefore, P remained in the soil solution phase (Pcacl₂). In this work, peat and high organic matter soils exhibited P sorption and desorption characteristics which suggest that these soils may not be suitable for heavy applications of manure or fertilizer P owing to their low capacities for P sorption and storage.     

pH对土壤重金属吸附动力学的影响

The pH effect on the sorption kinetics of heavy metals in soils was studied using a constant flow leaching method. The soil samples were red soil collected from Yingtan, Jiangxi, and yellow-brown soil from Nanjing, Jiangsu. The heavy metals tested were zinc and cadmium. Assuming that the experimental data fitted to the following kinetic rate equation: 1/c·dx/dt = kx_∞-kx, the rate constant k of sorption could be determined from the slope of the straight line by plotting of 1/c·dx/dt vs. x. The results showed that the pH effect on the rate constants of heavy mental sorption in soils was very significant. The values of k decreased with increasing pH. The sorptions were more sensitive to pH in red soil than in yellow-brown soil.     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

稻田甲烷排放影响因素及其研究进展

CH4是大气中仅次于CO2的最重要的温室气体之一,其温室效应贡献已达15～20%。中国稻田是CH4的重要排放源,对全球大气的CH4排放起着重要的作用。本文较为详细地介绍了近几十年来国内外关于稻田CH4排放的研究进展。对稻田CH4的排放机理、CH4的排放规律及影响稻田CH4排放的各种因素作了详细分析,并相应地提出了控制稻田CH4排放的各种措施,最后提出了今后我国稻田CH4排放研究应加强的几个方面内容。     

Nature and significance of anthropogenic urban soils

Background, Aims and Scope

Anthropogenic and natural urban soils are of increasing significance in a world with accelerating urbanization. Thus, anthropogenic urban soils must be considered as an fundamental ecological asset for land-use planning. Furthermore, they are of interest for fundamental soil sciences, since there properties are rarely investigated and can differ substantially from landscape soils. Numerous studies on their properties exist, in particular with respect to contamination. It is argued that urban soils are ecological assets of cities, a point of view shared with the AKS (working group on urban soils within the German Soil Science Society). In this commentary, an overview of less recognized topics is presented with specific reference to topics such as ‘co-development of anthropogenic urban soils within their cities’ and the principles of ‘stock flow of anthropogenic urban soils forming materials’ are discussed to complete the pedological and ecological view on urban soils. Additionally, the significance of (anthropogenic) urban soils is highlighted to strengthen consideration in urban spatial planning.

Main Features

Historical and recent impacts on soils and parent materials are related with soil properties. Definitions and taxonomic terms for anthropogenic soils are presented. Furthermore, the context with the functionality of such soils is discussed. The principles of mapping and evaluation of anthropogenic urban soils are explained to stress the practicability of management tools for such soils.

Results and Discussion

A semi-quantitative consideration of parent material flows in anthropogenic urban soils indicates the enormous increase of the areas of supply of cities since the pre-industrial period. Since 1950, the inner-urban deposition of solid materials, including dust stopped to increase or increases slowly in the early industrialized regions. In contrast, the deposition and reuse of rubble, inorganic and organic waste as well as dust increases much in the late industrialized regions of the last decades.

Conclusions

The significance of anthropogenic urban soils in ecological soil management became obvious by numerous scientific studies. Moreover, it is recognized that management of different areas in urban environments must respect the functionality of their soils. It is therefore of importance that pedology is integrated with related disciplines such as archaeology, history and urban planning. The scientific knowledge, the appropriate methods and tools are now available to promote and support the management of anthropogenic urban soils.

Recommendations and Perspectives

It is recommended that research conducted over the past two decades should be introduced into soil management, especially with regard to the evaluation of soil quality. Accordingly, results of collaborative studies by soil scientists and city planners need to be integrated into political frameworks like the European Soil Strategy. It is also recognized that knowledge regarding anthropogenic urban soils in the tropics, the southern hemisphere and far north is lacking, a point which will need to be addressed in the future.

Dedication

This publication is dedicated to the 20th anniversary of the AKS (Arbeitskreis Stadtböden).

     

Methane suppression by iron and humic acids in soils of the Arctic Coastal Plain

Methane–climate interactions are reasonably well understood; the biogeochemical controls on net methane fluxes are less so. Within anoxic soils, alternative electron acceptors such as iron and humic substances influence microbial metabolic function, and thus affect the amount of carbon lost as methane (CH₄). We present three years of data from wet sedge tundra landscapes near Barrow, Alaska that show an inverse relationship between dissolved iron and CH₄ concentrations. We found increasing organic layer thickness related to increases in active layer organic matter content, and decreases in both bulk density and extractable iron. Organic layer depth was also a good proxy for carbon dioxide (CO₂) and CH₄ dynamics, with increasing organic layer depths relating to lower dissolved iron, higher amounts of dissolved CH₄, and lower CO₂:CH₄ ratios in the upper active layer. Net CH₄ fluxes were also significantly suppressed following the experimental addition of iron and humic acids. Iron and humic acid treatment effects were indistinguishable for CH₄ net flux; in contrast, post-treatment CH₄ fluxes were an average of 0.74-fold the control treatment flux rates. These results suggest that in-situ CH₄ production is tied to alternative electron acceptor availability, and that organic layer thickness is a good predictor of biogeochemical controls on CH₄ fluxes in wet-sedge Arctic Alaskan tundra.     

Methane oxidation in the soil surface layer of a flooded rice field and the effect of ammonium

Summary The CH₄ flux from intact soil cores of a flooded rice field in Italy was measured under aerobic and anaerobic incubation conditions. The difference between the anaerobic and aerobic CH₄ fluxes was apparently due to CH₄ oxidation in the oxic soil surface layer. This conclusion was supported by measurements of the vertical CH₄ profile in the upper 2-cm layer, and of the V _max of CH₄ oxidation in slurried samples of the soil surface layer. About 80% of the CH₄ was oxidized during its passage through the soil surface layer. CH₄ oxidation was apparently limited by the concentration of CH₄ and/or O₂ in the active surface layer. The addition of ammonium to the water layer on top of the soil core reversibly increased the aerobic CH₄ fluxes due to inhibition of CH₄ oxidation in the soil surface layer.     

铁氧化物对厌氧水稻土中乙酸的矿化、转化及其激发效应的影响

乙酸是甲烷产生过程的重要底物,其在水稻土中的矿化和转化过程对水稻土碳循环和固碳减排具有重要意义。在长期淹水的水稻土中,铁作为重要的变价金属元素,对乙酸的矿化和转化可能具有重要影响。因此,本研究向水稻土中添加13C-乙酸、水铁矿和针铁矿,动态监测厌氧培养（100 d）期间CO2和CH4排放规律和土壤环境因子的变化规律,同时分析乙酸的矿化和转化特征以及CO2和CH4的激发效应,并解析不同铁氧化物在其中的作用效应。结果表明,培养结束后,只添加乙酸的处理中33%和36%的乙酸分别矿化为CH4和CO2,另外0.12%、2%和28%的乙酸分别形成了可溶性有机碳（DOC）、微生物量碳（MBC）和土壤有机碳（SOC）。乙酸添加引起了CO2负激发效应和CH4正激发效应。土壤产生CO2和CH4比例因乙酸的添加由3.46:1变为1.83:1。针铁矿的添加显著增加了乙酸来源的CO2累积排放量,但水铁矿对乙酸来源的CO2累积排放量却无显著影响。水铁矿和针铁矿均显著降低了SOC来源的CO2累积排放量,加剧了乙酸引起的CO2负激发效应。水铁矿和针铁矿均显著降低了乙酸来源的CH4累积排放量,对SOC来源的CH4累积排放量无显著影响。水铁矿和针铁矿显著增加了乙酸转化为MBC和SOC的比例。因此,乙酸在土壤中的矿化和转化行为会影响土壤原有有机碳产生CO2和CH4;水铁矿和针铁矿结晶程度不同,对乙酸的矿化、转化及其激发效应的影响也不同。研究结果可为稻田的固碳减排提供一定的理论依据和技术支撑。     

Contribution of technic materials to the mobile fraction of metals in urban soils in Marrakech (Morocco)

Background, Aim and Scope  In urban areas, soils are often dramatically altered by anthropogenic activity and these modifications distinguish these soils (Anthrosols, Technosols) from those in natural systems. In urban environments, they receive considerable pollution from industry, traffic and refuse. Since contaminated soil particles can be easily inhaled or ingested, there is a potential transfer of toxic pollutants to humans. Risk assessment is essentially based on the determination of the total or mobile contents of pollutants in soils using chemical extractions. This approach could be improved by taking into consideration the bioavailable fractions of these toxic elements as measured by biotests. The coarse soil fraction usually neglected in analyses can nevertheless have an effect on the concentration of metals in the soil solution. This coarse fraction is made up of the natural materials and of technic materials constituting anthropogenic soils (plastic, paper, fabric, wood, bones, metallic elements and building materials). These materials have variable capacities to release or adsorb trace elements. Samples representative of different technic fraction components of Marrakech urban soils permit one to quantify their contribution to the enrichment of the soluble metal concentrations. Works are carried out to achieve partial extractions of metals from the three fractions (less than 2 mm, coarse natural and coarse technic) of selected urban soils in order to determine their contribution to the metal contamination of soils. Materials and Methods  Selected soils were collected from 9 sites according to a gradient of increasing anthropogenic influence from suburban to urban zones. Soils were air-dried, homogenized, and sieved (2 mm). The coarse fraction was sorted to separate the different technic materials and natural materials. Water extractions were run, on the natural, coarse fraction, on the complete technic fraction of the 9 soils and on average samples made of technic materials sorted out of 58 topsoils sampled from different sites in the city of Marrakech. Results  Results show that the percentage of the technic fraction increases while approaching the historic city center. It represented about 14% in the most anthropogenically disturbed soils. Along this gradient, soils changed progressively from Anthrosols to Technosols according to the WRB classification of urban and industrial soils. Analyses of metal contents showed that the fine fraction (<2 mm) mainly contributed to the metallic contamination of the water soluble fraction. The natural coarse fraction had the highest contribution to the copper release and was responsible for the release of all water-extractable copper in some soils. Concerning the technic fraction, it has a significant contribution essentially in the most anthropogenically disturbed soils as characterized by an elevated percentage of anthropogenic elements. The water extractable metal contents of average samples of these anthropogenic elements shows that elevated metal concentrations were released by bones, wood, plastic and fabric/paper. Discussion  This study concerns soils in urban areas, which are strongly impacted by human activities. Part of the soils can be classified as Anthrosols, profoundly impacted through the addition of organic materials from household wastes, irrigation, or cultivation. Other soils strongly impacted by human activities are Technosols dominated or strongly influenced by man-made materials. Technosols appear mostly in urban and industrial areas and are more likely to be contaminated than Anthrosols. The composition and heterogeneity of urban soils lead to modifications of the mobility and availability of pollutants depending on successive land-uses and on the composition of technic materials. The fine fraction offers a high transferring surface capacity, leading to a high mobilization of metals. The technic fraction contributes significantly to the metal release in the Technosols. This property can be explained by a reversible adsorption of metals on the organic matter. Conclusions  Results confirm that anthropogenic activity causes a wide spatial diversity of soil quality in the urban and suburban area. It introduces large amounts of technic materials in soils that could have an impact on the metal availability. It therefore acts on the metal bioavailability in the urban Technosols. Recommendations and Perspectives  These results show that it is necessary, in addition to the characterization of the fine particles, to take into account the contribution of the coarse fraction of the Technosols in the evaluation of risks of transfer of metals to the food chain.     

Anaerobic reoxidation of Mn2+, Fe2+, S0 and S2– in submerged paddy soils

Anaerobic reoxidation of reduced products in paddy soils was investigated. Ferrous iron (Fe²⁺) and monosulfide ion (S^2–) added to the soil chemically reduced MnO₂ to Mn²⁺, and MnO₂ and Fe(OH)₃ to Mn²⁺ and Fe²⁺, respectively, where Fe²⁺ and S^2– were considered to be oxidized to Fe³⁺ and S⁰. Elemental sulfur was oxidized to sulfate by anaerobic incubation with NO₃ ^– MnO₂ and Fe(OH)₃. A new conceptual model for the reduction processes in submerged paddy soil including the reoxidation processes of reduced products, in which soil heterogeneity in paddy fields was taken into consideration, was proposed based on the results. Received: 20 October 1996