Home About us Contact
|
Home About us Contact | ||
|
|
||
Natural Soil (natural + soil)
Selected AbstractsThe influence of groundwater on surface flow erosion processes during a rainstormEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2002D. L. RockwellArticle first published online: 27 MAY 200 Abstract Surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms. Erosion rate increases did not correlate well with surface hydraulic flow conditions, and all significant erosion increases began before the full soil depth was saturated, before the water table reached the soil surface, and before seepage was possible. Groundwater influenced erosion processes primarily by increasing unsaturated pore-water pressures and decreasing soil shear strength in surface rainflow, rather than through the direct entrainment of soil particles by seepage flow. There was no unique morphologic expression of the influence of groundwater during a rainstorm. Subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation, which included micropiezometers, tensiometers and time domain reflectometry. Erosion rate increases occurred all along the slope, and were not concentrated at the base of slope due to a seepage zone. Soil depth was crucial to determining surface erosion increase. It is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects. Groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data. Copyright © 2002 John Wiley & Sons, Ltd. [source] Transcription dynamics of the functional tfdA gene during MCPA herbicide degradation by Cupriavidus necator AEO106 (pRO101) in agricultural soilENVIRONMENTAL MICROBIOLOGY, Issue 3 2008Mette Haubjerg Nicolaisen Summary A modified protocol for simultaneous extraction of RNA and DNA, followed by real-time polymerase chain reaction quantification, was used to investigate tfdA gene expression during in situ degradation of the herbicide MCPA (4-chloro-2-methylphenoxy-acetic acid) in soil. tfdA encodes an ,-ketoglutarate-dependent dioxygenase catalysing the first step in the degradation pathway of MCPA and 2,4-D (2,4-dichlorophenoxy-acetic acid). A linear recovery of tfdA mRNA over three orders of magnitude was shown, and the tfdA mRNA level was normalized using the tfdA mRNA/DNA ratio. The density of active cells required for tfdA mRNA detection was 105 cells g,1 soil. Natural soil microcosms inoculated with Cupriavidus necator (formerly Ralstonia eutropha) AEO106 (pRO101) cells were amended with four different MCPA concentrations (2, 20, 50 and 150 mg kg,1). Mineralization rates were estimated by quantification of 14CO2 emission from degradation of 14C-MCPA. tfdA mRNA was detected 1 h after amendment at all four concentrations. In soils amended with 2 and 20 mg kg,1, the mRNA/DNA ratio for tfdA demonstrated a sharp transient maximum of tfdA expression from no to full expression within 3 and 6 h respectively, followed by a decline and complete loss of expression after 19 and 43 h. A more complex pattern of tfdA expression was observed for the higher 50 and 150 mg kg,1 amendments; this coincided with growth of C. necator AEO106 (pRO101) in the system. Repeated amendment with MCPA after 2 weeks in the 20 mg kg,1 scenario revealed a sharp increase of tfdA mRNA, and absence of a mineralization lag phase. For all amendments, tfdA mRNA was detectable only during active mineralization, and thus revealed a direct correlation between tfdA mRNA presence and microbial degrader activity. The present study demonstrates that direct analysis of functional gene expression dynamics by quantification of mRNA can indeed be made in natural soil. [source] Soil and plant diet exposure routes and toxicokinetics of lindane in a terrestrial isopodENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2000José Paulo Sousa Abstract In most studies dealing with effects of toxic substances in saprotrophic isopods, animals are exposed to the test substance through contaminated food. Because these animals can be in a close contact with the soil surface, the substrate, as an exposure pathway, should not be neglected. Here the authors analyze the toxicokinetic behavior of lindane (,-hexachlorocyclohexane [,-HCH]) in the isopod species Porcellionides pruinosus, comparing two exposure routes: food and two soil types (artificial Organisation for Economic Cooperation and Development [OECD] soil and a natural agricultural soil). In the feeding experiment, a strong decrease of ,-HCH concentration over time was observed on the food material, with the animals showing a broader range in chemical assimilation efficiency values (averaging 17.7% and ranging from 10 to 40%). The ,-HCH bioaccumulation results indicate that when animals incubated under both soil types reached a steady state, they displayed much higher body burdens (1,359.60 pg/animal on OECD soil and 1,085.30 pg/animal on natural soil) than those exposed to contaminated food (43.75 pg/animal). Kinetic models also revealed much lower assimilation and elimination rates in the food experiment (20.66 pg/d and 0.10 pg/d) than in both soil experiments (238.60 pg/d and 350.54 pg/d for the assimilation rate and 0.19 pg/d and 0.32 pg/d for the elimination rate). Differences in results between exposure routes are discussed according to equilibrium-partitioning theory and the enhanced relevance of the substrate exposure route is analyzed under future prospects on chemical toxicity testing using isopods. [source] Sensitivity of multi-coil frequency domain electromagnetic induction sensors to map soil magnetic susceptibilityEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2010D. Simpson Magnetic susceptibility is an important indicator of anthropogenic disturbance in the natural soil. This property is often mapped with magnetic gradiometers in archaeological prospection studies. It is also detected with frequency domain electromagnetic induction (FDEM) sensors, which have the advantage that they can simultaneously measure the electrical conductivity. The detection level of FDEM sensors for magnetic structures is very dependent on the coil configuration. Apart from theoretical modelling studies, a thorough investigation with field models has not been conducted until now. Therefore, the goal of this study was to test multiple coil configurations on a test field with naturally enhanced magnetic susceptibility in the topsoil and with different types of structures mimicking real archaeological features. Two FDEM sensors were used with coil separations between 0.5 and 2 m and with three coil orientations. First, a vertical sounding was conducted over the undisturbed soil to test the validity of a theoretical layered model, which can be used to infer the depth sensitivity of the coil configurations. The modelled sounding values corresponded well with the measured data, which means that the theoretical models are applicable to layered soils. Second, magnetic structures were buried in the site and the resulting anomalies measured to a very high resolution. The results showed remarkable differences in amplitude and complexity between the responses of the coil configurations. The 2-m horizontal coplanar and 1.1-m perpendicular coil configurations produced the clearest anomalies and resembled best a gradiometer measurement. [source] Soil infiltration, runoff and sediment yield from a shallow soil with varied stone cover and intensity of rainEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005Uttam Kumar Mandal Summary Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side-effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi-arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour,1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour,1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l,1 for 64.7% stone cover with rainfall of 48.5 mm hour,1 to 70 g l,1 for 3.5% stone cover with rain falling at 136.8 mm hour,1. The soil loss rate was less than 2 t ha,1 hour,1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour,1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size. [source] Behaviour and mechanism of Zn(II) adsorption on Chinese loess at dilute slurry concentrationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2008Xiaowu Tang Abstract BACKGROUND: Zn(II) is commonly present in mining drainage in developing countries. Since loess is abundant and always located near mining sites in China, it would be useful to investigate the possibility and efficiency of using loess to remove Zn(II) from aqueous solution. RESULTS: The Zn(II) adsorption capacity of Chinese loess was determined as 215.9 mg g,1. The adsorption followed pseudo-second-order kinetics and took place mainly by surface diffusion. Generally, higher initial pH and solute concentration resulted in higher % Zn(II) removal, while higher temperature and slurry concentration led to lower % Zn(II) removal. A thermodynamic study revealed that the adsorption process was exothermic, with the predicted enthalpy change ranging from ,20.87 to ,4.06 kJ mol,1. With the assistance of X-ray photoelectron spectroscopy and X-ray diffraction, the high adsorption capacity was ascribed to the growth of micro-organisms and mineral constituents such as kaolinite and goethite. CONCLUSION: Chinese loess proved effective for Zn(II) adsorption in this study. The optimal adsorption conditions included pH > 3.0, temperature ,15 °C and contact time , 400 min. As an abundant natural soil in arid areas with very low population density, it would be appropriate to develop this material into a wastewater-purifying agent. Copyright © 2008 Society of Chemical Industry [source] Reservoir and Non-reservoir Hosts of Bean-Wilt Pathogen, Fusarium oxysporum f. sp. phaseoliJOURNAL OF PHYTOPATHOLOGY, Issue 7-8 2001O. D. Dhingra Abstract The capacity of Fusarium oxysporum f. sp. phaseoli to multiply in the roots of 12 non-host plant species was determined with the objective of selecting potential candidates for crop rotation and/or green manuring in infested bean fields. The plants were inoculated at the seedling stage by a benomyl-resistant mutant of the pathogen using the root-dip technique and transplanted to natural soil. The number of colony forming units/g dry root tissue (CFU/g) was determined at the full bloom stage. Quantitatively, the root colonization differed greatly among the plant species. The roots and lower stem of Dolichos lablab, Phaseolus lunatus, Mucuna aterrima, Canavalia ensiforme and Vigna unguiculata were the most compatible with the pathogen and those of Sorghum bicolor, Crotalaria juncea, Oryza sativa and Zea mays were least compatible. No disease symptoms developed on any plant species. Chlamydospore germination in the rhizosphere also differed significantly among the plant species. There was no correlation between percentage chlamydospore germination in the rhizosphere and extent of root colonization. Most plant species recommended for green manuring in bean fields allowed extensive root and stem colonization by F. o. f. sp. phaseoli and were considered as reservoir hosts. All three of the gramineous species tested and C. juncea were classed as non-reservoir host, because the pathogen did not colonize the stem and its multiplication in the roots was very low. These plant species appear to be good candidates for long-term field evaluation to determine their usefulness in an integrated management of Fusarium bean-wilt. [source] Capacity of model biobeds to retain and degrade mecoprop and isoproturonPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 10 2003Vibeke V Henriksen Abstract Biobeds are used to increase the adsorption and degradation of pesticide spillage on sites used for mixing and loading and for cleaning of sprayers. The adsorption and the rate of degradation of 14C-labelled isoproturon and mecoprop (MCPP) at concentrations from 0.0005 to 25 000 mg kg,1 were determined in biobed soil. Further leaching of the two herbicides was determined in a model biobed with a surface area of 2 m2. The biobed material showed enhanced ability to adsorb the two herbicides. Kd was 5.2 litre kg,1 for isoproturon and 1.6 litre kg,1 for MCPP in biobed material, which is higher than in natural soil. In different experiments with natural soil, Kd ranges from 0.07 to 0.6 litre kg,1 for MCPP and from 1.5 to 4.6 litre kg,1 for isoproturon in soils with varying organic carbon content. Degradation of MCPP was rapid at concentrations from 0.0005 to 500 mg kg,1, delayed at 5000 mg kg,1, and very slow at 25 000 mg kg,1. For isoproturon, the relative degradation was most rapid at the lowest concentration and decreasing with increasing concentrations. After 120 days, between 55% and 8% 14C was evolved as 14CO2 at concentrations between 0.0005 and 25 000 mg kg,1. The rate of evolution of 14CO2 indicated that degradation rates at low concentrations were of first-order and at higher concentrations of zero-order. Leaching of MCPP and isoproturon was determined in a newly established model biobed during a 2-year period. About 13% of applied MCPP and 1.4% of applied isoproturon leached out during the winter following the first autumn application (worst-case scenario). Leaching was completely prevented when the biobed had a well-developed grass cover and was covered during the winter. Copyright © 2003 Society of Chemical Industry [source] Stable strontium accumulation by earthworms: A paradigm for radiostrontium interactions with its cationic analogue, calciumENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2001John E. Morgan Abstract The accumulation of stable strontium and its chemical analogue calcium by four species of earthworm, representing three distinct ecophysiological groups inhabiting celestite (SrSO4)-rich natural soils, was investigated. An increase in soil strontium concentration over a four-orders-of-magnitude range was accompanied by an increase in earthworm tissue strontium concentration. In contrast, no relationship between soil and tissue calcium concentrations was apparent, indicating that this essential cation is strongly regulated within earthworm tissues but that nonessential strontium burdens are not physiologically regulated. Concentration factors for strontium ranged from 0.1 to 1.42, with an inverse relationship between this parameter and soil strontium concentration. The use of concentration factors and discrimination coefficients lead to the conclusion that earthworms discriminate against strontium accumulation at increased soil calcium concentrations, such that strontium would be predicted to be more efficiently accumulated by worms inhabiting acidic, calcium-poor soils. Although few consistent trends in strontium and calcium concentration were apparent between earthworm species, the species with the highest calcium turnover (i.e., the litter-inhabiting Lumbricus rubellus) typically accumulated higher concentrations of strontium than representatives of contrasting ecophysiological classes. These findings are considered in the context of the distribution, retention, and cycling of radiostrontium in soils. [source] Increase in the fracture toughness and bond energy of clay by a root exudateEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008B. Zhang Summary Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg,1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 ± 2.5 kPa m,1/2 for 0 g PGA kg,1 to 86.9 ± 4.7 kPa m,1/2 for 12.2 g PGA kg,1. Washing increased KIC to 61.3 ± 1.2 kPa m,1/2 for 0 g PGA kg,1 and 132.1 ± 4.9 kPa m,1/2 for 12.2 g PGA kg,1. The apparent bond energy, ,, of the fracture surface increased from 5.9 ± 0.6 J m,2 for 0 g kg,1 to 12.0 ± 1.1 J m,2 for 12.2 g kg,1 PGA in the unwashed specimens. The washed specimens had , of 13.0 ± 1.9 J m,2 for 0 g kg,1 and 21.3 ± 2.6 J m,2 for 12.2 g PGA kg,1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability. [source] Effects of wetting and drying cycles on in situ soil particle mobilizationEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Majdalani Summary Understanding particle mobilization and transport in soils is a major concern for environmental protection and water resource management as they can act as vectors for sorbing pollutants. In natural soils, the existence of a finite size and renewable pool of dispersible particles has been hypothesized. Even though freeze-thaw and wetting-drying cycles have been identified as possible mechanisms of pool replenishment between rainfall events, to date the underlying phenomena ruling the renewal of particle pools are still largely unexplored. We carried out a series of infiltration-drainage experiments to study systematically the effects of periods without rain (pauses) on in situ particle mobilization in undisturbed soil columns. We found that, for a given column, pause duration between two rainfall events has a major influence on subsequent particle mobilization: the mass of leached particles increases with pause duration until it reaches a maximum (mass for a 200-hours pause is 15 time greater than for a 1-hour pause), and then it decreases for even longer pauses. This behaviour was correlated with soil water content, and can be explained by soil matrix weakening due to differential capillary stresses during drying. The consequences of this finding are important because the 15-fold increase in mass of leached particles, when pause duration is changed from 1 hour to 4 days, might overwhelm variations caused by changes in other parameters such as the ionic strength of the incoming solution or the rainfall intensity. [source] Darkness visible: reflections on underground ecologyJOURNAL OF ECOLOGY, Issue 2 2005A. H. FITTER Summary 1Soil science and ecology have developed independently, making it difficult for ecologists to contribute to urgent current debates on the destruction of the global soil resource and its key role in the global carbon cycle. Soils are believed to be exceptionally biodiverse parts of ecosystems, a view confirmed by recent data from the UK Soil Biodiversity Programme at Sourhope, Scotland, where high diversity was a characteristic of small organisms, but not of larger ones. Explaining this difference requires knowledge that we currently lack about the basic biology and biogeography of micro-organisms. 2It seems inherently plausible that the high levels of biological diversity in soil play some part in determining the ability of soils to undertake ecosystem-level processes, such as carbon and mineral cycling. However, we lack conceptual models to address this issue, and debate about the role of biodiversity in ecosystem processes has centred around the concept of functional redundancy, and has consequently been largely semantic. More precise construction of our experimental questions is needed to advance understanding. 3These issues are well illustrated by the fungi that form arbuscular mycorrhizas, the Glomeromycota. This ancient symbiosis of plants and fungi is responsible for phosphate uptake in most land plants, and the phylum is generally held to be species-poor and non-specific, with most members readily colonizing any plant species. Molecular techniques have shown both those assumptions to be unsafe, raising questions about what factors have promoted diversification in these fungi. One source of this genetic diversity may be functional diversity. 4Specificity of the mycorrhizal interaction between plants and fungi would have important ecosystem consequences. One example would be in the control of invasiveness in introduced plant species: surprisingly, naturalized plant species in Britain are disproportionately from mycorrhizal families, suggesting that these fungi may play a role in assisting invasion. 5What emerges from an attempt to relate biodiversity and ecosystem processes in soil is our extraordinary ignorance about the organisms involved. There are fundamental questions that are now answerable with new techniques and sufficient will, such as how biodiverse are natural soils? Do microbes have biogeography? Are there rare or even endangered microbes? [source] Sorption of HOC in soils with carbonaceous contamination: Influence of organic-matter compositionJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2005Kerstin Abelmann Abstract Detailed information about structure and composition of organic sorbents is required to understand their impact on sorption capacity and sorption kinetic of organic pollutants. Therefore, the chemical composition of organic material from 18 geosorbents was investigated by solid-state 13C nuclear-magnetic-resonance (NMR) spectroscopy. Structural parameters such as aromaticity, polarity, and alkyl-C content were related to the Freundlich sorption exponent (1/n) and the sorption coefficient . The geosorbents included three natural and four combusted coals (carbonaceous material), three Histosols, five mineral soils from Germany containing inputs of technogenic carbonaceous material, derived from industrial activities, and four non-contaminated mineral soils from Germany. Equilibrium sorption was measured for five hydrophobic organic compounds and analyzed with the solubility-normalized Freundlich sorption isotherm. With increasing maturation degree, the proportion of polar constituents decreases from the natural soils to the coals. In contrast to the non-polluted mineral soils, the soils with technogenic input are characterized by high aromaticity and low polarity. A positive correlation between sorption coefficient and aromaticity was found. The Freundlich exponent (1/n) is negatively correlated with the aromaticity, denoting an increase of adsorption processes with increasing aromaticity. Likewise, the contribution of partitioning decreases. This sorption mechanism predominates only if the organic matter in the samples contains a high proportion of polar compounds. Sorption von HOC in Böden mit kohleartiger Kontamination: Einfluss der Zusammensetzung des organischen Materials Um den Einfluss von organischen Sorbenten auf die Sorptionskapazität und die Kinetik organischer Schadstoffe zu verstehen, müssen detaillierte Informationen über deren Struktur und Zusammensetzung vorliegen. Aus diesem Grund wurde das organische Material von 18 Geosorbenten mittels der Festkörper- 13C-NMR-Spektroskopie untersucht. Strukturelle Parameter wie zum Beispiel die Aromatizität, die Polarität und der Alkyl-C-Gehalt wurden mit dem Freundlich-Exponenten 1/n und dem Sorptionskoeffizienten korreliert. Die Geosorbenten bestehen aus drei natürlichen und vier thermisch behandelten Kohlen, drei Histosolen und fünf deutschen Mineralböden, die technogenes kohlehaltiges Material aus industriellen Aktivitäten enthalten, sowie vier nicht kontaminierten deutschen Böden. Die Gleichgewichtssorption wurde für fünf hydrophobe, organische Verbindungen gemessen und mit Hilfe der löslichkeitsnormalisierten Freundlich-Isotherme analysiert. Der Anteil der polaren Komponenten nimmt von den natürlichen Böden zu den Kohlen mit zunehmendem Inkohlungsstadium ab. Im Gegensatz zu den nicht kontaminierten Mineralböden weisen die Böden mit technogenen Bestandteilen eine hohe Aromatizität und eine geringe Polarität auf. Zwischen dem und der Aromatizität ergab sich ein positiver Zusammenhang. Der Freundlich Exponent (1/n) korreliert negativ mit der Aromatizität. Dies weist auf eine Zunahme der Adsorptionsprozesse mit Erhöhung der Aromatizität hin. Der Beitrag der Partitionierung sinkt ebenfalls. Dieser Sorptionsmechanismus dominiert nur in den Proben, in denen das organische Material einen hohen Anteil polarer Bestandteile besitzt. [source] A new dawn , the ecological genetics of mycorrhizal fungiNEW PHYTOLOGIST, Issue 2 2000D. LEE TAYLOR Many human activities, such as ore mining and smeltering, sewage sludge treatment and fossil fuel consumption, result in toxic soil concentrations of ,heavy metals' (Al, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Ti, Zn and others) (Gadd, 1993). There are also natural soils, such as serpentine, with levels of heavy metals that inhibit or preclude the growth of many plants and soil micro-organisms. However, certain plants and microorganisms do grow in these metalliferous sites. Understanding the physiology, ecology and evolution of tolerance to elevated soil metal concentrations is important in an applied setting, and is also of interest in theoretical biology. Applied importance relates to the improvement of forest health in areas subject to increasing pollution, rehabilitation of severely polluted sites by phytostabilization of metals, and metal removal using hyperaccumulating plants (Krämer, 2000; Ernst, 2000). Areas of theoretical interest include the evolution of local adaptation (Sork et al., 1993) and how it is shaped by the combined influences of natural selection, gene flow and genetic architecture, as well as metal influences on various species interactions (Pollard, 2000). A paper appears on pages 367,379 in this issue by Jan Colpaert and coworkers which adroitly combines the disparate fields of physiology, genetics and ecology to answer several outstanding questions concerning heavy metal tolerance in mycorrhizal fungi. Mycorrhizal fungi, which interact mutualistically with the majority of plant species, are well known for improving the P status of their hosts (Smith & Read, 1997). Some mycorrhizal fungi are also able to mobilize N and P from organic substrates and to provide plants with improved micronutrient and water acquisition, pathogen resistance, and a variety of other benefits (Smith & Read, 1997). One of these additional benefits is the amelioration of toxicity in metalliferous soils. [source] | ||||||||||||||||