Soil Sections Research Articles

Explosive eruptive record in the Katmai region, Alaska Peninsula: an overview

At least 15 explosive eruptions from the Katmai cluster of volcanoes and another nine from other volcanoes on the Alaska Peninsula are preserved as tephra layers in syn- and post-glacial (Last Glacial Maximum) loess and soil sections in Katmai National Park, AK. About 400 tephra samples from 150 measured sections have been collected between Kaguyak volcano and Mount Martin and from Shelikof Strait to Bristol Bay (∼8,500 km2). Five tephra layers are distinctive and widespread enough to be used as marker horizons in the Valley of Ten Thousand Smokes area, and 140 radiocarbon dates on enclosing soils have established a time framework for entire soil–tephra sections to 10 ka; the white rhyolitic ash from the 1912 plinian eruption of Novarupta caps almost all sections. Stratigraphy, distribution and tephra characteristics have been combined with microprobe analyses of glass and Fe–Ti oxide minerals to correlate ash layers with their source vents. Microprobe analyses (typically 20–50 analyses per glass or oxide sample) commonly show oxide compositions to be more definitive than glass in distinguishing one tephra from another; oxides from the Kaguyak caldera-forming event are so compositionally coherent that they have been used as internal standards throughout this study. Other than the Novarupta and Trident eruptions of the last century, the youngest locally derived tephra is associated with emplacement of the Snowy Mountain summit dome ( 6 ka), two tephras (∼3,700 and ∼2,700 14C years B.P.), and a summit scoria cone with a crater still steaming today. Mount Katmai has three times produced very large explosive plinian to sub-plinian events (in 1912; 12–16 ka; and 23 ka) and many smaller pyroclastic deposits show that explosive activity has long been common there. Mount Griggs, fumarolically active and moderately productive during postglacial time (mostly andesitic lavas), has three nested summit craters, two of which are on top of a Holocene central cone. Only one ash has been found that is (tentatively) correlated with the most recent eruptive activity on Griggs (<3,460 14C years B.P.). Eruptions from other volcanoes NE and SW beyond the Katmai cluster represented in this area include: (1) coignimbrite ash from Kaguyak’s caldera-forming event (5,800 14C years B.P.); (2) the climactic event from Fisher caldera (∼9,100 14C years B.P.—tentatively correlated); (3) at least three eruptions most likely from Mount Peulik (∼700, ∼7,700 and ∼8,500 14C years B.P.); and (4) a phreatic fallout most likely from the Gas Rocks (∼2,300 14C years B.P.). Most of the radiocarbon dating has been done on loess, soil and peat enclosing this tephra. Ash correlations supported by stratigraphy and microprobe data are combined with radiocarbon dating to show that variably organics-bearing substrates can provide reliable limiting ages for ash layers, especially when data for several sites is available.

Constraints on understory vegetation communities of tidal freshwater swamps: a reciprocal transplant experiment1

Plant community composition may be limited by propagule availability, environmental constraints, or both. In the Nanticoke River watershed in Maryland and Delaware, herbaceous communities of tidal freshwater swamps in upstream areas are less diverse than in downstream areas. To test factors constraining plant community composition, a reciprocal transplant study was conducted between an upstream site with lower diversity, Broad Creek, and a downstream site with higher diversity, Deep Creek. Species composition, height, biomass, and below-canopy PAR were measured in sections of soil with rooted vegetation (sods) assigned to one of three treatments arranged in a randomized block design: transplant (excavated and moved between sites), disturbed control (excavated and replaced in same location), or undisturbed control (no excavation). Data were also collected on soil seed bank composition, hydrology, and salinity. Vegetation measures in sods transplanted from Deep to Broad Creek were not significantly different from control sods left at Deep Creek, but sods transplanted from Broad to Deep Creek developed a community intermediate to controls at either site. Broad Creek was inundated 10% longer than Deep Creek (P < 0.0001), and had lower light levels for four of five sample periods (P < 0.021); salinity was significantly higher in Deep Creek for all months (P < 0.001) and exceeded 3 parts per thousand in July. Seedling density (P = 0.013) and taxa density (P = 0.001) were four times higher in seedlings emerging from seed bank samples of Deep Creek than Broad Creek. The community that developed in sods transplanted into Broad Creek suggests that over short time scales, diversity may be increased by propagule additions. However, a combination of propagule availability and suitable environmental conditions over longer periods may be necessary to sustain a robust vegetation community.

Use of magnetic signatures to correlate tephra layers in Holocene loessial soil profiles from a small region, SE Iceland

Rock magnetic measurements have been applied to two adjacent loessial soil sections from a small region, SE Iceland. The soils are composed of reworked locally derived sediment (including airfall tephra) and also contain several visible discrete airfall tephra layers. The main magnetic minerals in the airfall tephras are ferrimagnetic (e.g. magnetite) with paramagnetic minerals also present. The main magnetic grain sizes in the tephras are pseudo single domain. The results show that individual tephras do not have unique magnetic signatures that can be used for identification and correlation between sedimentary sequences. However, a correlation of tephra layers was achieved through the application of statistical techniques to a comprehensive dataset of magnetic parameters. Similarity coefficients and Euclidian distance measures were used to identify the best correlation between tephra layers in the two soil profiles. The technique works well providing some tephras present within both profiles have been formally identified (e.g. Oraefajokulla ad 1362) using electron microprobe analyses. Given this initial framework, the statistical analyses of the magnetic parameters can help in the identification and correlation of unknown tephras between two soil profiles.

Persistence and movement of fipronil termiticide with under‐slab and trenching treatments

To have an effective barrier against invading termites around building structures and to assess the potential risks to the urban environment and human beings, we need to understand the fate of termiticides applied in urban soil. The movement and degradation of a new termiticide, fipronil, were investigated in Australian soils following standard termiticide treatment methods (surface application under slab and trenching treatments along walls). Surface application studies in three field sites showed slow dissipation and little movement for fipronil in all three soils under the simulated slab during a three-year period. The greatest mass of the chemical residues remained in the quartzite sand layer (thickness, 5 cm), and only small amounts of these were found to have migrated into the soil layers (depth, 0-15 cm) underneath the quartzite sand layer. Of the three metabolites (desulfinyl, sulfide, and sulfone) found in the soils, the sulfone derivative had the highest concentration. Persistence of fipronil was affected by application rate. The time for 50% loss of the total toxic components (fipronil plus its metabolites) in the quartzite sand layer (thickness, 5 cm) ranged from 200 to 326 d for the low rate (0.15 g active ingredient/m2) and from 633 to 674 d for the high application rate (3 g active ingredient/m2). One-year trenching studies at two sites in Adelaide (Roseworthy Farm [RF] and Terretfield [TF]; South Australia, Australia) showed that vertical movement and dissipation of fipronil occurred in the soils. The average concentration of fipronil in the trenches (depth, 0-30 cm) decreased from 33.7 to 14.9 mg/kg in the loam soil at the RF site and from 39.4 to 14.6 mg/kg in the clay soil at the TF site over the year. With time under the natural weather condition, fipronil and its derivatives were found in the deeper soil sections without treatment (depth, 20-30 cm). However, laboratory studies using repacked soil columns showed low mobility in the loam soil from the RF site and a variably charged clay soil from Malanda (Queensland, Australia) under intermittent wetting and drying conditions.

Carbon and nitrogen stable isotopes in forest soils of Siberia

N) stableisotopes in various biological objects. Since most bio-logical processes discriminate isotopes, i.e., use lighterisotopes for fermentative reactions [10] and leaveheavier isotopes in substrate, the study of isotopic com-positions of various habitats of organisms yields infor-mation on intensity and direction of biological pro-cesses. However, the interpretation of carbon and nitro-gen isotopic compositions in complex objects, such assoil, meets difficulties because of the far too great num-ber of factors that control isotope fractionation [2, 6,11, 13]. The forest soils of the Yenisei meridian signif-icantly vary in terms of environmental factors, and thisvariability opens up possibilities to reveal the mostimportant factors that determine carbon and nitrogenisotopic compositions of soils. In this work, the distri-bution of carbon and nitrogen isotopes in the forestsoils of the Yenisei region of Siberia was investigatedfor the first time. It has been shown that these isotopesare good indicators of (a) the intensity of organic matter(OM) mineralization, (b) the contribution of nitrogenfixation to the nitrogen status of ecosystems, and (c) theprovision of ecosystems with moisture.The soil samples were taken in August 2003 fromtest sites of the Siberian IGBP transect set up by theSukachev Institute of Forestry, Siberian Division, Rus-sian Academy of Sciences within the framework of theInternational Geosphere–Biosphere Program (IGBP) [7].The sections were set up in the northern taiga forests(lower reaches of the Nizhnyaya Tunguska River) andat the boundary between the southern taiga and the for-est–steppe zone (Pogorel’sky Bor Station). Thixotropiccryosol (kriozem) and brown taiga soil (podbur) werestudied in the northern taiga. Two sections of gray for-est soil in the birch and larch types of forest were stud-ied at the boundary between the southern taiga and for-est–steppe zones. The soil types chosen for the investi-gation are the most typical of the northern taiga andforest–steppe zones. The ecological and genetic charac-teristics of these soils are given in [9, 10]. Some chem-ical properties of the soils are presented in the table.Three soil samples were taken from each soil horizon,followed by an average composite sample. The sampleswere dried outdoors and screened through a sieve of 1mm. Carbon and nitrogen concentrations and isotoperatios (

The control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment

The study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape. These measurements are done with in-situ-produced cosmogenic nuclides (e.g., 10Be, 26Al), mostly in quartz from alluvial sediment. Cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the Earth's surface. They are produced within a characteristic depth scale of about 1 m, which means that the measured concentrations record an integrated denudation history while material passed through this depth interval. Depending on the denudation rate the resulting integration time scales are 103 to 105 years, and one obtains a robust long-term estimate of natural denudation that is relatively insensitive to short-term changes. The last 10 years have seen significant research activity using these methods, and an array of fascinating tectono-geomorphologic and geochemical insights are emerging. Amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change. A compilation of world-wide denudation rates in non-glaciated areas, that however, does not yet include some of the world's most active mountain belts, has resulted in the following findings, some of which have been unexpected: (1) No obvious relationship between precipitation or mean annual temperature and total denudation is apparent. (2) Topographic relief alone does not result in high rates of denudation. (3) Denudation rates are high in areas of landscape rejuvenation; that is triggered and controlled by tectonic activity (faulting, escarpment formation and retreat, rifting, surface uplift). (4) Rates of weathering (using a combination of cosmogenic nuclides and zirconium-normalised cation loss balances) co-vary primarily with physical erosion rates and much less with temperature or precipitation. (5) In some areas of high land use short-term rates (from river load gauging) exceed those from cosmogenic nuclides by several orders of magnitude, which serve to highlight the severity of geomorphic change caused by human action. In the future, the control mechanisms over denudation will be determined on all spatial scales, ranging from the single soil section to entire river basins. The same analysis can be done back through time on well-dated terraces, lake records, and marine sediment cores, which is possible with 10Be for the past 1–2 My. The rates obtained will be used to develop a quantitative understanding of tectonic, geomorphologic, and geochemical landscape processes, which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic, climate, and anthropogenic forcing.

Avoidance Test Using Earthworms (Eisenia fetida) for Contaminated Sites Evaluation: Preliminary Results for Hydrocarbon Contamination

Problems related to contaminated sites are increasing in Brazil. These sites can be represented by gas station, waste disposal areas, abandoned industrial facilities, etc. and in general are located in the neighborhood of important ecosystems, being cause of negative impacts. Evaluation of contaminated sites in Brazil has been done using only chemical parameters, without ecotoxicological studies. The aim of this study was initiate preliminary tests according to the draft of ISO that describes an avoidance test used to assess soil quality and toxicity from chemical to Eisenia fetida (earthworm). This test can be applied as a rapid screening test to determinate the bioavailability of chemicals or contaminants in soil to E. fetida, where the avoidance behaviour is used as indicator. In accordance to the results, it can be decided if reproduction test with the same species must be performed. Samples from contaminated sites with different hydrocarbons concentrations collected from a bus garage, a gas station and a contaminated oil spilling area were analysed. The results of the sample from the bus station showed that 96% of the organisms escaped from the contaminated sample section to the control soil section. This indicates that the sample can be considered toxic, presenting the habitat function limited. The toxicity of this sample was confirmed later by mortality and reproduction tests. The preliminary results indicated that avoidance test was a rapid indicator of sample toxicity and can be applied as a complement to evaluate hydrocarbons contaminated sites.

Pilot-scale electrokinetic treatment of a Cu contaminated red soil

A pilot-scale experiment for electrokinetic treatment of 700 kg of copper contaminated red soil was conducted using a constant voltage of 80 V. Dynamic removal percentages of Cu from the soil and energy consumption during the treatment were evaluated together with changes of soil pH, electrical conductivity and soil microbial functional diversity before and after the electrokinetic treatment. The results indicate that 76% of Cu was successfully removed from the soil after 140 d of treatment when lactic acid was used as enhancing reagent for adjusting the catholyte pH and dissolving soil Cu by complexation, and the pilot-scale electrokinetic experiment consumed electric energy of 224 kW h t −1 soil. The post-treatment soil pH values decreased about 0.1–1.6 units compared with the initial value (pH 4.8), and soil electrical conductivities in most of soil sections also significantly decreased. Soil microbial functional diversity varied after the electrokinetic treatment, particularly the increase of substrate richness index, which is possibly due to the stimulation of lactic acid that was introduced into the soil column during the experiment.

Influence of image resolution and evaluation algorithm on estimates of the lacunarity of porous media

In recent years, experience has demonstrated that the classical fractal dimensions are not sufficient to describe uniquely the interstitial geometry of porous media. At least one additional index or dimension is necessary. Lacunarity, a measure of the degree to which a data set is translationally invariant, is a possible candidate. Unfortunately, several approaches exist to evaluate it on the basis of binary images of the object under study, and it is unclear to what extent the lacunarity estimates that these methods produce are dependent on the resolution of the images used. In the present work, the gliding-box algorithm of Allain and Cloitre [Phys. Rev. A 44, 3552 (1991)] and two variants of the sandbox algorithm of Chappard et al. [J. Pathol. 195, 515 (2001)], along with three additional algorithms, are used to evaluate the lacunarity of images of a textbook fractal, the Sierpinski carpet, of scanning electron micrographs of a thin section of a European soil, and of light transmission photographs of a Togolese soil. The results suggest that lacunarity estimates, as well as the ranking of the three tested systems according to their lacunarity, are affected strongly by the algorithm used, by the resolution of the images to which these algorithms are applied, and, at least for three of the algorithms (producing scale-dependent lacunarity estimates), by the scale at which the images are observed. Depending on the conditions under which the estimation of the lacunarity is carried out, lacunarity values range from 1.02 to 2.14 for the three systems tested, and all three of the systems used can be viewed alternatively as the most or the least "lacunar." Some of this indeterminacy and dependence on image resolution is alleviated in the averaged lacunarity estimates yielded by Chappard et al.'s algorithm. Further research will be needed to determine if these lacunarity estimates allow an improved, unique characterization of porous media.

The control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment

The study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape. These measurements are done with in-situ produced cosmogenic nuclides (e.g. 10Be, 26Al), mostly in quartz from alluvial sediment. Cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the Earth's surface. They are produced within a characteristic depth scale of about 1 m, which means that the measured concentrations record an integrated denudation history while material passed through this depth interval. Depending on the denudation rate the resulting integration time scales are 10 3 to 10 5 years, and one obtains a robust long-term estimate of natural denudation that is relatively insensitive to short-term changes. The last 10 years have seen significant research activity using these methods, and an array of fascinating tectono-geomorphologic and geochemical insights are emerging. Amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change. A compilation of world-wide denudation rates in non-glaciated areas, that however, does not yet include some of the world's most active mountain belts, has resulted in the following findings, some of which have been unexpected: (1) No obvious relationship between precipitation or mean annual temperature and total denudation is apparent. (2) Topographic relief alone does not result in high rates of denudation. (3) Denudation rates are high in areas of landscape rejuvenation; that is triggered and controlled by tectonic activity (faulting, escarpment formation and retreat, rifting, surface uplift). (4) Rates of weathering (using a combination of cosmogenic nuclides and zirconium-normalised cation loss balances) co-vary primarily with physical erosion rates and much less with temperature or precipitation. (5) In some areas of high land use short-term rates (from river load gauging) exceed those from cosmogenic nuclides by several orders of magnitude, which serves to highlight the severity of geomorphic change caused by human action. In the future, the control mechanisms over denudation will be determined on all spatial scales, ranging from the single soil section to entire river basins. The same analysis can be done back through time on well-dated terraces, lake records, and marine sediment cores, which is possible with 10Be for the past 1–2 My. The rates obtained will be used to develop a quantitative understanding of tectonic, geomorphologic, and geochemical landscape processes, which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic, climate, and anthropogenic forcing.

Changes in Zinc Speciation in Field Soil after Contamination with Zinc Oxide

Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS) spectroscopy. Soil sections were studied by micro-X-ray fluorescence (micro-XRF) and micro-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn-LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled bythermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.

Impact of irrigation with As rich groundwater on soil and crops: A geochemical case study in West Bengal Delta Plain, India

The distribution of As was explored in soils and crops in order to investigate the influence of irrigation with As rich groundwater on the soil–plant system, and to determine its impact on the environment and human health. The study was carried out in an intensively cultivated agricultural area of the Bengal Delta Plain, West Bengal, India. Soils, plants, and irrigation water from adjacent rice and wheat fields were analysed for As and other elements. Irrigation water has concentrations of up to 780 μg L −1 As in the study area. Rice and wheat grains are not contaminated by As (about 0.3 and 0.7 mg kg −1, respectively), but concentrations in rice roots were found to be 169–178 mg kg −1 As, which is more than 20 times higher than value of 7.7 mg kg −1 measured at the uncontaminated reference site. This high content is due to an Fe-rich plaque which coats the rice roots. A significant increase of As concentration was registered also in the stems of the rice plants irrigated with As rich groundwater (6.55–7.06, relative to 0.36 mg kg −1 As in the reference plant). Arsenic concentration in the uppermost soil layers of the rice paddy field (38 mg kg −1) was found to be roughly twice as high as in the soil of the less intensively watered wheat field (18 mg kg −1) and more than 5 times higher than in the soil of a rice paddy irrigated with uncontaminated water (7 mg kg −1). In both soil sections As contents decreased downwards to 11 mg kg −1 at 100–110 cm depth, approaching the background value of 5–10 mg kg −1 measured in an unaffected reference area. Sequential extraction experiments show that most of the mobile As in soils is bound to Fe-oxides. Though no tight correlation was found between Fe and As in the bulk soil samples, these experiments coupled with μ-synchrotron radiation XRF analysis of single soil particles from the rice paddy also indicates that additional to the mobile fraction a substantial part of As is immobilized in (chiefly Fe bearing) silicates. In rice soil some As was also found in the sulphide-bearing phase of the extraction.

Cyst Distribution and Hatching Pattern ofChirocephalus ruffoi (Crustacea, Anostraca) in an Experimental Undisturbed Pool

The pattern of cyst distribution in the absence of turbation and their hatching behaviour were studied in an outdoor artificial pool, where just differentiated adults of the anostracan Chirocephalus ruffoi (sex ratio 1:3) lived until it dried up. The horizontal and vertical distributions of cysts in the pool bed were determined. The comparison between cyst bank estimate (Mura, 2004) and the actual number of cysts counted in the pool bed revealed an estimate error of 20.9%. Resting eggs occurred only in the upper 2.5 cm thick soil sections and decreased within this section as depth increased. Peripheral areas of the pool contained significantly larger numbers of cysts than the central area. Multiway analysis on the results recorded in hatching success (nested ANOVA) revealed that the differences were significantly affected by initial soil conditions, treatment and vertical distribution of cysts. Among these factors, vertical distribution (sections nested in cores) was the most influential. Hatching success was significantly inversely related to depth. Differences in the timing of hatching depending on the above considered factors were also noted. A nearly synchronous hatching pattern was observed only for cysts from initially dry sediment of the uppermost layers. In all successively deeper layers, hatching showed multiple peaks and was increasingly delayed and erratic (already mentioned). ANCOVA within each of the experimental conditions revealed significant differences in hatching frequencies (time as covariate) depending on sediment depth. Within any given layer, ANCOVA revealed a significant influence of initial sediment conditions and treatment on the timing of hatching. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fractal and multifractal analysis of pore-scale images of soil

We examine critically the fractal and multifractal analysis of two-dimensional images of soil sections. We demonstrate that, dependent on the porosity displayed in the image, both a fractal dimension and a multifractal spectrum can be extracted from such images irrespective of whether these images exhibit fractal structures and multifractal scaling of local density and porosity. We suggest ways to transform the data arising from the analysis in order to differentiate better between fractal and non-fractal images. We examine three soil images and conclude that there is no compelling evidence of scaling properties associated with mass fractal and multifractal structures. Our results point to a need for alternative methods for characterizing soil pore structures and to extend our modelling of complex and multiscale porous media to cases where scaling symmetries are relaxed.

Root stimulated nitrogen removal: only a local effect or important for water treatment?

Plants in constructed wetlands serve as carriers for attached microbial growth. They mainly transfer oxygen and release exsudates to the root zone. In consequence of this an area around the roots, called the rhizosphere exists, in which bacteria are stimulated by root growth. The goals were to ascertain whether stimulating the microbial cenosis only has a local effect on the rhizoplane, and to establish the importance of this stimulation for the water purification process in the root zone. Observations were carried out in a laboratory batch reactor filled with sand and planted with reeds (Phragmites australis). A small section was separated with gauze to avoid root growth outside this zone. The reactor was incubated with an artificial waste water containing a high concentration of ammonium. Samples were taken at intervals of 10 mm away from the gauze. The chemical and physical conditions and enzyme activities in soil sections at different distances from the roots affecting the efficiency of nitrogen removal were characterized. An influence was detectable by several parameters up to a specific root distance. Indirect parameters such as the total bacterial number and the DNA amount seem to be affected up to a distance of 50 mm from the root whereas the oxygen amount and DOC are unaffected at a distance exceeding 20-30 mm. This is an initial indication that improved nitrogen removal is also possible in the wider root surroundings. In view of the average root-to-root distance of 35 mm, the root-influenced area could therefore be expanded to the whole rooted zone in a constructed wetland. The influence on bacteria by roots is not just a local effect but may also play an important role in the whole purification process.

Electrokinetic remediation of a Cu–Zn contaminated red soil by controlling the voltage and conditioning catholyte pH

Electrokinetics is an innovative technique for treating heavy metals contaminated soil, especially low pH soils such as the Chinese red soil (Udic Ferrisols). In this paper, a Cu–Zn contaminated red soil is treated by electrokinetics. When the Cu–Zn contaminated red soil was treated without control of catholyte pH during the electrokinetic treatment, the soil pH in the soil sections near cathode after the experiment was high above 6, which resulted in accumulation of large amounts of Cu and Zn in the soil sections with such high pH values. Compared to soil Cu, soil Zn was more efficiently removed from the soil by a controlled electrokinetic method. Application of lactic acid as catholyte pH conditioning solution caused an efficient removal of Cu and Zn from the soil. Increasing the electrolyte strength (salt concentration) of the conditioning solution further increased Cu removal, but did not cause a significant improvement for soil Zn. Soil Cu and Zn fractions after the electrokinetic treatments were analyzed using sequential extraction method, which indicated that Cu and Zn precipitation in the soil section closest to the cathode in the treatments without catholyte pH control limited their removal from the soil column. When the catholyte pH was controlled by lactic acid and CaCl 2, the soil Cu and Zn removal percentage after 554 h running reached 63% and 65%, respectively. Moreover, both the residual soil Cu and Zn concentrations were lower than 100 mg kg −1, which is adequate and meets the requirement of the Chinese soil environmental quality standards.

The distribution and natural degradation of cyanide in goldmine tailings and polluted soil in arid and semiarid areas

Farmlands and rivers have been seriously polluted by cyanide from a goldmine tailings dam that collapsed in early spring of 1995 in Yining County, Xinjiang Autonomous Region of China. The cyanide distribution in the polluted farmland and the abandoned tailings dam was studied, three and 4 years after the accident occurred. The results indicated that natural degradation of cyanide in soils is slower than in natural water bodies. The cyanide transport in the soil section is similar to freely soluble salts. In arid and semiarid areas, cyanide can be highly enriched in the salt crust in which the concentration is even higher than the fresh tailings debris though cyanide has decomposed for 4 years. In the polluted farmland, the sticky layer in the soil section can highly adsorb and enrich cyanide so it can partly prevent cyanide transfer to groundwater. According to the characteristics of cyanide natural degradation in soil, the measures for prevention and cure of soil polluted by goldmine tailing dam collapse have been discussed.

Physical properties of soils under intensive agricultural management

Pedologic alterations after long-term sugar cane (Saccharum officinarum) cropping cycles under traditional soil management systems were studied on a farm in Bariri, SP, Brazil. A toposequence was established to evaluate the effects of the soil position in the relief in changing soil physical attributes. Morphological field descriptions and laboratory analyses were carried out on vertical profiles of the upper, middle and lower thirds of a Typic Haplorthox slope. Soil bulk density and macroporosity changed along the toposequence reflecting on soil hydrodynamics, especially in the lower slope parts. At sites with high clay levels, empty spaces were filled forming block shaped structures together with the micro-aggregate structure. The intensive cultivation induced the greatest soil structure alterations, even at the deepest layers. The study pointed out the importance of performing detailed morphological observations in vertical profiles, due to the great variation on pedological attributes over short distances. Compacted soil sections were observed side-by-side with desaggregated mottles in the same soil profile. This fact evidenced that both vertical (in each profile) and horizontal gradients (along a toposequence) need to be considered in studies of time sequence variation of pedological parameters.

Progressive Consolidation Settlement of Naturally Deposited Clayey Soil Under Embankment Loading

ABSTRACT In a naturally deposited soil foundation subject to embankment loading, a delayed settlement can often be observed after the embankment's completion, sometimes also showing acceleration over time. Frequently in such cases the soil exhibits an increase rather than a dissipation of excess pore pressure in some of its parts, a phenomenon which cannot be explained by conventional elasto-plastic consolidation theory. In this paper the possible mechanism for this kind of delayed settlement is investigated numerically using a soil-water coupled elasto-plastic computation under plane strain conditions. It is assumed that the soil section contains a medium dense sand layer and highly structured clay layers. A Super/subloading Yield Surface Cam-clay model is used to describe the elasto-plastic behavior of both the sand and the clay with respect to soil structure, overconsolidation and anisotropy. It is found that the delayed settlement behavior occurs under a certain constant embankment load, and persists over a period of 40 years, with increases in the settlement rate accompanied by both dissipation and a rise in excess pore pressure. The cause of this is the softening that co-occurs with the plastic compression of the soil skeleton. In other words, consolidation settlement can be considered as an example of “progressive consolidation with decay of structure”. Some typical characteristics of this delayed settlement behavior are also numerically examined with reference to the height and weight of the embankment, and to soil improvements using sand drains. When the embankment is much lower, the foundation does not undergo delayed consolidation, and when it is higher, the foundation becomes subject to circular slip failure. Soil improvement with sand drains can effectively shorten the length of time up to final settlement.

Paleoecology and dynamics of forest ecosystems in Central Evenkia during the past 2400 years

New data on the composition of surface assemblages of plant macroremains from soil and swamp samples have been obtained in the study of geomorphologically different localities in the middle reaches of the Nizhnyaya Tunguska River. The results of paleocarpological analysis of forest soil sections supported by relevant palynological and geochronological data are presented. Natural changes of the forest cover over the past 2400 years and quantitative characteristics of the paleoclimate during each stage are described.