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Carbon Content (carbon + content)
Kinds of Carbon Content Selected AbstractsDetermination of Total Organic Carbon Content and ,13C in Carbonate-Rich Detrital SedimentsGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 3 2007Valier Galy carbone organique; décarbonatation; solubilisation; sediment; carbonate The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (Corg) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble Corg respectively. In Himalayan and Amazon river sediments, the proportion of Corg solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the Corg content for the dissolved organic carbon content measured after decarbonation. Data presented here show that Corg dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment. La détermination de la teneur totale en carbone organique et de sa composition dans des sédiments détritiques requiert leur décarbonatation préalable. l'élimination complète de carbonates tels que la dolomite ne peut être réalisée qu'au moyen d'une attaque avec un acide en phase liquide ce qui peut entrainer la solubilisation d'une partie du carbone organique. Pour un ensemble de sédiments détritiques provenant du système Himalayen et de l'Amazone ainsi que pour cinq matériaux géologiques de référence, nous avons déterminé la proportion de carbone organique (Corg) solubilisé lors de la décarbonatation. Celle-ci est significative pour l'ensemble des sédiments analysés et tend à augmenter avec la teneur en carbone organique. En comparaison avec les autres types de sédiments analysés, les fractions argileuses extraites de sédiments de rivière et les sédiments de fond très pauvres en Corg ont une proportion de Corg soluble dans l'acide respectivement élevée et faible. Dans les sédiments himalayens et amazoniens, la proportion de Corg solubilisé lors de la décarbonatation est plutôt constante avec des valeurs moyennes respectives de 14 et 19%. Nous pouvons donc calculer avec précision la teneur totale en carbone organique à partir de la teneur en Corg déterminée après décarbonatation. Nos données montrent que la solubilisation de Corg lors de la décarbonatation par un acide en solution est importante et doit être prise en compte lors de la détermination de la teneur en carbone organique. Moyennant une calibration minutieuse, la méthode que nous présentons devrait donc être utilisée pour l'analyse de sédiments détritiques riches en carbonates. [source] The Dry Limit of Microbial Life in the Atacama Desert Revealed by Calorimetric ApproachesENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2008N. Barros Abstract The Atacama desert in Chile is one of the driest and most lifeless environments on Earth. It rains possibly once a decade. NASA examined these soils as a model for the Martian environment by comparing their degradation activity with Martian soil and looking for "the dry limit of life". The existence of heterotrophic bacteria in Atacama soil was demonstrated by DNA extraction and by the isolation of microorganisms. So far, however, no data have been available about the metabolic activities in these soils due to the limitations of the existing methodologies when applied to desert soils. Calorimetry was used to obtain information on the metabolic and thermal properties of eleven soil samples collected at different sites in the Atacama desert. Differential scanning calorimetry and isothermal calorimetry were employed to determine the pyrolysis properties of the carbon-containing matter and to measure biomass and microbial metabolism. They were compared to other soil properties such as total carbon and nitrogen, carbon to nitrogen ratio and pH. There was measurable organic matter in nine of the eleven samples and the heat of pyrolysis of those soils was correlated to the carbon content. In five of the eleven samples no biomass could be detected and the existence of basal microbial metabolism could not be established because all samples showed endothermic activity, probably from inorganic reactions with water. Six samples showed microbial activation after the addition of glucose. Carbon content, nitrogen content and the microbial activity after glucose amendment were correlated to the altitude and to the average minimum temperature of the sampling sites calculated from meteorological data. The detectable microbial metabolism was more dissipative with increasing altitude and decreasing temperature. [source] NITROGEN LIMITATION EFFECTS OF DIFFERENT NITROGEN SOURCES ON NUTRITIONAL QUALITY OF TWO FRESHWATER ORGANISMS, SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AND SYNECHOCOCCUS SP. (CYANOPHYCEAE)JOURNAL OF PHYCOLOGY, Issue 5 2003Gunnel Ahlgren Food quality for grazers has been related to mineral (nitrogen, phosphorus) and biochemical (amino acids, fatty acids) constituents. The aim of the study was to examine the influence of different nitrogen sources on these constituents in two organisms, the green alga Scenedesmus quadricauda Turp. and the cyanobacterium Synechococcus sp., commonly used in feeding experiments. The two organisms were grown in continuous cultures at different growth rates. Nitrate or ammonium salts were used as nitrogen sources under both replete and limited conditions. Carbon content (mg·g,1 dry weight) was stable in both organisms independent of nitrogen source, nitrogen limitation, and growth rate. Nitrogen content decreased with limitation and growth rate in Scenedesmus and to a lesser degree in Synechococcus, whereas changes in phosphorus content were not statistically significant. The relative proportions of amino acids (% of total amino acids) were relatively stable in both organisms, whereas the proportions of fatty acids varied with growth rate and limitation. Fatty acid content was much lower in Synechococcus than in Scenedesmus. At N limitation, polyunsaturated fatty acids (PUFAs) showed lower levels in both organisms. The change occurred in the ,3 PUFA (linolenic acid) of the green alga and in the ,6 PUFA (linoleic acid) of the cyanobacterium. The difference in the response of N limitation in the two organisms may be traced to the different composition of the chloroplast membranes (the prokaryotic way) and the microsomal membranes (the eukaryotic way) where the desaturation takes place. [source] Host plant variation in plant-mediated indirect effects: moth boring-induced susceptibility of willows to a specialist leaf beetleECOLOGICAL ENTOMOLOGY, Issue 2 2008SHUNSUKE UTSUMI Abstract 1.,We examined the plant-mediated indirect effects of the stem-boring moth Endoclita excrescens (Lepidoptera: Hepialidae) on the leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) in three willow species, Salix gilgiana, S. eriocarpa, and S. serissaefolia. 2.,When the stem-boring moth larvae damaged stems in the previous year, willows were stimulated to produce vigorously growing lateral shoots on these stems. These new lateral shoots were significantly longer and the upper leaves had significantly higher nitrogen and water content than current-year shoots on unbored stems, although the carbon content and leaf dry mass were not different between lateral and current-year shoots. 3.,In the field, leaf beetle larvae and adults had significantly greater densities on lateral shoots of bored stems than on current-year shoots of unbored stems. A laboratory experiment showed that female beetles had significantly greater mass and fecundity when fed on leaves of newly-emerged lateral shoots. Thus, the stem-boring moth had a positive effect on the temporally and spatially separated leaf beetle by increasing resource availability by inducing compensatory regrowth. 4.,The strength of the indirect effects on the density and performance of the leaf beetle differed among willow species, because there was interspecific variation in host quality and herbivore-induced changes in plant traits. In particular, we suggest that the differences in magnitude of the changes among willow species in shoot length and leaf nitrogen content greatly affected the strength of the plant-regrowth mediated indirect effect, coupled with host-plant preference of the leaf beetle. [source] A review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emissionECOLOGY LETTERS, Issue 10 2009Lingli Liu Abstract Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO2, CH4 and N2O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO2 exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH4 emission by 97%, reduced CH4 uptake by 38% and increased N2O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO2 reduction could be largely offset (53,76%) by N stimulation of global CH4 and N2O emission from multiple ecosystems. [source] Rainwater Dissolved Organic Carbon: Characterization of Surface Active Substances by Electrochemical MethodELECTROANALYSIS, Issue 19-20 2007osovi Abstract Surface active substances as organic constituents of bulk precipitation were studied by AC voltammetric method. Adsorption characteristics at the mercury electrode of real rainwater samples are compared with aqueous solutions of a number model substances suggested to be representative of water soluble organic compounds (WSOC) in atmospheric aerosols and droplets: monocarboxylic, dicarboxylic, and polyacidic compounds, levoglucosan, polyaromatic hydrocarbon naphtalene and anionic surfactant sodium dodecylbenzene sulfonate. On the basis of the capacitance vs. potential curves and the surfactant activity normalized to the organic carbon content it is concluded that humic like substances, monocarboxylic acids and polyaromatic hydrocarbons may play an important role in atmospheric aquatic system because of their surface active potential. [source] Nanodiamond Thin Film Electrodes: Metal Electro-Deposition and Stripping ProcessesELECTROANALYSIS, Issue 3 2003Hian, Lau Chi Abstract The properties of a nanodiamond thin film deposit formed on titanium substrates in a microwave-plasma enhanced CVD process, are investigated for applications in electroanalysis. The nanodiamond deposit consists of intergrown nano-sized platelets of diamond with a high sp2 carbon content giving it high electrical conductivity and electrochemical reactivity. Nanodiamond thin film electrodes (of approximately 2,,m thickness) are characterized by electron microscopy and electrochemical methods. First, for a reversible one electron redox system, Ru(NH3)63+/2+, nanodiamond is shown to give well-defined diffusion controlled voltammetric responses. Next, metal deposition processes are shown to proceed on nanodiamond with high reversibility and high efficiency compared to processes reported on boron-doped diamond. The nucleation of gold is shown to be facile at edge sites, which are abundant on the nanodiamond surface. For the deposition and stripping of both gold and copper, a stripping efficiency (the ratio of electro-dissolution charge to electro-deposition charge) of close to unity is detected even at low concentrations of analyte. The effect of thermal annealing in air is shown to drastically modify the electrode characteristics probably due to interfacial oxidation, loss of active sp2 sites, and loss of conductivity. [source] The Dry Limit of Microbial Life in the Atacama Desert Revealed by Calorimetric ApproachesENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2008N. Barros Abstract The Atacama desert in Chile is one of the driest and most lifeless environments on Earth. It rains possibly once a decade. NASA examined these soils as a model for the Martian environment by comparing their degradation activity with Martian soil and looking for "the dry limit of life". The existence of heterotrophic bacteria in Atacama soil was demonstrated by DNA extraction and by the isolation of microorganisms. So far, however, no data have been available about the metabolic activities in these soils due to the limitations of the existing methodologies when applied to desert soils. Calorimetry was used to obtain information on the metabolic and thermal properties of eleven soil samples collected at different sites in the Atacama desert. Differential scanning calorimetry and isothermal calorimetry were employed to determine the pyrolysis properties of the carbon-containing matter and to measure biomass and microbial metabolism. They were compared to other soil properties such as total carbon and nitrogen, carbon to nitrogen ratio and pH. There was measurable organic matter in nine of the eleven samples and the heat of pyrolysis of those soils was correlated to the carbon content. In five of the eleven samples no biomass could be detected and the existence of basal microbial metabolism could not be established because all samples showed endothermic activity, probably from inorganic reactions with water. Six samples showed microbial activation after the addition of glucose. Carbon content, nitrogen content and the microbial activity after glucose amendment were correlated to the altitude and to the average minimum temperature of the sampling sites calculated from meteorological data. The detectable microbial metabolism was more dissipative with increasing altitude and decreasing temperature. [source] Molecular diversity and characterization of nitrite reductase gene fragments (nirK and nirS) from nitrate- and uranium-contaminated groundwaterENVIRONMENTAL MICROBIOLOGY, Issue 1 2003Tingfen Yan Summary Nitrate-contaminated groundwater samples were analysed for nirK and nirS gene diversity. The samples differed with respect to nitrate, uranium, heavy metals, organic carbon content, pH and dissolved oxygen levels. A total of 958 nirK and 1162 nirS clones were screened by restriction fragment length polymorphism (RFLP) analysis: 48 and 143 distinct nirK and nirS clones, respectively, were obtained. A single dominant nirK restriction pattern was observed for all six samples and was 83% identical to the Hyphomicrobium zavarzinii nirK gene. A dominant nirS pattern was observed for four of the samples, including the background sample, and was 95% identical to the nirS of Alcaligenes faecalis. Diversity indices for nirK and nirS sequences were not related to any single geochemical characteristic, but results suggested that the diversity of nirK genes was inversely proportional to the diversity of nirS. Principal component analysis (PCA) of the sites based on geochemistry grouped the samples by low, moderate and high nitrate but PCA of the unique operational taxonomic units (OTUs) distributions grouped the samples differently. Many of the sequences were not closely related to previously observed genes and some phylogenetically related sequences were obtained from similar samples. The results indicated that the contaminated groundwater contained novel nirK and nirS sequences, functional diversity of both genes changed in relation to the contaminant gradient, but the nirK and nirS functional diversity was affected differently. [source] Effect of organic carbon content, clay type, and aging on the oral bioavailability of hexachlorobenzene in rats,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2007Shakil A. Saghir Abstract Bioavailability of lipophilic chemicals is influenced by the physicochemical properties of soils/sediment such as particle size, pH, clay, and organic carbon content. The present study investigated the effects of sediment composition and aging on the oral bioavailability of hexachlorobenzene (HCB) in rats. Formulated sediments were prepared using various ratios of kaolinite and montmorillonite clay, sand, peat moss, and black carbon, spiked with 14C-HCB, and orally administered to rats prior to and after one year of aging in dark at 10°C. In the nonaged sediments there was a 21 to 45% reduction in the oral bioavailability of HCB when compared to the corn oil standard without any clear pattern of the impact of the sediment clay and/or organic carbon content. One year of aging resulted in statistically significant (p = 0.049) reduction in the oral bioavailability of HCB from the sediments compared to the corn oil standard and nonaged sediment indicating stronger interactions between HCB and sediment contents with aging. The mean reduction in oral bioavailability after one year of aging ranged from approximately 5 to 14% greater than that observed for nonaged sediments. The fecal elimination of the HCB-derived radioactivity from the one-year-aged sediments was much higher than the nonaged sediments, consistent with the lower absorption from the gastrointestinal tract due to lower desorption of HCB from the aged sediments. Increase in the fecal elimination and decrease in oral bioavailability of 14C-HCB was related to the increase in clay and black carbon. [source] The long-term fate of polychlorinated biphenyls in San Francisco Bay (USA)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2004Jay A. Davis Abstract A simple one-box mass budget model is presented as a first step toward a quantitative understanding of the long-term fate of polychlorinated biphenyls (PCBs) in San Francisco Bay (USA). Sensitivity analysis indicated that the most influential input parameters were degradation half-life in sediment, Kow, outflow, average PCB concentration in sediment, and depth of the active sediment layer. Moderately influential parameters included organic carbon content of suspended solids, sediment burial mass transfer coefficient, and Henry's law constant. If external loading could be eliminated entirely, the mass of PCBs in the bay is predicted to drop to half of the present value in 20 years. The model predicts that sustained loading of 10 kg year,1 would prevent the total PCB mass in the bay from ever dropping below 10% of the present mass. With a sustained loading of 20 kg year,1, the model predicts that the total PCB mass would never fall below about 25% of the present mass. The half-lives in the bay for the individual PCB congeners evaluated in this report ranged from four years for PCB 18 to 30 years for PCB 194. [source] The potential for estradiol and ethinylestradiol to sorb to suspended and bed sediments in some English riversENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Karlijn I. E. Holthaus Abstract The endocrine-disrupting impact of steroid estrogens on fish will be strongly influenced by their distribution between sediment and water. Laboratory studies were performed to investigate the potential for sorption of 17,-estradiol (E2) and 17,-ethinylestradiol (EE2) to bed and suspended sediments taken from five British rivers. Sediment material was collected from the Rivers Aire and Calder (located in urban and industrialized areas in Yorkshire, UK), the River Thames (at a relatively rural site in Oxfordshire, UK), and from the estuaries of the Rivers Tees and Tyne. Using anaerobic conditions to inhibit biodegradation, it was found that 80 to 90% of binding to bed sediments was complete within 1 d, but that an equilibrium had not been reached after 2 d. Bed sediments gave distribution coefficients (Kd) ranging from 4 to 74 L/kg for E2 and from 8 to 121 L/kg for EE2 for samples taken over a range of seasons and locations. Sorption to suspended sediment gave Kd values ranging from 21 to 122 L/kg for E2 and 19 to 260 L/kg for EE2. However, these Kd values suggest less than 1% removal of the steroid estrogens from the aqueous phase given the ambient suspended sediment concentration. In the bed sediments, higher Kd values were associated with smaller particle size and higher organic carbon content. In most cases, the Kd values obtained for EE2 were higher than those for E2 by a factor of up to three. [source] Mutagenicity and disinfection by-products in surface drinking water disinfected with peracetic acidENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2002Silvano Monarca Abstract The aims of this research were to study the influence of peracetic acid (PAA) on the formation of mutagens in surface waters used for human consumption and to assess its potential application for the disinfection of drinking water. The results obtained using PAA were compared to those found with sodium hypochlorite (NaClO) and chlorine dioxide (ClO2). The Ames test, root anaphase aberration assay, and root/micronuclei assay in Allium cepa and Tradescantia/micronuclei test were used to evaluate the mutagenicity of disinfected samples. Microbiological tests were also performed, and disinfection by-products (DBPs) were identified using gas chromatography/mass spectrometry (GC/MS). A slight bacterial mutagenicity was found in raw lake and river water, and similar activity was detected in disinfected samples. A plant test revealed genotoxicity in raw river water, and microbiological analysis showed that PAA has bactericidal activity but lower than that of the other disinfectants. The DBPs produced by PAA were mainly carboxylic acids, which are not recognized as mutagenic, whereas the waters treated with the other disinfectants showed the presence of mutagenic/carcinogenic halogenated DBPs. However, additional experiments should be performed with higher concentrations of PAA and using water with higher organic carbon content to better evaluate this disinfectant. [source] Chlorinated hydrocarbons in flatfishes from the Southern California, USA, BightENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2000Kenneth Schiff Abstract Alhough inputs of chlorinated hydrocarbon compounds to the Southern California Bight (SCB) are presently low, historical deposits represent a source of bioaccumulation potential to sediment-associated fauna. To assess this bioaccumulation potential, 14 chlorinated hydrocarbon classes were measured in livers of three species of flatfish collected from 63 randomly selected sites on the coastal shelf between Point Conception and the United States,Mexico international border. Tissue contamination was widespread throughout the SCB, but was limited to just two chlorinated hydrocarbon classes. Virtually 100% of Pacific sanddab (Citharichthys sordidus) and longfin sanddab (Citharichthys xanthostigma) populations were estimated to be contaminated with dichlorodiphenyltrichloroethane (total DDT = sum of o,p, and p,p, isomers of DDT + dichlorodiphenyldichloroethylene [DDE] + dichlorodiphenyldichloroethane [DDD]) and/or polychlorinated biphenyls (total PCBs). Total DDT also contaminated the majority (64%) of the Dover sole (Microstomus pacificus) population in the SCB. Total PCB measurements in tissues of SCB flatfish were dominated by 12 congeners (52, 66, 87, 101, 105, 118, 128, 138, 153, 170, 180, and 187), which averaged 95% of the combined mass of the 27 congeners analyzed. Sediment concentrations (normalized by total organic carbon content) accounted for most of the variability observed in tissue concentrations (normalized by lipid content) for 8 of these 12 congeners and total PCBs. Normalized sediment concentrations were also significantly correlated to normalized tissue concentrations for total DDT and p,p,-DDE. Tissue concentrations measured in this study from reference areas of the SCB were compared to tissue concentrations measured from reference areas in studies conducted in 1977 and 1985. Total DDT and total PCB liver concentrations were found to have decreased one to two orders of magnitude in Pacific and longfin sanddabs between 1985 and 1994. Total DDT and total PCB liver concentrations decreased 5- to 35-fold in Dover sole between 1977 and 1994. [source] Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Jorge Barcena Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [source] Designing Ultrahigh Strength Steels with Good Ductility by Combining Transformation Induced Plasticity and Martensite AgingADVANCED ENGINEERING MATERIALS, Issue 7 2009Dierk Raabe We present results on precipitation hardened ductile high strength maraging-TRIP steels with up to 1.5 GPa strength and good ductility. The alloys have low carbon content (0.01 wt% C), 9,15 wt% Mn, and additions of Ni, Ti, and Mo (1,2 wt%) for precipitation. Martensite aging leads to a surprising simultaneous increase in strength and total elongation for samples with 9 wt% Mn and 12 wt% Mn. [source] Using soil knowledge for the evaluation of mid-infrared diffuse reflectance spectroscopy for predicting soil physical and mechanical propertiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008B. Minasny Summary Mid-infrared diffuse reflectance spectroscopy can provide rapid, cheap and relatively accurate predictions for a number of soil properties. Most studies have found that it is possible to estimate chemical properties that are related to surface and solid material composition. This paper focuses on prediction of physical and mechanical properties, with emphasis on the elucidation of possible mechanisms of prediction. Soil physical properties that are based on pore-space relationships such as bulk density, water retention and hydraulic conductivity cannot be predicted well using MIR spectroscopy. Hydraulic conductivity was measured using a tension-disc permeameter, excluding the macropore effect, but MIR spectroscopy did not give a good prediction. Properties based on the soil solid composition and surfaces such as clay content and shrink-swell potential can be predicted reasonably well. Macro-aggregate stability in water can be predicted reasonably as it has a strong correlation with carbon content in the soil. We found that most of the physical and mechanical properties can be related back to the fundamental soil properties such as clay content, carbon content, cation exchange capacity and bulk density. These connections have been explored previously in pedotransfer functions studies. The concept of a spectral soil inference system is reiterated: linking the spectra to basic soil properties and connecting basic soil properties to other functional soil properties via pedotransfer functions. [source] Changes in shrinkage of restored soil caused by compaction beneath heavy agricultural machineryEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008B. Schäffer Summary Compaction is a major cause of soil degradation. It affects not only the porosity of the soil, but also the soil's hydrostructural stability. Soil that is restored after temporary removal is particularly sensitive to compaction. We investigated the effects of trafficking with a heavy combine harvester on the shrinkage behaviour of a restored soil that had been gently cultivated for several years. We tested the hypothesis that compaction decreases the hydrostructural stability of restored soil by analysing simultaneously measured shrinkage and water retention curves of undisturbed soil samples. Shrinkage strongly depended on clay and organic carbon content. Taking account of this influence and normalizing the shrinkage parameters with respect to these soil properties, we found pronounced effects of trafficking on shrinkage. Ten passes with the combine harvester decreased the structural porosity by about 40% at maximum swelling and by about 30% at the shrinkage limit and increased the bulk density by 8% at maximum swelling and by 10% at the shrinkage limit, but did not significantly affect the porosity of the soil plasma. Moreover, trafficking modified shrinkage, increasing the slopes of the shrinkage curve in the basic and structural shrinkage domains by about 30% and more than 150% after 10 passes, respectively. Evidently the aggregate structure was strongly destabilized. The results indicate that the hydrostructural stability of the soil was still very sensitive to compaction by trafficking even 5 years after restoration. The analysis of shrinkage seemed well suited for the assessment of compaction effects on soil structure. [source] Temporal denitrification patterns in different horizons of two riparian soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2003A-C. Cosandey Summary The dynamics of biological denitrification in riparian soil is still poorly understood. We studied the spring-time pattern of denitrifying enzyme activity (DEA) and the rate of denitrification (DNT) in two hydromorphic riparian soils, one a mollic Gleysol and the other a terric Histosol. The average DEA ranged from 73 to 1232 ng N g,1 hour,1, and DNT ranged from 4 to 36 ng N g,1 hour,1. Both DEA and DNT diminished with increasing depth in both soil types. This decrease corresponded to a decrease in total and K2SO4 -extractable organic carbon and K2SO4 -extractable mineral nitrogen. The DEA and DNT differed in their dynamics. The former had no evident pattern in subsurface horizons but increased with temperature at the end of spring in surface and structural horizons. The DNT diminished as the soil dried in the mollic Gleysol when the water table fell. In the terric Histosol, the water table was still too high at the end of spring to affect the DNT. The results suggest that the vertical pattern of denitrification is related to that of organic carbon content. This organic carbon content determines biological activity and the supply of carbon and nitrous oxides. In biologically active horizons temperature drives the dynamics of DEA, whereas soil moisture drives the dynamics of DNT. Our results show the importance of the dynamic soil,water relationship in controlling denitrification within the riparian zone. [source] Soil solution concentration of Cd and Zn canbe predicted with a CaCl2 soil extractEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2003F. Degryse Summary Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ,labile' and ,fixed' pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C). [source] Predicting carbon content in illitic clay fractions from surface area, cation exchange capacity and dithionite-extractable ironEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2002M. Kahle Summary We used the specific surface area (SSA), the cation exchange capacity (CEC) and the content of dithionite-extractable iron (Fed) to predict the content of organic carbon in illitic clay fractions of topsoils from loess. We determined SSA (BET-N2 method) and CEC of clay fractions after removing organic C or reducing oxides or both. The CEC and the SSA of the carbon- and oxide-free clay fraction explained 56% and 54% of the variation in C content, respectively. The Fed content of the clay fractions was strongly and negatively related to the C content, and with the SSA of the carbon-free clay fraction it predicted C content almost completely (R2 = 0.96). The results indicate that the amount of cations adhering to the silicate clay minerals and the size of the silicate mineral surface area are important properties of the mineral phase for the storage potential of C. The reason for the negative relation between iron oxides and C content remains unclear. [source] The effect of aging biosolids on the availability of cadmium and zinc in soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2001S. Stacey Summary A major concern with the safe re-use of biosolids on land is the potential for release of metals from organic matter in the biosolids, due to decomposition proceeding as biosolids age. To quantify the effects of biosolid aging on Cd and Zn bioavailability, two sewage sludges (Lagoon sludge and Filtered sludge) and a garden compost were incubated at 25°C and 35°C for 100 days. Changes in availability of Cd and Zn were determined using isotope dilution principles, with the materials being labelled with carrier-free 109Cd and 65Zn. We determined isotopically exchangeable metal pools (E values) and plant available metal pools (L values) by measuring specific activities of Cd and Zn in soil extracts and in wheat plants, respectively. Changes in carbon content over time were determined using 13C-NMR spectroscopy and chemical extraction methods, and related to changes in availability of metal pools as determined by isotopic procedures. Hot-water-extractable carbon content, assumed to represent easily decomposable organic matter, decreased during the 100 days by 80,190 mg kg,1. The Compost and Lagoon sludge showed no change in L values for Cd or Zn with time, but in the Filtered sludge the L values for Cd and Zn increased significantly, by 43% and 56%, respectively. The isotopically exchangeable pools of Cd and Zn did not change with incubation treatment of the biosolids. These data indicate that the potential for metal release from biosolids as organic matter decomposes depends to a large extent on the biosolid composition. [source] High-Performance Carbon-LiMnPO4 Nanocomposite Cathode for Lithium BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Seung-Min Oh Abstract A cathode material of an electrically conducting carbon-LiMnPO4 nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO4 electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 °C. This electrode delivers a discharge capacity of 158 mAh g,1 at 1/20 C, 126 mAh g,1 at 1 C, and 107 mAh g,1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confirm that the carbon particles surrounding the LiMnPO4 protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C-LiMnPO4 electrode are also verified by electrochemical impedance spectroscopy. [source] Essential fatty acids and phosphorus in seston from lakes with contrasting terrestrial dissolved organic carbon contentFRESHWATER BIOLOGY, Issue 1 2007KELLY GUTSEIT Summary 1. It is often assumed that lakes highly influenced by terrestrial organic matter (TOM) have low zooplankton food quality because of elemental and/or biochemical deficiencies of the major particulate organic carbon pools. We used the biochemical [polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA) , 20:5,3] and elemental (C : P ratio) composition of particulate matter (PM) as qualitative measures of potential zooplankton food in two categories of lakes of similar primary productivity, but with contrasting TOM influence (clear water versus humic lakes). 2. C : P ratios (atomic ratio) in PM were similar between lake categories and were above 400. The concentration (,g L,1) and relative content (,g mg C,1) of EPA, as well as the particulate organic carbon concentration, were higher in the humic lakes than in the clear-water lakes. 3. Our results show high fatty acid quality of PM in the humic lakes. The differences in the biochemical quality of the potential zooplankton food between lake categories can be attributed to the differences in their phytoplankton communities. 4. High biochemical quality of the food can result in high efficiency of energy transfer in the food chain and stimulate production at higher trophic levels, assuming that zooplankton are able to ingest and digest the resource available. [source] Low algal carbon content and its effect on the C : P stoichiometry of periphytonFRESHWATER BIOLOGY, Issue 11 2005PAUL C. FROST Summary 1. We examined the contribution of algal cells to periphytic organic carbon and assessed the effects of variable biomass composition on the carbon : phosphorus (C : P) ratio of periphyton. We compiled more than 5000 published and unpublished observations of periphytic carbon : chlorophyll a (C : Chl) ratios, an index of algal prevalence, from a variety of substrata collected from lake and low-salinity coastal habitats. In addition, we converted estimates of algal biovolume into algal C to obtain an independent measure of cellular algal carbon in periphyton. This information was used in a model relating periphyton C : P ratio to algal cellular carbon, the algal C : P ratio, and the C : P ratio of non-algal organic matter in periphyton. 2. The mean C : Chl ratio of periphyton (405) was relatively high with values in >25% of the samples exceeding 500. On average, 8.4% of total periphyton C was accounted for by C in algal cells. Only 15% of samples were found to have more than 15% periphyton C in cellular algal carbon. Our model showed a nonlinear relationship between periphytic C : P ratios and the C : P ratio of algal cells in the periphyton when non-algal organic matter was present. However, even at relatively low cellular algal C (<10% of total C), algal C : P ratios can strongly affect the C : P ratio of periphyton as a whole (i.e. algal cells plus other organic matter). 3. The high C : Chl ratios and the low biovolume-derived algal C of periphyton samples in our data set indicate that algal cells are typically a minor component of organic carbon in periphyton, However, this minor contribution would not preclude algal cellular stoichiometry from notably influencing periphyton C : P ratios. [source] Overpressure and petroleum generation and accumulation in the Dongying Depression of the Bohaiwan Basin, ChinaGEOFLUIDS (ELECTRONIC), Issue 4 2001X. Xie Abstract The occurrence of abnormally high formation pressures in the Dongying Depression of the Bohaiwan Basin, a prolific oil-producing province in China, is controlled by rapid sedimentation and the distribution of centres of active petroleum generation. Abnormally high pressures, demonstrated by drill stem test (DST) and well log data, occur in the third and fourth members (Es3 and Es4) of the Eocene Shahejie Formation. Pressure gradients in these members commonly fall in the range 0.012,0.016 MPa m,1, although gradients as high as 0.018 MPa m,1 have been encountered. The zone of strongest overpressuring coincides with the areas in the central basin where the principal lacustrine source rocks, which comprise types I and II kerogen and have a high organic carbon content (>2%, ranging to 7.3%), are actively generating petroleum at the present day. The magnitude of overpressuring is related not only to the burial depth of the source rocks, but to the types of kerogen they contain. In the central basin, the pressure gradient within submember Es32, which contains predominantly type II kerogen, falls in the range 0.013,0.014 MPa m,1. Larger gradients of 0.014,0.016 MPa m,1 occur in submember Es33 and member Es4, which contain mixed type I and II kerogen. Numerical modelling indicates that, although overpressures are influenced by hydrocarbon generation, the primary control on overpressure in the basin comes from the effects of sediment compaction disequilibrium. A large number of oil pools have been discovered in the domes and faulted anticlines of the normally pressured strata overlying the overpressured sediments; the results of this study suggest that isolated sandstone reservoirs within the overpressured zone itself offer significant hydrocarbon potential. [source] Determination of Total Organic Carbon Content and ,13C in Carbonate-Rich Detrital SedimentsGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 3 2007Valier Galy carbone organique; décarbonatation; solubilisation; sediment; carbonate The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (Corg) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble Corg respectively. In Himalayan and Amazon river sediments, the proportion of Corg solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the Corg content for the dissolved organic carbon content measured after decarbonation. Data presented here show that Corg dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment. La détermination de la teneur totale en carbone organique et de sa composition dans des sédiments détritiques requiert leur décarbonatation préalable. l'élimination complète de carbonates tels que la dolomite ne peut être réalisée qu'au moyen d'une attaque avec un acide en phase liquide ce qui peut entrainer la solubilisation d'une partie du carbone organique. Pour un ensemble de sédiments détritiques provenant du système Himalayen et de l'Amazone ainsi que pour cinq matériaux géologiques de référence, nous avons déterminé la proportion de carbone organique (Corg) solubilisé lors de la décarbonatation. Celle-ci est significative pour l'ensemble des sédiments analysés et tend à augmenter avec la teneur en carbone organique. En comparaison avec les autres types de sédiments analysés, les fractions argileuses extraites de sédiments de rivière et les sédiments de fond très pauvres en Corg ont une proportion de Corg soluble dans l'acide respectivement élevée et faible. Dans les sédiments himalayens et amazoniens, la proportion de Corg solubilisé lors de la décarbonatation est plutôt constante avec des valeurs moyennes respectives de 14 et 19%. Nous pouvons donc calculer avec précision la teneur totale en carbone organique à partir de la teneur en Corg déterminée après décarbonatation. Nos données montrent que la solubilisation de Corg lors de la décarbonatation par un acide en solution est importante et doit être prise en compte lors de la détermination de la teneur en carbone organique. Moyennant une calibration minutieuse, la méthode que nous présentons devrait donc être utilisée pour l'analyse de sédiments détritiques riches en carbonates. [source] Quantifying carbon sequestration as a result of soil erosion and deposition: retrospective assessment using caesium-137 and carbon inventoriesGLOBAL CHANGE BIOLOGY, Issue 12 2007TIMOTHY ANDREW QUINE Abstract The role of soil erosion in the global carbon cycle remains a contested subject. A new approach to the retrospective derivation of erosion-induced quantitative fluxes of carbon between soil and atmosphere is presented and applied. The approach is based on the premise that soil redistribution perturbs the carbon cycle by driving disequilibrium between soil carbon content and input. This perturbation is examined by establishing the difference between measured carbon inventories and the inventories that would be found if input and content were in dynamic equilibrium. The carbon inventory of a profile in dynamic equilibrium is simulated by allowing lateral and vertical redistribution of carbon but treating all other profile inputs as equal to outputs. Caesium-137 is used to derive rates of vertical and lateral soil redistribution. Both point and field-scale estimates of carbon exchange with the atmosphere are derived using the approach for a field subject to mechanized agricultural in the United Kingdom. Sensitivity analysis is undertaken and demonstrates that the approach is robust. The results indicate that, despite a 15% decline in the carbon content of the cultivation layer of the eroded part of the field, this area has acted as a net sink of 11 ± 2 g C m,2 yr,1 over the last half century and that in the field as a whole, soil redistribution has driven a sink of 7 ± 2 g C m,2 yr,1 (6 ± 2 g C m,2 yr,1 if all eroded carbon transported beyond the field boundary is lost to the atmosphere) over the same period. This is the first empirical evidence for, and quantification of, dynamic replacement of eroded carbon. The relatively modest field-scale net sink is more consistent with the identification of erosion and deposition as a carbon sink than a carbon source. There is a clear need to assemble larger databases with which to evaluate critically the carbon sequestration potential of erosion and deposition in a variety of conditions of agricultural management, climate, relief, and soil type. In any case, this study demonstrated that the operation of erosion and deposition processes within the boundaries of agricultural fields must be understood as a key driver of the net carbon cycle consequences of cultivating land. [source] Carbon emission and sequestration by agricultural land use: a model study for EuropeGLOBAL CHANGE BIOLOGY, Issue 6 2002L. M. Vleeshouwers Abstract A model was developed to calculate carbon fluxes from agricultural soils. The model includes the effects of crop (species, yield and rotation), climate (temperature, rainfall and evapotranspiration) and soil (carbon content and water retention capacity) on the carbon budget of agricultural land. The changes in quality of crop residues and organic material as a result of changes in CO2 concentration and changed management were not considered in this model. The model was parameterized for several arable crops and grassland. Data from agricultural, meteorological, soil, and land use databases were input to the model, and the model was used to evaluate the effects of different carbon dioxide mitigation measures on soil organic carbon in agricultural areas in Europe. Average carbon fluxes under the business as usual scenario in the 2008,2012 commitment period were estimated at 0.52 tC ha,1 y,1 in grassland and ,0.84 tC ha,1 y,1 in arable land. Conversion of arable land to grassland yielded a flux of 1.44 tC ha,1 y,1. Farm management related activities aiming at carbon sequestration ranged from 0.15 tC ha,1 y,1 for the incorporating of straw to 1.50 tC ha,1 y,1 for the application of farmyard manure. Reduced tillage yields a positive flux of 0.25 tC ha,1 y,1. The indirect effect associated with climate was an order of magnitude lower. A temperature rise of 1 °C resulted in a ,0.05 tC ha,1 y,1 change whereas the rising CO2 concentrations gave a 0.01 tC ha,1 y,1 change. Estimates are rendered on a 0.5 × 0.5° grid for the commitment period 2008,2012. The study reveals considerable regional differences in the effectiveness of carbon dioxide abatement measures, resulting from the interaction between crop, soil and climate. Besides, there are substantial differences between the spatial patterns of carbon fluxes that result from different measures. [source] Carbon storage and fluxes in ponderosa pine forests at different developmental stagesGLOBAL CHANGE BIOLOGY, Issue 7 2001B.E. Law Abstract We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, eddy flux estimates of net ecosystem exchange (NEE), and Biome-BGC simulations of fluxes. The young forest (Y site) was previously an old-growth ponderosa pine forest that had been clearcut in 1978, and the old forest (O site), which has never been logged, consists of two primary age classes (50 and 250 years old). Total ecosystem carbon content (vegetation, detritus and soil) of the O forest was about twice that of the Y site (21 vs. 10 kg C m,2 ground), and significantly more of the total is stored in living vegetation at the O site (61% vs. 15%). Ecosystem respiration (Re) was higher at the O site (1014 vs. 835 g C m,2 year,1), and it was largely from soils at both sites (77% of Re). The biological data show that above-ground net primary productivity (ANPP), NPP and net ecosystem production (NEP) were greater at the O site than the Y site. Monte Carlo estimates of NEP show that the young site is a source of CO2 to the atmosphere, and is significantly lower than NEP(O) by c. 100 g C m,2 year,1. Eddy covariance measurements also show that the O site was a stronger sink for CO2 than the Y site. Across a 15-km swath in the region, ANPP ranged from 76 g C m,2 year,1 at the Y site to 236 g C m,2 year,1 (overall mean 158 ± 14 g C m,2 year,1). The lowest ANPP values were for the youngest and oldest stands, but there was a large range of ANPP for mature stands. Carbon, water and nitrogen cycle simulations with the Biome-BGC model suggest that disturbance type and frequency, time since disturbance, age-dependent changes in below-ground allocation, and increasing atmospheric concentration of CO2 all exert significant control on the net ecosystem exchange of carbon at the two sites. Model estimates of major carbon flux components agree with budget-based observations to within ±,20%, with larger differences for NEP and for several storage terms. Simulations showed the period of regrowth required to replace carbon lost during and after a stand-replacing fire (O) or a clearcut (Y) to be between 50 and 100 years. In both cases, simulations showed a shift from net carbon source to net sink (on an annual basis) 10,20 years after disturbance. These results suggest that the net ecosystem production of young stands may be low because heterotrophic respiration, particularly from soils, is higher than the NPP of the regrowth. The amount of carbon stored in long-term pools (biomass and soils) in addition to short-term fluxes has important implications for management of forests in the Pacific North-west for carbon sequestration. [source] | ||||||||||||||||||||||||||||