AUTOMATED DETERMINATION OF [Fe/H] AND [C/Fe] FROM LOW-RESOLUTION SPECTROSCOPY

We develop an automated spectral synthesis technique for the estimation of metallicities ([Fe/H]) and carbon abundances ([C/Fe]) for metal-poor stars, including carbon-enhanced metal-poor stars, for which other methods may prove insufficient. This technique, autoMOOG, is designed to operate on relatively strong features visible in even low- to medium-resolution spectra, yielding results comparable to much more telescope-intensive high-resolution studies. We validate this method by comparison with 913 stars which have existing high-resolution and low- to medium-resolution to medium-resolution spectra, and that cover a wide range of stellar parameters. We find that at low metallicities ([Fe/H] less than or similar to -2.0), we successfully recover both the metallicity and carbon abundance, where possible, with an accuracy of similar to 0.20 dex. At higher metallicities, due to issues of continuum placement in spectral normalization done prior to the running of autoMOOG, a general underestimate of the overall metallicity of a star is seen, although the carbon abundance is still successfully recovered. As a result, this method is only recommended for use on samples of stars of known sufficiently low metallicity. For these low- metallicity stars, however, autoMOOG performs much more consistently and quickly than similar, existing techniques, which should allow for analyses of large samples of metal-poor stars in the near future. Steps to improve and correct the continuum placement difficulties are being pursued.

Evaluation of the carbon content of aerosols from the burning of biomass in the Brazilian Amazon using thermal, optical and thermal-optical analysis methods

Aerosol samples were collected at a pasture site in the Amazon Basin as part of the project LBA-SMOCC-2002 (Large-Scale Biosphere-Atmosphere Experiment in Amazonia - Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was conducted during the late dry season, when the aerosol composition was dominated by biomass burning emissions, especially in the submicron fraction. A 13-stage Dekati low-pressure impactor (DLPI) was used to collect particles with nominal aerodynamic diameters (D(p)) ranging from 0.03 to 0.10 mu m. Gravimetric analyses of the DLPI substrates and filters were performed to obtain aerosol mass concentrations. The concentrations of total, apparent elemental, and organic carbon (TC, EC(a), and OC) were determined using thermal and thermal-optical analysis (TOA) methods. A light transmission method (LTM) was used to determine the concentration of equivalent black carbon (BC(e)) or the absorbing fraction at 880 nm for the size-resolved samples. During the dry period, due to the pervasive presence of fires in the region upwind of the sampling site, concentrations of fine aerosols (D(p) < 2.5 mu m: average 59.8 mu g m(-3)) were higher than coarse aerosols (D(p) > 2.5 mu m: 4.1 mu g m(-3)). Carbonaceous matter, estimated as the sum of the particulate organic matter (i.e., OC x 1.8) plus BC(e), comprised more than 90% to the total aerosol mass. Concentrations of EC(a) (estimated by thermal analysis with a correction for charring) and BC(e) (estimated by LTM) averaged 5.2 +/- 1.3 and 3.1 +/- 0.8 mu g m(-3), respectively. The determination of EC was improved by extracting water-soluble organic material from the samples, which reduced the average light absorption Angstrom exponent of particles in the size range of 0.1 to 1.0 mu m from >2.0 to approximately 1.2. The size-resolved BC(e) measured by the LTM showed a clear maximum between 0.4 and 0.6 mu m in diameter. The concentrations of OC and BC(e) varied diurnally during the dry period, and this variation is related to diurnal changes in boundary layer thickness and in fire frequency.

Determination of parathion and carbaryl pesticides in water and food samples using a self assembled monolayer/acetylcholinesterase electrochemical biosensor

An acetylcholinesterase (AchE) based amperometric biosensor was developed by immobilisation of the enzyme onto a self assembled modified gold electrode. Cyclic voltammetric experiments performed with the SAM-AchE biosensor in phosphate buffer solutions ( pH = 7.2) containing acetylthiocholine confirmed the formation of thiocholine and its electrochemical oxidation at E-p = 0.28 V vs Ag/AgCl. An indirect methodology involving the inhibition effect of parathion and carbaryl on the enzymatic reaction was developed and employed to measure both pesticides in spiked natural water and food samples without pre-treatment or pre-concentration steps. Values higher than 91-98.0% in recovery experiments indicated the feasibility of the proposed electroanalytical methodology to quantify both pesticides in water or food samples. HPLC measurements were also performed for comparison and confirmed the values measured amperometrically.

Stability of biomass-derived black carbon in soils

Black carbon (BC) may play ail important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO(2). In order to fully evaluate the influence of BC oil the global C cycle, in understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61-80% lower (P < 0.05) CO(2) evolution per unit C over 532 days compared to their respective adjacent soils with low BC contents. No significant (P > 0.05) difference in CO(2) respiration per unit C was observed between Anthrosols with contrasting ages of BC (600-8700 years BP) Lind soil textures (0.3-36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics or fresh BC. BC decomposed extremely slowly to ail extent that it was not possible to detect chemical changes between Youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation oil the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72-90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2-70%), Suggesting some degree of physical stabilization. (c) 2008 Elsevier Ltd. All rights reserved.

Do plant species influence soil CO(2) and N(2)O fluxes in a diverse tropical forest?

To test whether plant species influence greenhouse gas production in diverse ecosystems, we measured wet season soil CO(2) and N(2)O fluxes close to similar to 300 large (>35 cm in diameter at breast height (DBH)) trees of 15 species at three clay-rich forest sites in central Amazonia. We found that soil CO(2) fluxes were 38% higher near large trees than at control sites >10 m away from any tree (P < 0.0001). After adjusting for large tree presence, a multiple linear regression of soil temperature, bulk density, and liana DBH explained 19% of remaining CO(2) flux variability. Soil N(2)O fluxes adjacent to Caryocar villosum, Lecythis lurida, Schefflera morototoni, and Manilkara huberi were 84%-196% greater than Erisma uncinatum and Vochysia maxima, both Vochysiaceae. Tree species identity was the most important explanatory factor for N(2)O fluxes, accounting for more than twice the N(2)O flux variability as all other factors combined. Two observations suggest a mechanism for this finding: (1) sugar addition increased N(2)O fluxes near C. villosum twice as much (P < 0.05) as near Vochysiaceae and (2) species mean N(2)O fluxes were strongly negatively correlated with tree growth rate (P = 0.002). These observations imply that through enhanced belowground carbon allocation liana and tree species can stimulate soil CO(2) and N(2)O fluxes (by enhancing denitrification when carbon limits microbial metabolism). Alternatively, low N(2)O fluxes potentially result from strong competition of tree species with microbes for nutrients. Species-specific patterns in CO(2) and N(2)O fluxes demonstrate that plant species can influence soil biogeochemical processes in a diverse tropical forest.

Stable isotopes of bulk organic matter to trace carbon and nitrogen dynamics in an estuarine ecosystem in Babitonga Bay (Santa Catarina, Brazil)

The biogeochemical processes affecting the transport and cycling of terrestrial organic carbon in coastal and transition areas are still not fully understood One means of distinguishing between the sources of organic materials contributing to particulate organic matter (POM) in Babitonga Bay waters and sediments is by the direct measurement of delta(13)C of dissolved inorganic carbon (DIC) and delta(13)C and delta(15)N in the organic constituents. An isotopic survey was taken from samples collected in the Bay in late spring of 2004. The results indicate that the delta(13)C and delta(15)N compositions of OM varied from -21.7 parts per thousand to -26 2 parts per thousand. and from + 9 2 parts per thousand. to -0 1 parts per thousand, respectively. delta(13)C from DIC ranges from +0.04 parts per thousand to -12.7 parts per thousand The difference in the isotope compositions enables the determination of three distinct end-members terrestrial, marine and urban Moreover, the evaluation of source contribution to the particulate organic matter (POM) in the Bay, enables assessment of the anthropogenic impact. Comparing the depleted values of delta(13)C(DIC) and delta(13)C(POC) it is possible to further understand the carbon dynamic within Babitonga Bay (C) 2010 Elsevier BV All rights reserved

Near infrared spectroscopy for soil bulk density assessment

P>Soil bulk density values are needed to convert organic carbon content to mass of organic carbon per unit area. However, field sampling and measurement of soil bulk density are labour-intensive, costly and tedious. Near-infrared reflectance spectroscopy (NIRS) is a physically non-destructive, rapid, reproducible and low-cost method that characterizes materials according to their reflectance in the near-infrared spectral region. The aim of this paper was to investigate the ability of NIRS to predict soil bulk density and to compare its performance with published pedotransfer functions. The study was carried out on a dataset of 1184 soil samples originating from a reforestation area in the Brazilian Amazon basin, and conventional soil bulk density values were obtained with metallic ""core cylinders"". The results indicate that the modified partial least squares regression used on spectral data is an alternative method for soil bulk density predictions to the published pedotransfer functions tested in this study. The NIRS method presented the closest-to-zero accuracy error (-0.002 g cm-3) and the lowest prediction error (0.13 g cm-3) and the coefficient of variation of the validation sets ranged from 8.1 to 8.9% of the mean reference values. Nevertheless, further research is required to assess the limits and specificities of the NIRS method, but it may have advantages for soil bulk density predictions, especially in environments such as the Amazon forest.

Gaseous and fluvial carbon export from an Amazon forest watershed

The transfer of carbon (C) from Amazon forests to aquatic ecosystems as CO(2) supersaturated in groundwater that outgases to the atmosphere after it reaches small streams has been postulated to be an important component of terrestrial ecosystem C budgets. We measured C losses as soil respiration and methane (CH(4)) flux, direct CO(2) and CH(4) fluxes from the stream surface and fluvial export of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate C over an annual hydrologic cycle from a 1,319-ha forested Amazon perennial first-order headwater watershed at Tanguro Ranch in the southern Amazon state of Mato Grosso. Stream pCO(2) concentrations ranged from 6,491 to 14,976 mu atm and directly-measured stream CO(2) outgassing flux was 5,994 +/- A 677 g C m(-2) y(-1) of stream surface. Stream pCH(4) concentrations ranged from 291 to 438 mu atm and measured stream CH(4) outgassing flux was 987 +/- A 221 g C m(-2) y(-1). Despite high flux rates from the stream surface, the small area of stream itself (970 m(2), or 0.007% of watershed area) led to small directly-measured annual fluxes of CO(2) (0.44 +/- A 0.05 g C m(2) y(-1)) and CH(4) (0.07 +/- A 0.02 g C m(2) y(-1)) per unit watershed land area. Measured fluvial export of DIC (0.78 +/- A 0.04 g C m(-2) y(-1)), DOC (0.16 +/- A 0.03 g C m(-2) y(-1)) and coarse plus fine particulate C (0.001 +/- A 0.001 g C m(-2) y(-1)) per unit watershed land area were also small. However, stream discharge accounted for only 12% of the modeled annual watershed water output because deep groundwater flows dominated total runoff from the watershed. When C in this bypassing groundwater was included, total watershed export was 10.83 g C m(-2) y(-1) as CO(2) outgassing, 11.29 g C m(-2) y(-1) as fluvial DIC and 0.64 g C m(-2) y(-1) as fluvial DOC. Outgassing fluxes were somewhat lower than the 40-50 g C m(-2) y(-1) reported from other Amazon watersheds and may result in part from lower annual rainfall at Tanguro. Total stream-associated gaseous C losses were two orders of magnitude less than soil respiration (696 +/- A 147 g C m(-2) y(-1)), but total losses of C transported by water comprised up to about 20% of the +/- A 150 g C m(-2) (+/- 1.5 Mg C ha(-1)) that is exchanged annually across Amazon tropical forest canopies.

Carbon sequestration in agricultural soils in the Cerrado region of the Brazilian Amazon

The introduction of crop management practices after conversion of Amazon Cerrado into cropland influences soil C stocks and has direct and indirect consequences on greenhouse gases (GHG) emissions. The aim of this study was to quantify soil C sequestration, through the evaluation of the changes in C stocks, as well as the GHG fluxes (N(2)O and CH(4)) during the process of conversion of Cerrado into agricultural land in the southwestern Amazon region, comparing no-tillage (NT) and conventional tillage (CT) systems. We collected samples from soils and made gas flux measurements in July 2004 (the dry season) and in January 2005 (the wet season) at six areas: Cerrado, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT), in each case after a 2-year period of rice under CT. Soil samples were analyzed in both seasons for total organic C and bulk density. The soil C stocks, corrected for a mass of soil equivalent to the 0-30-cm layer under Cerrado, indicated that soils under NT had generally higher C storage compared to native Cerrado and CT soils. The annual C accumulation rate in the conversion of rice under CT into soybean under NT was 0.38 Mg ha(-1) year(-1). Although CO(2) emissions were not used in the C sequestration estimates to avoid double counting, we did include the fluxes of this gas in our discussion. In the wet season, CO(2) emissions were twice as high as in the dry season and the highest N(2)O emissions occurred under the NT system. There were no CH(4) emissions to the atmosphere (negative fluxes) and there were no significant seasonal variations. When N(2)O and CH(4) emissions in C-equivalent were subtracted (assuming that the measurements made on 4 days were representative of the whole year), the soil C sequestration rate of the conversion of rice under CT into soybean under NT was 0.23 Mg ha(-1) year(-1). Although there were positive soil C sequestration rates, our results do not present data regarding the full C balance in soil management changes in the Amazon Cerrado. (C) 2008 Elsevier B.V. All rights reserved.

Dynamics of carbon, biomass, and structure in two Amazonian forests

Amazon forests are potentially globally significant sources or sinks for atmospheric carbon dioxide. In this study, we characterize the spatial trends in carbon storage and fluxes in both live and dead biomass (necromass) in two Amazonian forests, the Biological Dynamic of Forest Fragments Project (BDFFP), near Manaus, Amazonas, and the Tapajos National Forest (TNF) near Santarem, Para. We assessed coarse woody debris (CWD) stocks, tree growth, mortality, and recruitment in ground-based plots distributed across the terra firme forest at both sites. Carbon dynamics were similar within each site, but differed significantly between the sites. The BDFFP and the TNF held comparable live biomass (167 +/- 7.6 MgC.ha(-1) versus 149 +/- 6.0 MgC.ha(-1), respectively), but stocks of CWD were 2.5 times larger at TNF (16.2 +/- 1.5 MgC.ha(-1) at BDFFP, versus 40.1 +/- 3.9 MgC.ha(-1) at TNF). A model of current forest dynamics suggests that the BDFFP was close to carbon balance, and its size class structure approximated a steady state. The TNF, by contrast, showed rapid carbon accrual to live biomass (3.24 +/- 0.22 MgC.ha(-1).a(-1) in TNF, 2.59 +/- 0.16 MgC.ha(-1).a(-1) in BDFFP), which was more than offset by losses from large stocks of CWD, as well as ongoing shifts of biomass among size classes. This pattern in the TNF suggests recovery from a significant disturbance. The net loss of carbon from the TNF will likely last 10 - 15 years after the initial disturbance (controlled by the rate of decay of coarse woody debris), followed by uptake of carbon as the forest size class structure and composition continue to shift. The frequency and longevity of forests showing such disequilibruim dynamics within the larger matrix of the Amazon remains an essential question to understanding Amazonian carbon balance.

Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths

1. Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil. 2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age - 25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected NO(3)(-)- (15)N, Rb(+) (analogue of K(+)) and Sr(2+) (analogue of Ca(2+)) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils. 3. Determination of foliar Rb and Sr concentrations and (15)N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer. 4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for NO(3)(-)- (15)N than for Rb(+) and Sr(2+) in the upper 50 cm of soil, the highest SRUP values for Sr(2+) and Rb(+) were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth. 5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

Late Pleistocene and Holocene vegetation changes in northeastern Brazil determined from carbon isotopes and charcoal records in soils

Northeastern Brazil represents a strategic area in terms of Quaternary records of environmental changes in South America due to its distinct semi-arid climate in near equatorial latitudes. In this study, carbon isotope and charcoal distribution records in soils are used to characterize vegetation dynamics, forest fires and their relation to climate change since the Late Pleistocene in the States of Ceara, Piaui and Paraiba, Northeastern Brazil. At the Ceara site, the carbon isotope record showed an enrichment trend from -24%(o) to 19%(o) during the early-mid Holocene, indicating an opening of vegetation and expansion of savanna vegetation (C(4) plants) during this period. A trend toward more depleted delta(13)C values (similar to-32%.) in the late Holocene indicates an expansion of forest vegetation (C(3) plants). A similar trend is observed at the Piaui and Paraiba sites where values of similar to-24%0 are associated with open forest vegetation during the late Pleistocene. In the early-mid Holocene, delta(13)C values of up to -18.0%(o), suggest the expansion of C4 plants. Based on the carbon isotope data, it is postulated that from similar to 18,000 cal yr B.P. to similar to 11,800 cal yr B.P.-similar to 10,000 cal yr B.P. arboreal vegetation was dominant in northeastern Brazil and is associated with humid climates. The savanna expanded from similar to 10,000 cal yr B.P. to similar to 4500-3200 cal yr B.P. due to a less humid/drier climatic phase, also supported by the significant presence of fires (charcoal fragments in the soil). From approximately 3200-2000 cal yr B.P. to the present, carbon isotope records suggest forest expansion and a more humid phase. These results form part of a regional pattern since they are in agreement with paleovegetation records obtained in regions of Maranhao, northeastern Brazil and in the Amazon and Rondonia States, northern Brazil. (C) 2010 Elsevier B.V. All rights reserved.

Evaluation of laser induced breakdown spectroscopy for cadmium determination in soils

Cadmium is known to be a toxic agent that accumulates in the living organisms and present high toxicity potential over lifetime. Efforts towards the development of methods for microanalysis of environmental samples, including the determination of this element by graphite furnace atomic absorption spectrometry (GFAAS). inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma-mass spectrometry (ICP-MS) techniques, have been increasing. Laser induced breakdown spectroscopy (UBS) is an emerging technique dedicated to microanalysis and there is a lack of information dealing with the determination of cadmium. The aim of this work is to demonstrate the feasibility of LIBS for cadmium detection in soils. The experimental setup was designed using a laser Q-switched (Nd:YAG, 10 Hz, lambda = 1064 nm) and the emission signals were collimated by lenses into an optical fiber Coupled to a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Samples were cryogenically ground and thereafter pelletized before LIBS analysis. Best results were achieved by exploring a test portion (i.e. sampling spots) with larger surface area, which contributes to diminish the uncertainty due to element specific microheterogeneity. Calibration curves for cadmium determination were achieved using certified reference materials. The metrological figures of merit indicate that LIBS can be recommended for screening of cadmium contamination in soils. (C) 2009 Elsevier B.V. All rights reserved.

Isotopic determination of silicon by mass spectrometry in plants and soils labeled with Si-30

A method for isotopic determination of silicon by mass spectrometry in plants and soils labeled with Si-30 is reported. The development of this method is for use with studies involving the physiological process of absorption, transport, and redistribution of Si in the soil-plant system by use of the stable isotope Si-30 as a tracer. The procedure leads to SiF4 formation, and the isotopic determination of Si was based on the measurements of the (SiF3+)-Si-28, (SiF3+)-Si-29, and (SiF3+)-Si-30 signals. Relative standard deviation of Si-30 abundance measurements (n = 6) were lower than 0.1%, and the detection limit was 0.5 mg Si (dry mass).

Partial microwave-assisted wet digestion of animal tissue using a baby-bottle sterilizer for analyte determination by inductively coupled plasma optical emission spectrometry

A procedure for partial digestion of bovine tissue is proposed using polytetrafluoroethylene (PTFE) microvessels inside a baby-bottle sterilizer under microwave radiation for multi-element determination by inductively coupled plasma optical emission spectrometry (ICP OES). Samples were directly weighed in laboratory-made polytetrafluoroethylene vessels. Nitric acid and hydrogen peroxide were added to the uncovered vessels, which were positioned inside the baby-bottle sterilizer, containing 500 mL of water. The hydrogen peroxide volume was fixed at 100 mu L The system was placed in a domestic microwave oven and partial digestion was carried out for the determination of Ca, Cu, Fe. Mg, Mn and Zn by inductively coupled plasma optical emission spectrometry. The single-vessel approach was used in the entire procedure, to minimize contamination in trace analysis. Better recoveries and lower residual carbon content (RCC) levels were obtained under the conditions established through a 2(4-1) fractional factorial design: 650 W microwave power, 7 min digestion time, 50 mu L nitric acid and 50 mg sample mass. The digestion efficiency was ascertained according to the residual carbon content determined by inductively coupled plasma optical emission spectrometry. The accuracy of the proposed procedure was checked against two certified reference materials. (C) 2009 Elsevier B.V. All rights reserved.