Bromine and iodine in plant-soil systems

Brom und Jod kommen in von Folge sowohl natürlichen als auch anthropogenen Prozessen (z.B.Verdunstung von Meerwasser, Verbrennung von Biomasse) als Spurenelemente in der Biosphäre vor. Obwohl das Verhalten von Halogenen in der Umwelt intensiv untersucht worden ist, bestehen nach wie vor große Lücken im Verständnis ihres Verhaltens, ihrer Verteilung und ihrer Bindungsformen in terrestrischen Milieu. Ziel dieser Arbeit war die Untersuchung natürlicher Anreicherungsprozesse von Halogenen in terrestrischen Milieu, sowie der Wechselbeziehungen zwischen Halogenen, Boden, Streu und Pflanzen. Sowohl terrestrische Pflanzen als auch Böden vermögen den natürlichen Halogen-Kreislauf entscheidend zu beeinflussen, indem sie sowohl als Speichermedium (Senke) als auch als Emittent (Quelle) einer vielzahl von Halogen-Spezies dienen. Das Verhalten von Brom und Jod wurde während des einjährigen Lebenszyklus (vom Samen bis zur Zersetzung) von Weidelgras (Lolium multiflorum) untersucht. Darüber hinaus wurden Blätter von Buchen (Fagus Sylvatica) unter aborbedingungen zersetzt, um diese Ergebnisse mit denen von Abbauprozessen unter natürlichen Umweltbedingungen zu vergleichen. Die Verteilung von Brom und Jod in Boden, Bodenlösung, Ausgangsgestein, Niederschlag, Blättern und Streu wurde in zwei Wald-Gebieten in der Umgebung von Heidelberg (Deutschland) untersucht. Zur Quantifizierung der Halogene kamen verschiedene Methoden zum Einsatz, unter ihnen INAA, XRF, ICP-MS und IC/ICP-MS. Während der Weidelgras-Zersetzung werden die beiden Halogene sowohl in organischer, als auch anorganischer Form freigesetzt Brom in überwiegend flüchtiger Form (bis zu ~80%), während kleine Mengen im Detritus verbleiben (bis zu ~2,6%) und die restliche Menge ausgewaschen wird. Das Verhalten von Jod während der Zersetzung ist weniger schlüssig und bedarf weiterer Untersuchungen. Bei der Verrottung von Buchen-Blättern zeigt sich für die Freisetzung von Brom ein anderes Muster als bei der Weidelgras-Verrottung, was auf die Bedeutung der Eigenschaften des jeweiligen Streus hinweist. Brom- und Jod-Konzentrationen in den untersuchten Bodenprofilen reichen von 0,6 μg/g bis 15 μg/g und die in den Bodenlösungen von 0,5μg/l bis 43μg/l. Dabei ist eine Abhängigkeit vom jeweiligen Bodenhorizont zu beobachten. Im Oberboden (reich an organischem Material) sind die Halogene bevorzugt in organischen Bindungsformen zu finden (zwischen 60 und 100%), während deren Anteil im Verlauf des Bodenprofils nach unten hin abnimmt. Bei einem der untersuchten Waldgebiete stellt die atmospärische Deposition die Quelle für Brom und Jod dar, während im zweiten Waldgebiet eine zusätzliche Beeinflussung durch das Ausgangsgestein festzustellen ist. Bei der Verrottung von Buchenblättern im Labor war die Bildung flüchtiger Bromver-bindungen geringer (12,9% ± 6.1) als es Berechnungen aus dem gleichen Prozeß unter natürlichen Bedingungen ergaben (24,4%). Man kann daher das Streu selbst als Quelle für Bromverbindungen ansehen. Die vorliegende Arbeit zeigt das Vorhandensein von Halogenen in den Komponenten terrestrischer Ökosysteme, sowie deren Austausch und die Beeinflussung der Halogenverteilung und Bindungsphase durch biologische Prozesse (z.B. Wachstum, Zerfall)

Emission of volatile halogenated organic compounds over various landforms at the Dead Sea

Abstract. Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH3X; X = Br, Cl and I) and very short-lived halogenated substances (VSLS; CHBr3, CH2Br2, CHBrCl2, C2HCl3, CHCl3 and CHBr2Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere, and for their key role in aerosol formation. Insufficient characterization of the sources and emission rate of VHOCs limits our present ability to understand and assess their impact in both the troposphere and the stratosphere. Over the last two decades several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge about emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and the fluxes of several chlorinated and brominated VHOCs from different landforms and vegetated sites at the Dead Sea during different seasons. Fluxes were highly variable but were generally positive (emissive), corresponding with elevated mixing ratios for all of the VHOCs investigated in the four investigated site types – bare soil, coastal, cultivated and natural vegetated sites – except for fluxes of CH3I and C2HCl3 over the vegetated sites. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr2Cl > CHBr3 > CHBrCl2 > CHCl3. This finding can be explained by the enrichment of soil with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the formation and emission of all the above trihalomethanes but also for CH2Br2. Also in line with previous reports, we observed elevated emissions of CHCl3 and C2HCl3 from mixtures of soil and different salt-deposited structures; the high correlations of flux with methyl halides, and particularly with CH3I, suggested that at least CH3I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevate emission of VHOCs from bare soil under semi-arid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes, and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes

DiaCurv: a value-based curvature analysis application in diatom taxonomy

<p>DiaCurv is a software application that uses a simple approach to calculating curvature by identifying the chord (length) and the sagitta (length) from a mid-point of an object or part of an object. This software application and associated R scripts provide the users with the possibilities to identify and apply curvature analysis in diatom taxonomy. Different taxa from the genera <i>Cymbella</i> and <i>Luticola</i>, with good size diminution series, were selected to validate curvature metrics for shape evaluations in taxonomy. The dorsal ventral curvature of <i>Cymbella</i> makes species within this genus a natural choice for comparison. In contrast, the lanceolate, elliptic-lanceolate to rhombic forms of species within <i>Luticola</i> are more problematic. Machine-learning techniques (principal component analysis and linear discriminant analysis (LDA)) were used to evaluate the curvature metrics for distinguishing diatom taxa. Selected taxa (<i>C. aspera</i>, <i>C. cymbiformis</i>, <i>C. diversa</i>, <i>C. excisa</i>, <i>C. japonica</i>, <i>C. neogena</i>, <i>C. neuquina</i>, <i>C. parva</i>, <i>C. saxoicola</i>, <i>C. tumidula</i>) were identified by valve curvature, except when valve shape was not a distinguishing character for the species. With the lanceolate, elliptic-lanceolate shapes of <i>Luticola</i>, curvature was effective in separating the linear-lanceolate forms (e.g., <i>L. australomutica</i>, <i>L. goeppertiana</i>, <i>L. murrayi</i>, <i>L. saprophila</i>), and some broadly lanceolate forms (<i>L. crozetensis</i>, <i>L. subcrozetensis</i>) but not elliptic-lanceolate forms within the same size range (e.g., <i>L. katkae</i>, <i>L. pseudocharcotii</i>, <i>L. yellowstonensis</i>). The experimental results indicated that LDA was more suitable for distinguishing taxa. Valve shapes which are circular, or centrally constricted or with polar differentiation or 3D in complexity may not be appropriate for curvature analysis unless specific parts of the valve are selected. The merits of this approach, or any other type of shape analysis, are that the subjective interpretation of shape differences between taxa is removed or reduced.</p

Stable bromine isotopic composition of methyl bromide released from plant matter

Abstract Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (δ 81 Br

Emission of volatile halogenated organic compounds over various landforms at the Dead Sea

Abstract. Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH3X; X = Br, Cl and I) and very short-lived halogenated substances (VSLS; CHBr3, CH2Br2, CHBrCl2, C2HCl3, CHCl3 and CHBr2Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere, and for their key role in aerosol formation. Insufficient characterization of the sources and emission rate of VHOCs limits our present ability to understand and assess their impact in both the troposphere and the stratosphere. Over the last two decades several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge about emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and the fluxes of several chlorinated and brominated VHOCs from different landforms and vegetated sites at the Dead Sea during different seasons. Fluxes were highly variable but were generally positive (emissive), corresponding with elevated mixing ratios for all of the VHOCs investigated in the four investigated site types – bare soil, coastal, cultivated and natural vegetated sites – except for fluxes of CH3I and C2HCl3 over the vegetated sites. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr2Cl &gt; CHBr3 &gt; CHBrCl2 &gt; CHCl3. This finding can be explained by the enrichment of soil with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the formation and emission of all the above trihalomethanes but also for CH2Br2. Also in line with previous reports, we observed elevated emissions of CHCl3 and C2HCl3 from mixtures of soil and different salt-deposited structures; the high correlations of flux with methyl halides, and particularly with CH3I, suggested that at least CH3I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevate emission of VHOCs from bare soil under semi-arid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes, and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes

Stable bromine isotopic composition of methyl bromide released from plant matter

Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (delta Br-81) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (epsilon) of -2.00 +/- 0.23 parts per thousand (1 sigma, n = 8) for pectin and -1.82 +/- 0.02 parts per thousand (1 sigma, n = 4) for Salicornia (the relative amount of the heavier Br-81 was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300 degrees C. For longer incubations of up to 90 h at 180 degrees C the delta Br-81 values increased from -2 parts per thousand to 0 parts per thousand for pectin and to -1 parts per thousand for Salicornia. These delta Br-81 source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget. (C) 2013 Elsevier Ltd. All rights reserved