22 search hits
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Photochemische Abbauprozesse von polybromierten Diphenylethern in homogenen und heterogenen Systemen
(2008)
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Ana Maria Geller
- Ziel dieser Arbeit war es, die photochemischen Abbauprozesse von technischen Produkten zu untersuchen, die als Flammschutzmittel verwendet werden: die polybromierten Diphenylether (PBDEs) Deca-, Octa- und PentaBDE. Die Bestrahlung der kommerziellen Mischungen wurde in einer Karussell-Bestrahlungsapparatur und/oder mittels Gesichtsbräuner durchgeführt. Für den photolytischen Abbau unter umweltrelevanten Bedingungen ist ein sonnenähnliches Spektrum notwendig. Dieses wurde durch die eingesetzte Xenon-Lampe (XOP-7, 500 W) mit einem Filter aus Duranglas (1,5 mm Wandstärken) und durch 4 oder 6 UV-Leuchtstoffröhren (TL29D16, 16 W) erreicht. Der Verlauf der Photolyse wurde mit HPLC-DAD und/oder mit GC-MS verfolgt. Von den PentaBDEs sind BDE 99 und BDE 100 am häufigsten in der Umweltprobe aufgetreten und haben zugleich den größten Gewichtsanteil in der kommerziellen Mischung DE-71. Während der Photolyse von BDE 100, 99 und 85 wird hauptsächlich TetraBDE 47 gebildet. Die Geschwindigkeitskonstanten für die Debromierung von BDE 85 und BDE 99 waren mit beiden Lampen deutlich größer als bei BDE 100. Die Quantenausbeuten der PentaBDEs 85, 99 und 100 in THF/Hexan (2/1 v/v) betrugen 0,22, 0,17 und 0,13. Die größere Quantenausbeute für BDE 85 verursacht den schnelleren Photoabbau dieses Penta-Kongeners im Vergleich zu BDE 99 und BDE 100. BDE 100 wurde als das photostabilste der drei Penta-Kongeneren der kommerziellen Mischung DE-71 identifiziert. Der Verlauf der Photolyse der kommerziellen Mischung DE-79 zeigt einen schnellen Abbau von DecaBDE 209 und NonaBDE 207+208. Nachdem DecaBDE 209 mehr als zur Hälfte abgebaut ist, beginnt die Debromierung des NonaBDE 206 mit einer Geschwindigkeit, die ca. der Hälfte der Geschwindigkeit der Summe BDE 207+208 entspricht. Auch beim Abbau der OctaBDEs 203, 197 und 196 und von HeptaBDE 180 in der kommerziellen Mischung DE-79 handelt es sich um Folgereaktionen mit fortschreitender Debromierung. Die Quantenausbeuten in THF der DecaBDE 209 und NonaBDE 207 waren 0,20 bzw. 0,14. Die Photodebromierung von HeptaBDE 183 als einzelnes Kongener verläuft über die Bildung von 7 Hexa-Kongeneren, hauptsächlich bei BDE 153. Eine Quantenausbeute von 0,11 wurde für den Abbau von BDE 183 in THF/Hexan (2/1 v/v) bestimmt. DecaBDE 209 wurde in THF-Lösung und auf anorganischem Trägermaterial photolysiert. Die Lebensdauer von DecaBDE 209 in Lösung ist ca. 1,7 Stunden. Als Octa-Produkte aus dem Abbau von DecaBDE 209 bzw. NonaBDEs traten (in Reihenfolge der Häufigkeit) BDE 196 > BDE 203 > BDE 201 > BDE 197 auf. Es wurden keine PBDEs mit Bromierungsgraden < 5 bei der Photolyse von DecaBDE auf den anorganischen Trägermaterialien Quarzglaspulver (Aerosil 380), Mikro-Glashohlkugeln und Kieselgel gefunden. Eine schnellere Debromierung von DecaBDE wurde auf Kieselgel und Aerosil 380 im Vergleich zu den Mikro-Glashohlkugeln beobachtet. Die unterschiedlichen Trägermaterialen haben einen Einfluss auf die Abbaugeschwindigkeit von DecaBDE, aber das Photolyseprodukt-Muster bleibt gleich. Bei der Photolyse der kommerziellen Mischung DE-79 und von DecaBDE 209 in Lösung wurden gleichzeitig mit der Debromierung der PBDEs verschiedene PBDFs und sogar das Muttermolekül Dibenzofuran gebildet. Die Bildung von polybromierten Dibenzofuranen spielt eine wichtige Rolle in dem Abbauweg bei der Photolyse von PBDEs mit höherem Bromierungsgrad. In der kommerziellen Mischung DE-79 nach 48 h Bestrahlung liegt der Gewichtsanteil von PBDFs bei. ca. 17 %. Während beim DecaBDE in Lösung nach 46 h Bestrahlung der Gewichtsanteil von PBDFs bei ca. 13 % liegt. Die PBDFs wurden bei der Photolyse von DecaBDE auf anorganischem Trägermaterial hauptsächlich bei Versuchen mit dem Kieselgel beobachtet. Bei DecaBDE in Lösung wurden polybromierte Dibenzofurane mit kleinerem Bromierungsgrad als bei der gesättigten Lösung mit Bodensatz und auf anorganischem Trägermaterial gebildet. Die Bildung der toxischen 2,3,7,8-bromierten Dibenzofurane konnte in allen Versuchen ausgeschlossen werden.
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Elasticity measurements at extreme conditions: application to FeO and FeNi-alloy
(2008)
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Anastasia Kantor
- The picture of Earth’s deep interior is rapidly improving from the seismic tomography data and indicates more complexity than previously thought. The presence of Earth’s seismic anisotropy requires the knowledge of fully anisotropic elasticity data for mineral phases. The single-crystal elastic constants of minerals, Cij, are elements of the fourth-rank elasticity tensor, which relates stress to strain. The fact that elastic strain also defines seismic wave propagation, the elastic tensor of minerals can be applied to interpret the bulk mineralogy of the interior from seismological observation. Knowledge of the elasticity of crystalline materials as a function of pressures and temperature is also of primary interest for solid state physics because elastic tensors reveal the nature of interatomic interactions. In order to determine the full elastic tensor of minerals under high pressure and temperature, several techniques are available, including ultrasonic interferometry and inelastic x-ray scattering methods. One of the most accurate techniques is high-frequency acoustic interferometry, which is capable for measuring sound wave velocities in very small samples under high pressures. The ultrasonic interferometry system operating at 0.5-2.0 gigahertz (GHz) frequencies was developed in the Bavarian Geoinstitut of the University of Bayreuth for in situ high pressure and temperature experiments. Here, GHz-ultrasonic interferometry has been used to study the elastic properties of monoxide minerals such as FeO, liquids and nanocrystalline samples, each with particular importance to Earth or material sciences. FexO, wüstite, is the end-member phase of the (Mg,Fe)O solid solution, thought to be the most abundant non-silicate oxide in the mantle. The full elastic tensor of wüstite is determined by three elastic constants (C11, C12, C44), which have been probed at high-pressures. At about 17-20 GPa, FeO is known to undergo a displacive cubic-to-rhomobhedral phase transformation. Prior to this transformation, we observe a pressure-induced mode softening of the C44 elastic constant. In addition, previously undetected discontinuities in the pressure derivatives of C11 and C12 at 4.7  0.2 GPa were observed. This pressure is consistent with that of the magnetic ordering commencement, as was observed by high-pressure Mössbauer spectroscopy in a 57Fe-enriched sample of FeO. The results indicate that an intermediate, partially magnetic but still cubic phase of FeO probably exists at room temperature and in pressure range from ~5 GPa to ~17 GPa. In order to provide deeper knowledge of the magneto-elastic coupling in the material, neutron diffraction experiments were performed under ambient pressure and low temperatures. The results indicate that the magnetically ordered cubic phase of FexO that was observed at high pressures also exists at ambient pressure at temperatures between 160 and 201 K. Combined inelastic x-ray scattering and x-ray diffraction studies on a single crystal of Fe0.95O were performed up to 20 GPa at room temperature. The results show strong anelastic behaviour of wüstite, which should be accounted for at high pressure. Transition-metal oxides, non-stoichiometric compounds, and materials with complex mesostructure have some internal degree of freedom, and could therefore experience internal relaxation and show deviations from normal elastic behaviour. A methodology to measure inelastic x-ray scattering in externally heated diamond anvil cells have also been developed. This technique was used to study polycrystalline fcc-Fe0.78Ni0.22 alloy at high pressures (up to 72 GPa) and temperature (up to 715 K). The bulk elasticity and its P and T derivatives were obtained for the material. No significant deviation of the elastic properties from those of pure iron was observed and furthermore no deviation from Birch’s law. Although the bulk elasticity of fcc Fe-Ni alloy and Fe seem to be very similar, the elastic anisotropy of hexagonal and cubic phases should be quite different. If the metal phase in the inner core is not hexagonal, but cubic (or a mixture of the two phases exists), seismic anisotropy may provide a better way to discriminate between them two.
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Assessment of the environmental acceptability of refrigerants by discrete mathematics: cluster analysis and Hasse diagram technique
(2008)
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Guillermo Restrepo
- The recognition of the adverse environmental impact of chlorofluorocarbons (CFCs), mainly used as refrigerants, has lead to look for environmentally acceptable CFC replacements. Main environmental concern CFCs face is their ability to deplete the stratospheric ozone layer, quantified by the ozone depletion potential (ODP). Some of the first replacements mooted were hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), which contribute to the global warming, quantified by the global warming potential (GWP). ODP and GWP are related to the atmospheric lifetime (ALT), a third indicator. Hence, the environmental impact of a refrigerant may be characterised by a triple of ODP, GWP and ALT values. In this respect, an acceptable refrigerant is a chemical with low ODP, GWP and ALT values. One of the first steps to assess the environmental acceptability of refrigerants is to classify them to find substances with common features. Hence, a supervised and unsupervised classification was performed over 40 refrigerants. First one was a classification based upon elemental composition and functional groups present in refrigerant molecules which leads to: CFCs, HCFCs, HFCs, hydrocarbons (HCs), hydrofluoro ethers (HFEs), chloromethanes (CMs), carbon dioxide, trifluoroiodomethane, dimethyl ether and ammonia. The unsupervised classification was performed using hierarchical cluster analysis. In this case, refrigerants were characterised by three kinds of descriptors: Environmental properties (ODP, GWP, ALT), thermodynamic features related to their refrigeration performance and molecular descriptors derived from their molecular structure. Eight clustering methodologies were applied to each kind of refrigerant descriptors. To assess the stability of these classifications, the cluster index, a method for quantifying classification similarities was developed and further applied to refrigerant results. It was found that environmental descriptors are the only case in which refrigerant classes are stable when varying the classification method. The chemotopological procedure, a method for studying similarity relationships, was applied to the environmental classification of refrigerants. It was found that CFCs are similar to themselves and also to 1,1,1,3,3,3-hexafluoropropane, a HFC. The most similar substances to all CFCs considered were trichlorofluoromethane and 1,1,2-trichloro-1,2,2-trifluoroethane. The other refrigerant families were found to be similar to many other substances, therefore there is no clear affiliation of refrigerants of one family to one certain class. It was found a disagreement between the supervised classification leading to refrigerant families and the three unsupervised classifications (environmental, thermodynamic and molecular ones). Therefore, refrigerant classification into families does not imply same classification based upon environmental properties, thermodynamic features and molecular descriptors. A different refrigerant classification was performed, i.e. the one based upon order relationships of refrigerant environmental properties. In this case the Hasse diagram technique, a method based on partial order theory, was applied to the 40 refrigerants characterised by environmental properties. A parameter free procedure for ordering classes based upon order relationships of their elements was developed. For that purpose, the dominance and separability degrees were introduced, first one indicates the extent to which members of one class hold higher descriptor values than the members of another class; while separability degree quantifies the lack of order relationships between two classes. Dominance and separability degrees were related by a theorem. By the application of dominance and separability degrees to refrigerant families three main classes were detected: problematic substances, gathering CFCs, octafluorocyclobutane and bromochlorodifluoromethane; least problematic ones, collecting HCs, CMs, carbon dioxide, trifluoroiodomethane, dimethyl ether and ammonia; and moderately problematic refrigerants, made from HCFCs, HFCs and HFEs. It was found that some HFEs are not dominated by CFCs, which raises the question on the applicability of these substances as environmentally acceptable replacements. METEOR (Method of evaluation by order theory), a procedure for prioritising descriptors and studying its effect on the order relationships of the objects considered was discussed. When applied to the refrigerants, the effect of prioritising ODP, GWP and ALT in the order relationships of these substances was studied. It was found that pentafluorodimethyl ether, a HFE, is one of the most problematic refrigerants under a large range of priorities of the environmental properties considered. Due to the mathematical generality of the methods here introduced, they are not restricted to the analysis of refrigerants but can be used to the study of different sets whose elements are characterised by various attributes.
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Experimental Constraints on Silicate Perovskite Forming Reactions and Elastic Properties: Geophysical Implications for Chemical Heterogeneity in the Deep Mantle
(2008)
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Saikia Ashima
- Three experimental investigations have been performed in order to understand how the composition of the mantle may influence mineral stability and elastic properties and how these may influence seismic properties of the deep mantle. The phase relations of calcium perovskite have been studied in high pressure and temperature experiments to examine the effect of its formation on seismic discontinuity features at 520 km depth in the mantle. The effect of varying composition on the compressibility of magnesium silicate perovskite has been examined in order to understand the geophysical consequences of chemical heterogeneity in the lower mantle. Calorimetric measurements of the pyrope-majorite garnet solid solution have been made to provide essential thermodynamic data for modeling the formation reactions of both magnesium and calcium silicate perovskite.
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Vulnerability to Drought Risk and Famine: Local Responses and External Interventions among the Afar of Ethiopia, a study on the Aghini Pastoral Community
(2008)
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Ali Hassen Muhaba
- In East African countries drought-related famine has been a number one risk. Ethiopia is among those countries that are repeatedly stricken by recurrent famine. Agricultural and pastoral households have increasingly become vulnerable to famine. The successive Ethiopian governments attributed the recurring famine and hunger to natural events, particularly to droughts. However, though drought triggers famines, it does not necessarily lead to famine disaster in every context. This is the current tone of literature in disaster causation. Each famine has its own specific causes in each context and this requires exploring the causal factors thereof. This study in the Afar region, in north-east Ethiopia, attempts to explain the root causes of vulnerability to famine, and assess the local and external responses. The central argument of the research is that pastoralists’ vulnerability to famine and food crisis has increased overtime because of the complex interplay of multiple factors such as environmental or ecological degradation, socio-economic destabilization, and political processes. It is also stated that despite efforts of internal and external actors, vulnerability of the pastoral groups to famine has increased over time. In that respect the study attempts to explain how these factors have led to an increase of vulnerability and livelihood insecurity among the Afar pastoralists. Three specific arguments are addressed through analyzing both secondary and primary data. These are: The Afar pastoralists’ vulnerability to famine has increased over the past decades because of the combined effects of drought, ecological crisis and external pressures (encroachments, loss of key pastoral resources, violent conflict and political instability). Pastoral households/communities are currently less able to cope with stresses through their traditional coping and adaptive strategies. Consequently, pastoral households/communities have become more dependent on public transfer (food aid) to cope with recurring food crisis. The empirical research used both qualitative and quantitative data in addressing the basic research questions. The outline of the research is structured to suit an approach of presenting discussions at macro and micro levels. An assessment of factors both, at macro (regional/national) and micro (community) levels, is made on the basis of secondary and primary data respectively. Accordingly, factors related to ecological degradation, socio-political processes and recurrent droughts, etc. are examined. The extent of these problems at the macro level is assessed mainly based on secondary data, while the magnitude of these problems at micro (community) level is assessed on the basis of primary data gathered through a household survey, and individual and focus group interviews. Based on the analyses of both primary and secondary data the research attempts to answer the question why the Afar pastoralists’ vulnerability to famine has increased over time and how the local and external actors have responded to recurring famine. The search for explanations of vulnerability to famine focuses on highlighting the interplay of multiple causal factors at different levels within historical socio-political and economic processes overlapping with ecological crisis and recurrent drought. Accordingly the research highlights the major factors that have created vulnerability to famine. These include: External pressures which include state intervention, land alienation, encroachment by cultivators, loss of dry season/drought retreats, curtailment of mobility and unfavourable terms of trade. Stresses which include frequent drought, conflicts, political instability, weakening mutual support systems, lack of trust in formal government institutions due to non-participatory, lack of commitment, patron-client relationship, and corruption. Ecological/environmental crises which are reflected in terms of loss of key pastoral resources (grass, natural fodder vegetation, and water). The conclusion of the research is that famine and the increase of vulnerability are not primarily the consequences of drought, but of external domination and uneven development. This suggests that the genesis of food crisis (famine) must be understood as an interaction of institutional, economic and political variables. Natural events like droughts don’t necessarily lead to famine in all contexts. It is only when livelihood assets are eroded, opportunities are constrained and people are not well-prepared that the consequences of natural events develop into famine or food crisis. This suggests that production or yield failures caused by drought do not become famines unless other conditions are propitious. Therefore, the current approach in social science research with regard to disaster causation is to look at the interrelationship between natural risks and social vulnerability.
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Investigation of high nighttime CO2-fluxes at the Wetzstein spruce forest site in Thuringia, Germany
(2008)
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Marcelo Zeri
- Nighttime fluxes of CO2 are uncommonly high at the Wetzstein spruce site, in Thuringia, Germany (Anthoni et al., 2004). As a result, the annual sums of CO2- flux obtained for this site are not comparable with the ones obtained at similar spruce ecosystems (Rebmann, 2004; Grünwald and Bernhofer, 2007). The site is located on a hill and subject to strong winds and high levels of turbulence for continuous periods. The unusual high fluxes of CO2 are predominantly associated with these situations. As reported by Anthoni et al. (2004), measurements of soil respiration performed with automatic chambers in 2003 did not explain such high ecosystem respiration. Also, recent results of soil respiration have revealed that the ecosystem respiration Reco should be comparable to the value obtained for the similar spruce site of Waldstein/Weidenbrunnen (Rebmann, 2004). According to the modeling work of Finnigan and Belcher (2004), the flow over low hills as the Wetzstein site disturbs the wind field at the sub-canopy space across the ridge. As a consequence, advective fluxes of scalars as CO2 are generated at the upwind and lee sides of the hill. Two results from the model were confirmed for the first time in an experiment, namely (1) higher wind speeds below the canopy at the slope, when compared with the same level at the crest, and (2) the flows above and below the canopy in opposite direction at the lee side of the hill. Besides the agreement of the measured wind field with the model results, the existence of horizontal advection was confirmed by Feigenwinter et al. (2007), using data from the advection experiment ADVEX. However, the sign of the advective flux was positive on average, meaning that CO2 was flushed out of the control volume enclosed by the additional towers. This result was not directly related to the high nighttime fluxes of CO2, as these situations were rarely observed during the experiment. However, it has shown that sub-canopy flows exist at the site and should be further investigated. The analysis of several cospectra of the vertical flux of CO2 have shown that the frequencies, or time scales, associated with the high nocturnal fluxes are mainly the turbulent ones, typically observed for nighttime turbulent regimes. The high turbulent activity observed during neutral situations leads then to enhanced turbulent fluxes of CO2. High nocturnal fluxes of CO2 were related to specific micrometeorological conditions, namely high values of friction velocity, southwesterly and northeasterly winds, and neutral stratification. These conclusions were used in a gap-filling approach as annual sums of CO2 were calculated (Rebmann et al., in preparation). As a result of this new approach the site presented a higher uptake of CO2 by the vegetation. Additionally, the newly found results have shown that the uptake of CO2 has been increasing since 2003, caused by factors as the improved growth rate induced by a thinning operation (after snow damage) in 2002, and the recovery from the drought of 2003. The tendency observed in the annual sums of CO2-flux indicates that the site may be in a transition period after the disturbances described above. The proposed removal of unusually high values of CO2-fluxes (with objective criteria) for the determination of annual sums should be also applied in future analysis, in order to capture changes in uptake rates. In this case the CO2 balance for the Wetzstein site would be more comparable to similar ecosystems as Waldstein/Weidenbrunnen (Rebmann, 2004) and Tharandt (Bernhofer et al., 2003; Grünwald and Bernhofer, 2007).
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Vogelgemeinschaften in südecuadorianischen Bergregenwäldern unterschiedlicher Struktur
(2008)
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Detlev Paulsch
- Im Rahmen der DFG-Forschergruppe 402 (Funktionalität in einem tropischen Bergregenwald Südecuadors: Diversität, dynamische Prozesse und Nutzungspotentiale unter ökosystemaren Gesichtspunkten) wurden die Vogelgemeinschaften verschiedener Strukturtypen des Bergregenwaldes im Gebiet der Estación Científica San Francisco (ECSF) im Süden Ecuadors untersucht. Durch Punkt-Stop-Beobachtungen, Netzfänge und Zufallsbeobachtungen wurden in einem Höhenbereich zwischen 1800m und 3150m N.N. die vorkommenden Vogelarten inventarisiert sowie Artenreichtum und Diversität der Vogelgemeinschaften der von PAULSCH, A. (2002) klassifizierten Waldstrukturtypen untersucht. Anschließend wurden funktionale Zusammenhänge zwischen dem Vorkommen ausgewählter Vogelarten und strukturellen Parametern der Vegetation näher betrachtet sowie Zusammensetzung und Diversität der Vogelgemeinschaften ungestörter und anthropogen beeinflusster Waldstrukturtypen vergleichend untersucht. Insgesamt konnten im Untersuchungsgebiet 227 Vogelarten nachgewiesen werden. Die wichtigsten Nahrungsgilden wurden durch die Insectivoren (100 Arten), Frugivoren (57) und Nectarivoren (35) gebildet, wobei mit 29 Arten eine gegenüber anderen Untersuchungen deutlich höhere Zahl an Kolibris (Trochilidae) anzutreffen war. Durch das azonale Vorkommen eines durch Purdiaea nutans (Cyrillaceae) geprägten Waldtyps wurde in der Höhenstufe zwischen 2150m und 2650m N.N. im Untersuchungsgebiet eine andere Vogelgemeinschaft angetroffen als in vergleichbaren Gebieten. Ein Vergleich der Vogelgemeinschaften der Waldstrukturtypen ergab die höchsten Mittelwerte des Artenreichtums im ‚Anthropogen beeinflussten Schluchtwald tieferer Lagen’ und am ‚Waldrand tieferer Lagen’. Mehr als ein Drittel der durch Punkt-Stop-Beobachtungen und Netzfänge nachgewiesenen Vogelarten kamen in einer Meereshöhe zwischen 1900m und 2000m N.N. vor. In diesem Bereich sind im Untersuchungsgebiet anthropogen beeinflusste Waldtypen sowie verschiedene Sukzessionsstadien anzutreffen, welche auch die beiden oben genannten Strukturtypen charakterisieren. Wie die Aufenthaltspräferenzen der Vogelarten zeigen, ist der hohe Artenreichtum in diesem Höhenbereich vor allem auf typische Waldrandarten und auf die Überlappung der Habitate von Waldarten mit denen der Arten offenerer Bereiche zurückzuführen. Für den anthropogen beeinflussten Schluchtwald und die Waldränder wurden mit 41,5 und 34 auch die höchsten Diversitätswerte (Fisher’s Alpha) berechnet. Die Abschätzung des potentiellen Artenreichtums (Chao1, ACE) ergab, dass in fast allen Waldstrukturtypen über 80% der Vogelarten nachgewiesen werden konnten. Die Ergebnisse der hier vorliegenden Untersuchung bestätigen somit die immense Artenvielfalt im Gebiet der ECSF, wie sie auch schon für andere Gruppen aus Fauna und Flora beschrieben wurde. Hinsichtlich der Habitatpräferenzen bzw. Höhenamplituden konnten für verschiedene Vogelarten Abweichungen gegenüber den Literaturangaben gefunden werden. Dies ist auf den noch immer recht geringen Kenntnisstand über die Avifauna der ecuadorianischen Bergregenwälder zurückzuführen. Für die Vogelarten verschiedener Familien konnten im Laufe der Untersuchung bestimmte Aufenthaltspräferenzen bezüglich Meereshöhe und Habitat gefunden werden, welche sich allerdings nicht mit strukturellen Vegetationsparametern begründen ließen. Es wurden aber auch 12 Vogelarten nachgewiesen, die als Kennarten für einen bestimmten Waldstrukturtyp gelten können. Für fünf dieser Arten konnten zudem funktionale Zusammenhänge zwischen ihrem Vorkommen im Untersuchungsgebiet und strukturellen Parametern der Vegetation im jeweiligen Waldstrukturtyp gefunden werden. Eine vergleichende Untersuchung der Vogelgemeinschaften entlang eines Gradienten menschlicher Einflussnahme (‚Primärer Schluchtwald tieferer Lagen’ - ‚Anthropogen beeinflusster Schluchtwald tieferer Lagen’ - ‚Reste von Schluchtwald tieferer Lagen’) zeigte den höchsten Artenreichtum und die größte Alpha-Diversität im anthropogen beeinflussten Schluchtwald. Die Anzahl typischer Waldarten nahm entlang des Gradienten ab, wogegen diejenige der typischen Waldrandarten bzw. Arten der halboffenen Habitate anstieg. Innerhalb der Nahrungsgilden zeigte sich eine Abnahme der Artenzahl entlang des Gradienten für die Insectivoren des Unterwuchses, die großen Frugivoren und die Omnivoren, während die Zahl der Granivoren zunahm. Die größte Zahl der Nectarivoren war, vermutlich aufgrund der großen Anzahl an Nahrungspflanzen, im anthropogen beeinflussten Schluchtwald anzutreffen. Vor allem der Rückgang typischer Waldarten unter zunehmendem anthropogenem Einfluss belegt die Wichtigkeit von Schutzmaßnahmen für große Flächen ungestörten Regenwaldes. Dies gilt insbesondere vor dem Hintergrund der extrem hohen Entwaldungsrate in den Bergregenwäldern Ecuadors und der gleichzeitig enorm hohen Biodiversität in diesen Gebieten, wie sie auch in dieser Untersuchung gezeigt werden konnte.
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Water solubility in diopside
(2008)
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Polina Gavrilenko
- (1) Water solubility in pure diopside was measured. Water-saturated diopside crystals were synthesized using piston-cylinder and multi-anvil presses at 20-30 and 100 kbar and 800-1100oC from an oxide and hydroxide starting mixture containing 10 % excess silica. The water concentration in diopside was determined from polarized infrared measurements on doubly polished single crystals. Water contents were calculated by integrating the absorption bands and using published extinction coefficients for water in diopside. All measured infrared spectra of pure diopside fall into two groups. The differences in the spectra point towards substitution mechanisms involving different vacancies, which in turn could be the result of different oxide activities in the starting material. Therefore, a separate series of experiments was carried out with starting materials with an excess or deficiency of MgO or SiO2. These experiments yielded diopside with different absorption spectra. Starting materials with low silica activity yielded Type I bands, which are therefore likely to be related to Si vacancies. Type II bands form at high silica activity and may therefore be related to Mg or Ca vacancies. Water solubility in pure diopside varies from 121 up to 568 ppm H2O. Water solubility at 30 kbar increases from 700 to 1000oC and drops again above 1000oC. At 900oC, water solubility increases to a maximum at 25 kbar and then decreases rapidly to higher pressures. Due to the low solubility of aluminum in clinopyroxene at high pressure, the data on pure diopside are probably a good guide for the water solubility in clinopyroxenes under the conditions of the deeper upper mantle. Since water solubility in diopside under those conditions is order of magnitude below the water solubility in olivine, clinopyroxene is not expected to be a major storage site for water in the deeper upper mantle, even if its modal abundance is significant. (2) Water-saturated Al-containing diopside was synthesized in an end-loaded piston-cylinder apparatus at 1.5-2.5 GPa and 900-1100oC. The compositions of the starting materials for Al-bearing diopside are along the join diopside (CaMgSi2O6) – Ca-Tschermak’s component (CaAl2SiO6) with different ratios of these two end members. The water solubility strongly increases with the presence of Al up to 2500 ppm H2O. The water solubility in aluminous diopside increasing with decreasing temperature. Estimated partition coefficients of water between clinopyroxene and orthopyroxene are close to unity, with Dcpx/opx possibly increasing with temperature. Together with previously published data on water in orthopyroxene, the results of this study clearly show that in the uppermost mantle, most of the water is dissolved in the pyroxenes. The relative importance of clinopyroxene and orthopyroxene is primarily a function of their modal abundance. This observation is consistent with the model of Mierdel et al (2007), which suggests that the Earth’s asthenosphere is due to a minimum in water solubility in nominally anhydrous minerals. (3) In order to determine the effect of water on the equation of state of diopsides, high-pressure single crystal X-ray diffraction experiments with a diamond anvil cell were performed. The compressibility of diopside decreases with increasing water and Al content in the structure. The bulk modulus Ko and its first pressure derivative K’ for the four diopside crystals are 106(1) GPa and 6.1(5) for pure anhydrous diopside (0 ppm H2O); 107(1) GPa and 6.5(4) for pure diopside with 63 ppm of H2O; 108(1) GPa and 6.3(4) for pure diopside with 600 ppm H2O; and 113(1) GPa and 5.7(5) for Al-bearing hydrous (containing 0.374 Al a.p.f.u.) diopside with 2510 ppm H2O. The results on compressibility of diopside contrast with previous work, which showed that compressibility of most other main mantle phases increases with water content. In addition, from the refinement of the crystal structures of both hydrous and dry diopside and comparison with the structure of Ca-Tschermak’s pyroxene it was possible to see the influence of protonation of oxygen atoms. Because of the contrasting effect of water on the equation of state of olivine and of pyroxenes in the upper mantle, detecting water from observations of seismic velocities alone is probably nearly impossible.
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Effects of Cadmium on Calcium homeostasis and physiological conditions of the freshwater Mussel Anodonta anatina
(2008)
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Thi Thuy Huong Ngo
- Summary As the result of the worldwide decline of freshwater mussels, some significant wetland and riverine habitats are threatened. It has been shown that cadmium (Cd), among other heavy metals, is present at surprisingly high levels in freshwater pearl mussels from mountain brooks in central Europe. This metal is likely to be one of the factors involved in the decline because of its high toxicity, bioaccumulation potential and transfer through food chains. In natural ecosystems, aquatic animals are usually exposed to Cd from both the dissolved- and the particulate-phase, and at lower levels than those used in standard toxicity testing. The aim of this study was to investigate the effects of environment-like Cd levels on its bioaccumulation, tissue distribution and on the redistribution of background Cd (Cd present in animals prior to the experiment) among body compartments of the freshwater mussel Anodonta anatina by exposure to both algae- and water-borne 111Cd (about 0.2 µg/L) for 35 days followed by 120 days of depuration. Furthermore, the effects of Cd on calcium (Ca) homeostasis, condition index, energy reserves, carbonic anhydrase activity and their correlations were examined and evaluated. Before mussels were exposed to Cd, a Cd-exposure experiment with the green algae Parachlorella kessleri was carried out for producing 111Cd-loaded algae suitable for exposed mussels as food of the same quality as non-contaminated algae. P. kessleri were grown at four Cd concentrations (0, 0.5, 2, 8 and 32 µg/L) for 5 days, starting from day 2 after inoculation. At 8 µg Cd/L and higher, Cd showed clear effects on algal growth, cell morphology, size and algal physiological state. The minimum Cd concentration at which the algae were significantly different from the control group was about 3 µg/L. At a Cd concentration of 2 µg/L, algae exhibited a comparable physiological state to the control which was used to grow 111Cd-carrying food for the test mussels. In the mussel exposure experiment, different types of samples were taken. Hemolymph (HML), extrapallial fluid (EPF), gills, mantle, digestive gland, kidney and other tissues were used to determine total Cd, the 114Cd/111Cd isotope ratio for studying Cd accumulation, distribution, elimination and redistribution of background Cd, and its effects on other element profiles (Ca, Mg and Zn). Effects of Cd on energy reserves (glycogen, glucose and proteins) and on carbonic anhydrase were investigated in the body fluids (HML and EPF), gills, mantle and digestive gland. During the exposure phase, newly incorporated Cd increased in all body compartments, the highest levels occurring in the kidney. Elimination of newly incorporated and background Cd was slow and mainly from the digestive gland; the increase of newly incorporated Cd in the mantle and of newly incorporated and background Cd in the kidney during exposure and the first half of depuration indicated the mobilization of the Cd pools from other body compartments and deposition in this organ. Ca concentrations in the body fluids increased during Cd exposure; at the same time, they were lowered in most organs, remaining unchanged only in the gills. Simultaneously, depletion of glycogen in the mantle and digestive gland accompanied by a rise in glucose and a decrease in protein levels in the HML and EPF were observed. This entailed a sharp decrease in condition index and relative dry weight (dw). Significant correlations of Cd with glycogen (mantle, digestive gland) and of Ca with glucose (body fluids) and glycogen (mantle, digestive gland) were found. Concerning enzymatic effects, significantly lower levels of carbonic anhydrase activities were observed in all tested tissues, especially in the gills and digestive gland; strong fluctuations were observed in the HML and EPF with a significant increase right after the rise of glucose in these compartments. The effects of Cd exposure on carbonic anhydrase activities in A. anatina were confirmed by significant negative correlations of both total and cytoplasmic carbonic anhydrase activities with newly incorporated Cd. In conclusion, A. anatina readily accumulates Cd at low exposure levels. This results in unfavorable effects on Ca profiles, energy reserves and carbonic anhydrase activities in tissue-specific and time-dependent manners. The effects are long lasting and entail interactions which finally influence Ca metabolism, e.g. adverse effects on energy reserves and enzyme activities. Among the organs, the digestive gland appears to be actively involved in the uptake of Cd from the outside environment and in distributing it to other organs via the HML. This makes it more sensitive to Cd exposure than other organs, reflected by a strong depression of glycogen, carbonic anhydrase activity and Ca level. HML and EPF are important compartments playing a crucial role in uptake and distribution of Cd, revealed by its effects on all tested parameters, i.e. Ca, glucose, proteins and carbonic anhydrase. The gills seem to be less sensitive due to their high amounts of calcareous concretions. The kidney acts as Cd sink for later excretion. Overall, these findings show that Cd at environment-like levels has distinct biochemical, toxicological and pathological effects which may constitute a critical component in the multitude of environmental factors leading to the observed general decline of freshwater mussel populations. Keywords: Anodonta anatina; Cd bioaccumulation; Cd redistribution; Ca homeostasis; freshwater mussel; stable isotope 111Cd; condition index; glycogen; glucose; protein; energy reserves; carbonic anhydrase; subcellular distribution of carbonic anhydrase; Parachlorella kessleri; Cd-loaded algae.
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Influence of natural organic matter on the mobility of arsenic in aquatic systems, soils and sediments
(2008)
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Markus Florian Bauer
- The element As is today recognized as one of the most dangerous inorganic contaminants and threats for the world’s water resources. Arsenic is ubiquitious in the earth crust and humans are especially affected through As polluted drinking water supplies. The occurrence of high As groundwater concentrations is often caused by geogenic processes of As release from the solid phase and accumulation in the water phase. Many contaminated aquifers are also characterized by high concentrations of natural organic matter (NOM). Previous studies showed that NOM presence may affect As mobility, but we are lacking evidence about the reactions pathways and about the importance As-DOM interactions in the environment. We therefore focussed on studying reactions between NOM and As, including redox reactions, complexation, colloid formation and sorption competition in laboratory experiments. Moreover we also studied As behaviour in columns experiments and wetland soils rich in organic matter. Arsenic mobility strongly depends on its redox state. Dissolved organic matter was previously found to be redox active but its redox properties are only poorly understood. In laboratory experiments we therefore elucidated the electron transfer characteristics of different DOM samples. The results showed the high potential of humic substances to chemically reduce different Fe(III) complexes and oxidize H2S and metallic Zn. Reactions occurred over short periods of time with reaction rates in the range from 0.03 to 27 h-1. Under otherwise identical conditions rising DOC concentrations caused higher total electron transfer. This supports the assumption that functional groups of DOM, such as quinones, were indeed the redox active moieties involved in the redox reactions. The calculated electron transfer capacities (ETC) ranged from 0.07 to 6.2 mequiv (g C)-1. The wide range of observed reaction rates and ETC values could be related to the different redox potential of the inorganic reactants used. This suggests that DOM molecules contain redox active moieties with different redox potential and that they possibly represent a redox ladder with the capacity to buffer electrons over a wide range of redox conditions. Humic substances also influenced the As redox speciation as dissolved H3AsO4 was - either chemically or microbially- reduced to H3AsO3 in DOM solution. No oxidation of As(III) to As(V) was found in these experiments. The presence of organic matter thus changes the redox speciation of As as well as that of other environmentally relevant elements like Fe or S. This possibly also contributes to a higher mobility of As due to the presence of reduced As and Fe species. The formation of complexes on mineral surfaces is one of the most important immobilization processes for As in soils or sediments. DOM strongly interfered with this As sequestration mechanism due to aqueous and surface complexation reactions. Humic substances were found to prevent the precipitation and sedimentation of iron oxide minerals and promote the formation of DOM and Fe containing colloids at aqueous molar Fe/C ratios of up to 0.1. This impeded the co-precipitation and sedimentation of As with Fe mineral structures and increased the amount of mobile As. Arsenic and Fe content were correlated in the different particle size classes was, suggesting As binding to Fe e.g. in cation bridging complexes or DOM stabilized Fe oxide colloids. DOM sorption on synthetic goethite and natural soil and sediment samples also caused a release of As from these solid phases due to sorption competition for mineral binding sites. Especially the weakly adsorbed fraction of As in the natural samples was affected by this process. Both the formation of aqueous complexes or colloids and the sorption competition in the presence of DOM lead to higher As concentration in the water phase and demonstrate the potential of humic substances to increase As mobility. In the studied laboratory columns As redox transformation and complexation by DOM could not be identified. Instead As mobilization was dominated by microbial processes in these experiments. At DOM input concentrations between 5 and 100 mg L-1 the release of As occurred mainly due to the reductive dissolution of the Fe oxide sorbent phase during microbial respiration. The occurrence of sulfate reduction and the precipitation of sulfide minerals at the highest DOM concentrations did not represent a substantial immobilization mechanism. The studied wetland soils represent natural sinks for geogenic As. Fe oxides were the main As sorbents, which is surprising as both soils were temporarily water saturated and likely under reducing conditions. Moreover, the high porewater DOC concentrations and the high organic carbon content in the solid phase apparently did not interfere with As sorption on the iron phases in these soils. Chemical extractions also showed that smaller As fractions were associated with solid phase organic matter pool and with a not identified residual pool, likely sulfide minerals. However, as most As was bound to Fe oxides its fate was strongly affected by changing redox conditions. Fast As immobilization sorption occurred under dry conditions when Fe was oxidized and precipitated, while short-term mobilization of As and Fe in their reduced form was observed upon rewetting. These soils therefore are As sinks as long as oxic conditions are maintained but may turn into As sources when reducing conditions prevail for longer periods of time. Organic molecules influence the redox state and the complexation of As and are able to shift As partitioning in favour of the solute phase. Our results showed that especially the association of As with aqueous complexes and colloids has a strong potential to reduce As retention and increase As mobility. This has to be considered in future studies of As behaviour in aquifers, surface waters, soils or sediments rich in organic substances. Peatland soils were found to represent sinks for geogenic As, showing that the presence of organic matter not necessarily prevents As immobilization. It also depends on the biogeochemical conditions whether an organic matter rich system will accumulate or release As.
