187 search hits
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Biomass and Nutrient Studies of Selected Tree Species of Natural and Plantation Forests: Implications for a Sustainable Management of the Munessa-Shashemene Forest, Ethiopia
(2004)
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Asferachew Abate
- Plantation forests with exotic tree species have been introduced to alleviate the problems of deforestation in Ethiopia. In the future, more plantation forests with fast growing species should be grown for coping with the ever-increasing demands for fuelwood and other forest products. However, it is not known whether plantation forests are sustainable or not. For the sustainability of plantation forests with exotic tree species, it is of paramount importance to thoroughly understand their ecological and social attributes through a holistic approach. For this reason, a multidisciplinary project was initiated in the Munessa-Shashemene Forest. Such an approach gives valuable information about the sustainability of plantation forests when the basic ecological features of the natural forests are compared with plantation forests. As an integral part of the multidisciplinary project, the objectives of this study are to: 1) quantify the fine roots and aboveground biomass of selected tree species in both natural and plantation forests; 2) quantify the macronutrient stocks of the fine roots and aboveground components of selected trees species in both natural and plantation forests; and 3) evaluate the implication of the changes in the biomass and macronutrient stocks for a sustainable management of forests. The study focused on four tree species, Podocarpus falcatus (Thunb.) Mirb., Podocarpaceae and Croton macrostachys Hochst. ex Del. Euphorbiaceae, were selected from a natural forest. Cupressus lusitanica Miller, Cupressaceae and Eucalyptus globulus Labill. Myrtaceae were selected from plantation forests. Root architectures of the study trees were studied by excavation. The live fine root biomass (<2 mm in diameter) of the dry and wet seasons was determined from samples collected at the distances of 1, 2 and 3 meters from the bole of the study trees. At each of the distances, root cores were taken at the depth intervals 0-10, 10-35, 35-60, 60-85 and 85-100 cm using a hand auger. Linear regression equations were used to estimate the aboveground biomass on the basis of the relation between DBH and dry weights of the aboveground plant components. Macronutrient concentrations were determined following a standard laboratory procedure. Studies on the root architecture revealed that C. lusitanica has a shallow root and is more susceptible to windthrow compared to E. globulus. With the exception of E. globulus, the dry season live fine root (LFR) biomass was higher for all trees studied. The seasonal variation in the fine root biomass was attributed to the changes in soil moisture of the study area. For all trees investigated, the mean annual LFR biomass was highest at the depth interval 0-10 cm at all distances. The favorable soil texture, pH and organic matter content at the depth interval 0-10 cm might be responsible for higher LFR biomass. The significantly higher LFR biomass of P. falcatus (1.34 kg m-2) coupled with its higher macronutrient stocks compared to C. macrostachys (0.32 kg m-2) suggest the importance of P. falcatus in the sustainability of the natural forest by transferring more macronutrients to the soil through its fine roots. Similarly, the significantly higher total LFR biomass of C. lusitanica (0.88 kg m-2) coupled with its higher macronutrient stock compared to E. globulus (0.27 kg m-2) indicated less depletion of soil nutrients by the former. The stand structure of the natural and plantation forests differed largely. In the natural forest, the density of C. macrostachys was much higher (143 ± 72 trees ha-1) than the density of P. falcatus (73 ± 39 trees ha-1). Generally, the structural change of the natural forest due to selective cutting of P. falcatus was found to have negative implications on the sustainability of the natural forest. The differences in the structure of C. lusitanica and E. globulus, despite their similar densities, resulted in a significantly lower understory ground cover by herbaceous and shrub species in the former. The effect of a poor understory growth on the floor litter thickness and thereby on nutrient capital of the soil may negatively affect the sustainability of C. lusitanica plantation. The harvesting of the stemwood of C. lusitanica and E. globulus removes a substantial amount of nutrients from the plantation sites. Furthermore, the current practice of collecting foliage, twigs and branches for firewood by the local people results in a higher depletion of nutrients. In order to make the plantation forests sustainable, the silvicultural practice in the future should consider on site conservation of foliage and bark. It is recommended that more studies on aboveground and belowground biomass, fine root turnover, and nutrient concentrations of the plantation forests should be carried out in a chronosequence in order to gain more insight on their sustainability.
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The use of 10Be surface exposure dating of erratic boulders in the reconstruction of the late Pleistocene glaciation history of mountainous regions, with examples from Nepal and Central Asia
(2004)
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Uwe Abramowski
- Be-10 surface exposure dating (SED) of erratic boulders is an innovative approach in Quaternary geochronology. It proves to be an excellent tool for the reconstruction of the glacial history of mountainous regions, which is an important part of climate change research. In the course of this work, I have 1) installed the analytical procedure to extract in-situ produced Be-10 from quartz-bearing rock surface samples in the laboratory of the Institute of Soil Science and Soil Geography at the University of Bayreuth; 2) developed and calibrated the program TEBESEA for quick calculation of Be-10 surface exposure ages with fully propagated errors, thereby evaluating the existing procedures; 3) deduced a new interpretation scheme for exposure age distributions from several stratigraphically related moraines in an area; 4) provided 37 new Be-10 exposure ages for the Nepal Himalaya, complementing earlier soil geographic studies in the Langtang Valley and the Macha Khola Valley; and finally 5) provided 108 new Be-10 exposure ages for the Pamir, and the Alay- and Turkestan Ranges, defining a new glacial chronology for Central Asia. The analytical procedure used to extract Be-10 from quartz-bearing rocks and to prepare it for measurement closely followed the one established at the ETH Zurich, where all Be-10 measurements have been done. The accuracy of the analytical work in Bayreuth was confirmed by preparation of five calibration samples from the Koefels landslide, Oetz Valley, Austria. The traditional scaling system of Lal (1991) as modified by Stone (2000) still proves to be the most suitable one to be used in Be-10 exposure age calculations. For this procedure, I have calibrated a total standard production rate at sea level, high latitude of 5.35 ± 0.15 atoms/(g a), using a contribution of capture of slow negative muons of 1.2%, and including all possible corrections. The altitude dependency of Be-10 production used in the scaling systems of Dunai (2001) and Desilets & Zreda (2003) is as yet not convincing, given the existing calibration data, but suggests that ages calculated for sites above 2000-3000 m a.s.l. in High Asia may be overestimates. Detailed error propagation shows that the uncertainties of Be-10 surface exposure ages at present are dominated by the errors of the scaling factor, the erosion rate, and the tectonic uplift rate. As long as surface erosion and tectonic uplift rates cannot be constrained to within 10%, however, exposure ages older than 30-40 ka have uncertainties of 20% or more and can be no more than rough approximations. For exposure age distributions from a set of stratigraphically related moraines, a new interpretation scheme is presented, which is able to detect ages older than the deposition age of the moraine (Be-10 inheritance), and to interpret age clusters younger than the deposition age, which may be synchronous on several moraines (phases of regionally enhanced surface activity). In the Nepal Himalaya, glacier advances in the Macha Khola Valley have occurred 70-100, 20-23, 11-12 and around 3 cal. ka B.P. Glacier advances in the Langtang Valley are dated to 14-15, 8-9 and ~3.5 cal. ka B.P. Late Pleistocene and Holocene glacial activity in the Nepal Himalaya seems to be controlled by the Indian monsoon rather than the westerly circulation. Only in the MIS 2, the westerly jetstream appears to have shifted as far south as to affect glaciation all over the Himalaya. During the Younger Dryas, the eastern limit of the influence of the westerly circulation on Himalaya glaciation may have been situated between the Manaslu and Langtang Himal. Glacial advances in the Pamir and in the Alay and Turkestan Ranges have occurred >93->136, ~60-80, (40-55), ~27-25, ~22-20, ~18, ~15.5, ~14.3, and 10.5 cal. ka B.P. The most extensive late Pleistocene glaciation occurred during the MIS 5-3, and is characterized by ELA depressions of ~370-380 m in the eastern Pamir, as well as 600 m and >750 m, in the Alay and Turkestan Ranges, respectively. Late Pleistocene glacier advances in northwestern High Asia, were triggered by climatic cold phases rather than by monsoonal maxima. Climate in the region seems to have been mostly under the influence of the westerly circulation and the Siberian anticyclone. Asynchrony of Central Asian and western hemisphere glacier advances is due to increasing aridity in Central Asia in the course of the last glacial cycle. High altitude glaciers seem to have reached their maximum extent earlier (MIS 5-4) than low altitude glaciers (first half of MIS 3). Some indirect monsoonal influence in the eastern Pamir may be responsible for the existence of some of the lateglacial moraine stages in this area.
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First principles phase diagram calculations in group IV carbides and Mg2SiO4 liquid from Molecular Dynamics
(2009)
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Omar Adjaoud
- Atomistic simulations on stability and physical properties of Earth materials are playing an increasingly important role in high pressure mineralogy. Such computations can provide guidance for experimental studies and insight into underlying causes of observations, or explore conditions and properties that are inaccessible to experiments at the current time. A variety of approaches have been applied in such research, with density functional theory based methods having become a reliable tool in computational mineral sciences. Despite this progress there are interesting problems which density functional theory based methods are not able to tackle on a routine basis. These include computations of phase diagrams and transport properties in liquids. The sub-solidus phase diagrams of the binary systems TiC-ZrC, TiC-HfC, ZrC-HfC at ambient pressure are computed based on electronic structure and energy calculations within density functional theory. Formation energies for a large number of supercells with compositions of (M1,M2)C, M1, M2 = Ti, Zr, or Hf, are computed by a plane-wave pseudopotential method. The energies serve as a basis for fitting cluster expansion Hamiltonians that are used to explore the sub-solidus phase diagram, i.e. stability of ordered intermediate compounds and the degree of miscibility in the systems by Monte Carlo simulations. Hamiltonians can be fit to the formation energies of the cells directly or after taking into account vibrational free energy. As it is prohibitive to compute vibrational free energy for all configurations they are approximated by the transferable force constant scheme: nearest neighbor force constants are computed for the end-member crystals with imposed but varying lattice parameters. The resulting bond stiffness versus bond length relationships are applied to the superstructures, using the relaxed bond lengths and their chemical identities as predictor. Significant miscibility gaps were predicted for the binaries TiC-ZrC and HfC-TiC, with consolute temperature in excess of 2000 K, in good agreement with experiments. The system HfC-ZrC shows complete miscibility at room temperature. Approximately symmetric phase diagram for HfC-TiC and asymmetric phase diagrams for HfC-ZrC and TiC-ZrC were predicted. With the success of the method in the simple carbide systems similar computations can now be performed for geologically relevant mineral families. Mg2SiO4 liquid at high pressure is of central importance in our understanding of melts that occur in the deep Earth and in particular in the early history of our planet, when it was in a magma ocean stage. Due to high melting temperatures little is known experimentally about its high pressure thermodynamic and transport properties that govern magma ocean structure and dynamics. Molecular dynamics simulations now fill this gap. Currently, density functional theory based computations are restricted to a few hundred atoms and a few picoseconds. While such simulations allow for determination of thermodynamic properties, longer run durations and larger cells are necessary to obtain transport properties such as diffusivity and viscosity with sufficient precision. By contrast, semi-empirical pair potentials provide an efficient route to perform large-scale molecular dynamics simulations. They suffer, however, from the fact that the transferability of the potentials to different conditions is not guaranteed. The development of aspherical flexible potentials that are fit to density functional theory results bridge the gap between ab-initio methods and classical potentials. Comprehensive large-scale molecular dynamics simulations using the aspherical ionic model were performed on Mg2SiO4 melt to obtain thermodynamic properties as well as diffusivity and viscosity. The pressure-temperature range covered was 0-32 GPa and 2600-3200 K. The thermodynamic parameters agree well with density functional theory based results: the Grüneisen parameter $gamma$ was found to increase significantly with pressure. Diffusivity is predicted to decrease and viscosity to increase with pressure. Both transport properties were readily fit with closed Arrhenius expression. Independent estimates on diffusivity and viscosity allows an examination of their relation through the Eyring equation, often employed to compute viscosity from diffusivity data. The proportionality factor between them, the translation distance for a diffusion event $lambda$, is determined as $lambda$=18 AA at 0 GPa, and decreases with pressure. This is in good agreement with previous molecular dynamics simulations using classical potentials, but significantly larger than other estimates of $lambda$ based on experimental data that yield 2.8 AA $ < lambda < $ 5 AA. Combining the thermodynamic and viscosity fits a magma ocean adiabat and the associated viscosity profile were computed.
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“Mad King Ludwig”, « Père Rhin » und “Foresta Nera”. Das Deutschlandbild in englisch-, französisch- und italienischsprachigen Reiseführern
(2003)
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Mechtild Agreiter
- Das Deutschlandbild, das von ausländischen zeitgenössischen Reiseführern gezeichnet wird, wurde in dieser Arbeit anhand aller zum 1. Januar 2000 auf dem internationalen Markt vorhandenen englisch-, französisch- und italienischsprachigen Reiseführer über Deutschland untersucht. Die von den Reiseführern beachteten Regionen Deutschlands wurden mittels quantitativer Methoden identifiziert. Die qualitative Inhaltsanalyse ließ Aussagen über Deutschland, aber auch über Regionen, die bei bestimmten Themen für ganz Deutschland stehen, zu. Es konnten anhand der Reiseführeranalyse Motive dargestellt werden, die für eine Reise nach Deutschland sprechen. Dies sind vor allem die deutsche Küche, die vorhandene Infrastruktur für Outdooraktivitäten und das romantische Deutschland. Deutschland wird von den ausländischen Reiseführern auf sehr wenige, klar umrissene und somit überschaubare Regionen und Zuschreibungen reduziert. Sie wählen für ihre Zwecke passende Highlights aus und vernachlässigen darüber in weiten Teilen die Beschreibung anderer Regionen und aktueller Entwicklungen. Die regionale Überbetonung Süddeutschlands zeigt sich vor allem darin, dass Bayern und der Schwarzwald stellvertretend für ganz Deutschland stehen. Eine Gegenüberstellung mit den tatsächlichen Zielregionen der Touristen in Deutschland aus den entsprechenden Herkunftsländern brachte eine noch stärkere regionale Fokussierung der Touristen zu Tage. Vor allem die Dominanz Bayerns wird noch deutlicher. Die Deutschlandbilder in allen Reiseführern aller Herkunftsländer weisen große Übereinstimmungen auf. Dies trifft besonders auf die regionalen Schwerpunktsetzungen zu, jedoch greifen die Reiseführer in erstaunlicher Übereinstimmung auch die gleichen, typischen Themen zu Deutschland heraus. Die vorhandenen Unterschiede zwischen den Reiseführern aus den verschiedenen Herkunftsländern liegen mehr in der Art und Weise der Behandlung der Themen und den damit verbundenen regionalen Zuweisungen. Diese Themen machen sich weniger an Deutschland fest, als dass ihre Begründung vielmehr im Herkunftsland des Reiseführerautors bzw. –verlags liegt und somit den Kundenwünschen. Alle ausländischen Reiseführer beschreiben kritische bzw. negative Aspekte in Deutschland. Sie weisen darauf hin, dass Deutschland ein zum Teil gefährliches Reiseland ist. Die Beschreibung von Sehenswürdigkeiten, die für das Dritte Reich und die beiden Weltkriege stehen ist ein deutlicher Hinweis auf die Existenz von Dark Tourism. Außerdem zeichnen die Reiseführer ein klares Bild des deutschen Paradoxons: umfangreicher Umweltschutz bei gleichzeitigem Fehlen eines allgemeinen Tempolimits.
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Rechnergestützte Identifikation von Böden
(2005)
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Christoph Albrecht
- Das in Deutschland verwendete Ordnungssystem zur Beschreibung der Pedosphäre ist die Deutsche Bodensystematik (DBS). Damit können die Morphologie und die Entstehung der Böden sehr gut erklärt werden. Bei der praktischen Anwendung, also der Einordnung von Böden in das bestehende System, kommt es jedoch zu Problemen. Sie zeigen sich vor allem darin, dass es verschiedene Interpretationsmöglichkeiten der Profilmorphologie gibt. Die fehlende Objektivität und Reproduzierbarkeit der bodensystematischen Angabe führt dazu, dass das inhaltliche Potenzial dieser Information bei weiterführenden Anwendungen (zum Beispiel Ableitung von Pedotransferfunktionen) nicht ausgeschöpft werden kann. Die wesentliche Ursache dafür ist eine funktionelle Überladung der DBS. Sie soll gleichermaßen die Ansprüche der wissenschaftlichen und der praktischen Bodenkunde erfüllen (umfassende Beschreibung der Böden und ihrer Beziehungen sowie schnelle und eindeutige Bodenansprache), obwohl sie nur für jeweils einen Zweck optimiert werden kann. Dieser Konflikt, zu dessen Erklärung die Ordnungssysteme Systematik und Klassifikation unterschieden werden, wird zusammen mit Lösungsmöglichkeiten in der Arbeit ausführlich dargestellt. Bei der Bodenidentifizierung (Einordnung von Böden in ein Ordnungssystem) müssen die kategoriebildenden Merkmale messbar sein. Das ist bei bodensystematischen Angaben nur selten möglich, weil bodenbildende Prozesse kaum messbar sind. Deshalb bleiben Identifizierungen mit der DBS oft hypothetisch. Zur Lösung des Identifikationsproblems müssen entweder die Pedogenesen exakt quantifiziert werden (Beweis der Systematik) oder eine einfache Klassifikation entwickelt werden. Die erste Strategie erfordert umfangreiche Forschungsarbeiten, so dass kurzfristig nur mit einer Klassifikation zufriedenstellende Ergebnisse erzielt werden können. Dazu werden drei Ansätze untersucht: 1. Bei der Entwicklung von Bestimmungsschlüsseln für Bodenhorizonte und Bodensubtypen soll geprüft werden, ob sich die Definitionen der DBS strukturieren lassen. 2. Mit einer fuzzy Cluster-/Diskriminanzanalyse werden die vorhandenen Bodendaten statistisch analysiert. 3. Das unscharfe regelbasierte System zur Horizontidentifikation erlaubt die automatisierte Verarbeitung von messbaren Grenzwerten und verbal vorliegendem Expertenwissen. Die verschiedenen Methoden werden anhand der Kriterien Datenbedarf, Definitionstreue, Ergebnisqualität, Robustheit und Anwendungsmöglichkeit vergleichen. Dabei wird deutlich, dass der statistische Ansatz aus methodischen und praktischen Gründen nicht zur Automatisierung der Identifikation geeignet ist. Die Bestimmungsschlüssel sind einfach und sehr definitionstreu, jedoch lässt sich deren Anwendung nicht automatisieren. Es zeigt sich, dass der regelbasierte Ansatz das beste Verfahren für die rechnergestützte Bodenidentifizierung ist. Zum gegenwärtigen Zeitpunkt gibt es noch Verbesserungspotenziale, aber die breiten Anwendungsmöglichkeiten, die Stabilität und die Robustheit des Verfahrens ermöglichen einen adäquaten Umgang mit den gegenwärtig verfügbaren pedologischen Informationen.
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Effects of land-use changes on the properties of a Nitisol and hydrological and biogeochemical processes in different forest ecosystems at Munesa, south-eastern Ethiopia
(2004)
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Yeshanew Ashagrie
- The effects of conversion of natural forest into different exotic tree species plantations and crop cultivation were investigated at Munesa, south-eastern Ethiopia with the objectives of (i) determining changes on soil physical and chemical properties, (ii) quantifying water and nutrient fluxes under the different forest ecosystems, and (iii) assessing nutrient dynamics in water flowing through the soil under the different forest ecosystems. Soil samples were taken from the organic layer and at 0-20, 20-40, 40-70, 70-100 cm depths from the mineral soil. Rainfall and throughfall were collected using plastic funnels mounted 1 m above the ground. Soil solutions were collected with zero-tension (organic layer) and tension (mineral soil at the depth of 20, 50 and 100 cm) lysimeters. After 26 years of cultivation, surface (20 cm depth) soil structure was deteriorated and total soil organic carbon (SOC) and N contents both in bulk soil and water stable aggregates were significantly reduced. Below 21 years old Eucalyptus plantation no significant changes on the above mentioned parameters could be identified, but significant reductions in SOC, N and S concentrations associated with the sand and silt separates were evident. There were also significant reductions both in quality and quantity of particulate organic matter (POM) due to cultivation and only in quality of POM due to 21 years Eucalyptus plantation. The organic layer mass under 21 years old Pinus patula, 21 years old Eucalyptus globulus and third rotation Eucalyptus globulus (established 42 yr ago) decreased by 43%, 57% and 15%, respectively, relative to the natural forest. There were also significant reductions in the organic layer C and N stocks (9 to 60% and 25 to 68%, respectively), being highest under Pinus and lowest under third rotation Eucalyptus. In the mineral soil, to 1 m depth, there was a significant (P<0.05) reduction (16 to 20%) in SOC stock after conversion of natural forest into forest plantations. The N stocks under the 21 years old Pinus and third rotation Eucalyptus plantations were significantly reduced amounting 27 and 20% respectively, whereas 21 years old Eucalyptus had nearly an equivalent amount of N as that of the natural forest, probably due to a dense forest floor vegetation, fixing N. The changes in the organic layer and mineral soil S stocks after plantation establishment were not significant. Of the total annual rainfall (1190 mm) recorded during the monitoring period (October 2001 to September 2002), about 47% and 18% were intercepted by the canopies of Cupressus and the natural forest, and Eucalyptus, respectively. Total annual nutrients (Ca, Cl, K, Mg, Na, NH4–N, NO3–N, PO4–P, SO4–S ) deposition by rainfall was 12 kg ha–1yr–1. Throughfall K, Mg, Ca and Cl fluxes were enriched relative to rainfall, whereas Na, NO3–N, NH4–N, PO4–P and SO4–S were depleted. Total annual throughfall nutrient inputs (Ca, Cl, K, Mg, Na, NH4–N, NO3–N, PO4–P, SO4–S) were 14 kg ha–1yr–1 under Cupressus, 21 kg ha–1yr–1 under the natural forest and 24 kg ha–1yr–1 under Eucalyptus. Water passing through the different forest floors differed only in K, Mg and NO3–N concentrations, the latter two being higher under the natural forest and Eucalyptus plantation than Cupressus. Potassium was greater under Eucalyptus than the natural forest and Cupressus. Except for NH4–N in the natural forest, forest floor leachate nutrient concentrations were enriched in all forest types in relation to throughfall. Most nutrient fluxes to the mineral soil decreased in relation to throughfall fluxes, whereas NO3–N fluxes increased by over 50% in all forest types. At all soil depths, the concentrations of most nutrients in the mineral soil solution decreased relative to the concentrations in the forest floor leachate, but Mg, Na and NO3–N at all depths in Cupressus plantation and SO4–S and Na at some soil depths in the natural forest and Eucalyptus plantation had increased. The vertical trends in soil solution nutrient concentrations showed a decreasing trend with depth increments for most of the nutrients, but the concentrations of Cl and Na in all forest types and Ca, Mg and NO3–N in Cupressus increased with increasing soil depth. At 1 m soil depth, the concentrations of Ca, Mg and NO3–N in Cupressus, respectively, were 8, 7 and 23 times higher than in the natural forest and 3, 4 and 81 times higher than in Eucalyptus indicating losses by leaching. Generally, the results of this study emphasize the importance of forest type, species composition and management in affecting carbon and nutrient storage, water and nutrient fluxes and dynamics.
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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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Vegetation ecology of springs: ecological, spatial and temporal patterns
(2009)
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Volker Audorff
- Acidification is a phenomenon, which affected the forested catchments of the northern hemisphere severely over recent decades. Acidic depositions depleted the buffering capacities of soil and groundwater, what lead to an impairment of forests, headwaters, and lakes. Even though the depositions were reduced considerably since the early 1990s, the recovery of catchments was found to occur time-delayed. The grade of recovery was found to vary significantly between regions. Biomonitoring is an appropriate tool to detect spatial and temporal patterns of ecosystem alterations, such as acidification and recovery. However, to know the interrelationships between organisms and their environment is an indispensable precondition for the identification of indicator species. The complexity of ecosystems and ecological processes hampers this quest oftentimes. Springs provide a natural setting that minimises such constraints. Compared to other habitat types, external factors are less relevant, which makes it easier to relate changes in species abundances to changes in their environment. Studying this species-environment relationship, here the response of plant species to the acidification of the spring waters was of particular interest. In a survey of five regions in Central Europe - taking spatial, hydrophysical as well as hydrochemical parameters of the springs into account - it was clearly shown that the species composition of springs is essentially determined by the spring water chemistry, and more precisely by the gradient of acidity and nutrient availability. This connection was reflected by spatial patterns within and between the regions. These patterns provide useful ecological information about spring water quality and in return about the acidity status of their forested catchments. Including catchment traits - like bedrock, climatic parameters, and forest vegetation - in the analyses, these emerged to be relevant for the species composition of springs, but less than the spring water chemistry. A path analysis showed that the catchments affect the vegetation of springs not directly, but indirectly via the determination of spring water quality. Hence, the catchments are a part of the functional chain, which is driven by the atmospheric depositions. The pH-value was found to represent the gradient of acidity and nutrient availability best. It can serve as a proxy measure that can be related to species occurrence and to species dynamics respectively, aiming to identify indicator species for assessing the status and alterations of spring water quality. With the aim to delineate niche optima and amplitudes, which in return can serve as indicator values, the realised niches of spring-inhabiting species were modelled with respect to pH. The niche attributes were found to be a matter of sampling scale. Larger plot sizes (grain) weakened the species-environment relationship, what consequently resulted in broader niche amplitudes. In contrast, the grain did not influence the species’ pH optima. Monitoring approaches that target to assess processes in time, such as acidification and recovery, are dependent on the response time of indicator species to changes in their environment. Investigating an interval of four consecutive years, inter-annual variability of the species composition could not be attributed to changes in the acidity of the spring waters. Looking at single species, bryophytes did not show a higher sensitivity to the inter-annual variability of the environment than vascular plants. Actually, only a minority of all species featured abundance changes which were significantly correlated to variations in spring water acidity. Our results suggest that the species inertia retards the vegetation dynamics of forest springs. A delayed or long-term integrating response of potential indicator species must be considered when evaluating their indicator suitability. In conclusion, the biomonitoring of spring water acidification or recovery is expedient only for longer time intervals. In a nutshell, the vegetation of springs is closely related to the hydrochemical traits of the spring waters, in particular to a gradient of acidity and nutrient availability. Individual species as well as whole plant communities are suitable indicators which allow for the monitoring of the acidity status of forested catchments. The results of this study contribute to a better understanding of the species-environment-relationships, and in return to an improvement of indicator systems.
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Diversität von Geometriden (Lepidoptera) und Gefäßpflanzen entlang von Habitatgradienten am Südwest-Kilimanjaro
(2003)
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Jan C. Axmacher
- Auf 63 Untersuchungsflächen am Südwesthang des Kilimanjaro wurden Zusammenhänge zwischen der Geometriden-Diversität und floristischer Diversität, Vegetationsstruktur und abiotischen Faktoren untersucht. Besonderes Interesse galt der Bergwaldregeneration, die auf 16 Flächen zwischen 2000 und 2350 m Höhe untersucht wurde. Entlang eines Höhentransektes, das sich vom unteren Kulturland bei 1200 m durch die Bergregenwaldstufe bis in die Ericaceenstufe in Höhen von 3700 m erstreckte, wurde die Änderung der Lebensgemeinschaften in Abhängigkeit von Höhenlage und Nutzungsintensität erfasst. Der Fang der Geometriden erfolgte an Leuchttürmen zwischen 19 und 22 Uhr, im zentralen Untersuchungsgebiet auch mit sieben automatischen Lichtfallen. Zum Anlocken der Falter wurden 15 W- Schwarzlichtröhren verwendet. Um die Leuchttürme herum wurden 400 m2 große Untersuchungsflächen ausgewiesen, auf denen alle Gefäßpflanzen nach Schichten getrennt erfasst und die Vegetationsstruktur aufgenommen wurde. Im zentralen Untersuchungsgebiet wurden an Leuchttürmen in 59 Fängen 118 Morphospezies und 2603 Falter aus der Familie Geometridae gefangen, mit den weniger effektiven Lichtfallen in 203 Fängen 77 Morphospezies und 662 Individuen. Die auf den zentralen Untersuchungsflächen aufgenommenen höheren Pflanzen verteilten sich auf 44 Familien und 98 Morphospezies. Die Artenzusammensetzung der Geometridenzönosen wie auch der Gefäßpflanzen änderte sich im Regenerationsverlauf. Die Artenzahl der Gefäßpflanzen nahm auf den Flächen insgesamt, in Baum-, Strauch- und Krautschicht, der Gruppe der Epiphyten und in den artenreichsten Pflanzenfamilien im Regenerationsverlauf von großen Lichtungen über junge und alte Sekundärwälder zu naturnahen Wäldern zu. Die Diversität der Geometridenzönosen, gemessen mit Fishers Alpha und Hurlbert Rarefaction, sowie die mit Chao 1 extrapolierte Gesamtartenzahl nahm dagegen ab. Die Werte von Fishers Alpha lagen bei sehr niedrigen Werten zwischen 3,4 und 17,8. Die Vegetationsstruktur korrelierte nur schwach mit der Zusammensetzung der Geometridenzönosen. Die Deckung der Moosschicht, ein Indikator für feuchte Verhältnisse, zeigte dabei die stärkste Korrelation. Im Höhentransekt wurden auf den Offenland-, Agroforst- und Waldflächen mit 212 Leuchtturmfängen insgesamt 304 Morphospezies und 8468 Einzeltiere aus der Familie der Geometridae gefangen. Wie im zentralen Untersuchungsgebiet war Mimoclystia corticearia (Larentiinae) die häufigste Art, gefolgt von Darisodes oritropha (Ennominae). Häufig waren auch Chiasmia fuscataria (Ennominae) aufgrund eines Massenvorkommens am unteren Waldrand sowie Chloroclystis derasata (Larentiinae). Bei den auf 51 Untersuchungsflächen durchgeführten Vegetationsaufnahmen wurden 451 Gefäßpflanzenarten aus 116 Familien erfasst. Die Gesamtartenzahlen der Gefäßpflanzen auf den Flächen schwankte zwischen 5 und 53. Sie zeigte auf den Wald- und Offenlandflächen keine Korrelation mit der Höhe, während sie auf den Agroforstflächen mit steigender Höhe signifikant zunahm, was auf die extensivere Nutzung höher gelegener Standorte zurückzuführen ist. Die Artenzahlen vaskulärer Epiphyten, der Aspleniaceen und Rubiaceen waren in mittleren Höhen zwischen 2200 und 2400 m am höchsten, während die Diversität der Baum- und Strauchschicht und der Leguminosen maximale Werte auf den unteren Flächen erreichte. Auch die Diversität der Geometriden war auf den unteren Flächen mit Fishers Alpha-Werten von maximal 40,2 am höchsten. Sie fiel im Transekt auf den Offenlandflächen gleichmäßig ab, während auf den Waldflächen im Bereich zwischen 1800 und 3100 m abgesehen von dem Bereich des zentralen Untersuchungsgebietes die Diversität bei Werten zwischen 8,3 und 12,5 annähernd konstant blieb. Die Analyse der Beta-Diversität und der Gesamtdiversität einzelner Höhenbereiche zeigte, das die Geometridenzönosen zwischen 2000 und 3000 m sehr homogen sind. Die Höhenlage erwies sich als „Master“-Variable, die einen starken Einfluss auf die Vegetationszusammensetzung wie auch die Zusammensetzung und Diversität der Geometridenzönosen hatte. In Bezug auf Geometriden sind insbesondere die feuchten Bergregenwälder am Kilimanjaro wenig divers. Dies kann auf die Insellage des Vulkans inmitten trockener Savannen, sein geringes Alter und die insgesamt arme afrikanische Lepidopterenfauna zurückgeführt werden. Neben dem Schutz der Bergregenwälder, der für die Aufrechterhaltung der Phytodiversität des Kilimanjaro wie auch für die Sicherung der Wasserversorgung Nordtansanias unerlässlich erscheint, sollte auch die traditionelle Agroforstwirtschaft erhalten bleiben, da sie eine hohe Diversität sowohl an Geometriden als auch an Pflanzenarten gewährleistet.
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Kinetische Untersuchungen der Halogen-Aktivierung einer simulierten Salzpfanne in einer Smogkammer
(2013)
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Natalja Balzer
- Reaktive Halogenverbindungen, insbesondere solche von Br und Cl, spielen eine wichtige Rolle beim atmosphärischen Abbau von Ozon und Kohlenwasserstoffen. Auch beeinflussen sie die Radikalzusammensetzung in der Troposphäre und haben somit eine Auswirkung auf klimarelevante Prozesse. Ziel dieser Arbeit war die Untersuchung der Halogenfreisetzung aus einer künstlichen Salzpfanne bei unterschiedlichen umweltrelevanten Bedingungen, wie relative Feuchte (RF) und Konzentrationen von Stickoxiden und Kohlenwasserstoffen, in einer Smogkammer. Diese Methode wurde in Rahmen dieser Arbeit entwickelt, um diese bislang wenig untersuchte Quelle von Halogenen zu untersuchen. Als Modell für die Salzpfanne wurde eine umweltrelevante Mischung von NaCl mit NaBr verwendet. Kinetische Berechnungen lieferten die zeitlichen Verläufe der Cl-Atome und OH-Radikale aus dem Verbrauch der zugesetzten Kohlenwasserstoffe und der Br-Atome aus dem Ozonverbrauch und UV-Absorptionsmessungen die Verläufe der BrO-Radikale. Während Salzpfannen-Experimenten bei einer mittleren RF von 37 % erreichte die Cl-Konzentration ein Maximum von 5 x104 cm-3. Ein rascherer Ozonabbau wurde bei größerer RF und zugleich höherer BrO-Konzentration beobachtet. Bei den Experimenten in Anwesenheit von sekundären organischen Aerosolen (SOA) verlangsamte sich der Ozonabbau um einen Faktor 16. Das BrO-Mischungsverhältnis erreichte in diesem Fall maximal 0.15 ppb im Vergleich zu Experimenten ohne SOA, bei denen das BrO Mischungsverhältnis 6 ppb erreichte. Nach Einwirkung der aus der Salzpfanne freigesetzten Halogene auf das SOA wurde ein erneutes Partikelwachstum beobachtet. Dies könnte eine Hauptsenke für Halogene in der Atmosphäre darstellen und einen neuen Weg zur Partikelbildung.
