9 search hits
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Jahresbericht 2010-11 zum Förderprojekt 01879 Untersuchung der Veränderung der Konzentration von Luftbeimengungen und Treibhausgasen im hohen Fichtelgebirge 2007 – 2014
(2012)
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Thomas Foken
Lisa Dirks
- no abstract
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Beyond productivity- Effects of extreme weather events on ecosystem processes and biotic interactions
(2012)
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Julia Walter
- Under global climate change, extreme weather events, such as heat waves, drought or heavy rain spells, are projected to increase in magnitude and frequency. As these may affect vegetation and ecosystems more than gradual shifts in mean climatic parameters, investigating the consequences of extreme weather events recently became an important issue in climate change research. The main focus of most experiments investigating effects of extreme weather events on vegetation is on primary productivity. In our experiment in artificially planted communities, even an extreme drought of 1000-year recurrence did not have effects on above- or below-ground biomass production from 2005-2010.
Thus, the main objectives of this thesis were (1) to investigate if extreme weather events have an effect on ecosystem functions beyond productivity, (2) to test if such a high resistance or resilience in response to drought regarding productivity also exists in more naturally grown plant communities and (3) to further elucidate possible mechanisms of the surprisingly large stability of the plant communities.
To investigate these objectives, several experimental studies were conducted in artificially planted, as well as in naturally grown grassland communities and consequences of extreme weather events for ecosystem processes, such as decomposition and herbivory were investigated. In a pot experiment, it was studied, if grass plants react improved towards repeated drought when compared to a first drought and thus reveal a kind of drought memory. Such a memory might be one possible, but up until now widely neglected mechanism of resilience.
Even though biomass production remained stable in our experiment in artificially planted communities, biomass quality was severely affected by extreme drought, thereby strongly affecting the development of a herbivore caterpillar feeding on drought-exposed leaves. Further, plant compounds of the host plant depended on the composition of the plant community it was grown in. This in turn resulted in strong effects on the larval mortality of herbivores feeding on such plants.
In contrast to the study in artificially planted communities, aboveground net primary productivity (ANPP) was reduced in naturally composed grassland in response to extreme rainfall variability, including an extreme drought followed by heavy rainfall. Forage quality was altered by drought. Furthermore, mowing frequency strongly altered forage quality and biomass production, but did not interact with rainfall variability and thus did neither buffer, nor amplify effects of extreme rainfall variability. Despite effects of rainfall variability on ANPP, grassland showed high resilience after drought followed by heavy rain, as effects were large shortly after the extreme event, but did not persist until a second harvest later in the year.
In natural grassland, rainfall variability and drought also affected ecosystem processes, here litter decomposition, beyond productivity. Drought followed by heavy rain pulses decreased decomposition rates. Decomposition in more frequently mown meadows was more vulnerable towards drought exposure. Winter warming and additional winter rain had no long-term effect on decomposition. To conclude, projected increases in drought frequency under climate change may inhibit decomposition and alter nutrient and carbon cycling along with soil quality in temperate grassland, whereas a reduction of snow cover leading to more variable soil surface temperatures may counteract increased decomposition under winter warming.
In this thesis, an ecological stress memory as one possible mechanism of resilience is defined as any response of a single plant after a stress experience that improves the reaction of the plant towards future stress experience and which is assessed on a whole plant level. This thesis further provides evidence of a drought memory in grass plants: Plants repeatedly subjected to drought showed improved photo-protection and a higher rate of living biomass when compared to plants faced with their first drought. Similarly, tree seedlings exposed to drought in summer revealed higher frost resistance during winter, providing evidence of a long-lasting “cross-stress-memory” .
To sum up, the thesis shows that extreme weather events, even though neither severely affecting biomass production in artificially composed, nor in naturally growing communities in the long-term, exert strong influence on physiological or biogeochemical parameters, such as plant compounds or soil biotic activity. These changes in turn modify ecosystem functions beyond productivity, for example herbivory or decomposition, possibly altering biotic interactions and nutrient cycling. Furthermore, the findings imply that plants exhibit a stress memory after stress exposure, which may be one mechanisms leading to a high stability and resilience upon frequent stress.
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The Nature of Fluids in Hydrothermal Copper and Molybdenum Ore Deposits - An experimental and analytical study
(2012)
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Linda Lerchbaumer
- The evolution of magmatic-hydrothermal fluids in porphyry Cu and porphyry Mo deposits was studied using synthetic and natural fluid inclusions by optical microscopy, microthermometry, Raman spectroscopy, and LA-ICP-MS.
The partitioning of Cu between vapor and brine in aqueous NaCl-S ± KCl ± FeCl2-rich fluids was investigated by means of hydrothermal experiments in rapid quench autoclaves at 600-800°C, 70-130 MPa and at both oxidizing and reducing fO2, covering all geologically relevant conditions. Resulting partition coefficients (DCuvap/brine) are between 0.2 and 0.4 for the range of studied S-concentrations, fluid pH, fO2, and P-T conditions. These values indicate that Cu does not partition into the vapor phase at any plausible condition in contrast to data from natural quartz-hosted vapor and brine inclusions which appear to indicate Cu enrichment in the vapor.
The formation of such Cu-rich vapor-type fluid inclusions was investigated in hydrothermal re-equilibration experiments. For this purpose, coexisting vapor and brine inclusions of known composition were re-equilibrated in a fluid of slightly different composition and lower pH than the trapped one at 800°C, 70-130 MPa. This procedure led to a dramatic increase in Cu concentrations in the vapor phase from 0.3 ± 0.03 to 5.7 ± 3.3 wt% after re-equilibration and the change of DCuvap/brine from a true value of 0.4 ± 0.05 to an apparent value of 8.3 ± 4.9. This post-entrapment modification can be traced back to the difference in fluid pH between the trapped and the surrounding fluid, inducing diffusion of H+ out of the inclusion and the diffusion of Cu+ (and Na+, Ag+) into the inclusion in order to maintain charge balance. Moreover, the presence of larger amounts of S within vapor inclusions as compared to brine inclusions can bind larger amounts of Cu. The re-equilibration of trails of vapor and brine inclusions in a natural quartz sample in a fluid similar to the trapped one, yet more acidic, showed that this modification process can be reversed, resulting in the loss of major amounts of Cu from natural vapor inclusions.
The composition of metal-bearing melts and magmatic fluids of Mo-mineralized granites resembling porphyry Mo deposits was investigated using natural melt-, fluid-, and solid-inclusions in quartz crystals found in miarolitic cavities from minor Mo-occurrences in Colorado and Norway. Melt inclusions from the Treasure Mountain Dome are highly enriched in Mo (4-43 ppm), also melt inclusions from the Drammen and Glitrevann granites (5-32 ppm, and 12 ppm, respectively), resembling highly fractionated melts. Copper concentrations are low (<1-30 ppm) in the melts, but high in the fluids: intermediate density, supercritical fluid inclusions of these three locations host 6-1900 ppm, 8-3500 ppm, and 5-180 ppm Cu, respectively. The comparison of these results with data from economic porphyry Mo and porphyry Cu (Mo, Au) deposits shows no difference in Mo concentrations in the particular melts and fluids. Hence, other factors probably control the evolution of a granitic intrusion into large, economic Mo deposits, minor Mo occurrences, or just into barren plutons. These may be mainly the size, position, and geometry of the parental magma chamber, the multiplicity of intrusions maintaining a constant flux of metalliferous, S-rich, hot melts, and the extent of fluid focusing within small rock volumes forming high-grade ore shells.
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Denying access to water? Moral values and commercialization policies in Khartoum governmental water management
(2012)
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Anne-Sophie Beckedorf
- This contribution draws on empirical fieldwork carried out in Khartoum/Sudan in 2009/2010 in order to examine the role of value systems in recent commercialization policies of Khartoum governmental water management. The first section provides background information about the current water supply system in Khartoum, which is a necessary precondition to understand current reform processes. The second section singles out three major aspects of commercialization policies and their contestations in greater detail: increases in water prices, increases in water cuts in case of unpaid water bills, and installations of prepaid water meters. The third section summarizes these contestations and argues that value systems are one major reason why current reform processes are not implemented in the way they were perceived.
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Copper exposure of freshwater mussels (Anodonta anatina): Some physiological effects
(2012)
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Andhika Puspito Nugroho
- Copper (Cu), a transition metal, has the tendency to increase in its concentration in freshwater ecosystems over natural levels, due to industrial and other anthropogenic sources. In water, copper can exist in dissolved form or associated with suspended food particles. Freshwater mussels living at the interface of the free-flowing water and the sediment phase can take up copper directly from the water or by consumption of lower trophic level organisms laden with copper. For mussels, copper is essential at low concentration as cofactor of metalloenzymes involved in growth regulation and development, but it may be toxic at higher levels by disturbing calcium (Ca) homeostasis. The duck mussel Anodonta anatina is a freshwater species found in abundance in limnic and lotic European ecosystems and is used as test organism in ecotoxicological studies. The potential involvement of Cu in the general decline of many European freshwater mussel species is the major motivation for this work. This research aims to study the relevance of Cu exposure pathways on its uptake, distribution, bioaccumulation, and elimination in the freshwater mussel A. anatina and its various potential physiological impacts. The work is started with raising Cu-loaded algae using the stable isotope 63Cu as marker for feeding of mussels without affecting the nutritional value of the algal food. In these latter experiments, mussels are exposed to 63Cu via water or via food to investigate the relative importance of Cu uptake to its distribution and accumulation among the mussel’s organs. Its consequences on calcium homeostasis, soluble carbohydrate and protein levels in various tissues, metallothionein induction, glutathione levels, activities of antioxidative enzymes and glutathione reductase, and on lipid peroxidation are examined. In the algal experiment, Parachlorella kessleri is grown at six 63Cu concentrations (0, 5.9, 11.7, 23.5, 47, and 94 µmol L-1) for 4 days, starting from day 3. When exposed to Cu at a level of up to 6 µmol L-1, P. kessleri is largely unchanged in its nutritional values; so this concentration is used to grow 63Cu-carrying food for mussel experiment. Concentrations above 6 µmol L-1 decrease significantly in the algal growth and alter the other physiological parameters. Three groups of 21 mussels each are used, one as control and two for exposure, receiving copper as the stable isotope 63Cu via the water at 0.3 µmol L-1 or via the food (1.5 mg L-1 freeze-dried Cu-loaded algae, equivalent to 0.06 µmol L-1 Cu) for 24 days, followed by 12 days of depuration. For analysis, three mussels each are taken randomly from every group at days 0, 6, 12, 18, 24, 30, and 36. The mussels are anaesthetized and hemolymph and extrapallial fluid are sampled before the mussels are dissected into gills, mantle, kidney, digestive gland, foot, adductors, intestines, and the remainder (gonads, heart, and labial palps). During copper exposure, the levels of exogenous copper (63Cu) and total Cu increase in all body compartments. Uptake via the water leads to higher Cu levels than via the food, but in relative terms food uptake is more efficient taking the five-fold lower nominal concentration of copper into consideration. Upon exposure via the water, the metal is compartmentalized mainly in the mantle, the gills, and the digestive gland, upon exposure via the food the major recipients are the digestive gland and the intestines. Upon depuration for two weeks, copper is quickly but not completely eliminated. Simultaneously with increasing Cu levels, Ca levels are increased in all body compartments, accompanied by decreases in soluble carbohydrates and proteins in the gills, mantle, digestive gland, and kidney. At the same time, Cu exposure results in increases in malondialdehyde levels, decreases in glutathione levels, strong increases in metallothionein levels, and changes in the activities of the antioxidative enzymes superoxide dismutase, catalase, and glutathione peroxidise, and of glutathione reductase in the gills, mantle, digestive gland, and kidney. During depuration, most parameters tend to normalize but do not return to control values. In conclusion, the overall pictures suggest that the considerable physiological stress elicited by low-level copper exposure may contribute to the factors involved in the decline of many European freshwater mussels.
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Structure and Reactivity of Terrestrial and Extraterrestrial Pyrrhotite
(2012)
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Dennis Harries
- Pyrrhotite (Fe1-xS) is a non-stoichiometric iron monosulfide common in terrestrial rocks, ore deposits, and many extraterrestrial materials. The non-stoichiometry due to metal vacancies relates to a variety of composition-dependent crystallographic superstructures, but little of the existing structural and microstructural complexity has been explored yet. This thesis investigates the occurrences and nature of pyrrhotite superstructures, examines the related nano- and microstructural phenomena, and explores their effects on chemical reactivity. The goal is to comprehend the relations of the nanoscale real structure of pyrrhotite to its physicochemical properties. A central tool in these studies is analytical transmission electron microscopy (TEM), which has been extensively used to study terrestrial and extraterrestrial samples. In three studies, published or submitted as scientific research articles, it is shown that structural complexity of pyrrhotites is a widespread feature in terrestrial and extraterrestrial materials and is strongly interrelated with its physicochemical properties and environments of formation and alteration. A new model based on translation interface modulation is being introduced to provide a realistic description of the structural state of natural NC-pyrrhotites. Novel insights into the thermodynamically stable phase assemblages in the Fe-S system at ambient temperatures are presented and the crystallography and connected thermochemistry of pyrrhotites are deployed to reach new conclusions about the petrogenetic history of chondritic meteorites and the alteration processes they were involved in. Finally, an experimental alteration study reveals for the fist time quantitatively that the vacancy superstructures and anisotropy of pyrrhotites have tremendous effects on their kinetic behaviors during dissolution under acidic and oxidizing conditions. Intrinsic reactivity differences between 4C- and NC-pyrrhotite are clearly resolved and discusses in the framework of the newly established structure model.
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Whole-air relaxed eddy accumulation for the measurement of isotope and trace-gas fluxes
(2012)
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Johannes Ruppert
Michael Riederer
Willi A. Brand
Thomas Foken
- Measuring the isotopic composition of trace gas fluxes can provide additional information on ecosystem gas exchange, when ecosystem processes, like assimilation, discriminate against heavier isotopes. In the case of CO2 exchange, different mass-balances for bulk CO2 and its 13CO2 or CO18O isotopes can be used to separate respiration from photosynthetic assimilation. Up to now, detectors for direct isotope measurements in the field lack the precision needed for fast eddy covariance (EC) flux measurements. The collection of updraft and downdraft whole-air samples using the relaxed eddy accumulation technique (REA) allows simultaneously determining trace gas concentrations and isotope ratios by high precision laboratory analysis. At the same time whole-air REA relaxes several of the technical problems related to REA sampling on traps. In tests using air from a tank the complete whole-air REA sampling system and its foil balloon bag reservoirs showed no signs of contamination after cleaning. The standard deviations of δ13C and δ18O isotope ratios were only slightly higher than the precision specified for the laboratory analysis procedure. First experiment results showed that isotopic differences (up-drafts−downdrafts) were large enough to yield signal to noise ratios greater than five when applying hyperbolic deadbands during REA sampling (HREA). The performance of the instrument and the HREA sampling method are investigated by simulation of the sampling process for bulk CO2, which serves as proxy scalar. Measurements by whole-air HREA in combination with high precision isotope analysis can quantify the isofluxes of 13CO2 and CO18O. Furthermore, additional information is collected on the scalar correlation of bulk CO2 and its stable isotopes, which represents the relatively short timescale of updrafts and downdrafts in the turbulent exchange above an ecosystem. This information is essential to check the scalar similarity assumptions made in the HREA and EC/flask method for the quan-tification of isofluxes.
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Klimawanderweg auf der Landesgartenschau in Bamberg 2012
(2012)
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Thomas Foken
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The Arctic Turbulence Experiment 2009 - additional laser Scintillometer measurement campaign 2009 at the Bayelva catchment on Svalbard: Technical documentation and visualization of the near surface measurements during the ARCTEX-2009 campaign, August, 10th to August, 20th 2009
(2012)
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Johannes Lüers
Jörg Bareiss
Martin Wagner
- Accurate quantification of turbulent fluxes between the surface and the atmospheric boundary layer in polar environments, characterized by frequent change of weather and exchange conditions (stable to very stable or intermittent; rapid, short term neutral to unstable stratified conditions) is a fundamental problem in soil-snow-ice-vegetation-atmosphere interaction processes. The observed rapid climate warming in the Arctic requires improvements in the permafrost and carbon cycle monitoring. To address these problems, it is essential to improve the databases with high-quality in-situ measurements of turbulent fluxes above tundra landscape surfaces applying the Eddy-Covariance method and the laser scintillometry. Results from the Arctic Turbulence Experiment 2006 on Svalbard helped to better understand physical exchange processes of energy and matter transport and to improve instrumentation standards as well as quality assessment techniques (Lüers and Bareiss 2010, 2011; http://www.arctex.uni-bayreuth.de). Therefore, the primary goal of this additional laser scintillometer measurement campaign is to estimate the flux contributions covering typical tundra surfaces across the Bayelva catchment during a summer season south-west of the Ny-Ålesund village, Kongsfjord, Svalbard. This effort makes it possible to define the spatial context of the fluxes, and to include land use features of the surrounding terrain in the quality assessment of all observations in the Bayelva catchment over the last 10 years performed by the Alfred Wegener Institute for Polar and Marine Research (AWI).
