189 search hits
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Detection and Analysis of Coherent Structures within and above Tall-vegetated Canopies
(2005)
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Christoph Thomas
- Coherent structures are an inherent phenomenon of the atmospheric turbulent flow in the proximity to tall-vegetated canopies. Although coherent structures have called increasing attention of the turbulence community during the past decades, the basic mechanisms of their emergence, their contributions to exchange processes and their importance for conventional flux determination methods remain poorly understood or even unknown. In particular, no studies have been published yet dealing with long-term observations rather than exemplary case studies using short-term data. This dissertation aims at the enhanced understanding of the driving mechanisms and statistical properties of coherent structures within and above tall-vegetated canopies through an extensive analysis using long-term observations. Thereby, it places a specific emphasis on the implications of coherent structures for exchange processes and assesses their impact on conventional flux determination methods such as the eddy covariance and relaxed eddy accumulation techniques. Data were mainly obtained using tower-based single-point turbulence measurements and acoustic remote sensing technique (Sodar-Rass) during extensive field campaigns conducted in summer 2003. The developed wavelet software tool for detection and analysis of coherent structures is verified to extract coherent structures objectively under varying environmental conditions and thus allows determining their statistics in long-term datasets. In the proximity to the plant canopy, the temporal scales of coherent structures typically range between 20 s and 35 s. The temporal scales of coherent structures in the horizontal wind velocity, the sonic temperature and the concentration of carbon dioxide and water vapour exceed those of the vertical wind velocity. Within the canopy, the temporal scales of all vector and scalar variables collapse at approx. 24 s to 28 s resulting in an enhanced symmetry. Besides this, coherent structures with temporal scales up to 220 s are evidenced well above the canopy with the aid of acoustic remote sensing. The application of the canopy mixing-layer analogy to the data partially yields departures of the ratio m between the streamwise structures spacing of coherent structures and the canopy shear scale from the prediction m = 7...10. The departures are due to the influence of the terrain affecting the shape of the canopy wind profile and therefore the vertical wind shear. An agreement is found for flows which are forced to reorganise downstream of flow obstacles. The vertical wind shear is identified as the main driving force from which coherent structures emerge close to the canopy. In the layer well above the canopy diabatic processes facilitate the generation of coherent structures of large temporal scales. Clearcuts in a fairly homogeneous canopy cause additional structures in the turbulent flow with large temporal scales. Coherent structures contribute about 16 % to total the momentum transfer and about 26 % to the total fluxes of buoyancy, carbon dioxide and latent heat. A scheme for the qualitative classification of exchange regimes between the atmosphere and the canopy is developed analysing the ejection and sweep phases of coherent structures along the vertical profile in the canopy. The presence of coherent structures causes flux errors in the eddy covariance method below 4 %. The effect of this flux error for long-term observations is negligible as individual flux errors average out. Coherent structures of large temporal scales significantly influence the scalar similarity required for the relaxed eddy accumulation technique. These flow structures are responsible for the diurnal changes of the scalar similarity observed in the traces of acoustic temperature and concentration of carbon dioxide and water vapour.
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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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Regionale Innovations- und Kooperationsförderung mit Hilfe gesteuerter regionaler Kompetenznetzwerke - eine Untersuchung am Beispiel der Region Nürnberg
(2005)
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Thorsten Nix
- Die Untersuchung hat ihren Ausgangspunkt im aktuellen Strukturwandel hin zu einer Wissensgesellschaft, in der Innovation und Kooperation wichtige Elemente des Wachstums sind. Vor diesem Hintergrund soll die Studie Aufschlüsse darüber liefern, inwieweit gesteuerte regionale Kompetenznetzwerke zur Innovations- und Kooperationsförderung eingesetzt werden können, und wie ein Modellkonzept eines solchen Netzwerkes aussehen könnte. Der aktuelle Strukturwandel von der Industrie zur Wissensgesellschaft wird sehr stark von der Globalisierung geprägt. Kennzeichnend hierfür ist die stetige Zunahme weltweiter Konkurrenz zwischen den Unternehmen. Um dieser Konkurrenz erfolgreich zu begegnen, muss sich die Gesellschaft in den Industrieländern immer weiter zu einer Wissensgesellschaft entwickeln. Ziel dieser Wissensgesellschaft ist es, Forschungs- und Innovationsimpulse zu liefern, die von den Unternehmen in neue, hochwertige Produkte und Dienstleistungen umgewandelt werden können. Ein zentrales Merkmal der Wissensgesellschaft ist die Wissensteilung. Ähnlich wie bei der Arbeitsteilung in der Industriegesellschaft, wird bei der Wissensgesellschaft das Wissen auf verschiedene Akteure verteilt, von diesen separat weiter entwickelt und schließlich wieder in einem größeren Wissenszusammenhang bzw. Projekt vereinigt. Auf der Suche nach einem wirkungsvollen und flexiblen System der Wissenszusammenführung kristallisiert sich dabei als Lösungskonzept immer mehr die Bildung von Netzwerken heraus. Basierend auf theoretischen Überlegungen über Wissen, Innovation, Kooperation, Netzwerke und Vertrauen wird ein Modellkonzept eines gesteuerten regionalen Kompetenznetzwerkes entworfen, das in den wichtigsten Punkten wie folgt aussieht: Es ist ein auf einen bestimmten Kompetenzbereich festgelegtes, offenes, von einem unabhängigen Koordinator gesteuertes regionales Netzwerk, das den freien Zugang für alle Interessierten gewährleistet. Das Netzwerk sollte ferner einen kreativen Freiraum schaffen, in dem sich die Akteure losgelöst vom aktuellen Tagesgeschäft persönlich treffen können. Durch die persönliche Kommunikation wird eine Atmosphäre des Vertrauens geschaffen, in der vertrauliche und personengebundene Informationen (tacit-knowledge) ausgetauscht werden können. Um das Modellkonzept an einem konkreten Netzwerk zu überprüfen, wird in der Untersuchung die Kompetenzinitiative Medizin-Pharma-Gesundheit (KIM) in Erlangen als Fallbeispiel herangezogen. Betreffend der Kooperationsförderung geben bei einer durchgeführten repräsentativen Akteursbefragung 96% der Antwortenden an, dass es für sie wichtig ist, mit anderen Akteuren persönlich in Kontakt treten zu können. Zudem ist für 73% der Befragten die Kompetenzinitiative wichtig, um regionale Kontakte im Bereich Medizin-Pharma-Gesundheit zu knüpfen und zu pflegen. Aufgrund dieser Angaben ist es nicht überraschend, dass 79% neue Kontakte knüpfen konnten, die für 31% in der Findung eines Kooperations- bzw. Geschäftspartners mündeten. Bezogen auf die der repräsentativen Akteursbefragung zugrunde liegenden Grundgesamtheit von 550 an der KIM interessierten Akteure bedeutet dies eine absolute Anzahl von ca. 170 neuen Kooperationen bzw. Geschäftsbeziehungen. Im Hinblick auf die Innovationsförderung ist die KIM für 78% ein wichtiges Instrument, um sich über regionale Neuigkeiten im Bereich Medizin-Pharma-Gesundheit zu informieren, und 86% der Befragten erfahren durch die KIM schneller etwas von Neuerungen in der Region als ohne sie. Des Weiteren geben 83% an, während der Sitzungen der KIM offener für neue Ideen und Anregungen zu sein, als im normalen Tagesgeschäft, und für 75% der Antwortenden entsteht während der Sitzungen sogar eine kreative Atmosphäre, die 66% in neue Ideen für Produkte, Dienstleistungen oder Management umsetzen konnten. Schließlich bewerten 71% der Befragten die KIM mit den Noten „sehr gut“ und „gut“, und 79% vertreten die Meinung, dass die KIM „wichtig“ bis „sehr wichtig“ ist, um den Bereich Medizin-Pharma-Gesundheit in der Region zu fördern. Aufgrund dieser Ergebnisse kann davon ausgegangen werden, dass zumindest durch die KIM, als ein Beispiel eines gesteuerten regionalen Kompetenznetzwerkes, Innovationen und Kooperationen gefördert werden können. Einen Anreiz für weitere Untersuchungen gibt darüber hinaus die Feststellung, dass für fast alle Befragten eine thematische Begrenzung der KIM auf den Bereich Medizin-Pharma-Gesundheit wichtig ist, wobei sich gleichzeitig fast genauso viele gegen eine weitere thematische Einschränkung (z.B. nur auf den Sektor Medizintechnik) aussprechen. Es liegt somit der Schluss nahe, dass sehr fachspezifische Innovationen u.a. wegen der geringen Anzahl der möglichen Kooperationspartner (Wissensspezialisierung) eher national bzw. international durchgeführt werden, wobei sich interdisziplinäre Innovationen aufgrund ihres hohen Abstimmungsbedarfes eher regional vollziehen.
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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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Aerob-thermophile Reinigung mineralölkontaminierter Abwässer
(2004)
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Alexandra Oberthür
- Unter aeroben Bedingungen ist der thermophile Mikroorganismus Geobacillus thermoleovorans im Labor- und Pilotmaßstab fähig, verschiedene mit Mineralölen kontaminierte Abwässer als einzige Kohlenstoffquelle zu nutzen. Die Verwertbarkeit eines synthetischen Dieselöls sowie eines Kühlschmierstoffs standardisierter Zusammensetzung durch die Kultur wurde untersucht. Des Weiteren wurden Kühlschmieremulsionen aus Kfz-Produktionsstätten und Spüllösungen zum Reinigen von Lackleitungen auf deren biologische Abbaubarkeit hin geprüft. Der Nachweis von Metaboliten erfolgte an einem GC-FID-System (Gaschromatograph mit Flammenionisationsdetektor). Im Vergleich zum Standardsubstrat Olivenöl wurden ähnliche, in Einzelfällen sogar höhere Wachstumsraten und Zelldichten erzielt. Hierbei wurde nachgewiesen, dass die Initialisierung der Lipaseexpression durch Triglyceride Voraussetzung für den effizienten Abbau von Mineralölkohlenwasserstoffen (MKW) durch Geobacillus thermoleovorans ist. Da MKW in der Praxis nahezu ausschließlich in Verbindung mit einer Vielzahl von Additiven gebraucht werden, wurde der Einfluss verschiedener Zusatzstoffe auf die Mikroorganismen erforscht. Als Kohlenstoffquelle diente das synthetische Dieselöl, als Zusatzstoffe wurden insbesondere Tenside, Flockungsmittel, Komplexbildner und Entschäumer verwendet. Es zeigte sich, dass alle eingesetzten anionischen Tenside (Natrimlaurylsulfat = SDS, Natriumlaurylbenzolsulfonat = SDBS) und nichtionischen Tenside (Tergitol NPX, Triton X 100) in Konzentrationen unterhalb der kritischen Mizellenbildungskonzentration (CMC, engl. Critical Micelle Concentration) nachweislich das Wachstum der Kultur durch die Verbesserung der Substrat-Bioverfügbarkeit stimulieren. Oberhalb der CMC fördern anionische Tenside das Wachstum der Kultur; nichtionische Tenside wirken mit ansteigender Konzentration zunehmend inhibierend. Triton X 100 unterdrückt in Konzentrationen oberhalb der CMC die extrazelluläre Lipaseaktivität vollständig. Positive und negative Effekte auf das Wachstumsverhalten der Kultur sind gleichermaßen das Resultat von Tensid-Membran-Interaktionen. Durch Einlagerung in die Zellmembranen erhöhen die Tenside die Permeabilität der Membranen für Enzyme, was wiederum zu einer Beschleunigung des MKW-Abbaus führt. Der inhibierende Einfluss von Triton X 100 hingegen kann auf die Konformation des Tensids zurückgeführt werden, die entweder die Ausscheidung von Enzymen behindert oder Zellmembran oder Enzyme direkt schädigt. Die experimentell ermittelten CMC im aerob-thermophilen System betrugen 50 mg/L für SDS und SDBS, 90 mg/L für Tergitol NPX® und 108 mg/L für Triton X 100. Darüber hinaus wurde nachgewiesen, dass SDBS in Anwesenheit von MKW metabolisiert wird. In Abwesenheit anderer Kohlenstoffquellen kann auch SDS von Geobacillus thermoleovorans verwertet werden. Ein Abbau nichtionischer Tenside wurde hingegen nicht beobachtet. Die Anwesenheit nichtionischer Tenside ist daher, wie nach der Durchführung einer Diskriminanzanalyse bestätigt wurde, das wichtigste Entscheidungskriterium bzgl. der Anwendbarkeit des Verfahrens zur Reinigung bislang nicht experimentell untersuchter MKW-haltiger Abwässer. Basierend auf den versuchsbegleitend erhobenen Wachstumsparametern wurde ein Vorhersagemodell zur Übertragbarkeit des aerob-thermophilen Verfahrens entwickelt. Geobacillus thermoleovorans weist eine hohe Resistenz gegenüber Bioziden, Schwermetallen und weiteren in Reinigungs- und Schmiermitteln eingesetzten Zusatzstoffen auf. Erst in Konzentrationen ab 1.500 mg/L bewirkt Antimon(III)oxid eine Inhibierung des Wachstums. Eine Anreicherung der genannten Substanzen im Abstrom der Anlage ist daher zu erwarten. Weiterer Forschungsbedarf besteht hinsichtlich der Aufklärung der Metabolisierungspfade von Geobacillus thermoleovorans in Bezug auf (Poly-)Ether und Biozide. Bei der weiteren Verfahrensoptimierung ist insbesondere die Reduktion des Energiebedarfs der Anlage anzustreben. Darüber hinaus empfiehlt sich der Einsatz des Verfahrens in (sub)tropischen Ländern sowie die Ausnutzung von Prozesswärme. Die Entsorgung metallbelasteter Schlämme und anderer nicht abbaubarer Feststoffe ist sicher zu stellen. Bei der Behandlung von Kühlschmierstoffen und ähnlich hoch CSB-belasteten Abwässern (CSB: Chemischer Sauerstoffbedarf) ist die Bereitstellung von Verdünnungswasser notwendig, da eine Raumlast von 13 kg CSB/m -3 d -3 die Belastungsobergrenze für das Verfahren darstellt. Aufgrund der hohen Prozess-Stabilität, der kurzen Anlaufzeiten, der hohen Wachstumsraten und der einfachen Betreuung ist das Verfahren sehr flexibel und vielfältig einsetzbar. Eine weitere Vertiefung dieses innovativen Ansatzes in der Abwasserreinigung ist von daher wünschenswert.
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Adoption of footprint methods for the quality control of eddy-covariance measurements
(2004)
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Mathias Göckede
- Footprint models determine the spatial context of a measurement by defining a transfer function between sources or sinks of the signal and the sensor position. The resulting source area provides an important quality control tool to improve the interpretation of micrometeorological data sets. However, to date no approaches have been presented in the literature that provide a standardised footprint-based methodology that allows observers to include terrain characteristics into quality assessment and quality control strategies. One problem in this context is the small number of studies that concentrate on the validation of footprint models under the non-ideal conditions in which they are frequently being used. Therefore, for many applications, the accuracy of the source areas computed by the footprint models cannot be evaluated. To further increase the acceptance of footprint-based studies, a stronger focus on footprint validation studies for a wide variety of experimental designs is needed. This dissertation focuses on the development of a footprint-based evaluation tool for complex measurement sites that allows the combination of quality assessment results for micrometeorological measurements with characteristics of the surrounding terrain. The standardised method is easy-to-use in order to encourage its application on a large number of sites. To improve the interpretation of the obtained results, a second objective of this thesis was to develop and test approaches to validation experiments for footprint models. Göckede et al. (2004) presented an approach for the evaluation of micrometeorological measurement sites in complex terrain, which combined a method for quality assessment of eddy-covariance measurements with an analytic footprint model. Their software package provided micrometeorologists a practical tool for determining the average flux contributions from the land use type intended to observe at a specific site, or to identify footprint areas for which a high data quality could be assumed. Rebmann et al. (2005) proved the efficiency of this evaluation approach for extensive studies on a large number of sites organised in a network. Their results may serve as a tool for an improved determination of yearly sums of the net ecosystem exchange, because fluxes originating from sectors of minor quality could be excluded from the analysis. Because of these important contributions to quality control, Foken et al. (2004) integrated the site evaluation approach into a comprehensive survey on micrometeorological post-field data quality control techniques. The experiences obtained during the extensive study by Rebmann et al. (2005) allowed us identification of the major weak points of the approach, which we were able to improve in subsequent studies. Using remote sensing methods Reithmaier et al. (2005) studied the influence of the characteristics of the land use maps and different roughness length assignment schemes on the performance of the site evaluation approach. Finally, Göckede et al. (2005a) developed an updated version of the site evaluation approach, which improved the basic method by replacing the analytic footprint model with a Lagrangian stochastic footprint model that is more suitable for studies above high vegetation, and by applying a more sophisticated microscale flux aggregation method for the determination of areally-averaged roughness lengths. Although the implemented models are far more sophisticated than in the original version, the approach by Göckede et al. (2005a) still permits a practical application that allows for comparative studies of a large number of sites. With respect to the development of validation methods for footprint models using natural tracer measurements from field scale experiments, Göckede et al. (2005b) presented two different experimental approaches. Firstly, a comparison of measured flux differences and modelled land use differences for pairs of measurement positions revealed general correlations between measurement data and model results. Secondly, Göckede et al. (2005b) tested a correlation analysis between measured and modelled parameters using reference measurements and footprint results. This approach resulted in an objective quantitative evaluation of the accuracy of the footprint model. The study by Reth et al. (2005) could not be employed for footprint validation purposes because of a large systemic scatter between these measurement systems. Overall, both the paper by Göckede et al. (2005b) and by Reth et al. (2005) provided successful methods to testing the suitability of natural tracer experiments in the validation of footprint models. Although experimental deficits prevented the working out of significant differences between the results of the employed footprint models, their studies developed an improved design for natural tracer experiments that are especially designed for footprint validation purposes.
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A macroscopic and microscopic investigation of the magnesite – otavite solid soluition
(2004)
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Fiona Bromiley
- The magnesite (MgCO3) – calcite (CaCO3) system is the most geologically important of the carbonate minerals. At intermediate compositions a distinct ordered phase exists, dolomite [MgCa(CO3)2], which has symmetry. A complete, disordered ( c symmetry) solid solution exists, but at temperatures in excess of 1400°C. Unmixing and ordering processes that occur at high temperatures in the magnesite – calcite system make experimental work difficult. However, the use of an analogue system allows syntheses under more accessible experimental conditions. The effects of cation substitution and ordering in the magnesite (MgCO3) – otavite (CdCO3) solid solution have, therefore, been investigated using X-ray powder diffraction and Hard Mode Infrared Spectroscopy (HMIS). The results from Rietveld refinements of the X-ray powder diffraction data show that the variation of the a-axis is linear as a function of composition and is not affected by different degrees of order at intermediate compositions. However, the c-axis shows a positive deviation from linearity as a function of composition for the 800°C series. The observed deviation decreases with increasing degree of order for samples of composition Mg0.5Cd0.5CO3. Oxygen-carbon-oxygen bond angles for samples with symmetry showed a decrease in bond angle from 120° (constrained by symmetry in samples with the c structure) with increase in degree of order. Site occupancies were used to determine the long-range order parameter, Q, for samples with symmetry. The square of the order parameter varies linearly as a function of temperature, suggesting a second-order phase transition, and a critical transition temperature of Tc = 719°C. Intensity ratios between reflections present only in the low symmetry phase and reflections present in both the low and high symmetry phases can be used to determine a value proportional to the square of the long-range order parameter, Q. Intensity ratios, between the (101) and (202) reflections for samples of composition Mg0.5Cd0.5CO3, were determined from X-ray powder diffraction patterns and show a linear variation as a function of temperature, with a critical transition temperature, Tc = 716°C. The local mixing and ordering behaviour of the magnesite – otavite solid soluition has been characterised using infrared powder absorption spectroscopy. Phonon bands due to cadmium-oxygen translations, and magnesium-oxygen translations were both observed in the IR spectra for samples of intermediate composition. Band positions for cadmium-oxygen translations remained constant as a function of composition, whereas band positions for magnesium-oxygen translations showed a decrease in wavenumber as a function of composition. Vibrational bands in other spectral regions (libration and translation of carbonate groups and doubly degenetrate in-plane bending and out-of-plane bending of carbonate groups) vary linearly as a function of composition and no effect of order on band position is observed. At high frequencies the samples with c symmetry (800°C series) show a linear shift in band position as a function of composition, whereas, samples in the cadmium dolomite stability field, with symmetry, show a marked increase in frequency compared to their c symmetry counterparts. Cation substitution, or disordering causes broadening of IR vibrational bands for a given material. In this study an alternative method was used, which makes use of the autocorrelation function to establish average line widths for six spectral regions. The autocorrelation results, delta corr, can be interpreted in terms of local strain fields present in the structure due to cation substitution and disordering. In the low frequency region, the delta corr values show a positive deviation from linearity as a function of composition. For samples of composition Mg0.5Cd0.5CO3 the delta corr values are virtually all the same, independent of the degree of order. Over all the spectral regions, the addition of 10mol% MgCO3 (1 Mg atom every 2 unit cells) to the otavite results in a large increase in line width. It is, therefore, suggested that the strain fields surrounding the substituting magnesium atoms into the otavite structure are on the order of 30Å. In the low MIR and at a composition of Mg0.5Cd0.5CO3, an effect of order is observed as a reduction in delta corr values with respect to the sample with c symmetry. The difference in delta corr values between the ordered and disordered samples was used to determine the local-order parameter, q, which scales linearly with the long-range order parameter, Q.
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Experimental deformation of forsterite, wadsleyite and ringwoodite: Implications for seismic anisotropy of the Earth’s mantle
(2004)
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Hélène Couvy
- The rheological properties of the major minerals of the Earth’s mantle are still not well constrained. However, these properties are crucial for the understanding of a wide range of processes in the Earth’s interior such as mantle convection. The purpose of this work is to address the issue of the rheology of the lowermost upper mantle and of the transition zone through the mechanical properties at high pressure of olivine (with forsterite composition Mg2SiO4) and of its high-pressure polymorphs wadsleyite and ringwoodite. Indeed, the properties of the Earth’s mantle can be inferred as a first approximation from the mechanical properties of those polymorphs which volumetrically dominate the mineralogy of the region of concern. Deformation experiments have been performed on hot-pressed forsterite samples and on pre-synthesized wadsleyite and ringwoodite samples under pressure conditions of the Earth’s mantle and at 1300-1400°C. The possible influence of the phase transformation from forsterite to wadsleyite on rheology has been also investigated. Deformation has been achieved by shear using the Kawai-type multianvil apparatus. Complementary experiments on forsterite have been performed in the newly developed Deformation-DIA. Some of them have been carried out on a synchrotron beam line to perform in-situ stress and strain measurements. In order to gain a maximum of information on the deformation mechanisms and on the Crystallographic Preferred Orientation (CPO), a special attention has been devoted to the microstructural characterisation of the samples. Electron BackScattering Diffraction (ESBD) and Transmission Electron Microscope (TEM) have been mainly used. An important pressure-induced change in deformation mechanism is shown in forsterite. The deformation of forsterite at high pressure and temperature is dominated by the [001]{hk0} slip system rather than the [100](010) glide which is extensively observed at low pressure and high temperature.. Concerning the high-pressure polymorphs, their plastic behaviour has been studied with a strong emphasis on the formation of CPO. ViscoPlastic Self Consistent (VPSC) modelling is used to link the CPO with known elementary deformation mechanisms of these phases. The main features of the CPO of wadsleyite are characterized by the alignment of the [100] axes parallel to the shear direction and the alignment of the [001] axes toward the normal to the shear plane. Too many uncertainties remain on the ringwoodite CPO for them being used to interpret seismic anisotropy. Finally, we suggest that strain-induced CPO might be responsible for the seismic anisotropy observed in the lowermost upper mantle and in the upper part of the transition zone. The low seismic anisotropy of the lowermost upper mantle can be explained from the slip system change in forsterite and the CPO of wadsleyite point toward a dominant tangential flow in the upper part of the transition zone.
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Biogeochemical Consequences of Hydrologic Conditions in a Tropical Montane Rain Forest in Ecuador
(2004)
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Rainer Goller
- Tropical montane forests regulate the hydrological cycles of high-elevation areas being an important service for the local population. The objectives of my work were (1) to determine the major hydrological flow paths, (2) to quantify concentrations of dissolved organic C and organic and inorganic forms of N, P, and S, and (3) to identify the major controls of the dissolved C, N, P, and S dynamics in a tropical montane forest in south Ecuador. Three 8-13 ha large microcatchments (MCs) under montane forest at an altitude of 1900-2200 m above sea level were selected. Scientific equipment was installed on five transects, about 20 m long with an altitude range of 10 m. Three unforested sites near the microcatchments were used for rainfall gauging. Within the three monitored years between May 1999 and April 2002, on average 2448 mm of precipitation fell on the study area. The delta 18O of rainfall shows large variations (-12.6 to +2.1 per mil) related to different air-masses. The delta 18O values of throughfall and lateral flow are similar to those in rainfall. Variations in delta 18O values of the soil solution and the stream water are smaller (-9.1 to -3.0 and -5.8 to -8.7 per mil) than those of rainfall, throughfall, and lateral flow. The delta 18O values in stream water increased immediately after an intense rainstorm event to isotope values similar to those of rainfall and lateral flow. This indicated that during elevated rainfall the water flows rapidly in the organic layers to the stream channel paralleling the surface. During this time the water content of the organic layer was higher than of the upper mineral soil. Results from an isotope two-component hydrograph separation for the three microcatchments showed that new rain water ('event water') contributed 44-81 % to the total stormflow runoff during one selected peak discharge. The canopy was a small and the organic layer the major source of DON, DOP, and DOS, which were almost completely retained in the mineral soil. The organically bound forms contributed, on average in all solutions, 54 %, 78 %, and 59 % to the total concentrations of N, P, and S, respectively. The contribution of organically bound forms to total nutrient concentrations was element-specific and differed among the ecosystem fluxes. The portions of DON (23-81 %) were similar and those of DOP (5-100 %) highly variable in all solutions. There were high DOS portions in the aboveground fluxes (51-100 %) and lower portions in the mineral soil (8-47 %). The pH was positively correlated with the DOC and organic N, P, and S concentrations at the scale of pedons. Increasing DOC concentrations in stream water following rainstorms indicated that rainstorms were an important control of the dissolved organic matter dynamics on a regional scale. During the passage of the water through the forest, dissolved inorganic N (DIN) and DIP concentrations increased between the canopy and the mineral soil and strongly decreased in the mineral soil. In contrast, DIS concentrations were highest in the mineral soil and stream water. Thus, the organic layer was the major source for DIN, the canopy for DIP and the mineral soil for DIS. The mineral soil was a sink for DIN and particularly for DIP. Soil drying and rewetting promoted the release of inorganic N. High discharge levels following heavy rainstorm events were associated with pulses of NO3-N and partly also NH4-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively related to runoff conditions. The DIP and DIS concentrations in throughfall and stemflow were negatively correlated to the respective water fluxes, whereas DIS concentrations in the mineral soil solutions of both studied soil depths were positively related to the rainfall volume. DIN and DIP concentrations and fluxes tended to be positively related to the pH of the organic layer. My results demonstrate that nutrient dynamics were mainly controlled by hydrological conditions in the studied steep forested catchments. Furthermore, small ecosystem inputs and outputs indicated tight cycles of dissolved N, P and S in the study forest, except for DIS.
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Biogeochemical Investigations in Old Growth and Disturbed Forest Sites at Mount Kilimanjaro
(2004)
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Marion Schrumpf
- Areas covered by mountain rainforests in East Africa have important functions as catchment areas for the streams in the savannah. Still, little is known about the biogeochemical processes in these often threatened ecosystems. The current study aims to present basic information on soils and different parameters of the water and nutrient cycle in intact as well as disturbed tropical mountain rainforest sites at Mt. Kilimanjaro in order to assess the long term effects of forest dissection on biogeochemical parameters. For this purpose, the chemical and physical soil properties, soil water tension, rainfall, throughfall, litter percolate and soil solution were determined on twelve study sites in mature forest, secondary forest and elder clearings between 2100 and 2300 m a.s.l. on the southwestern slopes of the mountain. The soil water tension was monitored from May 2000 to August 2002. The simultaneously collected water samples were combined to form fortnight samples and subsequently analysed for their content of K, Mg, Ca, Na, NO3-N, NH4-N, TOC, TON, TOS and TOP. The soils, which comprised of several buried horizons, were Andisols with high C and N stocks, some hydromorphic properties and comparatively low pH values. The latter led to very small ECEC values and low base saturation. Consequently, the retention of cationic nutrients in the soil was considered to be poor. Rainfall amounts were slightly less at the higher sampling sites where the mature forest was located and differed between the study years (2600 mm and 2480 mm at 2100 m, 2210 mm and 1960 mm at 2250 m). Rainfall interception was close to zero in the clearings, but reached up to 30% of incident rainfall in both studied forest types. The analyses of the soil water tension revealed the driest conditions to be under secondary forests. The reason for this was probably a combination of the topographic position of the secondary forest sites and the forest fragmentation. Since the secondary forest sites and the clearings had higher sand contents, the water holding capacity of these sites was lower than in the mature forest. With the exception of NO3-N in the forests, all nutrients in rainfall were increased upon passage through the forest canopy, but nutrient fluxes in rainfall as well as throughfall were still low compared to other mountain rainforests, especially for Mg, Ca and K. Considering the lower biomass of the clearings compared to the forest, the amount of nutrients leached from the vegetation of the clearings was relatively high. Since NO3-N was not assimilated by the vegetation of the clearings, NO3-N throughfall fluxes were higher in the clearings as were the K fluxes, which was probably attributable to different leaf properties of the vegetation at the different sites. In the mature forest, the highest concentrations of nutrients were found in the litter percolate, followed by a pronounced decline in the soil solution. This was especially the case for K. NO3-N was an exception since it exhibited the highest concentrations only in the topsoil solution. Nutrient concentrations in litter percolate and the topsoil solution were usually higher in the clearings than in both forest types. This probably resulted in higher belowground nutrient fluxes since greater water amounts reached the ground surface in the clearings. The high belowground nutrient concentrations were likely the result of the higher mineralisation rates in the clearings induced by higher temperatures and the greater nutrient contents of the litter. With increasing soil depths, nutrient concentrations in seepage water below the clearings declined so that the differences among sites were not significant at deeper soil layers. The contribution of organically bound nutrients to the total concentrations of respective nutrients was highest in throughfall water and lowest in the soil solution, in which OM concentrations were overall lower than in other mountain forests. This was most likely attributable to the adsorption of organically bound nutrients to the mineral phase of the Andisols studied. Again, the highest concentrations in seepage water were measured in the clearings. The results show that mature forests at Mt. Kilimanjaro exhibit a more closed nutrient cycle, especially for basic cations, while the nutrient cycle in the clearings is more open. This probably reflects the different nutrient usage and conservation strategies of the pioneer and the late successional vegetation. Therefore, the forest disturbance on Mt. Kilimanjaro leads to long term changes in biogeochemical cycles. The opening of the forest at lower elevations, which resulted in the formation of large clearings with impeded regeneration and highly fragmented secondary forest patches, led to a higher spatial and seasonal variability of soil moisture and nutrient contents in seepage water. The large scale effects of these forest conversions on water yields and nutrient outputs need to be tested in the future.
