1,402 research outputs found
Geothermie – Energiequelle aus dem Untergrund
No full textGeothermie – Energiequelle aus dem Untergrund.
Gespräch mit PD. Dr. Christoph Wanner, Institut für Geologie, Universität Bern.
Moderation: Christian von Bur
Vom Holozän zum Anthropozän - Fakten und Fragen zu 10'000 Jahren Klima- und Menschheitsgeschichte
No full textReactive transport modeling as a tool for the integrated interpretation of laboratory and field studies in environmental geochemistry
No full textThe interaction between moving water and stationary rock within the Earth's crust and on its surface is typically controlled by a series of coupled processes occurring in porous media at various spatio-temporal scales. An example is chemical weathering, which takes place within a thin layer at the Earth’s surface called the Critical Zone and eventually leads to the formation of soils on the time-scale of hundreds to thousands of years. Chemical weathering is kinetically limited and its rate depends on the transport of CO2 and O2 through the Critical Zone. It is also strongly affected by physical weathering processes controlling the grain size distribution within the Critical Zone and thus the available mineral surface area where chemical reactions can take place. In addition, variations in biological activity that produce CO2 may change chemical weathering rates. The complex feedbacks and interrelationships within such coupled systems cannot be understood by traditional geochemical approaches that combine field observations, laboratory analyses and theoretical treatments of the individual uncoupled processes. Therefore, the quantitative interpretation of field studies requires a numerical simulation tool that is able to capture the coupled behavior of subsurface systems and to upscale experimental findings. The main requirements for such a tool are to (i) simulate the relevant geochemical and biogeochemical processes in a mechanistic way and (ii) simultaneously couple these processes to flow and transport rates. Over the past 30 years, the field of reactive transport modeling (RTM) has mastered these requirements and thus has become an essential method for the entire Earth Sciences.
This Habilitationsschrift describes the contributions by the Author to advancing the field of reactive transport modeling, thereby demonstrating how RTM enables an integrated interpretation of laboratory and/or field studies. In addition, this Habilitationsschrift emphasizes how RTM contributes to solving environmental challenges, such as those identified by the United Nations’ Sustainable Development Goals 6 (Clean Water and Sanitation), 7 (Affordable and Clean Energy), and 13 (Climate Action).
Chapter 1 introduces groundwater contamination, geothermal energy, and silicate weathering as important topics in environmental geochemistry and describes the role of coupled processes in the corresponding systems. Moreover, the Chapter introduces the general concept of reactive transport modeling and illustrates its ability to numerically capture the coupling between non-isothermal geochemical and biogeochemical processes, as well as fluid flow and transport rates.
Chapter 2 provides a detailed summary of the key accomplishments by the Author to advancing RTM. These include (i) the integration of stable isotopes in RTM simulations that address challenges relevant to environmental geochemistry, and (ii) the use of reactive transport models as an exploration tool for geothermal systems. These contributions resulted, among others, in the publication of nine peer-reviewed publications, which are presented in Chapters 3–5 and form the core of this Habilitationsschrift.
Chapter 3 presents three selected RTM applications where Cr or U isotopes are integrated in reactive transport model simulations to understand Cr- and U-contaminated groundwaters. In the first two studies, small-scale laboratory experiments are numerically simulated using a novel approach for obtaining a high spatial resolution of the simulated systems. The model results and their comparison to measured Cr and U isotope ratios provide fundamental insights into the processes controlling the magnitude of Cr and U isotope fractionation occurring in porous media. Obtaining a predictive understanding of such isotopic fractionation is crucial, because it opens the way to quantify the most important processes limiting the mobility of Cr and U in the subsurface. The third application presents a benchmarking exercise, which allowed testing and improvement of the approaches for numerically simulating stable Cr isotope fractionation in geochemical processes. Altogether, the RTM applications presented in Chapter 3 contribute to a more informed assessment and management of groundwater bodies contaminated by Cr and U.
Chapter 4 presents three applications where RTM is used as an exploration tool for geothermal systems. The first one involves 2D simulations carried out for the Dixie Valley geothermal system located in the western USA. The model output is then applied via a geochemical method called solute geothermometry, which is used to estimate the maximum temperature of deep geothermal systems. Eventually, the combined approach demonstrates which particular solute geothermometry method works best for various scenarios of rock–water interactions and thus contributes to an improved estimation of deep reservoir temperatures. Obtaining reliable temperatures is important because the reservoir temperature is a major limit on the energy that can be exploited from the deep subsurface. In the other two applications, RTM simulations are performed to quantitatively assess the geothermal potential of two geothermal systems in the Swiss Alps. All simulations are carried out in 3D and are constrained and calibrated by multiple field observations, such as chemical and isotopic compositions of thermal and cold springs, as well as temperature measurements along tunnels. The model results suggest that mountain belts such as the Swiss Alps are more promising targets for geothermal power production than previously thought, and they identify the favorable geological settings for such systems, which leads to useful implications for exploration.
Chapter 5 presents a sequence of three RTM applications, which for the first time integrate Li isotopes in the simulations. The motivation for numerically simulating the fate of Li isotopes is that their ratios serve as proxies to track and quantify the rates of silicate weathering, which in turn constitutes a major natural sink for atmospheric CO2. The first study describes a new numerical approach to integrate Li isotopes in RTM simulations. In the first and second applications, the developed approach is used to simulate the fate of Li and its isotopes in granitic and basaltic rainwater catchments, respectively. Subsequently, the model results are compared to Li data from major worldwide rivers and from a series of small streams draining the Columbia River Basalt area in the western USA. This model-based, integrated interpretation of measured Li isotope ratios permits identification of the processes governing Li isotope ratios in groundwater, riverwater and even seawater. Moreover, the results imply that seawater Li isotope ratios may be closely related to the amount of CO2 globally consumed by continental silicate weathering. In the third application, the numerical approach to simulate the fate of Li isotopes is expanded to account for the limited amount of Li that precipitates in secondary minerals. The updated approach is used to unravel a complex set of Li data collected from groundwater samples discharging into the Gotthard railway base tunnel in the Swiss Alps. This study reveals that the behavior of Li isotopes in environmental samples is more complicated than hitherto realized. Overall, the applications presented in Chapter 5 contribute to assessing the use of Li isotopes as a proxy for silicate weathering and may help to better quantify this important natural sink for CO2.
Chapter 6 summarizes the main implications of this Habilitationsschrift regarding the use of RTM in environmental geochemistry and how it contributes to meeting the listed Sustainable Development Goals. In particular, this final chapter concludes that the inclusion of stable isotopes into RTM simulations provides fundamental new insights into the processes controlling stable isotope ratios in environmental samples. This underscores how RTM serves as a powerful tool for the integrated interpretation of multiple datasets obtained from field and laboratory studies. Moreover, the Chapter discusses how RTM simulations are limited by the availability of thermodynamic and kinetic data, and by the need for detailed geochemical, biogeochemical, hydrological, and geophysical site-characterizations in order to calibrate such simulations. Finally, the Chapter contains a brief outlook emphasizing the numerous opportunities for new code development and for laboratory as well as field studies to constrain and calibrate future RTM applications. These activities will enable even more powerful RTM simulations to meet the environmental challenges of the future
Quantifying the glacial meltwater contribution to mountainous streams using stable water isotopes: What are the opportunities and limitations?
No full textThis study aims to determine the opportunities and limitations of using stable water isotopes to quantify the glacial meltwater contribution to mountainous streams. For this purpose, three partially glaciated catchments in the Swiss Alps were selected as the study area. In the three catchments, stable isotope analysis (δ18O and δ2H) was conducted of the streams and the end-members that contribute to the stream discharge (glacial meltwater, rain, snow). The investigations revealed that the contribution of glacial meltwater to mountainous streams can be quantified using stable water isotopes if three criteria are met: (A) The snow meltwater contribution to mountainous streams must be negligible due to its highly variable stable isotope signature; (B) the groundwater input needs to be either insignificant during this snow-free period or the groundwater residence time must be short such that groundwater contribution does not delay the end-member signal arriving in the streams; and (C) the isotope signal of the glacial melt end-member needs to be distinct from the other end-members. One of the three investigated catchments fulfilled these criteria in August and September, and the glacial meltwater contribution to the mountainous streams could be estimated based on stable water isotopes. During this time period, the glacial meltwater contribution to the stream discharge corresponded to up to 85% ± 2% and to 28.7% ± 10% of the total annual discharge, respectively. This high glacial meltwater contribution demonstrates that the mountainous stream discharges in August and September will probably strongly decrease in the future due to global warming-induced deglaciation. Overall, this study demonstrates that many hydrogeological conditions need to be met so that stable water isotopes can be used to quantify the glacial meltwater contribution to mountainous streams. This highlights the challenges when using stable water isotopes for hydrograph separation and serves as a guide for future stable water isotope studies in mountainous regions
Cardiovascular disease: Is CABG really better than PCI in dialysis patients?
No full textA new study by Chang et al. reports that coronary artery bypass grafting (CABG) may be preferable to percutaneous coronary intervention (PCI) for multivessel coronary revascularization in appropriately selected patients on maintenance dialysis. Wanner, C. & Jager, K. J. Nat. Rev. Nephrol. 9, 197-198 (2013); published online 12 March 2013; doi:10.1038/nrneph.2013.4
Untersuchungen zum Stoffwechsel der Flechte Parmelia sulcata Taylor im Zusammenhang mit dem Grad der Luftverschmutzung
No full textImportant physiological processes as well as the content of certain cell components were measured in samples of the relatively pollution-resistant lichen species PARMELIA SULCATA TAYLOR at 13 locations with different levels of air pollution in the city of Biel. Surprisingly, there was no difference in the activities of either photosynthesis or dark respiration at the various Stations. There were significant differences in growth rates, transfer of photosynthates from algae to fungi, chlorophyll content, sulfate content, sulfate uptake and protein synthesis, however. Statistical analysis of these measurements showed a definite correlation with deposition measurements of several important air pollutants as well as with the index of atmospheric purity (IAP) determined on the basis of lichen frequencies. The effect of air pollution on the chlorophyll content was studied in detail. Because of the pronounced differences in chlorophyll content found under various conditions, the simple method of measuring it, and the small standard deviation, chlorophyll content is a suitable bioindicator for approximate determination of overall atmospheric pollution.Les principaux processus de la physiologie ainsi que les substances internes importantes du lichen PARMELIA SULCATA TAYLOR - lichen relativement résistant a la pollution atmosphérique - ont été analyses sur des échantillons provenant de 13 stations de la ville de Bienne, soumises a des niveaux de pollution atmosphérique différents. De manière surprenante, l'activité photosynthétique et la respiration obscure ne varient pas selon les sites. En revanche on observe des différences sensibles en ce qui concerne la croissance, le transfert des produits de la photosynthèse de l'algue vers le champignon, la concentration de chlorophylles, la concentration et de l'absorption de sulfate, ainsi que la protéosynthèse. La comparaison statistique de ces données avec celles provenant des mesures de déposition de quelques polluants importants, ainsi qu'avec les valeurs IAP (index of atmospheric purity), a donné des corrélations bonnes a très bonnes. La teneur en chlorophylle a été tout particulièrement étudiée. En raison de sa sensibilité aux fluctuations de la charge de polluant, de La simplicité de la méthode de mesure et de la faible variabilité, ce paramètre constitue en effet un excellent bioindicateur pour la détermination approximative de la charge totale de la pollution de l'air.Wichtige Stoffwechselvorgänge und Inhaltsstoffe der gegen Luftbelastung relativ widerstandsfähigen Flechtenart PARMELIA SULCATA TAYLOR wurden an Proben von 13 Stationen mit unterschiedlicher Verschmutzung in der Stadt Biel gemessen. Überraschenderweise unterschieden sich an den einzelnen Stationen weder die Aktivitäten der Photosynthese noch die der Dunkelatmung. Deutliche Differenzen resultierten dafür aus den Messungen des Wachstums, des Transfers von Photosyntheseprodukten von Alge zu Pilz, des Chlorophyllgehaltes, des Sulfatgehaltes, der Sulfataufnahme sowie der Proteinsynthese. Die statistische Analyse dieser Daten ergab eine gesicherte Korrelation mit Depositionsmessungen einiger wichtiger Luftschadstoffe, wie auch mit den Luftqualitätswerten (IAP), welche aufgrund von Flechtenhäufigkeiten ermittelt wurden. Am besten untersucht wurde die Abhängigkeit des Chlorophyllgehaltes von der Luftbelastung. Er eignet sich in der Praxis aufgrund der ausgeprägten Unterschiede bei verschiedener Luftbelastung, der einfachen Messmethode und der geringen Streuung als Bioindikator für die ungefähre Bestimmung der Gesamtbelastung der Luft
Benchmarking the simulation of Cr isotope fractionation
No full textA benchmark problem set consisting of four problem levels was developed for the simulation of Cr isotope fractionation in 1D and 2D domains. The benchmark is based on a recent field study where Cr(VI) reduction and accompanying Cr isotope fractionation occurs abiotically by an aqueous reaction with dissolved Fe 2+ (Wanner et al., 2012., Appl. Geochem., 27, 644–662). The problem set includes simulation of the major processes affecting the Cr isotopic composition such as the dissolution of various Cr(VI) bearing minerals, fractionation during abiotic aqueous Cr(VI) reduction, and non-fractionating precipitation of Cr(III) as sparingly soluble Cr-hydroxide.
Accuracy of the presented solutions was ensured by running the problems with four well-established reactive transport modeling codes: TOUGHREACT, MIN3P, CRUNCHFLOW, and FLOTRAN. Results were also compared with an analytical Rayleigh-type fractionation model. An additional constraint on the correctness of the results was obtained by comparing output from the problem levels simulating Cr isotope fractionation with the corresponding ones only simulating bulk concentrations. For all problem levels, model to model comparisons showed excellent agreement, suggesting that for the tested geochemical processes any code is capable of accurately simulating the fate of individual Cr isotopes
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