@article{SteinhoefelBreuervonBlanckenburgetal.2017, author = {Steinh{\"o}fel, Grit and Breuer, J{\"o}rn and von Blanckenburg, Friedhelm and Horn, Ingo and Sommer, Michael}, title = {The dynamics of Si cycling during weathering in two small catchments in the Black Forest (Germany) traced by Si isotopes}, series = {Chemical geology : official journal of the European Association for Geochemistry}, volume = {466}, journal = {Chemical geology : official journal of the European Association for Geochemistry}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2541}, doi = {10.1016/j.chemgeo.2017.06.026}, pages = {389 -- 402}, year = {2017}, abstract = {Silicon stable isotopes have emerged as a powerful proxy to investigate weathering because Si uptake from solution by secondary minerals or by the vegetation causes significant shifts in the isotope composition. In this study, we determined the Si isotope compositions of the principle Si pools within two small catchments located on sandstone and paragneiss, respectively, in the temperate Black Forest (Germany). At both settings, clay formation is dominated by mineral transformation preserving largely the signature of parental minerals with delta Si-30 values of around -0.7\%. Bulk soils rich in primary minerals are similar to bulk parental material with delta Si-30 values close to -0.4\%. Topsoils are partly different because organic matter degradation has promoted intense weathering leading to delta Si-30 values as low as -1.0\%. Water samples expose highly dynamic weathering processes in the soil zone: 1) after spring snowmelt, increased release of DOC and high water fluxes trigger clay mineral dissolution which leads to delta Si-30 values down to -0.7\% and 2) in course of the summer, Si uptake by the vegetation and secondary mineral formation drives dissolved Si to typical positive delta Si-30 values up to 1.1\%. Groundwater with delta Si-30 values of around 0.4\% records steady processes in bedrock reflecting plagioclase weathering together with kaolinite precipitation. An isotope mass balance approach reveals incongruent weathering conditions where denudation of Si is largely driven by physical erosion. Erosion of phytoliths contributes 3 to 21\% to the total Si export flux, which is in the same order as the dissolved Si flux. These results elucidate the Si dynamics during weathering on catchments underlain of sedimentary origin, prevailing on the Earth surface and provide therefore valuable information to interpret the isotope signature of large river systems.}, language = {en} } @article{SommerKaczorekKuzyakovetal.2006, author = {Sommer, Michael and Kaczorek, Danuta and Kuzyakov, Yakov and Breuer, J{\"o}rn}, title = {Silicon pools and fluxes in soils and landscapes : a review}, year = {2006}, abstract = {Silicon (Si) is the second-most abundant element in the earth's crust. In the pedosphere, however, huge spans of Si contents occur mainly caused by Si redistribution in soil profiles and landscapes. Here, we summarize the current knowledge on the different pools and fluxes of Si in soils and terrestrial biogeosystems. Weathering and subsequent release of soluble Si may lead to (1) secondarily bound Si in newly formed Al silicates, (2) amorphous silica precipitation on surfaces of other minerals, (3) plant uptake, formation of phytogenic Si, and subsequent retranslocation to soils, (4) translocation within soil profiles and formation of new horizons, or (5) translocation out of soils (desilication). The research carried out hitherto focused on the participation of Si in weathering processes, especially in clay neoformation, buffering mechanisms for acids in soils or chemical denudation of landscapes. There are, however, only few investigations on the characteristics and controls of the low-crystalline, almost pure silica compounds formed during pedogenesis. Further, there is strong demand to improve the knowledge of (micro)biological and rhizosphere processes contributing to Si mobilization, plant uptake, and formation of phytogenic Si in plants, and release due to microbial decomposition. The contribution of the biogenic Si sources to Si redistribution within soil profiles and desilication remains unknown concerning the pools, rates, processes, and driving forces. Comprehensive studies considering soil hydrological, chemical, and biological processes as well as their interactions at the scale of pedons and landscapes are necessary to make up and model the Si balance and to couple terrestrial processes with Si cycle of limnic, fluvial, or marine biogeosystems}, language = {en} } @article{AbelStojkovicBreuer2006, author = {Abel, Markus and Stojkovic, Dragan and Breuer, Michael}, title = {Nonlinear stochastic estimation of wall models for LES}, issn = {0142-727X}, doi = {10.1016/j.heatfluidflow.2005.10.011}, year = {2006}, abstract = {A key technology for large eddy simulation (LES) of complex flows is an appropriate wall modeling strategy. In this paper we apply for the first time a fully nonparametric procedure for the estimation of generalized additive models (GAM) by conditional statistics. As a database, we use DNS and wall-resolved LES data of plane channel flow for Reynolds numbers, Re = 2800, 4000 (DNS) and 10,935, 22,776 (LES). The statistical method applied is a quantitative tool for the identification of important model terms, allowing for an identification of some of the near-wall physics. The results are given as nonparametric functions which cannot be attained by other methods. We investigated a generalized model which includes Schumann's and Piomelli et al.'s model. A strong influence of the pressure gradient in the viscous sublayer is found; for larger wall distances the spanwise pressure gradient even dominates the tau(w,zy). component. The first a posteriori LES results are given.}, language = {en} } @article{SteinhoefelBreuervonBlanckenburgetal.2011, author = {Steinhoefel, Grit and Breuer, J{\"o}rn and von Blanckenburg, Friedhelm and Horn, Ingo and Kaczorek, Danuta and Sommer, Michael}, title = {Micrometer silicon isotope diagnostics of soils by UV femtosecond laser ablation}, series = {Chemical geology : official journal of the European Association for Geochemistry}, volume = {286}, journal = {Chemical geology : official journal of the European Association for Geochemistry}, number = {3-4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2541}, doi = {10.1016/j.chemgeo.2011.05.013}, pages = {280 -- 289}, year = {2011}, abstract = {This study presents the first Si isotope data of the principle Si pools in soils determined by a UV femtosecond laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). This method reveals accurate and precise Si isotope data on bulk materials, and at high spatial resolution, on the mineral scale. The following Si pools have been investigated: a) the Si source to soils on all major silicate minerals on thin sections from bedrock fragments in the soil profiles; b) bulk soils (particle size <2 mm) after fusion to glass beads with an iridium-strip heater or pressed into powder pellets: c) separated clay fractions as pressed powder pellets and e) separated phytoliths as pressed powder pellets. Multiple analyses of three rock standards, BHVO-2, AGV-1 and RGM-1 as fused glass beads and as pressed powder pellets, reveal delta(30)Si values within the expected range of igneous rocks. The MPI-DING reference glass KL2-G exhibits the same Si isotope composition after remelting by an iridium-strip heater showing that this technique does not alter the isotope composition of the glass. We used this approach to investigated two immature Cambisols developed on sandstone and paragneiss in the Black Forest (Germany), respectively. Bulk soils show a largely uniform Si isotope signature for different horizons and locations, which is close to those of primary quartz and feldspar with delta(30)Si values around -0.4 parts per thousand. Soil clay formation is associated with limited Si mobility, which preserves initial Si isotope signatures of parental minerals. An exception is the organic horizon of the paragneiss catchment where intense weathering leads to a high mobility of Si and significant negative isotope signatures as low as to -1.00 parts per thousand in bulk soils. Biogenic opal in the form of phytoliths, exhibits negative Si isotope signatures of about -0.4 parts per thousand. These results demonstrate that UV femtosecond laser ablation MC-ICP-MS provides a tool to characterize the Si isotope signature of the principle Si pools left behind after weathering and Si transport have altered soils. These results can now serve as a fingerprint of the residual solids that can be used to explain the isotope composition of dissolved Si in soil solutions and river water, which is mostly enriched in the heavy isotopes.}, language = {en} } @misc{WilskeEccardZistlSchlingmannetal.2015, author = {Wilske, Burkhard and Eccard, Jana and Zistl-Schlingmann, Marcus and Hohmann, Maximilian and Methler, Annabel and Herde, Antje and Liesenjohann, Thilo and Dannenmann, Michael and Butterbach-Bahl, Klaus and Breuer, Lutz}, title = {Effects of short term bioturbation by common voles on biogeochemical soil variables}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {499}, issn = {1866-8372}, doi = {10.25932/publishup-40837}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-408375}, pages = {19}, year = {2015}, abstract = {Bioturbation contributes to soil formation and ecosystem functioning. With respect to the active transport of matter by voles, bioturbation may be considered as a very dynamic process among those shaping soil formation and biogeochemistry. The present study aimed at characterizing and quantifying the effects of bioturbation by voles on soil water relations and carbon and nitrogen stocks. Bioturbation effects were examined based on a field set up in a luvic arenosol comprising of eight 50 x 50 m enclosures with greatly different numbers of common vole (Microtus arvalis L., ca. 35-150 individuals ha(-1) mth(-1)). Eleven key soil variables were analyzed: bulk density, infiltration rate, saturated hydraulic conductivity, water holding capacity, contents of soil organic carbon (SOC) and total nitrogen (N), CO2 emission potential, C/N ratio, the stable isotopic signatures of C-13 and N-15, and pH. The highest vole densities were hypothesized to cause significant changes in some variables within 21 months. Results showed that land history had still a major influence, as eight key variables displayed an additional or sole influence of topography. However, the delta N-15 at depths of 10-20 and 20-30 cm decreased and increased with increasing vole numbers, respectively. Also the CO2 emission potential from soil collected at a depth of 15-30 cm decreased and the C/N ratio at 5-10 cm depth narrowed with increasing vole numbers. These variables indicated the first influence of voles on the respective mineralization processes in some soil layers. Tendencies of vole activity homogenizing SOC and N contents across layers were not significant. The results of the other seven key variables did not confirm significant effects of voles. Thus overall, we found mainly a first response of variables that are indicative for changes in biogeochemical dynamics but not yet of those representing changes in pools.}, language = {en} } @book{MientusKlempinNowaketal.2023, author = {Mientus, Lukas and Klempin, Christiane and Nowak, Anna and Wyss, Corinne and Aufschnaiter, Claudia von and Faix, Ann-Christin and te Poel, Kathrin and Wahbe, Nadia and Pieper, Martin and H{\"o}ller, Katharina and Kallenbach, Lea and F{\"o}rster, Magdalena and Redecker, Anke and Dick, Mirjam and Holle, J{\"o}rg and Schneider, Edina and Rehfeldt, Daniel and Brauns, Sarah and Abels, Simone and Ferencik-Lehmkuhl, Daria and Fr{\"a}nkel, Silvia and Frohn, Julia and Liebsch, Ann-Catherine and Pech, Detlef and Schreier, Pascal and Jessen, Moiken and Großmann, Uta and Skintey, Lesya and Voerkel, Paul and Vaz Ferreira, Mergenfel A. and Zimmermann, Jan-Simon and Buddeberg, Magdalena and Henke, Vanessa and Hornberg, Sabine and V{\"o}lschow, Yvette and Warrelmann, Julia-Nadine and Malek, Jennifer and Tinnefeld, Anja and Schmidt, Peggy and Bauer, Tobias and J{\"a}nisch, Christopher and Spitzer, Lisa and Franken, Nadine and Degeling, Maria and Preisfeld, Angelika and Meier, Jana and K{\"u}th, Simon and Scholl, Daniel and Vogelsang, Christoph and Watson, Christina and Weißbach, Anna and Kulgemeyer, Christoph and Oetken, Mandy and Gorski, Sebastian and Kubsch, Marcus and Sorge, Stefan and Wulff, Peter and Fellenz, Carolin D. and Schnell, Susanne and Larisch, Cathleen and Kaiser, Franz and Knott, Christina and Reimer, Stefanie and Stegm{\"u}ller, Nathalie and Boukray{\^a}a Trabelsi, Kathrin and Schißlbauer, Franziska and Lemberger, Lukas and Barth, Ulrike and Wiehl, Angelika and Rogge, Tim and B{\"o}hnke, Anja and Dietz, Dennis and Großmann, Leroy and Wienmeister, Annett and Zoppke, Till and Jiang, Lisa and Gr{\"u}nbauer, Stephanie and Ostersehlt, D{\"o}rte and Peukert, Sophia and Sch{\"a}fer, Christoph and L{\"o}big, Anna and Br{\"o}ll, Leena and Brandt, Birgit and Breuer, Meike and Dausend, Henriette and Krelle, Michael and Andersen, Gesine and Falke, Sascha and Kindermann-G{\"u}zel, Kristin and K{\"o}rner, Katrina and Lottermoser, Lisa-Marie and P{\"u}gner, Kati and Sonnenburg, Nadine and Akarsu, Selim and Rechl, Friederike and Gadinger, Laureen and Heinze, Lena and Wittmann, Eveline and Franke, Manuela and Lachmund, Anne-Marie and B{\"o}ttger, Julia and Hannover, Bettina and Behrendt, Renata and Conty, Valentina and Grundmann, Stephanie and Ghassemi, Novid and Opitz, Ben and Br{\"a}mer, Martin and Gasparjan, David and Sambanis, Michaela and K{\"o}ster, Hilde and L{\"u}cke, Martin and Nordmeier, Volkhard and Schaal, Sonja and Haberbosch, Maximilian and Meissner, Maren and Schaal, Steffen and Br{\"u}chner, Melanie and Riehle, Tamara and Leopold, Bengta Marie and Gerlach, Susanne and Rau-Patschke, Sarah and Skorsetz, Nina and Weber, Nadine and Damk{\"o}hler, Jens and Elsholz, Markus and Trefzger, Thomas and Lewek, Tobias and Borowski, Andreas}, title = {Reflexion in der Lehrkr{\"a}ftebildung}, series = {Potsdamer Beitr{\"a}ge f{\"u}r Lehrkr{\"a}ftebildung und Bildungsforschung}, journal = {Potsdamer Beitr{\"a}ge f{\"u}r Lehrkr{\"a}ftebildung und Bildungsforschung}, number = {4}, editor = {Mientus, Lukas and Klempin, Christiane and Nowak, Anna}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, isbn = {978-3-86956-566-8}, issn = {2626-3556}, doi = {10.25932/publishup-59171}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-591717}, publisher = {Universit{\"a}t Potsdam}, pages = {452}, year = {2023}, abstract = {Reflexion ist eine Schl{\"u}sselkategorie f{\"u}r die professionelle Entwicklung von Lehrkr{\"a}ften, welche als Ausbildungsziel in den Bildungsstandards f{\"u}r die Lehrkr{\"a}ftebildung verankert ist. Eine Verstetigung universit{\"a}r gepr{\"a}gter Forschung und Modellierung in der praxisnahen Anwendung im schulischen Kontext bietet Potentiale nachhaltiger Professionalisierung. Die St{\"a}rkung reflexionsbezogener Kompetenzen durch Empirie und Anwendung scheint eine phasen{\"u}bergreifende Herausforderung der Lehrkr{\"a}ftebildung zu sein, die es zu bew{\"a}ltigen gilt. Ziele des Tagungsbandes Reflexion in der Lehrkr{\"a}ftebildung sind eine theoretische Sch{\"a}rfung des Konzeptes „Reflexive Professionalisierung" und der Austausch {\"u}ber Fragen der Einbettung wirksamer reflexionsbezogener Lerngelegenheiten in die Lehrkr{\"a}ftebildung. Forschende und Lehrende der‚ drei Phasen (Studium, Referendariat sowie Fort- und Weiterbildung) der Lehrkr{\"a}ftebildung stellen Lehrkonzepte und Forschungsprojekte zum Thema Reflexion in der Lehrkr{\"a}ftebildung vor und diskutieren diese. Gemeinsam mit Teilnehmenden aller Phasen und von verschiedenen Standorten der Lehrkr{\"a}ftebildung werden zuk{\"u}nftige Herausforderungen identifiziert und L{\"o}sungsans{\"a}tze herausgearbeitet.}, language = {de} } @article{PeukertSchaeferLoebigetal.2023, author = {Peukert, Sophia and Sch{\"a}fer, Christoph and L{\"o}big, Anna and Br{\"o}ll, Leena Kristina and Brandt, Birgit and Breuer, Meike and Dausend, Henriette and Krelle, Michael and Andersen, Gesine and Falke, Sascha and Kindermann-G{\"u}zel, Kristin and K{\"o}rner, Katrina and Lottermoser, Lisa-Marie and P{\"u}gner, Kati}, title = {Professionalisierung von Lehrkr{\"a}ften zur Bildung in der digitalen Welt}, series = {Reflexion in der Lehrkr{\"a}ftebildung: Empirisch - Phasen{\"u}bergreifend - Interdisziplin{\"a}r (Potsdamer Beitr{\"a}ge zur Lehrerbildung und Bildungsforschung ; 4)}, journal = {Reflexion in der Lehrkr{\"a}ftebildung: Empirisch - Phasen{\"u}bergreifend - Interdisziplin{\"a}r (Potsdamer Beitr{\"a}ge zur Lehrerbildung und Bildungsforschung ; 4)}, number = {4}, editor = {Mientus, Lukas and Klempin, Christiane and Nowak, Anna}, publisher = {Universit{\"a}tsverlag Potsdam}, address = {Potsdam}, isbn = {978-3-86956-566-8}, issn = {2626-3556}, doi = {10.25932/publishup-63181}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-631816}, pages = {329 -- 334}, year = {2023}, abstract = {Im BMBF-Projekt DigiLeG - digitale Lernumgebungen in der Grundschule des Zentrums f{\"u}r Lehrerbildung der Technischen Universit{\"a}t (TU) Chemnitz werden ausgehend von einem gemeinsamen Lehrkonzept in Veranstaltungen der beteiligten Fachdidaktiken gemeinsam mit Studierenden Lernumgebungen entwickelt und reflektiert, die digitale Medien lernf{\"o}rderlich in den Grundschulunterricht einbinden. Im folgenden Beitrag werden zun{\"a}chst das Lehrkonzept und seine theoretischen Grundlagen vorgestellt. Anschließend wird die praktische Umsetzung am Beispiel der Fachdidaktik Philosophieren mit Kindern (PmK) veranschaulicht. Der Beitrag schließt mit einer Zusammenfassung der Erfahrungen in der Umsetzung des Lehrkonzepts.}, language = {de} } @article{SommerJochheimHoehnetal.2013, author = {Sommer, Michael and Jochheim, H. and H{\"o}hn, Axel and Breuer, J{\"o}rn and Zagorski, Z. and Busse, J. and Barkusky, Dietmar and Meier, K. and Puppe, D. and Wanner, Manfred and Kaczorek, Danuta}, title = {Si cycling in a forest biogeosystem - the importance of transient state biogenic Si pools}, series = {Biogeosciences}, volume = {10}, journal = {Biogeosciences}, number = {7}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1726-4170}, doi = {10.5194/bg-10-4991-2013}, pages = {4991 -- 5007}, year = {2013}, abstract = {The relevance of biological Si cycling for dissolved silica (DSi) export from terrestrial biogeosystems is still in debate. Even in systems showing a high content of weatherable minerals, like Cambisols on volcanic tuff, biogenic Si (BSi) might contribute > 50\% to DSi (Gerard et al., 2008). However, the number of biogeosystem studies is rather limited for generalized conclusions. To cover one end of controlling factors on DSi, i.e., weatherable minerals content, we studied a forested site with absolute quartz dominance (> 95 \%). Here we hypothesise minimal effects of chemical weathering of silicates on DSi. During a four year observation period (05/2007-04/2011), we quantified (i) internal and external Si fluxes of a temperate-humid biogeosystem (beech, 120 yr) by BIOME-BGC (version ZALF), (ii) related Si budgets, and (iii) Si pools in soil and beech, chemically as well as by SEM-EDX. For the first time two compartments of biogenic Si in soils were analysed, i.e., phytogenic and zoogenic Si pool (testate amoebae). We quantified an average Si plant uptake of 35 kg Si ha(-1) yr(-1) - most of which is recycled to the soil by litterfall - and calculated an annual biosilicification from idiosomic testate amoebae of 17 kg Si ha(-1). The comparatively high DSi concentrations (6 mg L-1) and DSi exports (12 kg Si ha(-1) yr(-1)) could not be explained by chemical weathering of feldspars or quartz dissolution. Instead, dissolution of a relictic, phytogenic Si pool seems to be the main process for the DSi observed. We identified canopy closure accompanied by a disappearance of grasses as well as the selective extraction of pine trees 30 yr ago as the most probable control for the phenomena observed. From our results we concluded the biogeosystem to be in a transient state in terms of Si cycling.}, language = {en} }