TY  - JOUR
A1  - Steinhöfel, Grit
A1  - Breuer, Jörn
A1  - von Blanckenburg, Friedhelm
A1  - Horn, Ingo
A1  - Sommer, Michael
T1  - The dynamics of Si cycling during weathering in two small catchments in the Black Forest (Germany) traced by Si isotopes
JF  - Chemical geology : official journal of the European Association for Geochemistry
N2  - 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.
KW  - Weathering
KW  - Sedimentary rocks
KW  - Biogeochemical Si cycle
KW  - Silicon isotopes
KW  - UV femtosecond laser ablation
Y1  - 2017
U6  - https://doi.org/10.1016/j.chemgeo.2017.06.026
SN  - 0009-2541
SN  - 1878-5999
VL  - 466
SP  - 389
EP  - 402
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Sommer, Michael
A1  - Kaczorek, Danuta
A1  - Kuzyakov, Yakov
A1  - Breuer, Jörn
T1  - Silicon pools and fluxes in soils and landscapes : a review
N2  - 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
Y1  - 2006
ER  - 
TY  - JOUR
A1  - Abel, Markus
A1  - Stojkovic, Dragan
A1  - Breuer, Michael
T1  - Nonlinear stochastic estimation of wall models for LES
N2  - 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.
Y1  - 2006
UR  - http://www.sciencedirect.com/science/journal/0142727X
U6  - https://doi.org/10.1016/j.heatfluidflow.2005.10.011
SN  - 0142-727X
ER  - 
TY  - JOUR
A1  - Steinhoefel, Grit
A1  - Breuer, Jörn
A1  - von Blanckenburg, Friedhelm
A1  - Horn, Ingo
A1  - Kaczorek, Danuta
A1  - Sommer, Michael
T1  - Micrometer silicon isotope diagnostics of soils by UV femtosecond laser ablation
JF  - Chemical geology : official journal of the European Association for Geochemistry
N2  - 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.
KW  - Silicon isotopes
KW  - Soils
KW  - UV femtosecond laser ablation
KW  - MC-ICP-MS
Y1  - 2011
U6  - https://doi.org/10.1016/j.chemgeo.2011.05.013
SN  - 0009-2541
VL  - 286
IS  - 3-4
SP  - 280
EP  - 289
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - GEN
A1  - Wilske, Burkhard
A1  - Eccard, Jana
A1  - Zistl-Schlingmann, Marcus
A1  - Hohmann, Maximilian
A1  - Methler, Annabel
A1  - Herde, Antje
A1  - Liesenjohann, Thilo
A1  - Dannenmann, Michael
A1  - Butterbach-Bahl, Klaus
A1  - Breuer, Lutz
T1  - Effects of short term bioturbation by common voles on biogeochemical soil variables
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - 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.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 499 
KW  - small mammalian herbivores
KW  - Microtus agrestis
KW  - pocket gophers
KW  - field voles
KW  - ecosystem services
KW  - functional traits
KW  - organic-carbon
KW  - nitrogen
KW  - population
KW  - landscape
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-408375
SN  - 1866-8372
IS  - 499
ER  - 
TY  - BOOK
A1  - Mientus, Lukas
A1  - Klempin, Christiane
A1  - Nowak, Anna
A1  - Wyss, Corinne
A1  - Aufschnaiter, Claudia von
A1  - Faix, Ann-Christin
A1  - te Poel, Kathrin
A1  - Wahbe, Nadia
A1  - Pieper, Martin
A1  - Höller, Katharina
A1  - Kallenbach, Lea
A1  - Förster, Magdalena
A1  - Redecker, Anke
A1  - Dick, Mirjam
A1  - Holle, Jörg
A1  - Schneider, Edina
A1  - Rehfeldt, Daniel
A1  - Brauns, Sarah
A1  - Abels, Simone
A1  - Ferencik-Lehmkuhl, Daria
A1  - Fränkel, Silvia
A1  - Frohn, Julia
A1  - Liebsch, Ann-Catherine
A1  - Pech, Detlef
A1  - Schreier, Pascal
A1  - Jessen, Moiken
A1  - Großmann, Uta
A1  - Skintey, Lesya
A1  - Voerkel, Paul
A1  - Vaz Ferreira, Mergenfel A.
A1  - Zimmermann, Jan-Simon
A1  - Buddeberg, Magdalena
A1  - Henke, Vanessa
A1  - Hornberg, Sabine
A1  - Völschow, Yvette
A1  - Warrelmann, Julia-Nadine
A1  - Malek, Jennifer
A1  - Tinnefeld, Anja
A1  - Schmidt, Peggy
A1  - Bauer, Tobias
A1  - Jänisch, Christopher
A1  - Spitzer, Lisa
A1  - Franken, Nadine
A1  - Degeling, Maria
A1  - Preisfeld, Angelika
A1  - Meier, Jana
A1  - Küth, Simon
A1  - Scholl, Daniel
A1  - Vogelsang, Christoph
A1  - Watson, Christina
A1  - Weißbach, Anna
A1  - Kulgemeyer, Christoph
A1  - Oetken, Mandy
A1  - Gorski, Sebastian
A1  - Kubsch, Marcus
A1  - Sorge, Stefan
A1  - Wulff, Peter
A1  - Fellenz, Carolin D.
A1  - Schnell, Susanne
A1  - Larisch, Cathleen
A1  - Kaiser, Franz
A1  - Knott, Christina
A1  - Reimer, Stefanie
A1  - Stegmüller, Nathalie
A1  - Boukrayâa Trabelsi, Kathrin
A1  - Schißlbauer, Franziska
A1  - Lemberger, Lukas
A1  - Barth, Ulrike
A1  - Wiehl, Angelika
A1  - Rogge, Tim
A1  - Böhnke, Anja
A1  - Dietz, Dennis
A1  - Großmann, Leroy
A1  - Wienmeister, Annett
A1  - Zoppke, Till
A1  - Jiang, Lisa
A1  - Grünbauer, Stephanie
A1  - Ostersehlt, Dörte
A1  - Peukert, Sophia
A1  - Schäfer, Christoph
A1  - Löbig, Anna
A1  - Bröll, Leena
A1  - Brandt, Birgit
A1  - Breuer, Meike
A1  - Dausend, Henriette
A1  - Krelle, Michael
A1  - Andersen, Gesine
A1  - Falke, Sascha
A1  - Kindermann-Güzel, Kristin
A1  - Körner, Katrina
A1  - Lottermoser, Lisa-Marie
A1  - Pügner, Kati
A1  - Sonnenburg, Nadine
A1  - Akarsu, Selim
A1  - Rechl, Friederike
A1  - Gadinger, Laureen
A1  - Heinze, Lena
A1  - Wittmann, Eveline
A1  - Franke, Manuela
A1  - Lachmund, Anne-Marie
A1  - Böttger, Julia
A1  - Hannover, Bettina
A1  - Behrendt, Renata
A1  - Conty, Valentina
A1  - Grundmann, Stephanie
A1  - Ghassemi, Novid
A1  - Opitz, Ben
A1  - Brämer, Martin
A1  - Gasparjan, David
A1  - Sambanis, Michaela
A1  - Köster, Hilde
A1  - Lücke, Martin
A1  - Nordmeier, Volkhard
A1  - Schaal, Sonja
A1  - Haberbosch, Maximilian
A1  - Meissner, Maren
A1  - Schaal, Steffen
A1  - Brüchner, Melanie
A1  - Riehle, Tamara
A1  - Leopold, Bengta Marie
A1  - Gerlach, Susanne
A1  - Rau-Patschke, Sarah
A1  - Skorsetz, Nina
A1  - Weber, Nadine
A1  - Damköhler, Jens
A1  - Elsholz, Markus
A1  - Trefzger, Thomas
A1  - Lewek, Tobias
A1  - Borowski, Andreas
ED  - Mientus, Lukas
ED  - Klempin, Christiane
ED  - Nowak, Anna
T1  - Reflexion in der Lehrkräftebildung
BT  - Empirisch – Phasenübergreifend – Interdisziplinär
T3  - Potsdamer Beiträge für Lehrkräftebildung und Bildungsforschung
N2  - Reflexion ist eine Schlüsselkategorie für die professionelle Entwicklung von Lehrkräften, welche als Ausbildungsziel in den Bildungsstandards für die Lehrkräftebildung verankert ist. Eine Verstetigung universitär geprägter Forschung und Modellierung in der praxisnahen Anwendung im schulischen Kontext bietet Potentiale nachhaltiger Professionalisierung. Die Stärkung reflexionsbezogener Kompetenzen durch Empirie und Anwendung scheint eine phasenübergreifende Herausforderung der Lehrkräftebildung zu sein, die es zu bewältigen gilt. Ziele des Tagungsbandes Reflexion in der Lehrkräftebildung sind eine theoretische Schärfung des Konzeptes „Reflexive Professionalisierung“ und der Austausch über Fragen der Einbettung wirksamer reflexionsbezogener Lerngelegenheiten in die Lehrkräftebildung. Forschende und Lehrende der‚ drei Phasen (Studium, Referendariat sowie Fort- und Weiterbildung) der Lehrkräftebildung stellen Lehrkonzepte und Forschungsprojekte zum Thema Reflexion in der Lehrkräftebildung vor und diskutieren diese. Gemeinsam mit Teilnehmenden aller Phasen und von verschiedenen Standorten der Lehrkräftebildung werden zukünftige Herausforderungen identifiziert und Lösungsansätze herausgearbeitet.
T3  - Potsdamer Beiträge zur Lehrkräftebildung und Bildungsforschung - 4 
KW  - Reflexion
KW  - Lehrkräftebildung
KW  - Reflexionskompetenz
KW  - Reflexivität
KW  - Feedback
KW  - Reflection
KW  - Teacher Education
KW  - Reflection Skills
KW  - Reflexivity
KW  - Feedback
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-591717
SN  - 978-3-86956-566-8
SN  - 2626-3556
SN  - 2626-4722
IS  - 4
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Peukert, Sophia
A1  - Schäfer, Christoph
A1  - Löbig, Anna
A1  - Bröll, Leena Kristina
A1  - Brandt, Birgit
A1  - Breuer, Meike
A1  - Dausend, Henriette
A1  - Krelle, Michael
A1  - Andersen, Gesine
A1  - Falke, Sascha
A1  - Kindermann-Güzel, Kristin
A1  - Körner, Katrina
A1  - Lottermoser, Lisa-Marie
A1  - Pügner, Kati
ED  - Mientus, Lukas
ED  - Klempin, Christiane
ED  - Nowak, Anna
T1  - Professionalisierung von Lehrkräften zur Bildung in der digitalen Welt
BT  - Entwicklung und Reflexion digitaler Lernumgebungen am Beispiel der Fachdidaktik „Philosophieren mit Kindern“
JF  - Reflexion in der Lehrkräftebildung: Empirisch – Phasenübergreifend – Interdisziplinär (Potsdamer Beiträge zur Lehrerbildung und Bildungsforschung ; 4)
N2  - Im BMBF-Projekt DigiLeG – digitale Lernumgebungen in der Grundschule des Zentrums für Lehrerbildung der Technischen Universität (TU) Chemnitz werden ausgehend von einem gemeinsamen Lehrkonzept in Veranstaltungen der beteiligten Fachdidaktiken gemeinsam mit Studierenden Lernumgebungen entwickelt und reflektiert, die digitale Medien lernförderlich in den Grundschulunterricht einbinden. Im folgenden Beitrag werden zunächst 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.
KW  - Lehrkonzept
KW  - Feedback
KW  - Digitale Medien
KW  - Lernumgebungen
KW  - Lehrkräfteprofessionalisierung
KW  - Kompetenzerwerb
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-631816
SN  - 978-3-86956-566-8
SN  - 2626-3556
SN  - 2626-4722
IS  - 4
SP  - 329
EP  - 334
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Sommer, Michael
A1  - Jochheim, H.
A1  - Höhn, Axel
A1  - Breuer, Jörn
A1  - Zagorski, Z.
A1  - Busse, J.
A1  - Barkusky, Dietmar
A1  - Meier, K.
A1  - Puppe, D.
A1  - Wanner, Manfred
A1  - Kaczorek, Danuta
T1  - Si cycling in a forest biogeosystem - the importance of transient state biogenic Si pools
JF  - Biogeosciences
N2  - 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.
Y1  - 2013
U6  - https://doi.org/10.5194/bg-10-4991-2013
SN  - 1726-4170
VL  - 10
IS  - 7
SP  - 4991
EP  - 5007
PB  - Copernicus
CY  - Göttingen
ER  -