Pore-Scale Modelling of Induced-Polarization Mechanisms in Geologic Materials

This thesis is concerned with mechanistic pore-scale models, which relate the induced-polarization (IP) response of geologic materials to the underlying physical and chemical processes. Although a sound understanding of these processes is essential for the interpretation of measured IP responses, the development of suitable mechanistic models is lagging far behind the fast growing amount of experimental IP data. Therefore, the main objective of this thesis is to improve theoretical models and advance the general understanding of the polarization processes. The first development is an analytic model to predict the influence of an immiscible liquid hydrocarbon phase on the membrane-polarization mechanism occurring in electrolyte-filled pore constrictions. The hydrocarbon is modelled as an electrically insulating phase with a negatively charged surface. Magnitude and phase of the predicted electrical conductivity of hydrocarbon-contaminated materials decrease with increasing hydrocarbon saturation irrespective of whether the hydrocarbon phase is wetting or non-wetting. Only non-wetting hydrocarbon droplets with highly charged surfaces yield an increase of the magnitude with the hydrocarbon saturation and a slight increase of the phase at intermediate hydrocarbon concentrations. This prediction offers the first theoretical explanation for a similar experimentally determined relation between complex conductivity and hydrocarbon saturation. The next two parts of this thesis examine the electrode-polarization mechanism responsible for the IP response of metal-bearing materials. The polarization of uncharged metallic particles is studied based on an electrochemical model, which includes the effect of oxidation-reduction reactions at the particle surface. The full solution of the underlying Poisson-Nernst-Planck (PNP) system is presented, which allows to visualize the micro-scale manifestations of two simultaneously acting polarization mechanisms. The first mechanism is related to the dynamic charging of field-induced diffuse layers and the second is a volume-diffusion mechanism activated by reaction currents through the particle surface. For the relaxation times of both processes analytic expressions are derived and a critical particle radius is determined. While the response of particles smaller than this radius is mainly determined by the diffuse-layer polarization, the effect of the volume-diffusion mechanism becomes significant around larger particles. The model is then extended to investigate the effect of surface charge on electrode polarization. Besides the dynamic charging of field-induced diffuse layers and the volume-diffusion processes related to the reaction currents, the numeric solution of the modified PNP system reveals the action of an additional volume-diffusion process caused by the unequal transport rates of anions and cations within the static diffuse covering the charged surface. This mechanism is found to have a second-order effect on the macroscopic polarization response, which is still dominated by the first two mechanisms. While the volume-diffusion process due to the reaction currents remains practically unaffected by the surface charge, a moderate increase of the low-frequency conductivity and the relaxation time as well as a slight reduction of the polarization magnitude with the surface charge are observed if the diffuse-layer relaxation dominates, i.e. in the case of small particles. In the last part of this thesis, the coupled polarization of Stern and diffuse layers covering dielectric surfaces is treated in a generalized numeric framework. First, this framework is used to model the response of spherical particles and guide the development of an improved analytic model for the coupled polarization of Stern and diffuse layer. Subsequently, it is applied to a cylindrical pore-constriction geometry. In the limiting case of a pure diffuse-layer polarization, the corresponding numeric results can be matched by an improved analytic membrane-polarization model. In both geometries, the response of the Stern layer dominates as long as the charged surfaces are not interconnected at the system scale. With increasing degree of interconnectivity, however, the response of the diffuse layer becomes more important and in the case of fully interconnected surfaces becomes as strong as the response of the Stern layer. In summary, this thesis brings together significant improvements of analytic models for all relevant induced-polarization mechanisms: Membrane polarization, electrode polarization, and Stern- and diffuse-layer polarization. The carefully validated numeric modelling framework furthermore lays the foundation for the future investigation of more realistic geometrical configurations of the various solid and liquid phases of real geologic materials.Porenskalenmodellierung der Mechanismen der Induzierten Polarisation in Geologischen Materialien Gegenstand dieser Dissertation sind mechanistische Porenskalenmodelle, die die Induzierte Polarisation (IP) geologischer Materialien mit den ihr zugrundeliegenden physikalischen und chemischen Prozessen verknüpfen. Obwohl ein umfassendes Verständnis dieser Prozesse für die Interpretation immer neuer experimenteller IP Daten wichtig wäre, hängt die Entwicklung mechanistischer Modelle weit hinterher. Ziel dieser Dissertation ist es daher, theoretische Modelle weiterzuentwickeln und damit das grundlegende Verständnis der Polarisationsprozesse zu verbessern. Den ersten Beitrag dazu liefert ein analytisches Modell, das den Einfluss unvermischbarer flüssiger Kohlenwasserstoffe (KW) auf die Membranpolarisation in elektrolytgefüllten Porenengstellen vorhersagt. Der flüssige KW wird hier als nichtleitende Phase mit negativ geladener Oberfläche modelliert. Betrag und Phase der resultierenden elektrischen Leitfähigkeit nehmen mit zunehmendem KW-Anteil ab – unabhängig davon, ob der KW die benetzende oder die nicht-benetzende Phase ist. Nur im Falle stark negativ geladener nicht-benetzender KW-Tropfen nimmt der Betrag mit dem KW-Anteil zu. Auch die Phase durchläuft hier zunächst ein Maximum bevor sie bei hohen KW-Anteilen schließlich abfällt. Diese Vorhersage kann erstmals einen ähnlichen experimentell nachgewiesenen Zusammenhang zwischen komplexer elektrischer Leitfähigkeit und KW-Anteil theoretisch erklären. Die folgenden zwei Teile behandeln die für die starke IP Antwort metallhaltiger Materialien verantwortliche Elektrodenpolarisation. Die Polarisierung ungeladener metallischer Partikel wird mithilfe eines elektrochemischen Modells untersucht, das auch Redoxreaktionen an der Partikeloberfläche einschließt. Die hier vorgestellte vollständige Lösung des zugrundeliegenden Poisson-Nernst-Planck (PNP) Gleichungssystems ermöglicht es die mikroskopischen Auswirkungen zweier gleichzeitig ablaufender Mechanismen grafisch darzustellen: Das dynamische Laden feldinduzierter diffuser Schichten und einen Volumendiffusionsmechanismus, der von Reaktionsströmen durch die Partikeloberfläche aktiviert wird. Für die Relaxationszeiten beider Prozesse werden analytische Ausdrücke abgeleitet und ein kritischer Partikelradius bestimmt. Während das Verhalten von Partikeln mit geringerem Radius hauptsächlich mit der Polarisation der diffusen Schicht zusammenhängt, wird im Fall größerer Partikel der Volumendiffusionsmechanismus bestimmend. Im Folgenden wird dieses Modell erweitert, um die Auswirkung elektrischer Ladungen an der Metalloberfläche auf die Elektrodenpolarisation zu untersuchen. Neben der dynamischen Ladung der feldinduzierten diffusen Schichten und dem durch die Reaktionsströme bedingten Volumendiffusionsmechanismus beschreibt die numerische Lösung des erweiterten PNP Systems einen weiteren Volumendiffusionsprozess. Dieser wird durch die unterschiedlichen Anionen- und Kationenflüsse in der statischen diffusen Schicht an der geladenen Grenzfläche hervorgerufen, beeinflusst die makroskopische Antwort, allerdings nur geringfügig: Während der durch die Reaktionsströme hervorgerufene Volumendiffusionsprozess praktisch unverändert bleibt, macht sich die geladene Partikeloberfläche genau dann durch einen moderaten Anstieg von Gleichstromleitfähigkeit und Relaxationszeit sowie durch eine leichte Abnahme der Polarisationsstärke bemerkbar, wenn die Relaxation der diffusen Schicht wichtig wird, d.h. vor allem im Falle sehr kleiner Partikel. Der letzte Teil widmet sich der gleichzeitigen Polarisierung von Stern-Schicht und diffuser Schicht an der geladenen Oberfläche dielektrischer Materialien. Ein entsprechender numerischer Modellierungsansatz wird zunächst benutzt, um die Polarisierung kugelförmiger Partikel zu simulieren und die analytische Modellierung der gleichzeitigen Polarisierung von Stern- und diffuser Schicht zu verbessern. Im Folgenden wird dieser Ansatz dann auf eine zylindrische Porenengstelle angewandt. Ein zu diesem Zweck verbessertes analytisches Modell der Membranpolarisation kann die Simulationsergebnisse allerdings nur im Grenzfall einer reinen Polarisierung der diffusen Schicht erklären. Solange die geladenen Oberflächen auf der Systemskala nicht durchgehend verbunden sind dominiert – wie im Falle kugelförmiger Partikel – die Polarisierung der Stern-Schicht. Mit zunehmender Kontinuität der Schichten nimmt der Beitrag der Polarisierung der diffusen Schicht aber zu. Bilden die Oberflächen durchgehende Verbindungen, sind beide Beiträge gleich groß. Insgesamt vereint diese Dissertation wichtige Weiterentwicklungen analytischer Modelle aller relevanten Mechanismen der induzierten Polarisation: Membranpolarisation, Elektrodenpolarisation, sowie Polarisation von Stern- und diffuser Schicht. Der sorgfältig validierte numerische Modellierungsansatz bildet außerdem die Grundlage für zukünftige Untersuchungen komplexerer geometrischer Anordnungen der verschiedenen festen und flüssigen Phasen, die reale geologische Materialien besser abbilden können

Rock Glacier Characteristics Under Semiarid Climate Conditions in the Western Nyainqêntanglha Range, Tibetan Plateau

Abstract Rock glaciers are receiving increased attention as a potential source of water and indicator of climate change in periglacial landscapes. They consist of an ice‐debris mixture, which creeps downslope. Although rock glaciers are a wide‐spread feature on the Tibetan Plateau, characteristics such as its ice fraction are unknown as a superficial debris layer inhibits remote assessments. We investigate one rock glacier in the semiarid western Nyainqêntanglha range (WNR) with a multi‐method approach, which combines geophysical, geological and geomorphological field investigations with remote sensing techniques. Long‐term kinematics of the rock glacier are detected by 4‐year InSAR time series analysis. The ice content and the active layer are examined by electrical resistivity tomography, ground penetrating radar, and environmental seismology. Short‐term activity (11‐days) is captured by a seismic network. Clast analysis shows a sorting of the rock glacier's debris. The rock glacier has three zones, which are defined by the following characteristics: (a) Two predominant lithology types are preserved separately in the superficial debris patterns, (b) heterogeneous kinematics and seismic activity, and (c) distinct ice fractions. Conceptually, the studied rock glacier is discussed as an endmember of the glacier—debris‐covered glacier—rock glacier continuum. This, in turn, can be linked to its location on the semiarid lee‐side of the mountain range against the Indian summer monsoon. Geologically preconditioned and glacially overprinted, the studied rock glacier is suggested to be a recurring example for similar rock glaciers in the WNR. This study highlights how geology, topography and climate influence rock glacier characteristics and development.Plain Language Summary Climate change has begun to impact all regions of our planet. In cold regions, such as high‐mountain areas, rising temperatures lead to massive melting of glaciers. Besides this evident loss of ice, permafrost, a long‐term ice resource hidden in the subsurface, has started to thaw. Rock glaciers as visible permafrost‐related landforms consist of an ice‐debris mixture, which makes them creep downslope. Due to this movement and their recognizable shape, rock glaciers are permafrost indicators in high‐mountain areas. We investigate one rock glacier in the western Nyaingêntanglha Range (Tibetan Plateau) using field and remote sensing methods to understand its development and to know the current state of its ice core. Our main outcome is, that the heterogeneous creeping behavior, the properties of the debris cover as well as the internal distribution of ice are the results of a continuous development from a glacier into today's rock glacier. In particular, the high ice content in particular sections points to such a glacial precondition. The debris layer covering the internal ice attenuates the effect of climate warming. This makes the rock glacier and similar rock glaciers found in the northern part of the mountain range important future water resources for the semiarid region.Key Points Geophysical and remote sensing methods in concert reveal the morphostructure, ice fraction, and kinematics of the studied rock glacier Rock glacier characteristics are controlled by geology, topography and climate on the Tibetan Plateau The studied rock glacier is conceptually interpreted as the endmember of a glacier—debris‐covered glacier—rock glacier continuu

Inhibition of Notch2 by Numb/Numblike controls myocardial compaction in the heart

Aims The ventricular wall of the heart is composed of trabeculated and compact layers, which are separated by yet unknown processes during embryonic development. Here, we wanted to explore the role of Notch2 and Numb/Numblike for myocardial trabeculation and compaction. Methods and results We found that Notch2 activity is specifically down-regulated in the compact layer during cardiac development in the mouse. The biological role of Notch2 down-regulation was investigated by the expression of constitutively active Notch2 in the myocardium of transgenic mice, resulting in hypertrabeculation, reduced compaction, and ventricular septum defects. To disclose the mechanism that inhibited Notch2 activity during the formation of myocardial layers, we analysed potential suppressors of Notch signalling. We unveiled that concomitant but not separate ablation of Numb and Numblike in the developing heart leads to increased Notch2 activity along with hypertrabeculation, reduced compaction, and ventricular septum defects, phenocopying effects gained by overexpression of constitutively active Notch2. Expression profiling revealed a strong up-regulation of Bmp10 in Numb/Numblike mutant hearts, which might also interfere with trabeculation and compaction. Conclusion This study identified potential novel roles of Numb/Numblike in regulating trabeculation and compaction by inhibiting Notch2 and Bmp10 signallin

Recruiting Hard-to-Reach Subjects for Exercise Interventions: A Multi-Centre and Multi-Stage Approach Targeting General Practitioners and Their Community-Dwelling and Mobility-Limited Patients

The general practitioner (GP)’s practice appears to be an ideal venue for recruiting community-dwelling older adults with limited mobility. This study (Current Controlled Trials ISRCTN17727272) aimed at evaluating the recruiting process used for a multi-centre exercise intervention (HOMEfit). Each of six steps resulted in an absolute number of patients (N1–N6). Sex and age (for N4–N6) and reasons for dropping out were assessed. Patient database screening (N1–N3) at 15 GP practices yielded N1 = 5,990 patients aged 70 and above who had visited their GP within the past 6 months, N2 = 5,467 after exclusion of institutionalised patients, N3 = 1,545 patients eligible. Using a pre-defined limitation algorithm in order to conserve the practices’ resources resulted in N4 = 1,214 patients (80.3 ± 5.6 years, 68% female), who were then officially invited to the final assessment of eligibility at the GP’s practice. N5 = 434 patients (79.5 ± 5.4 years, 69% female) attended the practice screening (n = 13 of whom had not received an official invitation). Finally, N6 = 209 (79.8 ± 5.2 years, 74% female) were randomised after they were judged eligible and had given their written informed consent to participate in the randomised controlled trial (overall recruitment rate: 4.4%). The general strategy of utilising a GP’s practice to recruit the target group proved beneficial. The data and experiences presented here can help planners of future exercise-intervention studies

Integrated land and water-borne geophysical surveys shed light on the sudden drying of large karst lakes in southern Mexico

Karst water resources play an important role in drinking water supply but are highly vulnerable to even slight changes in climate. Thus, solid and spatially dense geological information is needed to model the response of karst hydrological systems to such changes. Additionally, environmental information archived in lake sediments can be used to understand past climate effects on karst water systems. In the present study, we carry out a multi-methodological geophysical survey to investigate the geological situation and sedimentary infill of two karst lakes (Metzabok and Tzibaná) of the Lacandon Forest in Chiapas, southern Mexico. Both lakes present large seasonal lake-level fluctuations and experienced an unusually sudden and strong lake-level decline in the first half of 2019, leaving Lake Metzabok (maximum depth ∼25 m) completely dry and Lake Tzibaná (depth ∼70 m) with a water level decreased by approx. 15 m. Before this event, during a lake-level high stand in March 2018, we collected water-borne seismic data with a sub-bottom profiler (SBP) and transient electromagnetic (TEM) data with a newly developed floating single-loop configuration. In October 2019, after the sudden drainage event, we took advantage of this unique situation and carried out complementary measurements directly on the exposed lake floor of Lakes Metzabok and Tzibaná. During this second campaign, we collected time-domain induced polarization (TDIP) and seismic refraction tomography (SRT) data. By integrating the multi-methodological data set, we (1) identify 5–6 m thick, likely undisturbed sediment sequences on the bottom of both lakes, which are suitable for future paleoenvironmental drilling campaigns, (2) develop a comprehensive geological model implying a strong interconnectivity between surface water and karst aquifer, and (3) evaluate the potential of the applied geophysical approach for the reconnaissance of the geological situation of karst lakes. This methodological evaluation reveals that under the given circumstances, (i) SBP and TDIP phase images consistently resolve the thickness of the fine-grained lacustrine sediments covering the lake floor, (ii) TEM and TDIP resistivity images consistently detect the upper limit of the limestone bedrock and the geometry of fluvial deposits of a river delta, and (iii) TDIP and SRT images suggest the existence of a layer that separates the lacustrine sediments from the limestone bedrock and consists of collapse debris mixed with lacustrine sediments. Our results show that the combination of seismic methods, which are most widely used for lake-bottom reconnaissance, with resistivity-based methods such as TEM and TDIP can significantly improve the interpretation by resolving geological units or bedrock heterogeneities, which are not visible from seismic data. Only the use of complementary methods provides sufficient information to develop comprehensive geological models of such complex karst environment

Participatory urban green knowledge on the first symposium on urban green in Braunschweig – water in garden and city

Das Gartennetzwerk Braunschweig veranstaltete im Jahre 2022 seinen ersten Braunschweiger Stadtgrüntag. Der Stadtgrüntag soll die Akteure des Gartennetzwerkes über wichtige Fragen der Funktion des Stadtgrüns informieren und Verständnis für Gestaltungsmöglichkeiten verschiedener Akteure schaffen. Der erste Stadtgrüntag widmete sich dem Thema Wasser in Garten und Stadt und untersuchte in Vorträgen und einer anschließenden Exkursion den Wasserkreislauf in der Stadt.In 2022, the Garden Network Braunschweig organized its first Urban Green Day. The Urban Green Day is intended to inform the actors in the garden network about important questions relating to the function of urban green plants and spaces and to create an understanding of the interactive options of various actors. The first Urban Green Day was dedicated to the topic of water in garden and city and examined the water cycle in the city in lectures and a subsequent excursion

Developing knowledge and tools for climate change mitigation and adaptation with multi­functional urban green infrastructure – kick-off symposium of the multidisciplinary project “Maximizing the carbon sequestration in urban trees (CliMax)”

Das interdisziplinäre Forschungsprojekt CliMax ist eine Kooperation des Julius Kühn-Instituts und der Technischen Universität Braunschweig. Das Projekt erforscht die Grundlagen für effizientere Entscheidungshilfen für Städte und Kommunen, mit deren Hilfe nicht nur der Status Quo des Beitrages des Stadtgrüns zur Kohlenstoffsequestrierung geschätzt, sondern auch die Klimawirksamkeit des Stadtgrüns maximiert werden kann. Die Berücksichtigung der Multifunktionalität des Stadtgrüns bezieht dessen positive Effekte in eine Entscheidungsmatrix mit ein und unterstützt dadurch die Integration des Klimaschutzaspektes bei Pflanz- oder Pflegeentscheidungen. Zum Anlass des Auftaktsymposiums berichten wir hier von den Projektvorhaben.The interdisciplinary research project CliMax is a cooperation between the Julius Kühn-Institute and the Technische Universität Braunschweig. It provides information on the status quo of the contribution of urban green spaces to carbon sequestration and aims for the development of decision-support tools for maximizing the climate effectiveness of urban green. Considering the multifunctionality of urban green spaces, such tools must incorporate many effects of urban green space into a decision matrix and thereby support the integration of the climate mitigation aspects in planting or maintenance decisions. On the occasion of the kick-off meeting, we report here on our plans for the project

Deep drilling at the Chalco lake:A technical report

En este artículo se presenta un resumen de las actividades realizadas para la recuperación de la totalidad de la secuencia lacustre del lago de Chalco. Mediante estudios geofísicos se determinó la distribución y espesor de los sedimentos lacustres con base en lo cual se seleccionó el sitio de perforación. Con datos de los espectros H/V de sísmica pasiva se hizo un mapa de isofrecuencias que definieron una región con sedimentos lacustres y material volcánico granulado de hasta 300 m de espesor. El uso de métodos electromagnéticos mostró cambios en la resistividad eléctrica relacionados con variaciones en la composición de la columna sedimentaria; entre 100 – 120 m de profundidad hay un primer aumento en la resistividad asociado al incremento de materiales volcaniclásticos, y entre 330 – 400 m de profundidad un segundo aumento asociado a la presencia de coladas de basalto. Fueron perforados tres pozos con recuperación continua, llegando a profundidades de 420 m en el pozo A, 310 m en el B y 520 en el C. Durante el trabajo de perforación se tomaron muestras para el análisis geomicrobiológicos y de metagenómica. Durante el proceso de perforación se recuperó un total de 1152 m de sedimentos con una profundidad máxima de 520 m. El porcentaje de recuperación de la columna sedimentaria varió entre 88 a 92 % en los tres sondeos. Los resultados del análisis de susceptibilidad magnética en las tres secuencias indica que los primeros 260 m son sedimentos lacustres, entre 260 y 300 m los sedimentos son más gruesos y debajo de los 300 m son predominantemente volcaniclásticos. El análisis de la secuencia sedimentaria del lago de Chalco de los últimos ~300000 años, permitirá documentar y ampliar el conocimiento acerca de la variabilidad climática de la zona, la historia paleoambiental, la historia del cierre de la cuenca, el desarrollo del sistema lacustre y la recurrencia de la actividad volcánica en la cuenca. Además, el estudio de las propiedades físicas de esta secuencia sedimentaria es importante para la modelación de la propagación de ondas sísmicas y de la estructura de la cuenca, así como para mejorar la capacidad de modelación del proceso de subsidencia del terreno que experimenta esta región. This paper presents a short description of the coring operations undertaken to recover the full lacustrine sedimentary sequence from Chalco. Geophysical techniques were used to determine the distribution and thickness of the sediments in order to select the drilling site. Resonance frequencies determined from H/V spectral ratios were used to determine an area where lake sediments reached 300 m thickness. Electromagnetic survey showed two changes in electric resistivity which were related to changes in sediment composition, the first from 100 to 120 m, related to an increase in volcanoclastic sediments and the second from 330 to 400 m related to the presence of a basaltic flows. Three wells were drilled with continuous recovery, reaching depths of 420 m in well A, 310 in B and 520 in C. Samples for geomicrobiological and metagenomics studies were collected during drilling operations. A total of 1152 m of core sediments were recovered reaching a maximum depth of 520 m. Recovery percentages were between 88 and 92 % in the three wells. Magnetic susceptibility analyses in the three sequences show that the first 260 m are mostly lake sediments, between 260 and 300 m sediments are coarser and below 300 m they are mostly volcaniclastic. Analysis of the sedimentary sequence of Lake Chalco that covers the last ~300000 years will allow documenting and extending the knowledge of climate variability in area, the paleoenvironmental history, basin closure history, lacustrian system development and volcanic activity recurrence. Studies of the physical properties of this sequence will be important for seismic propagation and basin structure modeling, and also will improve modeling of the subsidence process that this region experiences