An Integrated Framework to Study Ecological Tipping Points in Social-Ecological Systems

Sudden regime shifts or tipping points pose a major threat to various ecosystems and people\u27s livelihoods worldwide. However, tipping points are still hard to predict and often occur without warning. To avoid dramatic social-ecological consequences, it is crucial to understand tipping point behaviour and to identify early warning indicators. Previous studies have hardly implemented an integrated social-ecological approach, which has led to a fragmented understanding and oversimplification of tipping point phenomena. Against this background, we present a systemic research framework that harmonizes ecological and social perspectives to gain a mechanistic understanding of tipping point behaviour. We utilize a social-ecological systems (SES) approach to identify drivers, consequences, and feasible preventive strategies. Our proposed framework consists of a retrospective, a comparative and a prospective perspective; each of them utilizes interdisciplinary studies in both sub systems at multiple scales. The research framework was developed by the members of NamTip, an inter- and transdisciplinary research project aiming to understand and manage desertification tipping points in Namibia’s semi-arid rangelands. The NamTip project represents a practical implementation of the research framework, that uses an integrated, social-ecological study design combining the threefold approach with dynamic modelling. This includes analyses of time-series and archival data, experimental and observational studies, as well as scenario development and exploration of decision-making with local farmers. After the initial practical implementation and with our ongoing evaluation, we are convinced that such an ambitious and complex framework will guide the way to a profound understanding of tipping point phenomena and feasible management options

Biogeochemie von Phosphat im Unterboden am Beispiel deutscher Dauerdüngungsversuche

Unterböden von Ackerstandorten verfügen über große Vorräte an Phosphat (P), allerdings ist nach wie vor unklar, ob, in welchem Umfang und unter welchen Bedingungen diese Nährstoffreserven im Unterboden zur Ernährung unserer Ackerkulturen beitragen. Wir vermuten, dass einerseits langjährige P-Limitierung dazu führen kann, dass mehr P aus dem Unterboden aufgenommen wird, dass aber andererseits die Zugänglichkeit zu P-Reserven im Unterboden auch abhängig ist von der Versorgung mit anderen Nährstoffen, wie z.B. Stickstoff (N) und Kalium (K). Um diese Hypothesen zu testen, beprobten wir unter anderem zwei Statische Nährstoffmangelversuche in Thyrow (Brandenburg) und Gießen (Hessen). Wir entnahmen Bodenproben bis in 100 cm Tiefe, aus Varianten, die seit über 60 Jahren entweder NPK, NK oder PK Düngung erhalten haben. Für diese Proben bestimmten wir die P Pools nach Hedley et al. (1), sowie die Sauerstoffisotopie des Phosphats nach Extraktion mit 1M HCl (δ18OHCl P), welches eine Differenzierung in primäre und sekundäre (d.h. nach vorherigem biologischem Cycling neu ausgefällte) P-Minerale ermöglicht. An beiden Standorten beobachteten wir, dass in den NK-gedüngten Varianten die Vorräte der labilen P Pools aus dem Hedley’schen Extraktionsschema im Unterboden (30 – 100 cm) 10 – 60% geringer waren als in den NPK-gedüngten Varianten. Die Vorräte an HCl P in den NK-Varianten waren jedoch v.a. in Thyrow bis zu 70% höher, während gleichzeitg die δ18OHCl P Werte deutlich niedriger waren als in den NPK-Varianten. Diese niedrigeren Isotopensignaturen deuten auf hauptsächlich primäre P-Minerale hin, sodass wir unsere Annahme von höherem P-Cycling im Unterboden bei Mangel im Oberboden widerrufen müssen. In den PK-gedüngten Varianten beobachteten wir, dass die Vorräte an labilem P im Unterboden 117% (Thyrow) und 22% (Gießen) größer waren als in der NPK-Variante. Dies stützt unsere zweite Annahme von einer Limitierung der P-Aufnahme aus dem Unterboden aufgrund des Mangels an anderen Nährstoffen, allerdings ergaben sich hier keine klaren Auswirkungen auf die δ18OHCl P Signatur des Phosphats. Im Folgenden sollen diese Beobachtungen nun an weiteren Standorten und unter weiteren Einflussparametern getestet werden. Zusammenfassend zeigen jedoch schon unsere bisherigen Ergebnisse, dass die effiziente Ausnutzung von P-Reserven im Unterboden nur unter optimaler Nährstoffversorgung im Oberboden erfolgt

Description of an aerodynamic levitation apparatus with applications in Earth sciences

<p>Abstract</p> <p>Background</p> <p>In aerodynamic levitation, solids and liquids are floated in a vertical gas stream. In combination with CO₂-laser heating, containerless melting at high temperature of oxides and silicates is possible. We apply aerodynamic levitation to bulk rocks in preparation for microchemical analyses, and for evaporation and reduction experiments.</p> <p>Results</p> <p>Liquid silicate droplets (~2 mm) were maintained stable in levitation using a nozzle with a 0.8 mm bore and an opening angle of 60°. The gas flow was ~250 ml min^-1. Rock powders were melted and homogenized for microchemcial analyses. Laser melting produced chemically homogeneous glass spheres. Only highly (e.g. H₂O) and moderately volatile components (Na, K) were partially lost. The composition of evaporated materials was determined by directly combining levitation and inductively coupled plasma mass spectrometry. It is shown that the evaporated material is composed of Na > K >> Si. Levitation of metal oxide-rich material in a mixture of H₂and Ar resulted in the exsolution of liquid metal.</p> <p>Conclusions</p> <p>Levitation melting is a rapid technique or for the preparation of bulk rock powders for major, minor and trace element analysis. With exception of moderately volatile elements Na and K, bulk rock analyses can be performed with an uncertainty of ± 5% relative. The technique has great potential for the quantitative determination of evaporated materials from silicate melts. Reduction of oxides to metal is a means for the extraction and analysis of siderophile elements from silicates and can be used to better understand the origin of chondritic metal.</p

Assembly of large-area, highly ordered, crack-free inverse opal films

Whereas considerable interest exists in self-assembly of well-ordered, porous “inverse opal” structures for optical, electronic, and (bio)chemical applications, uncontrolled defect formation has limited the scale-up and practicality of such approaches. Here we demonstrate a new method for assembling highly ordered, crack-free inverse opal films over a centimeter scale. Multilayered composite colloidal crystal films have been generated via evaporative deposition of polymeric colloidal spheres suspended within a hydrolyzed silicate sol-gel precursor solution. The coassembly of a sacrificial colloidal template with a matrix material avoids the need for liquid infiltration into the preassembled colloidal crystal and minimizes the associated cracking and inhomogeneities of the resulting inverse opal films. We discuss the underlying mechanisms that may account for the formation of large-area defect-free films, their unique preferential growth along the 〈110〉 direction and unusual fracture behavior. We demonstrate that this coassembly approach allows the fabrication of hierarchical structures not achievable by conventional methods, such as multilayered films and deposition onto patterned or curved surfaces. These robust SiO2 inverse opals can be transformed into various materials that retain the morphology and order of the original films, as exemplified by the reactive conversion into Si or TiO2 replicas. We show that colloidal coassembly is available for a range of organometallic sol-gel and polymer matrix precursors, and represents a simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for a variety of applications.Engineering and Applied Science

Kinetics of spinel formation and growth during dissolution of MgO in CaO-Al2O3-SiO2 slag

The formation and growth of MgAl2O4 spinel crystals on a single crystal MgO substrate submerged in a 40% CaO, 40% SiO2 and 20% Al2O3 slag was directly observed using high temperature microscopy. This showed that the crystals initially form on the MgO surface, but may break off and be carried out into the liquid slag. Still pictures extracted from digitally recorded images were used to measure the size of these crystals at 1420, 1440 and 1460oC as a function of time. Growth of the crystals was found to follow the parabolic rate law, with rates increasing with temperature. An estimate of the activation energy made from the data (564 kJ mol-1) was found to be comparable with previously published results from different types of experiments on spinel formation