8. Ein anschauliches Lichtbild aus dem algerischen Phosphatbezirk von Tocqueville

Ohne Zusammenfassung     

Distribution,behavior, and transport of inorganic and methylmercury in a high gradient stream

Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14 km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1 N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg.     

Source-rock identification by isotope analyses of natural gases from fields in the Val Verde and Delaware basins,west Texas

Methane, ethane and propane carbon-isotope ratios are controlled by the maturity of the organic material in their source rocks. Isotope data of natural gases can be used in some instances to identify their source rocks. Migration seems to cause no essential changes in the carbon-isotopic composition of the gas components. Under certain circumstances the isotope-maturity relationship can be used in approximating displacement along fault systems or in determining the direction of gas migration.     

Origin and age of The Hillocks and implications for post‐glacial landscape development in the upper Lake Wakatipu catchment,New Zealand

Ambiguous landscape histories can arise from equivocal or incomplete geomorphological, sedimentological or geochronological evidence. In this study, we apply quantitative analyses to robustly assess the origin and age of a field of rounded mounds, known as ‘The Hillocks’. Using clast analysis, the sediment is shown to be consistent with a landslide origin but inconsistent with other glacial sediments in the region. Cosmogenic ¹⁰Be exposure age dating suggests The Hillocks formed ~8 ka. Ground‐penetrating radar reveals that the deposit rests upon deltaic foreset beds; combined with topographical data, we calculate a deposit volume of ~15–27 M m³, consistent with the estimated volume of the proposed source area. Overall, our data support a rock avalanche origin, indicating that by 8 ka the valley was ice‐free at The Hillocks’ location, and the level of Lake Wakatipu was lower than 340 m asl by this time. The Dart River delta shoreline was situated somewhere between The Hillocks and the present day shoreline at that time, and has prograded at a maximum average rate of 1 m a^?1 since ~8 ka. These findings are significant given the lack of landforms by which to constrain glacial or post‐glacial landscape histories in this region of New Zealand. Copyright © 2019 John Wiley & Sons, Ltd.     

The spatio-temporal development of Copenhagen’s bicycle infrastructure 1912–2013

Cycling plays an important role in low-carbon transitions. Around the globe, cities are constructing bicycle infrastructure. The city of Copenhagen has a bicycle-friendly infrastructure celebrated for its fine-meshed network. This study documents the spatio-temporal development of Copenhagen’s bicycle infrastructure and explores how the development corresponds to other processes of urban transformation. The study builds on historical maps of bicycle infrastructure that are digitised into geographical information, which allows for a comprehensive analysis of the formation of the network. In search for identifying drivers, the study analyses the city’s spatial growth pattern, migration pattern, development of road network and changes in the transport culture. Analyses reveal that the bicycle infrastructure expanded at a relatively constant pace during distinct periods of urban transformation, including periods when the city suffered from spatial, economic and demographic decline, and dominance of car traffic. By discussing reasons and demands for constructing bicycle infrastructure, the study identifies four distinct periods in which bicycle infrastructure was constructed to enhance comfort and safety (first cycling city); the flow for cars (car city); urban liveability for soft transport (liveable city); and, finally, to improve the flow for cyclists as part a strategic re-design of urban space (liveable cycling city).     

Discrete element simulation of geogrid-stabilised soil

A particle-based numerical simulation procedure is presented for the generation and calibration of geogrid-stabilised soil on the basis of experimental data. The paper describes how to simulate a biaxial geogrid depending on a specific particle and parallel bond model. Numerical and experimental pull-out tests have been performed to reproduce the pull-out force–strain behaviour of a biaxial geogrid specimen embedded in granular material under special consideration of the grain-size distribution, initial relative density, normal stress state as well as sample installation. Model analysis of soil mobilisation and geogrid deformation is presented to understand the significance of the interlocking effect as key mechanism for soil stabilisation. The procedure can be used for further investigations of the influence and effects of soil stabilisation depending on the significant properties of the interacting components (soils and geogrids).     

Spectroscopic studies of southern-hemisphere cepheids: WW Car,SX Car,UZ Car,UY Car,GX Car,HW Car,YZ Car

For seven faint southern Cepheids (WW Car, SX Car, UZ Car, UY Car, GX Car, HW Car, YZ Car), we have determined their atmospheric parameters and chemical composition for the first time based on ten high-resolution (R = 50 000) spectra taken with the 1.5-m Hexapod telescope at the Joint Observatory of the Northern Catholic University (Antofagasta, Chile) and the Ruhr University (Bochum, Germany). Six objects from the list demonstrate atmospheric parameters and chemical composition typical of Cepheids that have passed through the first dredge-up phase, while WW Car is probably an anomalous Cepheid. According to our preliminary estimates, it has an overabundance of CNO, a deficit of sodium and aluminum, and a slight deficit of magnesium, with iron and other elements being underabundant relative to the Sun.     

12. Betrachtungen zur Großtektonik des subäquatorialen Afrika

Zusammenfassung Gegen die Einpassung des afrikanischen Werdeganges in den Rahmen eines uralten ONO gerichteten Felderbaues der Kruste werden Bedenken geltend gemacht. Einer Deutung der Großtektonik im Sinne der Verschiebungstheorie wird der Vorzug gegeben.     

Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics

The hydrodynamic properties and the capability to measure sediment-water solute fluxes, at assumed steady state conditions, were compared for three radically different benthic chamber designs: the “Microcosm”, the “Mississippi” and the “Göteborg” chambers. The hydrodynamic properties were characterized by mounting a PVC bottom in each chamber and measuring mixing time, diffusive boundary layer thickness (DBL thickness) shear velocity (u∗), and total pressure created by the water mixing. The Microcosm had the most even distribution of DBL thickness and u∗, but the highest differential pressure at high water mixing rates. The Mississippi chamber had low differential pressures at high u∗. The Göteborg chamber was in between the two others regarding these properties. DBL thickness and u∗ were found to correlate according to the following empirical formula: DBL=76.18(u∗)−0.933. Multiple flux incubations with replicates of each of the chamber types were carried out on homogenized, macrofauna-free sediments in four tanks. The degree of homogeneity was determined by calculating solute fluxes (of oxygen, silicate, phosphate and ammonium) from porewater profiles and by sampling for porosity, organic carbon and meiofauna. All these results, except meiofauna, indicated that there were no significant horizontal variations within the sediment in any of the parallel incubation experiments. The statistical evaluations also suggested that the occasional variations in meiofauna abundance did not have any influence on the measured solute fluxes. Forty-three microelectrode profiles of oxygen in the DBL and porewater were evaluated with four different procedures to calculate diffusive fluxes. The procedure presented by Berg, Risgaard-Petersen and Rysgaard, 1989 [Limnol. Oceanogr. 43, 1500] was found to be superior because of its ability to fit measured profiles accurately, and because it takes into consideration vertical zonation with different oxygen consumption rates in the sediment. During the flux incubations, the mixing in the chambers was replicated ranging from slow mixing to just noticeable sediment resuspension. In the “hydrodynamic characterizations” these mixing rates corresponded to average DBL thickness from 120 to 550 μm, to u∗ from 0.12 to 0.68 cm/s, and to differential pressures from 0-3 Pa. Although not directly transferable, since the incubations were done on a “real” sediment with a rougher surface while in the characterizations a PVC plate simulated the sediments surface, these data give ideas about the prevailing hydrodynamic condition in the chambers during the incubations. The variations in water mixing did not generate statistically significant differences between the chamber types for any of the measured fluxes of oxygen or nutrients. Consequently it can be concluded that, for these non-permeable sediments and so long as appropriate water mixing (within the ranges given above) is maintained, the type of stirring mechanism and chamber design used were not critical for the magnitude of the measured fluxes. The average measured oxygen flux was 11.2 ± 2.7 (from 40 incubations), while the diffusive flux calculated (from 43 profiles using the Berg et al., 1989 [Limnol. Oceanogr. 43, 1500] procedure) was 11.1 ± 3.0 mmol m⁻² day⁻¹. This strongly suggests that accurate oxygen flux measurements were obtained with the three types of benthic chambers used and that the oxygen uptake is diffusive.     

SID flare production is independent of Mt. Wilson magnetic class

We have analyzed the observed frequency distributions of SID flare days for the different sunspot magnetic classes, taking flare days as well as no flare days into account. We find that there is no significant difference between any observed distribution for a specific magnetic class, and the Poisson random theoretical distribution, computed for that class.St. Augustine, Trinidad, West Indies.Cave Hill, St. Michael, Barbados, West Indies.