Characterization of geosynthetic clay liner bentonite using micro-analytical methods

In barrier design, familiarity of the structure and composition of the soil material at the micron scale is necessary for delineating the retention mechanisms of introduced metals, such as the formation of new mineral phases. In this study, the mineralogical and chemical makeup of the bentonite from a geosynthetic clay liner (GCL) was extensively characterized using a combination of conventional benchtop X-ray diffraction (XRD) and micro X-ray diffraction (μXRD) with synchrotron-generated micro X-ray fluorescence (μXRF) elemental mapping and μXRD (S-μXRD). These methods allow for the non-destructive, in situ investigation of a sample, with μm spatial resolution. Synchrotron-based hard X-ray microprobes are specifically advantageous to the study of trace metals due to higher spatial resolution (<10 μm) and higher analytical sensitivity (femtogram detection) than is possible using normal laboratory-based instruments. Minerals comprising less than 5% of the total bentonite sample such as gypsum, goethite and pyrite were identified that were not accessible by other conventional methods for the same GCL bentonite. Two dimensional General Area Diffraction Detector System (GADDS) images proved to be particularly advantageous in differentiating between the microcrystalline clay, which appeared as homogeneous Debye rings, and the ‘spotty’ or ‘grainy’ appearance of primary, more-coarsely-crystalline, accessory minerals. For S-μXRD, the tunability of the synchrotron X-rays allowed for efficient distinction of both clay minerals at low scattering angles and in identifying varying Fe oxide minerals at higher angles. GCL samples permeated with metal-bearing mining solutions were also examined in order to consider how mechanisms of metal attenuation may be identified using the same techniques. In addition to the cation exchange capacity from the montmorillonite clay, tests showed how minerals comprising only 1–2% of the bentonite such as goethite could potentially play a significant role in sequestering a range of metals, specifically Ni, Zn and Cu.     

Thermomagnetic analysis of meteorites, 3. C3 and C4 chondrites

Thermomagnetic analysis was made on samples of all known C3 and C4 chondrites in a controlled oxygen atmosphere. Considerable variation was noted in the occurrence of magnetic minerals, comparable to the variation observed earlier in the C2 chondrites. Magnetite was found as the only major magnetic phase in samples of only three C3 chondrites (2–4 wt.%) and the Karoonda C4 chondrite (7.7 wt.%). The magnetite content of these three C3 chondrites is only about one-third that observed in the C1 and C2 chondrites which were found to contain magnetite as the only magnetic phase. Five C3 chondrites were observed to undergo chemical change during heating, producing magnetite: this behavior is characteristic of troilite oxidation. Upper limits on initial magnetite content of about 1–9% were established for these meteorites. Samples of the remaining five C3 chondrites and the Coolidge C4 chondrite were found to contain both magnetite and metallic iron. In two samples, iron containing ≤2% Ni was observed, while in the other four, the iron contained 6–8 wt.% Ni. In addition to containing both magnetite and iron metal, three of these samples reacted during heating to form additional magnetite. Variations in the magnetic mineralogy and, hence by inference bulk mineralogy, of C3 and C4 chondrites indicate a more complex genesis than is evident from whole-rock elemental abundance patterns.     

Projecting the demographic impact of Syrian migration in a rapidly ageing society,Germany

Trends of persistent low fertility and increasing life expectancy have set Germany to undergo rapid population ageing and decline. In the context of the Syrian refugee crisis, immigration has been considered as a key mechanism to combat these demographic outlooks. This study assesses the demographic impact of Syrian migration into Germany. Deterministic and Bayesian probabilistic projection methods are used to determine the contribution of Syrian migrants to aggregate total fertility rate and the likelihood of subsequent population growth. Findings reveal that Syrian migration is projected to increase German period total fertility but not by the required levels to prevent depopulation. Whilst Syrian migration into Germany has been substantial over the past few years, fertile female cohorts are largely underrepresented in the migrant population and so only a moderate net-effect of Syrian migrants on German fertility is forecasted. A solution to Germany’ population decline may thus not be offered through Syrian migration, with depopulation projected to be a likely scenario.

     

MODELING LAND-SURFACE ALBEDOS FROM VEGETATION CANOPY ARCHITECTURE

Over the past decade, the climatic impact of changes in terrestrial albedo has been studied using numerous climate models, ranging from simple, one-dimensional energy balance climate models to the more sophisticated, three-dimensional general circulation models of the atmosphere. In most of these, however, the land-surface albedos have been prescribed both spatially and temporally from albedo observations. To overcome the limitations of using prescribed land-surface albedos, a model of radiation transfer in plant canopies was used to predict vegetation albedos. Because of the model's reliance on the physical properties of the land-surface cover, it is able to account explicitly for albedo variations caused by factors both internal to and external from the vegetation canopy. The model is described and the results of simulations for three representative canopy types are discussed. The dependence of albedo on irradiance distribution predicted by the model agrees well with established theory. [Key words: albedo, modeling, vegetation canopy, climatology.]     

Comparative biomass structure and estimated carbon flow in food webs in the deep Gulf of Mexico

A budget of the standing stocks and cycling of organic carbon associated with the sea floor has been generated for seven sites across a 3-km depth gradient in the NE Gulf of Mexico, based on a series of reports by co-authors on specific biotic groups or processes. The standing stocks measured at each site were bacteria, Foraminifera, metazoan meiofauna, macrofauna, invertebrate megafauna, and demersal fishes. Sediment community oxygen consumption (SCOC) by the sediment-dwelling organisms was measured at each site using a remotely deployed benthic lander, profiles of oxygen concentration in the sediment pore water of recovered cores and ship-board core incubations. The long-term incorporation and burial of organic carbon into the sediments has been estimated using profiles of a combination of stable and radiocarbon isotopes. The total stock estimates, carbon burial, and the SCOC allowed estimates of living and detrital carbon residence time within the sediments, illustrating that the total biota turns over on time scales of months on the upper continental slope but this is extended to years on the abyssal plain at 3.6 km depth. The detrital carbon turnover is many times longer, however, over the same depths. A composite carbon budget illustrates that total carbon biomass and associated fluxes declined precipitously with increasing depth. Imbalances in the carbon budgets suggest that organic detritus is exported from the upper continental slope to greater depths offshore.The respiration of each individual “size” or functional group within the community has been estimated from allometric models, supplemented by direct measurements in the laboratory. The respiration and standing stocks were incorporated into budgets of carbon flow through and between the different size groups in hypothetical food webs. The decline in stocks and respiration with depth were more abrupt in the larger forms (fishes and megafauna), resulting in an increase in the relative predominance of smaller sizes (bacteria and meiofauna) at depth. Rates and stocks in the deep northern GoM appeared to be comparable to other continental margins where similar comparisons have been made.     

Weak gravitational shear and flexion with polar shapelets

We derive expressions, in terms of 'polar shapelets', for the image distortion operations associated with weak gravitational lensing. Shear causes galaxy shapes to become elongated, and is sensitive to the second derivative of the projected gravitational potential along their line of sight; flexion bends galaxy shapes into arcs, and is sensitive to the third derivative. Polar shapelets provide a natural representation, in which both shear and flexion transformations are compact. Through this tool, we understand progress in several weak lensing methods. We then exploit various symmetries of shapelets to construct a range of shear estimators with useful properties. Through an analogous investigation, we also explore several flexion estimators. In particular, some of the estimators can be measured simultaneously and independently for every galaxy, and will provide unique checks for systematics in future weak lensing analyses. Using simulated images from the Shear TEsting Programme, we show that we can recover input shears with no significant bias. A complete software package to parametrize astronomical images in terms of polar shapelets, and to perform a full weak lensing analysis, is available on the Internet.     

Effects of turbidity on the migration of juvenile banded kokopu (Galaxias fasciatus) in a natural stream

Laboratory experiments have shown that the juvenile migratory stage of banded kokopu (Galaxias fasciatus (Gray 1842)) is more sensitive to turbidity than other native fish species and avoids turbidity levels of >25 nephelometric turbidity units (NTU). Field trials using juvenile fish collected from the Tarawera River and Hays Stream, New Zealand, were used to test the results from these laboratory experiments by measuring the effects of turbidity on the migration direction and rate for banded kokopu in a natural stream setting. In the stream setting, neither the migration rate nor the migration direction were affected at turbidity <25 NTU. At higher turbidity levels, significantly fewer fish migrated up stream within a given time period. Because there was rarely any downstream movement, this suggests the fish either halted or slowed their upstream movement. A slower rate of migration could result in fewer juveniles reaching adult habitat, and would account for the reduced abundance of adult banded kokopu in rivers that are turbid during the migration season. Achieving turbidity levels of <25 NTU in rivers and streams during the migration season would therefore help maintain upstream migrations and populations of banded kokopu, and hence other native fish species.     

Video and seismic observations of Strombolian eruptions at Erebus volcano,Antarctica

Between 1986 and 1990 the eruptive activity of Erebus volcano was monitored by a video camera with on-screen time code and recorded on video tape. Corresponding seismic and acoustic signals were recorded from a network of 6 geophones and 2 infrasonic microphones. Two hundred Strombolian explosions and three lava flows which were erupted from 7 vents were captured on video. In December 1986 the Strombolian eruptions ejected bombs and ash. In November 1987 large bubble-bursting Strombolian eruptions were observed. The bubbles burst when the bubble walls thinned to ∼ 20 cm. Explosions with bomb flight-times up to 14.5 s were accompanied by seismic signals with our local size estimate, “unified magnitudes” (m_u), up to 2.3. Explosions in pools of lava formed by flows in the Inner Crater were comparatively weak.     

Radiometric dating of the Middle Palaeolithic tool industry and associated fauna of Pin Hole Cave,Creswell Crags,England

Uranium-series dating of derived speleothem suggests that the sediments enclosing a Middle Palaeolithic stone artefact assemblage in Pin Hole Cave probably accumulated after about 64 ka, and ¹⁴C dates indicate a likely age of > 40 ka for the large mammal fauna associated with it. Electron spin resonance data from the fauna conform with these age constraints and are consistent with accumulation between 38 and 50 ka. This evidence supports the view that Britain was recolonised by hominids during Oxygen Isotope Stage 3. Stratigraphically higher stone tool industries demonstrate the local presence of both early Upper and late Upper Palaeolithic cultures. © 1998 John Wiley & Sons, Ltd.