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Are old regions less attractive? Interregional labour migration in a context of population ageing
(2021)
Abstract
Regional demographic change is often conceptualized as a circular process, where out‐migration continuously worsens conditions of population ageing and shrinkage. Thus, if migration acts as a consequence as well as cause of ageing, migration patterns should be influenced by the age structure of origin and destination regions. This paper analyses individual‐level migration decisions of full‐time employees across 326 German regions between 1997 and 2013 using binary choice models. The results show that individuals are more likely to migrate out of and less likely to migrate towards ageing regions. Moreover, the identified patterns are consistent with age‐selective migration reinforcing ageing processes and polarization of demographic structure.
Abstract
We investigated four subaerial (paleo)lacustrine landforms at the north‐eastern shoreline of Schweriner See, north‐eastern Germany. These included two beach ridges, one subaerial nearshore bar and a silting up sequence located close to a fossil cliff, which marks the former maximum extent of Schweriner See. We used luminescence profiling with a SUERC portable OSL device (POSL) on all four sediment sequences in combination with sedimentological investigations such as grain size, loss‐on‐ignition and magnetic susceptibility to provide information on the various formations in a lacustrine depositional environment. The POSL reader was used on pre‐treated polymineral samples to gain an insight into luminescence distribution within the individual sediment sequences, but also among the four sequences. POSL proved valuable to understand depositional processes, which were not visible in lithology or sedimentological parameters. With somewhat larger uncertainty this method provides relative chronologies of the sediment sequences. Additionally, we carried out radiocarbon dating and full optical stimulated luminescence (OSL) dating to establish a chronological framework. OSL ages proved to be more reliable to date beach ridges in this setting than radiocarbon samples, which were severely influenced by sediment reworking. This combined approach of sedimentological analyses, luminescence profiling and absolute age determinations revealed details in depositional processes at Schweriner See which otherwise would have remained undetected. Furthermore, it helped to set these subaerial (paleo)lacustrine landforms in a chronological framework.
Bentonite is currently proposed as a potential backfill material for sealing high-level radioactive waste in underground repositories due to its low hydraulic conductivity, self-sealing ability and high adsorption capability. However, saline pore waters, high temperatures and the influence of microbes may cause mineralogical changes and affect the long-term performance of the bentonite barrier system. In this study, long-term static batch experiments were carried out at 25 °C and 90 °C for one and two years using two different industrial bentonites (SD80 from Greece, B36 from Slovakia) and two types of aqueous solutions, which simulated (a) Opalinus clay pore water with a salinity of 19 g·L−1, and (b) diluted cap rock solution with a salinity of 155 g·L−1. The bentonites were prepared with and without organic substrates to study the microbial community and their potential influence on bentonite mineralogy. Smectite alteration was dominated by metal ion substitutions, changes in layer charge and delamination during water–clay interaction. The degree of smectite alteration and changes in the microbial diversity depended largely on the respective bentonite and the experimental conditions. Thus, the low charged SD80 with 17% tetrahedral charge showed nearly no structural change in either of the aqueous solutions, whereas B36 as a medium charged smectite with 56% tetrahedral charge became more beidellitic with increasing temperature when reacted in the diluted cap rock solution. Based on these experiments, the alteration of the smectite is mainly attributed to the nature of the bentonite, pore water chemistry and temperature. A significant microbial influence on the here analyzed parameters was not observed within the two years of experimentation. However, as the detected genera are known to potentially influence geochemical processes, microbial-driven alteration occurring over longer time periods cannot be ruled out if organic nutrients are available at appropriate concentrations.
: Compacted bentonite is currently being considered as a suitable backfill material for sealing
underground repositories for radioactive waste as part of a multi-barrier concept. Although showing
favorable properties for this purpose (swelling capability, low permeability, and high adsorption
capacity), the best choice of material remains unclear. The goal of this study was to examine and
compare the hydration behavior of a Milos (Greek) Ca-bentonite sample (SD80) in two types of
simulated ground water: (i) Opalinus clay pore water, and (ii) a diluted saline cap rock brine using
a confined volume, flow-through reaction cell adapted for in situ monitoring by X-ray diffraction.
Based on wet-cell X-ray diffractometry (XRD) and calculations with the software CALCMIX of the
smectite d(001) reflection, it was possible to quantify the abundance of water layers (WL) in the
interlayer spaces and the amount of non-interlayer water uptake during hydration using the two
types of solutions. This was done by varying WL distributions to fit the CALCMIX-simulated XRD
model to the observed data. Hydrating SD80 bentonite with Opalinus clay pore water resulted
in the formation of a dominant mixture of 3- and 4-WLs. The preservation of ca. 10% 1-WLs and
the apparent disappearance of 2-WLs in this hydrated sample are attributed to small quantities of
interlayer K (ca. 8% of exchangeable cations). The SD80 bentonite of equivalent packing density
that was hydrated in diluted cap rock brine also contained ca. 15% 1-WLs, associated with a slightly
higher concentration of interlayer K. However, this sample showed notable suppression of WL
thickness with 2- and 3-WLs dominating in the steady-state condition. This effect is to be expected for
the higher salt content of the brine but the observed generation of CO2 gas in this experiment, derived
from enhanced dissolution of calcite, may have contributed to the suppression of WL thickness. Based
on a comparison with all published wet-cell bentonite hydration experiments, the ratio of packing
density to the total layer charge of smectite is suggested as a useful proxy for predicting the relative
amounts of interlayer and non-interlayer water incorporated during hydration. Such information is
important for assessing the subsequent rates of chemical transport through the bentonite barrier.
Pilot sites are currently used to test the performance of bentonite barriers for sealing high-level radioactive waste repositories, but the degree of mineral stability under enhanced thermal conditions remains a topic of debate. This study focuses on the SKB ABM5 experiment, which ran for 5 years (2012 to 2017) and locally reached a maximum temperature of 250 °C. Five bentonites were investigated using XRD with Rietveld refinement, SEM-EDX and by measuring pH, CEC and EC. Samples extracted from bentonite blocks at 0.1, 1, 4 and 7 cm away from the heating pipe showed various stages of alteration related to the horizontal thermal gradient. Bentonites close to the contact with lower CEC values showed smectite alterations in the form of tetrahedral substitution of Si4+ by Al3+ and some octahedral metal substitutions, probably related to ferric/ferrous iron derived from corrosion of the heater during oxidative boiling, with pyrite dissolution and acidity occurring in some bentonite layers. This alteration was furthermore associated with higher amounts of hematite and minor calcite dissolution. However, as none of the bentonites showed any smectite loss and only displayed stronger alterations at the heater–bentonite contact, the sealants are considered to have remained largely intact.
ABSTRACT
The small terrestrial gastropod Vertigo pseudosubstriata Ložek, 1954 is one of the rarest glacial indicator species in the Pleistocene of Central and Eastern Europe. In all, this species has been found at only about 15 sites in Europe. V. pseudosubstriata was initially described as a fossil in Central Europe and was discovered only later alive in Central Asia. With regard to its modern distribution, 25 habitats with V. pseudosubstriata have been examined in Tien Shan and in the central and southern Altai. These findings seem to capture the contemporary distribution of the species and provide information on the boundaries of its ecological requirements. These data are of great significance for the interpretation of the fossil assemblages. Since the few fossil specimens in Europe date from very different glacial periods in the Elsterian, Saalian Complex and Weichselian, it can be concluded that V. pseudosubstriata apparently immigrated in at least three distinct waves. Most of the Pleistocene specimens in eastern Central Europe and Eastern Europe are reported from archaeological sites of the Upper Middle Weichselian (Gravettian), roughly between 33 and 29 ka cal
bp. In this paper, we review all reported modern and fossil occurrences and discuss the species' ecological range.