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Pilleriine Kamenjuk Anto Aasa Jaanus Sellin 《International journal of geographical information science》2017,31(7):1425-1447
Similar to every process involving quantitative research, the study of migration heavily depends on the data available for analysis. The available movement data limit the type of questions that can be asked, and as a result, certain aspects of human spatial mobility have yet to be examined. The development of information and communication technologies and their widespread adoption offers new datasets, methods and interpretations that make it possible to study social processes at a new level. For example, mobile positioning data can aid in overcoming certain constraints embedded in traditional data sources (such as censuses or questionnaires) for study of the connections between daily mobility and change of residence. This study presents a framework for mapping changes of residence using data from passive mobile positioning and an anchor point model to better understand the limits of these methods and their contribution to understanding long-term mobility. The study concludes that the most important considerations in monitoring change of residence using passive mobile position data include the continuity of the time-series data, the varying structure of the mobile tower network and the diversified nature of human mobility. The fine spatial and temporal granularities of passive mobile positioning data allow us to study human movement at a detailed scale. 相似文献
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Jaanus Terasmaa Liisa Puusepp Agáta Marzecová Egert Vandel Tiit Vaasma Tiiu Koff 《Journal of Paleolimnology》2013,49(4):663-678
This study uses the Holocene lake sediment of Lake ?ū?i (Latvia, Vidzeme Heights) for environmental reconstruction with multi-proxy records including lithology, computerised axial tomography scan, grain-size analysis, geochemistry, diatoms and macrofossils, supported by AMS radiocarbon dating. Numerical analyses (PCA; CONISS) reveal three main phases in the development of the lake. Response to the Lateglacial–Holocene transition in Lake ?ū?i took place around 11,300 cal. BP. Organogenic sedimentation started with distinctive 5-cm-thick peat layer and was followed by lacustrine sedimentation of carbonaceous gyttja. Several findings of the peat layer with similar dated age and position at different absolute altitudes indicate that lake basin was formed by glaciokarstic processes. In the Early Holocene (until around 8,500 cal. BP), the lake was shallow and holomictic, surrounded by unstable catchment with erosion and inflow events. Predominance of diatom species of Cyclotella and Tabellaria, large numbers of respiratory horns of phantom midge pupae (Chaoboridae), high Fe/Mn ratio, as well as the presence of laminated sediments indicates the transition to a dimictic and oligo-mesotrophic lake conditions with high water level, anoxia in the near-bottom and stable catchment in the Middle Holocene (8,500–2,000 cal. BP). This contrasts with many hydrologically sensitive lakes in Northern and Eastern Europe in which the water level fell several meters during this period. During the Late Holocene (from 2,000 cal. BP to the present), the lithological and biotic variables reveal major changes, such as the increase in erosion (coarser grain-size fraction) and eutrophication [diatoms Aulacoseira ambigua (Grun.) Sim., Stephanodiscus spp., Cyclostephanos dubius (Fricke) Round]. Characteristics of lake-catchment system during the Late Holocene reflect anthropogenic signal superimposed on the natural forcing factors. To date, the Late Quaternary palaeolimnological reconstructions using lake sediment has been limited in the Baltic region. Therefore, findings from Lake ?ū?i provide important information about environmental and climatic changes that took place in this part of Eastern Europe. This study shows that the relative importance of climate and local factors has varied over the time and it is essential to consider the lake basin topography, catchment size and land cover as potential dominant forcing factors for changes in sedimentary signal. 相似文献
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To describe and analyse the role of sediments in the matter cycling in large shallow transboundary Lake Peipsi (L. Peipsi)
in north-eastern Europe, detailed surface-sediment mapping was conducted. On the basis of grain size the surface sediments
fall into three groups: coarse-grained sediments (prevailingly sands in the lake’s southern part), fine-grained sediments
(mainly silts) and silty sands, both in the central deeper part within the 8-m depth contour. The groups of deposits have
a distinct spatial distribution, determined mainly by the current system in the lake. The main source of bottom sediments
is the erosion of the lake floor and shores, the role of the river input seems to be limited. Fine-grained organic-rich sediments
are very cohesive, playing the main role in the circulation of various inorganic and organic pollutants like nutrients and
xenobiotics. Due to the cohesive character of the sediments their physical and chemical properties are extremely diverse and
if the near-bottom shear stress increases (extreme meteorological events, changes in the water level, etc.), the lake floor
may be subjected to episodic erosion and resuspension, which may cause remobilisation of impurities in muddy sediments and
their return to the food chain. 相似文献
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