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Ojala Antti E. K. Virtasalo Joonas J. Lindsberg Elina Markovaara-Koivisto Mira 《Geotechnical and Geological Engineering》2021,39(7):4855-4876
Geotechnical and Geological Engineering - Understanding the local stratigraphy and geometry of sediment units is necessary for successful 3D modelling and the prediction of ground behaviour and... 相似文献
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To be able to understand year-round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross-sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice-covered flow with a hydrodynamic two-dimensional (2D) model in a meandering subarctic river (Pulmanki River, Finland) in mid-winter conditions and compare them to the pre-winter open-channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect (1) how ice-covered mid-winter flow characteristics vary spatially and (2) the erosion and sedimentation potential of the ice-covered flow compared to open-channel conditions. The 2D hydrodynamic model replicated the observed flow characteristics in both open-channel and ice-covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid-winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depended on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open-channel conditions than during ice-covered flow. The results indicate spatially extensive sediment transport in open-channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice-covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open-channel conditions and are prone to deposition in winter. The long ice-covered season can greatly affect the annual morphology of the submerged channel. © 2019 John Wiley & Sons, Ltd. 相似文献
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Elina Ahokangas Joni Mäkinen 《Boreas: An International Journal of Quaternary Research》2014,43(1):90-106
We provide evidence for the subglacial to ice‐marginal successive deposition of the Lohtaja?Kivijärvi ice lobe margin esker influenced by the changes in the meltwater delivery and proglacial water depth within the Finnish Lake District lobe trunk during the last deglaciation in Finland. The study is mostly based on the sedimentological data from the 100 km long esker chain with 15 logged sites. The long breaks in the lobe margin esker and the re‐emerged deposition along the stable position of the subglacial meltwater route were related to the discontinuities and reappearances of the neighbouring eskers. This considerable variability in the meltwater discharge and debris transport under the described deglacial conditions cannot be explained by markedly decreased meltwater production due to palaeoclimatic factors or lack of debris within the trunk region. The primary control on the changes in meltwater availability and related esker deposition was thus due to the spatial and temporal changes in ice mass properties and shifting of the meltwater flow paths within the trunk. These changes were initiated by the topographically higher and partly supra‐aquatic Suomenselkä watershed area with subsequent deepening of the proglacial water during the deglaciation. The understanding of the long‐lived esker deposition along the former ice‐stream trunk margin adds to the evaluation of palaeoglaciological reconstructions and geomorphologically based spatial models for ice‐stream landscapes. 相似文献
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ABSTRACT Changes in growing season length (GSL) are of concern for agricultural, phenological, economic, epidemiological, and bioclimatological reasons. This research identifies spatial and temporal changes over the last several decades in GSL, along with the day-of-year of the last spring freeze and first autumn freeze, for the northeastern United States – a region particularly susceptible to such changes due to the large population and intense economic activities. Results suggest that growing season has significantly increased in length since 1980 as compared to prior to 1980, and both spatial and temporal variation in GSL has decreased for the region over time. Changes to GSL for this region are driven more by a shift in the first autumn freeze date than the last spring freeze date. The areas of greatest increase in GSL in the pre- vs. post-1980 period tend to be in the high elevations, near large water bodies, and near the largest cities. Results will assist environmental planners as they prepare mitigation and adaptation strategies amid a changing environment. 相似文献
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Elina Kasvi Matti Vaaja Petteri Alho Hannu Hyyppä Juha Hyyppä Harri Kaartinen Antero Kukko 《地球表面变化过程与地形》2013,38(6):577-590
This study investigates the impact of flow structure of different discharges on meander point bar morphology. We carried out mobile and terrestrial laser scanning campaigns before and after a flood on two sandy‐bed point bars. Between the scans, the flow structure was examined using an Acoustic Doppler Current Profiler at three flow stages. The results indicated that a meander point bar both affects and in turn, is itself modified by the flow at different discharges. The lower flow stages also have a significant effect on point bar morphology, especially on deposition over the bar head. Secondary circulation is responsible for scroll bar formation on the point bar margin beyond the apex. Flow separation at the inner bank, by contrast, does not require secondary circulation, but is dependent on flow depth over the point bar. A sudden increase in depth beyond the point bar top causes decreased stream power over the bar tail. The flow separation and decreased stream power cause a slow flow zone and net deposition over point bar tail. The backwater effect, if evident, may strengthen the process. Thus, filling over the bar tail seems generic for point bars and independent on secondary flow. Chutes and chute bars, scroll bars, bar head filling and bar platform filling, by contrast, require special fluvio‐morphological circumstances discussed in this paper. Whilst this paper confirms that the three‐dimensional flow structure has a major effect on point bar morphology, the flow structure seems to depend on how the point bar affects the flow trajectory which, in turn, depends upon the flow stage. Finally, the shape of the bend and the grain size distribution control the impacts of the flow structure, leading to divergent morphologies of point bars with certain generic features. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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This paper evaluates the concentration of Polyaromatic hydrocarbons - PAHs in the Estuarine area of the Patos Lagoon, more precisely in a local named "Saco do Laranjal" in Pelotas City (southern Brazil). The samples were collected in May 2008. The concentrations of 16 US-EPA priority polycyclic aromatic hydrocarbons (PAHs) were determined by gas chromatography with a mass spectrometry detector (GC/MS). The sum of PAHs concentration ranged from 7.3 to 92.8μgkg(-1) in dry weight. The positive correlation (Pearson test) between the total organic material (TOM) and the total PAH concentration (0.98) suggests that TOM plays an important role in controlling the PAHs levels in the sediments. According to the observed ratios of individual PAHs, the contamination in the studied area is originated, predominantly pyrolytic sources. The values found are considered under normal levels and indicates a not impacted area. 相似文献
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Ocean Dynamics - We studied the water age and transport of passive tracers in the Archipelago Sea, Baltic Sea, using the COHERENS 3D hydrodynamic model and the OpenDrift Lagrangian particle model.... 相似文献
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Robert Barouki Manolis Kogevinas Karine Audouze Kristine Belesova Ake Bergman Linda Birnbaum Sandra Boekhold Sebastien Denys Celine Desseille Elina Drakvik Howard Frumkin Jeanne Garric Delphine Destoumieux-Garzon Andrew Haines Anke Huss Genon Jensen Spyros Karakitsios Jana Klanova Paolo Vineis 《Chemie der Erde / Geochemistry》2012
The outbreak of COVID-19 raised numerous questions on the interactions between the occurrence of new infections, the environment, climate and health. The European Union requested the H2020 HERA project which aims at setting priorities in research on environment, climate and health, to identify relevant research needs regarding Covid-19. The emergence and spread of SARS-CoV-2 appears to be related to urbanization, habitat destruction, live animal trade, intensive livestock farming and global travel. The contribution of climate and air pollution requires additional studies. Importantly, the severity of COVID-19 depends on the interactions between the viral infection, ageing and chronic diseases such as metabolic, respiratory and cardiovascular diseases and obesity which are themselves influenced by environmental stressors. The mechanisms of these interactions deserve additional scrutiny. Both the pandemic and the social response to the disease have elicited an array of behavioural and societal changes that may remain long after the pandemic and that may have long term health effects including on mental health. Recovery plans are currently being discussed or implemented and the environmental and health impacts of those plans are not clearly foreseen. Clearly, COVID-19 will have a long-lasting impact on the environmental health field and will open new research perspectives and policy needs. 相似文献
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Archaeomagnetism in Greece has continuously developed during the last decades. Numerous studies have provided high quality data and accurate secular variation curves for the direction and intensity of the geomagnetic field have been constructed. The Greek Secular Variation Curves (SVCs) cover the last 8 millennia for intensity and 6 millennia for direction. The coverage of the archaeological periods remains uneven, with several gaps, mostly in the directional dataset, with only two results for periods older than 2500 B.C. In the present contribution, the first archaeomagnetic results from Neolithic settlements in northern Greece are presented. For the present study, samples were collected from three different archaeological sites: burnt structures in Avgi (Kastoria) and Vasili (Farsala) and one oven from Sosandra (Aridaia). The natural remanent magnetization (NRM) grouping of all specimens indicated that the majority of the samples were burnt in situ, providing thus a reliable direction of the ancient field. Magnetic cleaning (both alternating-field and thermal) revealed the presence of one stable component of magnetisation. Rock magnetic experiments (acquisition of isothermal remanent magnetization (IRM), thermal demagnetisation of the IRM, thermomagnetic curves) have been performed on pilot samples indicating that low coercivity magnetic minerals such as magnetite or Timagnetite are prevailing. The mean directions (declination D, inclination I and parameters of the Fisherian statistics), which arose from the three sites are as follows: Sosandra: D = 343°, I = 55.6°, ??95 = 4.8°; Avgi: D = 10.1°, I = 53.4°, ??95 = 4.2° and Vasili: D = 357.5°, I = 43.1°, ??95 = 4.1°. The obtained data are in a very good agreement with results from Neolithic Bulgaria. This study represents the beginning of an effort to fill the gaps of the Greek secular variation curves and their extension to the Neolithic period. 相似文献