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21.
Intra-City Variation in Urban Morphology and Turbulence Structure in Helsinki, Finland 总被引：3，自引：3，他引：0
Annika Nordbo Leena Järvi Sami Haapanala Joonas Moilanen Timo Vesala 《Boundary-Layer Meteorology》2013,146(3):469-496
Most atmospheric boundary-layer theories are developed over vegetative surfaces and their applicability at urban sites is questionable. Here, we study the intra-city variation of turbulence characteristics and the applicability of boundary-layer theory using building-morphology data across Helsinki, and eddy-covariance data from three sites: two in central Helsinki (400 m apart) and one 4 km away from the city centre. The multi-site measurements enable the analysis of the horizontal scales at which quantities that characterize turbulent transport vary: (i) Roughness characteristics vary at a 10-m scale, and morphometric estimation of surface-roughness characteristics is shown to perform better than the often used rule-of-thumb estimates (average departures from the logarithmic wind profile are 14 and 44 %, respectively). (ii) The drag coefficient varies at a 100-m scale, and we provide an updated parametrization of the drag coefficient as a function of z/z H (the ratio of the measurement height to the mean building height). (iii) The transport efficiency of heat, water vapour and CO2 is shown to be weaker the more heterogeneous the site is, in terms of sources and sinks, and strong scalar dissimilarity is observed at all sites. (iv) Atmospheric stability varies markedly even within 4 km across the city: the median difference in nocturnal sensible heat fluxes between the three sites was over 50W m?2. Furthermore, (v) normalized power spectra and cospectra do not vary between sites, and they follow roughly the canonical theory as developed over vegetated terrain. 相似文献
22.
Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools 
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下载免费PDF全文 Annika S. Fjordbøge Gry S. Janniche Torben H. Jørgensen Bernt Grosen Gary Wealthall Anders G. Christensen Henriette Kerrn‐Jespersen Mette M. Broholm 《Ground Water Monitoring & Remediation》2017,37(3):45-61
Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30‐ to 50‐year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple‐lines‐of‐evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (S t > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m. 相似文献
23.
Incorporating landscape depression heterogeneity into the Soil and Water Assessment Tool (SWAT) using a probability distribution 下载免费PDF全文
下载免费PDF全文 Modelling the hydrology of North American Prairie watersheds is complicated because of the existence of numerous landscape depressions that vary in storage capacity. The Soil and Water Assessment Tool (SWAT) is a widely applied model for long‐term hydrological simulations in watersheds dominated by agricultural land uses. However, several studies show that the SWAT model has had limited success in handling prairie watersheds. In past works using SWAT, landscape depression storage heterogeneity has largely been neglected or lumped. In this study, a probability distributed model of depression storage is introduced into the SWAT model to better handle landscape storage heterogeneity. The work utilizes a probability density function to describe the spatial heterogeneity of the landscape depression storages that was developed from topographic characteristics. The integrated SWAT–PDLD model is tested using datasets for two prairie depression dominated watersheds in Canada: the Moose Jaw River watershed, Saskatchewan; and the Assiniboine River watershed, Saskatchewan. Simulation results were compared to observed streamflow using graphical and multiple statistical criterions. Representation of landscape depressions within SWAT using a probability distribution (SWAT–PDLD) provides improved estimations of streamflow for large prairie watersheds in comparison to results using a lumped, single storage approach. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
24.
Aguasanta M. Sarmiento Manuel A. Caraballo Daniel Sanchez-Rodas José Miguel Nieto Annika Parviainen 《Applied Geochemistry》2012
Intensive mining has taken place in the Iberian Pyrite Belt since 3000 B.C. generating Acid Mine Drainage (AMD) and releasing high amounts of SO4, acidity, metals and metalloids into surface water. Concentrations of elements in AMD-impacted waters are regulated by the precipitation of Fe-rich materials and particulate matter can influence the mobility and the bioavailability of metals. In this paper a study on the dissolved As species concentration along a polluted stream has been performed. Two sampling campaigns were conducted during the dry and the rainy seasons. Concentrations of dissolved elements are higher during the dry season and increase progressively along the water course in both seasons. Concentrations up to 80 μg L−1 of As3+ and 5 mg L−1 of As5+ were determined. The concentration of As species increases and the As3+/As5+ ratio decreases downstream. The Fe2+/Fe3+ and As3+/As5+ ratios show the same pattern with respect to pH for all the examined samples, except those taken from Au cyanidation wastes. The particulate phase is mainly composed of Fe, As and Pb, with As being associated with the Fe minerals while Pb seems to be associated with the clay colloids. 相似文献
25.
With growing urbanization, an increasing number of landslides worldwide are linked to construction works, especially along transportation routes. To get a better understanding of these post-construction landslides at artificial waterways, archive studies have been conducted, in addition to analysis of historical scientific literature and technical reports. The resultant database is used to describe the occurrence and the characteristics of the landslides at the Mittelland Canal, and to evaluate aspects of conditioning and preparatory factors, potential triggers and applied mitigation measures. The Mittelland Canal has been chosen because it is one of the most important artificial waterways in Europe, and the high number of landslides that occur there is unique. In particular, landslides at the Mittelland Canal were frequently reported in the first half of the 20th century. The susceptibility to landslides is strongly influenced by material characteristics, as a large number of landslides is linked to sites where fine-grained mudstone is abundant, which quickly decomposes under immersion in water or under dynamic stress. In addition, landslides can be linked to the creation of over-steepened slopes. Construction works can also be considered another preparatory factor for landslides. In addition, some landslides in World War II appear to be connected to the blast of aerial bombings. Precipitation seems to play a minor role in triggering landslides. The applied mitigation measures were developed recently, marking the importance of the canal as a transportation route. © 2020 John Wiley & Sons, Ltd. 相似文献
26.
Don A. Driscoll Adam Felton Philip Gibbons Annika M. Felton Nicola T. Munro David B. Lindenmayer 《Climatic change》2012,111(3-4):533-557
There are three key drivers of the biodiversity crisis: (1) the well known existing threats to biodiversity such as habitat loss, invasive pest species and resource exploitation; (2) direct effects of climate-change, such as on coastal and high elevation communities and coral reefs; and (3) the interaction between existing threats and climate-change. The third driver is set to accelerate the biodiversity crisis beyond the impacts of the first and second drivers in isolation. In this review we assess these interactions, and suggest the policy and management responses that are needed to minimise their impacts. Renewed management and policy action that address known threats to biodiversity could substantially diminish the impacts of future climate-change. An appropriate response to climate-change will include a reduction of land clearing, increased habitat restoration using indigenous species, a reduction in the number of exotic species transported between continents or between major regions of endemism, and a reduction in the unsustainable use of natural resources. Achieving these measures requires substantial reform of international, national and regional policy, and the development of new or more effective alliances between scientists, government agencies, non-government organisations and land managers. Furthermore, new management practices and policy are needed that consider shifts in the geographic range of species, and that are responsive to new information acquired from improved research and monitoring programs. The interactions of climate-change with existing threats to biodiversity have the potential to drive many species to extinction, but there is much that can be done now to reduce this risk. 相似文献
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David A. Jay Philip M. Orton Thomas Chisholm Douglas J. Wilson Annika M. V. Fain 《Estuaries and Coasts》2007,30(6):1106-1125
Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities
in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly
advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects
of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability
of scaling parameters and the response of ETM phenomena to a range of river flow (U
r
) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current
amplitude (UT), represented by low values of the Supply number Sr.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to
deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly,
scaling variables and data are combined to express ETM properties in terms of the friction velocity (U*),U
r
, andU
T
, allowing a considerable simplification of the parameters used to describe ETM. 相似文献
30.
Desens Annika Houben Georg Sültenfuß Jürgen Post Vincent Massmann Gudrun 《Hydrogeology Journal》2023,31(3):621-640
The travel time of groundwater plays a major role in the understanding of hydrogeological systems; however, large data sets necessary for regional studies of groundwater age are rare. In this study, a unique large data set of groundwater samples analysed for tritium and helium isotopes collected over the last 20 years from Cenozoic aquifers of the North German Plain is explored. Hereby, the variety of natural and technical influences on the tritium-helium age, including screen depth and length, groundwater recharge rate and climatic effects, are investigated. To a sampling depth of ~40 m below ground level, the median tritium-helium age increases almost linearly with depth, reaching a maximum of 40 years. Below, the portion of older, tritium-free water rises. The tritium-helium ages of the tritium-bearing portion increase only slightly to a maximum of about 46 years. The depth distribution of the tritium-helium age shows a dependency on groundwater recharge rates. Considering the same depth level, younger ages are related to higher groundwater recharge rates as compared to groundwater that infiltrated in areas with lower recharge rates. This is especially observed for shallow depths. Tritium-helium ages younger than 40 years are reflected well in the atmospheric tritium input curves, while deviations from it can be related to anthropogenic influences such as input from nuclear power plants and irrigation with deep, tritium-poor groundwater. The regional distribution for shallow wells indicates increasing tritium-helium ages from west to east, corresponding to decreasing groundwater recharge rates due to the more continental climate in the east.
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