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排序方式: 共有207条查询结果,搜索用时 218 毫秒
61.
Veltman K Hendriks J Huijbregts M Leonards P van den Heuvel-Greve M Vethaak D 《Marine pollution bulletin》2005,50(10):1085-1102
Food chain accumulation of organochlorines and brominated flame retardants in estuarine and marine environments is compared to model estimations and fresh water field data. The food chain consists of herbivores, detritivores and primary and secondary carnivores i.e. fish, fish-eating birds and marine mammals. Accumulation of polychlorinated biphenyls is predicted well by OMEGA for herbi-detritivores and primary and secondary carnivorous fish. Ratios are similar to those found for fresh water species. Accumulation ratios for fish-eating birds and mammals are overestimated by the model, which is attributed partly to biotransformation of meta-para unsubstituted congeners. Additionally, birds may feed in other less polluted areas. For brominated diphenylethers (BDE) accumulation patterns are highly species and congener specific. Accumulation depends on both K(ow) and metabolization capacities. BDE47 is the predominant congener in lower trophic levels. For marine birds and mammals accumulation ratios of BDE99 and 100 are similar to or higher than ratios of persistent PCBs. 相似文献
62.
Hanna Sofia Sundqvist y Baker Karin Holmgren 《Geografiska Annaler: Series A, Physical Geography》2005,87(4):539-548
Two fast‐growing stalagmites from a cellar vault in Uppsala, southeast Sweden, are analysed for their luminescent properties. The results indicate that variations in luminescence intensity in the stalagmites are annual. Due to problems in finding a suitable absolute dating method this assumption cannot yet be firmly tested; however, results from radiocarbon dating of one of the stalagmites do not contradict the proposal that the laminae are annual. If so, the speleothems have been growing for 10–15 years with a growth rate of 3–8 mm per year, which is a similar rate to other fast‐growing speleothems in Great Britain that have formed from the reaction of lime mortar and carbon dioxide. It is likely that the assumed annual laminae of the luminescence record represent a flush of organic material. 相似文献
63.
Groundwater ‐ the disregarded component in lake water and nutrient budgets. Part 1: effects of groundwater on hydrology 下载免费PDF全文
Lake eutrophication is a large and growing problem in many parts of the world, commonly due to anthropogenic sources of nutrients. Improved quantification of nutrient inputs is required to address this problem, including better determination of exchanges between groundwater and lakes. This first of a two‐part review provides a brief history of the evolution of the study of groundwater exchange with lakes, followed by a listing of the most commonly used methods for quantifying this exchange. Rates of exchange between lakes and groundwater compiled from the literature are statistically summarized for both exfiltration (flow from groundwater to a lake) and infiltration (flow from a lake to groundwater), including per cent contribution of groundwater to lake‐water budgets. Reported rates of exchange between groundwater and lakes span more than five orders of magnitude. Median exfiltration is 0.74 cm/day, and median infiltration is 0.60 cm/day. Exfiltration ranges from near 0% to 94% of input terms in lake‐water budgets, and infiltration ranges from near 0% to 91% of loss terms. Median values for exfiltration and infiltration as percentages of input and loss terms of lake‐water budgets are 25% and 35%, respectively. Quantification of the groundwater term is somewhat method dependent, indicating that calculating the groundwater component with multiple methods can provide a better understanding of the accuracy of estimates. The importance of exfiltration to a lake budget ranges widely for lakes less than about 100 ha in area but generally decreases with increasing lake area, particularly for lakes that exceed 100 ha in area. No such relation is evident for lakes where infiltration occurs, perhaps because of the smaller sample size. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
64.
Shyhrete Shala Karin F. Helmens Tomi P. Luoto Minna Väliranta Jan Weckström J. Sakari Salonen Peter Kuhry 《Journal of Paleolimnology》2014,52(4):311-329
This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry 14C dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies. 相似文献
65.
Karin Bäckstrand 《Global Environmental Change》2011,21(2):275-281
Over the past decade carbon capture and storage (CCS) has attracted increasing international attention as a climate change mitigation option and moved into the center of climate policy debates and negotiations. This special issue of Global Environmental Change brings together leading scholars to analyze the politics, policy and regulation of CCS in cross-country comparisons as well as in a global context. The aim is to contribute on two fronts: first, by applying concepts, theories and methodologies from the social and policy sciences, to elucidate how societies are engaging with CCS as a mitigation option; and secondly, to point toward a future research agenda which, while exploring basic aspects of technology development as situated in a social context, would also be aligned with the needs of the climate and environmental policy community. The contributions address at least one of three inter-related research areas; CCS and the emergence of long-term climate and energy strategies; regulation, policy instruments and public acceptance; and international politics and CCS in developing countries. 相似文献
66.
Karin Sesetyan Can ZulfikarMine Demircioglu Ufuk HancilarYaver Kamer Mustafa Erdik 《Soil Dynamics and Earthquake Engineering》2011
Potential impact of large earthquakes on urban societies can be reduced by timely and correct action after a disastrous earthquake. Modern technology permits measurements of strong ground shaking in near real-time for urban areas exposed to earthquake risk. The Istanbul Earthquake Rapid Response System equipped with 100 instruments and two data processing centers aims at the near real time estimation of earthquake damages using most recently developed methodologies and up-to-date structural and demographic inventories of Istanbul city. The methodology developed for near real time estimation of losses after a major earthquake consists of the following general steps: (1) rapid estimation of the ground motion distribution using the strong ground motion data gathered from the instruments; (2) improvement of the ground motion estimations as earthquake parameters become available and (3) estimation of building damage and casualties based on estimated ground motions and intensities. The present paper elaborates on the ground motion and damage estimation methodologies used by the Istanbul Earthquake Rapid Response System with a special emphasis on validation and verification of the different methods. 相似文献
67.
D. von Schiller V. Acuña D. Graeber E. Martí M. Ribot S. Sabater X. Timoner K. Tockner 《Aquatic Sciences - Research Across Boundaries》2011,73(4):485-497
Temporary streams are a dominant surface water type in the Mediterranean region. As a consequence of their hydrologic regime,
these ecosystems contract and fragment as they dry, and expand after rewetting. Global change leads to a rapid increase in
the extent of temporary streams, and more and more permanent streams are turning temporary. Consequently, there is an urgent
need to better understand the effects of flow intermittency on the biogeochemistry and ecology of stream ecosystems. Our aim
was to investigate how stream nutrient availability varied in relation to ecosystem contraction, fragmentation and expansion
due to hydrologic drying and rewetting. We quantified the temporal and spatial changes in dissolved nitrogen (N) and phosphorus
(P) concentrations along a reach of a temporary Mediterranean forest stream during an entire contraction–fragmentation–expansion
hydrologic cycle. We observed marked temporal changes in N and P concentrations, in the proportion of organic and inorganic
forms as well as in stoichiometric ratios, reflecting shifts in the relative importance of in-stream nutrient processing and
external nutrient sources. In addition, the spatial heterogeneity of N and P concentrations and their ratios increased substantially
with ecosystem fragmentation, reflecting the high relevance of in-stream processes when advective transport was lost. Overall,
changes were more pronounced for N than for P. This study emphasizes the significance of flow intermittency in regulating
stream nutrient availability and its implications for temporary stream management. Moreover, our results point to potential
biogeochemical responses of these ecosystems in more temperate regions under future water scarcity scenarios. 相似文献
68.
A simulation of probabilistic wildfire risk components for the continental United States 总被引:3,自引:1,他引:2
Mark A. Finney Charles W. McHugh Isaac C. Grenfell Karin L. Riley Karen C. Short 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):973-1000
This simulation research was conducted in order to develop a large-fire risk assessment system for the contiguous land area
of the United States. The modeling system was applied to each of 134 Fire Planning Units (FPUs) to estimate burn probabilities
and fire size distributions. To obtain stable estimates of these quantities, fire ignition and growth was simulated for 10,000
to 50,000 “years” of artificial weather. The fire growth simulations, when run repeatedly with different weather and ignition
locations, produce burn probabilities and fire behavior distributions at each landscape location (e.g., number of times a “cell” burns at a given intensity divided by the total years). The artificial weather was generated for
each land unit using (1) a fire danger rating index known as the Energy Release Component (ERC) which is a proxy for fuel
moisture contents, (2) a time-series analysis of ERC to represent daily and seasonal variability, and (3) distributions of
wind speed and direction from weather records. Large fire occurrence was stochastically modeled based on historical relationships
to ERC. The simulations also required spatial data on fuel structure and topography which were acquired from the LANDFIRE
project (). Fire suppression effects were represented by a statistical model that yields a probability of fire containment based on
independent predictors of fire growth rates and fuel type. The simulated burn probabilities were comparable to observed patterns
across the U.S. over the range of four orders of magnitude, generally falling within a factor of 3 or 4 of historical estimates.
Close agreement between simulated and historical fire size distributions suggest that fire sizes are determined by the joint
distributions of spatial opportunities for fire growth (dependent on fuels and ignition location) and the temporal opportunities
produced by conducive weather sequences. The research demonstrates a practical approach to using fire simulations at very
broad scales for purposes of operational planning and perhaps ecological research. 相似文献
69.
We present a simple unifying model that can be used to analyze, within a single framework, different dynamic regimes of shear deformation of brittle, plastic, and granular materials. The basic dynamic regimes seen in the response of both solids and granular materials to slowly increasing loading are scale-invariant behavior with power law statistics, quasi-periodicity of system size events, and persisting long term mode switching between the former two types of response. The model provides universal analytical mean field results on the statistics of failure events in the different regimes and distributed versus localized spatial responses. The results are summarized in a phase diagram spanned by three tuning parameters: dynamic strength change (weakening, neutral or strengthening) during slip events, dissipation of stress transfer (related to the void fraction in granular materials and damaged solids), and the ratio of shear rate over healing rate controlling the regaining of cohesion following failures in brittle solids. The mean field scaling predictions agree with experimental, numerical, and observational data on deformation avalanches of solids, granular materials, and earthquake faults. The model provides additional predictions that should be tested with future observation and simulation data. 相似文献
70.
When performing landslide susceptibility mapping of rotational slides in fine grained soils, slope algorithms found in common GIS software have two major shortcomings. Firstly, these types of terrain algorithms only consider the slope angle at the surface. Secondly, the algorithm is local by its design i.e. it only considers neighbouring pixels. Due to the behaviour of a retrogressive rotational landslide, it would be more preferable to consider slope information as a predetermined cross-section angle from the base of the slope. This paper presents a new method using shadow casting algorithms for preliminary landslide susceptibility mapping in cohesive soils. A case study from western Sweden is also presented. 相似文献