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排序方式: 共有111条查询结果,搜索用时 15 毫秒
81.
Colin G. Jones Ulrika Willén Anders Ullerstig Ulf Hansson 《Ambio-人类环境杂志》2004,33(4):180-190
描述了罗斯比中心区域气候模型(RCA2)并依据观测评估了其对整个欧洲当前气候的模拟结果.指出了模型平均气候和气候变率中的系统偏差,确定了关键参数化的缺欠.对一些近地面参数,尤其是温度、降水、地表能量收支和云量进行了较为详细的研究.模型模拟的最近的气候和变率与真实情况高度吻合.强调了地表辐射收支分量的补偿误差,这些偏差的基本原因追溯到云、降水和辐射参数化的相关方面.模型有过于频繁产生小量级降水的倾向,这直接影响到云-辐射相互作用和地表温度的模拟.在评估由分析的边界条件驱动的高分辨率RCM时,对观测结果的使用要非常小心.当考虑到降水和云量时更是如此,因为观测的不确定性经常大于RCM的偏差. 相似文献
82.
Andreas Westergaard-Nielsen Magnus Lund Stine Højlund Pedersen Niels Martin Schmidt Stephen Klosterman Jakob Abermann Birger Ulf Hansen 《Ambio》2017,46(1):39-52
Climate-induced changes in vegetation phenology at northern latitudes are still poorly understood. Continued monitoring and research are therefore needed to improve the understanding of abiotic drivers. Here we used 14 years of time lapse imagery and climate data from high-Arctic Northeast Greenland to assess the seasonal response of a dwarf shrub heath, grassland, and fen, to inter-annual variation in snow-cover, soil moisture, and air and soil temperatures. A late snow melt and start of growing season is counterbalanced by a fast greenup and a tendency to higher peak greenness values. Snow water equivalents and soil moisture explained up to 77 % of growing season duration and senescence phase, highlighting that water availability is a prominent driver in the heath site, rather than temperatures. We found a significant advance in the start of spring by 10 days and in the end of fall by 11 days, resulting in an unchanged growing season length. Vegetation greenness, derived from the imagery, was correlated to primary productivity, showing that the imagery holds valuable information on vegetation productivity. 相似文献
83.
The aims of this study were to investigate spatial patterns and temporal changes in understorey vegetation at four forest catchments forming a depositional gradient. Inventories of the bottom and field layers were carried out in the 1990s and repeated after 5-14 years, depending on catchment. It was hypothesized that changes and patterns in ground vegetation would be related to changes and patterns in N and S deposition. The data were analyzed using Ellenberg indices and multivariate methods. All catchments showed temporal changes in species composition. Analyses of the bottom layer were confounded by a change of field staff, but after accounting for this observer effect, differences in species composition between the catchments remained. Within catchments, the changes in species composition were unrelated to N or S deposition. Relationships between environmental factors, expressed as Ellenberg indices, and compositional patterns differed between catchments although Ellenberg indices showed small temporal changes. 相似文献
84.
Maik Bergmann Ulf Kirchner Rainer Vogt Thorsten Benter 《Atmospheric environment (Oxford, England : 1994)》2009,43(11):1908-1916
Modern diesel particulate filter (DPF) systems are very effective in reducing particle emissions from diesel vehicles. In this work low-level particulate matter (PM) emissions from a DPF equipped EURO-4 diesel vehicle were studied in the emission test laboratory as well as during real-world chasing on a high-speed test track. Size and time resolved data obtained from an engine exhaust particle sizer (EEPS) and a condensation particle counter (CPC) are presented for both loaded and unloaded DPF condition. The corresponding time and size resolved emission factors were calculated for acceleration, deceleration, steady state driving and during DPF regeneration, and are compared with each other. In addition, the DPF efficiency of the tested vehicle was evaluated during the New European Driving Cycle (NEDC) by real time pre-/post-DPF measurements and was found to be 99.5% with respect to PM number concentration and 99.3% for PM mass, respectively. PM concentrations, which were measured at a distance of about 10 m behind the test car, ranged from 1 to 1.5 times background level when the vehicle was driven on the test track under normal acceleration conditions or at constant speeds below 100 kmh?1. Only during higher speeds and full load accelerations concentrations above 3 times background level could be observed. The corresponding tests in the emission laboratory confirmed these results. During DPF regeneration the total PM number emission of nucleation mode particles was 3–4 orders of magnitude higher compared to those emitted at the same speed without regeneration, while the level of the accumulation mode particles remained about the same. The majority of the particles emitted during DPF regeneration was found to be volatile, and is suggested to originate from accumulated sulfur compounds. 相似文献
85.
Efrem Garedew Mats Sandewall Ulf Söderberg Bruce M. Campbell 《Environmental management》2009,44(4):683-694
Understanding the complexity of land-use and land-cover (LULC) changes and their driving forces and impacts on human and environmental
security is important for the planning of natural resource management and associated decision making. This study combines
and compares participatory field point sampling (pfps) and remote sensing to explore local LULC dynamics. The study was conducted
in two peasant associations located in the central Ethiopian Rift Valley, which is a dry-land mixed farming area exposed to
rapid deforestation. From 1973–2006, the area of cropland doubled at the expense of woodland and wooded-grassland in both
of the study sites. Major deforestation and forest degradation took place from 1973–1986; woodland cover declined from 40%
to 9% in one of the study sites, while the other lost all of its original 54% woodland cover. Our study concludes that assessing
LULC dynamics using a combination of remote sensing and pfps is a valuable approach. The two methods revealed similar LULC
trends, while the pfps provided additional details on how farmers view the changes. This study documents dramatic trends in
LULC over time, associated with rapid population growth, recurrent drought, rainfall variability and declining crop productivity.
The alarming nature of these trends is reflected in a decrease in the livelihood security of local communities and in environmental
degradation. Given these dry-land conditions, there are few opportunities to improve livelihoods and environmental security
without external support. If negative changes are to be halted, action must be taken, including building asset bases, instituting
family planning services, and creating opportunities outside these marginal environments. 相似文献
86.
Marine protected areas (MPAs) have become a key component of conservation and fisheries management to alleviate anthropogenic pressures. For MPA networks to efficiently promote persistence and recovery of populations, ecological connectivity, i.e. dispersal and movement of organisms and material across ecosystems, needs to be taken into account. To improve the ecological coherence of MPA networks, there is hence a need to evaluate the connectivity of species spreading through active migration and passive dispersal. We reviewed knowledge on ecological connectivity in the Baltic Sea, Kattegat and Skagerrak in the northeast Atlantic and present available information on species-specific dispersal and migration distances. Studies on genetic connectivity are summarised and discussed in relation to dispersal-based analyses. Threats to ecological connectivity, limiting dispersal of populations and lowering the resilience to environmental change, were examined. Additionally, a review of studies evaluating the ecological coherence of MPA networks in the Baltic Sea, Kattegat and Skagerrak was performed, and suggestions for future evaluations to meet management needs are presented.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01684-x. 相似文献
87.
Ambio - Improving water clarity is a core objective for eutrophication management in the Baltic Sea, but may influence fisheries via effects on fish habitat suitability. We apply an ensemble of... 相似文献
88.
The development of three pikeperch (Sander lucioperca (L.)) populations in the northern Baltic Sea was monitored using standardized multimesh gillnets in 1995–2009. Declining trends in the abundances of pikeperch over 40 cm total length, low numbers of individuals older than 6 years, and high mortality rates were observed in all three populations. In the site with the largest commercial catches per unit area and a rapidly increased colony of great cormorants (Phalacrocorax carbo sinensis Blumenbach 1798), also the abundance of pikeperch below 40 cm total length and year-class strength showed declining trends. The adverse population level changes did not correlate with changes in water quality or eutrophication status. Together, the results suggest that in all study sites fisheries are harvesting a large proportion of the pikeperch soon after or even before reaching the maturity, and that predation from great cormorants may increase mortality of juveniles. Pikeperch is important not only for fisheries but also for ecosystem functioning, and our results point at the need for further management measures to ensure viable populations in the areas studied.
Electronic supplementary material
The online version of this article (doi:10.1007/s13280-013-0429-z) contains supplementary material, which is available to authorized users. 相似文献89.
Psychological and physiological stress responses of 36 male and 29 female assembly workers were examined during and after work at a car engine factory. Two different ways of organizing assembly work were compared, (1) a more traditional assembly line with fixed work stations organized as a chain and involving short repetitive work cycles and, (2) a new and more flexible work organization with small autonomous groups having greater opportunities to influence the pace and content of their work. Each worker was examined during and after a normal day at work on 2 consecutive days and, in order to obtain endocrine baseline data, during a corresponding work‐free period at home. As expected, both female and male workers in the flexible organization reported significantly more variation, independence and abilities to learn new skills at work. Workers in both forms of work organization showed a significant increase in urinary epinephrine and norepinephrine during work compared to the work‐free day at home. Males had significantly higher epinephrine and systolic blood pressure levels than females. Successive self‐reports of tiredness increased significantly more at the assembly line compared to the flexible work organization. In keeping with this, systolic blood pressure, heart rate and epinephrine increased significantly during the work shift at the assembly line but not during work in the flexible organization. Catecholamine levels revealed that the subjects were able to unwind more rapidly after work in the flexible organization. This pattern was particularly pronounced for the female workers. In summary, the various stress indicators support the notion that the flexible work organization induces less stress than the assembly line and that the female workers were able to benefit most from this new form of work organization. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
90.
Clay minerals show a variety of reactive properties, which make them used in industrial processes but are mostly neglected in soil science. In this overview these various properties of clay minerals are listed. Thereby it shall be pointed out, that these capabilities can also be of some importance in soils. 相似文献