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排序方式: 共有137条查询结果,搜索用时 15 毫秒
1.
Alan M Bond Julie R Bradbury Henry A Hudson John S Garnham Peter J Hanna Stanley Strother 《Marine Chemistry》1985,16(1):1-9
Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent. 相似文献
2.
Susan S. Hanna 《Ocean & Coastal Management》1995,28(1-3)
Fish populations have the potential to contribute to the long-term economic and social benefit of humans, but to do so they must be managed in ways which maintain ecological health. There are many ways that management performance can be assessed, but four measures are particularly pertinent to sustainability: equity, stewardship, regulatory resilience, and efficiency. A key factor in management performance is the process by which management tools are developed and implemented. One approach that has been recommended to improve performance is to structure the management process around user participation. The paper analyzes three case studies of user participation in ad hoc processes of Pacific groundfish management: the development of a license limitation program; an inter-gear sablefish allocation; and the development of a sablefish individual quota (IQ) program. The case studies illustrate the role played by participation in contributing to the equity, stewardship, resilience, and efficiency of the management process. The effect of user participation was mixed in the three cases, depending on the history of participation, the structure and process of participation, on resource conditions and on the characteristics of the program under consideration. Participation can contribute positively to fishery management performance when there is a history of collective decision-making, the time line is slow enough to allow a full consideration of the issues, educational possibilities are pursued and the condition of the resource allows equitable compromises. 相似文献
3.
Many applied dispersion models require the knowledge of boundary-layer parameters such as sensible heat flux,Q
H
, friction velocity,u
*, and turbulent energy components, w and
v
. Formulas are suggested for calculating these parameters over a wide variety of types of ground surfaces, based on simple observations of wind speed near the ground and fractional cloud cover, and specification of constants such as roughness length, albedo, and soil moisture availability. Observations ofu
*,Q
H
,
w
, and
v
during field experiments in St. Louis and Indianapolis are used to test the formulas for urban sites. Relative errors of about ±20% in the predictions are seen to occur whenu
*,Q
H
,
w
, and
v
are large. However, when these quantities are small (e.g.,u
* < 0.2 m/s), the errors in the predictions are as large as the mean value of the quantity itself.In addition, it is concluded from studies of available field data and theories that the magnitude of
w
is not well-known at elevations above about 100m during the late afternoon and night. Some simple parameterizations for
w
. are suggested that are consistent with the observed steady decrease in ground-level concentration in the afternoon and the sudden increase in concentration that can occur a few hours after sunset due to wind shears associated with a low-level jet, for continuous plumes emitted from moderate to tall stacks. 相似文献
4.
Alar Rosentau Merle Muru Aivar Kriiska Dmitry A. Subetto Jüri Vassiljev Tiit Hang Dmitry Gerasimov Kerkko Nordqvist Anna Ludikova Lembi Lõugas Hanna Raig Kersti Kihno Raivo Aunap Nikolay Letyka 《Boreas: An International Journal of Quaternary Research》2013,42(4):912-931
Based on geological and archaeological proxies from NW Russia and NE Estonia and on GIS‐based modelling, shore displacement during the Stone Age in the Narva‐Luga Klint Bay area in the eastern Gulf of Finland was reconstructed. The reconstructed shore displacement curve displays three regressive phases in the Baltic Sea history, interrupted by the rapid Ancylus Lake and Litorina Sea transgressions c. 10.9–10.2 cal. ka BP and c. 8.5–7.3 cal. ka BP, respectively. During the Ancylus transgression the lake level rose 9 m at an average rate of about 13 mm per year, while during the Litorina transgression the sea level rose 8 m at an average rate of about 7 mm per year. The results show that the highest shoreline of Ancylus Lake at an altitude of 8–17 m a.s.l. was formed c. 10.2 cal. ka BP and that of the Litorina Sea at an altitude of 6–14 m a.s.l., c. 7.3 cal. ka BP. The oldest traces of human activity dated to 8.5–7.9 cal. ka BP are associated with the palaeo‐Narva River in the period of low water level in the Baltic basin at the beginning of the Litorina Sea transgression. The coastal settlement associated with the Litorina Sea lagoon, presently represented by 33 Stone Age sites, developed in the area c. 7.1 cal. ka BP and existed there for more than 2000 years. Transformation from the coastal settlement back to the river settlement indicates a change from a fishing‐and‐hunting economy to farming and animal husbandry c. 4.4 cal. ka BP, coinciding with the time of the overgrowing of the lagoon in the Narva‐Luga Klint Bay area. 相似文献
5.
G. Robbert Biesbroek Rob J. Swart Timothy R. Carter Caroline Cowan Thomas Henrichs Hanna Mela Michael D. Morecroft Daniela Rey 《Global Environmental Change》2010,20(3):440-450
For the last two decades, European climate policy has focused almost exclusively on mitigation of climate change. It was only well after the turn of the century, with impacts of climate change increasingly being observed, that adaptation was added to the policy agenda and EU Member States started to develop National Adaptation Strategies (NASs). This paper reviews seven National Adaptation Strategies that were either formally adopted or under development by Member States at the end of 2008. The strategies are analysed under the following six themes. Firstly, the factors motivating and facilitating the development of a national adaptation strategy. Secondly, the scientific and technical support needed for the development and implementation of such a strategy. Thirdly, the role of the strategy in information, communication and awareness-raising of the adaptation issue. Fourthly, new or existing forms of multi-level governance to implement the proposed actions. Fifthly, how the strategy addresses integration and coordination with other policy domains. Finally, how the strategy suggests the implementation and how the strategy is evaluated. The paper notes that the role of National Adaptation Strategies in the wider governance of adaptation differs between countries but clearly benchmarks a new political commitment to adaptation at national policy levels. However, we also find that in most cases approaches for implementing and evaluating the strategies are yet to be defined. The paper concludes that even though the strategies show great resemblance in terms of topics, methods and approaches, there are many institutional challenges, including multi-level governance and policy integration issues, which can act as considerable barriers in future policy implementation. 相似文献
6.
Parametric cubic splines provide a versatile means of describing and sampling shapes and curves commonly found in geology. These splines allow the researcher to treat easily curves which are not single-valued in Cartesian or polar coordinates. In addition, they simultaneously provide approximations to positions, slopes, and curvatures of the curve being considered. In conjunction with simple digitizing equipment and a small computer, the method of parametric cubic spline approximation allows the researcher to analyze curves or outlines in cases where the more rapid technique involving video imaging equipment is either not applicable or not available. 相似文献
7.
8.
Vinod K. Hanna M. S. Ravichandran S. P. S. Kushwaha 《Journal of the Indian Society of Remote Sensing》2001,29(1-2):41-46
This paper deals with corridor analysis in Rajaji-Corbett Elephant Reserve in the Shivaliks of Uttaranchal state. Efforts were made to detect changes in the state of forest covervis- à -vis the status of corridors during the three periods i.e. 1967. 1986 and 1998 using remote sensing and GIS. TheERDAS Imagine digital image processing andArcView GIS software packages were used for this purpose. Temporal satellite imagery and ground observations in the Rajaji-Corbett Elephant Reserve revealed forest loss, degradation and disturbances in the corridor areas, hindering elephant movement and restricting them to forests islands. Motichur-Chilla corridor, despite being a highly favoured habitat for the elephants was found to be highly threatened followed by Kotdwar and Ramnagar corridors. Construction of wide bridges across Kunao-Chilla Canal, recreation of corridors through reforestation, reduction of all kinds of pressures in the corridor areas and providing higher protection to corridors are recommended. 相似文献
9.
Mark S. T. Bukowinski Philip E. Wannamaker Manfred Koch Yukio Fujinawa Dr. Pradeep Talwani D. Möhlmann Andrew H. Knoll Lucia Lovison-Golob Krzysztof Haman Hanna Pawłowska Henryk Piwkowski Dr. Anthony Dore Nguyen Xuan Huy Edward R. Cook Jan Błecki Jacek Leliwa-Kopystynski Magdalena Sroczynska-Kozuchowska 《Pure and Applied Geophysics》1993,140(1):139-177
10.
A variety of methods devised in the last twelve years for measuring two-dimensional strain ratios have been applied to the same deformed oolitic limestone from southwest Dyfed. Their relative merits are discussed. A graphical method for studying relative locations of marker objects is described and its application to a variety of rocks illustrated. It is shown to have theoretical and practical advantages, while giving values of two-dimensional strain ratios comparable with those of other methods. 相似文献