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11.
R Kerry Turner Stavros Georgiou Roy Brouwer Ian J Bateman I J Langford 《The Geographical journal》2003,169(2):99-116
This paper develops a decision support system for evaluation of wetland ecosystem management strategy and examines its, so far partial, application in a case study of an important complex coastal wetland known as the Norfolk and Suffolk Broads, in the east of England, UK. Most managed ecosystems are complex and often poorly understood hierarchically organized systems. Capturing the range of relevant impacts on natural and human systems under different management options will be a formidable challenge. Biodiversity has a hierarchical structure which ranges from the ecosystem and landscape level, through the community level and down to the population and genetic level. There is a need to develop methodologies for the practicable detection of ecosystem change, as well as the evaluation of different ecological functions. What is also required is a set of indicators (environmental, social and economic) which facilitate the detection of change in ecosystems suffering stress and shock and highlight possible drivers of the change process. A hierarchical classification of ecological indicators of sustainability would need to take into account existing interactions between different organization levels, from species to ecosystems. Effects of environmental stress are expressed in different ways at different levels of biological organization and effects at one level can be expected to impact other levels, often in unpredictable ways. The management strategy, evaluation methodologies and indicators adopted should also assess on sustainability grounds whether any given management option is supporting, or reducing, the diversity of functions which are providing stakeholders with the welfare benefits they require. 相似文献
12.
Louisiana barrier islands, such as the chain surrounding the southeast region of the state, are experiencing rapid loss of
land area, shoreline erosion, and landward migration due to transgression and in-place drowning, and the landfall of several
major hurricanes in the last decade. Observations of migration rates and overall impacts to these barrier islands are poorly
understood since they do not respond in a traditional way, such as barrier rollover. This paper aims to verify how wave energy
and potential longshore sediment transport trends have influenced the recent evolution of the Chandeleur Islands, by direct
comparison with recent observations of migration and erosion trends. The Chandeleur Islands are characterized by a bidirectional
transport system, with material moving from the central arc to the flanks. The longshore sediment transport along the barrier
islands was calculated after propagation and transformation of waves to breaking (generated using observed winds), and through
the use of a common longshore sediment transport formula. Seasonal variations in wind climate produced changes in the transport
trends and gradients that agree with migration and rotation patterns observed for this barrier island system. Results suggest
that wind dominance produces seasonal oscillations that cause an imbalance in the resulting transport gradients that over
time are responsible for higher rates of transport in the northward direction. These results and data from other works verify
the evolutionary model previously suggested, and qualitatively confirm the recent observations in asymmetric shoreline erosion. 相似文献
13.
P. Stogianidis D. P. Georgiou G. A. Georgantopoulos 《Astrophysics and Space Science》1985,109(2):309-326
the influence of radiation absorption on the flow-field of an unsteady laminar boundary layer due to free convection is considered. The flow is that of an incompressible viscous dissipative and electrically conducting fluid past an infinite vertical porous plate, when the flow is subjected to the action of a transverse magnetic field and the mainstream is oscillating around a mean value and an oscillating suction. The radiation is absorbed by a second material in a small concentration within the fluid and the absorption rate is proportional to the local concentration. The solution of the problem is obtained in the form of power series of Eckert numberE, which is very small for incompressible fluids, analytical expression for the velocity, temperature and the induced magnetic field are given for both the steady and the unsteady flows. The solution is also given in a number of figures that present the combined influence of the absorption withE,G r , and the frequency of oscillation. In addition the influence of the absorption on the skin friction the heat flux is given. The results indicate the importance of the absorption which can be significant under certain conditions. 相似文献
14.
D. P. Georgiou T. V. Pampoucas G. A. Georgantopoulos 《Astrophysics and Space Science》1987,132(1):73-83
The influence of radiation absorption on the free-convection currents on a vertical porous flat plate has been considered. A steady transverse magnetic field has been assumed, while the absorption is the result of the presence of a strong radiation-absorbing second material, in a small concentration within the main fluid. The analytical solution is in terms of the very small Eckert number, which expresses the viscous dissipation term. The solution shows small influence on the general velocity and temperature profile, but a strong one in the skin friction and the heat flux. 相似文献
15.
AbstractThis study focuses on the calibration and validation of a dual-permeability soil water flow model for simulating soil water dynamics during the growing period in an irrigated corn field and during the rainy winter period in an uncropped field in northern Greece. The 1D numerical transient dual-permeability model MACRO 5.0 was used to describe the soil water dynamics, the water balance and deep percolation considering both macropore (two-domain) flow and non-macropore (one-domain) flow. The simulated results were compared with measurements of total soil water content at different depths in the soils. The values of the statistical criteria RMSE, E and CRM were better when macroporosity flow was considered; the soil water content showed better redistribution in the soil profile. The limited irrigation of the corn field during the growing period and the irrigation rates did not create conditions for deep percolation of water. In the uncropped field (bare soil), the wet conditions and the high rainfall during the simulation period created conditions for significant deep percolation, whether macropore flow was included in the model or not. The two-domain approach significantly affects the actual evaporation and the deep percolation. The difference between these two approaches is in the amount of deep percolation and the flow path of drainage flow. In the two-domain approach, most deep percolation follows the macropore domain (79.8%). The errors due to macropore parameter uncertainty and to the difficulties of measuring the macropore water content and flow were estimated by a sensitivity analysis for the more important parameters of the model.Editor Z.W. KundzewiczCitation Antonopoulos, V.Z., Georgiou, P.E., and Kolotouros, C.A., 2013. Soil water dynamics in cropped and uncropped fields in northern Greece using a dual-permeability model. Hydrological Sciences Journal, 58 (8), 1748–1759. 相似文献
16.
The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using 15N‐labelled substrates across a range of Ni levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm 15NH4Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g?1 DW h?1) than the root uptake rate (4.54 ± 0.28 μmol·g?1 DW h?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (Vmax) and the half‐saturation constant (Km) of leaves (9.79 μmol·g?1 DW h?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g?1DW h?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = Vmax/Km) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of 15N incorporated as ammonium was detected between plant parts, whereas the translocation of 15N incorporated as nitrate was higher (40–100%). We conclude that the Ni acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean. 相似文献
17.
Robust classification for the joint velocity‐intermittency structure of turbulent flow over fixed and mobile bedforms 
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下载免费PDF全文 Christopher J. Keylock Arvind Singh Jeremy G. Venditti Efi Foufoula‐Georgiou 《地球表面变化过程与地形》2014,39(13):1717-1728
Two datasets of turbulence velocities collected over different bedform types under contrasting experimental conditions show similarity in terms of velocity‐intermittency characteristics and suggest a universality to the velocity‐intermittency structure for flow over bedforms. One dataset was obtained by sampling flow over static bedforms in different locations, and the other was based on a static position but mobile bedforms. A flow classification based on the velocity‐intermittency behaviour is shown to reveal some differences from that based on an analysis of Reynolds stresses, boundary layer correlation and turbulent kinetic energy. This may be attributed to the intermittency variable, which captures the local effect of individual turbulent flow structures. Locations in the wake region or the outer layer of the flow are both shown to have a velocity‐intermittency behaviour that departs from that for idealized wakes or outer layer flow because of the superposition of localized flow structures generated by bedforms. The combined effect of this yields a velocity‐intermittency structure unique to bedform flow. The use of a time series of a single velocity component highlights the potential power of our approach for field, numerical and laboratory studies. The further validation of the velocity‐intermittency method for non‐idealized flows undertaken here suggests that this technique can be used for flow classification purposes in geomorphology, hydraulics, meteorology and environmental fluid mechanics. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
18.
The influence of the internal heat generation and radiation absorption in the free-convection flow of an incompressible viscous fluid past an impulsively started infinite vertical porous plate is considered. The set of the governing equations is solved by incorporating a finite-difference, algorithm. The influence of the vairous parameters for two fluids (air and water) is discussed with the aid of graphs. 相似文献
19.
D. Sakellariou V. Lykousis S. Alexandri H. Kaberi G. Rousakis P. Nomikou P. Georgiou D. Ballas 《Basin Research》2007,19(2):273-295
Swath bathymetry, single‐channel seismic profiling, gravity and box coring, 210Pb down‐core radiochemical analyses and sequence stratigraphic analysis in the Gulf of Alkyonides yielded new data on the evolution of the easternmost part of the Gulf of Corinth. Three fault segments, the South Strava, West Alkyonides and East Alkyonides faults, dipping 45, 30 and 45°, respectively, northwards, form the southern tectonic boundary of the Alkyonides Basin. Two 45° southwards dipping segments, the Domvrena and Germeno Faults, form the northern tectonic margin. The Alkyonides Basin architecture is the result of a complex interaction between fault dynamics and the effects of changes in climate and sea/lake level. Chrono‐stratigraphic interpretation of the seismic stratigraphy through correlation of the successive seismic packages with lowstands and highstands of the Late Quaternary indicates that the evolution of the basin started 0.40–0.45 Ma BP and can be divided in two stages. Subsidence of the basin floor during the early stage was uniform across the basin and the mean sedimentation rate was 1.0 m kyear?1. Vertical slip acceleration on the southern tectonic margin since 0.13 Ma BP resulted in the present asymmetric character of the basin. Subsidence concentrated close to the southern margin and sedimentation rate increased to 1.4 m kyear?1 in the newly formed depocentre of the basin. Actual (last 100 year) sedimentation rates were calculated to >2 mm year?1, but are significantly influenced by the presence of episodic gravity flow deposits. Total vertical displacement of 1.1 km is estimated between the subsiding Alkyonides Basin floor and the uplifting Megara Basin since the onset of basin subsidence at a mean rate of 2.4–2.75 m kyear?1, recorded on the East Alkyonides Fault. Gravity coring in the Strava Graben and in the lower northern margin of Alkyonides Basin proved the presence of whitish to olive grey laminated mud below thin marine sediments. Aragonite crystals and absence of the marine coccolithophora Emiliania huxleyi indicate sedimentation in lacustrine environment during the last lowstand glacial interval. 相似文献
20.
The European Union (EU) Bathing Water Directive of 1976 ([Commission of the European Communities, 1976. Council Directive of 8th December 1975 Concerning the Quality of Bathing Water (76/160/EEC). Official Journal of the European Community. 5th February 1976, L31/1, Brussels]) sets out standards for designated bathing waters which should be complied with by all member states. Intervening advances in pollution science, related technology and managerial expertise have allowed the European Commission to consider revision of EU environmental legislation where appropriate. As a result, a number of revisions to the 1976 Directive have been proposed ([Commission of the European Communities, 1994. Commission Proposal for a Council Directive Concerning the Quality of Bathing Water. Communication from the Commission to the European Parliament and the Council, COM (94) 36 Final, Brussels; Commission of the European Communities, 2000. Developing a New Bathing Water Policy, Communication from the Commission to the European Parliament and the Council, COM (2000) 860 Final, 21/12/200, Brussels; Commission of the European Communities, 2002. Commission Proposal for a Directive of the European Parliament and of the Council Concerning the Quality of Bathing Water, COM (2002) 581 Final, 24/10/2002, Brussels]). This paper considers these revisions in terms of the economic costs and benefits associated with any change in policy. The focus is on the public's willingness to pay for a revised Directive and the consequent public health benefits afforded to individuals and society. These economic benefits are compared to the costs of implementing changes to bring bathing waters up to the required standard. 相似文献