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981.
The Pentland Firth, located between the north coast of mainland Scotland (UK) and the Orkney Islands, is recognised as an excellent location for the utilisation of tidal stream technology. Potential ecological impacts associated with tidal stream technology may ultimately depend on device design, array size and deployment location. Available ecological data for the Pentland Firth is summarised and strategic priorities for assessing ecological impacts are provided. Baseline data on marine species and habitats in the Pentland Firth is severely lacking and consequently the integrity of any environmental impact assessment could be compromised by this lack of data. 相似文献
982.
Julian Augley Mark Huxham Teresa F. Fernandes Alastair R. Lyndon 《Journal of Sea Research》2008,60(4):292-296
Previous population estimates of the 0+ plaice (Pleuronectes platessa L.) in the Firth of Forth, east central Scotland, did not take account of the Forth estuary west of the Forth bridges. Previous work found plaice in the estuary grew as fast as, or faster than, the outer firth plaice. It was hypothesised that salinity may affect growth rates of early 0+ plaice. This hypothesis was tested in a laboratory experiment, by exposing juvenile plaice to three different, but naturally — experienced by the juveniles, salinities; 25, 30 and 35. Plaice fed a minimum ration did not grow in length. Mean weight decreased at all three salinities, however, the lowest weight loss was found at the lowest salinity (25) and the highest weight loss was found at the highest salinity (35). The minimum feeding ration was halted and plaice were then fed ad libitum. Consumption rates were not significantly different during the ad libitum feeding, while significant differences in mean weight change were found between the highest and lowest salinities. 相似文献
983.
A combination of archaeological evidence, 14C dates, terrace mapping, heavy metal analysis, grain size analysis and historical maps is used in a detailed analysis of the alluvial history of the River Severn floodplain around Welshpool in mid-Wales, U.K. ‘Welshpool Gravels’ underlie a higher terrace surface up to 6–7 m above the present channel. They form a sequence of gravels at least 30 m in thickness. The upper surface is characterized by a series of braided palaeochannel patterns. These sediments were probably deposited at the end of the last glaciation as outwash, and are contemporaneous with other high, gravelly terrace deposits found in the Severn and other mid-Wales basins. Overlying the Welshpool Gravels on the contemporary floodplain are a variable thickness of finer sediments, the ‘Leighton Silts’. Morphological mapping and dating of two cut-offs to 2850 ± 60 a BP and 1190 ± 70 a BP indicates that a channel pattern similar to the present planform had formed by the mid to late Holocene. From this period, floodplain development has been dominated by a single-thread meandering channel with fine vertical sedimentation and limited lateral gravel accretion. Abandonment of extended lengths of channel formed by an avulsion mechanism is apparent. A combination of historical map data, 14C dates and the analysis for heavy metals in fine sediments, which were washed into the river system during mining, indicates that there has been at least 4 m of sedimentation since the early 17th century, but only in a central belt of varying width. Metal-rich waste, identified in the fine sediments of this zone of ‘Trehelig Silts’, indicates those areas which were most heavily sedimented during the peak of metalliferous mining in the 18th and 19th centuries. Although the near-channel margins appear to be superficially similar to the older floodplain, the spatial and vertical pattern of historic sedimentation is complex, and is not reflected in marked elevation differences. The division of sedimentation periods into these three broad time-spans (Late Quaternary Terraces, Late Holocene alluviation and avulsion, and the historical metal-mining period) shows that an apparently simple planar floodplain is in reality underlain by complex sedimentation units. Floodplain construction has involved the development of inset units, in cut-offs and adjacent to migrating channels, as well as the expected contrasts between in-channel and overbank environments. This has implications both for alluvial sedimentation modelling and for the identification of high-pollution zones on the floodplain. These cannot be predicted on the basis of simple ‘in-channel’ and ‘overbank’ environments given the historically complex evolution. 相似文献
984.
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986.
987.
Transpiration of four different rainforest types in north Queensland, Australia, was determined using the heat pulse technique for periods ranging between 391 and 657 days. Despite the complexity of the natural rainforest systems being studied, the relationship between sample tree size and daily water use was found to be strong, thus providing a robust means by which to scale transpiration from individual trees to the entire forest stand. Transpiration was shown to be dependent on solar radiation and atmospheric demand for moisture with little evidence of limitation by soil moisture supply. Total stand transpiration was controlled by forest characteristics such as stem density, size distribution and sapwood area. Annual transpiration for each of the four sites ranged between 353 mm for cloud forest and 591 mm for montane rainforest. In comparison with the international literature, transpiration from Australian rainforests is low; the reasons for this could be related to a combination of differences in forest structure, climatic conditions, canopy wetness duration and tree physiology. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
988.
Elliot M. Schneiderman Tammo S. Steenhuis Dominique J. Thongs Zachary M. Easton Mark S. Zion Andrew L. Neal Guillermo F. Mendoza M. Todd Walter 《水文研究》2007,21(25):3420-3430
Many water quality models use some form of the curve number (CN) equation developed by the Soil Conservation Service (SCS; U.S. Depart of Agriculture) to predict storm runoff from watersheds based on an infiltration-excess response to rainfall. However, in humid, well-vegetated areas with shallow soils, such as in the northeastern USA, the predominant runoff generating mechanism is saturation-excess on variable source areas (VSAs). We reconceptualized the SCS–CN equation for VSAs, and incorporated it into the General Watershed Loading Function (GWLF) model. The new version of GWLF, named the Variable Source Loading Function (VSLF) model, simulates the watershed runoff response to rainfall using the standard SCS–CN equation, but spatially distributes the runoff response according to a soil wetness index. We spatially validated VSLF runoff predictions and compared VSLF to GWLF for a subwatershed of the New York City Water Supply System. The spatial distribution of runoff from VSLF is more physically realistic than the estimates from GWLF. This has important consequences for water quality modeling, and for the use of models to evaluate and guide watershed management, because correctly predicting the coincidence of runoff generation and pollutant sources is critical to simulating non-point source (NPS) pollution transported by runoff. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
989.
Anton T. Kearsley Giles A. Graham Mark J. Burchell Michael J. Cole Zu Rong Dai Nicholas Teslich John P. Bradley Richard Chater Penelope A. Wozniakiewicz John Spratt Gary Jones 《Meteoritics & planetary science》2007,42(2):191-210
Abstract— The known encounter velocity (6.1 kms?1) and particle incidence angle (perpendicular) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild‐2 fall within a range that allows simulation in laboratory light‐gas gun (LGG) experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminum foil components of the Stardust collector. Buckshot of a wide size, shape, and density range of mineral, glass, polymer, and metal grains, have been fired to impact perpendicularly on samples of Stardust Al 1100 foil, tightly wrapped onto aluminum alloy plate as an analogue of foil on the spacecraft collector. We have not yet been able to produce laboratory impacts by projectiles with weak and porous aggregate structure, as may occur in some cometary dust grains. In this report we present information on crater gross morphology and its dependence on particle size and density, the pre‐existing major‐ and trace‐element composition of the foil, geometrical issues for energy dispersive X‐ray analysis of the impact residues in scanning electron microscopes, and the modification of dust chemical composition during creation of impact craters as revealed by analytical transmission electron microscopy. Together, these observations help to underpin the interpretation of size, density, and composition for particles impacted on the Stardust aluminum foils. 相似文献
990.
Comparisons between snow water equivalent (SWE) and river discharge estimates are important in evaluating the SWE fields and to our understanding of linkages in the freshwater cycle. In this study, we compared SWE drawn from land surface models and remote sensing observations with measured river discharge (Q) across 179 Arctic river basins. Over the period 1988‐2000, basin‐averaged SWE prior to snowmelt explains a relatively small (yet statistically significant) fraction of interannual variability in spring (April–June) Q, as assessed using the coefficient of determination (R2). Averaged across all basins, mean R2s vary from 0·20 to 0·28, with the best agreement noted for SWE drawn from a simulation with the Pan‐Arctic Water Balance Model (PWBM) forced with data from the European Centre for Medium‐Range Weather‐Forecasts (ECMWF) Re‐analysis (ERA‐40). Variability and magnitude in SWE derived from Special Sensor Microwave Imager (SSM/I) data are considerably lower than the variability and magnitude in SWE drawn from the land surface models, and generally poor agreement is noted between SSM/I SWE and spring Q. We find that the SWE versus Q comparisons are no better when alternate temporal integrations–using an estimate of the timing in basin thaw–are used to define pre‐melt SWE and spring Q. Thus, a majority of the variability in spring discharge must arise from factors other than basin snowpack water storage. This study demonstrates how SWE estimated from remote sensing observations, or general circulation models (GCMs), can be evaluated effectively using monthly discharge data or SWE from a hydrological model. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献