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排序方式: 共有419条查询结果,搜索用时 15 毫秒
161.
I. A. Malcolm C. Soulsby A. F. Youngson D. M. Hannah I. S. McLaren A. Thorne 《水文研究》2004,18(9):1543-1560
The spatial and temporal variability of groundwater–surface‐water (GW–SW) interactions was investigated in an intensively utilized salmon spawning riffle. Hydrochemical tracers, were used along with high‐resolution hydraulic head and temperature data to assess hyporheic dynamics. Surface and subsurface hydrochemistry were monitored at three locations where salmon spawning had been observed in previous years. Temperature and hydraulic head were monitored in three nests of three piezometers located to characterize the head, the run and the tail‐out of the riffle feature. Hydrochemical gradients between surface and subsurface water indicated increasing GW influence with depth into the hyporheic zone. Surface water was characterized by high dissolved oxygen (DO) concentrations, low alkalinity and conductivity. Hyporheic water was generally characterized by high levels of alkalinity and conductivity indicative of longer residence times, and low DO, indicative of reducing conditions. Hydrochemical and temperature gradients varied spatially over the riffle in response to changes in local GW–SW interactions at the depths investigated. Groundwater inputs dominated the head and tail of the riffle. The influence of SW increased in the area of accelerating flow and decreasing water depth through the run of the riffle. Temporal GW–SW interactions also varied in response to changing hydrological conditions. Gross changes in hyporheic hydrochemistry were observed at the weekly scale in response to changing flow conditions and surface water inputs to the hyporheic zone. During low flows, caused by freezing or dry weather, hyporheic hydrochemistry was dominated by GW inputs. During higher flows hyporheic hydrochemistry indicated that SW contributions increased. In addition, high‐resolution hydraulic head data indicated that rapid changes in GW–SW interactions occurred during hydrological events. The spatial, and possibly the temporal, variability of GW–SW interactions had a marked effect on the survival of salmon ova. It is concluded that hyporheic dynamics and their effect on stream ecology should be given increased consideration by fisheries and water resource managers. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
162.
Melissa J. Oxford F. JohnGregory Malcolm B. Hart rew S. Henderson Michael D. Simmons & Matthew P. Watkinson 《地学学报》2002,14(3):205-209
Unequivocal planktonic foraminifera have been discovered in Oxfordian strata from Dorset and Scotland. These assemblages are, in part, coeval with previously reported occurrences of planktonic taxa in the Oxfordian of Normandy and Seine Maritime (France). Three species are now reported from the United Kingdom for the first time: Globuligerina oxfordiana ( Grigelis, 1958 ), Haeuslerina helvetojurassica ( Haeusler, 1881 ) and Compactogerina sp. cf. C. stellapolaris ( Grigelis, 1977 ). There appears to be a close relationship between the distribution of these planktonic taxa in the UK and a marked sea-level highstand. 相似文献
163.
Lisa Kaltenegger Malcolm Fridlund Anders Karlsson 《Astrophysics and Space Science》2006,306(3):147-158
The requirements on space missions designed to study Terrestrial exoplanets are discussed. We then investigate whether the
design of such a mission, specifically the Darwin nulling interferometer, can be carried out in a simplified scenario. The
key element here is accepting somewhat higher levels of stellar leakage. We establish detailed requirements resulting from
the scientific rationale for the mission, and calculate detailed parameters for the stellar suppression required to achieve
those requirements. We do this utilizing the Darwin input catalogue. The dominating noise source for most targets in this
sample is essentially constant for all targets, while the leakage diminishes with the square of the distance. This means that
the stellar leakage has an effect on the integration time only for the nearby stars, while for the more distant targets its
influence decreases significantly. We assess the impact of different array configurations and nulling profiles and identify
the stars for which the detection efficiency can be maximized. 相似文献
164.
Malcolm L. Spaulding Saul B. Saila Ernesto Lorda Henry Walker Eric Anderson J.Craig Swanson 《Estuarine, Coastal and Shelf Science》1983,16(5):511-541
An oil-spill fishery impact assessment model composed of an oil-spill fates model, a shelf hydrodynamics model, an ichthyoplankton transport and fate model, and a fishery population model originally developed by Reed & Spaulding, has been improved and applied to the Georges Bank-Gulf of Maine region to assess the probable impact of oil spills on several key fisheries. The model addresses direct impacts of oil on the commercial fishery through hydrocarbon-induced egg and larval mortality. This early life stage hydrocarbon-induced mortality is estimated by assuming a toxicity threshold approach and by mapping the spatial/temporal interaction between the subsurface oil concentrations caused by the spill and the developing eggs and larvae. Model output is given in terms of differential catch, with a comparison made of hydrocarbon-impacted fisheries.Simulations of tanker and blowout spills at two separate locations for each season of the year in the Outer Continental Shelf lease areas have been completed for Atlantic herring, haddock, and Atlantic cod. Results to date suggest a complex interaction among spill location and timing, the spatial and temporal spawning distribution of the species, and the hydrodynamics of the area. The largest impacts occur for spring and winter spills. 相似文献
165.
Malcolm K. Jenyon 《Marine and Petroleum Geology》1984,1(1):27-36
The presence of probable salt dissolution-associated collapse structures in the North Sea based on the evidence of contemporary seismic data was discussed by Lohmann (1972). Since then, little attention has been paid to them in North Sea literature, although many oil companies will have studies on file. This Paper describes and illustrates a selection of such features in the area from recent seismic data, and suggest a broad classification for them as they are seen on the seismic section, based on mode of origin. Reference will also be made to certain types of carbonate dissolution and collapse effects. 相似文献
166.
Alisha?CooteEmail authorView authors OrcID profile Phil?Shane Claudine?Stirling Malcolm?Reid 《Contributions to Mineralogy and Petrology》2018,173(2):14
Late Quaternary, porphyritic basalts erupted in the Kaikohe-Bay of Islands area, New Zealand, provide an opportunity to explore the crystallization and ascent history of small volume magmas in an intra-continental monogenetic volcano field. The plagioclase phenocrysts represent a diverse crystal cargo. Most of the crystals have a rim growth that is compositionally similar to groundmass plagioclase (~?An65) and is in equilibrium with the host basalt rock. The rims surround a resorbed core that is either less calcic (~?An20–45) or more calcic (>?An70), having crystallized in more differentiated or more primitive melts, respectively. The relic cores, particularly those that are less calcic (<?~?An45), have 87Sr/86Sr ratios that are either mantle-like (~?0.7030) or crustal-like (~?0.7040 to 0.7060), indicating some are antecrysts formed in melts fractionated from plutonic basaltic forerunners, while others are true xenocrysts from greywacke basement and/or Miocene arc volcanics. It is envisaged that intrusive basaltic forerunners produced a zone where various degrees of crustal assimilation and fractional crystallization occurred. The erupted basalts represent mafic recharge of this system, as indicated by the final crystal rim growths around the entrained antecrystic and xenocrystic cargo. The recharge also entrained cognate gabbros that occur as inclusions, and produced mingled groundmasses. Multi-stage magmatic ascent and interaction is indicated, and is consistent with the presence of a partial melt body in the lower crust detected by geophysical methods. This crystallization history contrasts with traditional concepts of low-flux basaltic systems where rapid ascent from the mantle is inferred. From a hazards perspective, the magmatic system inferred here increases the likelihood of detecting eruption precursor phenomena such as seismicity, degassing and surface deformation. 相似文献
167.
New Zealand Census 2013: A short commentary on the role which the Census plays and the findings of the 2013 Census 下载免费PDF全文
Malcolm Campbell 《New Zealand geographer》2015,71(2):105-109
This short paper aims to discuss the role and the importance of the Census in New Zealand. It also discusses some of the multitude of uses of Census data in various contexts to help us understand the demographic and socio‐economic landscape of New Zealand. Debates internationally on the nature, scale and frequency of a national Census, or even whether a Census is necessary at all, mean that we cannot take this valuable resource for granted. With this in mind, we as geographers have a wealth of data to explore and analyse that we should take full advantage of. What gets counted counts! 相似文献
168.
The ~5 ka Mt. Gambier Volcanic Complex in the Newer Volcanics Province, Australia is an extremely complex monogenetic, volcanic system that preserves at least 14 eruption points aligned along a fissure system. The complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner. The facies are (1) coherent to vesicular fragmental alkali basalt (effusive/Hawaiian spatter and lava flows); (2) massive scoriaceous fine lapilli with coarse ash (Strombolian fallout); (3) bedded scoriaceous fine lapilli tuff (violent Strombolian fallout); (4) thin–medium bedded, undulating very fine lapilli in coarse ash (dry phreatomagmatic surge-modified fallout); (5) palagonite-altered, cross-bedded, medium lapilli to fine ash (wet phreatomagmatic base surges); and (6) massive, palagonite-altered, very poorly sorted tuff breccia and lapilli tuff (phreato-Vulcanian pyroclastic flows). Since most deposits are lithified, to quantify the grain size distributions (GSDs), image analysis was performed. The facies are distinct based on their GSDs and the fine ash to coarse+fine ash ratios. These provide insights into the fragmentation intensities and water–magma interaction efficiencies for each facies. The eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles, except for a “magmatic horizon” of effusive activity occurring at both ends of the volcanic complex simultaneously. The eruption foci are located along NW–SE trending lineaments, indicating that the complex was fed by multiple dykes following the subsurface structures related to the Tartwaup Fault System. Possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates, viscosity, crystallinity, degassing and magma discharge rate, as well as hydrological parameters. 相似文献
169.
Benni Thiebes Rainer Bell Thomas Glade Stefan Jäger Julia Mayer Malcolm Anderson Liz Holcombe 《Landslides》2014,11(5):859-875
Landslides are a significant hazard in many parts of the world and exhibit a high, and often underestimated, damage potential. Deploying landslide early warning systems is one risk management strategy that, amongst others, can be used to protect local communities. In geotechnical applications, slope stability models play an important role in predicting slope behaviour as a result of external influences; however, they are only rarely incorporated into landslide early warning systems. In this study, the physically based slope stability model CHASM (Combined Hydrology and Stability Model) was initially applied to a reactivated landslide in the Swabian Alb to assess stability conditions and was subsequently integrated into a prototype of a semi-automated landslide early warning system. The results of the CHASM application demonstrate that for several potential shear surfaces the Factor of Safety is relatively low, and subsequent rainfall events could cause instability. To integrate and automate CHASM within an early warning system, international geospatial standards were employed to ensure the interoperability of system components and the transferability of the implemented system as a whole. The CHASM algorithm is automatically run as a web processing service, utilising fixed, predetermined input data, and variable input data including hydrological monitoring data and quantitative rainfall forecasts. Once pre-defined modelling or monitoring thresholds are exceeded, a web notification service distributes SMS and email messages to relevant experts, who then determine whether to issue an early warning to local and regional stakeholders, as well as providing appropriate action advice. This study successfully demonstrated the potential of this new approach to landslide early warning. To move from demonstration to active issuance of early warnings demands the future acquisition of high-quality data on mechanical properties and distributed pore water pressure regimes. 相似文献
170.