AASG Introduction     

Noel Tyler 《Marine Georesources & Geotechnology》2013,31(2-3)

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The development of a rapid screening technique to measure antibiotic activity in effluents and surface water samples     

Smith AJ  Balaam JL  Ward A 《Marine pollution bulletin》2007,54(12):1940-1946

Use of antibiotics in medicine, farming and aquaculture results in a continual supply of these pharmaceuticals and their breakdown products reaching the environment. A method has been developed to use for screening environmental samples to establish whether they contain antibiotics. The assay is based on a commercially available test kit and uses some modifications of the test procedure and SPE techniques to deliver a fast, semi-quantifiable result. Development of the assay and results from spiked and environmental samples are discussed.  相似文献   

PDS 456: an extreme accretion rate quasar?     

J. N. Reeves  P. T. O'Brien  S. Vaughan  D. Law-Green  M. Ward  C. Simpson  K. A. Pounds  R. Edelson 《Monthly notices of the Royal Astronomical Society》2000,312(2):L17-L21

We present quasi-simultaneous ASCA and RXTE observations of the most luminous known active galactic nucleus in the local ( z <0.3) Universe, the recently discovered quasar PDS 456. Multiwavelength observations have been conducted that show that PDS 456 has a bolometric luminosity of ∼10⁴⁷ erg s⁻¹ peaking in the ultraviolet part of the spectrum. In the X-ray band the 2–10 keV (rest-frame) luminosity is 10⁴⁵ erg s⁻¹. The broad-band X-ray spectrum obtained with ASCA and RXTE contains considerable complexity. The most striking feature observed is a very deep, ionized iron K edge, observed at 8.7 keV in the quasar rest-frame. We find that these features are consistent with reprocessing from highly ionized matter, probably the inner accretion disc. PDS 456 appeared to show a strong (factor of ∼2.1) outburst in just ∼17 ks, although non-intrinsic sources cannot be completely ruled out. If confirmed, this would be an unusual event for such a high-luminosity source, with a light-crossing-time corresponding to ∼2 R _S . The implication would be that flaring occurs within the very central regions, or else that PDS 456 is a 'super-Eddington' or relativistically beamed system. Overall we conclude on the basis of the extreme blue/UV luminosity, the rapid X-ray variability and from the imprint of highly ionized material on the X-ray spectrum, that PDS 456 is a quasar with an unusually high accretion rate.  相似文献   

A multiwavelength view at the heart of the superwind in NGC 253     

Duncan A. Forbes  Edward Polehampton  Ian R. Stevens  Jean P. Brodie  Martin J. Ward 《Monthly notices of the Royal Astronomical Society》2000,312(4):689-697

We present a new method of studying quadruple lenses in elliptical power-law potentials parametrized by ψ ( x , y )∝( x ²+ y ² q ²) ^{β /2} β (0 β <2). For this potential, the moments of the four image positions weighted by signed magnifications (magnification times parity) have very simple properties. In particular, we find that the zeroth moment – the sum of four signed magnifications satisfies ≃2/(2− β ); the relation is exact for β =0 (point-lens) and β =1 (isothermal potential), independent of the axial ratio. Similar relations can be derived when a shear is present along the major or minor axes. These relations, however, do not hold well for the closely related elliptical density distributions. For a singular isothermal elliptical density distribution without shear, the sum of signed magnifications for quadruple lenses is ≈2.8, again nearly independent of the ellipticity. For the same distribution with shear, the total signed magnification is around 2–3 for most cases, but can be significantly different for some combinations of the axial ratio and shear where six or eight images can appear.  相似文献   

Perceptions and realities of land degradation in arid Otjimbingwe, Namibia     

David Ward  Ben T. Ngairorue  Andr Apollus  Hermanus Tjiveze 《Journal of Arid Environments》2000,45(4):337

We examined the perceptions and realities of land degradation in a communal ranching area, Otjimbingwe, in arid Namibia (in south-western Africa). It is commonly perceived that large-scale degradation of Otjimbingwe has occurred due to a mixture of improper pastoral practices and pressures induced by a high human population growth rate. We sought to determine whether the inhabitants perceived land degradation to have taken place and whether their perceptions were consistent with empirical data on environmental quality. Furthermore, we wished to determine whether these pastoralists had management strategies to help them withstand the harsh environmental conditions in which they live. All respondents in our surveys perceived that the environment had become degraded. The claimed source of this degradation, a decline in annual rainfall, is inconsistent with long-term rainfall records (there was neither change nor cyclicity in rainfall over time). There is also little evidence of a decline in plant cover and soil quality in spite of the very high stocking densities. No overall pastoral strategy exists in Otjimbingwe. Options for management are extremely limited due to a variety of external and internal pressures such as a high human population growth rate, high immigration into Otjimbingwe, restricted water availability due to dams constructed upstream, and limited movement opportunities for livestock in drought periods.  相似文献   

Polychaete Assemblages in the San José Gulf (Chubut, Argentina), in Relation to Abiotic and Biotic Factors     

Catalina T. Pastor de Ward 《Marine Ecology》2000,21(3-4):175-190

Abstract. The composition and distribution of the polychaete assemblages of the San José Gulf (Chubut, Argentina) are described in relation to environmental variables using indicator species (TWINSPAN) and canonical correspondence analysis (CCA). The polychaetes were collected during a benthic cruise in October 1984. Sediments were collected at 110 sampling sites using a 0.25 m² van Veen bottom grab or by divers in near-shore areas and sieved with 1 mm mesh. A total of 73 polychaete taxa were collected and identified. Both analyses revealed the presence of four main assemblages distributed according to depth as well as bivalve and seaweed abundance gradients: ' Syllis-Eunice ' and ' Harmothoe-Eunice ' assemblages occurred at the same depths (0 –­ 185 m) and substrata (poorly sorted rock and coarse sand), but were separated by bivalve and seaweed abundance, wherby the highest abundances of bivalves and the minimum abundances of seaweeds corresponded to the ' Syllis-Eunice ' association. The ' Ninoe-Glycera ' and ' Aglaophamus- Fabriciinae indet. 6' assemblages also occurred at similar depths (0 – 60 m) and substrata (very well-sorted medium-fine sand), but differed in their composition of bivalves and seaweed abundances; the ' Aglaophamus- Fabriciinae indet. 6' association corresponded with minimum bivalve and maximum seaweed abundances.  相似文献   

Fabry–Perot imaging of NGC 6090 in H₂ emission     

H. Sugai  R. I. Davies  M. Ishii  M. J. Ward 《Monthly notices of the Royal Astronomical Society》2000,317(2):447-452

We have obtained an H₂ v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H₂ emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging.  相似文献   

Creation of Temperate-Climate Intertidal Mudflats: Factors Affecting Colonization and Use by Benthic Invertebrates and their Bird Predators     

P. R. Evans  R. M. Ward  M. Bone  M. Leakey 《Marine pollution bulletin》1999,37(8-12):535-545

Colonization of a recreated area of intertidal land by marine invertebrates and their bird predators was studied from April 1993 to August 1997. The most important food of large shorebirds, the ragworm Nereis diversicolor, did not reappear until late summer 1995 and did not become abundant until the following autumn. Annual attempts at colonization by the crustacean Corophium volutator, the main food of several small shorebird species, failed until summer 1996 when animals survived through the subsequent winter for the first time. Colonization by the mud-snail Hydrobia ulvae took place a year after flooding of the site, but densities in 1997 were still well below those found elsewhere on the adjacent estuary.

The delay in successful colonization by Nereis and Corophium may be attributable in part to the compaction of the intertidal muds caused by the earthmoving equipment used to contour the site. The slow increase in Hydrobia density may be a consequence of low organic content of the mud. Bird use is concentrated chiefly during the hours when the adjacent estuarine mudflats (with unrestricted tidal flow) are covered by the tide, since the new site then provides a supplementary feeding area. Peak daytime usage occurs during the migratory passage periods when birds need to feed for longer periods than usual, in order to refuel for their migrations; high usage is also anticipated in cold winters.

On this evidence, creation of intertidal areas in mitigation for any lost nearby to industrial or other development should take place at least three years before the losses, in order to make the new areas profitable for feeding waterfowl.  相似文献   

Riparian vegetation and island formation along the gravel‐bed Fiume Tagliamento,Italy     

A. M. Gurnell  G. E. Petts  D. M. Hannah  B. P. G. Smith  P. J. Edwards  J. Kollmann  J. V. Ward  K. Tockner 《地球表面变化过程与地形》2001,26(1):31-62

After more than 300 years of river management, scientific knowledge of European river systems has evolved with limited empirical knowledge of truly natural systems. In particular, little is known of the mechanisms supporting the evolution and maintenance of islands and secondary channels. The dynamic, gravel‐bed Fiume Tagliamento, Italy, provides an opportunity to acquire baseline data from a river where the level of direct engineering intervention along the main stem is remarkably small. Against a background of a strong alpine to mediterranean climatic and hydrological gradient, this paper explores relationships between topography, sediment and vegetation at eight sites along the active zone of the Tagliamento. A conceptual model of island development is proposed which integrates the interactions between large woody debris and vegetation, geomorphic features, sediment calibre and hydrological regime. Islands may develop on bare gravel sites or be dissected from the floodplain by channel avulsion. Depositional and erosional processes result in different island types and developmental stages. Differences in the apparent trajectories of island development are identified for each of the eight study sites along the river. The management implications of the model and associated observations of the role of riparian vegetation in island development are considered. In particular, the potential impacts of woody debris removal, riparian tree management, regulation of river flow and sediment regimes, and changes in riparian tree species' distribution are discussed. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Mapping the archaeological soil archive of sand and gravel mineral reserves in Britain     

Ingrid Ward  Barry Smith  Russell Lawley 《Geoarchaeology》2009,24(1):1-21

Primary sand and gravel deposits in Britain play an important role in preserving our cultural heritage and are also a valuable aggregate resource. While an understanding of the extrinsic properties of the soil archive (such as pH, redox, groundwater) can provide a firstorder assessment of the potential risk to any archaeologically sensitive deposits, we have very poor definition of spatial variations in the extrinsic properties of soil that influence archaeological preservation at a regional and national scale. Developments in digital geological mapping, remote sensing, and geochemical survey data undertaken by the British Geological Survey (BGS) have, however, significantly extended capabilities in this respect and can potentially be used to provide a primary assessment of the sensitivity of the present soil archive and the potential risk from changes to the soil process on cultural material in areas earmarked for aggregate extraction. Two of the major factors affecting archaeological preservation—soil acidification and groundwater—can be mapped or predicted at scales of better than 1:50,000 across increasingly large parts of the country using a combination of regional hydrogeological, geophysical, and geochemical data. Additional data from site investigations may further refine preservation potential as a function of changes in redox potential and acidity. These data, maps and models can be used to (1) better establish a baseline for archaeological preservation at a regional and national scale and (2) improve our understanding of how the physical and chemical properties of the near surface environment can be managed to sustainably preserve archaeological materials in areas impacted by sand and gravel extraction. © 2009 Wiley Periodicals, Inc.  相似文献