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排序方式: 共有102条查询结果,搜索用时 305 毫秒
51.
Hazel Matias-Peralta Fatimah Md. Yusoff Mohamed Shariff Aziz Arshad 《Marine pollution bulletin》2005,51(8-12):722
The effects of salinity, temperature, and light conditions on the reproduction and development of harpacticoid copepod, Nitocra affinis f. californica under controlled laboratory conditions were determined. Seven different salinity levels (5, 10, 15, 20, 25, 30, 35 ppt), four temperatures (20, 25, 30, 35 °C), three different light intensities (25, 56, 130 μmol m−2 s−1) and photoperiods (24 h:0 h, 1 h:23 h, 12 h:12 h LD cycle) were employed in this study. The highest (p < 0.05) overall reproduction and fastest development time were achieved by copepods reared under 30–35 ppt salinity. The optimum temperature required for the maximum reproduction was 30 °C while under 30 °C and 35 °C the copepod development time was shortest (p < 0.05) compared to other temperature levels. The overall reproduction was highest (p < 0.05) and development rate of N. affinis was shortest (p < 0.05) under lowest light intensity (25 μmol m−2 s−1). Continuous light (24 h:0 h LD) inhibited the egg production while, continuous darkness (1 h:23 h LD) and 12 h:12 h LD significantly favoured the overall reproductive activity of the female. Photoperiods 1 h:23 h and 12 h:12 h LD yielded highest total (p < 0.05) offspring female−1 coupled with highest (p < 0.05) survival percentage. This study illustrated that although N. affinis can tolerate wide range of environmental conditions, prolonged exposure to subnormal environments affect its reproduction and development. This study showed that this species can be mass cultured for commercial purposes and has a potential to be used for toxicity studies due to its high reproductive performance fast development and a wide range of tolerance to environmental conditions. 相似文献
52.
53.
Paul A. Delcourt Hazel R. Delcourt Patricia A. Cridlebaugh Jefferson Chapman 《Quaternary Research》1986,25(3)
Human occupation and utilization of plant resources have affected vegetation in the lower Little Tennessee River Valley of East Tennessee for 10,000 yr. Changes in Indian cultures and land use are documented by radiocarbon chronologies, lithic artifacts, ceramics, settlement patterns, and ethnobotanical remains from 25 stratified archaeological sites within the Holocene alluvial terrace. The ethnobotanical record consists of 31,500 fragments (13.7 kg) of wood charcoal identified to species and 7.7 kg of carbonized fruits, seeds, nutshells, and cultigens from 956 features. Pollen and plant macrofossils from small ponds both in the uplands and on lower stream terraces record local vegetational changes through the last 1500 to 3000 yr. Human impact increased after cultigens, including squash and gourd, were introduced ca. 4000 yr B.P. during the Archaic cultural period. Forest clearance and cultivation disturbed vegetation on both the floodplain and lower terraces after 2800 yr B.P., during the Woodland period. Permanent Indian settlements and maize and bean agriculture extended to higher terraces 1.5 km from the floodplain by the Mississippian period (1000 to 300 yr B.P.). After 300 yr B.P., extensive land clearance and cultivation by Historic Overhill Cherokee and Euro-Americans spread into the uplands beyond the river valley. 相似文献
54.
We compared results of three quantitative methods for reconstructing past vegetation, including (1) calibrations of per cent dominance vs. per cent pollen for individual tree taxa; (2) coefficients of dissimilarity between fossil and modern pollen assemblages; and (3) simulation modelling of long-term forest succession. For calibration, we used 1684 modern pollen samples and 1742 forest-inventory summaries from eastern North America. We applied the calibrations at 1 000-year intervals to the 19000-year pollen record from Anderson Pond, Tennessee. Dominance values reconstructed using taxon calibrations typically paralleled the changes in percentages of arboreal pollen. Dissimilarity values between fossil and modern pollen assemblages were lowest from 19 000 yr BP to 15 000 yr BP and from 9 000 yr BP to the present, indicating good modern analogues for both full-glacial and Holocene time periods. During times of good analogue, forest composition estimated from forest inventories at the locations of best pollen analogues was similar to that reconstructed using taxon calibrations. Relatively poor modern analogues exist for late glacial and early Holocene pollen spectra from Anderson Pond. During times of poor analogues, forest composition reconstructed from taxon calibrations differed from that derived from analogue methods. FORET-model simulations of forest-stand biomass differed markedly from palaeovegetation estimates made from the other two methods. This is primarily because the FORET model is scaled to forest succession on 1/12-ha forest plots rather than forest dynamics integrated over a broad landscape mosaic. Because they are based upon fundamental relationships of pollen production and dispersal, taxon calibrations provide the best available means for reconstructing forest history both during times of good and of poor analogues. 相似文献
55.
Zhangdong Jin Mike Bickle Hazel Chapman Jimin Yu Mervyn Greaves Sumin Wang Shiyue Chen 《Journal of Paleolimnology》2006,36(2):211-218
To evaluate the effect of sample preparation on the trace element composition of ostracod shells, fossil shells subjected to various cleaning steps were analyzed by ICP-AES. The variations in ostracod Mg/Ca ratios reveal that fossil ostracod samples cleaned by ultrasonic methanol yield lower values than those by other methods, including increasingly rigorous reductive cleaning. In our sample sets, shell Mg/Ca decreases ∼
∼1.5 mmol/mol during clay removal. Sample Sr/Ca results do not seem to vary significantly under the equivalent cleaning steps. For ostracod analysis, pre-treatment using multiple methanol ultrasonic cleaning is suggested to be used for gaining an appropriate result. 相似文献
56.
Luke Wooller Benjamin van Wyk de Vries Emmanuelle Cecchi Hazel Rymer 《Bulletin of Volcanology》2009,71(10):1111-1131
Long-term fault movement under volcanoes can control the edifice structure and can generate collapse events. To study faulting
effects, we explore a wide range of fault geometries and motions, from normal, through vertical to reverse and dip-slip to
strike-slip, using simple analogue models. We explore the effect of cumulative sub-volcanic fault motions and find that there
is a strong influence on the structural evolution and potential instability of volcanoes. The variety of fault types and geometries
are tested with realistically scaled displacements, demonstrating a general tendency to produce regions of instability parallel
to fault strike, whatever the fault motion. Where there is oblique-slip faulting, the instability is always on the downthrown
side and usually in the volcano flank sector facing the strike-slip sense of motion. Different positions of the fault beneath
the volcano change the location, type and magnitude of the instability produced. For example, the further the fault is from
the central axis, the larger the destabilised sector. Also, with greater fault offset from the central axis larger unstable
volumes are generated. Such failures are normal to fault strike. Using simple geometric dimensionless numbers, such as the
fault dip, degree of oblique motion (angle of obliquity), and the fault position, we graphically display the geometry of structures
produced. The models are applied to volcanoes with known underlying faults, and we demonstrate the importance of these faults
in determining volcanic structures and slope instability. Using the knowledge of fault patterns gained from these experiments,
geological mapping on volcanoes can locate fault influence and unstable zones, and hence monitoring of unstable flanks could
be carried out to determine the actual response to faulting in specific cases. 相似文献
57.
Economic valuation for the conservation of marine biodiversity 总被引:3,自引:0,他引:3
Policy makers are increasingly recognising the role of environmental valuation to guide and support the management and conservation of biodiversity. This paper presents a goods and services approach to determine the economic value of marine biodiversity in the UK, with the aim of clarifying the role of valuation in the management of marine biodiversity. The goods and services resulting from UK marine biodiversity are detailed, and 8 of the 13 services are valued in monetary terms. It is found that a decline in UK marine biodiversity could result in a varying, and at present unpredictable, change in the provision of goods and services, including reduced resilience and resistance to change, declining marine environmental health, reduced fisheries potential, and loss of recreational opportunities. The results suggest that this approach can facilitate biodiversity management by enabling the optimal allocation of limited management resources and through raising awareness of the importance of marine biodiversity. 相似文献
58.
59.
Marie-Emilie Clémence Silvia Gardin Annachiara Bartolini Guillaume Paris Valérie Beaumont Jean Guex 《Swiss Journal of Geoscience》2010,103(2):293-315
A high-resolution micropalaeontological study, combined with geochemical and sedimentological analyses was performed on the
Tiefengraben, Schlossgraben and Eiberg sections (Austrian Alps) in order to characterize sea-surface carbonate production
during the end-Triassic crisis. At the end-Rhaetian, the dominant calcareous nannofossil Prinsiosphaera triassica shows a decrease in abundance and size and this is correlated with a increase in δ18O and a gradual decline in δ13Ccarb values. Simultaneously, benthic foraminiferal assemblages show a decrease in diversity and abundance of calcareous taxa and
a dominance of infaunal agglutinated taxa. The smaller size of calcareous nannofossils disturbed the vertical export balance
of the biological carbon pump towards the sea-bottom, resulting in changes in feeding strategies within the benthic foraminiferal
assemblages from deposit feeders to detritus feeders and bacterial scavengers. These micropalaeontological data combined with
geochemical proxies suggest that changes in seawater chemistry and/or cooling episodes might have occurred in the latest Triassic,
leading to a marked decrease of carbonate production. This in turn culminated in the quasi-absence of calcareous nannofossils
and benthic foraminifers in the latest Triassic. The aftermath (latest Triassic earliest Jurassic) was characterised by abundance
peaks of “disaster” epifaunal agglutinated foraminifera Trochammina on the sea-floor. Central Atlantic Magmatic Province (CAMP) paroxysmal activity, superimposed on a major worldwide regressive
phase, is assumed to be responsible for a deterioration in marine palaeoenvironments. CAMP sulfuric emissions might have been
the trigger for cooling episodes and seawater acidification leading to disturbance of the surface carbonate production at
the very end-Triassic. 相似文献
60.
Hazel A. Oxenford Ramon Roach Angelique Brathwaite Leonard Nurse Renata Goodridge Fabian Hinds Kim Baldwin Christine Finney 《Climatic change》2008,87(3-4):435-449
In late summer 2005 a mass coral bleaching event occurred in the Caribbean. Here we quantify coral bleaching in Barbados at
six sites on the island’s sheltered west and exposed southwest coasts, including nearshore fringing and patch reefs and offshore
bank reef habitats. Onset of coral bleaching occurred in late August 2005 and persisted for many months after temperatures
cooled. All reef habitats and virtually all coral taxa were affected, with an average of 70.6% of all colonies bleaching.
Nearshore reefs (<10 m depth) were affected more severely than offshore deeper reefs (>15 m) with an average of 80.6% of all
coral colonies bleaching compared with 60.5% on the latter. Inter-species variation in susceptibility to bleaching was marked
with >90% of colonies bleaching in some species whilst <10% bleached in others. Follow-up surveys revealed low coral mortality,
with an overall mean of 3.8% partial colony death across all species and reefs by February 2006. However, bleached condition
has persisted with a mean of 37.7% of all coral colonies still bleached after 5 1/2 months, indicating that loss of live coral
is likely to continue for some time. This event represents the most severe bleaching episode ever witnessed on Barbados’ reefs
and emphasises the vulnerability of small island states, with a high reliance on healthy coral reef ecosystem services, to
elevated sea water temperatures associated with climate variability and global climate change. 相似文献