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141.
Laura J. Morrissey Karin M. Barovich Martin Hand Katherine E. Howard Justin L. Payne 《地学前缘(英文版)》2019,10(1):175-194
U-Pb monazite and zircon geochronology and calculated metamorphic phase diagrams from drill holes in the northern Gawler Craton, southern Australia, reveal the presence of ca. 1.45 Ga magmatism and metamorphism. Magmatism and granulite facies metamorphism of this age has not previously been recognised in the Gawler Craton. The magmatic rocks have steep LREE-enriched patterns and high Ga/Al values, suggesting they are A-type granites. Calculated metamorphic forward models suggest that this event was associated with high apparent thermal gradients and reached pressures of 3.2 -5.4 kbar and temperatures of 775-815℃. The high apparent thermal gradients may reflect pluton-enhanced metamorphism, consistent with the presence of A-type granites. The recognition of ca. 1.45 Ga tectonism in the northern Gawler Craton is added to a compilation of ca. 1.50 -1.40 Ga magmatism, shear zone reactivation, rift basin development and isotope resetting throughout the South and North Australian Cratons that shows that this event was widespread in eastern Proterozoic Australia. This event is stylistically similar to ca. 1.45 Ga A-type magmatism and high thermal gradient metamorphism in Laurentia in this interval and provides further support for a connection between Australia and Laurentia during the Mesoproterozoic. The tectonic setting of the 1.50-1.40 Ga event is unclear but may record rifting within the Nuna(or Columbia) supercontinent, or a period of intracontinental extension within a long-lived convergent setting. 相似文献
142.
Ju-Duk Yoon Jeong-Hui Kim Sang-Hyeon Park Eve Kim Min-Ho Jang 《Ocean Science Journal》2017,52(1):147-164
The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish. 相似文献
143.
David P. Hamilton Katherine R. O’Brien Michele A. Burford Justin D. Brookes Chris G. McBride 《Aquatic Sciences - Research Across Boundaries》2010,72(3):295-307
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic
lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were
taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples
from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the
longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r
2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite
for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely
dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton
distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth
of the euphotic zone (z
eu) is consistently shallower than the depth of the surface mixed layer (z
SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear
to disrupt the annual cycle of maximum chlorophyll in winter. 相似文献
144.
云南南滚河自然保护区大中型陆生哺乳动物初步调查 总被引:1,自引:1,他引:0
During surveys for wild felids in Nangunhe Nature Reserve, Yunnan province, China, we conducted a wider mammal survey of the core nature reserve area, using camera trapping techniques. Forty motion-triggered digital camera traps had been set in oldest forest tract of protected area to conduct a species inventory. The total camera trapping effort of 2460 camera trap nights yielded 232 digital photographs of mammals represented by 17 species in five orders. The species photographed include rare and elusive species and those that are of high conservation value, such as IUCN endangered species Asiatic elephant (Elephas maximus), and Phayre’s leaf monkey (Trachypit hecus phayrei). In addition, IUCN vulnerable species including Asiatic black bear (Ursus thibetanus), sambar (Rusa unicolor), northern pig-tailed macaque (Macaca leonine), and marbled cat (Pardofelis marmorata), and more common species were found. All mammals were also listed as key protected wild animals by the State Forestry Administration of China. Of particular importance were the carnivores, with 7 different species recorded. Ungulates and other taxa forming a prey base for these predators,such as rhesus macaque (Macaca mulatta), red muntjac (Muntiacus muntjac), sambar, wild boar (Sus scrofa), and Chinese serow (Capricornis milneedwardsii), were found to be the most frequently photographed and most widespread species. Opportunities for local people to develop standardized monitoring designs for targeted species were identified by these initial assessment results. Local nature reserve staff lacked technical ability to produce standardized survey designs, yet a by product of this type of non-standardized data collection can be very informative and produce inventory information that gives a species richness analysis, as well as initial estimates for occupancy and detection probability for abundant species to drive future standardized survey designs and efforts. 相似文献
145.
Managing Ontong Java: Social institutions for production and governance of atoll resources in Solomon Islands 总被引:2,自引:2,他引:0
Tim Bayliss-Smith Katherine V. Gough reas Egelund Christensen Søren Pilgaard Kristensen 《Singapore journal of tropical geography》2010,31(1):55-69
This paper explores the changing nature of social institutions and organizations for resource management on Ontong Java and their central role in maintaining livelihoods. Using detailed field data for three time periods, 1970–72, 1986 and 2006–07, and drawing on earlier secondary data, a longitudinal analysis of changes in governance and livelihoods is undertaken. Increased exploitation of marine resources has widened the resource base and increased people's access to goods and services. Following the ban in 2005 on the bêche-de-mer trade, however, livelihoods have reverted to being more subsistence oriented. For almost two decades after 1978, a communal organization, the Area Council, succeeded in regulating exploitation of the atoll's marine resources to ensure sustainable use, but in the 1990s it collapsed. In addition there was a paralysis of institutions that had once settled land disputes. This failure of atoll governance is a greater threat to future 'sustainability' than the usual processes that are invoked for atolls and small islands generally. As the Solomon Islands state is also failing, we argue that local institutions and organizations have a vital role to play in managing access to resources and the future of livelihoods on Ontong Java atoll. 相似文献
146.
147.
We report an improved method for determining the intramolecular carbon isotopic composition of acetate using direct injection of aqueous samples. The system builds upon prior work that established pyrolytic conditions for online analysis and represents a significant advance in that it requires minimal preparation for samples containing as little as 1 mM sodium acetate in aqueous solution. The technique is applicable for analysis of oilfield brines, culture samples, biological samples and natural porewaters. We demonstrate its accuracy by use of a stable isotope dilution series. We also show that addition of a base and cryogenic preconcentration may induce an isotopic effect on the carboxyl carbon. This isotopic fractionation does not appear to extend to the measured methyl carbon isotope value although it can significantly alter the measured isotopic composition of the whole molecule. Our preconcentration experiments demonstrate that the method is suitable for carbon isotopic measurements of acetate methyl carbon in natural samples at concentrations as low as 90 μM, considerably broadening potential applications. 相似文献
148.
Spectral filtering was compared with traditional mean spatial filters to assess their ability to identify and remove striped artefacts in digital elevation data. The techniques were applied to two datasets: a 100 m contour derived digital elevation model (DEM) of southern Norway and a 2 m LiDAR DSM of the Lake District, UK. Both datasets contained diagonal data artefacts that were found to propagate into subsequent terrain analysis. Spectral filtering used fast Fourier transformation (FFT) frequency data to identify these data artefacts in both datasets. These were removed from the data by applying a cut filter, prior to the inverse transform. Spectral filtering showed considerable advantages over mean spatial filters, when both the absolute and spatial distribution of elevation changes made were examined. Elevation changes from the spectral filtering were restricted to frequencies removed by the cut filter, were small in magnitude and consequently avoided any global smoothing. Spectral filtering was found to avoid the smoothing of kernel based data editing, and provided a more informative measure of data artefacts present in the FFT frequency domain. Artefacts were found to be heterogeneous through the surfaces, a result of their strong correlations with spatially autocorrelated variables: landcover and landsurface geometry. Spectral filtering performed better on the 100 m DEM, where signal and artefact were clearly distinguishable in the frequency data. Spectrally filtered digital elevation datasets were found to provide a superior and more precise representation of the landsurface and be a more appropriate dataset for any subsequent geomorphological applications. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
149.
Moganti S Richardson BJ McClellan K Martin M Lam PK Zheng GJ 《Marine pollution bulletin》2008,57(6-12):672-680
In order to test its ability as a bioaccumulator, the deposit feeding clam Asaphis deflorata, collected from a clean coastal area in Hong Kong (Ding Chau, Ma On Shan), was exposed to field-collected sediments representing a gradient of contamination. Sediments were collected from four sites, namely Shek O in the southeast of Hong Kong Island, Ap Lei Chau in Aberdeen district, Tai Kok Tsui in the Mong Kok waterfront, and To Kwa Wan near Kowloon City pier. Shek O was the cleanest and To Kwa Wan was the most polluted site. Replicate 30L fiberglass tanks containing equal numbers of organisms were maintained for 28 days, with equal quantities of sediment and filtered seawater. Prior to this the animals were depurated for 10 days in clean sediment. During the 28-day holding period, sampling of both sediment and clams was performed on days 0, 10 and 28, along with condition index measurements. Concentrations of organochlorine pesticides and PCBs in sediments showed that Shek O was the cleanest of the sites, followed by Ap Lei Chau, Tai Kok Tsui and To Kwa Wan. There were marked differences among the sites, especially in PAH concentrations, with To Kwa Wan showing extremely high sediment concentrations. Following exposure, the biota concentrations of various organochlorine pesticides and PCBs suggested that there was sediment concentration-dependent accumulation by A. deflorata on day 10 of the experiment. However, there was no significant increase on day 28 for any of the compounds tested. Contaminant concentrations in clams feeding on Shek O sediments were minimal and almost the same on all sampling days, indicating the presence of only baseline contaminant concentrations. The condition indices (CI) of the clams on various sampling days showed that the animals were relatively more stable in sediment from Shek O. There were some deaths in all the test tanks (including those containing Shek O sediments). In addition, clams appeared to bury faster in the cleaner Shek O sediment and remained buried, unlike those in the sediment from the other locations, where some remained predominantly on the surface. Nevertheless, despite not completely burying, the clams in other test sediments still exhibited sediment concentration-dependent tissue accumulation. The results of the investigation indicate the possibility of developing a standard test protocol for bioaccumulation by sediment dwelling invertebrates, for practical use in Hong Kong, using A. deflorata. 相似文献
150.
Shanti Moganti Bruce J. Richardson Katherine McClellan Michael Martin Paul K.S. Lam Gene J. Zheng 《Marine pollution bulletin》2008,57(6-12):672
In order to test its ability as a bioaccumulator, the deposit feeding clam Asaphis deflorata, collected from a clean coastal area in Hong Kong (Ding Chau, Ma On Shan), was exposed to field-collected sediments representing a gradient of contamination. Sediments were collected from four sites, namely Shek O in the southeast of Hong Kong Island, Ap Lei Chau in Aberdeen district, Tai Kok Tsui in the Mong Kok waterfront, and To Kwa Wan near Kowloon City pier. Shek O was the cleanest and To Kwa Wan was the most polluted site. Replicate 30 L fiberglass tanks containing equal numbers of organisms were maintained for 28 days, with equal quantities of sediment and filtered seawater. Prior to this the animals were depurated for 10 days in clean sediment. During the 28-day holding period, sampling of both sediment and clams was performed on days 0, 10 and 28, along with condition index measurements. Concentrations of organochlorine pesticides and PCBs in sediments showed that Shek O was the cleanest of the sites, followed by Ap Lei Chau, Tai Kok Tsui and To Kwa Wan. There were marked differences among the sites, especially in PAH concentrations, with To Kwa Wan showing extremely high sediment concentrations.Following exposure, the biota concentrations of various organochlorine pesticides and PCBs suggested that there was sediment concentration-dependent accumulation by A. deflorata on day 10 of the experiment. However, there was no significant increase on day 28 for any of the compounds tested. Contaminant concentrations in clams feeding on Shek O sediments were minimal and almost the same on all sampling days, indicating the presence of only baseline contaminant concentrations. The condition indices (CI) of the clams on various sampling days showed that the animals were relatively more stable in sediment from Shek O. There were some deaths in all the test tanks (including those containing Shek O sediments). In addition, clams appeared to bury faster in the cleaner Shek O sediment and remained buried, unlike those in the sediment from the other locations, where some remained predominantly on the surface. Nevertheless, despite not completely burying, the clams in other test sediments still exhibited sediment concentration-dependent tissue accumulation. The results of the investigation indicate the possibility of developing a standard test protocol for bioaccumulation by sediment dwelling invertebrates, for practical use in Hong Kong, using A. deflorata. 相似文献