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Distribution and source apportionments of polychlorinated biphenyls (PCBs) in mariculture sediments from the Pearl River Delta, South China 总被引:1,自引:0,他引:1
Wang HS Du J Leung HM Leung AO Liang P Giesy JP Wong CK Wong MH 《Marine pollution bulletin》2011,63(5-12):516-522
Surface and core sediments collected from six mariculture farms in the Pearl River Delta (PRD) were analyzed to evaluate contamination levels of polychlorinated biphenyls (PCBs). The ∑PCBs (37 congeners) concentrations ranged from 5.10 to 11.0 ng g(-1) (mean 7.96 ng g(-1)) in surface and 3.19 to 22.1 ng g(-1) (mean 7.75 ng g(-1)) in core sediments, respectively. The concentrations were significantly higher than that measured in the sediments of their corresponding reference sites, whereby the average enrichment percentages were 62.0% and 42.7% in surface and core sediments, respectively. Significant correlations (R2=0.77, p<0.05) of PCB homologue group proportions between fish feeds and surface mariculture sediments suggested that fish feed input was probably the main source for the enrichment of PCBs. Due to the fact that PCBs could be transferred along food chains, PCB contamination in fish feeds and mariculture sediments should not be overlooked. 相似文献
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本文拟从分析土地资源主要因素入手,通过研究土地结构和功能,划分出四个土地资源区,并对各区土地资源综合开发利用和改造措施作一阐述。 相似文献
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Jules M. Goldspiel 《Icarus》2011,211(1):238-743
Young gullies and gully deposits on walls of martian craters have been cited as evidence that liquid water flowed on the surface of Mars relatively recently. Effects of variable environmental conditions at the surface of Mars are modeled and applied to the case of groundwater emergence from shallow aquifers to investigate whether groundwater is a viable source to enable the erosion of these gullies. The model includes detailed treatment of ice growth in the aquifer. Model results indicate that groundwater discharge can be maintained under the current environmental conditions if the aquifer permeability is like that of terrestrial gravel or higher, if the aquifer is 350 K or warmer, or if the aquifer is a brine with a freezing point depressed to 250 K or below. Groundwater discharge cannot be maintained for the conservative case of a cold, pure water, semi-pervious aquifer. Cold (275 K) pure water pervious (gravel) aquifers, warm (350 K) pure water semi-pervious aquifers, and cold (275 K) CaCl2 brine semi-pervious aquifers all exhibit a dependence of discharge on season, latitude and slope orientation in our modeling. Seasonal, latitudinal and azimuthal discharge variations are strongest for cold CaCl2 brine semi-pervious aquifers, with discharges from this aquifer type favoring equator-facing slopes at mid and high southern latitudes. At all latitudes and slope azimuths under our nominal conditions, the cold pure water pervious aquifer, the cold pure water semi-pervious aquifer and the cold CaCl2 brine semi-pervious aquifer all freeze completely shortly after the simulations are started. Discharge restarts in the summer for the cold pure water pervious aquifer and the cold brine aquifer, but discharge does not restart for the cold pure water semi-pervious aquifer. The warm pure water semi-pervious aquifer maintains daily seeps throughout the year at all but high latitudes. In the case of the cold pure water pervious aquifer, approximately 500,000 m3 of water could be discharged from a mid-latitude, 150-m thick aquifer with a 20-m wide seepage face orientated towards the equator or the pole after a single undermining-induced event before ice growth seals the seepage face. For a brine semi-pervious aquifer with the same dimensions, 200-300 m3 of water could be released from a mid-latitude 20-m wide equator-facing seepage face before the fresh exposure is sealed for the fall and winter seasons. Our results do not rule out groundwater emergence as a means of creating some recent gullies, but they indicate that rather special and perhaps unusual conditions would be required. 相似文献
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Laurent Koechlin Jean-Pierre Rivet Paul Deba Denis Serre Truswin Raksasataya René Gili Jules David 《Experimental Astronomy》2012,33(1):129-140
This paper presents high contrast images of sky sources, obtained from the ground with a novel optical concept: Fresnel arrays. We demonstrate the efficiency of a small 20?cm prototype Fresnel array for making images with high brightness ratios, achieving contrasts up to 4 × 105 on sky sources such as Mars and its satellites, and the Sirius?A?CB couple. These validation results are promising for future applications in space, for example the 4 m array we have proposed to ESA in the frame of the ??Call for a Medium-size mission opportunity for a launch in 2022??. Fresnel imagers are the subject of a topical issue of Experimental Astronomy published in 2011, but only preliminary results were presented at the time. Making images of astronomical bodies requires an optical component to focus light. This component is usually a mirror or a lens, the quality of which is critical for sharp and high contrast images. However, reflection on a mirror and refraction through a lens are not the only ways to focus light: an alternative is provided by diffraction through binary masks (opaque foils with multiple precisely etched sub-apertures). Our Fresnel arrays are such diffractive focusers, they offer weight, price and size advantages over traditional optics in space-based astronomical instruments. This novel approach requires only void apertures of special shapes in an opaque material to form sharp images, thus avoiding the wavefront distortion, diffusion and spectral absorption associated with traditional optical media. In our setup, lenses and/or mirrors are involved only downstream (at small sizes) for focal instrumentation and chromatic correction. Fresnel arrays produce high contrast images, the resolution of which reaches the theoretical limit of diffraction. Unlike mirrors, they do not require high precision polishing or positioning, and can be used in a large domain of wavelengths from far IR to far UV, enabling the study of many science cases in astrophysics from exoplanet surfaces and atmospheres to galaxy evolution. 相似文献
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Emily M. Stewart Neal Michelutti Jules M. Blais Mark L. Mallory Marianne S. V. Douglas John P. Smol 《Journal of Paleolimnology》2013,49(2):205-219
Nutrients from the waste products of large seabird colonies can enter freshwater ecosystems, markedly altering water quality and biotic assemblages, especially in nutrient-poor regions like the Canadian High Arctic. Here, we investigate the influence of nutrient-rich seabird wastes on freshwater larval chironomid assemblages from two distinct seabird colonies. The study sites include four ponds dominated by northern fulmars (Fulmarus glacialis) at Cape Vera, Devon Island, as well as one pond near a large group of common eider ducks (Somateria mollissima borealis) on Tern Island (unofficial name) near Cornwallis Island, Nunavut. The rare combination of nutrient-enriched and well-oxygenated waters allowed us to contrast the effects of nutrients, oxygen, and temperature on chironomid community structure in shallow Arctic ponds using sediment cores. Despite highly elevated nutrient levels, the subfossil assemblages were dominated by cold stenotherms typical of oligotrophic waters. Although nutrient inputs appear to have increased chironomid head capsule numbers due to enhanced food availability, the fertilization had little direct effect on assemblage composition, at least at the taxonomic level achievable based on fossil material. The presence of low abundances of eutrophic/anoxic taxa, such as Chironomus plumosus-type, suggests that biogeographic barriers to dispersal are not influencing the assemblages. These data demonstrate that, in the presence of high concentrations of dissolved oxygen, nutrient enrichment had little direct effect on chironomid community composition in shallow Arctic ponds. 相似文献
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Denudation rates on cratonic landscapes: comparison between suspended and dissolved fluxes,and 10Be analysis in the Nyong and Sanaga River basins,south Cameroon 下载免费PDF全文
Vincent Regard Sébastien Carretier Jean‐Loup Boeglin Jules‐Rémy Ndam Ngoupayou Jean‐Guy Dzana Jean‐Pierre Bedimo Bedimo Jean Riotte Jean‐Jacques Braun 《地球表面变化过程与地形》2016,41(12):1671-1683
South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long‐term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main south Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub‐humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub‐basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub‐basin). Moreover the Nyong basin is dam‐free and less impacted by agriculture and logging. We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment‐averaged erosion and denudation datasets. The first one consists of an 11‐year long gauging dataset, while the second one comes from cosmogenic radionuclides [CRNs, here beryllium‐10 (10Be)] from sand sampled in the river mainstreams (timescale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km2/yr); our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60% and 40%, respectively, of the total denudation. Beryllium‐10 denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km2/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10Be‐derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献