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91.
Fabio Ricci Nunzio Penna Samuela Capellacci Antonella Penna 《Chemistry and Ecology》2014,30(4):364-375
In the northern Adriatic Sea, Mediterranean Sea, the mucilage phenomenon is usually related to the aggregation of extracellular organic matter of phytoplanktonic origin under special seasonal and trophic conditions. Environmental factors, such as temperature, salinity, nitrogen, phosphorus and N/P ratio as well as polysaccharide and monosaccharide levels in the presence and absence of mucilage were investigated in the northern Adriatic Sea. Variations in temperature and salinity during spring in years characterised by mucilage events have been recognised having an important role in preparing a favourable physical environment where mucilage formation could take place. Since the DIN/TP ratio increased markedly during the spring months (March–April) in 2002, 2003 and 2004, preceding the early summer mucilage outbreaks, it appeared that the DIN/TP ratio may be a more robust predictor than the DIN/DIP ratio, which, although more commonly used, exhibited a discontinuous trend. The contents of total carbohydrates, including monosaccharides and polysaccharides, in seawater also varied according to the presence or absence of mucilage, with an increase of polysaccharide levels during the late spring or early summer in the period of the mucilage appearance. The role of carbohydrates in the macro-aggregate formation was also investigated. 相似文献
92.
The effect of the upstream conditions on propagation of gravity current over a slope is investigated using three-dimensional numerical simulations. The current produced by constant buoyancy flux, is simulated using a large eddy simulation solver. The dense saline solution used at the inlet is the driving force of the flow. Higher replenishment of the current is possible either by a high inflow discharge or high initial fractional density excess. In the simulations, it is observed that these two parameters affect the flow in different ways. Results show that the front speed of the descending current is proportional to the cube root of buoyancy flux, $(g_o^{\prime } Q)^{1/3}$ , which agrees with the previous experimental and numerical observations. The height of the tail of the current grows linearly in the streamwise direction. Formation of a strong shear layer at the boundary of mixed upper layer and dense lower layer is observed within the body and the tail of the current. Over the tail of the current far enough from the inlet, the vertical velocity and density profiles are compared to the ones from an experimental study. Distance from the bed to the point of maximum velocity increases with an increase in inflow discharge, while it remains practically unchanged with increasing initial fractional excess density in the simulations. Even though the velocity profiles are in good agreement, some discrepancies are observed in fractional excess density profiles among experimental and numerical results. Possible reasons for these discrepancies are discussed. Generally, gravity current type of flows could be expressed in layer-integrated formulation of governing equations. However, layer integration introduces several constants, commonly known as shape factors, to the equations of motion. The values of these shape factors are calculated based on simulation results and compared to the values from experiments and to the favorably used ‘top hat’ assumption. 相似文献
93.
94.
Levels of organochlorine pesticides in Amazon turtle (Podocnemis unifilis) in the Xingu River,Brazil
Marina Teófilo Pignati Larissa Costa De Souza Rosivaldo de Alcântara Mendes Marcelo de Oliveira Lima Wanderlei Antonio Pignati Juarez Carlos Brito Pezzuti 《Journal of environmental science and health. Part. B》2013,48(12):810-816
AbstractDue to the toxicity and high environmental persistence of organochlorine pesticides in aquatic organisms, turtles have been studied as environment biomonitors. These animals are important sources of protein for the riverside and indigenous peoples of the Brazilian amazon. In the present study, organochlorine pesticide contamination was investigated in Podocnemis unifilis. Liver, muscle and fatty tissue samples were removed from 50 specimens collected from five sampling points located in the Xingu River basin. Fourteen organochlorine pesticides were analysed via gas chromatography with an electron capture detector (CG-ECD). Eight organochlorine pesticides were detected with average concentrations of ∑DDT, ∑Endossulfan and ∑HCH which were 26.17?±?26.35, 14.38?±?23.77 and 1.39?±?8.46?ng g?1 in moisture content, respectively. DDT compounds were the most predominant, with a greater concentration of pp′-DDT in the liver and pp′-DDD in the muscle. Significant differences were noted between the types of tissues studied, and the concentration of OCPs varied between sampling sites. 相似文献
95.
Claudio A. Alister Patricio A. Gomez Sandra Rojas Marcelo Kogan 《Journal of environmental science and health. Part. B》2013,48(4):337-343
A four-year field study was conducted to determine the effect of pluviometric conditions on pendimethalin and oxyfluorfen soil dynamics. Adsorption, dissipation and soil movement were studied in a sandy loam soil from 2003 to 2007. Pendimethalin and oxyfluorfen were applied every year on August at 1.33 and 0.75 kg ha?1, respectively. Herbicide soil concentrations were determined at 0, 10, 20, 40, 90 and 340 days after application (DAA), under two pluviometric regimens, natural rainfall and irrigated (30 mm every 15 days during the first 90 DAA). More than 74% of the herbicide applied was detected at the top 2.5 cm layer for both herbicides, and none was detected at 10 cm or deeper. Pendimethalin soil half-life ranged from 10.5 to 31.5 days, and was affected mainly by the time interval between application and the first rain event. Pendimethalin soil residues at 90 DAA fluctuated from 2.5 to 13.8% of the initial amount applied, and it decreased to 2.4 and 8.6% at 340 DAA. Oxyfluorfen was more persistent than pendimethalin as indicated by its soil half-life which ranged from 34.3 to 52.3 days, affected primarily by the rain amount at the first rainfall after application. Oxyfluorfen soil residues at 90 DAA ranged from 16.7 to 34.8% and it decreased to 3.3 and 17.9% at 340 DAA. Based on half-life values, herbicide soil residues after one year, and soil depth reached by the herbicides, we conclude that both herbicides should be considered as low risk to contaminate groundwater. However, herbicide concentration at the top 2.5 cm layer should be considered in cases where runoff or soil erosion could occur, because of the potential for surface water contamination. 相似文献
96.
Maria Aparecida Macêdo Silva Gilmara Fernandes Eça Danielle Felix Santos Alonso Góes Guimarães Michelle Coêlho Lima Marcelo Friederichs Landim de Souza 《Environmental monitoring and assessment》2013,185(7):5387-5399
Sampling was conducted monthly during a transition period between the dry and rainy seasons in order to evaluate the effectiveness of a municipal sewage treatment plant (STP) in eutrophication control. STP effluent and fluvial input data were also estimated. In the dry period, high concentrations of nutrients, chlorophyll a (up to 360 μg?L?1), and anoxia in bottom waters were observed in the upper portion of the estuary. Nitrate was scarce during the dry months, although high concentrations were observed at the river sources and the upper estuary. The N:P and Si:P molar ratios were usually below 16:1, and the Si:N ratio was higher than 1:1. The fluvial inputs were a greater source of nutrients to the estuary than the STP, but nutrient loading by these effluents were also important in contributing to the eutrophication of the upper estuarine zone, especially in the dry season when symptoms were more intense. 相似文献
97.
João Marcelo de Castro e Sousa Ana Paula Peron Louridânya da Silva e Sousa Mércia de Moura Holanda Ataíde de Macedo Vieira Lima Vitor Alves de Oliveira Felipe Cavalcanti Carneiro da Silva Leonardo Henrique Guedes de Morais Lima Leomá Albuquerque Matos Sandra Maria Mendes de Moura Dantas Raí Pablo Sousa de Aguiar Muhammad Torequl Islam Ana Amélia de Carvalho Melo-Cavalcante Cláudia Costa Bonecker Horácio Ferreira Júlio Junior 《Environmental monitoring and assessment》2017,189(6):301
In general, tropical rivers have a great impact on human activities. Bioaccumulation of toxins is a worldwide problem nowadays and has been, historically, overlooked by the supervisory authorities. This study evaluated cytogenotoxic effects of Guaribas river (a Brazilian river) water during dry and rainy seasons of 2014 by using the Allium cepa test system. The toxicogenetic variables, including root growth, mitotic index, and chromosomal aberrations, were analyzed in meristematic cells of A. cepa exposed to water samples taken from the up-, within, and downstream of the city Picos (state: Piauí). The physical-chemical parameters were also analyzed to explain water quality and possible anthropogenic action. Additionally, the presence of heavy metals was also analyzed to explain water quality and possible damaging effects on eukaryotic cells. The results suggest that the river water exerted cytotoxic, mutagenic, and genotoxic effects, regardless of the seasons. In addition, Guaribas river presented physico-chemical values outside the Brazilian laws, which can be a characteristic of human pollution (domestic sewage, industrial, and local agriculture). The genetic damage was positively correlated with higher levels of heavy metals. The pollution of the Guaribas river water may link to the chemical contamination, including the action of heavy metals and their impacts on genetic instability in the aquatic ecosystem. In conclusion, necessary steps should be taken into account for further toxicogenetic studies of the Guaribas river water, as it has an influence in human health of the same region of Brazil. 相似文献
98.
流域的可持续管理:国际多个流域的案例研究 总被引:3,自引:0,他引:3
Walter Wagner James Gawel Hiroaki Furumai Marcelo Pereira de Souza Denilson Teixeira Leonardo Rios Shinichiro Ohgaki Alexander J.B.Zehnder Harold F. Hemond 《Ambio-人类环境杂志》2002,31(1):2-13
全球淡水资源正在不断受到污染和亏耗,威胁着可持续发展及人类和生态系统的健康.本文通过美国、日本、瑞士和巴西四个不同流域的案例研究,阐述了与淡水资源密切相关的可持续发展中的缺陷,指明了水资源可持续管理的总体方向.由于近几十年来人口的增长和经济的发展,每个流域的水质、流量和生物资源量都在下降.但是对于不同的流域来说,与水有关的这些问题的严重程度和文化观念大不相同,因而形成各自独特的水资源管理政策.在工业化国家,例如美国、瑞士和日本,这类政策允许采用资金密集型和能源密集型技术,使得这些国家在满足其水资源需求的同时还能尽量降低人类健康风险.然而,从可持续发展的观点看,以有限的自然资源为基础制定的这类政策,并非长久之计.对于新兴工业化国家(如巴西)来说,昂贵的水资源管理技术在经济上常常行不通,因而限制了新兴工业化国家和发展中国家对发达国家提供的技术的利用程度.要实现水资源的可持续管理,发达国家、新兴工业化国家和发展中国家都需要经历一个学习的过程,同时还需要遵循本文介绍的可持续发展的通用原则. 相似文献
99.
Euglena gracilis as a model for the study of Cu2+ and Zn2+ toxicity and accumulation in eukaryotic cells 总被引:1,自引:0,他引:1
Einicker-Lamas M Mezian GA Fernandes TB Silva FL Guerra F Miranda K Attias M Oliveira MM 《Environmental pollution (Barking, Essex : 1987)》2002,120(3):779-786
We have observed the effect of copper and zinc on the biology of Euglena gracilis. The cells displayed different sensitivities to these metals, as the apparent LC50 for Cu2+ was 0.22 mM, and for Zn2+ it was 0.88 mM. While Zn2+ was able to increase cell proliferation even at 0.1 mM, the minimal CuCl2 concentration tested (0.02 mM) was sufficient to impair cell division. Higher concentrations of these metals not only inhibited cell division in a concentration-dependent manner, but also interfered with the metabolism of E. gracilis. A higher accumulation of proteins and lipids per cell was observed at the DI50 concentration for metal-treated cells. These results suggest that the test concentration of both metals leads to a failure in completing cell division. Ultrastructural analysis indicated a chloroplast disorganization in copper-treated cells, as well as the presence of electron dense granules with different shapes and sizes inside vacuoles. Microanalysis of these granules indicated an accumulation of copper, thus suggesting a detoxification role played by the vacuoles. These results indicate that E. gracilis is an efficient biological model for the study of metal poisoning in eukaryotic cells. They also indicate that copper and zinc (copper being more poisonous) had an overall toxic effect on E. gracilis and that part of the effect can be ascribed to defects in the structure of chloroplast membranes. 相似文献
100.
Marcelo?Azevedo?CostaEmail author Renato?Martins?Assun??o 《Environmental and Ecological Statistics》2005,12(3):301-319
Routine surveillance of a large geographic region for clusters of adverse health events, particularly cancers, often involves
small area health data, possibly controlling for exposure information. Many different methods have been proposed to test for
the presence of geographical clusters. Two of the most popular methods are the spatial scan method proposed by Kulldorff and
that using a fixed number of cases within scanning circles proposed by Besag and Newell. Although the second test is very
popular, it has some difficulties. While the scan test controls for the multiple testing problem, the Besag and Newell test
does not. Additionally, the latter method requires the setting of several tuning parameters whose values affect the test performance
and are subjectively chosen by the user. This creates a difficulty to make a fair comparison between the two methods and it
explains why there have been few formal studies evaluating their relative performances. In this paper, we modify the Besag
and Newell test allowing for the control of the error type I probability and compare its power with respect to that of the
spatial scan test. We used data sets from a publicly available simulated benchmark. We found that the two methods have similar
results, except for clusters located in sparsely populated regions, where the spatial scan method presented a better performance. 相似文献