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Rivas Zulay de Medina Hilda Ledo Gutiérrez Janio Gutiérrer Elizabeth 《Water, air, and soil pollution》2000,117(1-4):27-37
Nitrogen (N) and phosphorus (P) concentrations were determined in sediment samples along the bed of Catatumbo river in both Colombian and Venezuelan territories until the river outlet in Maracaibo lake. Total phosphorus was determined by digestion with HCl followed by analysis using the ascorbic acid method and total nitrogen was done using the standard microkjeldahl method plus nitrate-nitrite. Ammonium, orthophosphate and nitrate were determined using standard methods after extraction steps. The mean concentrations along the river bed were found in an interval of 0.035 and 1.492 mg g-1 dry sed. for nitrogen and 0.027 and 1.039 mg g-1 dry sed. for phosphorus at 95% confidence level. The mean molar ratio N/P in the river bed was 4.42 and 3.46 for river outlet zones in the lake, which indicates that nitrogen is the limiting nutrient. For comparison with previous results of lake sediments from sites near the river outlet it was concluded that Catatumbo river is a significant source of nutrients to the Maracaibo Lake system because sediment nutrients concentrations from Catatumbo river were higher than the ones in Maracaibo Lake. Statistic studies showed significant differences between countries, zones and similar behaviour in the river bed as related to the affluent rivers. 相似文献
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J A Sousa J L Romalde A Ledo J C Eiras J L Barja A E Toranzo 《Journal of fish diseases》1996,19(1):83-89
A comparative bacteriological and virological survey was conducted in two fish farms in the North of Portugal. The fish species examined included cultured rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., as well as wild fish captured near both facilities. The microbial load in the internal organs of apparently healthy fish was nonitored over a year, an all the disease problems occurring during this period were investigated. Although both farms presented intermediate levels of infection(30–40% infected fish), farm B showed the poorest microbiological quality since constant but low mortalities were observed throughout the year. Flavobacterium and Psedomonas-Xanthomonas were the predominant bacterial groups, comprising around 40–50% of the isolates from each farm. In farm B, members of the Enterobacteriaceae and mortile Aeromonas also showed significant prevalence (about 20%). The only outbreak of a notifiable disease was an occurrence of furunculosis, caused by Aeromonas salmonicida subsp. salmoncida, in farm A. However, Yersinia ruckeri was isolated not only from diseased fish, but also from asymptomatic fish, usually in mixed infections with motile Aeromonas or infections with motile Aeromonas or infectious pancreatic necrosis virus (IPNV). While Y. ruckeri isolates associated with mortalities belonged to the serotype O1 (subgroup a), those isolated from asymtomatic fish corresponded to serotype O3. Two strains of IPNV (serotype Ab) were isolated in farm B, which represents the first viral agent detected in Portuguese aquaculture. Qualitative and quantitative differences in microbial load were observed between cultured and wild fish. No notifiable bacterial or viral pathogens were detected in any of the feral species studied. 相似文献
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de Medina Hilda Ledo Marín Julio César Gutiérrez Elizabeth Morales José 《Water, air, and soil pollution》2003,145(1-4):341-357
Nitrogen is one of the two most important elements in the metabolism of aquatic ecosystems. At low concentrations it can limit primary productivity and when present at very high concentrations it can participate in the eutrophication process of these environments. The mechanism of nitrogen transport in sediments is almost unknown, nevertheless it is of vital importance for establishing mass balances in aquatic systems. In the study presented here, we assessed the nitrogen flux in sediments of the central part of tropical Lake Maracaibo, Venezuela, in particular with regard to dissolved oxygen concentrations. Experiments were performed under laboratoryconditions in a batch system, and at varying dissolved oxygenregimes (aerobic and anaerobic). Every two days, during 3 months,overlying water samples were taken to analyze nitrite, nitrate,ammonium and Kjeldahl total nitrogen. Average release rates oftotal nitrogen were 0.86 in aerobic, and 1.06 mmol N m-2 d-1 in anaerobic systems corresponding to 41.7% of total N input to the lake. The behavior of nitrogen was strongly influenced by nitrate concentrations under aerobic conditions, and by organic nitrogen under anaerobic conditions during the course of the experiment. A major trend for the release of organic nitrogen during anaerobic conditions, and of nitrate, during aerobic conditions, was observed. Also fluxes of NO3 -, NH4 +, organic N and Total N across the sediment-water interface were measured. In anaerobic conditions, which are predominant in the hypolimnetic cone of LakeMaracaibo, denitrification was estimated to be 0.02 mmol N m-2 d-1, which corresponds to 1.89% of the total N released from sediments.This is to our knowledge the first study of nitrogen fluxes insediments from Lake Maracaibo. The laboratory data presented herereflects conditions in the lake when major nutrients accumulation occurs. 相似文献
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Rosa Karla Nogueira Pestanana Edson Perito Amorim Cláudia Fortes Ferreira Vanusia Batista de Oliveira Amorim Larissa Santos Oliveira Carlos Alberto da Silva Ledo Sebastião de Oliveira e Silva 《Euphytica》2011,178(2):151-158
Bananas are tropical fruits grown worldwide playing a key role in market trade and especially used as main food source for
low income populations. In Brazil, bananas are mainly consumed in natura, occupying the second largest internal market. Nevertheless, this crop presents low availability of productive commercial
varieties with good agronomic characteristics. A strategy undertaken to solve this problem is the development of new cultivars
through conventional genetic breeding methods. However, this strategy presents some obstacles such as female sterility and
low number of seeds. In order to overcome these shortcomings, use of mutation induction aiming the selection of mutants with
desirable agronomic characteristics seems to have great potential for developing new cultivars. The objective of the present
work was to evaluate the genetic variability in putative banana ‘Pacovan’ (AAB genome, subgroup Prata Type) mutants submitted
to gamma ray irradiation, using a set of agronomical and molecular data (ISSR markers). The distance between the putative
‘Pacovan’ mutants varied from 0.26 to 0.64 with cophenetic correlation coefficient of 0.7669. Four mutants were selected based
on best agronomical characteristics and height. This data also shows that there is variability that can be explored after
the irradiation of ‘Pacovan’ banana mutants, which can be used in the genetic breeding program of banana aiming to develop
short new varieties that also present good agronomic characteristics. This is the first attempt to use combined data in order
to evaluate the genetic variability in putative banana mutants. 相似文献
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Ledo Hilda Rivas Zulay Gutiérrez Janio Gutiérrez Elizabeth Ojeda Jesús Avila Hendrik 《Water, air, and soil pollution》2004,155(1-4):117-135
Ca, Mg, Fe, Mn and Al were determined in surficial sediment samples from Catatumbo River (including sediments from major tributaries) a binational basin shared by both Venezuela and Colombia in approximately 30% and 70%, respectively. The global mean concentration of the metals was Al > Fe > Mg > Ca > Mn (0.376; 0.304; 0.063; 0.042; 5.9 × 10-4 mmol g-1 dry weight). The objectives of this investigation were (1) to establish metal-concentration baselines, and (2) to determine spatial distribution of Ca, Mg, Fe, Mn and Al concentrations, in bed sediment samples from Catatumbo River (including sediments from major tributaries). As Catatumbo River is the main tributary to Lake Maracaibo system (South America's largest inland lake), its impact on the eutrophication process of Lake Maracaibo due to the formation of metal/phosphorus complexes is discussed. 相似文献
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Wei W Unsworth M Jones A Booker J Tan H Nelson D Chen L Li S Solon K Bedrosian P Jin S Deng M Ledo J Kay D Roberts B 《Science (New York, N.Y.)》2001,292(5517):716-719
Magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north-to-south width of the Tibetan plateau. The integrated conductivity (conductance) of the Tibetan crust ranges from 3000 to greater than 20,000 siemens. In contrast, stable continental regions typically exhibit conductances from 20 to 1000 siemens, averaging 100 siemens. Such pervasively high conductance suggests that partial melt and/or aqueous fluids are widespread within the Tibetan crust. In southern Tibet, the high-conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust. In northern Tibet, the conductive layer is at 30 to 40 kilometers and is due to partial melting. Zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow. 相似文献
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