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491.
Foragers of the stingless bees genus Melipona may produce intranidal sounds that are correlated with food location and quality. In this study, we provide the first detailed
analysis of pulsed sounds produced by Melipona panamica foragers while feeding on a carbohydrate food source. We trained foragers to a 2.5-M sucrose feeder under normal, ambient
temperature (23–33°C) and lower temperature (11–25°C) conditions. We recorded forager sounds under both conditions and tested
the effect of temperature of the thorax, feeder plate, and air on sound temporal characteristics. Forager energetic expenditure
and the number of pulses per visit were significantly higher in the cold condition than in the normal condition. Foragers
spent a longer time at the feeder under the cold condition than during the normal condition. Interpulse durations were significantly
shorter in the cold condition than in the normal condition and became progressively and significantly shorter at the end of
each performance. Thus, pulse production increased before departure. Foragers increased their thoracic temperatures above
ambient at all experimental air temperatures. Under chilled conditions, foragers had a significantly greater difference between
thorax temperature and ambient air temperature than under normal conditions. Foragers must achieve a minimum flight muscle
temperature before take-off, and thus forager sounds may be linked to muscle warm-up. 相似文献
492.
Long-term patterns in tropical reforestation: plant community composition and aboveground biomass accumulation. 总被引:1,自引:0,他引:1
Primary tropical forests are renowned for their high biodiversity and carbon storage, and considerable research has documented both species and carbon losses with deforestation and agricultural land uses. Economic drivers are now leading to the abandonment of agricultural lands, and the area in secondary forests is increasing. We know little about how long it takes for these ecosystems to achieve the structural and compositional characteristics of primary forests. In this study, we examine changes in plant species composition and aboveground biomass during eight decades of tropical secondary succession in Puerto Rico, and compare these patterns with primary forests. Using a well-replicated chronosequence approach, we sampled primary forests and secondary forests established 10, 20, 30, 60, and 80 years ago on abandoned pastures. Tree species composition in all secondary forests was different from that of primary forests and could be divided into early (10-, 20-, and 30-year) vs. late (60- and 80-year) successional phases. The highest rates of aboveground biomass accumulation occurred in the first 20 years, with rates of C sequestration peaking at 6.7 +/- 0.5 Mg C x ha(-1) x yr(-1). Reforestation of pastures resulted in an accumulation of 125 Mg C/ha in aboveground standing live biomass over 80 years. The 80 year-old secondary forests had greater biomass than the primary forests, due to the replacement of woody species by palms in the primary forests. Our results show that these new ecosystems have different species composition, but similar species richness, and significant potential for carbon sequestration, compared to remnant primary forests. 相似文献
493.
494.
The Microtox bioassay was used to establish dose-response curves for some toxic elements in aqueous solutions, namely, Zn(II), Pb(II), Cu(II), Hg(II), Ag(I), Co(II), Cd(II), Cr(VI), As(V) and As(III). Experiments were carried out at either pH 6.0 or pH 7.0 to indicate that pH may influence the measured toxicity of some elements due to pH-related changes of their chemical speciation. EC20 values, which represent a measurable threshold of toxicity, were determined for each element and were found to rank as Pb(II)>Ag(I)>Hg(II) approximately Cu(II)>Zn(II)>As(V)>Cd(II) approximately Co(II)>As(III)>Cr(VI). These values were compared to the limit concentrations allowed in industrial wastewater according to the official regulations in Catalonia (Spain). It appears that the Microtox test is sensitive enough for detecting some of the tested elements with respect to official regulations of Catalonia (Spain) dealing with pollution control, with the exception of cadmium, mercury, arsenate, arsenite and chromate. 相似文献
495.
The rainbow trout fish cell lines RTG-2 and RTL-W1 were used to determine the cytotoxic effects of the pesticides bifenthrin, cypermethrin, cyhalothrin, lambda-cyhalothrin, quinalphos and chlorpyrifos. Cytotoxicity was measured by EROD and beta-Gal enzymatic activities, the neutral red (NR) uptake assay, and the FRAME KB protein (KBP) assay. The beta-Gal activity was unaffected by the pesticide exposure. The EROD activity was induced by cyhalothrin and lambda-cyhalothrin (RTG-2 and RTL-W1) and by bifenthrin (RTL-W1). Dose dependent inhibition responses were observed for EROD activity in cells exposed to quinalphos (RTL-W1) and chlorpyrifos (RTG-2 and RTL-W1). RTL-W1 offered a better response for EROD induction. The EC50 values on EROD endpoint were more sensitive than NR and KBP. The acute fish toxicity of chlorpyrifos and quinalphos depends highly on the species; the species sensitivity distributions cover several orders of magnitude and the values obtained for EROS were within the lowest part of the reported ranges. 相似文献
496.
The photocatalytic disinfection of urban waste waters 总被引:7,自引:0,他引:7
Herrera Melián JA Doña Rodríguez JM Viera Suárez A Tello Rendón E Valdés do Campo C Arana J Pérez Peña J 《Chemosphere》2000,41(3):323-327
In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples. 相似文献
497.
Rodríguez ME Narros GA Molleda JA 《Journal of the Air & Waste Management Association (1995)》1995,45(3):156-160
An evaluation of the influence and degradation of ground multilayer containers, such as Tetra Brik Aseptic (TBA), in the composting process of municipal solid wastes (MSW) is presented. Two composting piles were formed by mixing, in different proportions, an organic fraction of MSW and TBA material ground as flakes or stripes. Piles were periodically aerated by mechanical mixing. Evolution of the composting was followed by frequent measurements of suitable parameters such as temperature, moisture, ashes, total organic carbon (TOC), nitrogen, C/N ratio, pH, conductivity, nutrients, and heavy metals. As expected, aluminum and polyethylene films from TBA were not degraded during the processes, but the cardboard fraction of TBA showed a partial decomposition that was more intense in the material ground as flakes. After two months of curing, the composts were refined and analyzed to determine their nutrient and heavy-metals contents. Despite their poor aesthetic properties, mainly resulting from the presence of little pieces of plastic and aluminum films, the composts contained the required amounts of nutrients; furthermore, their heavy-metals content was below the limits proposed by some official European organizations. 相似文献
498.
Peña-Méndez EM Astorga-España MS García-Montelongo FJ 《Environmental pollution (Barking, Essex : 1987)》2001,111(2):177-187
Chemical fingerprinting approach to environmental assessment is illustrated in the evaluation of marine oil pollution in the coasts using two limpet species as bioindicator organisms, and based on profiles and concentrations of n-alkanes and aromatic hydrocarbons in their tissues. Accidental and chronic releases of hydrocarbons can contaminate the marine environment of the Canary Islands not only because of their geographical situation but also because of the very dense tanker traffic around. This situation affects coastal areas, fishing activities, tourism resort, etc. Concentrations of n-alkanes and aromatic hydrocarbons (polycyclic aromatic hydrocarbons and methyl-polycyclic aromatic hydrocarbons) in the soft tissues of the marine intertidal and subtidal limpets, Patella crenata and Patella ullysiponensis aspera, were evaluated. Limpet samples were collected at monthly intervals, at three locations on the southeast coast of Tenerife over a 3-year period (1991-93). Levels of hydrocarbons found in limpets are similar to concentrations found in unpolluted areas around the world. From application of principal component analysis, the interpretation of variable loading plots gives information on variable correlation and can be used to distinguish among potential sources of pollution and the ability of studied molluscs to be used as bioindicator organisms. 相似文献
499.
Martin Paidar Karel Bouzek Ludek Jelínek Zdenek Matejka 《Water environment research》2004,76(7):2691-2698
The process of electrochemical treatment of a solution after strong basic anion exchanger regeneration was studied. The goal of the study was to reduce the nitrate content in the solution to allow its use in a closed loop. Diaphragmless, flow-through cells in a recirculation mode with and without a fluidizing bed of inert particles in the interelectrode space equipped with copper (Cu) cathodes and activated titanium anodes were used. The temperature was maintained at 20 degrees C. To assess the influence of recirculation of the regenerant solution on the quality of the treated water, the effect of the addition of copper ions to the solution, postelectrolysis cathode treatment, and enhanced mass transfer on the electrolysis results with respect to current efficiency and residual nitrate and nitrite concentration were investigated using an artificial solution. On the basis of the experimental results, a laboratory-scale unit for selective nitrate removal was designed and constructed that integrated ion exchange and electrochemical cell to one assembly. The process of recirculation of regenerant solution was tested using groundwater. 相似文献
500.
The aerobic visible-light-photosensitised irradiation of methanolic solutions of either of the phenolic-type contaminants model compounds (ArOH) p-phenylphenol (PP), p-nitrophenol (NP) and phenol (Ph), and for two additional phenolic derivatives, namely p-chlorophenol (ClP) and p-methoxyphenol (MeOP), used in some experiments, was carried out. Employing the natural pigment riboflavin (Rf) as a sensitiser, the degradation of both the ArOH and the very sensitiser was observed. A complex mechanism, common for all the ArOH studied, operates. It involves superoxide radical anion (O2√−) and singlet molecular oxygen (O2(1Δg)) reactions. Maintaining Rf in sensitising concentrations levels (≈0.02 mM), the mechanism is highly dependent on the concentration of the ArOH. Kinetic experiments of oxygen and substrate consumption, static fluorescence, laser flash photolysis and time-resolved phosophorescence detection of O2(1Δg) demonstrate that at ArOH concentrations in the order of 10 mM, no chemical transformation occurs due to the complete quenching of Rf singlet excited state. When ArOH is present in concentrations in the order of mM or lower, O2√− is generated from the corresponding Rf radical anion, which is produced by electron transfer reaction from the ArOH to triplet excited Rf. The determined reaction rate constants for this step show a fairly good correlation with the electron-donor capabilities for Ph, PP, NP, ClP and MeOP. In this context, the main oxidative species is O2√−, since O2(1Δg) is quenched in an exclusive physical fashion by the ArOH. The production of O2√− regenerates Rf impeding the total degradation of the sensitiser. This kinetic scheme could partially model the fate of ArOH in aquatic media containing natural photosensitisers, under environmental conditions. 相似文献