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81.
A. Keller D. Bruggmann A. Neff B. Müller E. Wintermantel 《Journal of Polymers and the Environment》2000,8(2):91-96
In a composite, fast degradable fibers determine the degradation of the slowly degradable matrix. Such biodegradable composites consisting of degummed hemp fibers and a polyester amide matrix were produced with fiber mass fractions between 0 and 0.48. The hot-pressed plates, 1-mm thick, were incubated in a standard soil. The degradation kinetics was quantified by the measurement of CO2 production. Furthermore, after termination of experiment, the carbon balance was uncovered. The results were fitted to an exponential law taking into account the degradation of fibers. The increased amount of pores realized by high fiber contents induces pronounced degradation. The degradation is fully characterized by the time constant , which is correlated to the fiber mass fraction. The model allows to predict the degradation kinetics of composites with a few well-defined experiments. 相似文献
82.
Effects of ultraviolet-B enhancement on marine trophic levels in a stratified coastal system 总被引:3,自引:0,他引:3
A. A. Keller P. Hargraves H. Jeon G. Klein-MacPhee E. Klos C. Oviatt J. Zhang 《Marine Biology》1997,130(2):277-287
We examined the effects of enhanced UV-B radiation (relative to ambient) on marine trophic levels inhabiting a stratified
coastal ecosystem, using living models (13 000 liter marine enclosures) of a temperate estuarine water column. The experiment
was carried out in June and July 1994 on a plankton community drawn from lower Narragansett Bay, Rhode Island, USA. The effects
of altered UV-B radiation (elevated 50% over ambient, tenfold DNA-weighted) on three trophic strata: the primary producers
(photosynthetic algae), primary herbivores (copepods), and fish eggs and larvae (Anchoa mitchilli Cuvier and Valenciennes) were examined. The goal was to determine if UV-B–induced alterations at the base of the food chain
had impacts on other elements of the trophic web. Phytoplankton abundance (P=0.02) and biomass (P=0.007) were significantly reduced in UV-B–enhanced treatments, above but not below the thermocline (2.25 m), during the second
week of the study. Copepod nauplii were significantly less abundant in UV-B–enhanced mesocosms than in control treatments
during the third and fourth weeks of the study (P=0.01). A portion of the impact on nauplii may be a result of alterations at the base of the food web. The greater mortality
of nauplii in UV-B–enhanced systems did not translate to reduced abundance of copepodite (P=0.83) or adult (P=0.29) copepods. No significant effects were observed for microzooplankton (P=0.15). Neither the mortality rates nor the growth rates of larval anchovy were significantly affected by the experimental
increase in UV-B (P>0.05). Despite the tenfold increase in biologically damaging UV-B, effects were not seen at higher trophic levels, most likely
because of the rapid extinction of UV-B in the highly colored coastal water.
Received: 13 November 1996 / Accepted: 18 July 1997 相似文献
83.
The effects of potassium fertilization and ozone stress were investigated in a clone of Picea abies (L.) Karst, by studies of the uptake of CO(2) by the crowns, the element content, on leaching of the youngest needles, and the longevity of the needles. All plants were exposed to 0.075 microl litre(-1) SO(2) from January to April 1986. The average ozone concentrations applied during the subsequent growing season (May-December) were 0, 0.027, 0.050 and 0.100 microl litre(-1). Half of the trees received liquid fertilizer applications from April to July 1986. CO(2) uptake by the crowns was significantly reduced in non-fertilized plants at ozone doses of 100-200 microl litre(-1) h, whereas similar reductions were recorded in fertilized plants only above an ozone dose of 300 microl litre(-1) h. Independent of the fertilization, however, the concentrations of calcium, magnesium and nitrogen in the needles increased in parallel with the ozone dose, whilst potassium, phosphorus and sulphur showed little response to ozone. In both nutrient regimes, the diffusive loss of elements from chloroform-washed needles was similar and tended to be reduced at the highest ozone concentration, when relating the leachate to the corresponding element content in the needles. Needles formed in the highest ozone treatment were significantly shed during the succeeding year, regardless of the nutrient supply. It appears that increased potassium supply has little compensating effect on ozone stress in spruce. 相似文献
84.
Keller T Matyssek R Günthardt-Goerg MS 《Environmental pollution (Barking, Essex : 1987)》1994,85(2):185-189
Since 1971 unshaded leaves from the top of marked beech trees (Fagus sylvatica L.) in the vicinity of a regional waste incinerator have been sampled every year in early September. The unwashed leaf samples were analyzed for the concentration of Cl- and, in some years, for 16 other elements. The operation of the waste incinerator distinctly increased the Cl- concentration in the foliage. When the flue gas filtration did not work properly, several other elements also accumulated (without any obvious dust accumulation). There were no significant correlations between precipitation and concentration of water-soluble elements in foliage samples. This suggested that precipitation was not accelerating foliar leaching so that the bioindication of pollutant accumulation is not restricted in foliage with a well developed cuticula. 相似文献
85.
86.
87.
An evaluation of Khmer refugee public health services found a strong cultural preference for older females as Community Health Workers (CHWs), in contrast to the young males employed. Class conflicts were identified between educated, upper-class CHWs and the uneducated camp majority. Poor community acceptance of the CHWs impaired their effectiveness, and was attributed to age, sex and socioeconomic barriers. Based on these evaluation findings, the refugee health program was restructured to include a preponderance of female workers. A repeat survey demonstrated enhanced program effectiveness following this change.
Selection of refugee health workers should be based on intrinsic community roles, taking age, sex, socioeconomic and other group distinctions into account. Additional research is needed on the adaptation of community health principles to the refugee context. 相似文献
Selection of refugee health workers should be based on intrinsic community roles, taking age, sex, socioeconomic and other group distinctions into account. Additional research is needed on the adaptation of community health principles to the refugee context. 相似文献
88.
Hauwa Atiku RMSR Mohamed AA Al-Gheethi AA Wurochekke Amir Hashim M. Kassim 《Environmental science and pollution research international》2016,23(24):24624-24641
The wide application of microalgae in the field of wastewater treatment and bioenergy source has improved research studies in the past years. Microalgae represent a good source of biomass and bio-products which are used in different medical and industrial activities, among them the production of high-valued products and biofuels. The present review focused on greywater treatment through the application of phycoremediation technique with microalgae and presented recent advances in technologies used for harvesting the microalgae biomass. The advantages and disadvantages of each method are discussed. The microbiological aspects of production, harvesting and utilization of microalgae biomass are viewed. 相似文献
89.
F. Coutelot V. Sappin-Didier C. Keller O. Atteia 《Environmental monitoring and assessment》2014,186(12):8929-8941
The unsaturated zone plays a major role in elemental fluxes in terrestrial ecosystems. A representative chemical analysis of soil pore water is required for the interpretation of soil chemical phenomena and particularly to assess Trace Elements (TEs) mobility. This requires an optimal sampling system to avoid modification of the extracted soil water chemistry and allow for an accurate estimation of solute fluxes. In this paper, the chemical composition of soil solutions sampled by Rhizon® samplers connected to a standard syringe was compared to two other types of suction probes (Rhizon®?+?vacuum tube and Rhizon®?+?diverted flow system). We investigated the effects of different vacuum application procedures on concentrations of spiked elements (Cr, As, Zn) mixed as powder into the first 20 cm of 100-cm columns and non-spiked elements (Ca, Na, Mg) concentrations in two types of columns (SiO2 sand and a mixture of kaolinite?+?SiO2 sand substrates). Rhizon® was installed at different depths. The metals concentrations showed that (i) in sand, peak concentrations cannot be correctly sampled, thus the flux cannot be estimated, and the errors can easily reach a factor 2; (ii) in sand?+?clay columns, peak concentrations were larger, indicating that they could be sampled but, due to sorption on clay, it was not possible to compare fluxes at different depths. The different samplers tested were not able to reflect the elemental flux to groundwater and, although the Rhizon®?+?syringe device was more accurate, the best solution remains to be the use of a lysimeter, whose bottom is kept continuously at a suction close to the one existing in the soil. 相似文献
90.
Thimonier A Kull P Keller W Moser B Wohlgemuth T 《Environmental monitoring and assessment》2011,174(1-4):47-63
At Swiss long-term forest ecosystem research sites, ground vegetation was assessed during the period 1994-2003/2008 following two approaches: (1) visual assessment of the cover of species occurring in sixteen 1 m(2) quadrats, distributed over a 43 × 43 m area, and (2) phytosociological relevés in concentric circular plots of 30, 200, and 500 m(2). We first compared the two approaches with respect to diversity assessment. The number of species recorded in the 16 quadrats was in general higher than in the 30 m(2) plot and it represented 42% to 108% of the number of species recorded in the 500 m(2) plot. In a second step, we tested whether any temporal trends were apparent. In a few cases, a decrease or increase in Landolt's mean indicator values for light, nitrogen availability, soil pH, soil moisture, or temperature was found to be significant. However, these changes were usually restricted to one approach or one area. The only clear trend was detected in an unmanaged former coppice beech stand, for which all survey approaches indicated canopy closure. At another site, vegetation reacted to the local opening of the canopy following windthrow. In a third step, we compared the leaf area index (LAI), measured with an LAI-2000 instrument (Licor, Inc.) over each quadrat, with the indicator value of the vegetation for light (L). Within a site, there was no clear relationship between LAI and L values per quadrat. In contrast, across all sites, the relationship between LAI and L, averaged per site for all available years, was highly significant. 相似文献