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121.
Tadashi Hasegawa Kakeru Usuba Soichiro Kondo Yutaka Maeda 《Environmental Chemistry Letters》2008,6(2):107-111
Here, we show that association of stilbene molecules is facilitated by water on silica gel because of hydrophobic interaction
and photodimerization becomes the main photochemical process. Irradiation of trans-stilbene (t-1) on silica gel gives cis-stilbene (c-1), phenanthrene (2), benzaldehyde (3), and dimers r-ctt-4 and r-tct-4. The yields of the dimers increase and those of 2 and 3 decrease with an increase in the amount of t-1 loaded on silica gel. Atmospheric oxygen is responsible for the formation of 2 and 3. The yields of the dimers also increase with an increase in the water on a silica-gel surface and change drastically at the
point where the percentage of water to silica gel is around 25 wt%. All active sites on a silica-gel surface would be covered
completely with 25 wt% of water. 相似文献
122.
The contamination of groundwater in the aquifer of the La Llagosta basin (Besòs river basin) due to waste disposal in quarries
formerly used for the extraction of dry raw materials has led to the cessation of groundwater extraction for public water
supply. The mobilization of pollutants was largely caused by fluctuations in piezometric levels, which led to the washing
of buried waste. The hydrogeochemical processes associated with uncontrolled waste disposal in these landfilled areas of the
La Llagosta basin aquifer were studied along a flow path that crosses the contaminated area. The PHREEQC code was used to
establish the reactions associated with the different mineral phases through inverse modeling. This transport code, ionic
exchange phenomena, surface reactions and balance (mineral phase) reactions were used to simulate the dilution phenomenon
associated with the pollution after the potential removal of the sources of contamination. One-dimensional advective–dispersive
modeling indicates a substantial reduction in Ca, Mg, Na and SO42− within one year and stabilization within four years. 相似文献
123.
An assertion deeply rooted in the ornithological literature holds that sex-specific mortality causes a sex ratio disparity
(SRD) between complete and incomplete broods. Complete broods are thought to reflect the primary sex ratio before any bias
introduced by developmental mortality. Contrary to this view, however, complete and incomplete broods should exhibit identical
sex ratio distributions even when the sexes experience differential mortality, as shown in the classic paper of Fiala (Am
Nat 115: 442–444, 1980). Therefore, in partially unsexed samples, primary sex ratio biases cannot be distinguished from biases
caused by differential mortality. In addition, complete broods do not represent primary sex ratio more accurately than incomplete
ones and might even be misleading. Despite Fiala’s prediction, SRD does occur in some empirical studies. We show that this
pattern could arise if (1) primary sex ratio affects chick mortality rates independently of sex (direct effect), (2) primary
sex ratio covaries with a variable that also affects mortality rate, or (3) sex differential mortality covaries with overall
mortality rate (indirect effects). Direct effects may cause stronger SRD than indirect ones with a smaller and opposite bias
in the overall sex ratio and could also lead to highly inconsistent covariate effects on brood sex ratios. These features
may help differentiate direct from indirect effects. Most interestingly, differences in covariate effects between complete
and incomplete broods imply that influential variables are missing from the analysis. 相似文献
124.
Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal
Veronica Fernandes Nagappa Ramaiah Jane T. Paul Sugandha Sardessai R. Jyoti Babu Mangesh Gauns 《Marine Biology》2008,153(5):975-985
With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s−1 and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no
nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of
Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance
and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect,
in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced
shelf/slope waters. Bacterioplankton abundances (<2 × 109cells l−1) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the
thymidine uptake rates along CB (average of 1.46 pM h−1) and WB (average of 1.40 pM h−1) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the
oligotrophic northwestern Sargasso Sea (<7 × 108 cells l−1; av 1.0 pM h−1). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic
production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in
the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m−2 d−1) than in the CB (306 mg C m−2 day−1). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher
abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through
discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize
in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous
organic matter, in particular in the western Bay, is important for meeting their carbon demand. 相似文献
125.
The decomposition of leaf litter is controlled by several factors. One factor that may play an important role is the content
of condensed tannins (proanthocyanidins). Here we designed a combined method to isolate proanthocyanidins from leaf extracts,
to convert them to anthocyanidins, and to quantify individual anthocyanidins exactly with a new, simple, but sensitive high-performance
liquid chromatography method. We used this method to show composition of proanthocyanidins and to monitor degradation of proanthocyanidins
and individual constituents in leaf litter in an aquatic environment over time. Despite the rapid decrease in the initial
concentrations, a fraction of the proanthocyanidins remained detectable for several weeks. 相似文献
126.
Many symbioses involve multiple partners in complex, multi-level associations, yet little is known concerning patterns of
nutrient transfer in multi-level marine mutualisms. We used the anemonefish symbiosis as a model system to create a balance
sheet for nitrogen production and transfer within a three-way symbiotic system. We quantified diel patterns in excretion of
ammonia by anemonefish and subsequent absorption by host sea anemones and zooxanthellae under laboratory conditions. Rates
of ammonia excretion by the anemonefish Amphiprion bicinctus varied from a high of 1.84 μmole g−1 h−1 at 2 h after feeding, to a basal rate of 0.50 μmole g−1 h−1 at 24–36 h since the last meal. Conversely, host sea anemones Entacmaea quadricolor absorbed ammonia at a rate of 0.10 μmole g−1 h−1 during the daytime in ammonia-enriched seawater, but during the night reduced their absorption rate to near zero, indicating
that ammonia uptake was driven by zooxanthella photosynthesis. When incubated together, net ammonia excretion was virturally
zero, indicating that host anemones absorbed most of the ammonia produced by resident fish. Adult anemonefish weighed about
11 g under laboratory conditions, but on the coral reef may reach up to 64 g, resulting in a maximal potential ammonia load
of >200 μmole h−1 produced by two adult fish during daylight hours. In contrast, host sea anemones weighed about 47 g in the laboratory, but
under field conditions, large individuals may reach 680 g, so their maximal ammonia clearance rates may reach about 70 μmole h−1 during the daytime. As such, the ammonia load produced by adult anemonefish far exceeds the clearance rate of host anemones
and zooxanthellae. Ammonia transfer likely occurs mainly during the daytime, when anemonefish consume zooplankton and excrete
rapidly, and in turn the zooxanthellae are photosynthetically active and drive rapid ammonia uptake. We conclude that zooplanktivorous
fishes that form mutualisms with coral reef cnidarians may serve as an important link between open water and benthic ecosystems,
through the transfer of large quantities of nutrients to zooxanthellate hosts, thus enhancing coral reef productivity. 相似文献
127.
Matteo Carpentieri Paolo Giambini Andrea Corti 《Environmental Modeling and Assessment》2008,13(3):415-429
Several wind tunnel experiments of tracer dispersion from reduced-scale landfill models are presented in this paper. Different
experimental set-ups, hot-wire anemometry, particle image velocimetry and tracer concentration measurements were used for
the characterisation of flow and dispersion phenomena nearby the models. The main aim of these experiments is to build an
extensive experimental data set useful for model validation purposes. To demonstrate the potentiality of the experimental
data set, a validation exercise on several mathematical models was performed by means of a statistical technique. The experiments
highlighted an increase in pollutant ground level concentrations immediately downwind from the landfill because of induced
turbulence and mean flow deflection. This phenomenon turns out to be predominant for the dispersion process. Tests with a
different set-up showed an important dependence of the dispersion phenomena from the landfill height and highlighted how complex
orographic conditions downwind of the landfill do not affect significantly the dispersion behaviour. Validation exercises
were useful for model calibration, improving code reliability, as well as evaluating performances. The Van Ulden model proved
to give the most encouraging results. 相似文献
128.
Felix Deutsch Jean Vankerkom Liliane Janssen Filip Lefebre Clemens Mensink Frans Fierens Gerwin Dumont Edward Roekens 《Environmental Modeling and Assessment》2008,13(3):431-437
The European Operational Smog (EUROS) integrated air quality modelling system has been extended to model fine particulate
matter (PM). From an extended literature study, the Caltech Atmospheric Chemistry Mechanism and the Model of Aerosol Dynamics,
Reaction, Ionisation and Dissolution were selected and recently coupled to EUROS. Currently, modelling of mass and chemical
composition of aerosols in two size fractions (PM2.5 and PM10–2.5) is possible. The chemical composition is expressed in terms of seven components: ammonium, nitrate, sulphate, elementary
carbon, primary inorganic compounds, primary organic compounds and secondary organic compounds. Calculated PM10 concentrations and chemical composition are presented for two summer months of the year 2003 (1 July to 31 August). 相似文献
129.
We describe the development and parameterization of a grid-based model of African savanna vegetation processes. The model
was developed with the objective of exploring elephant effects on the diversity of savanna species and structure, and in this
formulation concentrates on the relative cover of grass and woody plants, the vertical structure of the woody plant community,
and the distribution of these over space. Grid cells are linked by seed dispersal and fire, and environmental variability
is included in the form of stochastic rainfall and fire events. The model was parameterized from an extensive review of the
African savanna literature; when available, parameter values varied widely. The most plausible set of parameters produced
long-term coexistence between woody plants and grass, with the tree–grass balance being more sensitive to changes in parameters
influencing demographic processes and drought incidence and response, while less sensitive to fire regime. There was considerable
diversity in the woody structure of savanna systems within the range of uncertainty in tree growth rate parameters. Thus,
given the paucity of height growth data regarding woody plant species in southern African savannas, managers of natural areas
should be cognizant of different tree species growth and damage response attributes when considering whether to act on perceived
elephant threats to vegetation. 相似文献
130.
We present a new mathematical programming framework that is adaptable to a variety of spatially explicit landscape problems
in environmental investment, conservation, and land-use planning, transport planning, and agriculture. As part of capturing
spatial interdependencies, the framework considers decision variables at two levels, finely spaced grid cells and landholdings.
We applied the framework to an environmental investment problem using objective functions representing biodiversity and carbon
sequestration. We also tested the model to optimize the path of a road through part of the landscape. Using the Nambucca case
study in eastern Australia, we applied a hybrid greedy randomised adaptive search procedure (GRASP) to find solutions to the
model. 相似文献